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Let's trace how a sponge eats. Step 1: Water containing food particles (like tiny bacteria) flows into the body through thousands of microscopic holes called ostia. Step 2: This water enters the main chamber, the spongocoel. Step 3: Choanocytes (collar cells) line this chamber. Their flagella move like little propellers to keep the water flowing. Step 4: These collar cells grab the food particles and digest them inside their cells (intracellular digestion). Step 5: The 'used' water, carrying waste, is pushed out through the large top opening called the osculum. This is how the sponge breathes and eats without a mouth or stomach.