Lesson 1 of 5 / Cell structure and organisation
The parts of a cell
What keeps a cell organised and working?
In this lesson: Identify six common cell structures and connect each to its function.
About 5 min
The key ideaA 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 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
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.
Is this true? "The cell wall controls everything entering a plant cell."
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.