TRANSPORTATION, CIRCULATION & EXCRETION IN ORGANISMS - III : LONG ANSWERS

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1. Describe : Xylem.
   
   ANS :
   
   
   
   
   • Xylem is a tissue associated with the transport of water in higher plants.
     
   • Water absorbed through roots is transported to the stem, branches, leaves and flowers by xylem.
     
   • Tracheids and vessels (tracheae) are the main components of xylem.
     
   • TRACHEIDS :
     
     
     
     • Tracheids are present in pteridophytes, gymnosperms and some angiosperms.
       
     • They are long, thin and spindle-shaped cells.
       
     • They are dead as their nuclei are disintegrated.
       
     • There is deposition of lignin on the inner wall of the cells which provides mechanical support to tracheids.
       
     • The cells are arranged one above the other.
       
     • At the junction of two cells, the wall possesses pits through which water is conducted upwards.
       
     
     
   • VESSELS (TRACHEAE) :
     
     
     
     • They are present in angiospermic plants.
       
     • They are short, comparatively broad and blunt at both ends.
       
     • They are dead because the cytoplasm and nucleus disintegrate during the formation of vessels.
       
     • The cells are arranged one above the other.
       
     • The transverse wall between the cells disintegrates to form a continuous passage for rapid upward transportation of water.
       
     • Lignin deposition on the inner wall provides mechanical support.
       
     
     
   
   
   
2. Describe : Transportation of Mineral Elements in Plants.
   
   ANS :
   
   
   
   
   • Plants absorb minerals (inorganic dissolved salts) by roots from the soil.
     
   • Absorption of minerals occurs simultaneously with the absorption of water but the process is independent. The minerals are in direct contact with the water film in between the soil particles.
     
   • Water enters roots through root hair along with minerals.
     
   • It then moves through root cortex and endodermis to reach the root xylem.
     
   • Then the water which contains minerals reaches to the leaf through inter-connected stem xylem.
     
   • The transportation of water and minerals from the roots to the leaves is known as ascent of sap.
     
   • Only about 5% of the absorbed water is used up in photosynthesis and other metabolic processes while remaining 95% is lost as vapour by the process of transpiration.
     
   
   
   
3. Describe : Phloem.
   
   ANS :
   
   
   
   
   • Phloem is a tissue which translocates the carbohydrates and essential substances produced in leaves, and hormones synthesized at the shoot and root tips from their place of origin to the site where needed.
     
   • In pteridophytic and gymnospermic plants, the main component of phloem is the sieve cell.
     
   • In angiospermic plants the main components of phloem are sieve tube and companion cell.
     
   • Sieve cells are living as they possess cytoplasm and nucleus.
     
   • Sieve tube cell and companion cell are formed by the longitudinal division of a single cell.
     
   • Sieve tube cells are broad and their nuclei are disintegrated.
     
   • Companion cells are narrow and possess nucleus.
     
   • Companion cells are arranged laterally and longitudinally to the sieve tube cells and their nuclei regulate metabolic activities carried out in sieve tube cells.
     
   • The transverse walls (sieve plates) present between sieve tube cells are perforated. These pores are known as sieve pores. Due to the sieve pores the food can be translocated in both upward and downward directions.
     
   • The transverse wall between two sieve cells does not have pores hence the translocation of food is indirect.
     
   • Transport of food from leaves to other parts of the plant is called translocation.
     
   • Translocation of food is necessary to fulfil daily requirements of energy, to replace worn out cells and for plant growth.
     
   
   
   
4. Write an explanatory note on blood.
   
   ANS :
   
   
   
   • Blood is a living, red coloured, liquid connective tissue which circulates constantly throughout the body.
     
   • The two main components of blood are : (1) Blood Plasma (2) Blood Corpuscles.
     
   • BLOOD PLASMA :
     
     
     
     • It is pale yellow, nonliving, intercellular matrix with basic properties.
       
     • It consists of 90% of water and 10% of various constituents like plasma proteins, nutrients, metabolic waste, enzymes, hormones, vitamins, etc.
       
