Complete Grade 6 Natural Sciences study guide in English, aligned to the CAPS curriculum. 15 chapters with explanations, worked examples, exercises with solutions, and original practice papers with memos.

Chapters

Chapter 1. 1. Photosynthesis: How Green Plants Make Food FREE

1. Photosynthesis: How Green Plants Make Food

Have you ever wondered how a tiny seed grows into a tall bluegum tree, or how the spinach in your garden gets bigger every week? Plants do something amazing that animals cannot do: they make their own food. This process is called photosynthesis. The word comes from two parts: photo meaning light, and synthesis meaning to make or build. So photosynthesis means making food using light.

Why plants are so important

Every living thing needs food for energy. Animals and people cannot make food inside their bodies, so we have to eat. But green plants are different. They are called producers because they produce (make) their own food. Animals are called consumers because they must eat plants or other animals. Without plants making food, there would be nothing for any animal to eat. This is why plants are the start of almost every food chain on Earth.

What a plant needs for photosynthesis

To make food, a green plant needs four things:

Sunlight – the energy that drives the whole process. Light from the Sun is free and powerful.
Carbon dioxide – a gas in the air. The plant takes it in through tiny holes in its leaves called stomata.
Water – taken up from the soil by the roots and carried up the stem to the leaves.
Chlorophyll – the green colouring inside leaves that traps sunlight. It is found in tiny parts of the cell called chloroplasts.

Chlorophyll is the reason leaves are green. It works like a tiny solar panel, catching sunlight so the plant can use that energy to build food.

What photosynthesis makes

When a plant photosynthesises, it makes two things:

Glucose – a type of sugar that is the plant’s food. The plant uses it for energy and to grow. Extra glucose is stored as starch in roots, stems, fruits and seeds – this is why a potato or a mielie cob is full of stored food.
Oxygen – a gas that the plant releases into the air through the stomata. This is the oxygen that we and all animals breathe to stay alive.

The photosynthesis word equation

Scientists write photosynthesis as a word equation. The things that go in are on the left, and the things that come out are on the right:

carbon dioxide + water →_{(light + chlorophyll)} glucose + oxygen

The arrow means “changes into”. Light energy and chlorophyll are written above the arrow because they are needed to make the change happen, but they are not used up like the carbon dioxide and water are.

A worked example: counting the gas

Imagine a healthy spinach plant in a vegetable patch in Polokwane on a sunny day. Suppose it takes in 6 small units of carbon dioxide to make 1 unit of glucose. If the plant has enough light and water to repeat this 4 times in an hour, how many units of carbon dioxide did it use?

We multiply the units per batch by the number of batches: \( 6 \times 4 = 24 \) units of carbon dioxide. So the plant used 24 units of carbon dioxide in that hour. The more sunlight a plant gets, the faster it can repeat photosynthesis and the more food it makes.

Where photosynthesis happens

Most photosynthesis happens in the leaves, because that is where the most chlorophyll is and where leaves are spread out flat to catch the most sunlight. A broad, flat leaf is like a hand held open to the Sun. Some green stems can also do a little photosynthesis, but leaves do most of the work.

Why this matters for us

Photosynthesis does two huge jobs for the whole planet. First, it makes the food that feeds nearly every living thing. Second, it puts oxygen into the air for us to breathe and removes carbon dioxide. This is why forests and grasslands are sometimes called the “lungs” of the Earth, and why planting trees and looking after plants helps everyone.