"Photosynthesis explained for kids" is typed by parents with a science project due and by children who have been given the equation and want to know what it means. This page gives the recipe in plain words, what each part of the plant does, the word and symbol equations, two experiments you can do at home with a leaf and a jar, the four things children get wrong (one of them is also wrong in a lot of adults), and where the topic goes in each school system. It is written for ages 8 to 13, with a free worksheet at the end.
The recipe
Plants make their own food, and they make it from three things that are almost free: water, which the roots drink from the soil; carbon dioxide, a gas in the air that goes in through tiny holes in the leaf; and light, usually from the sun. The green stuff in the leaf, chlorophyll, catches the light and uses its energy to join the water and carbon dioxide together into sugar (glucose). The plant uses the sugar to grow, stores some of it as starch, and gives out the leftover, which is oxygen, the gas we breathe.
So: water + carbon dioxide + light (caught by chlorophyll) → sugar + oxygen.
In symbols, for children who have met chemical formulas: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2. Six molecules of carbon dioxide and six of water make one molecule of glucose and six of oxygen.
What each part of the plant does
| Part | Job in photosynthesis |
|---|---|
| Roots | Take in water (and minerals) from the soil |
| Stem | Carries the water up to the leaves in tubes, and carries the sugar from the leaves to wherever it is needed |
| Leaf | The kitchen: flat and wide to catch as much light as possible, packed with chlorophyll |
| Stomata (tiny holes, mostly under the leaf) | Let carbon dioxide in and oxygen out; they close in the heat to save water |
| Chlorophyll | Catches the light energy; it is green because it reflects green light and uses the red and blue |
That last row answers a question children ask: leaves are green because green is the colour they do not use.
Two experiments at home
The starch test (does the leaf need light?). Keep a potted plant in a dark cupboard for two days so it uses up its stored starch. Clip a strip of kitchen foil over part of one leaf and put the plant in the sun for a day. Pick the leaf, drop it in boiling water for a minute (an adult does this), then into a jar of warm alcohol (methylated spirit) until the green comes out, then rinse it in warm water so it is soft. Put a few drops of iodine on it. The part that was in the light turns blue-black: it made starch. The part under the foil stays brownish: no light, no food.
The bubble count (does light change how fast it works?). Put a sprig of pondweed (Elodea, from any aquarium shop) in a jar of water on a sunny windowsill and count the bubbles rising from the cut end in one minute. Move the jar into shade and count again. The bubbles are oxygen, and there are fewer without bright light. Add a pinch of baking soda to the water (more carbon dioxide) and count a third time.
The four things children get wrong
- "Plants breathe in carbon dioxide and breathe out oxygen." Plants breathe the same way we do (respiration: oxygen in, carbon dioxide out) all day and all night. Photosynthesis is a second, separate process that only runs in light. In daylight it is much bigger than respiration, so a plant gives out more oxygen than it takes in; at night only respiration runs.
- "Plants eat soil." Van Helmont tested this in 1640: a willow gained 74 kg in five years and the soil lost 57 grams. The plant's body is made from carbon dioxide and water; the soil supplies water and minerals, not food.
- "The roots make the food." The leaves do; the roots collect water. A plant with its leaves removed starves.
- "Leaves are green because they use green light." They reflect green and use red and blue, which is why grow lights are purple.
Where it goes next
| Level | What is taught |
|---|---|
| Ages 7 to 11 (US Grade 2 to 5, UK KS2, Australia Years 3 to 6) | Plants need light, water and air to grow; the leaf, root and stem jobs |
| Ages 11 to 14 (US middle school, UK KS3, CBSE Class 7 "Nutrition in Plants") | The word equation, chlorophyll, stomata, the starch test |
| Ages 14 to 16 (GCSE, IGCSE, CBSE Class 10 "Life Processes", Grade 9 to 10 biology) | The symbol equation, the rate experiments (light, carbon dioxide, temperature), limiting factors, the leaf's cross-section |
| A-level, IB, AP Biology | The light-dependent and light-independent reactions, chloroplast structure, the Calvin cycle |
The free worksheet
Fifteen questions on the recipe, the plant parts, the experiments and the common mistakes, with answers on the second page: Photosynthesis for kids worksheet (PDF). Question 9 (do plants give out carbon dioxide at night?) is the one to talk about afterwards.
Where to get help
A 1-on-1 online science class with a tutor who holds a master's in biology, from elementary science to Class 7 and 10, KS3, GCSE, IGCSE, AP and IB: the picture first, the experiment, then the equation. The recording and notes after every class, US$10 to $13 an hour. The biology page has the courses, and the free 30-minute first class is a real lesson; for this age, usually the starch test on the whiteboard.
Questions parents ask
1What is photosynthesis in simple words for kids?
2What is the equation for photosynthesis?
3Do plants breathe?
4What experiment shows photosynthesis for kids?
See how we teach this, 1-on-1 online →
Shobha
Founder and lead tutor, Science with Shobha
Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.