The plant hormone ABA (abscisic acid), which is transported from roots to leaves in the xylem stream when soils begin to dry out, causes the turgor pressure of guard cells toand the stoma toa. increase; openb. decrease; openC.increase; closed. decrease; close
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ABA induces closure of stomata by: A. Increasing the ion concentration of the guard cells B. Increasing the activity of the H+ pumps C. Increasing the amount of water in the stomata D. Inactivating the H+ pumps ABA induces closure of stomata by inactivating H+ pumps, which leads to the opening of outward A. The Έs of the cell has not changed. B. Guard cells have a lower Έs C. Guard cells have a higher Έs Which of these conditions would tend to cause leaf stomata to be open? A. hot, dry conditions B. low levels of blue light and abscisic acid (ABA) C. low levels of blue light and high levels of abscisic acid (ABA) D. high levels of blue light and low levels of abscisic acid (ABA) E. high levels of blue light and abscisic acid (ABA)
Adi S.
What evidence suggests that ABA from roots can signal guard cells to close? a. If roots are given sufficient water, guard cells close anyway. b. If roots are dry, guard cells begin to close-even though leaves are not experiencing water stress. c. Applying ABA on guard cells directly causes them to close. d. If roots are dry, ABA concentrations in leaf cells drop dramatically.
In plant stomata (guard cells) ABA triggers an increase in cytosolic calcium (Ca2+) which activates anion channels (A-) allowing Cl- to leave the cell. ABA activates channels that move potassium out of the cell (K+out) and inhibits channels that move potassium into the cell (K+in). The net result is a large movement of ions out of the cell. This signalling ultimately allows for the stomata to close preventing water loss. How does the movement of ions out of the guard cells allow for the guard cells to close? a.) As the ions leave the cell, water enters the cell (by osmosis), causing the cells to lose volume and close over the pore. b.) As ions leave the cell, so does water (by osmosis), causing the cells to lose volume and close over the pore. c.) As ions leave the cell, so does water (by osmosis), and the cells are able to build up more osmo-protectants within the cells.
Madhur L.
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