NCERT Curiosity · Class 7 · Science
Life Processes in Plants
Animals eat food to grow — but have you ever seen a plant eating? What actually happens as a plant grows?
Key idea
How Do Plants Grow?
Three potted plants tested different conditions.
Grew poorly despite water.
Key idea
Leaves: The Food Factories
1
Chlorophyll
The green pigment in leaves that captures sunlight efficiently — it's why most leaves are green.
→
2
Starch
The carbohydrate form in which plants store their food.
Key idea
The Iodine Test
A decolourised leaf treated with iodine turns blue-black if starch is present.
Only where there's chlorophyll and sunlight
Only the green, sunlit parts of a leaf test positive for starch — parts kept in the dark, or non-green patches, do not.
Key idea
Carbon Dioxide Is Essential Too
Proven by denying it. A leaf part sealed away from carbon dioxide (using a CO2-absorbing chemical) does not form starch, while the exposed part does.
Key idea
Photosynthesis
Plants use sunlight and chlorophyll to convert carbon dioxide and water into food, releasing oxygen.
Carbon dioxide + Water →(Sunlight, Chlorophyll)→ Glucose + Oxygen — Glucose is used instantly for energy, or converted to starch for storage.
Key idea
Photosynthesis Releases Oxygen
The glowing matchstick test. A water plant kept in sunlight releases a gas that relights a glowing matchstick — proof that the gas is oxygen.
Key idea
Gas Exchange: Stomata
Stomata. Tiny pores, usually on a leaf's lower surface, that let carbon dioxide and oxygen move in and out during photosynthesis and respiration.
Key idea
Transport in Plants
Roots (water absorbed here)
Key idea
Respiration in Plants
Germinating seeds turn lime water milky
even in the dark — showing they respire.
Glucose + Oxygen → Carbon dioxide + Water + Energy
Every part of a plant, green or not, respires — the energy released supports growth and development.
Key idea
Photosynthesis vs Respiration
| Photosynthesis | Respiration
Raw materialsCarbon dioxide + water (+ sunlight, chlorophyll) — Glucose + oxygen
ProductsGlucose + oxygen — Carbon dioxide + water + energy
ImportanceMakes food and releases oxygen — Releases energy for growth
Chapter · Key terms to remember
Key Terms
Chlorophyll
The green pigment that captures sunlight.
Starch
The stored form of a plant's food.
Photosynthesis
Making food using sunlight, CO2, and water.
Chapter · Key terms to remember
More Key Terms
Stomata
Tiny pores for gas exchange on a leaf.
Xylem
Carries water and minerals upward.
Phloem
Carries food to the rest of the plant.
Chapter · Key terms to remember
More Key Terms
Respiration
Releasing energy from glucose using oxygen.
Glucose
The simple sugar made by photosynthesis.
Questions for your notebook
Write these down, then discuss
1Complete the table comparing photosynthesis and respiration: raw materials, products, word equation, and importance of each.
2Imagine every photosynthesising organism on Earth disappeared. What impact would this have on living things?
3A potato slice tests positive for starch with iodine. Where does this starch come from, and how does it reach the potato?
Project as-is — students copy the questions, then the class discusses answers together.