Educational Wealth

Reproduction

Abdullah 0 Article, biology Friday, January 31, 2014

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<span style="font-size: large;">Basic character of life </span><br />
<span style="font-size: large;"> The most basic characteristic of life is reproduction i.e. the production of new structures and individuals similar to the existing structures and individuals. Reproduction occurs at different levels of organization. Parts of the ceil such as the chromosomes produce new chromosomes.</span><br />
<span style="font-size: large;"> Cells then produce new cells; and individuals produce offspring like themselves. Rudolf Virchow proposed an important biological principle i.e. all cells come from cells. This principle tells us that the continuation of life, including all aspects of reproduction, is based on the reproduction of cells. </span><br />
<span style="font-size: large;">We commonly refer cellular reproduction as cell division and it is a part of the whole life of a cell i.e. cell cycle.
Cell cycle

The cell cycle is the series of events from the time a cell is produced until it completes <a href="http://educational-wealth.blogspot.com/2014/02/phases-of-mitosis-process-of-mitosis-is.html" target="_blank"><b>mitosis </b></a>and produces new cells. The cell cycle consists of two major phases i.e. interphase and mitotic phase (M phase). The mitotic phase is a relatively short period of the cell cycle.</span><br />
<span style="font-size: large;"> It alternates with the much longer interphase, where the cell prepares itself for division.

Typically interphase lasts for at least 90% of the total time required for the cell cycle.
Interphase

Interphase is the time when a cell's metabolic activity is very high, as it performs its various functions.</span><br />
<span style="font-size: large;"> It is divided into three phases, </span><br />
<span style="font-size: large;">G1 (first gap), </span><br />
<span style="font-size: large;">S (synthesis),</span><br />
<span style="font-size: large;"> and G2 (second gap). </span><br />
<span style="font-size: large;">G1 phase: </span><br />
<span style="font-size: large;">After its production, a cell starts its cell cycle in G1 phase. During this phase, the cell increases its supply of proteins, increases the number of many of its organelles (such as mitochondria, ribosomes), and grows in size. This phase is also marked by the synthesis of various enzymes that are required in the next phase i.e. S phase for DNA replication. </span><br />
<span style="font-size: large;"> A German biologist, Walther Flemming in the 1880's, gave the detailed account of the stages of cell division. He observed that in a dividing cell the nucleus passes through a series of changes which he called mitosis.

Inhibition of protein synthesis during G2 phase prevents the cell from undergoing mitosis. </span><br />
<span style="font-size: large;">The eukaryotic cell cycle

Somatic cells are those which are forming the body of organisms while germ line cells are those which give rise to gametes. Somatic cells undergo mitosis while germ line cells undergo meiosis.

In common mitosis, nuclear envelope disappears and spindles are formed inside the cytoplasm. It is called “open k, mitosis”. </span><br />
<span style="font-size: large;">Fungi and some protists undergo a variation called A.

Karyokinesis:

The division of the nucleus is “closed mitosis” where the further divided into four phases i.e. prophase, spindle forms inside the nucleus.

metaphase, anaphase and telophase. .i. Prophase:

Normally, the genetic material in the nucleus is in a loose thread-like form called chromatin. </span><br />
<span style="font-size: large;">At the onset of prophase, chromatin condenses into highly ordered structures called chromosomes. Since the genetic material has already been duplicated earlier in S phase, each chromosome is made of two sister chromatids, bound together at the centromere. Each chromosome has kinetochore at the centromere.</span><br />
<span style="font-size: large;"> A kinetochore ls a complex protein structure that is the point where spindle fibers attach.

close to the nucleus are two centrioles collectively called a centrosome. Each centriole replicates and thus two daughter antrosomes are formed.</span><br />
<span style="font-size: large;"> Each daughter centrosome acts as a coordinating center for e cell's microtubules. The two centrosomes give rise to microtubules by polymerizing vdning monomers to form polymers) the tubulin proteins present in the cytoplasm. The Cells that have temporarily or permanently stopped dividing are said to have entered a state of quiescence called GO phase. </span><br />
<span style="font-size: large;"> S phase: In this phase the cell duplicates its chromosomes. The DNA molecule of each chromosome is copied, and new protein molecules are attached. The result is that each chromosome consists of two sister chromatids, which contain identical genes.

G2 phase: In the G2 phase the cell prepares proteins that are essential for mitosis, mainly forthe production of spindle fibres.</span><br />
<span style="font-size: large;"> After the G2 phase of interphase, the cell enters the division phase i.e. M phase. It is characterized by mitosis, in which the cell divides into the two daughter cells.
GO phase:

In multicellular eukaryotes, cells enter the GO state from G1 and may remain quiescent for long periods of time, possibly indefinitely (as is often the case for neurons). </span><br />
<span style="font-size: large;">Some cell types in mature organisms, such as some cells of the liver and kidney, enter the GO phase semi-permanently and can only be induced to begin dividing again under very specific circumstances. Other cells, such as epithelial cells, do not enter GO and continue to divide throughout an organism's life.

The events of cell cycle are ordered and directional i.e each event occurs in a sequential fashion and it is impossible to "reverse" the cycle.</span><br />
<span style="font-size: large;"> Our body consists of about 200 trillion cells, all of them derived from a single cell at the start of our life as a fertilized egg. Many millions of successive cell divisions occurred while our body was reaching its present form. In each of these divisions, the genetic material was equally partitioned between the daughter cells and it happened through mitosis. </span><br />
<span style="font-size: large;">Mitosis is the type of cell division in which a cell divides into two daughter cells, each with the genetic equivalent of the parent cell i.e. same number of chromosomes as were present in the parent cell. Because each resultant daughter cell should be genetically identical to the parent cell,

the parent cell must make a copy of each chromosome before mitosis. </span><br />
<span style="font-size: large;">This occurs during S phase of interphase. Mitosis occurs exclusively in eukaryotic cells. In multicellular organisms, the somatic cells undergo mitosis. Prokaryotic cells undergo a process similar to mitosis called binary fission. However, prokaryotes cannot be properly said to undergo mitosis because they lack a nucleus and only have a single chromosome with no centromere.

membrane-bounded disc called the cell plate or phragmoplast. </span><br />
<span style="font-size: large;">The plate grows outward and more vesicle fuse with it. Finally, the membranes of the cell plate fuse with the plasma membrane and its contents join the parental cell wall.</span><br />
<span style="font-size: large;"> The result is two daughter cells, each bounded by its own plasma membrane and cell wall . Nuclear membrane breaks during cell division so there is no distinct nucleus.</span><br />
<span style="font-size: large;"> In interphase

nuclear material is in the form of fine chromatin which condenses during prophase to get the

shape of chromosome.There are several features unique to <a href="http://educational-wealth.blogspot.com/2014/02/hoiw-meiosis-takes-place.html" target="_blank"><b>meiosis</b></a>, most importantly the pairing and genetic recombination between homologous chromosomes.</span></div>

Reproduction

Basic character of life The most basic characteristic of life is reproduction i.e. the production of new structures and individuals simi...

Cell size and relation between prokayotic and Eukaryotic cells

Abdullah 0 Article, biology Thursday, January 30, 2014

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<span style="font-size: large;">Similarities between Prokaryotic and Eukaryotic cells </span></h3>
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<span style="font-size: large;">DNA </span></h4>
<span style="font-size: large;"> They both have DNA as their genetic material.
Membrane

They are both membrane bound. </span><br />
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<span style="font-size: large;">Ribosomes </span></h4>
<span style="font-size: large;"> They both have ribosome. </span><br />
<h4 style="text-align: left;">
<span style="font-size: large;">Metabolism </span></h4>
<span style="font-size: large;">They have similar basic metabolism. </span><br />
<h4 style="text-align: left;">
<span style="font-size: large;">Diverse </span></h4>
<span style="font-size: large;"> They are both amazingly diverse in forms. </span><br />
<span style="font-size: large;">Difference between Prokaryotic and Eukaryotic cells</span><br />
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<span style="font-size: large;"> Nucleus</span></h3>
<span style="font-size: large;"> The significant difference between prokaryotic and eukaryotic cell is that eukaryotic cell has a prominent nucleus and many membrane-bound organelles, which are not present in prokaryotic cell . </span><br />
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<span style="font-size: large;">DNA</span></h3>
<span style="font-size: large;"> The DNA of a prokaryotic cell floats in cytoplasm near the centre (this region is called nucleoid); the DNA of eukaryotic cell is held within the nucleus.</span><br />
<span style="font-size: large;"> Intracellular division </span><br />
<span style="font-size: large;">There is much higher level of intracellular division of labour in eukaryotic cells than in prokaryotic. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Size</span></h3>
<span style="font-size: large;"> Eukaryotic cells are, on average,
Genome composition and length

The DNA of eukaryotes is much more complex and extensive than the DNA of prokaryotes. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Cell wall</span></h3>
<span style="font-size: large;"> Prokaryotes have a cell wall composed of peptidoglycan that is a single large polymer of amino acids and sugar. The cell walls of eukaryotic cells is made of cellulose (in plants) or chitin (in fungi) </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Size </span></h3>
<span style="font-size: large;">Cells vary greatly in size. The smallest cells are bacteria called mycoplasmas, with diameter between 0.1 pm to 1.0 pm. The bulkiest cells are bird eggs, and the longest cells are some muscle cells and nerve cells. Most cells lie between these extremes.
Relative Sizes of cells

Cell size and shape are related to cell function. Bird eggs are bulky because they contain a large amount of nutrient for the developing young. </span><br />
<span style="font-size: large;">Long muscle cells are efficient in pulling different body parts together. Lengthy nerve cells can transmit nerve signals between distant parts of animal’s body. On the other hand small cell size also has many benefits. For example human red blood cells are only 8 pm in diameter and therefore can move through our tiniest blood vessels. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Relation between cell size and surface area </span></h3>
<span style="font-size: large;"> Most cells are small in size. Large cells have less surface area in relation to their volume while small cells of the same shape have more surface area. This relationship between cell size and surface area to volume ratio works to limit cell size. As the size of a ceil increases, cell volume increases more rapidly than its surface area. The need of nutrients and rate of waste production are directly proportional to cell volume. </span><br />
<span style="font-size: large;">The cell takes up nutrients and excretes wastes through its surface cell membrane. So a large volume cell demands large surface area. But a large cell has a much smaller surface area relative to its volume than smaller cells have. Hence we conclude that the membranes of small cells can serve their small volumes more easily than the membrane of large cell. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Effect of cell size on surface area </span></h3>
<span style="font-size: large;"> Cell membranes act as barriers to most, but not all, molecules. </span><br />
<span style="font-size: large;">That is why cell membranes are called differentially or semi-permeable membranes separating the inner cellular environment from the outer environment. While exchanging matter with cells' environment, cell membranes maintain equilibrium inside the cell as well as outside. This control of the passage of molecules into and out of cells is made possible through the phenomena of diffusion, facilitated diffusion, osmosis, filtration, active transport, endocytosis and exocytosis. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Relationship between Cell function and structure </span></h3>
<span style="font-size: large;">The bodies of animals and plants are made of different cell types. Each type performs specific function and all coordinated functions become the life processes of the organism.

