Different parts of plants are made up of different types of plant tissue. The structure of each type of plant tissue is related to its function.
Plant tissues form plant organs, which include roots, stems and leaves.
The leaves are the organs for photosynthesis and they have many adaptations to help them carry out photosynthesis effectively. This involves carrying out the following processes:
The table below shows the structure and function of different structures of a leaf.
|Waxy cuticle||Protective, waterproof layer on top of the leaf that reduces water loss by evaporation|
|Upper epidermis||A thin and transparent layer of cells that allows light to pass straight through (it has no chloroplasts)|
|Palisade mesophyll||Tightly packed palisade cells, which contain a lot of chloroplasts – Photosynthesis mostly takes place in the palisade mesophyll|
|Spongy mesophyll||Contains spaces that increase the surface area to volume ratio for the diffusion of gases|
|Vascular bundle||Contains the xylem and phloem tubes, which transport substances to and from the leaf|
|Xylem||Narrow, hollow tubes that transport water and minerals from the roots, up the stem and into the leaves|
|Phloem||Hollow tubes that transport amino acids and sugars around the plant|
|Lower epidermis||Contains guard cells and tiny holes called stomata, which allow gases to diffuse in and out of the leaf|
|Guard cell||Opens and closes the stomata by absorbing and losing water, which allows carbon dioxide to diffuse in and oxygen to diffuse out|
|Stomata||Microscopic openings on the surfaces of leaves and stems that allow for gas exchange|
Stomata close to minimise water loss and open to increase evaporation and transpiration. When they are open, gas exchange can occur
The structure of leaves has adapted over time to be efficient at photosynthesis. The table below shows the main adaptations of leaves and their functions:
|Thin shape||This means there is a short distance for carbon dioxide to diffuse in and oxygen to diffuse out. If there is a shorter diffusion distance, then diffusion happens at a faster rate.|
|Large surface area||The leaf can absorb a lot of light for photosynthesis|
|Waxy cuticle||Allows light in while preventing water loss|
|Thin and transparent epidermis||Allows light to reach the palisade mesophyll cells|
|Network of veins||Supports the structure of the leaf and transports substances to and from the cells|
|Chlorophyll||Absorbs light energy for photosynthesis and gives the leaf its green colour|