Inside the membrane and cytoplasm, cells of plants, animals, fungi and protists have small working parts called organelles. Many are wrapped in their own membranes.
| Organelle | Job | Like a factory's … |
|---|---|---|
| Mitochondria | Release the energy stored in food, using oxygen | power plant |
| Ribosomes | Build proteins | assembly machines |
| Rough endoplasmic reticulum | Folds and finishes proteins made by its ribosomes | assembly hall |
| Golgi apparatus | Packages proteins and ships them out | shipping department |
| Lysosomes | Break down wastes and worn-out parts | recycling crew |
| Vacuoles | Store water, food and wastes | storage room |
Key idea
Each organelle does a job, and they work as a team: ribosomes on the rough ER build a protein, the ER folds it, the Golgi packages it, and a small bubble carries it to the membrane.
Why it works
Mitochondria do not create energy. Energy is never made from nothing; it only changes form. Sugar from food holds chemical energy. Mitochondria use oxygen to break the sugar down and pass its energy to a molecule called ATP that the rest of the cell can use.
Worked examples
Worked example: Busy cells
Muscle cells in your legs work hard. Which organelle would you expect them to have a lot of?
- Hard work takes a lot of energy.
- Mitochondria release energy from food.
Answer: Many mitochondria.
Worked example: Follow a protein
A cell makes a protein to send outside. Which organelles does it pass through, in order?
- Built by ribosomes on the rough ER.
- Folded in the rough ER.
- Packaged by the Golgi apparatus.
- Carried in a bubble to the membrane, then released.
Answer: Ribosome → rough ER → Golgi → membrane.
Common mistake
Saying mitochondria "make energy." They release energy stored in food. Check by tracing it back: the energy in sugar came from sunlight captured by a plant.