Cell Biology and Organisation, Paper 2 essay guide

Essay themes this chapter supports

• Describing the organelles of a plant cell and how a plant cell differs from an animal cell: Name each organelle of a generalised cell and state its one main function. → Identify the three structures a plant cell has that an animal cell lacks. → Explain the function of the cell wall, the chloroplast and the large permanent vacuole. → State the structures both cell types share, such as the nucleus, cytoplasm and mitochondria. → Conclude by explaining why the plant cell keeps a fixed shape and the animal cell does not.
• Comparing life processes in a unicellular and a multicellular organism: Explain that an Amoeba carries out every life process using its one cell. → Describe how it feeds, respires, removes excess water and moves. → Explain why a large organism cannot rely on diffusion across its surface alone. → Describe how a human shares the processes among specialised systems (division of labour). → Compare one process, such as gas exchange, in both organisms to show the difference.
• Explaining how the structure of specialised cells suits their functions: State the general principle that a cell's shape and structure match its function. → Explain the red blood cell: biconcave and without a nucleus, to carry more oxygen. → Explain the root hair cell: long and thin, to increase the surface area for absorbing water. → Explain the nerve cell and the sperm cell as further named examples. → Conclude that specialisation makes a multicellular organism more efficient.
• Explaining the levels of organisation from cell to organism: Define each level: cell, tissue, organ, system and organism. → Trace one animal example upward, from muscle cell to the whole human. → Trace one plant example upward, from palisade cell to the whole plant. → Explain how each level depends on the correct structure of the level below. → Conclude that a fault at a lower level can affect the levels built above it.

How to structure your essay

1. Open with one or two sentences that define the topic and set the scope.
2. Devote one paragraph to each key concept, in a logical order.
3. Use precise biological terms and, where relevant, a labelled diagram.
4. Give an example or state where the process happens in the body or plant.
5. Close by linking the ideas back to the question.

Planning grid

Key terms to include

• plasma membrane
• nucleus
• cytoplasm
• mitochondrion
• ribosome
• cell wall
• chloroplast
• permanent vacuole
• turgid
• specialised cell
• surface area to volume ratio
• diffusion
• division of labour
• tissue
• organ
• system
• levels of organisation

A model essay outline

1. Cell structure, A generalised cell has a nucleus that controls its activities, cytoplasm where chemical reactions take place, mitochondria that release energy through respiration, and ribosomes that build proteins. A plant cell adds three structures an animal cell lacks: a rigid cellulose cell wall for support, chloroplasts that trap light energy, and one large permanent vacuole that keeps the cell turgid.
2. Animal vs plant cells, Plant cells have a cellulose cell wall outside the plasma membrane, chloroplasts for photosynthesis, and a large permanent vacuole for water storage and turgor; animal cells have none of these three structures. Both cell types still share a nucleus, cytoplasm, mitochondria, ribosomes and a plasma membrane that controls what enters and leaves.
3. Living processes in unicellular organisms, Organisms such as Amoeba and Paramecium consist of a single cell that must carry out nutrition, respiration, excretion, growth, movement and response entirely on its own, without any other cell to share the work. Food, oxygen and waste all cross the same cell surface, and the cell has no separate organs to help, unlike the many cells of a multicellular animal.
4. Living processes in multicellular organisms, In a multicellular organism, no single cell performs every life process alone. Specialised cells, tissues, organs and systems divide the work between them, nutrients absorbed by the digestive system are transported by the circulatory system to cells all over the body, which could not happen inside one isolated cell.
5. Levels of organisation, Multicellular organisms are built as a hierarchy: similar cells form a tissue, different tissues working together form an organ, related organs form a system, and every system together forms the organism. A fault at one level, such as damaged cells in a tissue, can disrupt the organ and system built from it. Examiners often test this hierarchy by asking you to place a named human example, such as a muscle cell, muscle tissue, the heart and the circulatory system, at the correct level.

Frequently asked questions

More for Cell Biology and Organisation

Source:SRC-DSKP-EN