Knowing an organelle means saying what it does and why the cell needs it. This page gives a sentence pattern you can reuse for any organelle.
It is part of cells and organisation. If the structures themselves are still unclear, revisit comparing animal and plant cells first.
What is the three-link pattern?
Write the structure, then the process it carries out, then the effect on the cell. Every full-mark explanation in this chapter follows that chain.
| Structure | Process | Effect on the cell |
|---|---|---|
| Nucleus | Contains DNA that carries instructions | Controls which proteins the cell makes and when it divides |
| Ribosome | Joins amino acids into proteins | Cell can make enzymes and structural proteins |
| Mitochondrion | Releases energy from glucose in respiration | Cell can move, divide and carry out active transport |
| Golgi apparatus | Modifies and packages proteins into vesicles | Proteins reach the cell surface for secretion |
| Chloroplast | Traps light energy for photosynthesis | Plant cell can make its own glucose |
Worked example: a cell that secretes enzymes
Question. A cell in the pancreas releases digestive enzymes. It contains many ribosomes, a large rough endoplasmic reticulum and a prominent Golgi apparatus.
Explain how these structures help the cell do its job. (4 marks)
Step 1. Ribosomes make the enzymes, which are proteins. The cell has many of them because enzymes are made continuously.
Step 2. The rough endoplasmic reticulum carries the newly made proteins through the cell and folds them.
Step 3. The Golgi apparatus packages the enzymes into vesicles.
Step 4. The vesicles fuse with the cell membrane, so the enzymes leave the cell.
Every sentence names a structure, says what it does, and connects to “secreting enzymes”.
Your textbook may describe this pathway in fewer steps, and that is fine as long as the order is correct.
The mistake that costs marks
Students often reverse the direction and write that the Golgi apparatus makes the enzymes. The Golgi apparatus processes and packages. The ribosomes do the making.
A simple check is to ask “what is leaving this organelle and where does it go?” Ribosome to endoplasmic reticulum to Golgi to vesicle to membrane. If your answer breaks that order, rewrite it.
Check yourself
A muscle cell in the leg has far more mitochondria than a skin cell. Explain why. (2 marks)
Answer
Mitochondria release energy from glucose during respiration. A leg muscle cell contracts often and needs a large supply of energy, so it needs more mitochondria to supply it.
A one-line answer of “because muscles need energy” earns only one mark, since it does not link the structure to the process.
What to study next
Put these sentences to work in explaining specialised cells and organisation. Use the biological data interpretation trainer to practise reading diagrams, and see online one-to-one Biology tuition if you would like a teacher to extend your sentences with you.