Which of the following processes is not a function of the mammalian skin?

Step 1: Analyze the question We need the process that the mammalian skin does NOT carry out. So we check each option against the known functions of the skin.

Step 2: Recall the functions of mammalian skin

• Temperature regulation: Sweat glands release sweat that cools the body as it evaporates. Blood vessels dilate (vasodilation) or constrict (vasoconstriction), and hair erector muscles adjust the insulating layer of air.
• Reception of stimuli: The skin contains sensory receptors for touch, pressure, pain, heat, and cold.
• Excretion: Sweat carries out water, salts, and a little urea.
• Protection: The skin guards against infection, water loss, and UV light. It also makes vitamin D and stores fat.

Step 3: Check each option

• A. Regulation of body temperature: this is a function of the skin.
• B. Reception of external stimuli: this is a function of the skin.
• C. Excretion: this is a function of the skin, through sweat.
• D. Gaseous exchange: this is not a function of mammalian skin. Mammals exchange gases in the lungs (alveoli). Their skin is thick, keratinized, and dry, so it is unsuitable for diffusion of respiratory gases. Gaseous exchange through the skin happens in animals like earthworms and amphibians (frogs), which have thin, moist skin.

Exam tip: Remember that skin respiration belongs to earthworms and amphibians. Whenever a question asks about mammals, gaseous exchange takes place in the lungs only. Also remember the skin's main roles with "PRESTO": Protection, Reception, Excretion, Secretion (oil), Temperature regulation, Osmoregulation (water balance).