explain the role of stomata in the exchange of oxygen and carbon dioxide.
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Each part of the plant takes care of its own gas exchange needs. Although plants have an elaborate liquid transport system, it does not participate in gas transport.
Roots, stems, and leaves respire at rates much lower than are characteristic of animals. Only during photosynthesis are large volumes of gases exchanged, and each leaf is well adapted to take care of its own needs.
The distance that gases must diffuse in even a large plant is not great. Each living cell in the plant is located close to the surface. While obvious for leaves, it is also true for stems. The only living cells in the stem are organized in thin layers just beneath the bark. The cells in the interior are dead and serve only to provide mechanical support.
Most of the living cells in a plant have at least part of their surface exposed to air. The loose packing of parenchyma cells in leaves, stems, and roots provides an interconnecting system of air spaces. Gases diffuse through air several thousand times faster than through water. Once oxygen and carbon dioxide reach the network of intercellular air spaces (arrows), they diffuse rapidly through them.
Oxygen and carbon dioxide also pass through the cell wall and plasma membrane of the cell by diffusion. The diffusion of carbon dioxide may be aided by aquaporin channels inserted in the plasma membrane.
Leaves
The exchange of oxygen and carbon dioxide in the leaf (as well as the loss of water vapor in transpiration) occurs through pores called stomata (singular = stoma).
Normally stomata open when the light strikes the leaf in the morning and close during the night.
The immediate cause is a change in the turgor of the guard cells. The inner wall of each guard cell is thick and elastic. When turgor develops within the two guard cells flanking each stoma, the thin outer walls bulge out and force the inner walls into a crescent shape. This opens the stoma. When the guard cells lose turgor, the elastic inner walls regain their original shape and the stoma closes.
Time Osmotic Pressure, lb/in2
7 A.M. 212
11 A.M. 456
5 P.M. 272
12 midnight 191
The table shows the osmotic pressure measured at different times of day in typical guard cells. The osmotic pressure within the other cells of the lower epidermis remained constant at 150 lb/in2 (~1000 kilopascal, kPa). When the osmotic pressure of the guard cells became greater than that of the surrounding cells, the stomata opened. In the evening, when the osmotic pressure of the guard cells dropped to nearly that of the surrounding cells, the stomata closed.
Opening stomata
The increase in osmotic pressure in the guard cells is caused by an uptake of potassium ions (K+). The concentration of K+ in open guard cells far exceeds that in the surrounding cells. This is how it accumulates:
Blue light is absorbed by phototropin which activates
a proton pump (an H+-ATPase) in the plasma membrane of the guard cell.
ATP, generated by the light reactions of photosynthesis, drives the pump.
As protons (H+) are pumped out of the cell, its interior becomes increasingly negative.
This attracts additional potassium ions into the cell, raising its osmotic pressure.
Closing stomata
❤
Roots, stems, and leaves respire at rates much lower than are characteristic of animals. Only during photosynthesis are large volumes of gases exchanged, and each leaf is well adapted to take care of its own needs.
The distance that gases must diffuse in even a large plant is not great. Each living cell in the plant is located close to the surface. While obvious for leaves, it is also true for stems. The only living cells in the stem are organized in thin layers just beneath the bark. The cells in the interior are dead and serve only to provide mechanical support.
Most of the living cells in a plant have at least part of their surface exposed to air. The loose packing of parenchyma cells in leaves, stems, and roots provides an interconnecting system of air spaces. Gases diffuse through air several thousand times faster than through water. Once oxygen and carbon dioxide reach the network of intercellular air spaces (arrows), they diffuse rapidly through them.
Oxygen and carbon dioxide also pass through the cell wall and plasma membrane of the cell by diffusion. The diffusion of carbon dioxide may be aided by aquaporin channels inserted in the plasma membrane.
Leaves
The exchange of oxygen and carbon dioxide in the leaf (as well as the loss of water vapor in transpiration) occurs through pores called stomata (singular = stoma).
Normally stomata open when the light strikes the leaf in the morning and close during the night.
The immediate cause is a change in the turgor of the guard cells. The inner wall of each guard cell is thick and elastic. When turgor develops within the two guard cells flanking each stoma, the thin outer walls bulge out and force the inner walls into a crescent shape. This opens the stoma. When the guard cells lose turgor, the elastic inner walls regain their original shape and the stoma closes.
Time Osmotic Pressure, lb/in2
7 A.M. 212
11 A.M. 456
5 P.M. 272
12 midnight 191
The table shows the osmotic pressure measured at different times of day in typical guard cells. The osmotic pressure within the other cells of the lower epidermis remained constant at 150 lb/in2 (~1000 kilopascal, kPa). When the osmotic pressure of the guard cells became greater than that of the surrounding cells, the stomata opened. In the evening, when the osmotic pressure of the guard cells dropped to nearly that of the surrounding cells, the stomata closed.
Opening stomata
The increase in osmotic pressure in the guard cells is caused by an uptake of potassium ions (K+). The concentration of K+ in open guard cells far exceeds that in the surrounding cells. This is how it accumulates:
Blue light is absorbed by phototropin which activates
a proton pump (an H+-ATPase) in the plasma membrane of the guard cell.
ATP, generated by the light reactions of photosynthesis, drives the pump.
As protons (H+) are pumped out of the cell, its interior becomes increasingly negative.
This attracts additional potassium ions into the cell, raising its osmotic pressure.
Closing stomata
❤
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The two main functions of stomata are as follows: Stomata help in exchange of gases uptake of carbon dioxide and release of oxygen. Stomata helps in the transpiration the loss of water from the surface of leaves in the form of water vapour. the role of stomata in gas exchange. ... Guard cells regulate the opening and closing of the stomata; allowing carbon dioxide and oxygen to be exchanged between the leaf and the atmosphere. The guard cells absorb water and become turgid- opening the stomata- during the day.Carbon dioxide from the air enters the plant leaves through tiny pores —mouth-like spaces that can open and close—called stomata. The oxygen left over from photosynthesis passes out of the leaves through the stomata and then into the air. Water also moves from the leaves into the air through the stomata.
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