Describe how plants make food by photosynthesis, state what they need and produce, and explain what plants need to grow well

What this dot point is asking

This dot point wants you to describe how green plants make their own food by photosynthesis, state what they take in and give out, and explain what plants need to grow well. The big idea is that plants are different from animals: instead of eating food, they make their own using light energy from the Sun. This process, photosynthesis, takes place in the leaves and produces food (a sugar) and oxygen.

The answer

How plants get their food

Animals eat food, but green plants make their own food. They do this by a process called photosynthesis, which happens mainly in the leaves. Photosynthesis uses the energy in sunlight to turn simple raw materials into food.

What photosynthesis needs

For photosynthesis, a plant needs three things:

• Light energy from the Sun, which provides the energy for the process.
• Carbon dioxide, a gas the plant takes in from the air through its leaves.
• Water, which the plant takes up from the soil through its roots.

The plant also needs a green substance called chlorophyll, found in the leaves, which traps the light energy. Chlorophyll is what makes leaves green.

What photosynthesis produces

Using these raw materials, the plant produces:

• Food in the form of a sugar (glucose), which the plant uses for energy and growth, and can store.
• Oxygen, a gas that is given out into the air through the leaves.

So photosynthesis can be summed up simply: light energy lets a plant turn carbon dioxide and water into food (sugar) and oxygen.

Why photosynthesis is so important

Photosynthesis matters for all living things, not just plants. It makes the food that plants need to grow, and plants are the start of nearly every food chain, so animals depend on it too. It also releases the oxygen that animals and people need to breathe, while removing carbon dioxide from the air. Without photosynthesis there would be little food and little oxygen.

What plants need to grow well

To grow well, a plant needs more than just the raw materials for photosynthesis:

• Enough light, so it can photosynthesise and make food. A plant kept in the dark grows poorly and turns pale.
• Water, both for photosynthesis and to keep the plant firm.
• Carbon dioxide from the air.
• A suitable temperature (warmth), as photosynthesis works best when it is not too cold.
• Minerals (nutrients) from the soil, such as those that help leaves grow green and healthy. This is why farmers add fertiliser to the soil.

Examples in context

Example 1. A houseplant leaning toward the window. A plant left near a window often grows and leans toward the light. This happens because the plant needs light for photosynthesis to make food, so it grows toward the brightest light. Turn the pot around and over a few days the plant will lean back toward the window again.

Example 2. Why farmers use fertiliser. Crops take minerals out of the soil as they grow. Farmers add fertiliser to put these minerals back, so the soil stays rich and the plants can grow healthy and green. This shows that, beyond light and water, plants need minerals from the soil to grow well.

Try this

• Cue. Name the two things a plant produces during photosynthesis. A plant produces food (a sugar) and oxygen.

• Cue. State where a plant gets the energy for photosynthesis and what traps it. The energy comes from sunlight, and it is trapped by the green substance chlorophyll in the leaves.

• Cue. Explain why a plant kept in a dark cupboard grows poorly even if it is watered. Without light, the plant cannot photosynthesise to make enough food, so it grows poorly and turns pale, even though it has water.