We can imagine the specialities of different cell types and the contribution of individual cells to the healthy functioning of the body. </span><br />
<span style="font-size: large;">For example in human body; Nerve cells conduct nerve impulse and thus contribute in coordination in body.

Muscle cells undergo contraction and share their role in movements in body.

Red blood cells carry oxygen and white blood cells kill foreign agents and so contribute in the roles of blood in transportation and defence. </span><br />
<span style="font-size: large;"> Some skin cells act as physical barriers against foreign materials and some as receptors for temperature, touch, pain etc.

The cells of bone deposit calcium in their extracellular spaces to make the bone tough and thus contribute to the supporting role of bones.

cell works as an open system i.e. it takes in substances needed for its metabolic activities through its cell membrane. </span><br />
<span style="font-size: large;">Then it performs the metabolic processes assigned it. Products and by-products are formed in metabolism. Cell either utilizes the Products or transports them to other cells. The by-products are either stored or are

excreted out of the cell. </span></div>

Cell size and relation between prokayotic and Eukaryotic cells

Similarities between Prokaryotic and Eukaryotic cells DNA They both have DNA as their genetic material. Membrane They are both memb...

Animal tissues

Abdullah 0 Article, biology Thursday, January 30, 2014

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<span style="font-size: large;">ANIMAL TISSUES </span></h3>
<span style="font-size: large;"> In the bodies of animals, there are four major categories of tissues: </span><br />
<span style="font-size: large;">epithelial tissue,</span><br />
<span style="font-size: large;"> connective tissue, </span><br />
<span style="font-size: large;">muscle tissue, </span><br />
<span style="font-size: large;">and nervous tissue </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Epithelial tissue</span></h3>
<span style="font-size: large;"> Epithelial tissue covers the outside of the body and lines organs and cavities. The cells in this type of tissue are very closely packed together and joined with little space between them. Epithelial tissue helps to protect organisms from microorganisms, injury and fluid loss. These tissues are commonly classified on the base of the shape of the cells as well as the number of cell layers. Some types include:

Simple Squamous </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Epithelium </span></h3>
<span style="font-size: large;">A single layer of tightly packed, flattened cells.

Found in lining of air sacs of the lungs, heart and blood vessels etc. Allows diffusion and filtration.

Simple Cuboidal Epithelium

Consists of single layer of tightly packed, cube-shaped cells.

Found in kidney tubules, ducts and small glands. Makes secretions and absorbs materials. </span><br />
<span style="font-size: large;"> Simple Columnar Epithelium

Consists of single layer of elongated cells. Found in the lining of digestive tract and gallbladder etc.

Makes enzyme secretions. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Ciliated Columnar Epithelium </span></h3>
<span style="font-size: large;">A tuft of cilia is present at the top of each columnar cell. Stratified

Squamous

Epithelium

Consists of many layers of flattened cells.

Found in the inner lining of esophagus, mouth, and at the surface of </span><br />
<span style="font-size: large;"> the skin. It Protects underlying tissues from abrasion. </span><br />
<span style="font-size: large;"> We know that an animal's survival depends on its ability to respond appropriately to stimuli from its environment. This ability requires the transmission of information from one part of the body to another. Nervous tissue forms a communication system and performs this task.

This tissue is mainly composed of nerve cells, or neurons, which are specialized to conduct messages in the form of nerve impulses. Nervous tissue is found in brain, spinal cord and nerves.

Exercise does not increase the numbers of our skeletal muscle cells; it simply enlarges those already present. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Muscle tissue</span></h3>
<span style="font-size: large;"> Muscle tissue consists of bundles of long cells called muscle fibers.

It is the most abundant tissue in a typical animal. The cells of this tissue have ability to contract. There are three kinds of muscle tissue in vertebrates i.e. skeletal muscles, smooth muscles and cardiac muscles. The skeletal muscles are voluntary in action i.e. their contraction is under the control of our will. The smooth and cardiac muscles are involuntary in action i.e. their contraction is not under the control of our will. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Nervous tissue </span></h3>
<span style="font-size: large;">An animal's survival depends on its ability to respond appropriately to stimuli from its environment. This ability requires the transmission of information from one part of the body to another. Nervous tissue forms a communication system and performs this task.

This tissue is mainly composed of nerve cells, or neurons, which are specialized to conduct messages in the form of nerve impulses. Nervous tissue is found in brain, spinal cord and nerves.</span></div>

Animal tissues

ANIMAL TISSUES In the bodies of animals, there are four major categories of tissues: epithelial tissue, connective tissue, muscle...

Ways of movement of material across the cell

Abdullah 0 Article, biology Thursday, January 30, 2014

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<span style="font-size: large;">Diffusion </span></h3>
<span style="font-size: large;"> "Diffusion is the net movement of a substance from an area of higher concentration to the area of lower concentration i.e. along concentration gradient."

Since the molecules of any substance (solid, liquid, or gas) are in motion when that substance is above 0 degrees Kelvin or -273 degrees C, energy is available for movement of the molecules from a higher potential state to a lower potential state. </span><br />
<span style="font-size: large;">The molecules move from higher to lower concentration, a though there will be some that move from low to high. The overall (or net) movement is us from high to low concentration. Eventually, if no energy is input into the system the molecules will reach a state of equilibrium where they will be distributed equally throughout the system.</span><br />
<span style="font-size: large;"> Because a cell does not expend energy when molecules diffuse across its membrane, the diffusion is type of passive transport.

Diffusion is one principle method of movement of substances within cells, as well as the method for essential small molecules to cross the cell membrane. Carbon dioxide and oxygen are among the few simple molecules that can cross the cell membrane by diffusion. Gas exchange in gills and lungs operates by this process. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Facilitated diffusion</span></h3>
<span style="font-size: large;"> Many molecules do not diffuse freely across cell membranes because of their size or charge. Such molecules are taken into or out of the cells with the help of transport- proteins present in cell membranes. When one of these transport proteins makes it possible for a substance to move it down its concentration gradient (from higher to lower concentration), the process is called facilitated diffusion. The rate of facilitated diffusion is higher than simple diffusion.

Facilitated diffusion is also a type of passive transport because there is no expenditure of energy in this process. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Osmosis </span></h3>
<span style="font-size: large;">Osmosis is the movement of water across a selectively permeable membrane from a solution of lesser solute concentration to a solution of higher solute concentration.

The rules of osmosis can be best understood through the concept of tonicity of the solutions. The term tonicity refers to the relative concentration of solutes in the solutions being compared. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Hypertonic solutions </span></h3>
<span style="font-size: large;">These are those in which more solute is present. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Hypotonic solutions </span></h3>
<span style="font-size: large;"> These are those with less solute.

Isotonic solutions have equal concentrations of solutes. </span><br />
<span style="font-size: large;"> In a hypertonic solution the solute molecules attract clusters of water molecules, so that fewer water molecules are free to diffuse across the membrane. On the other hand in a hypotonic solution with fewer solute molecules, there are more free water molecules and there is net movement of water from hypotonic solution to the hypertonic solution. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Water balance problems: </span></h3>
<span style="font-size: large;">When an animai cell, such as the red blood cell, is placed in an isotonic solution, the cells volume remains constant because the rate at which water is entering the cell is equal to the rate at which it is moving out. When a cell is placed in a hypotonic solution (which has lower salt concentration than the cell) water enters and the cell swells and may rupture like an over-filled balloon. </span><br />
<span style="font-size: large;">Similarly an animal cell placed in a hypertonic solution (which has higher salt concentration than the cell) will lose water and will shrink in size. So in hypotonic environments (freshwater) animal cells must have ways to prevent excessive entry of water and in hypertonic environments (seawater) they must have ways to prevent excessive loss of water. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Turgor</span></h3>
<span style="font-size: large;"> Turgor  of the cells is responsible for maintaining shapes of non-woody plants and soft portions of trees and shrubs.

Water balance problems are somewhat different for plant cells because of their rigid cell walls. Most plant ceils live in hypotonic environment because there is low concentration of solutes in extracellular fluids than in their cells. </span><br />
<span style="font-size: large;">As a result water tends to move first inside the cell and then inside the vacuole. When vacuole increases in size the cytoplasm presses firmly against the interior of the cell wall, which expands a little. Due to strong cell wall, plart cell does not rupture but instead becomes rigid. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Turger pressure </span></h3>
<span style="font-size: large;">The internal pressure of such a rigid cell is known as turgor pressure and this phenomenon is known as turgor.</span><br />
<span style="font-size: large;"> In isotonic environment the plant cell is flaccid (loose / not firm), because the net uptake of water is not enough to make it turgid. In a hypertonic environment a plant cell loses water, causing the cytoplasm to shrink within the cell wall. </span><br />
<span style="font-size: large;">The shrinking of cytoplasm is called plasmolysis.

