Comparing animal and plant cells

25 min

Two slides without labels

A laboratory technician finds two stained slides whose labels have fallen off. One came from a goat's liver, the other from a bean leaf. She has no notes, only a light microscope. Within a minute she can say which is which, and so can you by the end of this lesson. All she needs is a short list of the features that animal and plant cells share and the few that only plant cells have.

Observation: what the microscope shows

Put the cheek cell slide from lesson 2 and the onion or leaf slide from lesson 3 side by side under the microscope, at the same magnification. Note for each: the shape of the cells, whether they fit tightly together, the thickness of the outline, the size of the clear spaces inside, and the colour.

The comparison

Figure 1: An animal cell and a plant cell. The labels in the middle name the parts both cells have; the labels at the bottom name the parts only one of them has.

Feature	Animal cell	Plant cell
Cell membrane, cytoplasm, nucleus, mitochondria	present	present
Cell wall	absent	present, made of cellulose
Chloroplasts	absent	present in cells that receive light
Vacuole	small and temporary, if any	one large, permanent central vacuole of cell sap
Shape	irregular; can change shape	regular and fixed, often box-shaped
Position of the nucleus	usually near the middle	at the edge, pushed there by the vacuole
Carbohydrate store	glycogen (and fat)	starch grains

Definition

Starch: the carbohydrate in which plant cells store glucose; it forms grains in the cytoplasm and in chloroplasts, and turns blue-black with iodine.

Glycogen: the carbohydrate in which animal cells, especially liver and muscle cells, store glucose.

Turgid: describes a plant cell whose vacuole is full of water, so that it presses firmly against the cell wall. Example: the cells of a crisp, freshly picked lettuce leaf.

Why the differences?

Chloroplasts: plants make their own food by photosynthesis; animals eat food, so their cells have no need for chloroplasts.
Cell wall and large vacuole: plants cannot run from danger and have no skeleton. Thousands of turgid cells, each pressing against its wall, hold a leaf flat and a young stem upright. An animal is supported by its skeleton, and its cells must be able to change shape, for example when a muscle contracts or a white blood cell squeezes through a blood vessel wall.
Mitochondria in both: every living cell must release energy by respiration, so plants and animals both have mitochondria.

Warning

Plant cells have mitochondria and a cell membrane too. A very common exam mistake is to list "cell membrane" or "mitochondria" as animal-only. The only structures in this lesson that belong to one kind of cell alone are the cell wall, the chloroplasts and the large permanent vacuole, and all three are in plant cells.

Worked example 1: which cell is which?

Three cells are described. Decide whether each is from a plant or an animal, giving evidence.

Cell	Observations	Decision and evidence
A	cell wall, large vacuole, many chloroplasts	plant (leaf): wall, large vacuole and chloroplasts
B	irregular shape, nucleus in the middle, no wall	animal: no cell wall, irregular shape
C	cell wall, large vacuole, no chloroplasts	plant (root or storage organ): wall and large vacuole; not in the light

Rule used: decide on the cell wall and the vacuole first; chloroplasts only show whether a plant cell was in the light.

Worked example 2: evaluating a claim

Ishimwe says: "Plant cells do not need mitochondria, because their chloroplasts give them energy." Evaluate this claim.

Chloroplasts use light energy to make glucose by photosynthesis. They store energy in food; they do not release it for the cell's work.
To use the energy in glucose, every cell must respire, and aerobic respiration happens in mitochondria.
Photosynthesis stops at night and in roots, which have no chloroplasts, but these cells still need energy all the time.

Conclusion: the claim is wrong. Plant cells need both organelles: chloroplasts make the food and mitochondria release the energy from it.

In the kitchen and the cattle shed

Cooking softens cassava leaves for isombe and beans for ibishyimbo: heat damages the cell membranes, so the vacuoles leak, and loosens the material that cements neighbouring cell walls together. Cattle can live on grass because microbes in their stomachs digest the cellulose of plant cell walls; humans do not have those microbes, so cellulose passes through our gut as fibre.

Introduction to Cells: The Grand Cell Tour, Amoeba Sisters. The comparison of plant and animal cells starts at about 7:10; check each difference they name against the table above.

Tip

Memory hook: the three Cs that only plant cells have: a Cellulose wall, Chloroplasts and a Central vacuole.

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Practice: comparing cells

List four structures found in both animal and plant cells.
Name three structures found in plant cells but not in animal cells.
What carbohydrate do plant cells store, and what do animal cells store?
Why is the nucleus of a plant cell usually at the edge of the cell?
A cell has a cell wall and a large vacuole but no chloroplasts. Where in a plant might it come from? Explain.
Explain why animal cells can change shape but plant cells cannot.
Evaluate: "A root hair cell is an animal cell because it has no chloroplasts."

Show answersHide answers

Cell membrane, cytoplasm, nucleus and mitochondria (also ribosomes).
Cellulose cell wall, chloroplasts and a large permanent vacuole.
Plant cells store starch; animal cells store glycogen (and fat).
The large central vacuole fills most of the cell and pushes the cytoplasm and nucleus against the cell wall.
A root, bulb or tuber (any part kept out of the light): chloroplasts only form in cells that receive light.
Animal cells have only a flexible cell membrane on the outside; plant cells are enclosed in a rigid cellulose cell wall.
Wrong. It has a cellulose cell wall and a large vacuole, so it is a plant cell; it lacks chloroplasts because it grows in the dark soil.

Key points

Both cells have a cell membrane, cytoplasm, a nucleus and mitochondria.
Only plant cells have a cellulose cell wall, chloroplasts and a large permanent vacuole.
Plant cells are regular in shape and store starch; animal cells are irregular and store glycogen.

1Two slides without labels

2Observation: what the microscope shows

3The comparison

4Why the differences?

5In the kitchen and the cattle shed

Two slides without labels

Observation: what the microscope shows

The comparison

Why the differences?

In the kitchen and the cattle shed