Life Processes · Lesson 5 of 13
How Do Organisms Obtain Their Nutrition?
“Amoeba proves that one cell can run a complete kitchen.”
• Describe food intake and digestion in Amoeba. • Explain the role of pseudopodia and food vacuoles. • Describe how Paramoecium directs food to a fixed site. • Compare nutrition in Amoeba and Paramoecium. • Relate cellular specialisation to body organisation.
A single cell has no mouth, stomach or intestine, yet it must still capture food, digest it, absorb nutrients and remove residues. Amoeba and Paramoecium accomplish the same basic functions using different parts of their cell surface.
Nutrition In Amoeba
Amoeba forms temporary finger-like extensions called pseudopodia around a food particle. The extensions meet and enclose the particle inside a food vacuole. Digestive substances act within the vacuole, converting complex food into simpler soluble substances. These diffuse into the cytoplasm and are used by the cell. Undigested residue moves to the surface and is expelled.
Pseudopodia are temporary extensions of the cell surface and cytoplasm used by Amoeba for movement and engulfing food.
A food vacuole is a membrane-bound compartment in which engulfed food is digested inside a cell.
| Stage | Change in Amoeba | Purpose |
|---|---|---|
| Capture | Pseudopodia extend around food | Brings the particle within the cell boundary |
| Ingestion | Membrane encloses the particle | Forms a food vacuole |
| Digestion | Complex food is broken into simpler substances | Makes nutrients usable |
| Absorption | Soluble products enter the cytoplasm | Supplies material and energy |
| Egestion | Undigested residue is expelled at the surface | Removes unusable material |
Nutrition In Paramoecium
Paramoecium has a definite body shape. Numerous cilia beat in a coordinated manner, creating water currents that sweep food toward a specific feeding region. A food vacuole then forms and circulates through the cytoplasm while digestion and absorption occur.
Cilia are short, hair-like cell-surface structures whose coordinated beating produces movement or directs materials.
| Feature | Amoeba | Paramoecium |
|---|---|---|
| Body shape | Continuously changing | Relatively definite |
| Food capture | Pseudopodia surround food | Cilia direct food to a fixed site |
| Site of intake | Can occur at different points on the surface | Occurs at a specialised region |
| Digestion | Inside food vacuoles | Inside food vacuoles |
Problem
Trace a food particle from capture to removal in Amoeba.
- 1.Pseudopodia extend toward and around the particle.
- 2.The cell membrane encloses it to form a food vacuole.
- 3.Digestive substances break complex food into simpler molecules.
- 4.Useful molecules enter the cytoplasm.
- 5.Undigested residue reaches the surface and is expelled.
The food vacuole is not a permanent stomach. It forms around engulfed food and moves within the cytoplasm while digestion occurs.
Quiz
Which structure surrounds food in Amoeba?
Where does digestion occur in Amoeba?
What directs food in Paramoecium?
Which feature is shared by Amoeba and Paramoecium?
Why can Amoeba take in food at different surface points?
Practice Problems
- Arrange capture, ingestion, digestion, absorption and egestion in the correct order for Amoeba.
- Explain how pseudopodia perform more than one function.
- Compare the role of cilia in Paramoecium with pseudopodia in Amoeba.
- Predict what would happen if an Amoeba formed a food vacuole but could not release digestive substances into it.
- Explain how increased cellular specialisation in Paramoecium changes the location of food intake.
Key Takeaways
• Unicellular organisms perform all nutritional functions within one cell. • Amoeba uses pseudopodia to engulf food. • Digestion in Amoeba occurs inside food vacuoles. • Useful products diffuse into the cytoplasm. • Undigested material is expelled through the surface. • Paramoecium uses cilia to direct food to a specialised site.