The electron microscope revealed that a eukaryotic cell is packed with membrane-bound compartments, each with its own job. Learn to recognise them in a micrograph, say what each does, and spot the differences between a plant cell and an animal cell.
All living organisms are made of cells, the basic units of life. A eukaryotic cell has a nucleus and many membrane-bound organelles, each with its own function. Proteins for secretion are made on 80S ribosomes on the rough ER, modified in the Golgi body and released by exocytosis. Mitochondria and chloroplasts have a double membrane, their own small circular DNA and 70S ribosomes. Plant cells add a cellulose cell wall, chloroplasts, a large permanent vacuole and plasmodesmata; animal cells have centrioles. Cells use ATP from respiration for every energy-requiring process.
Rotate the animal cell and click each organelle to read its function. Then press Test yourself: the sim names a function and you click the organelle that performs it.
| Structure | Outline structure | Function |
|---|---|---|
| cell surface membrane | phospholipid bilayer with proteins, about 7 nm thick | controls entry and exit; cell signalling |
| nucleus | nuclear envelope (double membrane with pores); chromatin; nucleolus | holds the chromosomes; controls the cell; the nucleolus makes rRNA and assembles ribosomes |
| rough ER | flattened membrane sacs (cisternae) with ribosomes | makes, folds and transports proteins |
| smooth ER | tubular membranes, no ribosomes | makes lipids and steroids; stores calcium ions |
| Golgi body | stack of curved, flattened sacs with vesicles | modifies proteins (for example into glycoproteins), packages them, makes lysosomes |
| mitochondrion | double membrane, inner folded into cristae; matrix with circular DNA and 70S ribosomes | aerobic respiration, making ATP |
| ribosomes | 80S in the cytoplasm (70S in mitochondria and chloroplasts); RNA and protein, no membrane | protein synthesis |
| lysosome | vesicle of hydrolytic enzymes, single membrane | digests worn-out organelles and engulfed material |
| centrioles | pair of hollow cylinders of microtubules at right angles | organise the spindle in cell division (animal cells only) |
Do not confuse cilia and microvilli. Cilia are longer, contain microtubules and move; microvilli are much smaller folds that only increase surface area. And ribosomes have no membrane: they are not membrane-bound organelles.
Now rotate the plant cell. It has everything the animal cell has except centrioles, plus a cell wall, chloroplasts and a large permanent vacuole. Click a chloroplast to see the grana.
| Feature | Plant cell | Animal cell |
|---|---|---|
| cell wall | cellulose, fully permeable, gives strength and resists bursting | absent |
| chloroplasts | in photosynthetic cells: double membrane, grana of thylakoids, stroma, circular DNA, 70S ribosomes | absent |
| vacuole | large and permanent, cell sap surrounded by the tonoplast | small and temporary, if any |
| plasmodesmata | channels through walls linking the cytoplasm of neighbouring cells | absent |
| centrioles | absent | present |
| carbohydrate store | starch grains | glycogen granules |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the 3D animal cell, which organelle modifies proteins and packages them into vesicles?
Which organelle in the animal cell is absent from the plant cell?
Which structure in the plant cell is surrounded by the tonoplast?
What is the function of the nucleolus?
Every step in Fig. 1 costs energy, and the cell pays for all of it in one currency.
ATP does not “make” energy and is not a long-term store. It transfers energy from respiration to the processes that need it, and each molecule is recycled within seconds of being made.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Which structures contain small circular DNA and 70S ribosomes?
A pancreatic cell secretes large amounts of a digestive enzyme. Which features would be most prominent in an electron micrograph of it?
Which describes microvilli?
Which process in a cell does NOT require ATP?
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