Fill in the blanks

(i) The ……………………… have thin and less muscular …………………… and have ……………..to prevent backflow of ……………….

(ii) …………………….carry blood to an organ and break up into ………......ending in capillaries.

(iii) Walls of capillaries consist of a single layer of squamous ………………… cells.

(iv) The substances to and from the tissues diffuse through the walls of …………………….

(i) The veins have thin and less muscular walls and have thin pocket – shaped valves to prevent backflow of blood.

Explanation: The characteristics of the vein are:

i. Thin muscular walls

ii. Has thin pocket – shaped valves whose opening face the direction of the heart to prevent the backflow of blood.

(ii) Artery carries blood to an organ and break up into arteriole ending in capillaries.

Explanation: The smallest or the final branch of an artery is the arteriole which in turn breaks up into capillaries.

(iii) Walls of capillaries consist of a single layer of squamous epithelial cells.

Explanation: A capillary is a very narrow tube consisting of a single-layered epithelium (endothelium) and is devoid of muscles.

(iv) The substances to and from the tissues diffuse through the walls of capillaries.

Explanation: The substances to and from the tissues diffuse through the walls of capillaries, for example, oxygen, carbon dioxide, nutrients, leucocytes, etc.