     
     
     
     
   • BLOOD CORPUSCLES :
     
     
     
     • Three main types of blood corpuscles in blood plasma are : (1) erythrocytes or red blood corpuscles (2) leucocytes or white blood corpuscles (3) thrombocytes (blood platelets).
       
     • They are formed from the undifferentiated stem cells found in the bone marrow of long bones.
       
     • ERYTHROCYTES (RBC) :
       
       
       
       • They are round, biconcave and light red in colour.
         
       • They do not possess nucleus and mitochondria.
         
       • The cell membrane is thin and elastic.
         
       • The cytoplasm contains haemoglobin which is a conjugated protein containing iron. Iron gives red colour to haemoglobin.
         
       • Haemoglobin absorbs oxygen from the walls of the lungs and forms oxyhaemoglobin. It takes this oxygen to every cell of the body.
         
       • Similarly haemoglobin collects carbon dioxide from each cell and brings it to lungs.
         
       • Since haemoglobin transports respiratory gases, it is known as respiratory pigment.
         
       • Every day about 30 lakh (3 million) erythrocytes die and as much of them are formed in the bone marrow.
         
       • The average life span of an erythrocyte is of 120 days.
         
       
       
     • LEUCOCYTES (WBC) :
       
       
       
       • The leucocytes vary in size, shape, appearance of the nuclei and the cytoplasmic constituents.
         
       • They do not contain any respiratory pigment.
         
       • They destroy pathogenic microorganisms and harmful toxic substances.
         
       • As they can pass through very thin membranes of capillaries, they are capable of reaching any part of the body.
         
       • Thus leucocytes provide protection to the body.
         
       • Lymphocytes (a type of WBC) produce immunoglobulins.
         
       
       
     • BLOOD PLATELETS :
       
       
       
       
       • They are very small, spindle-shaped fragments of cells in blood plasma.
         
       • They do not have any nucleus.
         
       • Their cell membrane is very thin and sensitive.
         
       • They rupture when they come in contact with air and release chemicals which initiate the process of blood clotting.
         
       
       
     
     
   
   
   
5. Describe : Clotting of Blood.
   
   ANS :
   
   
   
   • Blood vessels rupture when there is a wound. Blood oozes out from the wound. This blood comes in contact with air and the process of clotting starts. The process of clotting takes place in the following manner.
     
   • The blood platelets rupture at the point of injury.
     
   • The ruptured platelets release thromboplastin.
     
   • Thromboplastin converts prothrombin found in the plasma into thrombin. This requires calcium.
     
   • Thrombin converts liquid fibrinogen (in the plasma) into solid fibrin fibres. These fibres form a network at the point of injury.
     
   • The blood corpuscles entangled in this network form a solid layer which dries up and forms a solid clot which stops the flow of blood.
     
   • After some time, a viscous pale yellow liquid (serum) oozes out from the periphery of the clot.
     
   
   
   
6. Explain : Blood Transfusion.
   
   ANS :
   
   
   
   • The transfer of blood from a healthy donor to a person in need is called blood transfusion.
     
   • Carl Landsteiner discovered that there are special antigens on the surface of erythrocytes and different antibodies in plasma.
     
   • If the antigen on the erythrocytes of the donor's blood and the antibody in the recipient's plasma are same, it causes clotting of the patient's blood and may lead to death.
     
   • There are two types of antigens 'A' and 'B' on the erythrocytes.
     
   • The corresponding antibodies which clump the blood are 'a' and 'b', respectively.
     
   • We have four different blood groups : A, B, AB and O.
     
   • Blood transfusion is possible between two persons having same blood group.
     
   • A person with 'O' group can donate blood to any person but can receive the blood of 'O' group only.
     
   • A person with 'AB' group can receive blood from any person but can donate blood only to a person with 'AB' group.
     
   • Rhesus factor (Rh) is also matched for blood transfusion.
     
   
   
   
7. Describe : Structure and Working of Human Heart.
   
   ANS :
   
   
   STRUCTURE :
   
   
   
   • Human heart is located slightly on the left side in the space between two lungs.
     
   • It is conical and of the size of a closed fist.
     
