Chapter 1 · P4 Science
🌱 Plant System
📚 Section A — Revision Notes
What I Will Learn
- Name the main parts of a plant and explain what each part does
- Describe how the same plant parts can look different across various plants
1
Parts of a Plant and Their Functions
System — a collection of parts that each have a role to play. All the parts depend on one another and work as a team to carry out a job.
- A plant is a system — its parts cooperate to keep the plant alive and growing.
- If any single part breaks down, the rest of the plant feels the impact too, and the plant can no longer function normally.
- The main parts of a plant include leaves, a stem and roots.
💡 Did You Know?
Mature plants also grow flowers and fruits, which are involved in reproduction. These are covered in Primary 5.
▲ Parts of a plant
🍃 Leaves
Every leaf consists of four parts: the leaf blade, the leaf stalk, a main vein running through the centre, and smaller veins branching off it.
▲ Parts of a leaf
- The leaf stalk connects the leaf to the plant’s stem.
- The main vein runs from the leaf stalk up through the centre of the leaf blade.
- The main vein splits into a network of smaller veins across the leaf.
- In some plants, the veins spread out in a web-like net pattern. In others, they run side by side in a parallel pattern.
- The main job of leaves is to make food for the plant using a green substance that captures sunlight.
- Leaves are also dotted with tiny openings that let the plant swap gases with the air around it.
💡 Did You Know?
The food-making process in plants is called photosynthesis. The green substance responsible for capturing sunlight is chlorophyll.
🌿 Stem
- For most plants, the stem grows above the ground.
- Stems come in two main types — hard and woody (like trees), or soft and non-woody (like garden plants).
- The stem holds the plant upright, positioning the leaves where they can catch enough sunlight to produce food.
- It also acts as a transport network, moving food and water between the roots, stem and leaves.
💡 Did You Know?
In trees, the stem is called the trunk. A tough outer layer known as bark shields the trunk from damage.
🌱 Roots
- Most plant roots grow underground, hidden beneath the soil.
- Roots act as anchors, holding the plant securely in place.
- They are also responsible for taking in water and mineral salts from the surrounding soil — both of which the plant needs to survive and stay healthy.
💡 Exam Tip
This set-up comes up regularly in tests. A plant sits in a beaker of water with a thin layer of oil floating on top. The oil seals the surface so no water can escape by evaporation — meaning any drop in water level must be caused by the roots drawing water up into the plant.
📋 Plant Parts & Their Functions
| Plant Part | Functions |
|---|---|
| Leaf |
|
| Stem |
|
| Roots |
|
📋 Checkpoint 1.1
1. Name three parts of a plant and state their functions.
- Leaf — produces food for the plant; lets the plant exchange gases with the air
- Stem — keeps the plant upright and supports the leaves; carries food and water between different parts of the plant
- Roots — anchor the plant firmly in the ground; draw in water and mineral salts from the soil
2
How Do Plant Parts Look in Different Plants?
- While all plants share the same basic parts, those parts can look quite different from one plant to another — there are both similarities and differences.
🍃 Leaves — Variation
- Leaves across different plants vary in edge, shape, colour and texture.
- Some are coated in wax to slow down water loss; others are covered in tiny hairs.
- While many leaves are green, some plants have leaves in shades of purple or red — and these can still produce food for the plant.
- Some leaves look nothing like typical leaves. A cactus, for instance, has leaves shaped like sharp spines — these cut down water loss and shield the plant from animals. Since the leaves can’t make food, the cactus relies on its green stem to do that job instead.
▲ Leaves with different edges and shapes
▲ The leaves of a cactus are shaped like spines
🎯 Get It Right!
Wrong concept: All leaves must be green.
Correct concept: Leaf colour varies — some plants have red, purple or even yellow leaves. Colour alone does not stop a leaf from making food for the plant.
🌿 Stems — Variation
- Stems range from thick and woody (like a tree trunk) to thin and non-woody (like a bean plant).
