Chapter 15: Body Fluids and Circulation Short Questions | biology Class 11 CBSE

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Chapter 15: Body Fluids and Circulation Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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What is plasma and what percentage of blood does it constitute?

Plasma is a straw-coloured, viscous fluid matrix of blood constituting nearly 55 per cent of the blood volume.
It is composed of 90–92 per cent water and 6–8 per cent proteins (fibrinogen, globulins, albumins) along with minerals, glucose, amino acids, and lipids.
Clotting factors are also present in plasma in inactive form; plasma without clotting factors is called serum.

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Question 2

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State the role of fibrinogen, globulins, and albumins in plasma.

Fibrinogen is essential for coagulation or clotting of blood at the site of injury.
Globulins are primarily involved in the body's defence mechanisms, contributing to immune responses.
Albumins help maintain osmotic balance between blood and tissue fluid.

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Question 3

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Why are RBCs called erythrocytes, and what is their average lifespan?

RBCs are called erythrocytes because they contain haemoglobin, an iron-containing complex protein that gives them a red colour ('erythro' means red).
A healthy adult has 5–5.5 million RBCs per mm3 of blood and they are biconcave and enucleate in most mammals.
Their average lifespan is 120 days, after which they are destroyed in the spleen, which is therefore called the graveyard of RBCs.

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Question 4

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Distinguish between granulocytes and agranulocytes with examples.

Granulocytes are WBCs with lobed nuclei and granular cytoplasm; they include neutrophils, eosinophils, and basophils.
Agranulocytes have non-granular cytoplasm and rounded or kidney-shaped nuclei; they include lymphocytes and monocytes.
Neutrophils (most abundant WBC at 60–65%) and monocytes are phagocytic, while lymphocytes are responsible for immune responses.

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Question 5

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What are thrombocytes and what is their normal count in blood?

Thrombocytes, also called platelets, are cell fragments produced from megakaryocytes — special cells in the bone marrow.
Blood normally contains 1,50,000–3,50,000 platelets per mm3 of blood.
Platelets release substances involved in coagulation; a reduction in their number leads to clotting disorders and excessive blood loss.

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Question 6

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On what basis is ABO blood grouping done? Name the four groups.

ABO blood grouping is based on the presence or absence of two surface antigens, A and B, on the surface of RBCs.
Corresponding natural antibodies (anti-A and anti-B) are present in the plasma of individuals lacking the respective antigen.
The four blood groups are A, B, AB, and O — AB individuals are universal recipients (no antibodies) and O individuals are universal donors (no antigens).

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Question 7

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Why must Rh grouping be checked before blood transfusion?

The Rh antigen, similar to that found in Rhesus monkeys, is present on the RBC surface of Rh-positive individuals (about 80% of humans).
If an Rh-negative person receives Rh-positive blood, they form specific antibodies against the Rh antigen, causing agglutination of the donor's RBCs.
Such Rh incompatibility can cause severe haemolytic reactions, making Rh matching as critical as ABO matching before any transfusion.

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Question 8

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What is erythroblastosis foetalis and how can it be prevented?

Erythroblastosis foetalis is a condition in which Rh antibodies produced by an Rh-negative mother cross the placenta in subsequent pregnancies and destroy the RBCs of an Rh-positive foetus.
This occurs because during the first delivery the mother is exposed to foetal Rh antigens and begins producing Rh antibodies.
It can be prevented by administering anti-Rh antibodies (anti-D immunoglobulin) to the mother immediately after the delivery of the first child.

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Question 9

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Briefly explain the role of thrombin and fibrin in blood clotting.

Thrombin is an enzyme formed from inactive prothrombin (present in plasma) through the action of thrombokinase during the clotting cascade.
Thrombin converts inactive, soluble fibrinogen in plasma into insoluble fibrin threads.
Fibrin threads form a network at the injury site that traps dead and damaged blood cells to form a stable clot (coagulum), preventing further blood loss.

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Question 10

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What is the role of calcium ions in blood coagulation?

Calcium ions (Ca2+) are essential cofactors at multiple steps of the blood clotting cascade.
They are required for the formation of the thrombokinase enzyme complex from inactive plasma factors.
Without calcium ions, the conversion of prothrombin to thrombin cannot proceed efficiently, and clot formation is impaired.

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Question 11

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How is tissue fluid (interstitial fluid) formed and what is it called when it enters the lymphatic system?

As blood passes through tissue capillaries, water and small water-soluble substances are filtered out into the intercellular spaces due to capillary pressure, forming interstitial or tissue fluid.
This fluid has the same mineral distribution as plasma but lacks most large proteins and formed elements.
When this tissue fluid is collected by the elaborate network of lymphatic vessels and enters the lymphatic system, it is called lymph.

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Question 12

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State two functions of lymph apart from fluid balance.

Lymph contains specialised lymphocytes that are responsible for the immune responses of the body, contributing to defence against pathogens.
Lymph acts as an important carrier for nutrients and hormones between tissues and the blood circulation.
Dietary fats (lipids) are absorbed from the intestine specifically through lymph via lacteals present in the intestinal villi, bypassing the portal circulation.

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Question 13

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Differentiate between open and closed circulatory systems.

In the open circulatory system (arthropods, molluscs), blood pumped by the heart passes through large vessels into open body cavities called sinuses and is not always contained in vessels.
In the closed circulatory system (annelids, chordates), blood is always circulated through a closed network of blood vessels and never leaves the vessels.
The closed system is more advantageous as the flow of fluid can be more precisely regulated according to metabolic demands.

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Chapter 15: Body Fluids and Circulation | Short Questions

What is plasma and what percentage of blood does it constitute?

State the role of fibrinogen, globulins, and albumins in plasma.

Why are RBCs called erythrocytes, and what is their average lifespan?

Distinguish between granulocytes and agranulocytes with examples.

What are thrombocytes and what is their normal count in blood?

On what basis is ABO blood grouping done? Name the four groups.

Why must Rh grouping be checked before blood transfusion?

What is erythroblastosis foetalis and how can it be prevented?

Briefly explain the role of thrombin and fibrin in blood clotting.

What is the role of calcium ions in blood coagulation?

How is tissue fluid (interstitial fluid) formed and what is it called when it enters the lymphatic system?

State two functions of lymph apart from fluid balance.

Differentiate between open and closed circulatory systems.

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