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| Summary
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- In lower organisms, there is no transport system as the cells are in touch with the surrounding medium. The transport is by the physical processes like diffusion, osmosis, etc.
- With the advancement in structure, the organisms have to evolve methods to transport nutrients and wastes. The actual transport into the cells involves the physical processes - active or passive transport.
- However, the transport of materials across the plant or animal body occurs by processes broadly called the mass flow system
called the vascular system
- Vascular system in plants relies mainly on physical processes whereas transport in animals utilises muscular energy
- The materials to be transported across the plant body are water, minerals, food, hormones, etc.
- The transport of materials in plants takes place through specialised
tissues called the xylem and the phloem
- Xylem transports water and
dissolved minerals and phloem transports food
- Two types of xylem cells are involved in transport of water - tracheids and vessels. They are dead cells with lignified walls. They are joined end to end forming a capillary system to draw water up the plant.
- Phloem is a living tissue. Sieve tubes and companion cells are the phloem cells involved in the transport of food. The sieve tube cells are also joined end to end. The end walls of sieve tube cells are perforated and the cytoplasm of the adjacent cells are continuous through it. They are enucleated. The companion cells are present next to the sieve tube cell and are nucleated.
- The upward movement of water is called ascent of sap. Ascent of sap involves root pressure and transpiration pull.
- Roots absorb water from the soil by osmosis or diffusion. The water ultimately enters the xylem. Thus, the xylem in the root develops a positive water potential called the root pressure with which the water is pushed up.
- In tall trees transpiration pulls water up the xylem. Transpiration is the loss of water from the aerial parts of the plant, mainly through the stomata of the leaves.
- Due to transpiration, the upper parts of the trees develop negative water potential. The water is then pulled up from the region of higher water potential in the lower regions. This is called transpiration pull.
- The continuous column of water resulting from the transpiration pull is called transpiration stream. The continuity of the stream is maintained by the adhesive and cohesive properties of water.
- Minerals are absorbed from the soil in the ionic form along with water as they are dissolved in water. Some of the mineral ions like the nitrates enter into the phloem along with the prepared food. From the xylem and the phloem, the minerals enter the cells by active transport as per requirement.
- Food is transported as sucrose along phloem in not only downward but also upward direction. Sucrose moves from the region of positive potential (region of synthesis - leaves) to the region of negative potential (region of utilisation - roots, young leaves, flowers and fruits) along the concentration gradient.
- Other than sucrose, phloem also transports hormones (from the site of synthesis to the site of action) and some of the mineral ions (from the leaves about to fall to the other regions). The transport of soluble substances like the sugars, amino acids and hormones by the phloem is called translocation.
- Animals in general have a higher metabolic rate than the plants and
thus require a more efficient transport system
- In man, there are two
circulatory systems - Blood circulatory system and Lymphatic circulatory
system
- There are two types of blood circulatory systems - open and closed. In open circulatory system the blood vessels are open-ended as they open into the common cavities called the haemocoel. It is seen in insects.
- In closed circulatory system the blood always remains inside the blood
vessels and never comes in direct contact with the cells. It is seen in
mammals including man.
- Blood is an alkaline fluid that consists of
the liquid portion called plasma and the formed elements called the cells
- Plasma consists of water and soluble components - proteins (like fibrinogen), nutrients ( like glucose), metabolic substances , inorganic ions and pigments
- The formed elements include the erythrocytes, leucocytes and the thrombocytes. The erythrocytes are called the red blood cells as they contain the red coloured haemoglobin pigment. Haemoglobin is the oxygen carrier. Leucocytes are called the white blood cells and are involved in the immune system. Thrombocytes are the platelets that are involved in the clotting of blood.
- The functions of blood include transport of nutrients, respiratory
gases, excretory wastes and hormones, protection against infections and
allergies, homeostasis (maintenance of pH, ionic balance and water content,
regulation of blood pressure, temperature) and clotting of blood
- In human circulatory system the blood is flows in closed blood vessels called the arteries, veins and their capillaries.
- Arteries and veins have elastic and muscular walls. Capillaries lack muscles.
- Arteries arise from the heart and carry oxygenated blood (except the pulmonary artery). The main artery is called the aorta. The aorta gives off branches called the arteries. Arteries branch into arterioles and then into capillaries. The arteries are more muscular than the veins.
- Veins take deoxygenated blood (except pulmonary vein) back to the heart. The capillaries in the tissue region unite to form venules which then form veins. The smaller veins join together to form two great veins called vena cavae. Vena cavae take the blood back to the heart.
- Heart is a muscular pumping organ which pumps the blood with enough pressure to transport the blood through the arteries into different parts of the body. Human heart is four chambered. There are two receiving chambers, the auricles and two pumping chambers, the ventricles. The right side of the heart is concerned with deoxygenated blood and the left side is concerned with the oxygenated blood.
- The pumping action results in a sequence of events called the cardiac cycle. Each cycle produces one heart beat. Adult human heart beats 72 times per minute.
- The normal blood pressure is considered to be 120/80 mm of Hg where 120
mm of Hg is the systolic pressure and 80 mm of Hg is the diastolic pressure
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Heart rate is the same as the pulse rate that can be felt at the wrist. It
is the rate at which the arterial muscles contract and relax
- Human
circulatory system shows double circulation where the blood passes through
the heart twice, once for circulation to the different parts of the body and
the other time for circulation to the lungs
- In man, there are three
circulations - systemic, hepatic portal and pulmonary
- In systemic
circulation, the blood is supplied to the different parts of the body by the
respective arteries and the blood is brought back to the heart by the
respective veins
- In pulmonary circulation, the blood is circulated
between the heart and lungs for its purification
- At the capillary end of the arteries, the plasma leaks into the interstitial space. This plasma is without the proteins (as the proteins cannot pass through the walls of the capillaries) and is called the interstitial fluid or the tissue fluid.
- In the interstitial spaces there are some blindly ending vessels called the lymph vessels. The lymph vessels form enlarged spaces called the lymph nodes. In these nodes, lymphocytes synthesise anitbodies and there are phagocytic cells.
- The tissue fluid enters the lymph vessels and is called the lymph. The lymph circulates in the body in only one direction and returns to the venous system near the heart.
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