The Leaf
ICSE Class 6 · Biology · Chapter 1
What this chapter covers
- Parts of a leaf
- Simple and compound leaves
- Venation: reticulate and parallel
- Functions of a leaf
- Leaf modifications
- Vegetative propagation by leaf
Key points
- A leaf has a leaf base, a petiole and a lamina; the lamina has a midrib, veins, an apex and a margin.
- Some leaves have stipules at the base; a sessile leaf has no petiole.
- A simple leaf has one undivided lamina; a compound leaf has many leaflets.
- A bud grows in the axil of a leaf but never in the axil of a leaflet.
- Reticulate venation forms a net (mango, peepal); parallel venation runs side by side (wheat, banana).
- Leaves make food by photosynthesis, using sunlight, water, carbon dioxide and chlorophyll, and give out oxygen.
- Leaves lose water vapour through stomata by transpiration, and exchange gases through the stomata.
- Leaves are modified into tendrils (pea), spines (cactus) and scale leaves (onion, ginger).
- Insectivorous plants, such as the pitcher plant, trap insects to get nitrogen from poor soil.
- Bryophyllum grows new plants from buds on the margin of its leaves.
Questions answered
Name the three main parts of a leaf.
The leaf base, the petiole and the lamina.
What is a sessile leaf? Give one example.
A sessile leaf has no petiole and is joined straight to the stem. The wheat leaf is an example.
A neem twig looks like a branch covered with many small leaves. How can you prove that it is one compound leaf?
A bud is found only in the axil of the whole stalk, not in the axil of each small part. The small parts are leaflets, and they all lie in one plane.
Which type of venation does a banana leaf show? Name one plant with the other type.
A banana leaf shows parallel venation. Mango, peepal or hibiscus shows reticulate venation.
Why do drops of water appear inside a polythene bag tied over a leafy branch?
The leaves lose water vapour through their stomata by transpiration. The vapour turns back into drops of water on the cool plastic.
Into what has the leaf changed in the cactus, and how does this help the plant?
The leaves have changed into spines. Spines lose very little water and protect the plant from animals.
Why does the pitcher plant catch insects even though it can make its own food?
It grows in soil that is poor in nitrogen. It digests insects to get the nitrogen it needs.
How does a Bryophyllum leaf give rise to new plants?
Buds in the notches on its margin grow roots and shoots when the leaf lies on moist soil. Each bud becomes a new plant.