Which of the following options correctly identifies excretory organs in animals?

Step 1: Analyze the question The question asks which option lists excretory organs. Excretion is the removal of metabolic waste products from the body, such as carbon dioxide, urea, excess water, and salts.

Step 2: Explain the concept Excretion is different from egestion. Excretion removes waste made by the body's cells (metabolism). Egestion removes undigested food from the gut.

The main excretory organs in mammals are:

• Lungs: remove carbon dioxide and some water vapour
• Kidneys: remove urea, excess water, and salts as urine
• Skin: removes sweat (water, salts, a little urea)
• Liver: breaks down toxins and produces urea, and is sometimes counted as excretory too

Step 3: Check each option

• A. Stomach, intestines, bladder: The stomach and intestines are digestive organs. They egest undigested food rather than excrete metabolic waste. The bladder only stores urine. ❌
• B. Lungs, kidneys, skin: All three remove metabolic wastes (CO₂, urea, sweat). ✅
• C. Brain, spinal cord, nerves: These are parts of the nervous system, which coordinates the body. ❌
• D. Heart, liver, spleen: The heart pumps blood and the spleen filters old red blood cells. The liver has some excretory roles, but this group as a whole is not excretory. ❌

Step 4: Answer The correct option is B. Lungs, kidneys, and skin.

💡 Exam tip: Remember the trio "LKS": Lungs, Kidneys, Skin. When a JAMB question asks about excretory organs, look for the option that contains these. Also remember that excretion ≠ egestion, since examiners often use digestive organs as distractors.