K325 / 2027

Lesson 1 of 6 / Cell structure and organisation

The parts of a cell

What keeps a cell organised and working?

I can identify six common cell structures and connect each to its function.

  • I can identify major cell structures and their functions using diagrams and light microscopy.Syllabus

    Syllabus K325, Topic 1(a). Identify major cell structures and their functions using diagrams and light microscopy.

About 5 min

Make a guess. You are not marked.

A plant cell is surrounded by both a cell wall and a cell membrane. Which one decides what enters the cell?

  1. Both equally, working as a double filter.
  2. The nucleus, because it controls the cell.
  3. The cell wall, because it is the outer layer.
  4. The cell membrane, which is partially permeable.
Show the answer

The cell membrane, which is partially permeable.

The membrane controls what enters and leaves. The wall lets water and most dissolved substances straight through.

The key idea

A cell has different structures that work together. Identify a structure by its position and appearance, then explain the job it performs.

A cell is a basic unit of a living organism. An organelle is a specialised structure within a cell. Choose a structure to see where it is and what it does.

Explore the idea

Which structure does this job?

Plant cell: Cell membraneThe thin inner boundary controls movement of substances into and out of the living cell. Smaller organelles are omitted in this simplified view.Cell sapWall outside membrane

Cell membrane. The thin inner boundary controls movement of substances into and out of the living cell. The selected structure has an orange outline or fill.

Original schematic, not to scale. The blue region is a vacuole; purple marks the nucleus. Plant cells also contain mitochondria and ribosomes, omitted here to focus on this comparison.

Explanation

The cell membrane forms the boundary of the living cell. It is partially permeable: it controls the movement of substances into and out of the cell. Inside it, the cytoplasm contains enzymes and is the site of many chemical reactions.

The nucleus contains genetic material that controls the activities of the cell. A stained nucleus often appears as a darker body in a light microscope image. Its position can vary, so do not identify it just because a label points towards the middle.

A typical plant cell also has a cellulose cell wall outside its membrane. The wall supports the cell and helps it keep its shape. It is freely permeable to water and many dissolved substances; it is not the selectively controlling boundary.

The large permanent vacuole in a mature plant cell contains cell sap, a solution of substances such as sugars and ions. When filled with water, it helps press the cell contents against the wall and keeps the cell firm. Animal cells may have small temporary vacuoles instead.

Chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis. They occur in photosynthetic plant cells, such as many leaf cells. A cell can belong to a plant without having chloroplasts.

Step by step
  1. 1

    Locate the boundary

    A plant cell has a wall outside its membrane. An animal cell has a membrane but no cell wall.

  2. 2

    Look inside

    Distinguish the nucleus from a large sap-filled vacuole and from the surrounding cytoplasm.

  3. 3

    Give a specific function

    Say that chloroplasts absorb light for photosynthesis, rather than saying they simply help the cell.

Worked example

A leaf cell needs light and support

A leaf cell has green oval structures and a rigid outer layer. Name each structure and explain its function.

One way to explain it

The green structures are chloroplasts, which contain chlorophyll to absorb light for photosynthesis. The rigid outer layer is the cellulose cell wall, which supports the cell and maintains its shape.

Why this answer works
  • Green colour suggests chlorophyll in chloroplasts.
  • The supporting outer layer is the wall, outside the membrane.
  • Connect each named structure to a different job.

Watch out for this

A student says: "The cell wall controls everything entering a plant cell." What is wrong with this?

Show the answer

The wall provides support and is freely permeable. The cell membrane inside it controls the movement of substances into and out of the living cell.

Check your understanding

Which pairing correctly describes a plant cell?

  1. Nucleus: absorbs light; chloroplast: controls cell activities.
  2. Cell wall: controls all exchange; membrane: stores cell sap.
  3. Membrane: controls exchange; cell wall: provides support.
Show the answer

Membrane: controls exchange; cell wall: provides support.

These are different structures with different functions. The membrane lies inside the wall.

Quick recall

Card 1 of 3. Answer in your head, then check.

What keeps a cell organised and working?

You can return to this lesson any time.