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  Compressed TOC
The Process of Protein Digestion
Adaptation of Parasites to their mode of Life
Micro-organisms and food processing:
   The Bacteria
   The Fungi 
Methods of Food Preservation
Adaptation of the Mammalian Heart to its Functions
Transportation of gases in the blood:
   Carbon Dioxide
The mechanism of movement of water from soil to leaves of a tall plant
The Mechanism of Translocation by:
   Cytoplasmic Streaming
   Mass Flow
Adaptations of the Phloem Tissue
The role of Transpiration in plants
The Environmental Factors Affecting Transpiration
Gaseous Exchange in plants and Animals
Adaptations of the airways for gaseous exchange
Adaptations of the Lungs for Gaseous exchange
The process of Inspiration and Expiration in Mammals
Mechanism of gaseous Exchange in:
       Bony Fish,
The Mechanism of Opening and Closing of Stomata
Adaptation of the Kidney to its Functions
Formation of Urea in Human Body
Adaptations of the Human Skin to its Functions
Changes on the Skin due to Temperature Variation
The Role of Hormones in Homeostasis
Reproduction In Animals
Adaptation of the Mammalian Male Reproductive Organ to its Functions
The Influence of Hormones on Menstrual Cycle
Mechanisms that hinder self-fertilization  in Plants
The adaptations of Insect-Pollinated flowers
Events that take place after fertilization until a new fruit is formed
Adaptation of seeds for Dispersal
Water and Air Pollution, and the remedies
Adaptation of plants to their Habitat
     Xerophytes (Desert Plants);
     Hydrophytes (Water Plants)


..Home/Contents/ Opening and closing of the Stomata



Photosynthetic theory:
For stomata to Open:

The guard cells have chloroplasts which carry out photosynthesis in the presence of sunlight.

Photosynthesis manufactures glucose which increases the osmotic pressure in the guard cells as compared to the epidermal cells.

Water moves into the guard cells by osmosis hence increasing its turgidity.

The inner walls of the guard cells are thicker than the hence the outer walls stretch more than the inner wall causing the inner wall to bulge outwards. In this process, the stomata opens.

For stomata to close:

In absence of light (at night), no photosynthesis takes place in the guard cells of the leafs.

The glucose in the cells that was manufactures in the day is converted into starch; which lowers the osmotic pressure of the guard cells than that of the epidermal cells.

The epidermal cells withdraws water from the guard cells through osmosis, making the guard cell flaccid.

The thinner outer wall shrinks and the curvature of the inner wall reduces; then the stomata closes. 

Starch-sugar inter-conversion theory:

During opening:

Photosynthesis occurs during the day due to the presence of light. This lowers the concentration of Carbon dioxide which is a raw material for the above process. This reduces the acidity of the guard.

This condition favours conversion of starch to glucose (sugar); which then increases the guard cells’ osmotic pressure; water from the nearby epidermal cells will move by osmosis to the guard cell making it more turgid.

The thinner outer walls stretches more causing the guard cells to bulge out hence opening the stomata.

During closing:

At night when there is no light, no photosynthesis takes place that means the level of carbon dioxide in the guard cells increases increasing acidity.

Acidic condition promotes conversion of glucose to starch; and the osmotic pressure of the guard cells reduces than that of the neighbouring cells hence loses water through osmosis.

The cell thus become flaccid and the stomata has no choice than to close.



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