Stomata (openings) in leaf epidermis are surrounded by guard cells. During daytime guards cells are making glucose and so are hypertonic (have higher concentration of glucose) than their nearby epidermis cells. </span><br />
<span style="font-size: large;">Water enters them from other cells and they swell. In this form they assume a rigid bowed shape, creating a pore between them. At night when there is low solute concentration in guard cells water leaves them and they become flaccid. In this form both guard cells rest against one another, closing the opening. </span><br />
<br />
<h3 style="text-align: left;">
<span style="font-size: large;">Semi-permeable membrane </span></h3>
<span style="font-size: large;">The knowledge about semi-permeable membranes is applied for various purposes. We know that semi-permeable membrane is capable of separating substances when a driving force is applied across it. Artificially synthesized semi-permeable membranes are used for separation of bacteria from viruses, because bacteria cannot cross a semi- permeable membrane. In advanced water-treatment technologies membrane-based filtration systems are used. </span><br />
<span style="font-size: large;">Semi-permeable membranes efficiently separate salts from water under pressure.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Filtration </span></h3>
<span style="font-size: large;"> Filtration is a process by which small molecules are forced to move across semi- permeable membrane with the aid of hydrostatic (water) pressure or blood pressure.

For example in the body of an animal, blood pressure forces water and dissolved molecules to move through the semi-permeable membranes of the capillary wall cells.</span><br />
<span style="font-size: large;"> In filtration the pressure cannot force large molecules, such as proteins, to pass through the membrane pores . </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Active transport </span></h3>
<span style="font-size: large;">Active transport is the movement of molecules from an area of lower concentration to the area of higher concentration. This movement against the concentration gradient requires energy in the form of ATP.

In this process, carrier proteins in the cell membrane use energy to move the molecules against the concentration gradient.</span><br />
<span style="font-size: large;"> For example the membranes of nerve cells have carrier proteins in the form of “sodium-potassium pump”. In a resting (not conducting nerve impulse) nerve cell, this pump spends energy (ATP) to maintain higher concentrations of K+ and lower concentrations of Na+ inside the cell. For this purpose, the pump actively moves Na+ to the outside of the cell where they are already in higher concentration. Similarly this pumps moves K+ from outside to inside the cell where they are in higher concentration

molecules.

Outside of cell

In diffusion and filtration, only small molecules can pass across membrane.

It is a special type of movement of material across cell membranes. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Endocytosis</span></h3>
<span style="font-size: large;">In endocytosis bulky materials, rather than individual molecules, are moved across the cell membrane. Endocytosis occurs in following steps:

Aportion of cell membrane invaginates (depressed inward).

The material from outside is taken inside the invagination.

The open ends of the invagination seal and form a small vesicle.

The vesicle detaches from the cell membrane and moves into the

cytoplasm.

The two forms of endocytosis are </span><br />
<span style="font-size: large;">phagocytosis (cellular eating) </span><br />
<span style="font-size: large;"> pinocytosis (cellular drinking).</span><br />
<br />
<h3 style="text-align: left;">
<span style="font-size: large;">Phagocytosis (cellular eating) </span></h3>
<span style="font-size: large;"> In phagocytosis cell takes in solid material </span><br />
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<span style="font-size: large;"> </span><span style="font-size: large;"> Pinocytosis (cellular drinking).</span></h3>
<span style="font-size: large;"> Pinocytosis cell takes in liquid in the form of droplets. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Exocytosis</span></h3>
<span style="font-size: large;"> It is the process through which bulky material is exported. Exocytosis occurs in following steps: </span><br />
<span style="font-size: large;">The bulky material is packed inside a membrane and a vesicle is formed.

The vesicle moves to the cell membrane.

The vesicle fuses with the membrane and releases its contents into the extracellular environment.

This process adds new membrane which replaces the part of cell membrane lost during endocytosis. </span><br />
<span style="font-size: large;">Bulky Cell material membrane

are familiar with the levels of structural organization of life and recognize tissue as a qroup of similar cells specialized for the performance of a common function. In this topic we will leam about the major types of animal and plant tissues, with reference to their cell specificities, locations and functions.</span><br />
<span style="font-size: large;"> In a colony of cells there are many cells and each cell performs all general functions on its own. Such a group does not get tissue level of organization because cells are not specific and there is no coordination among them.

</span></div>

Ways of movement of material across the cell

Diffusion "Diffusion is the net movement of a substance from an area of higher concentration to the area of lower concentration i....

Plant tissues

Abdullah 0 Article, biology Thursday, January 30, 2014

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<span style="font-size: large;">As in animals, the cells of plants are grouped into tissues with characteristic functions such as photosynthesis, transport etc. There are two major categories of tissues in plants i.e. simple tissues and compound (complex) tissues. </span><br />
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<span style="font-size: large;">Simple tissues</span></h3>
<span style="font-size: large;"> The tissues which are made of single type of cells, are called simple tissues. They are of two types i.e. meristematic tissues and permanent tissues. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Meristematic tissues </span></h3>
<span style="font-size: large;">These tissues are composed 'of cells, which have the ability to divide. The cells of meristematic tissues show following properties:

They have thick cytoplasm, with large nucleus in the center and with small or no vacuoles.

They are thin-walled. </span><br />
<span style="font-size: large;">They are all alike and there are no inter-cellular spaces among them.

In plants cell division occurs solely in meristematic regions. Two main types of meristematic tissues are recognized in plants.

Apical meristems are located at the apices or tips of roots and shoot. </span><br />
<span style="font-size: large;">When they divide they cause increase in the length of plant. Such a growth is called primary growth.

Lateral meristems are located on the lateral sides of roots and shoot. By dividing they are responsible for horizontal expansion of the parts of plant. Such a growth is called secondary growth.</span><br />
<span style="font-size: large;"> Lateral mersitems are further of two types i.e. vascular cambium and cork cambium. Vascular cambium is present between the xylem and phloem tissues. Its cells divide and form new xylem tissue toward the center and new phloem tissue towards the outside. Cork cambium is present in the outer lateral sides and its cells are responsible for making the characteristic corky layer. </span><br />
<span style="font-size: large;">Intercalary meristem occurs in the form of small patches of meristem present among the mature tissues. These are common in grasses and help in the regeneration of parts removed by herbivores etc.
Permanent tissues

Permanent tissues originate from the meristematic tissue. </span><br />
<span style="font-size: large;">These tissues are composed of cells, which do not have the ability to divide. They are further classified into following types:
Epidermal Tissues Epidermal and sclerenchyma tissues .</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Epidermal tissues </span></h3>
<span style="font-size: large;">Epidermal tissues are composed of a single layer of cells and they cover the plant body. They act as a barrier between the environment and the internal plant tissues. They are also responsible for the absorption of water and minerals primarily in the root region. On stem and leaves they secrete cutin (the coating of cutin is called cuticle) which prevents

evaporation.</span><br />
<span style="font-size: large;"> Leaf hairs reflect light and are important for j plants in dry regions.

Here excess light may lead to photobleaching of pigments and excess absorption may overheat the tissues.

Epidermal tissues also have some specialized cells that perform specific functions. For example;

Root hairs absorb water and minerals.</span><br />
<span style="font-size: large;"> Leaf hairs reflect light to protect against overheating and excessive water loss. The layer of leaf hairs acts to hold in a layer of humidity 'trapped'. This layer also prevents air moving directly against the stomata which would encourage water loss.

Stomata are made by guard cells and are most abundant on underside of leaves. They regulate diffusion of carbon dioxide into the leaf for photosynthesis as well as regulate loss of water from the leaf

Salt glands are the waste-bins for the excess salt absorbed from the soil. </span><br />
<span style="font-size: large;">They form a crust of salt on leaves which reflects light to prevent overheating.

Ground Tissues

Most parenchyma cells I can develop the ability to  divide and differentiate into other types of cells \ and they do so during the process of repairing an injury.

Ground tissues are simple tissues made up of parenchyma cells. Parenchyma cells are the most abundant cells in plants.

Overall they are spherical but flat at point of contact. </span><br />
<div style="text-align: left;">
<span style="font-size: large;">They have thin primary cell walls and have large vacuoles for storage of food. In leaves they are called mesophyll and are the sites of photosynthesis. In other parts they are the sites of respiration and protein synthesis.
Support Tissues

These tissues provide strength and flexibility to the plants. They are further of two types,  </span></div>
<h3 style="text-align: left;">
<span style="font-size: large;">Collenchyma Tissue</span></h3>
<span style="font-size: large;"> They are found just beneath the epidermis in the cortex of young herbaceous stems and the midribs of leaves and in petals of flowers. They are made of elongated cells with unevenly thickened primary cell walls. They are flexible and function to support the organs in which they are found. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Sclerenchyma Tissue </span></h3>
<span style="font-size: large;"> They are composed of cells with rigid secondary cell walls. </span><br />
<span style="font-size: large;">The cell walls are hardened With lignin, which is the main chemical component of wood. Mature sclerenchama cells cannot elongate and most of them are dead. </span><br />
<span style="font-size: large;">There are two types of cells in tissues, </span><br />
<span style="font-size: large;">(i) fibre cells are associated with xylem and phloem tissues, and cells are found in seed coats. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">xylem and phloem tissue </span></h3>
<span style="font-size: large;">A plant tissue composed of more than one type of cell is called a compound or complex tissue. Xylem and phloem tissues, found only in vascular plants, are examples of compound tissues. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Xylem Tissue </span></h3>
<span style="font-size: large;">Xylem tissue is responsible for the transport of water and dissolved substances from roots to the aerial parts. Due to the presence of lignin, the secondary walls of its cells are thick and rigid. That is why xylem tissue provides support to the plant body .</span><br />
<span style="font-size: large;"> Following types of cell are found in xylem tissue; </span><br />
<b><span style="font-size: large;">Vessel Elements or Cells: </span></b><br />
<span style="font-size: large;"> These are short and wide cells with thick secondary cell walls. The vessel cells are dead and hollow. They lack end walls and join together to form long tubes.

b- Tracheids: These are long, slender cells with overlapping ends. </span><br />
<span style="font-size: large;">Water moves upward from tracheid to tracheid

Phloem tissue is responsible for the conduction of

dissolved organic matter.These are long cells. Their walls have small pores and are called sieve Plates. Many sieve tube cells join to form long Pipelines called sieve tubes. During development they lose their nuclei and ribosomes etc and Possess little protoplasm.

