Adaptations of the leaf for photosynthesis and gaseous
The leaf is a plant organ adapted to carry out photosynthesis. The table describes some of its adaptations:
|Large surface area||· To absorbs maximum light energy.|
|Thin flat lamina||· Provides a short distance for carbon dioxide to move by diffusion into the leaf(into palisade mesophyll quickly)
· Enables sunlight to reach all mesophyll cells.
|Chlorophyll||· Absorbs light energy to help the leaf to carry out the process of photosynthesis means light energy converts into chemical energy which is used in the manufacture of sugar.|
|Stomata present in the epidermal layers||· Open in sunlight.
· Allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out.
|More chlorophyll are present in upper palisade tissue.||· More light energy is absorbed near the surface of the leaf.|
|network of veins||· It is called vascular tissues that consist of phloem and xylem.
· Xylem transport water and mineral salts from roots till mesophyll cells from down to upwards.
· Phloem transports glucose away from leaves to all body parts of the plant from up to down and vice versa.
· Both xylem and phloem give mechanical support to the leaf and stem.
|spaces in spongy mesophyll||· Air spaces allow carbon dioxide to diffuse through the leaf.|
|petiole||· It holds the leaf in position to absorb maximum light for the process of photosynthesis.|
What is the function of a stoma?
Stomata are tiny holes found on the lower side of a leaf. Stomata control the water loss and gaseous exchange by the opening and closing(depends upon turgor pressure). They take out excess water vapour and oxygen out of the leaf and taken in carbon dioxide.
What are guard cells?
Stomata are composed of two guard cells which are bean shaped. These guard cells have walls that are thicker from the inner side than their outer side that are thin. This imbalanced thickening of the paired guard cells causes the stomata to open when they take in water and close when they lose water. The opening and closing of stomata is guarded by increases or decreases of solutes in the guard cells, which cause them to take up or lose water, respectively.
What sre Factors affecting the opening and closing of stomata?
Plants growing in dry conditions have small numbers of stomata. To save the water loss st aromata are present only on their lower surface of the leaf. Most of plants control the size of the stomata with the help of guard cells. Guard cells are bean shaped. In a bright light the guard cells take in water by the process of osmosis and become fat and turgid(because of turgid pressure). While In less light the guard cells become flaccid causing the stomata close because of the lose of water. Normally they would close only in the dark when there is no requirement of carbon dioxide for the process of Photosynthesis. By allowing gas exchanges and controlling water loss within the leaf, guard cells are adapted for their function. The size of the opening of stomata is used by the plant to control the rate of transpiration and therefore a limited amount of water loss occurs from the leaves. Thus this helps to stop the wilting in plants.
In a nut shell the opening or closing of stomata occur in response to signals from the external environment.
- When light is present ………………… Stomata open.
- When there is dark means no light……………….Stomata close.
- High Carbon dioxide inside leaf ………………….stomata close.
- Low Carbon dioxide inside leaf ………………………stomata open.
- When Drought occurs……………….stomata close.