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Tuesday, March 6, 2012

Structure And The Functions Of The Blood Circulatory System

The blood circulatory system has a special place as the main transport system of the body. There are 3 main characteristics common to all blood circulatory systems.
  • Activity of a circulating fluid or blood.
  • Activity of an organ to pressurize the liquid to flow.
  • Activity of vessels for the blood circulation.
The heart of man is shaped like a very young coconut and the size is just similar to your first and the circulatory system consists of arteries and veins. A closed blood circulatory system has the following features.
  • Blood flows inside the vessels.
  • Blood has no direct contact with the organs.
  • Heart pumps out the blood throughout the body and it comes back to the heart.
  • Blood is supplied to the organs, tissues as required by them.
  • Substances are exchanged through the walls of the blood vessels.
There are two types of blood vessels according to the structure and the functions they perform.
  1. The vessels that carry away blood from the heart are called Arteries  - except Pulmonary Arteries.
  2. The vessels that bring the blood back to the heart are called veins - except Pulmonary Veins 
Have you seen the veins raised up in hands and legs of some people? A vein is used to denote a type of blood vessel. Think of an instance when your pulse has been checked. You can find out the speed of the flow of blood in a vessel by testing your pulse. You can test your pulse at the following places. Inner side of the elbow, under the arm pit, on both sides of your neck, inner side of the ankle and the wrist.

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Wednesday, February 29, 2012

How Blood Helps for the Functions of the Human Body

If you have a cut, a wound or a bruise on your body, blood flows out of the wound. Blood flows within the body in blood vessels. Although blood appears to be a homogenous fluid as you take it out of the body it gets separated into two if you leave it in a test tube. The dark red gelatinous part and the yellow colored fluid are the two parts. A normal person has about 5.5 liters of blood in his body.

Components of Blood

You can see the components of it by preparing a slide of blood and looking through a microscope. You will see a large amount of cells floating in a fluid. Most of them are red in color. You may see other cells of different sizes and a very small type of bodies. Cover the smear of blood with a cover slip and add a small drop of dilute acetic acid. If you look at the slide now, you will find that the red cells are not seen, but some other cells are seen. These cells are white in color. Let us now discuss these various components in detail.

Red Blood Cells - Erythrocytes

The red cells seen in blood are called erythrocytes or red blood corpuscles. The red color of blood is due to these cells. These cells have bi-concave shape and move singly or in a group within the blood vessels. As a result the exchange of gases through their surfaces is more efficient. Red cells are large and they cannot pass through capillary tubes easily. As a result there is more time for the exchange of gases.

The red color of erythrocytes comes from hemoglobin. This is made from a pigment named haematin which has iron and a protein named globin. The life time of an erythrocyte is about 3 months. These are broken down in the liver and the spleen. The proteins and the iron in hemoglobin is absorbed then. Erythrocytes are formed in the bone marrow.

White Blood Cells - Leukocytes

These are larger than erythrocytes but less in number. The number of leukocytes is just about one per 600 erythrocytes. The white blood cells are known as leukocytes have a nucleus and are colorless. There are about 4000 - 11000 white blood cells in 1ml of human blood. The white blood cells are divided into two categories depending on the availability of granules in the cytoplasm. Lymphocytes are round in shape and the nucleus is so large that it almost fills up the entire cell. These are also produced in the bone marrow.


In addition to the above cells, there is another type of cells. These cells are very small and have no nuclei. They have granules and are known as platelets. Platelets too are produced within the bone marrow. All blood cells are inside a yellow fluid. This fluid is known as blood plasma. The blood plasma is about 55% of the blood. 92% of the plasma is water. A lot of substances necessary for the body are in the plasma.

Functions of Erythrocytes

Oxygen combines with the hemoglobin in the red cells and forms oxy-hemoglobin. Blood  turns bright red as a result. When blood goes to the cells through the blood vessels, the oxy-hemoglobin breaks up and releases oxygen. This oxygen diffuses into the cell.

Functions of Leukocytes

Some leukocytes show amoeboid movements and engulf bacteria and virus that enter the body. This is know as Phagocytosis. Some leukocytes produce antibodies against disease causing bacteria.

Functions of Platelets

Blood flows out of a wound if you injure yourself. Continuous flow of blood is prevented by blood clotting on the wound. A number of substances take part in this process. This action is made quicker by platelets.

