Question
How does Amoeba obtain its food? Explain the process with the help of a labelled diagram description.
Solution — Step by Step
Amoeba is a unicellular organism that uses holozoic nutrition — it ingests solid food particles and digests them internally. Unlike plants, it cannot make its own food. The process Amoeba uses to engulf food is called phagocytosis (from Greek: phagein = to eat, kytos = cell).
When Amoeba detects a food particle (like a bacterium or algae), it extends temporary finger-like projections of its cytoplasm called pseudopodia (“false feet”). These projections surround the food particle from multiple sides — think of it as a slow-motion embrace. The pseudopodia are formed by cytoplasmic streaming: the gel-like outer ectoplasm converts to the more fluid endoplasm and flows outward.
The pseudopodia meet around the food particle, enclosing it completely. This forms a temporary pocket called a food cup. The food cup then pinches off from the cell membrane, becoming a membrane-bound sac inside the cell called a food vacuole. The food particle is now trapped inside the cell, surrounded by a membrane.
Digestive enzymes secreted by the cell enter the food vacuole. These enzymes break down complex food molecules into simpler ones — proteins into amino acids, carbohydrates into glucose. The digested nutrients diffuse out of the food vacuole into the cytoplasm, where they are used for energy and growth.
Undigested material remains in the food vacuole. When the vacuole moves to the cell surface, the membrane fuses with the cell membrane and the waste is expelled outside. This is called egestion. Unlike excretion (removal of metabolic waste), egestion removes undigested food.
Why This Works
Amoeba lacks a mouth, stomach, or any specialised organ. The cell membrane itself becomes the “mouth” wherever a food particle is detected. This flexibility is possible because Amoeba’s body is a single cell — the entire cell participates in feeding.
The pseudopodia work because the cytoplasm can reversibly shift between a gel state (ectoplasm) and a sol state (endoplasm). Pressure changes inside the cell drive cytoplasm to flow outward in the direction of the food particle. This mechanism — phagocytosis — is also used by our own white blood cells (neutrophils and macrophages) to engulf bacteria and foreign particles.
The diagram you draw should show: Amoeba body with nucleus → pseudopodia extending → food cup → food vacuole with food inside → digestive enzymes entering vacuole. Label all these structures. In CBSE, a diagram without labels gets no marks.
Diagram Description
Draw Amoeba as an irregular blob shape. Label:
- Nucleus — dark oval structure inside
- Cell membrane — outer boundary
- Pseudopodia — two finger-like extensions reaching toward a small oval (food particle)
- Food cup — the U-shape formed by pseudopodia around the food
- Food vacuole — a circle inside the cell after the food is engulfed
- Ectoplasm — thin outer clear region
- Endoplasm — granular inner region
Common Mistake
Many students write that Amoeba “absorbs” food directly through its membrane the way plants absorb water. That is osmosis (for water) or diffusion (for dissolved molecules) — both passive processes. Amoeba actively engulfs solid food by phagocytosis. The distinction matters: digestion happens inside the food vacuole, not at the membrane surface. CBSE examiners deduct marks for this confusion.