Photosynthesis in Green Plants
How Plants Make Food
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How Plants Make Food
Open with the idea that plants do not eat food like animals. This lesson explains how they make their own food and why that matters for life on Earth.
Learning goal
I can explain the basics of photosynthesis and why it is essential for plant growth.
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What words come to mind when you hear photosynthesis?
Use this to surface prior ideas such as plants, light, leaves, oxygen, food or Sun. Invite students to notice which ideas they already know and which they will check during the lesson.
What is photosynthesis?
Photosynthesis is how green plants make food
It uses light energy to make glucose
It also releases oxygen as a by-product
Keep the definition simple at KS3 level: plants use light energy to make glucose. Oxygen is produced, but the main purpose for the plant is making food.
Chlorophyll and light
Chlorophyll is a green substance in plant cells
It absorbs light energy
This light energy is needed for photosynthesis
Leaves look green because of chlorophyll
You may mention that chlorophyll is found in chloroplasts, but keep the focus on its role in absorbing light.
Where it happens
Photosynthesis happens mainly in the leaf
Leaf cells contain many chloroplasts
Chloroplasts contain chlorophyll
Link structure to function: leaves are broad to catch light, and their cells near the top of the leaf contain many chloroplasts.
The raw materials
Photosynthesis needs three main things:
light
water
carbon dioxide
Without these, the plant cannot make glucose.
Emphasise that light provides energy, while water and carbon dioxide are the substances used to make glucose.
How plants get what they need
Light comes from the Sun
Water is absorbed by the roots
Carbon dioxide enters the leaf from the air
If useful, mention stomata as tiny openings in leaves where carbon dioxide enters, but do not overload the slide.
What does chlorophyll do in photosynthesis?
Stores water
Absorbs light
Makes roots
Releases carbon dioxide
Checks the key role of chlorophyll after the first teaching block. Distractors match likely confusions with other plant functions.
Complete the summary
Photosynthesis happens mainly in the leaf. The plant needs light, water and carbon dioxide to make food. Chlorophyll absorbs light energy for this process.
The blanks focus on location and raw materials from slides 4 to 6.
The word equation
carbon dioxide + water → glucose + oxygen
Light energy and chlorophyll are needed for this process.
Read the equation aloud slowly. Explain that this is a word equation, so it shows the substances going in and the substances produced.
What is made?
Glucose is the plant's food
Oxygen is released as a by-product
The plant uses glucose for energy and growth
Clarify that oxygen is important for many living things, but for the plant the key product is glucose.
Why glucose matters
Glucose is used in respiration
It helps make new plant material
This is why photosynthesis is essential for growth
At this level, 'new plant material' is enough. You may briefly note that glucose can be turned into substances the plant needs to build tissues.
Which word equation is correct?
glucose + oxygen → water + carbon dioxide
carbon dioxide + water → glucose + oxygen
oxygen + glucose → carbon dioxide + water
water + oxygen → glucose + carbon dioxide
Tests whether students can recognise the correct inputs and products, not just single keywords.
Fill the missing words
In photosynthesis, carbon dioxide and water are used to make glucose and oxygen. Glucose is the plant's food and helps with energy and growth.
This anchors the main products and why glucose matters for the plant.
Photosynthesis and the food chain
Plants are producers in food chains
They make food that animals cannot make for themselves
Energy stored in glucose passes to other living things when plants are eaten
Stress that photosynthesis supports more than just the plant itself. It provides the starting point for most food chains.
Why photosynthesis matters to life
It provides food for plants
It supports food chains
It adds oxygen to the air
This slide resolves the lesson's central question: photosynthesis is essential because it allows plants to grow and supports other living things directly and indirectly.
How does photosynthesis help animals in a food chain?
Expected answer elements: plants make glucose by photosynthesis; animals eat plants or organisms that ate plants; energy in glucose passes along the food chain. Accept simple explanations in students' own words.
Why is photosynthesis essential for plant growth?
It makes oxygen for roots
It makes glucose for growth
It cools the leaf surface
It changes soil into food
Checks the lesson goal directly: plant growth depends on glucose made in photosynthesis.
What is one thing you learned about photosynthesis today?
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Which part of this lesson helped you understand best?
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Glossary
photosynthesis - the process by which green plants use light to make glucose
chlorophyll - a green substance that absorbs light energy
chloroplast - a part of a plant cell that contains chlorophyll
glucose - a sugar made by plants as food
carbon dioxide - a gas from the air used in photosynthesis
oxygen - a gas released during photosynthesis
producer - a living thing that makes its own food
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