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General characters & Structure of leaf

Introduction:

  • Leaves are the laterally flattened green structures arising from the nodes.
  • They are developed by the shoot apical meristem as leaf primordium which gradually becomes enlarged.
  • They perform photosynthesis hence are the food manufacturing organs of the
  • plant.
  • Leaves bear buds in their axil called axillary buds, these later develop to form the branches.
  • Leaves are arranged in an acropetal order i.e older leaves are present at the base while newer leaves are near the apex.

Detailed Explanation:

Structure of a Leaf:
The leaf mainly comprises three parts:
1. Leaf lamina/ leaf blade/ Epipodium
2. Petiole/ Mesopodium
3. Leaf base/ Hypopodium
 

structure-of-leaf


1. Leaf-blade/ Lamina/ Epipodium:

  • It is the flat, broad green coloured part with a conspicuous system of veins and veinlets.
  • The lamina consists of a prominent vein in the middle called the midrib.
  • Veins act as channels on the lamina and provide rigidity.
  • They also help in the transport of food, water and minerals.
  • Leaf lamina may vary in different leaves in terms of shape, margin, apex, surface and extent of incision.

2. Petiole/ Mesopodium:

  • The petiole is the long, thin and flexible stalk of the leaf that attaches the lamina with the leaf base.
  • It helps to hold the leaf blade to the light.
  • They allow the leaf blade to flutter in the air thereby having a cooling effect by bringing fresh air to the leaf.
  • Leaf may or may not possess petiole.
  • Leaf with petiole is petiolate leaf while the leaf without a petiole is a sessile leaf.

3. Leaf base:

  • It is the lowermost part of the leaf which is present at the node of the stem.
  • It may bear two leaf-like appendages called the stipules.
  • A leaf with stipule is called stipulate and without stipule is called ex-stipulate.
  • In leguminous plants, the leaf base may become swollen up called the pulvinus.
  • In monocots, the leaf base becomes sheath-like which partially or completely covers the stem.

FAQ

1. General characters & Structure of leaf

Q1:

What is the axillary bud?

Solution:
- The axillary bud is present in the axil of the lead, it later develops to form the branches.

Q2:
What is meant by the term pulvinus?

Solution:
- In leguminous plants, the leaf base becomes swollen up called the pulvinus.

Q3:
Leaves are arranged in which order?

Solution:
- Leaves are arranged in an acropetal order i.e older leaves are present at the base while newer leaves are found at the apex.

2. Types of Leaves

Q1:
Give a differentiating feature leaf and leaflet?

Solution:
- Both in simple & compound leaf, a bud is present in the axil of the petiole but it is absent in the leaflets of the compound leaf.

Q2:
Define rachis?

Solution: - The rachis is a common axis onto which leaflets are arranged.
- It represents the midrib of the leaf
- Example - neem.

Q3:
What forms the basis of classifying leaves?

Solution:
- On the basis of incisions of the lamina, leaves can be of two types: Simple leaf & Compound leaf.
- The leaf which has either a single entire lamina or if the lamina is incised, the incisions do not touch the midrib or petiole breaking it into a number of leaflets is called a simple leaf.
- The leaf in which the incisions touch the midrib or petiole such that it breaks the leaf into a number of leaflets is called a compound leaf.

3. Venation
Q1:
Which type of venation is a characteristic of dicotyledonous plants?

Solution:
- Reticulate venation is a characteristic of dicotyledonous plants.
- If the veins and veinlets are distributed irregularly and form a network such type of venation is termed reticulate venation.

4. Phyllotaxy
Q2:

Define alternate phyllotaxy?

Solution:
- The type of arrangement in which only a single leaf is borne on each node of the stem in an alternate manner is called alternate phyllotaxy.
- Examples - Mustard, China rose, Sunflower.

Q3:
What is the aim of phyllotaxy?

Solution:
- The objective of phyllotaxy is to orient leaves in such a way that they receive the maximum sunlight for performing photosynthesis.

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