SolveItClass 11 · NCERT

NCERT Solutions · Class 11 Biology Body Fluids and Circulation

14 questions · 14 still being checked

Exercises 15.1–15.10 (part 1 of 2)

  1. Exercise 15.1

    Name the components of the formed elements in the blood and mention one major function of each of them.

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    The formed elements are erythrocytes (RBCs), leucocytes (WBCs) and platelets (thrombocytes); together they make up nearly $\displaystyle 45$ per cent of the blood.
    Erythrocytes (red blood cells) — they carry the red, iron-containing protein haemoglobin, which plays a significant role in the transport of respiratory gases (\(\displaystyle O_2 \) and \(\displaystyle CO_2 \)).
    Leucocytes (white blood cells) — they defend the body: neutrophils and monocytes are phagocytic and destroy foreign organisms entering the body, basophils secrete histamine, serotonin and heparin in inflammatory reactions, eosinophils resist infections, and B and T lymphocytes are responsible for immune responses.
    Platelets (thrombocytes) — cell fragments from megakaryocytes that release substances involved in the coagulation (clotting) of blood; a fall in their number causes clotting disorders and excessive blood loss.
    NCERT_Solution_Class11_Biology_Ch15_Q15-1

  2. Exercise 15.2

    What is the importance of plasma proteins?

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    Plasma proteins form $\displaystyle 6$–$\displaystyle 8$ per cent of plasma, and each of the three major proteins has a distinct role.
    Fibrinogen — needed for the clotting or coagulation of blood.
    Globulins — primarily involved in the defence mechanisms of the body.
    Albumins — help in maintaining the osmotic balance of the blood.
    Plasma from which the clotting factors have been removed is called serum.

  3. Exercise 15.3

    Match Column I with Column II : Column I
    (a)
    Eosinophils
    (b)
    RBC
    (c)
    AB Group
    (d)
    Platelets
    (e)
    Systole Column II
    (i)
    Coagulation
    (ii)
    Universal Recipient
    (iii)
    Resist Infections
    (iv)
    Contraction of Heart
    (v)
    Gas transport

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    (a) – (iii) Eosinophils – Resist Infections (eosinophils resist infections and are also associated with allergic reactions).
    (b) – (v) RBC – Gas transport (RBCs carry haemoglobin, which transports the respiratory gases).
    (c) – (ii) AB Group – Universal Recipient (persons of AB group can accept blood of AB, A, B and O groups).
    (d) – (i) Platelets – Coagulation (platelets release substances that bring about clotting of blood).
    (e) – (iv) Systole – Contraction of Heart (systole is the contraction phase of the atria and ventricles in a cardiac cycle).

  4. Exercise 15.4

    Why do we consider blood as a connective tissue?

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    Blood is a special connective tissue because it is made of a fluid matrix, plasma, in which the formed elements are suspended — the same matrix-plus-cells plan that defines a connective tissue.
    The cells (erythrocytes, leucocytes, platelets) are not attached to one another; they lie dispersed in the non-cellular plasma, which forms nearly $\displaystyle 55$ per cent of blood while the formed elements form about $\displaystyle 45$ per cent.
    Like other connective tissues, it links and supports the rest of the body: it transports nutrients, \(\displaystyle O_2 \), hormones and other essential substances to the cells and carries \(\displaystyle CO_2 \) and waste substances away from them.
    It is therefore classed as a fluid connective tissue.

  5. Exercise 15.5

    What is the difference between lymph and blood?

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    Lymph is blood minus the RBCs and the larger proteins — it is the tissue fluid that has escaped from the blood capillaries and been collected by the lymphatic system.
    Colour: lymph is colourless (no haemoglobin); blood is red because of the haemoglobin in its RBCs.
    Cells: lymph contains only specialised lymphocytes; blood contains all the formed elements — erythrocytes, leucocytes and platelets.
    Proteins: lymph has less protein, since the larger plasma proteins are left behind in the blood vessels; blood plasma is rich in fibrinogen, globulins and albumins. Mineral distribution in lymph is the same as in plasma.
    Vessels: lymph flows through the lymphatic system and is drained back into the major veins; blood is circulated through arteries, capillaries and veins by the pumping of the heart.
    Function: lymph carries nutrients, hormones, etc., absorbs fats through the lacteals of the intestinal villi, and its lymphocytes give immune responses; blood transports \(\displaystyle O_2 \), \(\displaystyle CO_2 \), nutrients and wastes throughout the body.
    Exchange of nutrients and gases between blood and the cells always takes place through this tissue fluid.

  6. Exercise 15.6

    What is meant by double circulation? What is its significance?

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    Double circulation means the blood passes through the heart twice in one complete circuit of the body, along two separate pathways — pulmonary and systemic.
    Pulmonary circulation: the right ventricle pumps deoxygenated blood into the pulmonary artery to the lungs, where it is oxygenated, and the pulmonary veins carry it back to the left atrium.
    Systemic circulation: the left ventricle pumps oxygenated blood into the aorta, and a network of arteries, arterioles and capillaries carries it to the tissues; the deoxygenated blood is collected by venules, veins and the vena cava and emptied into the right atrium.
    Significance — the two pathways are kept completely separate, so oxygenated and deoxygenated blood never mix and the tissues always receive fully oxygenated blood.
    Significance — systemic circulation supplies nutrients, \(\displaystyle O_2 \) and other essential substances to the tissues and takes \(\displaystyle CO_2 \) and other harmful substances away for elimination.
    Crocodiles, birds and mammals (including humans) possess a $\displaystyle 4$-chambered heart with two atria and two ventricles; in birds and mammals the blood received by the left and right atria passes to the ventricles of the same side and is pumped out without any mixing up, i.e., they have complete double circulation.
    Amphibians and the reptiles except crocodiles have a $\displaystyle 3$-chambered heart with two atria and a single ventricle, in which the two bloods get mixed up, so the ventricle pumps out mixed blood — incomplete double circulation.

