What prevents backflow of blood inside the heart during contraction?

In which part of the alimentary canal is food finally digested?

Where do the following processes take place?
$(i)$ Filtration of blood
$(ii)$ Reabsorption of glucose and water
$(iii)$ Secretion of salts to make final filtrate
$(iv)$ Collection of the final filtrate

The walls of auricles are comparatively thicker than ventricles.

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.

Name the cell organelle in which the breakdown of pyruvate to give carbon dioxide,water,and energy takes place.