Which of the following organs is primarily responsible for excretion in humans?

Step 1: Analyze the question The question asks which organ is primarily responsible for excretion. Excretion is the removal of metabolic waste products from the body, such as urea, excess salts, excess water, and carbon dioxide.

Step 2: Explain the concept Several organs take part in excretion, but each has a different main role:

• Liver: Breaks down amino acids (deamination) and forms urea. It makes the waste but does not remove it from the body. It also produces bile pigments, which are excreted through the gut.
• Pancreas: Produces digestive enzymes and hormones (insulin and glucagon). It is not an excretory organ.
• Kidneys: Filter the blood and remove urea, excess water, and mineral salts as urine. They are the main excretory organs in humans.
• Lungs: Excrete carbon dioxide and water vapour. This is a secondary excretory role, since the lungs' main job is gas exchange.

Step 3: Work through the options

• A. Liver: processes waste but does not eliminate it from the body, so it is not correct.
• B. Pancreas: it is a digestive and endocrine gland, so it is not correct.
• C. Kidneys: they filter nitrogenous waste (urea) from the blood and expel it in urine, so this is correct.
• D. Lungs: they do excrete CO₂, but the question asks for the organ primarily responsible, which is the kidneys.

Step 4: Answer The correct answer is C. Kidneys.

Exam tip: Remember "Liver makes urea, Kidneys remove urea." When JAMB asks about the main excretory organ, think of the kidneys. If the question instead mentions CO₂ or gaseous exchange, think of the lungs. If it mentions sweat and salts, think of the skin.