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Stoma in a tomato leaf shown via colorized scanning electron microscope image A stoma in horizontal cross section The underside of a leaf. In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.
Photosynthesis depends on the diffusion of carbon dioxide (CO 2) from the air through the stomata into the mesophyll tissues. Oxygen (O 2), produced as a byproduct of photosynthesis, exits the plant via the stomata. When the stomata are open, water is lost by evaporation and must be replaced via the transpiration stream, with water taken up by ...
The stomata complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Typically, the stomata are more numerous over the abaxial (lower) epidermis of the leaf than the (adaxial) upper epidermis. An exception is floating leaves where most or all stomata are on the upper surface.
Some xerophytes have tiny hair on their surfaces to provide a wind break and reduce air flow, thereby reducing the rate of evaporation. When a plant surface is covered with tiny hair, it is called tomentose. Stomata is located in these hair or in pits to reduce their exposure to wind. This enables them to maintain a humid environment around them.
When the stomata are closed at night, water pressure can build up in the plant. Excess water is excreted through pores known as hydathodes . [ 24 ] The movement of water out of the leaf stomata sets up transpiration pull or tension in the water column in the xylem vessels or tracheids.
However, if this phylogeny is correct, then the complex sporophyte of living vascular plants might have evolved independently of the simpler unbranched sporophyte present in bryophytes. [25] Furthermore, this view implies that stomata evolved only once in plant evolution, before being subsequently lost in the liverworts. [26] [29]
In plants, the substomatal cavity is the cavity located immediately proximal to the stoma. It acts as a diffusion chamber connected with intercellular air spaces and allows rapid diffusion of carbon dioxide and other gases (such as plant pheromones ) in and out of plant cells .
Turgor pressure within the stomata regulates when the stomata can open and close, which plays a role in transpiration rates of the plant. This is also important because this function regulates water loss within the plant. Lower turgor pressure can mean that the cell has a low water concentration and closing the stomata would help to preserve water.