1. Abscissic acid stimulates the guard cells of stomates to close by: a. increas
ID: 210156 • Letter: 1
Question
1. Abscissic acid stimulates the guard cells of stomates to close by: a. increasing the rate of proton pumping to the point where the guard cells swell. b. releasing large quantities of ions from storage vacuoles in the guard cells which increases the solute potential of the guard cells c. activating molecular water pumps that increase the pressure potential of the guard cells. d. indirectly increasing the solute potential of guard cells so that they lose water 2. In a healthy mammalian kidney, the vasa recta serves to: a. gather water and nutrients from tissues around the nephron and return them to the bloodstream. b. move fluids and ions dissolved in them into the Malpighian tubules. c. Jorce fluids and dissolved ions in the blood through the glomerulus and into the Bowman's capsule. d. take red blood cells from the distal tubule and collecting duct and return them to the bloodstreamExplanation / Answer
The epidermis of the leaf has the guard cells that surround the stomatal pores. The opening and closing of these stomatal pores is under the regulation of signal transduction mechanisms in guard cells. The hormone abscisic acid is synthesized by plants in response to the stress induced by drought and the hormone triggers the closure of stomatal pores during conditions of drought stress. A signaling cascade is triggered in guard cells in response to abscisic acid which involves the increase of cytosolic calcium. Elevated calcium ions activate anion channels that result in potassium ion efflux from guard cell vacuoles to the cell exterior. This results in membrane depolarization and loss of turgor pressure in the guard cells resulting in the closure of stomata. So, the correct option is option B, releasing large quantities of ions from storage vacuoles in the guard cells, which increases the solute potential of the guard cells. Parallel to the loop of Henle of the juxtamedullary nephrons are located the long and thin-walled vessels known as the vasa recta. Vasa recta, by countercurrent exchange mechanism, reabsorb fluids and solutes in medulla and return them to the blood stream. They also help in the maintenance of NaCl gradient between cortex and medulla of the kidney. So, the correct option is option A, gather water and nutrients from tissues around the nephron and return them to the blood stream.
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