Plant cells contain all the organelles found in animal cells, plus three unique structures:
🌿 Chloroplasts
- Site of photosynthesis
- Contain chlorophyll — green pigment absorbing light energy
- Convert light energy, carbon dioxide, and water into glucose and oxygen
- Double membrane; inner membrane forms thylakoids (stacked into grana)
- Have their own DNA and ribosomes — evidence of ancient bacterial origin
- Only in cells that photosynthesise (leaves, green stems)
🧱 Cell Wall
- Rigid layer outside the cell membrane — made of cellulose
- Provides structural support and maintains cell shape
- Prevents cells from bursting when they absorb water (supports turgor pressure)
- Fully permeable to water and dissolved substances
- NOT the same as cell membrane — completely different structure and function
💧 Permanent Vacuole
- Large, central, fluid-filled space
- Bounded by the tonoplast membrane
- Contains cell sap: water + dissolved salts, sugars, pigments
- Maintains turgor pressure — pushes against cell wall to keep plant rigid
- When vacuole loses water, plant cells become flaccid → plant wilts
Quick Check: Plant cells placed in pure water do not burst, but animal cells do. Explain why, referring to specific structures.
Plant cells have a rigid cellulose cell wall outside the cell membrane. When water enters by osmosis, the cell wall prevents the cell from expanding too far — the cell becomes turgid but does not burst. Animal cells have only a cell membrane (no cell wall), so they swell and can burst (lyse) when too much water enters.
This deep dive covers Plant Cells: Three Additional Organelles within Cell Organelles for GCSE Biology. Revise Cell Organelles in Cell Biology for GCSE Biology with 12 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 14 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Cell Organelles
Scientists studying mitochondria use electron microscopes rather than light microscopes. Which statement correctly explains why electron microscopes are more useful for studying cell ultrastructure?
The diameter of a ribosome is approximately 0.00002 mm. (a) Write this diameter in standard form, in millimetres. (b) Convert this diameter into nanometres (nm).