Leaf

Adaptations of a leaf to carry out photosynthesis

In order to carry out photosynthesis, the leaf needs:

  • A path for transport of glucose and water to the other parts of a leaf.
  • A path to exchange oxygen and carbon dioxide.
  • A structure that can help in the absorption of light efficiently.

Absorption of light

Absorption of light occurs in the palisade mesophyll tissue of the leaf. The column-shaped palisade cells are packed with many chloroplasts. They are closely arranged to increase the efficiency of absorption of light.

Features of leaves and their functions

  • Large surface area – It helps in maximization of light absorption.
  • Thin – Carbon dioxide can easily diffuse into the leaf cells due to the thin outlay of the leaf.
  • Cuticle- It is covered with wax and is waterproof. It helps in the reduction of water loss and is also transparent enough to allow the passage of light through the leaf.

The role of stomata

The exchange of gases occurs through small pores called stomata. These work like a door that opens and closes depending on the turgidity around the guard cells. The opening and closing of stomata are to regulate transpiration and allow gas exchange.

Diffusion of oxygen, carbon dioxide, and water occurs rapidly when the stomata are open. It usually happens in the day time.

Xylem and Phloem

Specialized tissues are present in plants for the transportation of water, minerals, and nutrients.

  • Xylem is responsible for the transport of water and minerals. It picks the water from roots and sends it to other parts of the plant. It is transported through the process of transpiration stream.

    • Mature xylem vessels do not contain cytoplasm.
    • These contain elongated dead cells
    • The cells are arranged in a closely packed arrangement to form continuous vessels and form tube-like structures.
    • Xylem cells are impermeable to water
    • Lignin is a woody material and is the main component forming the walls of the vessels.

 

  • Phloem is responsible for the transport of nutrients like sucrose and amino acids from one part to other parts of plants. The process of transfer is called translocation. This process is generally found to occur between the manufacturing place of sucrose and its storage place.
    • Phloem cells are living
    • These are also arranged in end to end tubular form.
    • These cells contain cytoplasm.
    • These also form sieve plates that connect one cell to the next.
    • Chemicals such as pesticides are also moved in plants through translocation

Vascular bundles

The group forming the xylem and phloem tissues are called vascular bundles. Its position is not fixed and changes according to the structure where it is found. In leaves, the phloem tissues can be seen near the lower surface.

Root

The position of the vascular bundle in roots is around the centre which allows the root to resist the force put on the ground by xylem vessels and prevent the plant from pulling out from the ground.

Stem

In stem, the vascular bundles are positioned near the edges while the phloem will be seen on the outside and the xylem can be seen on the inner side. This helps in resisting the compression and bending forces being applied by the weight of the plant and winds.