- Plants with weak stems may wind around a nearby structure — such as a trellis or fence — to lift their leaves into the sunlight (e.g. cucumber, morning glory).
- Others spread out by trailing along the ground, with their leaves still facing up to catch light (e.g. pumpkin).
💡 Did You Know?
Not all stems grow above ground. The onion is actually an underground stem packed with stored food for the plant.
▲ Woody, climbing, and creeping stems
🌱 Roots — Variation
- Trees and large land plants tend to have thick, tough and sturdy roots that grip deep into the soil.
- Plants that float or grow in water often have slender, hair-like roots that dangle beneath them.
💡 Did You Know? — Mangrove roots
The mangrove tree beats the norm — its roots arch above the ground before plunging into the waterlogged soil of coastal swamps.
💡 Did You Know? — Sweet potato roots
The sweet potato plant has roots that swell up to store energy reserves for the plant — and a tasty meal for us!
▲ Thick/strong roots, thin/hairy roots, and above-ground mangrove roots
📋 Checkpoint 1.2
1. Name one way in which leaves of different plants may differ from one another.
2. Describe how the roots of a plant that grows in water differ from those of a plant that grows in soil.
- Q1: Any one of: edge / shape / colour / texture
- Q2: Water plants have slender, hair-like roots, whereas plants rooted in soil (such as large trees) develop thick, tough and sturdy roots.
⚙️ Worked Example 1.1
Evan set up an experiment using two identical beakers. Beaker A held a plant with its roots submerged in water, topped with a thin layer of oil. Beaker B contained only water and oil — no plant.
He tracked the water level in both beakers over 7 days. Which graph correctly shows what happened?
▲ Beaker A (with plant) and Beaker B (control, no plant)
Choose the correct graph:
Answer: Option (2)
- Beaker A has a plant whose roots draw up water → the water level falls steadily over the 7 days.
- Beaker B has no plant, so nothing is consuming the water → the level stays flat.
- Because the oil layer blocks evaporation, any change in Beaker A can only be explained by the roots absorbing water.
💡 Exam Tip — MCQ Strategy
Even when you feel sure about an answer early on, work through all four options before committing. Another option might be more precise, and checking every choice also catches careless slips.
💡 Exam Tip — Control Set-up
- A control set-up keeps every variable the same except the one being tested — making it a reliable baseline for comparison.
- It rules out other explanations and confirms that the result is caused by the changed variable alone.
- In this experiment, Beaker B (no plant) is the control. It rules out evaporation as a cause, confirming that only the roots are responsible for the drop in water level in Beaker A.
📌 Chapter Summary
- A plant is a system — leaves, stem and roots each play a role, and together they keep the plant alive.
- Leaves manufacture food through photosynthesis and let the plant breathe through tiny surface openings.
- The stem props the plant upright and ferries food and water around the plant.
- Roots anchor the plant in place and draw water and mineral salts up from the soil.
- The same plant part can look very different across species — leaves vary in shape, edge, colour and texture; not all leaves are green.
- A cactus’s leaves are spine-shaped — limiting water loss and deterring predators; its green stem takes on the food-making role.
- Stems may be woody, non-woody, climbing, creeping, or hidden underground storing food (e.g. onion).
- Roots may be thick and strong (land trees), slender and hairy (water plants), above-ground (mangrove), or swollen food stores (sweet potato).
- A control set-up isolates the changed variable, proving that results come from that variable and nothing else.
✏️ Practice Questions — MCQ
1. Which row correctly matches each plant part to its function?
✅ Correct! Roots draw in water and mineral salts from the soil; the stem moves food and water around the plant; leaves produce food through photosynthesis.
❌ Not quite. It’s the roots that take in water and mineral salts — not the stem or leaves. Leaves make food. Check each part carefully.
2. The leaves of a cactus are shaped like spines. What is ONE function of this adaptation?
✅ Correct! Spine-shaped leaves cut down water loss and ward off animals. The green stem steps in to make food instead.
