Learning objectives
- Name major cell organelles.
- Explain the function of each organelle.
- Compare plant and animal cells.
- Describe diffusion and osmosis.
The cell as a basic unit
Cells are the basic structural and functional units of living organisms. Unicellular organisms perform all life processes within one cell, while multicellular organisms have specialised cells working together.
The plasma membrane forms the cell boundary and controls movement of substances. Cytoplasm contains organelles and is the site of many chemical reactions.
Important organelles
The nucleus stores genetic material and coordinates cell activities. Mitochondria release usable energy through cellular respiration. Ribosomes make proteins.
Plant cells usually have a cellulose cell wall, chloroplasts and a large central vacuole. Chloroplasts contain chlorophyll and are the main site of photosynthesis.
Movement across membranes
Diffusion is the movement of particles from a region of higher concentration to lower concentration. Osmosis is the movement of water through a selectively permeable membrane from higher water concentration to lower water concentration.
These processes help cells exchange gases, water and dissolved substances with their surroundings.
Practice questions with explanations
Try each question before opening the answer. The explanation shows the reasoning, not only the final response.
Q1. What is the basic structural and functional unit of life?
Answer: The cell.
Explanation: All organisms are made of one or more cells.
Q2. What is the main function of the plasma membrane?
Answer: It controls movement into and out of the cell.
Explanation: It is selectively permeable.
Q3. Which organelle contains genetic material?
Answer: The nucleus.
Explanation: DNA in the nucleus carries hereditary information.
Q4. Why are mitochondria called powerhouses of the cell?
Answer: They release usable energy during respiration.
Explanation: Cells use this energy for life processes.
Q5. Where are proteins made?
Answer: At ribosomes.
Explanation: Ribosomes assemble amino acids into proteins.
Q6. Which structure supports a plant cell outside the membrane?
Answer: The cell wall.
Explanation: The cellulose wall gives strength and shape.
Q7. What is the role of chloroplasts?
Answer: They carry out photosynthesis.
Explanation: Chlorophyll captures light energy.
Q8. What is diffusion?
Answer: Movement from higher to lower particle concentration.
Explanation: It occurs because particles move randomly.
Q9. What is osmosis?
Answer: Movement of water through a selectively permeable membrane.
Explanation: Water moves according to differences in water concentration.
Q10. Name one structure common in plant cells but not typical animal cells.
Answer: A chloroplast, cell wall or large central vacuole.
Explanation: These structures support photosynthesis, rigidity and storage.