Lesson 1 of 5 / 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 the six named cell structures and functions from diagrams and light microscopy.Syllabus
Syllabus K224 / K225, Topic 1(a). Identify the six named cell structures and functions from 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?
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?
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 is the outer edge of the living cell. It is partially permeable. This means it controls what goes into and out of the cell. Inside the membrane is the cytoplasm. Many chemical reactions happen in the cytoplasm, helped by enzymes.
The nucleus contains genetic material. This controls what the cell does. In a stained cell, the nucleus often looks like a darker blob. It is not always in the middle, so look for its shape and colour, not its position.
A plant cell also has a cell wall made of cellulose, outside the membrane. The wall supports the cell and keeps its shape. Water and most dissolved substances pass straight through the wall. So the wall does not control what enters; the membrane does.
A mature plant cell has a large permanent vacuole full of cell sap. Cell sap is water with sugars and ions dissolved in it. When the vacuole is full of water, it pushes the cell contents against the wall. This makes the cell firm. Animal cells may have only small, temporary vacuoles.
Chloroplasts contain chlorophyll. Chlorophyll absorbs light energy for photosynthesis. Many leaf cells have chloroplasts. But some plant cells, such as root cells, have none, and they are still plant cells.
Step by step
- 1
Locate the boundary
A plant cell has a wall outside its membrane. An animal cell has a membrane but no cell wall.
- 2
Look inside
Distinguish the nucleus from a large sap-filled vacuole and from the surrounding cytoplasm.
- 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?
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
What keeps a cell organised and working?