Disciplinary Ideas Of Biology

Key ConceptsThis chapter covers how cells are organised, how plant and animal cells differ, and how cell specialisation links to function. You need these ideas to answer comparison questions and explain “structure → function” in exam mark schemes.

Core ideas you MUST know:Cells are the basic units of living organisms and have internal structures that carry out specific roles.

Eukaryotic cells have a nucleus; prokaryotic cells do not (so the presence of a nucleus is a key exam comparison point).

Plant cells are usually larger and have cell wall, chloroplasts, and a permanent vacuole (not found in typical animal cells).

Animal cells have no cell wall, no chloroplasts, and smaller vacuoles (often not permanent).

Cell specialisation means cells develop structures suited to their job (e.g., adaptations that increase surface area or allow transport).

The microscope image question type often tests whether you can identify structures and state their function.

Before you continue:What are two structural differences you would expect between a plant cell and an animal cell?

Key TermsCell - the basic unit of life, made of cytoplasm and (in eukaryotes) a nucleus.

Nucleus - a membrane-bound structure containing genetic material that controls cell activities.

Cell wall - a rigid structure (in plant cells) that supports the cell and helps maintain shape.

Chloroplast - an organelle in plant cells where photosynthesis happens.

Permanent vacuole - a large vacuole in plant cells that stores cell sap and helps maintain turgor pressure.

Specialisation (cell specialisation) - when a cell develops particular structures suited to a specific function.

Organelle - a specialised structure inside a cell that has a particular role.

Active RecallCell - __________

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Nucleus - __________

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Cell wall - __________

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Chloroplast - __________

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Permanent vacuole - __________

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Specialisation (cell specialisation) - __________

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Organelle - __________

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Worked ExamplesExample 1: Comparing plant and animal cells (straightforward)Question scenario: State one feature present in plant cells but absent in animal cells.

Identify a plant-only structure you know: chloroplast, cell wall, or permanent vacuole.

Choose one and state its absence in animal cells.

Link to function if asked (often: chloroplast → photosynthesis).

Answer (example): A plant cell has a cell wall; animal cells do not.

Now you try:State two features present in plant cells but absent in animal cells.

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Example 2: Structure → function (medium)Question scenario: A cell has many mitochondria. Explain what this suggests about its function.

Mitochondria are the site of aerobic respiration (releasing energy).

More mitochondria means the cell needs more energy.

State a likely function: active transport, movement, or synthesis of substances.

Answer (example): It likely has a high energy demand, so the cell probably carries out active processes requiring ATP.

Now you try:A cell has a large permanent vacuole. Explain how this helps the cell function.

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Example 3: Exam-style combined comparison (more complex)Question scenario: Compare transport in plant and animal cells using vacuole information.

Plant cells typically have a permanent vacuole that stores cell sap.

Animal cells have smaller vacuoles and do not usually have a single permanent vacuole.

For plant cells, the vacuole helps maintain turgor pressure, supporting the cell for transport of materials across the cell membrane.

Answer (example): The plant vacuole supports the cell and helps maintain turgor, which supports efficient functioning; animal cells rely more on other cytoplasmic arrangements rather than turgor.

Now you try:Explain one similarity and one difference between plant and animal cell vacuoles in terms of function.

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