Which of the following is NOT an excretory organ?

Step 1: Analyze the question You need to find the organ that does NOT take part in excretion. Excretion is the removal of metabolic waste products from the body, such as urea, carbon dioxide, excess water and salts.

Step 2: Explain the concept The main excretory organs and what they remove are:

• Kidney: removes urea, excess water and salts as urine.
• Lung: removes carbon dioxide and some water vapour.
• Skin: removes sweat, which contains water, salts and a little urea.
• Liver: breaks down excess amino acids into urea, and breaks down haemoglobin into bile pigments. These are excretory products, so the liver is counted as an excretory organ.

Step 3: Check each option

• A. Heart: pumps blood around the body. It removes no waste from the body, so it is not an excretory organ.
• B. Kidney: excretory.
• C. Liver: excretory, because it produces urea and bile pigments.
• D. Lung: excretory, because it removes CO₂.
• E. Skin: excretory, because it removes sweat.

Step 4: Answer The heart is the only organ listed that is not involved in excretion. It belongs to the circulatory system, not the excretory system.

Exam tip: Link each organ to the waste it removes. Kidney → urea, lung → CO₂, skin → sweat, liver → bile pigments. If an organ has no waste product to remove, such as the heart, it is the odd one out.