What Are the Functions of Organelles?
Learn the functions of the nucleus, mitochondria, ribosomes and other cell structures for AQA A Level Biology, with key links between them and an exam tip.
The nucleus contains the cell’s DNA and controls which genes are expressed. Mitochondria are the site of aerobic respiration, which transfers energy for ATP production. Ribosomes make proteins by joining amino acids in the order specified by messenger RNA.
Other structures to know
- Nucleolus: a region inside the nucleus where ribosomal RNA is made and ribosomal subunits are assembled.
- Rough endoplasmic reticulum (rough ER): a network of membranes with ribosomes attached. It helps process and transport proteins made by those ribosomes.
- Smooth endoplasmic reticulum (smooth ER): makes lipids.
- Golgi apparatus: modifies and packages proteins into vesicles for transport or secretion. A vesicle is a small membrane-bound sac.
- Lysosomes: contain enzymes that break down unwanted material, including worn-out cell components.
- Cell-surface membrane: controls the movement of substances into and out of the cell. It is a cell structure, rather than an organelle inside the cell.
Plant and algal cells also have chloroplasts, where photosynthesis takes place. Plant cells have a large vacuole containing cell sap; it helps maintain turgor, which keeps the cell firm. Their cell wall provides support and helps prevent the cell from bursting. The wall is outside the cell-surface membrane.
How they work together
If a cell makes a protein for secretion, its DNA provides the instructions, ribosomes on the rough ER make the protein, and the Golgi apparatus modifies and packages it into vesicles. This is why questions may ask you to link several structures to one function.
Exam mistake to avoid: ribosomes make proteins; mitochondria do not make energy. Respiration in mitochondria transfers energy from respiratory substrates to ATP. Also, a prokaryotic cell has ribosomes but no nucleus or other membrane-bound organelles.
