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Science

How Plants Make Food

Overview

Students explore how plants are different from animals in the way they get energy, discovering the remarkable process of photosynthesis.

Learning Objective
Students understand the process of photosynthesis and can explain what plants need and what they produce.

Resources needed

  • A green leaf
  • None otherwise

Lesson stages

0 / 7 done
  1. 1 Ask: how do you get energy? (eating food). How does a plant get energy?
  2. 2 Introduce: plants make their own food using sunlight — they do not eat.
  3. 3 Write the word equation: carbon dioxide + water + sunlight → glucose + oxygen.
  4. 4 Ask: where does each ingredient come from? (CO₂ from air, water from roots, sunlight from the Sun).
  5. 5 Ask: where does the product go? (glucose feeds the plant, oxygen is released into the air).
  6. 6 Hold up a leaf: ask: why is it green? Introduce chlorophyll — the green chemical that captures sunlight.
  7. 7 Ask: what would happen to all life on Earth if plants could not photosynthesise?

Tap a step to mark it as done.

Variations

  • Test whether leaves need light: cover part of a leaf with paper for a week and test for starch with iodine.
  • Discuss the oxygen-carbon dioxide cycle between plants and animals.
  • Connect to food chains: why do all food chains start with a plant or producer?
More information

Teach: photosynthesis, chlorophyll, carbon dioxide, oxygen, glucose, producer, energy. The word equation is the most important single piece of scientific writing students will learn at this level.

Focus on the inputs and outputs only before introducing chlorophyll and the word equation.

Can students write or state the word equation for photosynthesis? Can they explain where each ingredient comes from and what each product is used for?

A single green leaf and sunlight are the only materials needed. The concept can be fully explored through discussion and diagram alone.

Students often think plants get food from the soil, like animals eating. Soil provides water and minerals but plants produce their own food using light — this is what makes them producers.

Photosynthesis is one of the most important chemical reactions on Earth. It produces virtually all the oxygen in the atmosphere and is the foundation of almost every food chain.