Biology [3 marks Question Answer]

A matured mammalian erythrocyte lacks a nucleus and mitochondria. The lack of a nucleus
increases the surface area-volume ratio of RBCs, thus increasing the area for oxygen absorption.
Also, the lack of a nucleus reduces the size of the cell, making it easy to flow through the blood
vessels and more cells can be accommodated in a small area.
The lack of mitochondria implies that the cell does not use any oxygen absorbed for respiration,
thus increasing the efficiency of the cell to transport oxygen as all the oxygen absorbed is
transported without any loss.

The types of blood vessels numbered 1 to 5:

• 1 represents Arteriole
• 2 represents Artery
• 3 represents Venule
• 4 represents Capillaries
• 5 represents Vein

Such an arrangement can be found in the Lungs.

1 - Arteriole
2 - Artery
3 - Venule
4 - Capillaries
5 - Vein

(a) A - Artery, B - Vein, C - Capillary
(b)
1 - External layer made of connective tissue
2 - Lumen
3 - Middle layer of smooth muscles and elastic fibres
4 - Endothelium
(c) An artery has thick muscular walls and a narrow lumen. It does not have any valve.
A vein on the other hand has thin muscular walls and a wider lumen. It has valves to prevent backflow of blood.
(d) A (Artery) - oxygenated blood, B (Vein) - deoxygenated blood
(e) At the capillary level the actual exchange of gases takes place.

Function of part 1 (RBC): Transport of respiratory gases to the tissues and from the tissues, transport of nutrients from the alimentary canal to the tissues.

Function of part 2 (WBC): WBCs play major role in defense mechanism and immunity of the body.

Function of part 3 (Blood Platelet): Blood platelets are the initiator of blood clotting.

Blood flows twice in the heart before it completes one full round. The full round thus includes
pulmonary and systemic circulation. In pulmonary circulation, blood enters the lungs through
pulmonary arteries. Pulmonary veins collect the blood from the lungs and carry it back to the
left atrium.
In systemic circulation, blood from the left ventricle enters the aorta through which the blood is
sent to the body parts. From the body parts blood is collected by veins and sent back to the heart.
Therefore, the blood circulation in the human body is called double circulation.

Structural Differences between White Blood Cells and Red Blood Cells:

White Blood Cells	Red Blood Cells
1. White blood cells are amoeboid.	Red blood cells are minute biconcave disclike structures.
2. They are nucleated cells.	They anucleated cells.
3. Haemoglobin is absent in white blood cells.	Haemoglobin is present in red blood cells.

The functions of the blood are:
(a) Transport of digested food from the alimentary canal to tissues. These substances are
simple sugars like glucose, amino acids, vitamins, mineral salts, etc.
(b) Transport of oxygen in the form of an unstable compound 'oxyhaemoglobin' from the lungsto the tissues.
(c) Transport of carbon dioxide from the tissues to the lungs.
(d) Transport of excretory materials from the tissues to the liver, kidney or the skin for
elimination.
(e) Distribution of hormones from glands to the target sites.
(f) Distribution of heat to keep the body temperature uniform.
(Any five)

During blood transfusion it is important that the blood groups of the donor and the recipient
are compatible. In case of an incompatible blood transfusion, the recipient develops
antibodies that attack the antigens present on the RBCs of the donor causing the blood cells
to clump together which may result in death. The examination of Rh factor is also necessary
for the blood transfusion. Therefore, the blood groups of both the donor and recipient must
be known before transfusing blood.

Double circulation: Double circulation in the heart refers to the way blood flows through the heart and the rest of the body in two separate loops or circuits. This system is composed of:
Pulmonary Circulation: Deoxygenated blood is sent from the heart to the lungs to get oxygenated, then returns to the heart. Systemic Circulation: Oxygenated blood from the heart is circulated throughout the body to deliver oxygen, then deoxygenated blood returns to the heart.
This efficient system enables high blood pressure in organs and quick oxygen delivery, vital for high metabolism in mammals and birds.