The part of the mammalian skin involved in excretion is the

Step 1: Analyze the question The question asks which part of the mammalian skin is involved in excretion. Excretion is the removal of metabolic waste products from the body, such as urea, excess salts and water.

Step 2: Explain the concept The skin has several layers and structures, each with its own function:

• Sweat glands: These are coiled tubular glands in the dermis. They remove water, mineral salts (mainly sodium chloride) and a small amount of urea from the blood and release them through pores onto the skin surface. This is excretion, and it also helps cool the body.
• Malpighian layer: This is the deepest layer of the epidermis. Its cells divide to produce new skin cells and contain melanin, which protects against UV rays. It is for growth and pigmentation, not excretion.
• Sebaceous gland: This gland secretes sebum, an oily substance that lubricates the skin and hair and has some antibacterial action. Sebum is a secretion (a useful substance), not an excretory waste.
• Horny layer (stratum corneum): This is the outer layer of dead, keratinised cells. It protects against water loss, germs and injury.

Step 3: Work through the options

• A. Sweat glands: remove water, salts and urea, so they are excretory. ✔
• B. Malpighian layer: produces new cells and pigment. ✘
• C. Sebaceous gland: secretes oil for lubrication. ✘
• D. Horny layer: protective covering. ✘

Step 4: Answer The part of the mammalian skin involved in excretion is the sweat glands, which is option A.

Exam tip: Remember the difference between excretion and secretion. Sweat is excreted (waste removal), while sebum is secreted (it has a useful function). Think "Sweat = Sewage out", and you will not confuse sweat glands with sebaceous glands.