The flame cells are used for excretion in

Step 1: Analyze the question The question asks which organism uses flame cells (also called protonephridia) for excretion and osmoregulation.

Step 2: Explain the concept Flame cells are specialized excretory cells found in Platyhelminthes (flatworms), such as planarians, flukes, and tapeworms. Each flame cell has a tuft of beating cilia that looks like a flickering flame under the microscope. The cilia move waste fluid into a network of excretory tubules, which carry it out of the body through pores.

Step 3: Check each option

• A. Fluke: A fluke (e.g., Fasciola, the liver fluke) is a trematode, which belongs to Platyhelminthes. It has flame cells. ✔
• B. Nematode: Roundworms (Nematoda) excrete using H-shaped or tubular excretory canals and gland cells, not flame cells. ✘
• C. Bacteria: Bacteria are single-celled prokaryotes. They have no specialized excretory cells and get rid of wastes by diffusion. ✘
• D. Volvox: Volvox is a colonial green alga. It excretes by diffusion and uses contractile vacuoles, not flame cells. ✘

Step 4: Answer The correct answer is A. Fluke.

Step 5: Exam tip Link the words: "Flame cells = Flatworms". Both start with F, which makes it easy to remember. Also remember that:

• Flatworms use flame cells.
• Earthworms (annelids) use nephridia.
• Insects use Malpighian tubules.
• Mammals use kidneys.