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What are the basic building blocks of all living things, and how do bacterial cells differ from plant and animal cells?

Describe the structure of plant, animal and bacterial cells and identify the functions of their main parts

A focused answer to the O-Level outcome on cell structure. The parts of animal, plant and bacterial cells, what each part does, and the key differences between eukaryotic and prokaryotic cells.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

This outcome asks you to describe the structure of plant, animal and bacterial cells and to say what each main part does. The big idea is that all life is made of cells, but they come in two broad types: the simpler prokaryotic cells of bacteria, and the more complex eukaryotic cells of plants and animals.

The answer

Parts common to all cells

Every cell, whatever its type, shares a few essentials:

  • Cell membrane. A thin layer that controls what enters and leaves the cell.
  • Cytoplasm. The jelly-like fluid where the cell's chemical reactions happen.
  • DNA. The genetic material that carries the cell's instructions.
  • Ribosomes. Tiny structures that build proteins.

The animal cell

An animal cell is eukaryotic, meaning it has a true nucleus and membrane-bound organelles:

  • Nucleus. Contains the DNA and controls the cell's activities.
  • Mitochondria. The site of aerobic respiration, releasing energy from glucose.
  • Cell membrane, cytoplasm and ribosomes as above.

It has no cell wall, no chloroplasts and no large permanent vacuole.

The plant cell

A plant cell has everything an animal cell has, plus three extra features:

  • Cell wall. Made of cellulose, it gives the cell shape and support.
  • Chloroplasts. The site of photosynthesis, using light to make glucose.
  • Large permanent vacuole. Filled with cell sap, it helps keep the cell firm.

The bacterial cell

A bacterial cell is prokaryotic and much simpler:

  • No true nucleus. Its single circular chromosome lies free in the cytoplasm.
  • No membrane-bound organelles such as mitochondria or chloroplasts.
  • A cell wall (of a different material from a plant's), a cell membrane, cytoplasm and ribosomes.
  • Plasmids. Small extra rings of DNA, important in genetic engineering.

Bacteria are also much smaller, typically a few micrometres across.

Examples in context

Example 1. Why bacteria are workhorses. Because a bacterial cell is simple, small and divides quickly, and carries handy plasmids, it is easy to grow in huge numbers and to engineer. This is exactly why bacteria are used to make products such as insulin, and it traces straight back to their cell structure.

Example 2. Reading a labelled diagram. In an examination you might be given a labelled cell diagram and asked to identify the cell type. Spotting chloroplasts and a large vacuole tells you it is a plant cell; their absence, together with a true nucleus, points to an animal cell.

Try this

Q1. Name three parts found in a plant cell but not in an animal cell. [3 marks]

  • Cue. Cell wall, chloroplasts and a large permanent vacuole.

Q2. State where the DNA is found in (a) a bacterial cell and (b) an animal cell. [2 marks]

  • Cue. (a) Free in the cytoplasm as a circular chromosome (plus plasmids). (b) Inside the nucleus.

Q3. Give the function of the mitochondria. [1 mark]

  • Cue. They are the site of aerobic respiration, releasing energy from glucose.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksCompare the structure of a bacterial cell with that of a plant cell, identifying three differences.
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Examiners want a true comparison with three clear, correct differences.

A bacterial cell is prokaryotic and a plant cell is eukaryotic, and this leads to several structural differences.

First, a bacterial cell has no true nucleus; its single circular chromosome lies free in the cytoplasm, whereas a plant cell has a nucleus enclosed by a membrane that holds the DNA. Second, a bacterial cell has no membrane-bound organelles such as mitochondria or chloroplasts, while a plant cell has both. Third, a bacterial cell is much smaller, typically a few micrometres, while a plant cell is tens of micrometres across.

Both, however, have a cell wall, a cell membrane, cytoplasm and DNA.

What markers reward: three valid differences, ideally the absence of a true nucleus, the absence of membrane-bound organelles, and the difference in size, with correct use of the terms prokaryotic and eukaryotic.

Original4 marksState the function of each of the following parts of a plant cell: cell membrane, mitochondria, chloroplasts and cell wall.
Show worked answer →

The answer should give a correct, concise function for each named part.

The cell membrane controls what enters and leaves the cell. The mitochondria are the site of aerobic respiration, releasing energy from glucose. The chloroplasts are the site of photosynthesis, using light to make glucose. The cell wall, made of cellulose, gives the cell shape and support.

What markers reward: one correct function per part, four in total, with the cell membrane controlling movement, mitochondria for respiration, chloroplasts for photosynthesis, and the cell wall for support and shape.

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