</span></div>

Plant tissues

As in animals, the cells of plants are grouped into tissues with characteristic functions such as photosynthesis, transport etc. There are ...

Structure of cell

Abdullah 0 Article, biology Sunday, January 26, 2014

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<h2 style="text-align: left;">
<span style="font-size: large;">Cell structure </span></h2>
<span style="font-size: large;"> There are some major structures that somewhat get lost in the shuffle when we talk about organelles. They are not organelles, but are still extremely important components of the cellular system. They are the cell wall, the cell membrane and the cytoplasm. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Cell wall </span></h3>
<span style="font-size: large;">We know that not all living organisms have cell walls around their cells, most notably animals and many animal-like protists. The cell wall is a non-living and strong component of the cell, located outside the plasma membrane. It provides shape, strength, protection and support to the inner living matter (protoplasm) of the cell. </span><br />
<span style="font-size: large;">Plant cells have a variety of chemicals in their cell walls. The outer layer of the plant cell wall is known as primary wall and cellulose is the most common chemical in it. Some plant cells, for example xylem cells, also have secondary walls on the inner side of the primary wall. It is much thicker and lignin and other chemicals are embedded in it. </span><br />
<span style="font-size: large;">In the walls of neighbouring cells there are cytoplasmic connections called Plasmodesmata. Through these connections, cells transfer chemicals among each other.

Fungi and many protists have cell walls although they do not contain cellulose. Their cell walls are made of a variety of chemicals. </span><br />
<span style="font-size: large;">For example chitin is present in the cell wall of fungi. Prokaryotes have a cell wall composed of peptidoglycan that is a single large polymer of amino acids and sugar. All prokaryotic and eukaryotic cells have a thin and elastic cell membrane covering the cytoplasm. The cell membrane functions as a semi-permeable barrier, allowing a very
few molecules across it while fencing the majority of chemicals inside the cell. </span><br />
<span style="font-size: large;">In this way the membrane maintains the internal composition of the cell to a constant or nearly constant level. In addition to this vital role, cell membrane can also sense chemical messages and can identify materials and other cells etc.

Chemical analysis reveals that cell membrane is mainly composed of proteins and lipids with small quantities of carbohydrates.</span><br />
<span style="font-size: large;"> Electron microscopic examinations of cell membranes have led to the development of the fluid-mosaic model of cell membrane .

When we talk about all the membranes of a cell, we say them as cell membranes.

When we talk about only the outer membrane of the cell, we say it as plasma membrane.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Cholesterol. </span></h3>
<span style="font-size: large;">Proteins may be fully submerged in the lipid bilayer or some of them may "stick out" into the interior and outside of the cell. These proteins function as gateways that allow certain molecules to cross into and out of the cell.

Small amounts of carbohydrates are also found in cell membranes. </span><br />
<span style="font-size: large;">These are joined with proteins (in the form of glycoproteins) or with lipids (in the form of glycolipids). Both these forms act as fingerprints of the cell.

Another lipid, cholesterol, is an important component of cell membranes embedded in e inner region of the lipid bilayer.</span><br />
<span style="font-size: large;"> Most bacterial cell membranes do not contain cholesterol.cell many organelles e.g. mitochondria, chloroplasts, Golgi apparatus, and plasmic reticulum are also bounded by cell membranes.
Cytoplasm

Cytoplasm is the material between the plasma membrane (cell membrane) and the nuclear envelope. </span><br />
<span style="font-size: large;">It is a semi-viscous and semi-transparent substance.

(proteins, carbohydrates, lipids) and inorganic salts are completely or partially dissolved.

The cytoplasm of the cell provides space forthe properfunctioning of the organelles and also acts as the site for various biochemical (metabolic) reactions for example Glycolysis (breakdown of glucose during cellular respiration). </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Cytoskeleton</span></h3>
<span style="font-size: large;"> The cytoskeleton is an important, complex and dynamic cell component. It is invisible under light microscope. It maintains the cell's shape, anchors organelles in place and moves parts of the cell in processes of growth and motility. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Plasma membrane</span></h3>
<span style="font-size: large;"> There are many types of filaments that make up the cytoskeleton but the mostimportant ones are microtubules and microfilaments.. Microtubules are made of tubulin subunits and are often

used by cells to hold their shape. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Endoplasmic Microtubules </span></h3>
<span style="font-size: large;"> These are also the major reticu|um

component of cilia and flagella. Ribosomes Microfilaments are made of actin subunits. These microfilaments are approximately one-third of the diameter of a microtubule and are often used by cells to change their Microfilaments shapes and to hold structures.
Cell organelles

Organelles are small structures within cells that perform dedicated functions. </span><br />
<span style="font-size: large;">There are about a dozen types of organelles commonly found in eukaryotic cells. We will go* through the basic facts about important cell organelles.
Nucleus

Nucleus

A prominent nucleus occurs in eukaryotic cells. In animal cells it is present in the center while in mature-plant cells, due to the formation of large central vacuole, it is pushed to side. The nucleus is bounded by a double membrane known as nuclear envelope. </span><br />
<span style="font-size: large;">The nuclear envelope contains many small pores that enable it to act as a differentially- permeable membrane. Inside the nuclear envelope a granular matrix, the nucleoplasm, is present. The nucleoplasm contains one or two nucleoli (singular; nucleolus) and chromosomes .</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Nucleolus </span></h3>
<span style="font-size: large;">The nucleolus is usually visible as a dark spot and it is the site where ribosomal RNA are formed and assembled as ribosomes. Chromosomes are visible only during cell division while during interphase (non-dividing phase) of the cell they are in the form of fine thread-like structures known as chromatin. </span><br />
<span style="font-size: large;">Chromosomes are composed of deoxyribonucleic acid (DNA) and histone proteins. Histone proteins provide structural support to DNAfor making the structure of chromosome.

mRNA contains the message for the synthesis of specific proteins. </span><br />
<span style="font-size: large;">According to this message, a molecule of messenger Ribonucleic Acid (mRNA) is synthesized. In this way, message is handed over to mRNA, which carries it to ribosomes. Ribosomes manufacture specific protein according to the message present on mRNA. </span><br />
<span style="font-size: large;">In this way DNA controls all the activities of the cell and is also responsible for the transmission of characteristics to the next generation. That is why it is honoured as the hereditary material.

The prokaryotic cells do not contain prominent nucleus rather their chromosome is made of DNAoniy and is submerged in the cytoplasm.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Ribosomes </span></h3>
<span style="font-size: large;">Ribosomes are tiny granular structures that are either floating freely in the cytoplasm or are bound to the dopiasmic reticulum (ER). Each ribosome is made up of f eclual amounts of proteins and ribosomal RNA . Ribosomes are not bound by membranes and so jealso found in prokaryotes. </span><br />
<span style="font-size: large;">Eukaryotic ribosomes are highly larger than prokaryotic ones.

Ribosomes are the sites of protein synthesis, where the protein carried by mRNA is translated into protein.

Animal cells have two centrioles located near the exterior surface of the nucleus .

In cells that contain cilia and or flagella, centrioles are involved in the formation

Vacuoles are fluid filled single-membrane bound organelles. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Vacuoles </span></h3>
<span style="font-size: large;">Cells have many small vacuoles in their cytoplasm. However, when a plant cells matures its small vacuoles absorb water and fuse to form a single large vacuole in the centre. The cell in this state becomes turgid. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Lysosomes </span></h3>
<span style="font-size: large;">Many cells take in materials from outside in the form of food vacuole and then digest the material with the help of lysosomes. Some unicellular organisms use contractile vacuole for the elimination of wastes from their bodies.

</span></div>

Structure of cell

Cell structure There are some major structures that somewhat get lost in the shuffle when we talk about organelles. They are not organe...

Cell theory

Abdullah 0 Article, biology Sunday, January 26, 2014

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<h3 style="text-align: left;">
<span style="font-size: large;">Aristotal view about cell </span></h3>
<span style="font-size: large;">Aristotle presented organized observations to support the idea that all animals and plants are some how related</span><br />
<span style="font-size: large;"> Later this idea gave rise to questions like “is there a fundamental unit of structure shared by all organisms?”. But before microscopes were first used in 17th century, no one knew with certainty that living organisms do share a fundamental unit i.e. cell.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Robert hook</span></h3>
<span style="font-size: large;">  Cells were first described by a British scientist, Robert Hooke in 1665. He used his self- made light microscope to examines thin slice of cork. Hooke observed a “honeycomb” of tiny empty compartments. </span><br />
<span style="font-size: large;">He called the compartments in the cork as “cellulae”. His term has come to us as cells . The first living cells were observed a few years later by the Dutch naturalist Antonie van Leeuwenhoek. He observed tiny organisms (from pond water) under his microscope and called them as “animalcules”.  </span><br />
<h3>
<span style="font-size: large;">Jean Baptist de-Lamark </span></h3>
<span style="font-size: large;"> For another century and a half, the general importance of cells was not appreciated by biologists. In 1809, Jean Baptist de-Lamarck proposed that “no body can have life if its constituent parts are not cellular tissues or are not formed by c ellular tissues”.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Robert brown </span></h3>
<span style="font-size: large;">In 1831, a lush botanist Robert Brown discovered nucleus in the cell. In 1838, a German  scientist  Matthias Schleiden studied plant tissues and made the first statement of the theory. He stated that all plants “are aggregates of individual cells which are fully separate beings”. One year later, in 1839, a German zoologist reported that all animal tissues are also composed of individuas.</span><br />
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<h3 style="text-align: left;">
<span style="font-size: large;">Schlieden and Schwann </span></h3>
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjX2ScCASyk3vRLEF0Uz1PuOMc16ycLnf8ywWpqKLjK7DsxIvHRXNRsk4QqWPKTMAohwINytf7vyDtK4nVESgUNJ6-qRXyrB3F-w3yUYJvJtYO3wSwXVdmz5RK5zomvZz5W_PRzMrWBoIo/s1600/M.Schleiden.bmp" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjX2ScCASyk3vRLEF0Uz1PuOMc16ycLnf8ywWpqKLjK7DsxIvHRXNRsk4QqWPKTMAohwINytf7vyDtK4nVESgUNJ6-qRXyrB3F-w3yUYJvJtYO3wSwXVdmz5RK5zomvZz5W_PRzMrWBoIo/s1600/M.Schleiden.bmp" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Schlieden</td></tr>
</tbody></table>
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<span style="font-size: large;">Thus Schleiden and Schwann proposed cell theory in its initial </span><br />
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<span style="font-size: large;"> <table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwQtLhdsDqQNVDRNWpnH5hdAJaH_fs8KFjLbPLBgLc6e6GWkkZEbxGj-aPZyG5uHz9PCfHrZeWVfzQljLGDVeaRSqPP19pxbgMDlo-jUIQhEaOiYeekvC0KJBOgvgz7atjxBYITwvDJRs/s1600/T.Shwann.bmp" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwQtLhdsDqQNVDRNWpnH5hdAJaH_fs8KFjLbPLBgLc6e6GWkkZEbxGj-aPZyG5uHz9PCfHrZeWVfzQljLGDVeaRSqPP19pxbgMDlo-jUIQhEaOiYeekvC0KJBOgvgz7atjxBYITwvDJRs/s1600/T.Shwann.bmp" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Schewamm</td></tr>
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<span style="font-size: large;">form i.e. all living

