Pls answer Q21 and 22
Dear student
Please find below the solution to the asked query
21.
It more important for arm and leg veins to have valves than it is for neck veins because gravity pulls blood downwards in the veins of legs and arms and causes pooling of blood in them but incase of neck, the gravity aids in the flow of blood towards the heart.
Thus, the valves prevent backflow of blood in the veins of arms and legs due to gravity.
Kindly post rest of the questions in separate threads.
Regards