☰ Year plan · Science

Photosynthesis

Week 7 · Chapter 5 Photosynthesis: 5-1 Sunlight and Starch; 5-2 Gas Exchange · 3 lessons
1

Sunlight makes food in leaves

Science P6: Term 1, Chapter 5, pp. 46–53
GoalExplain that leaves use sunlight, carbon dioxide and water to make food and release oxygen.
New words
photosynthesis · how plants use light to make food from carbon dioxide and waterchlorophyll · the green material in leaves that captures lightstarch · a food store that plants keep in leaves, roots and seeds
Explanation

Plants do not eat soil. They make their own food, and they make it in their leaves. In sunlight, a leaf takes carbon dioxide from the air through tiny holes and water from the roots. The green material called chlorophyll captures the light energy. The leaf uses it to join carbon dioxide and water into sugar, and it lets oxygen go into the air. This is photosynthesis. The plant uses some sugar for energy and growth, and stores the rest as starch. Without light, the leaf cannot do this. That is why plants grow toward windows, and why the leaves of plants kept in the dark turn pale. The leaf is green because of chlorophyll, not because it likes the Sun.

Worked examples
wheatsunlightwater
A farmer in the Delta waters her field of wheat. The water goes up from the roots to the leaves. In the sunshine, the leaves use that water and carbon dioxide to make sugar for the grain.
PlantPlaceAfter a week (expected)
Asunny windowgreen and healthy
Bdark cupboardpale and weak
Karim puts one potted plant by a sunny window and another in a dark cupboard for a week. The one in the dark makes little food, and its new leaves are pale and weak.
A plant puts out new leaves toward the light. This helps it catch more sunlight for photosynthesis.
Class activity

Light and leaves. With a grown-up, look at a potted plant on a window sill. Which way do the leaves face? Turn the pot around and look again after three days. Draw what you see. Do not look at the Sun.

Practice
1
Which gas do leaves take in for photosynthesis?
2
Which gas do leaves let out?
3
What does chlorophyll do?
4
Do plants take their food from the soil?