things are composed of living cells”. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Rudolf Virchow  </span></h3>
<span style="font-size: large;">Twenty years later in 1855 Rudolf Virchow, a German physician, proposed an important extension of cell theory. He proposed that all living cells arise from preexisting cells . </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Lious Pasture</span></h3>
<span style="font-size: large;"> In 1862, Louis <a href="http://educational-wealth.blogspot.com/2014/03/louis-pasteur.html" target="_blank"><span style="color: lime;"><b>Pasteur</b></span></a> provided the experimental proof of this idea.

The cell theory is regarded as one of the most fundamental generalizations in biology. It has wide ranging effects in all fields of research. </span><br />
<span style="font-size: large;">After the initial presentation of the cell theory by Schleiden and Schwann, many details of cells were studied and cell theory was extended. The cell theory, in its modern form, includes the following principles;

All organisms are composed of one or more cells, within which all life processes occur.

Cells are the smallest living things, the basic unit of organization of all organisms.

Cells arise only by divisions in previously existing cells. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Sub-cellular or Aceilular Particles: </span></h3>
<span style="font-size: large;"> According to the first principle of the cell theory all organisms are composed of one or more cells. Discovery of virus, prions and viroids claim that the statement is not so universal. They are not composed of cells; rather they are sub-cellular or aceilular particles, which do not run any metabolism inside them. </span><br />
<span style="font-size: large;">But they show some characteristics of living organisms i.e. they can increase in number and can transmit their characters to the next generations.</span><br />
<span style="font-size: large;"> There are two general classes of cells: .

The evolution of prokaryotic cells preceded that of eukaryotic cells by 2 billion years. </span><br />
<span style="font-size: large;"> Streptococcus pyogenes, the bacterium that causes infections in the upper
respiratory tract (e.g. sore throat), is an example of prokaryotes.

Yeast, the organism that carries out fermentation and makes our bread rise,
is an example of unicellular eukaryotes.

Humans, of course, are an example of multicellular eukaryotes.

We are well familiar with the basic organization of a eukaryotic cell. Here we will get some detailed learning about the cellular structure and functions.

</span></div>

Cell theory

Aristotal view about cell Aristotle presented organized observations to support the idea that all animals and plants are some how relate...

Microscopes

Abdullah 0 Article, biology Friday, January 24, 2014

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<h3 style="text-align: left;">
<span style="font-size: large;">Microscopy</span></h3>
<span style="font-size: large;"> "The use of microscope is known as microscopy. "

The first compound microscope was developed by Zacharhs Janssen, in Holland in 1595. It was simply a tube with lenses at each end and its magnification ranged from 3X to 9X.

Two important terms are used in microscopy i.e. magnification and resolving power.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Magnification</span></h3>
<span style="font-size: large;"> "Magnification is the increase in the apparent size of an object and it is an important factor in microscopy."
Resolving power 
"Resolving Power or resolution is the measure of the clarity of an image."
 It is the minimum distance at which two objects can be seen as separate objects, The human naked eye can differentiate between two points, which are at least 0.1 mm apart. </span><br />
<span style="font-size: large;">This is known as the resolution of human eye. If we place two objects 0.05 m art, human eye would not be able to differentiate them as two separate objects. The resolution can be increased with the help of lenses.

Light microscopy and electron microscopy

Now two types of microscope i.e. light microscope (LM) and electron microscope (EM) are used in microscopy.</span><br />
<span style="font-size: large;"> When we see a micrograph on the page of a book, we see some words like “LM 109X” printed along the edge of the micrograph. It tells us that the photomicrograph was taken through a light microscope and that the image has been magnified 109 times. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Light Microscope</span></h3>
<span style="font-size: large;"> A light microscope works by passing visible light through a specimen. It uses two glass lenses. One lens produces an enlarged image of the specimen and the second lens magnifies the image and projects it into the viewer's eye or onto photographic film. A photograph taken through a microscope is called a micrograph. </span><br />
<span style="font-size: large;"> A light microscope can magnify objects only about 1500 times without causing blurriness i.e. its magnification is 1500X.</span><br />
<span style="font-size: large;"> Its resolving power is 0.2 micrometer (pm) and 1pm = 1/1000 mm. In other words, the LM cannot resolve (distinguish) objects smaller than 0.2 pm. It is about the size of the smallest bacterium. </span><br />
<span style="font-size: large;">The image of bacterium can be magnified many times, but the light microscope cannot show the details of its internal structure amoebae (left), unicellular algae (right)</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Electron Microscope</span></h3>
<span style="font-size: large;">

It is the most advanced form of microscope. In EM, the object and the lens is placed in a vacuum chamber and a beam of electrons is passed through he object. Electrons pass through or are reflected from the object and make image. </span><br />
<span style="font-size: large;">lectromagnetic lenses enlarge and focus the image onto a screen or photographic film.

The EM has much higher resolving power than the LM. The most modern EM can th objects as small as 0.2 nanometer (nm) and 1 nm = 1/1000,000 mm. It is a ousand-fold Improvement over the LM. Linder special conditions EM can detect lndividual atoms. Cells, organelles and even molecules like DNA and protein are much higher than single atoms. Biologists use two types of electron microscopes.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Transmission Electron Microscope (TEM)</span></h3>
<span style="font-size: large;"> It is used to study the details of the internal cell structure. The TEM can magnify objects about 250,000 times. In this microscopy specimen is cut into extremely thin sections. When electron beam is directed through the chamber, the electrons hit the specimen and are transmitted. </span><br />
<span style="font-size: large;">The lenses focus the transmitted electron beam onto a screen or photographic film for used to study the detailed architecture of cell surfaces. It uses an electron beam to scan the surface that has been coated with metal. When beam hits the metal, it is not absorbed or transmitted. Electrons are reflected from the metal . </span></div>

Microscopes

Microscopy "The use of microscope is known as microscopy. " The first compound microscope was developed by Zacharhs Janssen,...

Classification systems of all organisms

Abdullah 0 Article, biology Tuesday, January 21, 2014

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<b><span style="color: #38761d;"><span style="font-size: large;">Biological classification </span></span></b></h2>
<span style="font-size: large;"> "Biological classification is a method by which biologists group and categorize species of organisms.</span><br />
<h3 style="text-align: left;">
<span style="color: #38761d;"><span style="font-size: large;">"
Aims of Classification: </span></span></h3>
<span style="font-size: large;">There are two main aims of classification </span><br />
<span style="font-size: large;">1- To determine similarities and differences among organisms so that they can be studied easily. </span><br />
<span style="font-size: large;"> 2- To find the evolutionary relationships among organisms. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Taxonomy </span></h3>
<span style="font-size: large;">"The branch of biology which deals with classification is"called taxonomy" </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Systematics</span></h3>
<span style="font-size: large;">' The branch of biology which deals with classification and also traces the evolutionary history of organisms is known as systematics. "</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Basis of classification </span></h3>
<h3 style="text-align: left;">
<span style="font-size: large;">Evolutionry history </span></h3>
<span style="font-size: large;">Classification is based on relationship amongst organisms and such relationship is got through similarity in form or structure. These similarities suggest that all organisms are related to one another at some point in their evolutionary histories.

However, some organisms are more closely related than others. For example sparrows are more closely related to pigeons than to the insects. It means that the former two have common evolutionary histories.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Similarities in structure,biochemistry </span></h3>
<span style="font-size: large;"> Biologists have classified all the known organisms into groups and subgroups on the basis of similarities. These similarities are seen in structures, biochemistry, cytology and genetics. Modern genetics has provided another type of information to taxonomists. The

genetic differences between two studied organisms can be determined and can be used about similarities and differences in their structures and functions. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Taxonomic Hierarchy</span></h3>
<span style="font-size: large;"> "Taxa form a ladder, called taxonomic hierarchy.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">"
Taxa</span></h3>
<span style="font-size: large;"> "The groups into which organisms are classified are known as taxonomic categories or taxa (singular “taxon”)" taxa form a ladder, called taxonomic hierarchy. All the organisms are divided into five Kingdoms. Then, on the basis of similarities, each K'ngdom is further divided. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Phylum</span></h3>
<span style="font-size: large;"> A Phylum is a group of related classes </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Class </span></h3>
<span style="font-size: large;">A class is a group of related orders </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Orders </span></h3>
<span style="font-size: large;"> A order is a group of related genera </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Genus </span></h3>
<span style="font-size: large;">A genus is a group of related species </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Species </span></h3>
<span style="font-size: large;">A species is a group of similar organisms </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Species –
The Basic Unit of Classification:</span></h3>
<span style="font-size: large;"> Species is the basic unit of classification. “A species is a group of organisms which can interbreed freely among them and produce fertile offspring, but are reproductively isolated from all other such groups in nature.” Each species possesses its own distinct structural, ecological and behavioural characteristics.

