Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for _____________
(a) maintaining osmotic balance.
(b) preventing Ca2+ from altering the activity of molecules in the cytosol.
(c) providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary for their catalytic activity.
(d) maintaining a negative membrane potential.
(b) The major purpose of the Ca2+-pumps is to keep the cytosolic concentration of Ca2+ low. When Ca2+ does move into the cytosol, it alters the activity of many proteins; hence Ca2+ is a powerful signaling molecule. It is not involved in the catalytic activity of endoplasmic reticulum enzymes [choice (c)]. Because the levels of Ca2+ are very low relative to the levels of K+ and Na+, the Ca2+ gradient does not have a significant effect on the osmotic balance of the cell [choice (a)] or the membrane potential [choice (d)].
You might also like to view...
Which of these methods of heat transfer is not relevant to biological systems?
A. radiation B. conduction C. convection D. evaporation E. reflection
Suppose that a group of climate scientists claims that they can predict future impacts of global climate change with 98% accuracy. Why should you be skeptical of this claim?
A) They do not have reliable methods to measure this change. B) Their predictions are based on incomplete information about species diversity and interactions of living organisms with each other and with their environments. C) They should be focusing their predictions based only on climate change in the polar regions where the greatest effects of climate change are experienced. D) They have not accounted for abiotic factors that affect global climate change in their predictions.
For a reaction to be spontaneous it must show a net decrease in both energy and entropy.
Answer the following statement true (T) or false (F)
Which of the following adaptations was a key to allowing conifers to be successful in diverse terrestrial habitats?
A. reduction of the sporophyte B. evolution of fruit C. evolution of pollen D. evolution of vascular tissues