The Leaf

Todays topic for Class 6| ICSC|Biology is The Leaf. We see different kinds of plants around us i.e big,small, flowering, non-flowering. Like our body plants also have different parts.

Parts of a Plant

The flowering plants consist of two main systems -

1.Root System - It is present below the ground. It consists of a main root which has several branches.Its main functions are -

*It holds the plant in the soil.

*It helps in absorbing water and minerals from the soil.

*It helps in preventing soil erosion.

2.Shoot System - It is present above the ground. It consists of stem, leaves, buds, flowers and fruits. Its main functions are

*The stem keeps the plant straight and upright.

*It helps in transferring water and minerals from the root to different parts of the plant.

Structure of the Leaf

It is flat and broad that arises from a point known as the node of the stem.The axillary bud present in the axil of the leaf grows into a new branch. Its main parts are-

(a) Petiole - The stalk of the leaf that connects the lamina and the stem is known as petiole with the help of leaf base which is the swollen end of the petiole. Leaves having petiole are known as stalked leaves while the leaves that don't have petioles are known as sessile leaves. Stalked leaves are found in dicot plants while sessile leaves are present in monocot plants.

(b) Lamina - It is flat and green in colour. It consists of a margin and a pointed end called the leaf apex.

(d) Veins - Several lateral branches arising from the midrib are called veins.

(e) Veinlets - Branches that arise from the veins are called as veinlets.

Types of leaves

(a) Simple leaves - The leaves that have a single leaf blade which is not divided into parts are known as simple leaves. For example - For example - mango, guava etc.

(b) Compound leaves - In these leaves, the lamina consist of two or more parts. These leaflets branch out from the midrib having a single petiole. For example - gulmohar, neem etc.

Venation and its types

The arrangement of veins and veinlets in the lamina is known as venation. It is of two types.

(a) Reticulate venation - In this type, veins and veinlets form a network as they are distributed irregularly in the lamina. For example - mango, guava etc.

(b) Parallel venation - In this type of venation,veins show a parallel arrangement to each other. For example - grass, wheat, banana, etc.

Arrangement of the leaves on the stem

The pattern of arrangement of leaves on the stem is called phyllolaxy. It is of three types -

(a) Alternate leaf arrangement - When only one leaf arises from the node of the stem, the arrangement is known as alternate leaf arrangement. For example - Mango, Hibiscus etc.

(b) Opposite leaf arrangement - When two leaves arise from the same node of the stem in the opposite direction the arrangement is known as opposite leaf arrangement. For example - Basil, guava etc.

(c) Whorled leaf arrangement - When several leaves grow from the same node of the stem, it is known as the whorled leaf arrangement. For example - alstonia schleris (devil tree), nerium oliander (kaner)

Functions of a leaf

The main functions of a leaf are -

(a) Photosynthesis - It is the process by which green plants make their own food with the help of water, carbon dioxide and chlorophyll in the presence of sunlight.

Sunlight

6CO2 + 6H2O ➡ C6H12O6 + 6O2

Chlorophyll

Photosynthesis don't take place at night.

(b) Gaseous exchange - This process takes place with the help of stomata which are tiny holes present on the outer surface of the leaf. Stomata remain open during the day and they close during night. Plants take in carbon dioxide and give out oxygen through stomata.

(c) Transpiration - Water is given out through stomata in the form of water vapours by the process of transpiration. Transpiration helps in keeping the plant cool.

Modification of leaves

(a) Tendrils - They are thread like long and thin parts that are mostly found in climbing plants. They give support to the plants and help in fastening them to a wall or stick.They can also undergo photosynthesis.For example - pea plant, money plant etc.

(b) Spines - Leaves of some plants are reduced to spines to reduce water loss preventing transpiration and to protect the leaves from grazing animals. For example - cactus etc.

(c) Scale leaves - In some plants, leaves are modified into scales for the protection of buds and the storage of food and water. For example - onion, ginger etc.

Insectivorous plants

(a)Pitcher Plant - Its shape is like a pitcher. As soon as an insect enters this plant, its lid gets closed and the juices released by the its leaf digests the insect.

(b) Bladder wort - They are mostly found in stream, lakes and swamps. The bladders which are found under the water act as traps to catch aquatic worms, tadpoles etc.These are digested with the help of enzymes and bacteria present in these sacks.

(c) Venus fly trap - It is a type of carnivorous plant. Pointed hair are present on the edges of its leaves.Its midrib works like a hinge and the lamina has two parts. The leaf shuts down when as soon as an insect touches it. The insect is digested by the juices secreted by the leaf.

Vegetative propagation or vegetative reproduction

In this process, new plants grow from leaves, stems and roots that are the vegetative parts of the plant. This is a type of sexual reproduction. In this type of reproduction only one parent is involved. The new plants formed resemble the parent plants. For example - Bryophyllum.

In some plants, buds are formed in the margin of the leaves that grow into new plants as soon as they found suitable conditions on detaching from the leaf but remain inactive until they don't fall off from the leaf.

Hope this topic The Leaf for ICSC|Class 6|Chemistry would be helpful to you. You may also practice this topic using Worksheets for Science Please comment if you want articles on any other topic.

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