❌ The spine shape limits water loss and protects the cactus. Food-making is handled by the green stem, not the leaves.
3. What is the purpose of the layer of oil in the water-uptake experiment?
✅ Correct! The oil seals the water surface so nothing can evaporate — any drop in water level must be the roots at work.
❌ The oil layer stops water from evaporating. That way, any decrease in water level can only be caused by the roots absorbing it.
4. Which of the following plant parts stores food underground?
✅ Correct! The onion bulb is an underground stem packed with stored food for the plant.
❌ The onion stores food in its underground stem. Mangrove roots grow above ground; cactus spine-leaves reduce water loss; water plant roots are thin and hair-like.
5. A plant has leaves that are purple in colour. Can this plant make its own food?
✅ Correct! Leaf colour doesn’t stop a plant from making food — purple and red leaves still contain chlorophyll.
❌ Purple leaves can still produce food. They contain chlorophyll regardless of their colour.
6. In the water-uptake experiment, Set-up B has no plant. What is the role of Set-up B?
✅ Correct! Beaker B is the control — it has no plant, so any difference in water level between the two beakers must be caused by the plant in Beaker A.
❌ Beaker B is the control set-up. Having no plant means it shows what happens without the changed variable, so we can be sure the plant caused the change in Beaker A.
7. Which plant part absorbs water and mineral salts from the soil?
✅ Correct! The roots are the plant’s intake system — they pull water and mineral salts up from the soil.
❌ It’s the roots that absorb water and mineral salts. The stem carries them; the leaves use them to make food.
8. The veins in a blade of grass are arranged side by side running the length of the leaf. What type of vein pattern is this?
✅ Correct! Veins running side by side along the length of the leaf is the parallel pattern — common in grasses.
❌ When veins run side by side lengthwise, that’s a parallel pattern. A net pattern looks like a branching web.
9. A mangrove tree has roots that grow above the ground. What does this show about plant roots?
✅ Correct! The mangrove is a great reminder that roots don’t always go underground — they can look very different across plant species.
❌ The mangrove shows that roots of different plants can look very different from one another — some even grow above ground.
10. Which of the following best explains why the stem keeps the plant upright?
✅ Correct! Without the stem holding it upright, a plant’s leaves would droop and miss out on the sunlight needed to make food.
❌ The stem keeps the plant upright so the leaves are positioned to receive enough sunlight to make food.
✏️ Practice Questions — Open-Ended
1. The cucumber plant has a weak stem that climbs around a support. How is this useful to the plant? [2]
Winding around a support lifts the stem and pushes the leaves higher up, where they can capture more sunlight to make food for the plant.
2. Evan set up an experiment with two identical beakers. Both had water and a layer of oil. Set-up A had a plant with roots in the water. Set-up B had no plant. Explain why Set-up B is needed in this experiment. [2]
Set-up B is the control set-up. It acts as a baseline so the results of Set-up A can be compared against it. This confirms that the falling water level in Set-up A is caused by the roots drawing in water — and nothing else.
3. A student says: “The cactus does not have leaves, so it cannot make food.” Do you agree with this statement? Explain your answer. [2]
I disagree. A cactus does have leaves — they are just shaped like spines. Because these spine-leaves cannot make food, the cactus uses its green stem to carry out that role instead.
4. Describe two ways in which the roots of a mangrove tree are different from the roots of a large tree growing in soil. [2]
Mangrove roots arch above the ground before entering the soil, while a large tree’s roots grow underground. Mangrove roots also support the tree in soft, waterlogged ground, whereas the roots of a large land tree are thick, tough and strong, gripping firmly into hard soil.
5. Explain why leaves are important to a plant. [2]
Leaves are the plant’s food factory — they contain chlorophyll, a green substance that captures sunlight and uses it to produce food through photosynthesis. Leaves also have tiny openings on their surface that allow the plant to take in and release gases from the surrounding air.