In the definition of species we must emphasize “in nature” because two organisms related to two different but closely related species can cross-breed under artificial conditions. In such unnatural crosses they produce infertile offspring.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Interbreeding </span></h3>
<span style="font-size: large;">Across between a male donkey and a female horse produces an infertile offspring, the mule.

The criteria of interbreeding apply primarily to those that regularly interbreed among themselves. However, it cannot be used as a criterion for species recognition in the group of organisms where asexual reproduction predominates and they do not interbreed with one another.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Early system of classification </span></h3>
<span style="font-size: large;">The earliest known system of classification of organises comes from the Greek philosopher Aristotle, who classified all living organisms known at that time as either in the group ‘plants’ or in ‘animals’. In 700s Abu-Usman Umer Aljahiz described the characteristics of 350 species of animals in his book. He wrote a lot about the life of ants. In 1172 Ibn Rushd (Averroes), who was a judge (Qazi) in Seville, translated and abridged Aristotle's book “de Anima (On the Soul)” into Arabic. His original commentary is now lost, but its translation into

Latin is available.

The last part of the 16th century and the beginning of the 17th, careful study of animals commenced, which </span><br />
<span style="font-size: large;">served as an anatomical basis for classification.</span><br />
<span style="font-size: large;"> Scientists concerned with classification
Since late in the 15th century, a number of science authors had become concerned with e method of classification. </span><br />
<span style="font-size: large;">Some of them are: </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> </span><span style="font-size: large;">Andrea Caesalpino </span></h3>
<span style="font-size: large;">An Italian botanist Andrea Caesalpino (1519-1603) proposed the first methodical arrangement of plants. He divided plants into fifteen groups called “genera”.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> </span><span style="font-size: large;">John Ray</span></h3>
<span style="font-size: large;"> An English naturalist John Ray (1627-1705) published important works on plants’classification. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> </span><span style="font-size: large;">
Augustus Quirinus Rivinus </span></h3>
<span style="font-size: large;"> Augustus Quirinus Rivinus (1652-1723; German botanist) and Pitton de Tournefort (1656-1708; French botanist) introduced the practice of naming the P'ants according to their genera.</span><br />
<span style="font-size: large;"> </span><span style="font-size: large;"> Rivinus</span><br />
<span style="font-size: large;"> Rivinus introduced the category of order and Tournefort introduced even more sophisticated categories of class, section, genus, and species. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Modern classification </span></h3>
<span style="font-size: large;"> Modern classification has its root in the work of a Swedish biologist, Carolus Linnaeus, who grouped species according to similar physical characteristics. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Preference of biologists </span></h3>
<span style="font-size: large;"> Biologists prefer the system that can provide maximum information about the basic differences and similarities among different organisms.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Earlier classification system </span></h3>
<span style="font-size: large;">According to earlier classification system, organisms were classified into two kingdoms but now taxonomists agree on five-kingdom classification system. We will see the basis of these classification systems and the drawbacks in the two-kingdom and three-kingdom classification systems. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Two-kingdom classification system</span></h3>
<span style="font-size: large;"> Two kingdom classification system

It classifies all organisms into two kingdoms i.e. </span><br />
<span style="font-size: large;"> 1-Plantae </span><br />
<span style="font-size: large;">2- Animalia. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Autotrophes </span></h3>
<span style="font-size: large;">According to it,

"All organisms that can prepare food from simple inorganic materials and thus can preserve energy are autotrophs"

These are included in kingdom plantae. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Heterotrophes</span></h3>
<span style="font-size: large;"> "The organisms that cannot synthesize their food and depend on autotrophs or others are heterotrophs".

These are included in kingdom animalia like Euglena have both plant-like (presence of chlorophyll) and animal-like (heterotrophic mode of nutrition in darkness and lack of cell wall) characters. So there should be a separate kingdom for such organisms. This system also ignores the difference between organisms having prokaryotic and those having eukaryotic cells. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Three-kingdom classification system</span></h3>
<span style="font-size: large;"> In 1866. Ernst Hackel solved the first objection and proposed a third kingdom; Protista to accommodate euglena-like organisms. He also included bacteria in kingdom protista. In this system, fungi were still included in the kingdom plantae.

This'system did not clear the difference between prokaryotes and eukaryotes.Some biologists disagreed about the position of fungi in kingdom plantae. Fungi resemble plants in many ways but are not autotrophs. </span><br />
<span style="font-size: large;">There are special form of heterotrophs that get their food by absorption. They do not have cellulose in their cell walls rather possess chitin. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Five-kingdom classification system </span></h3>
<span style="font-size: large;"> In 1937, E-Chatton suggested the terms of, “Procariotique” to describe bacteria and “Eucariotique” .to describe animal and plant cells.

In 1967, Robert Wbittaker introducec the five-kingdom classification system. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Basis of five -kingdom classification system </span></h3>
<span style="font-size: large;">1-The levels of cellular organization i.e. prokaryotic, unicellular eukaryotic and multicellular eukaryotic.</span><br />
<span style="font-size: large;"> 2-The principal modes of nutrition i.e. photosynthesis, absorption, and ingestion.

On this basis, organisms are classified into five Kingdoms

1-Monera

2-Protista

3-Fungi

4-Plantae

5-Animalia. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Modification of five kingdom classification system</span></h3>
<span style="font-size: large;"> Tin Margulis and Karlene Schwartz modified the five-kingdom classification

organelles of symbiotic origin (mitochondria and chloroplast). They classified the organisms into the same five kingdoms as proposed by Whittaker. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Kingdom monera: </span></h3>
<span style="font-size: large;"> It includes prokaryotic' organisms i.e. they are made of prokaryotic cells. Monerans are unicellular, although some types form chains, clusters, or colonies of cells. Prokaryotic cells are radically different from eukaryotic cells. Most are heterotrophic but some perform photosynthesis because they have chlorophyll in their cytoplasm. Within this kingdom there are two vastly different kinds of organisms i.e. archaebacteria and eubacteria. </span><br />
<span style="font-size: large;">Many biologists believe that these two groups should be considered separate kingdoms. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Kingdom protista:</span></h3>
<span style="font-size: large;"> It includes eukaryotic unicellular and simple multicellular organisms. There are three main types of protists.

Algae are unicellular, colonial or sometime simple multicellular. They resemble plant cells with cell walls and chlorophyll in chloroplasts. Simple multicellular means that they do not have multicellular sex organs and do not form embryos during their life cycles.

Protozoans resemble animals whose cells lack chlorophyll and cell walls.

Some protists are like the fungi. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Kingdom fungi:</span></h3>
<span style="font-size: large;"> It includes eukaryotic multicellular reducers for example mushrooms. Fungi are heterotrophic organisms that are absorptive in their nutritional mode. Most fungi are decomposers. They live on organic material, secrete digestive enzymes and absorb small organic molecules formed by the digestion by enzymes.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Kingdom plantae: </span></h3>
<span style="font-size: large;"> It includes eukaryotic multicellular autotrophs. Plants are autotrophic in nutritional mode, making their own food by photosynthesis. They have multicellular reproductive organs and form embryos during their life cycles. Mosses, ferns and flowering plants are included in this kingdom.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Kingdom animalia: </span></h3>
<span style="font-size: large;"> It includes eukaryotic multicellular consumers. Animals live mostly by ingesting food and digesting it within specialized cavities. They lack cell wall and show movements.
Division of five kingdoms Into  groups on the basis of types of cells

Biologists believe that kingdom protista evolved from monera and then it gave rise to the other 3 eukaryotic kingdoms .</span><br />
<span style="font-size: large;"> 1-Fungi

2-plantae

3-Animalia.

Viruses are acellular .They do not possess cellular organization yet show some characters of only and act as infectious particles livings. Viruses are infectious entities which contain either RNA or DNA, normally encased in circular RNA only and act as protein coat, and reproduce only in living cells, and cause a number of diseases. </span><br />
<span style="font-size: large;">Thus they are not included in the five-kingdom classification system. Prions and viroids are also acellular organisms and are not included in the five-kingdom classification system.

</span></div>

Classification systems of all organisms

Biological classification "Biological classification is a method by which biologists group and categorize species of organisms. ...

Impacts of human beings on biodiversity

Abdullah 1 Article, biology Tuesday, January 21, 2014

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<h2 style="text-align: left;">
<span style="font-size: large;">Habitat loss and deforestation</span><span style="font-size: large;"> </span></h2>
<span style="font-size: large;"> Habitat loss and deforestation (cutting down of 
trees) are greatest threat to important causes of<a href="http://educational-wealth.blogspot.com/2014/01/classification-systems-of-all-organisms.html" target="_blank"><b> species</b></a> extinctions. 
As deforestation biodiversity on this Planet proceeds in tropical 
forests present in <a href="http://educational-wealth.blogspot.com/2014/01/worlds-regions.html" target="_blank"><b>tropical zone</b></a> of the world. it becomes the main cause of today. the mass extinction of 
species. All species have specific food and habitat needs. Tropical 
forests are important

because they harbour at least 50 percent of the world's 
biodiversityDirect observations prove that these forests are declining. </span><br />
<span style="font-size: large;">The original extent of tropical rain forests was 15 million square km. 
Now there remains about 7.5-8 million square km, so half is gone.

More significant is the persistent spread of farmers into the forests; 
the killing of trees through lopping, burning, and tapping; the 
development of small agricultural plots among the trees; and excessive 
grazing by domestic animals. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Over-hunting </span></h3>
<span style="font-size: large;">Over-hunting has been a significant cause of the extinction of hundreds 
of species and the endangerment of many more, such as whales, ibex, 
urial, markhor etc. Commercial hunting, both legal and illegal, is the 
principal threat.

