B.

lipid metabolism

SER or Smooth Endoplasmic Reticulum is an organelle present in both animals as well as plants. The function of SER is lipid metabolism. It does not contain ribosomes and is specialised to synthesize lipids and steroids.

RER or Rough Endoplasmic Reticulum is attached with ribosomes on its surface and its main function is in protein synthesis.

D.

reptiles and mammals

Ornithorhynchus is a connecting link between reptiles and mammals. They bear hair and mammary glands (like-mammals), but also possess some of the reptilian characteristics such as egg laying, presence of cloaca and some skeletal similarities.

C.

Castle's intrinsic gastric factor

Castle's intrinsic gastric factor is secreted by the parietal cells of the stomach. It helps in absorption of Vitamin- B₁₂.

A.

Gambusia

Gambusia is a small fish that is introduced into a water body to control mosquito population. It is a fresh water fish. It feeds on larvae of mosquitoes.

B.

sesamoid bones

Sesamoid bones are small rounded masses of bones formed in tendons at the joints, where they are subjected to great pressure. e.g., patella, fabellae.