Assertion Reason Questions for Biology Chapter 18 Body Fluids and Circulation

Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Q.1. Assertion : WBCs accumulate at the site of wounds by diapedesis.
Reason : It is the squeezing of leucocytes from the endothelium. [AIIMS 2002]

Answer Answer: (b) During wound, germs are removed by the process of phagocytosis by WBC. WBCs accumulate at the site of wound by diapedesis. It is the squeezing of leucocytes out from the endothelium of capillaries to fight against foreign agent.

Q.2. Assertion: In most of the mammal RBCs are devoid of nucleus.
Reason: Red colour is filled in the entire cytoplasm of RBCs, iron containing complex protein called haemoglobin.

Answer Answer: (b) Matured mammalian RBCs lacks cell organelles including nucleus, mitochondria, ribosomes, centrioles and endoplasmic reticulum. It increases the surface area of RBCs and enables them to contain more haemoglobin. Thus, almost entire cytoplasm is filled with haemoglobin.

Q.3. Assertion: In lymphatic system, lymph is known as tissue fluid.
Reason: It comprises of plasma proteins, RBCs and WBCs.

Answer Answer: (c) Lymphatic system comprises of lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes and lymphatic ducts. Lymph is a transparent fluid derived from blood and other tissues, that accumulates in the interstitial spaces as the interstitial fluid. It also contains leucocytes, mainly the lymphocytes. This fluid has a composition similar to that of plasma, except that it is low in proteins.

Q.4. Assertion: Type ‘O’ blood group individuals are called ‘universal donors’.
Reason: RBCs of ‘O’ blood group consists both ‘A’ and ‘B’ surface antigens.

Answer Answer: (c) If a blood transfusion is made between an incompatible donor and recipient, reaction of antigens on the cells and antibodies in the plasma will produce clots that will clog the capillaries. Type O blood group individuals are without A and B antigens on their RBCs, but consists antibodies for both these antigens in their plasma. Hence, these persons can donate blood to anyone. O blood group is the most important blood group for transfusion.

Q.5. Assertion (A) : Blood coagulates in uninjured blood vessels.
Reason (R) : Uninjured blood vessels release an anticoagulant heparin. [AIIMS 2007]

Answer Answer: (d) When an injury is caused to a blood vessel, bleeding starts which is stopped by blood clotting. At the site of injury blood platelets release platelet factor – 3 and injured tissues release thromboplastin. The two combine to form prothrombinase enzyme which converts prothrombin to thrombin. The latter stimulates formation of fibrin thread or clot. Blood contains an anticoagutant heparin which prevents blood clotting in uninjured vessels.

Q.6. Assertion: Fibrins are produced by the conversion of inactive fibrinogens in the plasma, in the presence of enzyme thrombin.
Reason: Plasma without fibrinogen and blood corpuscles is called serum.

Answer Answer: (c) A coagulam is mainly formed of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. Fibrins are produced by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. An enzyme complex, prothrombinase, is required for the above reaction.
The clot seals the wound and stops bleeding. After its formation, clot starts contracting and a pale yellow fluid, the serum, oozes out. This serum is blood plasma minus fibrinogen and blood corpuscles.

Q.7. Assertion: The clotting process can occur in the absence of all cellular elements except platelets.
Reason: Activated platelets release vitamin K.

Answer Answer: (c)

Q.8. Assertion : Prothrombinase enzyme act as antiheparin.
Reason : Heparin prevent coagulation of blood in blood vessels. [AIIMS 2010]

Answer Answer: (b) Prothrombinase enzyme is necessary for blood clotting. It acts as antiheparin. Coagulation of blood in vessels is prevented by heparin, a quick acting anticoagulant. It inhibits conversion of prothrombin to thrombin and is used in open-heart surgery.

Q.9. Assertion : Blood is coloured in the insects.
Reason : Insect blood has no role in O2 transport.
[AIIMS 2012, 2013]

Answer Answer: (b) Insect blood is colourless and does not play any role in transport of oxygen. Insects have tracheal respiration.

Q.10. Assertion : When there is a fall in the blood
pressure due to loss of blood volume, this is
compensated by vasoconstriction of veins.
Reason : Veins hold the extra amount of blood
which can be shifted to the arteries as required.
[AIIMS 2010, 2015]

Answer Answer: (a) When the blood pressure of an individual decreases due to loss of blood volume, then vasoconstriction of veins occurs. This shifts the little amount of blood from veins to arteries.

Q.11. Assertion: Sympathetic nerves can increase the
strength of ventricular contraction neural
Reason: To increase the cardiac output
parasympathetic neural signals synergistically
act with sympathetic neural signal.

Answer Answer: (c) Through the sympathetic nerves (part of ANS) neural signals can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. On the other hand, parasympathetic neural signals (another component of ANS) decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output.

Q.12. Assertion: Open circulatory system is more
efficient than closed circulatory system.
Reason: In closed circulatory system rather than
in open circulatory system, the blood flow is

Answer Answer: (d) The closed circulatory system is more efficient than the open circulatory system because in open circulatory system, open spaces and channels the blood flows through whereas in closed circulatory system, the blood flows through proper blood vessels. Also, in closed circulatory system arterial musculature and precapillary sphincters regulate the flow of blood, due to the volume of blood flowing through a tissue or an organ may be regulated according to needs. Moreover in closed circulatory system, the blood flows far more rapidly in closed blood vesssels than in wide open channels and body cavities. Thus, blood takes much shorter time to circulate through the closed system than in open circulatory system.

Q.13. Assertion: In amphibians and reptiles, double
circulation is incomplete.
Reason: Unlike in birds and mammals, in
amphibian and reptiles, the left atrium receives
oxygenated blood and right atrium receives
deoxygenated blood.

Answer Answer: (c)

Q.14. Assertion: Left atrium possesses the thickest
Reason: Left atrium receives blood from the

Answer Answer: (d) Left ventricle has thickest muscles because it pumps the blood to the whole body.

Q.15. Assertion: In the human heart, there is no mixing
of oxygenated and deoxygenated blood.
Reason: Presence of valves in the heart allows
the movement of blood in one direction only.

Answer Answer: (b) In the human heart, there is no mixing of deoxygenated and oxygenated blood due to the presence of inter – atrial and inter – ventricular septum. These septa completely divide the atria and ventricles into right and left and thus avoid mixing of blood. The presence of valves that prevents the backflow of the blood. The two atria are separated from the ventricles by membranous valves. The valve separating the right atrium from the right ventricle is known as the right atrioventricular valve or tricuspid valve (as it is made of three flaps or cusps). The valve separating the left atria and the left ventricle is called left atrioventricular valve or the bicuspid valve or the mitral valve (since it is made of two flaps). They allow the flow of blood from atria to ventricles and not in the backward direction. At the base of the aorta are present three membranous, pocket-shaped semilunar valves. These valves check the return of the blood to the ventricle.

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