- Organelle
- A specialised subunit within a cell that has a specific function, surrounded by its own membrane (in eukaryotic cells).
- Nucleus
- The control centre of the cell. Contains chromosomes made of DNA, which carry genetic information controlling cell activity. Surrounded by a double nuclear membrane with pores.
- Mitochondria
- The site of aerobic respiration. Mitochondria transfer energy from glucose and oxygen, producing ATP â the usable energy currency of the cell. They have their own DNA and ribosomes.
- Ribosome
- Tiny structures (not membrane-bound) found either free in the cytoplasm or attached to membranes within the cell. They are the site of protein synthesis â reading mRNA to build proteins from amino acids.
- Golgi Apparatus
- A stack of flattened membrane sacs that receives newly made proteins from ribosomes, modifies them, packages them into vesicles, and sends them to their destination inside or outside the cell.
- Lysosome
- A membrane-bound organelle containing digestive enzymes. It breaks down old organelles, engulfed bacteria, and worn-out cell components.
- Chloroplast
- Found only in plant cells (and some algae). Contains chlorophyll, which absorbs light energy for photosynthesis. Has its own DNA and ribosomes. Surrounded by a double membrane.
Must Memorise: Mitochondria = site of aerobic respiration (energy release). Present in ALL eukaryotic cells.
Must Memorise: Ribosomes = site of protein synthesis. Found in ALL cells â even prokaryotic cells have them.
Must Memorise: Nucleus = controls all cell activities via DNA. Only in eukaryotic cells.
This definitions covers Key Terms: Cell 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 8 of 14 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
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).