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

Excretion means getting rid of the waste your own body cells make. So an excretory organ must actually remove a waste product from the blood and send it out of the body.

The lungs breathe out carbon dioxide and some water vapour, which are wastes from respiration. The kidneys filter the blood and remove urea, extra water and extra salts as urine. The skin sweats out water, salts and a small amount of urea. All three remove waste from the blood, so lungs, kidneys and skin is the correct set.

The other sets are not excretory groups. The heart only pumps blood, the spleen stores and destroys old blood cells, and the spleen is not an excretory organ (the liver only helps by changing ammonia into urea, which the kidney then removes). The stomach and intestines handle digestion and push out undigested food as faeces, which is egestion, not excretion, and the bladder only stores urine. The brain, spinal cord and nerves make up the nervous system and carry messages.