Which of the following groups of organisms has kidney as the excretory organ?

Analyze the question: We need the group in which every organism uses the kidney as its excretory organ. Kidneys are found in vertebrates.

Concept: Excretory structures differ across animal groups:

• Protozoans (e.g., Amoeba): contractile vacuole and diffusion
• Tapeworms (flatworms): flame cells
• Annelids (e.g., earthworm): nephridia
• Insects: Malpighian tubules
• Vertebrates (fishes, amphibians, reptiles, birds, mammals): kidneys

Step-by-step check of the options:

• A. Fishes, amphibians, birds, man: All are vertebrates, and all have kidneys. ✔
• B. Fishes, amphibians, annelids, insects: Annelids have nephridia and insects have Malpighian tubules. ✘
• C. Fishes, reptiles, birds, tapeworm: The tapeworm uses flame cells. ✘
• D. Fishes, protozoans, amphibians, man: Protozoans use contractile vacuoles. ✘

Answer: Option A is the only one in which every group has kidneys.

Exam tip: Match the excretory organ to the animal group:

• Protozoa → contractile vacuole
• Flatworms → flame cells
• Annelids → nephridia
• Insects → Malpighian tubules
• Vertebrates → kidneys

In a question like this, look for the option made up entirely of vertebrates, and eliminate any option that includes an invertebrate.