Why does modification of leaf occur
Answers
Answer:
Leaves can be modified in the form of spines that reduce water loss and also act as a defence. Some are modified into tendrils to provide support to the plant. Some leaves are thick that help in water storage. Some are modified to catch and digest insects.
Plants are an essential part of the ecosystem. Every life on the earth is directly or indirectly dependent on plants. Among the different parts of a plant, the leaf is the most essential.
Primarily, leaves have two functions: photosynthesis and transpiration. In some plants, it takes up the responsibility of reproduction also.
Modification Of Leaves
We know leaves are specialised to perform photosynthesis. In addition, they also have other significant roles to play, such as support, storage of food, defence, etc. For each of these functions, they have been modified into different forms.
For example, tendrils of peas, spines of cacti, onion bulb, leaves of insectivorous plants, etc. are different modified leaves. Let us have a detailed look at some of the modification of leaves:
Storage Leaves
The xerophytic plants and plants belonging to the Crassulaceae family have thick and succulent leaves that store water in their tissues. The parenchymatous cells of these leaves have large vacuoles filled with hydrophilic colloid. This modification helps the plant to resist desiccation.
Leaf Tendrils
Leaf tendrils exist in plants with weak stems. The leaves get modified into thread-like structures called tendrils. These tendrils climb a nearby stick or wall and provide support to the plant. For eg., In Lathyrus aphaca, the whole leaf is modified into tendrils. The upper leaflets of Pisum sativum get modified into tendrils.
Leaf Spines
A few plants have their leaves modified into needle-like structures known as spines. The spines act as defensive structures. They also reduce water loss due to transpiration. For eg., in Opuntia, the leaves are modified into spines.
Scale Leaves
These are thin, membranous structures, without stalks, brownish or colourless in appearance. They protect the auxiliary bud present in their axil. Scale leaves in onion are fleshy and thick and store food and water. Casuarina and Asparagus also contain sale leaves
Leaflet Hooks
In some plants, the terminal leaflets of leaf get modified into hook-like structures that help them in climbing. Eg., Bignonia unguiscati.
Leaf Roots
In a few plants, one of the leaves present at the nodes gets modified into adventitious roots which helps them to float over the water surface. Eg., Salvinia
Phyllode
In some plants, the petiole becomes flattened, taking the shape of a leaf and turns green in colour. This is known as phyllode. For eg., Australian Acacia.
Insectivorous Leaves
Few plants require nitrogen for their development. In such plants, the leaves are modified to catch and digest insects. Few of the modifications are mentioned below:
Leaf Pitcher- In a few plants like Nepenthes, the leaf-lamina is modified into a pitcher-like structure. The insect is digested into the inner walls of the pitcher which secretes a digestive fluid into the pitcher cavity.Leaf Bladder- In such plants, the segments of the leaves are modified into bladders. These plants are found in water. The inner wall is provided with digestive glands which helps in digesting the trapped insect. For eg., UtriculariaIn Drosera– The lamina possesses numerous hair with a sticky globule at its tip containing digestive enzymes. The moment an insect sits on the lamina, the hair covers the insect completely.
Functions of Leaves
The leaves perform the following functions:
Photosynthesis
Photosynthesis is the primary function of leaves. They convert carbon dioxide, water, and UV light into glucose through the process of photosynthesis.
Also Refer: Photosynthesis
Transpiration
Transpiration is the removal of excess water from the plants into the atmosphere. This occurs by the opening of stomata present in the leaves.
Guttation
Removal of excess water from the xylem at the edges of the leaves when the stomata are closed is known as guttation.
Storage
Leaves are a site of photosynthesis. Therefore, they store water and nutrients. The succulent and thick leaves particularly adapt to water storage.
Defence
Some leaves are modified into spines to protect them from being damaged or eaten by animals. For eg., Opuntia.
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