Plant Cell Structure
In 1831, Scottish botanist Robert Brown peered through a microscope at orchid cells and spotted a dark round blob inside each one — the nucleus, the first organelle ever described, found in over 200 specimens.
Printable Worksheets
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Q1 · A plant has to stand upright in the wind without bones. What do you think holds plants up?
Q2 · Plants don't eat food like you do. So where do they get their energy from, and what part of the plant cell do you think handles this?
● Know
- The main parts of a plant cell and what each one does
- That chloroplasts contain chlorophyll and run photosynthesis
- How a light microscope is used to view plant cells
● Understand
- Why plant cells need a cell wall and a large vacuole
- Why leaves are green and roots are not
- That every part of the cell has a specific job
● Can do
- Label a diagram of a plant cell
- Match each part to its function
- Describe how to prepare an onion-skin slide
- Cell wall
- Chloroplast
- Vacuole
- Nucleus
- Chlorophyll
- Large sac that stores water inside the cell
- Strong cellulose layer that holds the cell rigid
- Green pigment that absorbs sunlight
- Control centre containing DNA
- Green organelle that runs photosynthesis
Peel one layer off an onion, lay it flat on a glass slide, add a drop of iodine solution, and look through a microscope — suddenly you can see hundreds of rectangular boxes stacked neatly side by side, each with a dark dot near the centre.
| Part | Job |
|---|---|
| Cell wall | Strong outer layer made of cellulose. Keeps the cell rigid; the reason plants can stand up without bones. |
| Plasma membrane | Thin layer just inside the cell wall. Controls what enters and leaves the cell. |
| Cytoplasm | Jelly-like fluid that fills the cell. All the other parts float around in it. |
| Nucleus | Control centre. Stores DNA and decides what proteins the cell makes. |
| Large vacuole | One huge water-filled sac that takes up most of the cell's space. Stores water and keeps the cell plump. |
| Chloroplasts | Green organelles that absorb sunlight (using chlorophyll) and turn CO₂ + water into glucose. |
| Mitochondria | Tiny "powerhouses" that release energy from glucose for the cell to use (respiration). |
If a plant cell gets short of water, the big vacuole shrinks — and the whole plant wilts. Water it and the vacuoles fill up again, and the plant perks back up.
The is made of cellulose and keeps the cell rigid. The big stores water. Green capture sunlight for photosynthesis using a pigment called .
Plant cells share many parts with animal cells (nucleus, membrane, cytoplasm, mitochondria). But three things are only found in plant cells:
- Cell wall — because plants need to stand upright without bones.
- Chloroplasts — because plants make their own food from sunlight, while animals eat food.
- A large central vacuole — because plants need a big water store; animals have many small vacuoles instead.
Notice how each "extra" part matches a job a plant has to do that an animal doesn't. The structure of the cell fits the way the plant lives. This is called structure-function fit, and it's a big idea you'll meet again in Lesson 9.
Wrong: "Every plant cell is green." Only cells that contain chloroplasts are green. Root cells, stem cells inside a trunk, and onion skin cells have very few chloroplasts — that's why those parts aren't green.
Right: Only cells with chloroplasts look green. Leaves are packed with them; roots and most stems are not.
Wrong: "The cell wall and the cell membrane are the same thing." They are two different layers — the membrane is thin and flexible, the wall is thick and rigid (only in plants).
Right: The plasma membrane sits inside the cell wall. The wall is the strong outer cage; the membrane is the gate that controls what gets in and out.
Wrong: "Plants don't need mitochondria — they have chloroplasts." Plants still need to release energy from glucose, just like animals do. They have both.
Right: Plant cells have BOTH chloroplasts (to make glucose) AND mitochondria (to release energy from that glucose).
The most common microscope in school labs is the light microscope. It uses lenses and a bright light to magnify things 40 to 400 times — easily enough to see plant cells.
A typical onion-skin prac:
- Peel a thin transparent layer from inside an onion.
- Lay it flat on a glass slide.
- Add one drop of iodine solution (stain) to make the parts easier to see.
- Lower a thin coverslip on top, avoiding air bubbles.
- Start on the lowest magnification (×40), then increase if you need to zoom in.
You should see a tidy grid of rectangular cells — each with a clear wall around the edge, a dark spot (the nucleus), and a pale centre (the big vacuole). Onion skin cells don't have chloroplasts (they live underground in the dark) so they won't look green.
Think about a sunflower. It has to stand 2 metres tall, sometimes in strong wind, but it doesn't have a single bone. So what holds it up?
The answer is millions of tiny cell walls. Each cell wall is made of cellulose, a very strong fibre. Stack them together and you get a structure stiff enough to hold up the whole plant.
The same cellulose is what makes celery snap when you bite it, why a tree trunk can support tonnes of branches, and why timber is strong enough to build a house. It's all just cellulose cell walls stacked together.
This is also why plants don't have a skeleton — they don't need one. Each cell brings its own tiny rigid box.
A lettuce leaf left in the fridge for a week becomes floppy and limp instead of crisp. The leaf hasn't died and the cells are still intact. Predict: what has happened inside the plant cells to make the leaf go floppy? Write 1–2 sentences, then reveal.
How close was your prediction?
Nice — you connected the vacuole to plant stiffness.
That's okay — most people don't realise their fridge salad is doing osmosis right in front of them.
At the start of the lesson you were asked: why are leaves green but tree trunks brown?
Now you know about plant cell parts, write your full answer. Which organelle is responsible for the green colour, why is it only in some cells, and what job does it do?
Q1. Name the three parts that are unique to plant cells (not found in animal cells) and give the job of each. (3 marks)
Q2. Describe the steps you would take to prepare a slide of onion skin cells to view under a light microscope. (4 marks)
Q3. Explain why a leaf cell from a gum tree is green but a cell from inside the trunk is not. Use the words chloroplast and chlorophyll in your answer. (4 marks)
Answers
▾MCQ 1
B — Chloroplasts contain chlorophyll, the green pigment that absorbs sunlight, and they run photosynthesis (making sugar from CO₂ + water using sunlight).
MCQ 2
D — Cellulose is a very strong fibre. Stacked cellulose cell walls give plants their stiffness.
MCQ 3
C — The large central vacuole stores water and dissolved minerals. Full vacuoles keep cells plump and the plant stiff.
MCQ 4
A — A school light microscope typically gives ×40 (low power) up to ×400 (high power). Electron microscopes go further but are not used in Year 7.
MCQ 5
B — Only plant cells have a cell wall. Nucleus, cytoplasm and mitochondria are in both plant and animal cells.
Short Answer 1
Model answer: (1) Cell wall — made of cellulose, holds the cell rigid and keeps the plant upright. (2) Chloroplast — contains chlorophyll, runs photosynthesis to make glucose from sunlight, CO₂ and water. (3) Large central vacuole — stores water and dissolved minerals, keeps the cell plump.
Short Answer 2
Model answer: Step 1 — peel a single thin transparent layer from inside an onion. Step 2 — lay it flat on a glass slide. Step 3 — add one drop of iodine solution as a stain. Step 4 — gently lower a coverslip on top, avoiding air bubbles. Step 5 — place the slide on the microscope stage and start at low magnification (×40), then increase to ×100 or ×400 if you need a closer look.
Short Answer 3
Model answer: A gum leaf cell is green because it is packed with chloroplasts, and each chloroplast contains the green pigment chlorophyll. The chlorophyll absorbs sunlight so the leaf can do photosynthesis. A cell from inside the trunk is not green because it has very few or no chloroplasts — it sits in the dark away from sunlight, so making one would be pointless. With no chlorophyll there's no green colour.