What makes/what causes the opening and closing of stomata?

Answer 1

A basic answer is that the guard cells have chloroplasts and can carry on photosynthesis while the surrounding epidermal cells have no chloroplasts.

In light:
-- Guard cells photosynthesize and make glucose.
-- More glucose in guard cells causes more water to diffuse into the cells than out of the cells.
-- Guard cells swell up as water pressure builds inside them.
-- Guard cells have a thicker cell wall on the inner side (next to the stoma) and a thinner cell wall on the outer side (away from the stoma), so a guard cell swells unevenly and becomes kind of curved or bent. The pair of guard cells bend in such a way that it leaves a gap between them which is the stoma.

In dark:
-- No photosynthesis. Guard cells use their glucose during cellular respiration.
-- More water diffuses out of the guard cells than into them.
-- The guard cells relax into a rather straight shape, so the gap between them (the stoma) closes.

Answer 2

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RE:
What makes/what causes the opening and closing of stomata?

Answer 3

The stomatal opening and closing depends upon the photosynthetic activity of guard cells. The photosynthetic activity results in K ion exchange by the guard cells, which inturn results in taking and giving out the water by guard cells. The tugidity changes in the guard cells set the stomata open and close during day and night respectively.

Answer 4

Stomata: controls the exchange of gases. Carbon dioxide is absorbed, while oxygen and
water vapor are released (by evaporation).

Stomata openings are controlled by guard cells.

Guard Cells: open and close in response to environmental conditions such as light, temp and humidity.

In hot conditions the guard cells close (swell up) to limit or stop water from being lost and "drying out" the tree or plant.

The water evaporation in "normal" weather conditiond helps cool the tree.

Answer 5

From the website "Science And Plants for Schools) ....There are many factors which lead to stomata opening and closing.

i) There is an endogenous rhythm (a biological clock). Stomata open during the day and close during the night. (Though certain succulents which are native to hot, dry conditions have a reversed rhythm to enable them to economise on water loss.) However, stomata continue to open and close on an approximately 24 hour clock (circadian = about a day) even when switched to continuous light. The phase of this opening and closure can be shifted (made to occur at other times of the day) by contol of the end of the dark period.

ii) The water balance of a plant affects stomatal apperture. Wilting plants close their stomata. The plant growth regulator abscisic acid (ABA) seems to act as a mediator under these conditions. Water stress in the roots can transmit (in xylem?) its influence to stomata in leaves by the signal of ABA.

iii) Low concentrations of CO2 cause stomata to open. If CO2-free air is blown across stomata in darkness, their stomates open. High CO2 causes stomates to close.

iv) Light causes stomates to open. The minimum light level for opening of stomates in most plants is 1/1000 to 1/30 of full sunlight, just enough to cause some net photosynthesis. Blue light (430-460nm) is nearly 10 times as effective as red light (630-680nm). The wavelengths that are effective in the red part of the spectrum are the same as those that are effective in photosynthesis ie is absorbed by chlorophyll. However, the blue light effect is quite independent of photosynthesis. Photosynthesis will change intercellular CO2 concentrations and may have its effect through number iii) above.

So, how are these movements brought about?

Blue-light wavelengths of daylight, detected by zeaxanthin (a carotenoid) activate proton pumps in the guard cell membranes, which proceed to extrude protons from the cytoplasm of the cell; this creates a "proton motive force" (an electrochemical gradient across the membrane) which opens voltage operated channels in the membrane, allowing positive K ions to flow passively into the cell, from the surrounding tissues. Chloride ions also enter the cell, with their movement coupled to the re-entry of some of the extruded protons (Cl/H symport) to act as a counter-ions to the potassium. Water passively follows these ions into the guard cells, and as their tugidity increases so the stomatal pore opens, in the morning. As the day progresses the osmotic role of potassium is supplanted by that of sucrose, which can be generated by several means, including starch hydrolysis and photosynthesis. At the end of the day (by which time the potassium accumulation has dissipated) it seems it is the fall in he concentration of sucrose that initiates the loss of water and reduced turgor pressure, which causes closure of the stomatal pore.

ABA also seems to trigger a loss of K ions from guard cells. Some workers suggest that in some species, ABA alters turgor pressure without changing solute potential or water potential.

There is evidence of a role for increased cytoplasmic calcium (Ca2+) in closure, possibly by effects on opening/closing of ion channels at the plasma membrane.

Starch break down to phosphoenol pyruvate (PEP) is stimulated by blue light. This PEP then combines with CO2 to fom oxaloacetic acid, which is converted to malic acid. It is H ions from the malic acid which leave the cell in the mechanism outlined above. Thus the intake of K ions is matched by formation of anions from malic acid in the guard cells. This causes an increase in osmotically active substances in exchange for the breakdown of starch in guard cells.

Hope that helped ya...

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