Cell Structure & Organisation
Master the fundamental building blocks of life. Understand the structural differences between animal and plant cells and the specialized functions of their organelles.
Figure 1.1: Comparative structure of typical animal and plant cells.
Structure of Animal Cells
Animal cells are the basic structural and functional units of animal tissues and organs. Unlike plant cells, they do not possess a rigid cell wall, which allows them greater flexibility in shape. Key organelles include the nucleus, which houses genetic material, the cytoplasm where most cellular activities occur, and the cell membrane, which acts as a selectively permeable barrier.
Vacuoles in animal cells are typically small and temporary, used for storage or transport, compared to the large, permanent central vacuole found in plant cells.
Structure of Plant Cells
Plant cells share many fundamental features with animal cells, such as a nucleus, cytoplasm, and cell membrane. However, they are characterized by several unique structures essential to their function. A rigid cell wall made of cellulose surrounds the cell membrane, providing structural support and shape.
Additionally, plant cells contain chloroplasts, the site of photosynthesis, and a large central vacuole filled with cell sap, which maintains turgor pressure against the cell wall.
Key Definitions
Master these terms for Paper 1 & 2.
Organelle
A specialized structure within a cell that performs a specific function.
Cytoplasm
The jelly-like substance inside a cell where most chemical reactions take place.
Mitochondria
The organelle responsible for aerobic respiration, releasing energy for the cell.
Chloroplast
An organelle found in plant cells containing chlorophyll, the site of photosynthesis.
Where Students Lose Marks
- Confusing the cell wall with the cell membrane: ALL cells have a membrane. Only plant (and fungal/bacterial) cells have a wall.
- Stating the nucleus 'controls the cell' without detail: be specific — it controls cell activities by containing genetic material (DNA).
- Assuming all plant cells have chloroplasts: root hair cells are plant cells but do not have chloroplasts because they don't receive light.
Quick Check (MCQs)
1. Which structure is found in a palisade cell but NOT a liver cell?
2. What is the function of mitochondria?
3. Which feature is present in a root hair cell but NOT a palisade mesophyll cell?
4. What is the main function of the cellulose cell wall?
5. Which organelle is responsible for protein synthesis?
6. Why do red blood cells lack a nucleus?
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