Functions of Blood Plasma

The fluid nature of blood is due to the plasma. It also transport all substances throughout the body. Blood plasma transports blood cells, hormones, nutrients and the excretory substances throughout the body. Another important function of blood is the regulation of body temperature.

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Tuesday, February 28, 2012

How Transpiration Influences the Survival of the Plants

In the end of my previous post I brought a word called transpiration, But I didn't explained it. So this post will do that task.

You have the experience that a wilted plant revitalizes if water is supplied to it. You can assume that main reason for the wilting of plants is the non-availability of water. Why do plants face a dearth of water?

You can use this method to test how water goes away from a plant. Select a plant and cover a twig with polythene bag around it. Then keep it for some time. Now take it away and put some anhydrous copper sulphate into the polythene bag.

There are droplets of a liquid formed on the inner walls of the polythene bag. These droplets turn anhydrous copper sulphate blue, indicating that the droplets  are water. Hence, you can conclude that plants give out water. You cannot see the water coming out. In which case water should have come out in the form of vapor. This vapor has condensed and got deposited on the inner walls of the bag.

Loss of water from a plant in the form of vapor is known as Transpiration. The main way in which transpiration takes place is through the stomata. Hence this is called stomatal transpiration. If transpiration takes place through the cuticle of the leaf or any other part of the plant it is known as cuticular transpiration. Transpiration can occur through the air pores available in the roots and the stem of the plant. This is known as airpore transpiration.

The amount of water that goes out of the plant in the form of vapor is very large. This water has not taken part in any metabolic process. This quantity amounts to 95% of the total amount of water taken in by the plant.

Factors Affecting Transpiration

As transpiration is the process of water going out in the form of vapor, the factors that given evaporation affects transpiration too. Environmental factors that affect the evaporation of water are:
  • Environmental temperature.
  • Humidity of the atmosphere.
  • Speed of wind.
  • Intensity of light.
  • Atmospheric pressure.
These factors affect transpiration too. In addition the supply of soil, water too has an affect. To test the effect of these factors on transpiration, You should be able to measure the rate of transpiration. A potometer is used to measure the rate of transpiration in the laboratory.

The twig used in the potometer should be cut and fitted inside the water. This is done in order to prevent any air particles entering the twig. The twig should cut using a sharp knife. A small air bubble should be allowed to enter the capillary tube.

When water evaporates through the leaves, the bubble of air moves towards the twig. A the capillary tube is graduated, the distance moved by the air bubble can be measured. You can use this apparatus to measure the rate of transpiration of a plant under different environmental situations.

Effects of the environmental temperature

The rate of evaporation of water increases with temperature. The amount of water vapor that can remain in the atmosphere too increases with temperature. Therefore more water can go out of the leaves with the increase of temperature.

Relative humidity of air

The decrease in humidity of the atmosphere means decrease of the water vapor in the atmosphere. Water molecules can enter the atmosphere easily as a result. The diffusion rate of water from the leaf to the atmosphere decreases with the increase of the percentage of water in the atmosphere.

The effect of the wind speed

The water particles around the leaf will get blown away when there is wind. As a result more and more water particles can join the atmosphere. The rate of diffusion of water increases with the speed of the wind. Hence the rate of transpiration increases when the speed of wind increases.

Effects of the atmospheric pressure

The evaporation rate of a liquid increases in a vacuum. Th rate of evaporation decreases with the increase in pressure. Hence the rate of transpiration increases with the decrease of atmospheric pressure.

The Adaptations in Plants to Reduce the Rate of Transpiration

Plants absorb water from the soil when water leaves the plant by transpiration. But the plants on land will not get enough water. The xerophytes face the lack of water severely. Hence the plants show adaptations to reduce transpiration.

1.) Dropping of leaves, leaves turning into thorns and having fleshy stems.

A very small number of leaves appear in certain plants like cactus and euphorbia. These leaves also drop off when young. Some of the leaves and auxiliary buds modify into thorns. The transpiration reduces as there are no leaves. In addition the stem is fleshy and a milky white thick liquid is formed. This liquid keeps behind the water. The leaves of aloe are fleshy.

2.) Sunken stomata.

The stomata in plants like cycas and oleander are at a lower level than the cells of the epidermis. As they are sunk, the sotmata do not make a direct contact with the atmospheric air. Hence, the effect of the environmental factors is less and the transpiration is less.

3.) Bristles on the leaf surface.