Introduction of new species

Introduction of non-native species is an important and often overlooked 
cause of extinction.</span><br />
<span style="font-size: large;"> When new species are introduced to ecosystems the 
established species in that ecosystem may not survive. The new organisms
 may be predators, parasites, or simply aggressive species that deprive 
the established species of nutrients, water and light. For example 
Eucalyptus plants were imported from Australia and introduced in 
Pakistan. </span><br />
<span style="font-size: large;">These plants consume more water and have disturbed the water 
table (level of underground water). It harms other small plants that 
grow near Eucalyptus trees.
Domino effects

Domino effects occur when the removal of one species (an extinction 
event) or the addition of one species (an invasion event) affects the 
entire <a href="http://educational-wealth.blogspot.com/2014/01/classification-systems-of-all-organisms.html" target="_blank"><b>classification</b> <b>system</b>.</a></span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Domino effects on species  </span></h3>
<span style="font-size: large;"> Domino effects are especially likely when two 
or more species are highly interdependent. For example a starfish, 
facilitates the coexistence of many other invertebrates by eating 
mussels, which otherwise would harm other organisms. If starfish are 
eliminated from an ecosystem, mussels grow in number and prey on other 
animals. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Effect of pollution on species</span></h3>
<span style="font-size: large;"> Pollution from chemical contaminants certainly poses a further threat to
 species and ecosystems. While not commonly a cause of extinction, it 
harms those species whose range is extremely small. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Effect of climate change on ecosystem</span></h3>
<span style="font-size: large;">A changing global climate (due to pollution and global warming) 
threatens species and ecosystems. The distribution of species 
(biogeography) is largely determined by climate. When changes in climate
 disturb the distributions of species, many species find it difficult to
 adjust themselves in new climates.

The race to produce cash through fruits, spices, sugar, tobacco, <a href="http://educational-wealth.blogspot.com/2014/01/classification-systems-of-all-organisms.html" target="_blank"><b>soap</b></a>, 
rubber, <a href="http://educational-wealth.blogspot.com/2014/01/paper-industry.html" target="_blank">paper</a>, and cloth has stimulated many to get them by using soil 
and by destroying the forests. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">Effect of deforestation on ecosystem</span></h3>
<span style="font-size: large;"> Deforestation means cutting down of trees for the conversion of a forest
 to non-forest land. It is done for using the land for various purposes 
such as pasture, urban use etc . The destruction of significant areas of
 forest has resulted in a degraded environment with reduced 
biodiversity.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Causes and effects of deforestation</span></h3>
<span style="font-size: large;"> Sometime there is slow forest 
degradation and sometime sudden and catastrophic clear-cutting for urban
 development. Deforestation can be the result of the deliberate removal 
of forests for agriculture or urban development, or it can be a 
consequence of Qrazing animals. </span><br />
<span style="font-size: large;"> Deforestation affects the amount of water in the soil and the moisture 
in the atmosphere. When there are no trees to keep the soil in place, 
the soil becomes exposed for erosion. There is less protection from wind
 and rain and heavy rainfall washes the soil into <a href="http://educational-wealth.blogspot.com/2014/02/worlds-rivers.html" target="_blank">rivers</a> . Essential 
nutrients are washed out of the soil all-together. </span><br />
<span style="font-size: large;">Rivers become choked 
up with mud and silt, which can cause floods. The silted water gets 
stored in dams and it reduces their water storage capacity and thus 
their lives. Deforestation also contributes to decrease  transpiration, 
which lessens cloud formation and less humidity. </span><br />
<span style="font-size: large;">This ultimately reduces
 the sources of rains.

Forests support considerable biodiversity, providing valuable habitat 
for wildlife. Moreover, forests look after medicinal conservation. The 
utilization of forest products, '"eluding timber and fuel wood, have 
played a key role in human societies, comparable to the roles of water 
and land. </span><br />
<span style="font-size: large;">Today, developed countries continue to utilize timber for houses, and wood pulp for making paper.

The forest products industry is a large Part of the economy in both 
developed and developing countries. Short-term economic

gains made by conversion of forest to agriculture often leads to loss of
 long-term income.

Forests are also important stores of organic carbon, and forests can 
extract carbon dioxide and pollutants from the air, thus contributing to
 biosphere stability. </span><br />
<span style="font-size: large;">Forests are also valued for their aesthetic beauty
 and as a cultural resource and tourist attraction.
Conservation of biodiversity

biodiversity

The conservation of biodiversity has become a global concern. Biologists
 consider biodiversity essential and agree on the significance of 
current extinction of species. </span><br />
<span style="font-size: large;">Biologists urge the national policy 
makers to state a set of rules necessary to protect a species. They 
demand that the laws should define species which are threatened by 
extinction and must be protected.

Though rich in biodiversity, world today faces severe threats for its 
biological resources. </span><br />
<span style="font-size: large;">The greatest concern is the continuing loss of 
species and the loss of natural habitats. Main causes of this loss are 
largely associated with rapid growth in human population and the 
prevailing poverty in the rural areas of Pakistan.</span><br />
<span style="font-size: large;"> In addition low 
literacy rate and meagre resources are the reasons for limited success 
in conservation measures taken so far.

The International Union for the Conservation of Nature and Natural

Resources (IUCN) and the World Wildlife work in close coordination with 
Pakistan's Ministry of Environment and other government and 
non-government institutions. </span><br />
<span style="font-size: large;">The IUCN

has prepared the first national Red list of endangered or threatened 
species. According to this list following are the figures of the living 
and threatened species in Pakistan.Following are a few examples of 
environmental work that has been carried out in Pakistan in orderto 
conserve species and the associated habitats. </span></div>

Impacts of human beings on biodiversity

Habitat loss and deforestation Habitat loss and deforestation (cutting down of trees) are greatest threat to important causes of spec...

Variety of living Organisms(Biodiversity)

Abdullah 0 Article, biology Monday, January 20, 2014

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<span style="font-size: large;">Variety of living Organisms </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;">  Biodiversity </span></h3>
<span style="font-size: large;">At least 10 million kinds of organisms have been studied and catalogued by biologists. Diversity among the Earth's organisms is more obvious than the fundamental unity of life. This diversity emerged as modifications in organisms. We see that all organisms share many biological characteristics. They are composed of one or more cells, carry out metabolism and transfer energy with ATP, and have hereditary information in DNA. </span><br />
<span style="font-size: large;">Yet diversity in life is seen in million of different types of living organisms. The five principal groups of organisms are

Prokaryotes

Protists

Fungi

Plants

Animal
Biodiversity

The term “biodiversity” has been derived from 'bio' and 'diversity'. </span><br />
<span style="font-size: large;">Formerly it was called "natural diversity". "Diversity" means variety within a species and among species.

Biodiversity is a measure of the variety of organisms present in different ecosystems
Biodiversity hotspot

"It is a region with a high level of established species, Plants' and animals' (flora and fauna)."</span><br />
<br />
<h3 style="text-align: left;">
<span style="font-size: large;">Dependence of Biodiversity</span></h3>
<span style="font-size: large;"> Diversity depends on climate, altitude, soils and the presence of other species. Biodiversity is not distributed evenly on Earth. It is rich in the tropics while there are fewer species in the polar regions.

In the year 2006 large number of the Earth's species were classified as endangered or threatened species. </span><br />
<span style="font-size: large;">Most of the hotspofs are located in the tropics and most of them are forests. For example, Brazil's Atlantic Forest contain
History of biodiversity

Biodiversity found on Earth today is the result of 4 billion years of evolution The origin of llfe is not well known to science, though limited evidence suggests that until.600 million years ago, all life consisted of celled organ.

Biodiversity provides food for humans. </span><br />
<span style="font-size: large;">A significant proportion of drugs are derived, directly or indirectly from biological sources. A wide range of industrial materials e.gbuilding materials, fibres, dyes, resins, gums, adhesives, rubber and oil are derived rectlyfrom biological resources.

Biodiversity plays important role in making and maintaining ecosystems. It plays a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is directly involved in recycling nutrients and providing fertile soil
.</span><br />
<span style="font-size: large;"> There is a large collection of very dissimilar forms of organisms, found on Earth. Over 1.5 million types of animals and over 0.5 million types of plants are known to biologists and these are only a small percentage of the total types estimated to live on <a href="http://educational-wealth.blogspot.com/2014/02/our-lovely-planetearth-creation-origin.html" target="_blank"><b>Earth</b></a>.

They range in complexity from small and simple bacteria to large and complex human beings. </span><br />
<span style="font-size: large;">Some of them live in sea, some on land; some walk, others fly, and still others are stationary. Each has its own way of life i.e. getting food, avoiding unfavourable environmental conditions, finding a place to live, and reproducing its kind. </span><br />
<span style="font-size: large;">When we realize that there are so many diverse kinds of organisms, it becomes clear that no one can learn about the way of life of each.

To study such a large collection, biologists classify the organisms into groups and subgroups and for this task they require some system.</span></div>

Variety of living Organisms(Biodiversity)

Variety of living Organisms Biodiversity At least 10 million kinds of organisms have been studied and catalogued by biologists. Dive...

levels of organisms

Abdullah 0 Article, biology Monday, January 20, 2014

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<h3 style="text-align: left;">
<span style="font-size: large;">Biological Organization at different levels </span></h3>
<span style="font-size: large;"> In order to understand the various phenomena of life, biologists study biological organization at different levels. The list goes from simpler to complex levels. Subatomic particles make atoms and atoms make molecules. Different molecules of life make organelles and different organelles assemble together to form the simplest living unit i.e. the cell.</span><br />
<span style="font-size: large;"> Cells are organized in the form of tissues and different coordinating tissues make an organ. Organs performing relative functions make organ system and different organ systems make a complete individual. Individuals of the same species live together and make a population. Populations of different species living in the same habitat constitute a community. </span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Biosphere </span></h3>
<span style="font-size: large;">"The part of the <a href="http://educational-wealth.blogspot.com/2014/02/our-lovely-planetearth-creation-origin.html" target="_blank"><b>Earth</b></a> inhabited by organisms’ communities is known as biospeher."

Biosphere
 
 
 
 
 
 
 
 
Protons and neutrons are located inside nucleus of atom while electrons orbit in energy levels (electron shells) around the nucleus. The number of electrons in the outermost shell determines the manner.</span><br />
<span style="font-size: large;">All types of matter are made up of elements and there are about 92 kinds of elements, found in nature. Each element is made up of a single kind of atoms .

These atoms are actually the structures formed by many subatomic particles.</span><br />
<span style="font-size: large;">The most stable subatomic particles are electrons, protons and neutrons.Each of these is found in definite number, in a specific atom.

