Name the organelle in which photosynthesis occurs.

Which of the following statement$(s)$ is/are true about the heart?

Why do ventricles have thicker walls than atria?

The blood leaving the tissues becomes richer in

Differentiate between an artery and a vein.

Name the following with reference to the alimentary canal:
$(a)$ $(i)$ The largest gland.
$(ii)$ The gland that secretes digestive enzymes as well as hormones.
$(iii)$ The part where digested food is absorbed.
$(b)$ What are villi? Mention their function.