There are hair like bristles on the surface of some leaves. These are formed by the cells of the epidermis. There is a wet, air strata between these bristles. Hence the loss of water is less and transpiration is less. eg: Pumpkin, Nettle

4.) Formation of a thick cuticle.

The cuticle of some leaves is very thick. As it has a wax on the surface of the leaf blade, the blade is shiny. Transpiration reduces as a result. eg: margosa, plumeria

5.) Rolling of leaves.

The leaves of certain grass types roll in and close down the stomata when there is a dry climate. As there are more stomata on the upper surface, these get closed down due to the rolling. Therefore transpiration reduces.

6.) Deciduousness (Dropping of leaves during certain times of the year)

The leaves of certain trees drop during the dry season. The transpiration reduces as there are no leaves. eg: rubber, terminelia

The effect of transpiration on plants

The following advantages are gained by plants due to transpiration.
  1. Certain substances are conducted to upper regions of the plant.
  2. The damage caused to plant leaves is reduced because of evaporation.
  3. Water is distributed within the plant body.
  4. The osmotic pressure inside the cells is maintained as a large amount of water is absorbed.
  5. More water enters to the plant.
  6. Plant is cooled.


On certain days in the morning even though there is no rain, you can see small droplets of water at the tips of leaf blades such as grass, alocasia and paddy. This water has come out of the plant leaves.

There are some holes known as hydathodes at the tip of the small veins. The water pushed up by root pressure comes out of these holes. This is called as guttation. It has been found out that the function of hydathodes is only guttation. As root pressure cannot push water to a great height guttation occurs in plants that grow short. Guttation occurs in alocasia, amorph phallus and grass.

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Monday, February 27, 2012

Transportation System for the Continuation of Living Organisms Part II

This post is the part two of previous post. in the previous post I wrote about Dormant Transportation or passive transportation. This post is about Active Transportation.

Active Transportation

You know that diffusion is due to a concentration gradient. Water enters living cells against to the concentration gradient too at certain times. Look at an example. There are more sodium ions than iodine ions in sea water. In certain marine plants there are less sodium ions than iodine ions. Sodium ions do not enter the plant though iodine ions enter. The number of potassium ions in the cells of the fresh water plant nitella is thousand times greater than the number of ions in the surrounding water. If the potassium ions enter the cell by diffusion from the surrounding medium, it can occur only till the concentrations of potassium ions inside and outside are equal. (For the ions of a lesser concentration to enter the cells, ions should move from a region with a higher concentration.) Therefore the sodium or iodine ions enter the cells against the diffusion process.

The passage of particles of matter through a plasma membrane into a cell or out of cell against the natural diffusion process is known as Active Transportation. Energy of metabolism is used up for this purpose.

This process occurs through carrier molecules. Carrier molecules are a type of molecules in the plasma. The mineral ions which are attached to these molecules enter the cytoplasm. Hence the plants have the ability of absorbing the required minerals only.

The water and the minerals absorbed by the root hairs are conducted to the various parts of the plant through the xylem cells in the roots and the stem. This occurs by the movement of substances from cell to cell by osmosis and active transportation.

The structure of a tender root

There are two types of plants. They are the dicotyledonous and the monocotyledonous. You can see some structural differences between them. The external layer called the epidermis is a layer of single cells. Some of these cells have protrusions coming out. These are known as root hairs. The cortex, which consists of circular cells is the inner layer next to the epidermis. There are inter cellular spaces between these two layers. There is a single layer of barrel-shaped cells next to the cortex and it is known as the endodermis. These cells are arranged close together. There are no intercellular spaces between them. Next to the endodermis, the pericycle is made out of a single layer of cells. The vascular system is underneath this layer. The xylem layer is in the form of a star and the phloem cells are in between the xylem layers. The cambium is in between the xylem and the phloem. The pith is in the center. This is a very small layer. The structure changes when the dicotyledonous plants undergo secondary thickening as they mature. The roots thicken with age.

The structure of tender root of a monocotyledonous plant too is similar to the root of a dicotyledonous plant. But there is no cambium and no secondary thickening. Hence roots do not thicken with age.

Adaptation of roots for the absorption of water and minerals

  • The roots of dicotyledonous plants are divided into many lateral roots.
  • The monocotyledonous plants have a large number of fibrous roots.
  • Presence of root hairs.
  • Presence of a fairly thin epidermis at the tip of the root.