Only six (O,C,H,N,Ca,&P makes 99% of the total mass.Other ten (K,S,Cl,Na,Mg,Fe,Cu,Mn,Zn,&I)collectively make one percent of the total mass.

Out of the 92 kinds of elements that occur in nature, 16 are called bioelements. </span><br />
<span style="font-size: large;">These take part in making the body mass of a living organism .

A molecule is the smallest part

combine through ionic or covalent bonding. The stable particles formed by the bonding between compound is called as molecule. Bioelements share their atoms in making biomolecules or molecules of life.</span><br />
<h3 style="text-align: left;">
<span style="font-size: large;"> Formation of organism</span></h3>
<span style="font-size: large;"> An organism is formed by enormous number of biomolecules of hundreds of different types. These molecules are the building material and are themselves constructed in great variety and complexity due to specific bonding arrangements. </span><br />
<span style="font-size: large;">Biomolecules may be classified as micromolecules and macromolecules. Micromolecules

These are with low molecular weight e.g. glucose, amino acids, fatty acids etc. Macromolecules

These are with high molecular weights e.g. starch, proteins, lipids etc. Two different molecules, belonging to different categories, usually combine together to form conjugated molecules e.g. glycoproteins, lipoproteins, nucleoproteins etc. </span><br />
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<b><span style="font-size: large;">Level 1-Organelle and Cell level: </span></b></h3>
<span style="font-size: large;">An enormous number of biomolecules become associated in a particular way and form organelles. The organelles are actually sub-cellular structures and when they assemble together, cells are formed. </span><br />
<span style="font-size: large;"> Each type of organelle is specialized to perform a specific function. For example; mitochondria are specialized for cellular respiration and ribosomes are specialized for protein synthesis.

In this way, functions of the cell are

accomplished by these specialized structures. </span><br />
<span style="font-size: large;"> It is an example of the division of labour within the cell.

Prokaryotes have only limited number and types of organelles in their cells. They are made up of simple cells which lack membrane bounded organelles e.g. mitochondria, Golgi complex.

Eukaryotes have large number and types of organelles in their cells. They are made up of complex cells which have membrane bounded organelles. </span><br />
<span style="font-size: large;">A cell membrane (outer covering of cell) is however present in all cells, whether prokaryotic or eukaryotic.

In the case of bacteria and most protists, the entire organism consists of a single cell. In the case of most fungi, animals and plants, the organism consists of up to trillions of cells.

There are some similarities and clear differences between Prokaryotc and Eukaryotic cells
Level 2 -</span><br />
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<span style="font-size: large;">Tissue level: </span></h3>
<span style="font-size: large;">In multicellular organisms, similar cells (performing similar functions) are organized into groups, called tissues.

Defination of tissue

We can define a tissue as" a group of similar cells specialized for the performance of a common function". Each cell in a tissue carries on its own life processes (like cellular respiration, protein synthesis), but it also carries on some special processes related to the function of the tissue.</span><br />
<span style="font-size: large;"> On the basis of their structures and functions, <a href="http://educational-wealth.blogspot.com/2014/01/plant-tissues.html" target="_blank">plant tissue</a>s are divided into two types i.e.

Meristematic tissues

Permanent tissues.

Meristematic tissues

These tissues are made of undifferentiated, small cells which have the ability to divide. These tissues are located at the tips of roots and shoots (apical meristem) and between the xylem and phloem tissues (lateral meristem).</span><br />
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<span style="font-size: large;"> Permanent tissues </span></h3>
<span style="font-size: large;">These tissues are made of differentiated cells of different shapes and sizes. They are further divided into

Epidermal tissues (the outermost covering of leaf, stem and root),

ground tissue (or prarenchyma: prepares food and stores food and water, supporting tissue (i.e. collenchyma / sclerenchyma; provides strength to the plant) and conducting tissue xylem and phloem (transports

water and food). </span><br />
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<span style="font-size: large;">Animal tissues </span></h3>
<span style="font-size: large;">There are four major types of animal tissues i.e.

epithelial, connective, nervous and muscular tissues. Epithelial tissues acts as the covering and glandular tissue.

Connective tissue acts as the connecting and supporting tissue. Nervous tissue conducts messages and muscular tissue acts as the contracting tissue. </span><br />
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<span style="font-size: large;">3-Organ and Organ system level: </span></h3>
<span style="font-size: large;">In higher multicellular organisms, particularly in animals, more than one type of tissue having related functions are organized together and make a unit, called organ. Different tissues of an organ perform their specific functions and these functions collectively become the functions of that organ.</span><br />
<span style="font-size: large;"> For example stomach is an organ specialized for the digestion of proteins and for storing food. Two major types of tissue are organized in

its structure. <b>Epithelial (glandular) tissue </b>secretes the gastric juice and muscular tissue performs contractions of stomach walls for grinding of food

mixing of enzymes with food and moving food to posterior end. So two tissues perform their specific function which collectively become the function of stomach.

The next level of organization in multicellular organisms is the organs system level. Different organs performing related functions are organized

together in the form of an organ system. In an organ system, each organ carries out its specific function and the functions of all organs appear as one process of the organ system. For example, digestive system is an organ system that carries out the process of digestion. </span><br />
<span style="font-size: large;">Major organs arranged in its framework are oral cavity, stomach, small intestine, large intestine, liver, and pancreas.

The whole organisms has it's individuality as far as its characteristics are concerned. For ! example; all human beings have same organs and organ systems which are organized in the same pattern. Yet they have different skin colors, heights, voice tones etc.

Such characteristics Makes the individuality in a human being. </span><br />
<span style="font-size: large;">The organ system level is less definite in plants as compared to animals .The complexity of organ and organ system level in animals is associated with a far greater range ot functions and activities than in plants. </span><br />
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<span style="font-size: large;">4- Individual level: </span></h3>
<span style="font-size: large;">Different organs (in plants) and organ systems (in animals) are organized together to form an individual / organism. In organism, various organs and organ systems are organized in such a way that all the functions, processes and activities are coordinated.</span><br />
<span style="font-size: large;">For example, when a man is engaged in continuous and hard exercise, not only his muscles are working but also there is an increase in the rate of respiration and heart beat. </span><br />
<span style="font-size: large;">This accelerated rate of respiration and heart beat supplies more oxygen and food to the muscles which they need for continuous work.

In animals, regulation of activities (coordination) is achieved by nervous system and hormones while in plants, coordination is brought about only by hormones.</span><br />
<span style="font-size: large;"> 5- Population level: </span><br />
<span style="font-size: large;">Biologists extend their studies to the population level where they study interactions among member of the same species living in the same habitat. A population is defined as" a group of organisms of the same species located in the same place, at the same time". For examples, number of rats in a field of rice in 2002, number of students in biology class in semester 2008 etc.</span><br />
<span style="font-size: large;"> Similarly human population comprises the number of human beings in a particular city or country at a particular time.

At population level, biologists study life in a number of new parameters, which cannot be considered at individual (organism) level. For example; gene frequency, gene flow,’ age distribution, population density, population pressure etc. </span><br />
<span style="font-size: large;">6-Community level: </span><br />
<span style="font-size: large;">"A community is an assemblage of different populations, interacting with one another within the same environment". A forest may be considered as a community. It includes different plant species e.g. oak trees, ash trees, grasses, bushes etc; different species of microorganisms and fungi; and different animal species.

Communities are collections of organisms, in which one population may increase and others may decrease.</span><br />
<span style="font-size: large;"> Usually populations change due to fluctuations in abiotic factors and changes in the size of other populations. Some communities are complex e.g. a forest community, a pond community etc. Other communities may be simpie e.g. a fallen log with various populations under it. </span><br />
<span style="font-size: large;">In a simple community number and size of populations is limited so any change in biotic or abiotic factors may have drastic and long lasting effects.
Cellular Organization

We have studied that there are two basic types of cells i.e. prokaryotic and eukaryotic cells. In living organisms the ceils organize in three ways to make the bodies of organisms. </span><br />
<span style="font-size: large;">Cells make unicellular, colonials and multicellular organizations and the organisms formed through these organizations are unicellular organisms, colonial organisms and multicellular organisms.

In unicellular organisms only one cell makes the life of an organism. All the life activities are carried out by the only cell. We are familiar with Amoeba, Paramecium, and Euglena etc .

In colonial type of cellular organization many unicellular organisms live together but do not have any division of labour among them.</span><br />
<span style="font-size: large;"> Each unicellular organism in a colony lives its own life and does not depend on other cells for its vital requirements. Volvox is a green alga found in water that shows colonial organization. Hundreds of Volvox cells make a colony. Sometimes a Volvox colony consists of daughter colonies. </span><br />
<span style="font-size: large;">Each cell of the colony has two flagella at the anterior end, which is directed towards the surface of the colony. The colony moves in water by the combined action of the flagella of all the cells.

In multicellular organization cells are organized in the form of tissues, organs and orga systems.</span><br />
<span style="font-size: large;"> Frog and mustard are the familiar examples of multicellular organization.

Mustard plant (scientific name: Brassica campestris) is sown in winter and it produces seeds at the end of winter. The plant body is used as vegetable and its seeds are used for extracting oil. The organs of the body can be divided into two groups on the basis of their functions.</span><br />
<span style="font-size: large;"> Root, stem, branches and leaves are the vegetative organs, which do not take part in the sexual reproduction of the plant. Flowers are the reproductive parts of the plant because they take part in reproduction and produce fruits and seeds

photomicrographs of different organs.</span><br />
<span style="font-size: large;"> Frog (scientific name: Rana tigrina) also shows the multicellular organization. The body is made of organ systems and each organ system consists of related organs. All the organs are made of specific tissues (epithelial, glandular, muscular, nervous etc).

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levels of organisms

Biological Organization at different levels In order to understand the various phenomena of life, biologists study biological organizat...

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Educational Wealth

Reproduction

Cell size and relation between prokayotic and Eukaryotic cells

Animal tissues

Ways of movement of material across the cell

Plant tissues

Structure of cell

Cell theory

Microscopes

Classification systems of all organisms

Impacts of human beings on biodiversity

Variety of living Organisms(Biodiversity)

levels of organisms

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