   • It has four chambers. Two upper chambers are called atrium and the lower chambers are called ventricle.
     
   • Left atrium, right atrium, left ventricle and right ventricle are the four chambers based on their location in the heart.
     
   • The walls of the atria are thin whereas the walls of ventricles are thick.
     
   • All four chambers are separated from one another by partition called septa.
     
   • There is a bicuspid valve between left atrium and left ventricle whereas there is a tricuspid valve between right atrium and right ventricle.
     
   • These valves allow blood to flow from atrium to ventricle but do not allow it to flow from ventricle to atrium.
     
   • Heart is made of cardiac muscles.
     
   
   
   WORKING :
   
   
   
   • When all four chambers of the heart are in relaxed state (diastolic stage), deoxygenated blood from the organs enters the right atrium through the superior and inferior vena cava.
     
   • At the same time oxygenated blood from lungs enters the left atrium through the pulmonary vein.
     
   • When both the atria are filled with blood , they contract and deoxygenated blood from right atrium is poured into right ventricle through tricuspid valve. Similarly the oxygenated blood from the left atrium is poured into left ventricle through bicuspid valve.
     
   • When both ventricles are filled with blood, they contract (systolic stage) and deoxygenated blood from the right ventricle goes to lungs through pulmonary artery and oxygenated blood from the left ventricle is distributed to all the parts of the body (except lungs) through aorta.
     
   • Since the blood flows twice through the heart it is called double circulation.
     
   
   
   
8. Write a note on blood vessels.
   
   ANS : There are three types of blood vessels : (1) Arteries (2) Veins (3) Blood capillaries.
   
   ARTERIES :
   
   
   
   • They carry blood from the heart to different organs of the body.
     
   • Their walls are thick and elastic.
     
   • They do not have valves.
     
   • After entering an organ, they branch into small arterioles.
     
   
   
   VEINS :
   
   
   
   • They carry blood from different organs to heart.
     
   • Their walls are thin and nonelastic.
     
   • They have valves.
     
   • After exiting an organ they unite to form vena cava.
     
   
   
   BLOOD CAPILLARIES :
   
   
   
   • Around the tissues, the arterioles break up into fine vessels called capillaries.
     
   • They are thin and narrow.
     
   • Capillaries unite to form small blood vessels called venules.
     
   • Venules unite to form veins.
     
   • Necessary substances diffuse from blood into the tissues through thin walls of the capillaries.
     
   
   
   
9. Write a note on Lymphatic system.
   
   ANS :
   
   
   
   • The transparent fluid that oozes out in the surrounding intercellular space and the tissue cells from the blood flowing in the capillaries is called lymph.
     
   • It is a pale yellow liquid connective tissue containing lymphocytes.
     
   • It is in direct contact with the tissue cells and provides them the necessary substances.
     
   • The excretory substances formed in the tissue cells diffuse into the lymph.
     
   • After this exchange of essential substances and excretory substances the lymph reaches the lymph vessel.
     
   • The lymphatic system begins with lymph vessels.
     
   • The lymphatic system consists of lymphatic vessels, lymphatic capillaries, lymph nodes and lymph glands.
     
   • Lymph circulates from tissue cells to the heart.
     
   
   
   
10. Explain : Excretion and Osmoregulation.
    
    ANS :
    EXCRETION :
    
    
    
    • During biochemical processes performed by body cells many unnecessary and toxic by-products are formed along with useful substances.
      
    • These unnecessary toxic substances are called excretory substances.
      
    • Excretion is the biological process involved in the removal of liquid excretory substances from the body.
      
    
    
    OSMOREGULATION :
    
    
    
    • The amount of water in the body may increase or decrease due to biological processes.
      
    • Osmoregulation is the process of maintaining the required amount of water and proper ionic balance in the body.
      
    • Excretion and osmoregulation occur simultaneously.
      
    • Methods of excretion, the type of excretory products and the amount of water required for excretion are correlated to the habitat of the organism, availability of water and necessity of osmoregulation.
      
    • Different animals have various structures for excretion and osmoregulation.
      
    • Amoeba has a contractile vacuole, sponges have osculum, hydra has oral opening, platyhelminthes have flame cells, earthworms have nephridia and human beings have kidneys.
      