Ascent of sap

    A column of water rises up from the roots of a plant to the leaves through the xylem vessels. This is a continuous column of water. There are no air bubbles inside this air column of water. Xylem vessels are similar to pipes. There are two reasons for continuity of this column of water.
    • The water particles are attracted to each other - Cohesion.
    • The water particles are tightly attached to the walls of the xylem vessels - Adhesion. 
    When water goes out from the leaves of a plant by transpiration, water flows up along the xylem vessels under the conditions. The flow of water from the roots to the leaves due to transpiration is known as transpiration pull.

    In the soil the minerals are dissolved in water as their salts. The roots absorb this water and the root system of a plant exerts a push on it and sends it up along the xylem tube. This push is known as the root pressure. It has been found out that the maximum height of water that can be pushed due to the root pressure is about 18m. The water rises up beyond this height only due to the transpiration pull. The process of transporting water and minerals dissolved in it through the xylem cells from roots up to the leaves is known as the transpiration of nutrients.

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    Wednesday, February 22, 2012

    Transportation System for the Continuation of Living Organisms Part I

    The water and minerals absorbed by the roots should be transported to all the cells of the plant. Transportation in plants occurs in two ways

    Dormant Transportation

    The transportation that occurs without spending metabolism energy called dormant transportation. This occurs by
    • Mass flow
    • Diffusion
    • Osmosis
    • Evaporation

    Mass Flow

    When water and minerals are able to flow due to the difference of pressure at two points. water flows along xylem conducting tissue and through the cell wall in this manner. The cell wall is made up of tiny fibers. There are small spaces in between these fibers. Water flows along these spaces by this process. The dissolved salts in water are also carried with it.


    When nyctanthes flowers bloom at night and when a joss stick is lit or a bottle of perfume is opened in a small room you get the pleasant smell spread all over the room. The smell spreads in particles. Matter is made up of particles and these particles continuously vibrate. When the particles are clustered together, each particle is surrounded by other particles, and they tend to get released from the other particles around. The process of spreading particles from a place with a higher particle concentration to a place with lower particle concentration is known as Diffusion. The particles of perfume spread into the air particles. The air particles as well as perfume particles are both vibrating. The gases can spread through liquid particles, solid particles and through gas particles.

    As a example take a small bottle which filled with some color and release it under a water bath. Then the color spreads to the water outside from the small bottle. This is due to diffusion of the color particles in the water. After some time - a longer time the color of the water in the vessel and the small bottle will be the same. The concentration of the particles of the colored solution in the bottle decreases while the concentration of particles in the vessel of water increases. At one stage the spreading of particles inside the water is even. Then you can say that the system is balanced. When water enters a plant, diffusion takes place.


    Osmosis is a process of diffusion taking place through tissues. If a certain substance can pass through a tissue, you can call it a permeable tissue for that substance. Some tissues are permeable to certain substances and non-permeable to others. Such tissues are known as selectively permeable membranes. The process of water flowing from a place with a lesser concentration to a place with high particle concentration through selectively permeable membrane - Permeable only to water is known as Osmosis.

    Root Hairs

    A special structure formed by a cell on the epidermis of the absorbing region of the root is called root hairs. Root hairs are inside the soil. The concentration of the cell liquid of the root hair is higher than the concentration of the water outside. Hence water diffuses into the root hairs. Then the water particles move into the xylem cells through the other cells in contact and move through the entire plant. Some particles can enter through the plasma membrane. Some mineral particles too enter through the root hairs.


    Water boils at its boiling point. Then water particles enter the vapor state from the liquid state. Water can get evaporated without reaching its boiling point. But the rate of evaporation is less than the evaporation at its boiling point. The entering of water particles into the vapor state from the liquid state without reaching its boiling point is known as evaporation. A cloth hanging on a clothes line or a wet floor dries up due to evaporation. The water passing to the central cells of the leaf along the xylem cells of the leaf veins enter the intercellular spaces by evaporation.

    I'll meet you up in the next post about Active Transportation which is part II of this post.
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    Tuesday, February 21, 2012

    The Factors Needed for the Process of Photosynthesis

    Now I think you what are the products and byproducts of photosynthesis process. Now I'm going to let you now some tests that will lead you to find what are the factors needed for this photosynthesis. Firstly these are the factors needed for the process.
    1. Carbon Dioxide.
    2. Sunlight.
    3. Water.
    4. Chlorophyll. 

