Give reason for the following:

Arteries have thick walls but no valves

Give reason for following:

Veins are provided with valves.

Give reason for the following:

Blood cannot flow back from ventricles into the auricles.

Give reason for the following:

White blood cells (leucocytes) are called soldiers of the body.

Differentiate between artery and vein.

Differentiate between xylem and phloem.

Differentiate between plasma and blood.

Differentiate between sweating and transpiration

Differentiate between white blood cells and platelets.