  7. Exercise 15.7

    Write the differences between :
    (a)
    Blood and Lymph
    (b)
    Open and Closed system of circulation
    (c)
    Systole and Diastole
    (d)
    P-wave and T-wave

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    (a) Blood and Lymph
    Blood is red, has a fluid matrix (plasma) with all three formed elements — RBCs, WBCs and platelets — and is rich in proteins such as fibrinogen, globulins and albumins.
    Lymph is colourless, lacks RBCs and platelets, contains only specialised lymphocytes, and has less protein because the larger proteins stay behind in the blood vessels.
    Blood is circulated by the heart through arteries, capillaries and veins; lymph flows through the lymphatic system and is drained back into the major veins.
    Blood transports \(\displaystyle O_2 \), \(\displaystyle CO_2 \), nutrients and wastes; lymph carries nutrients and hormones, absorbs fats through the lacteals of the intestinal villi, and its lymphocytes give immune responses.
    (b) Open and Closed system of circulation
    In an open circulatory system the blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses; it is found in arthropods and molluscs.
    In a closed circulatory system the blood pumped by the heart is always circulated through a closed network of blood vessels; it is found in annelids and chordates.
    The closed pattern is considered more advantageous because the flow of fluid can be more precisely regulated.
    (c) Systole and Diastole
    Systole is the contraction of a heart chamber; diastole is its relaxation.
    Atrial systole increases the flow of blood into the ventricles by about $\displaystyle 30$ per cent; ventricular systole raises ventricular pressure, closing the tricuspid and bicuspid valves and forcing the semilunar valves open so that blood is pushed into the pulmonary artery and the aorta.
    During ventricular diastole the ventricular pressure falls, the semilunar valves close and prevent backflow, and the tricuspid and bicuspid valves are pushed open so that blood again flows from the atria into the ventricles.
    When all four chambers are relaxed together it is called joint diastole.
    (d) P-wave and T-wave
    The P-wave represents the electrical excitation (depolarisation) of the atria, which leads to the contraction of both the atria.
    The T-wave represents the return of the ventricles from the excited to the normal state (repolarisation).
    The P-wave comes at the beginning of the ECG trace, before the QRS complex; the T-wave comes after it, and the end of the T-wave marks the end of systole.

  8. Exercise 15.8

    Describe the evolutionary change in the pattern of heart among the vertebrates.

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    The heart evolved from two chambers to four, and the circulation from single to complete double circulation.
    Fishes — a $\displaystyle 2$-chambered heart with one atrium and one ventricle. The heart pumps out deoxygenated blood, which is oxygenated by the gills and supplied to the body parts, from where deoxygenated blood returns to the heart. This is single circulation.
    Amphibians and reptiles (except crocodiles) — a $\displaystyle 3$-chambered heart with two atria and a single ventricle. The left atrium receives oxygenated blood from the gills/lungs/skin and the right atrium the deoxygenated blood from other body parts, but the two get mixed in the single ventricle, which pumps out mixed blood. This is incomplete double circulation.
    Crocodiles, birds and mammals — a $\displaystyle 4$-chambered heart with two atria and two ventricles. Oxygenated and deoxygenated blood received by the left and right atria pass to the ventricles of the same side and are pumped out without any mixing, so two separate circulatory pathways exist. This is double circulation.
    The trend is towards keeping oxygenated and deoxygenated blood completely separate, so the tissues receive fully oxygenated blood.

  9. Exercise 15.9

    Why do we call our heart myogenic?

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    Our heart is called myogenic because its normal activity is initiated and regulated by its own specialised muscles (the nodal tissue), not by any nerve.
    The nodal musculature is autoexcitable — it can generate action potentials without any external stimulus.
    The sino-atrial node (SAN) generates the maximum number of action potentials ($\displaystyle 70$–$\displaystyle 75$ \(\displaystyle min^{-1} \)) and so initiates and maintains the rhythmic contractile activity of the heart.
    Nerves only moderate this intrinsic rhythm: a neural centre in the medulla oblongata acts through the autonomic nervous system, sympathetic signals increasing and parasympathetic signals decreasing the heart rate and cardiac output.

  10. Exercise 15.10

    Sino-atrial node is called the pacemaker of our heart. Why?

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    The sino-atrial node (SAN) is called the pacemaker because it generates the maximum number of action potentials — $\displaystyle 70$–$\displaystyle 75$ \(\displaystyle min^{-1} \) — and therefore sets the pace of the heart's activity.
    It is a patch of nodal tissue in the right upper corner of the right atrium, and like all nodal musculature it is autoexcitable.
    Every cardiac cycle begins with an action potential from the SAN, so it initiates and maintains the rhythmic contractile activity of the heart.
    Because of it the heart normally beats $\displaystyle 70$–$\displaystyle 75$ times a minute (average $\displaystyle 72$ beats \(\displaystyle min^{-1} \)), i.e., $\displaystyle 72$ cardiac cycles per minute.
    NCERT_Solution_Class11_Biology_Ch15_Q15-10