    Carbon Dioxide test for Photosynthesis

    Carbon dioxide is absorbed by potassium hydroxide. Take two similar, transparent polythene bags and put some potassium hydroxide pellets into one bag. Insert some leaves of a potted plant which has kept in the dark for two days into this bag and tie the mouth well. Insert some leaves into the other bag and tie the mouth of this bag too. Allow them to receive sunlight for some time and then test these for starch. I'll tell you late how to test for the starch.

    *There is no starch produced in the leaves in the bag containing potassium hydroxide.
    *Starch is available in the leaves of the bag without potassium hydroxide.
    *This shows that carbon dioxide is necessary for photosynthesis.

    Light Energy test for Photosynthesis

    Select a leaf from a potted plant kept in the dark for two days. Cover the leaf with two pieces of black paper on either side. Allow the plant to get sunlight for a few hours. Test the leaf for starch.

    You will notice that the covered part of the leaves will not turn blue. But the uncovered leaves turn blue. this experiment shows you that sunlight is necessary for photosynthesis.

    **If you want to show that water is necessary for photosynthesis you should have green leaves without water. If you remove water from leaves they will die. Therefore you can't design an experiment to show that water is necessary for photosynthesis.

    Chlorophyll test for Photosynthesis

    Select a leaf that does not contain chlorophyll for this experiment. Multicolour leaves like hibiscus, colacasia or choleas may be used. Let the leaf remain in sunlight for a few hours and pick it up. Draw a diagram of the leaf and mark the shite spots that do not contain chlorophyll. Next test the leaf for starch and compare it with the diagram drawn. you will see that the portions which were green in color have turned into blue. This shows that chlorophyll is necessary for photosynthesis.

    Ok this is the time for starch test!

    First you should remove chlorophyll of the leaf by dipping the leaves in alcohol heat bath. Then put some iodine to chlorophyll removed leaf. That's it!

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    Monday, February 20, 2012

    The Most Wanted Process of Photosynthesis

    You know that photosynthesis is a process that must happen. Because If it loose it's process, our world won't be like this. So You also need to contribute to maintain that Most Wanted process. Most people don't know about this and they put all of us in risks by making down this photosynthesis.

    Concept of Photosynthesis

    Scientists believe that the earth was formed about 4.5 billion years ago and that it had a high temperature and and an atmosphere which had simple molecules such as hydrogen, nitrogen, carbon dioxide and water. As the atmosphere cooled gradually the water vapour condensed and formed the oceans. Scientists believe that amino acid and other simple molecules dissolved in this water to form the"Primitive Soup" and life originated as chemosynthetic organisms inside this primitive soup. The chemosynthetic organisms use the energy released by the oxidation of iron to produce food in the form shown below.

    C02 + H20 -----------> Simple Sugars.

    As time passed by, after another 12 million years the evolution of a complex molecule named chlorophyll took place. This molecule had the ability of obtaining energy from sunlight. hence the process,

    6CO2 + 6H2O + ------------------> C6H12O6 + 6O2

    Started. This action, which involves light energy is known as photosynthesis.

    Importance of Photosynthesis

    The chemosynthetic bacteria which lived for over the last 27 million years exist as unicellular organisms even today. The unicellular photosynthetic organisms evolved to be multicellular and could change into trees on land and marine plants which are hundreds of metres long. This shows the importance and the environmental suitability of photosynthesis. In addition to the food production, oxygen is released as a byproduct. This created an environment for the living organisms to have an efficient aerobic respiration. The oxygen that rose to the higher levels changed to ozone and formed a layer which protects the earth from destructive sun's rays such as ultra-violet rays. As carbon dioxide which is considered to be a green house gas is needed as raw material in photosynthesis. The atmosphere provides a friendly environment for life.

    The first stage of any food chain is a green plant which is the producer. The green plants are producers because of chlorophyll. There will be no living organisms on earth if not for this process. Now you may realize that the origin of man - Who has developed the ability to control the environment is also due to photosynthesis.

    Products of Photosynthesis

    Carbon dioxide and water react in the presence of sunlight to produce a simple sugar named glucose while giving out oxygen as the byproduct. This process is know as photosynthesis.

    Carbon Dioxide + Water +  ----------------> Glucose + Oxygen

    6CO2 + 6H20 + ---------------> C6H12O6 + 6O2

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