    • Fresh water organisms get large amount of water easily. In order to remove this excess water they excrete ammonia which is soluble in water.
      
    • Marine and terrestrial animals possess mechanism to conserve water as they do not get fresh water easily. Their excretory system is capable of reabsorbing water and they excrete concentrated urine after a long interval. Urine mainly contains urea.
      
    • Desert animals convert the concentrated waste into crystals of uric acid as they cannot afford to lose water.
      
    • Birds do not have urinary bladder. They excrete waste in the form of uric acid.
      
    
    
    
11. Describe excretion in earthworm.
    
    ANS :
    
    
    
    
    • The body of earthworm is divided into a series of segments separated internally by septa.
      
    • Excretory organs of the earthworm are called nephridia which are absent in first three segments.
      
    • Nephridia are coiled tubes.
      
    • There are three types of nephridia : (i) septal (ii) pharyngeal (iii) integumentary.
      
    • There are two types of excretion : (i) enteronephric (ii) exonephric.
      
    • In enteronephric excretion the excretory products are poured into alimentary canal through nephridia.
      
    • In exonephric excretion the excretory products are thrown out of the body through skin.
      
    • There is a funnel-like structure called nephrostome at the anterior end of the nephridium.
      
    • Its posterior end has an opening called nephridiopore.
      
    • The fluid carrying wastes enters nephrostome.
      
    • The cilia present in the tubule help the fluid to move through the nephridium.
      
    • During the process useful substances are reabsorbed by the cells lining the tubules.
      
    • These useful substances are then passed into the blood.
      
    • The remaining waste fluid is thrown out through nephridiopore.
      
    
    
    
12. Describe excretion in human being.
    
    ANS :
    EXCRETORY SYSTEM :
    
    
    
    
    
    • Excretory organs consist of a pair of reddish brown bean-shaped kidneys, located in the abdomen.
      
    • From each kidney opens an excretory tube called ureter into the urinary bladder.
      
    • The bladder passes into a muscular tube called urethra.
      
    • Urethra opens out as small opening called urinary opening.
      
    • Kidney is divided into cortex and medulla.
      
    • Kidney consists of excretory units called nephrons.
      
    
    
    STRUCTURE OF A NEPHRON :
    
    
    
    
    • A kidney has very minute tubular and convoluted structures known as uriniferous tubules (nephrons).
      
    • A kidney has about 10 lac (one million) such units.
      
    • Each nephron has a double-walled cup-shaped structure called Bowman's Capsule at its beginning.
      
    • Bowman's capsule encloses a small group of capillaries called glomerulus.
      
    • The short region after Bowman's capsule is called the neck.
      
    • The tubule after the neck is narrow and coiled.
      
    • It consists of proximal convolution, Henle's loop and distal convolution.
      
    • The distal convolutions of many nephrons join a common collecting duct which leads to the renal pelvis.
      
    • Renal pelvis opens into the ureter.
      
    
    
    PROCESS OF FORMATION OF URINE :
    
    
    
    • Renal arteries bring blood containing the waste material to the kidney.
      
    • By ultrafiltration the blood is filtered out from blood capillaries into Bowman's capsule under pressure.
      
    • During the passage of this filtrate through tubular parts of nephron, useful products such as water, amino acids, minerals, ions, etc. are reabsorbed by blood capillaries surrounding the nephron.
      
    • The remaining fluid contains excretory substance called urine which passes into urinary bladder through ureter. When the bladder is filled with urine, it contracts and urine passes out of the body.
      
    
    
    
13. Mention functions of blood.
    
    ANS :
    
    
    
    • Blood carries oxygen from lungs to other parts of the body.
      
    • It brings carbon dioxide from all parts of the body to lungs.
      
    • It carries digested food (nutrients) from alimentary canal to all parts (cells) of the body.
      
    • It carries hormones from different glands to the target area in the body.
      
    • It carries excretory waste products to throw them out through urine.
      
    • It regulates body temperature.
      
    • It fights pathogenic organisms through WBC and protects the body from various diseases.