Aprimary function of cholesterol in the plasma membranes of some animals is to a) a primary function of cholesterol in the plasma membranes of some animals is to enable the membrane to stay fluid more easily when the temperature drops. b) facilitate the removal of hydrogen atoms from saturated phospholipids. c) make the membrane more rigid, allowing it to resist pressure from outside the cell. d) facilitate cell-cell interactions by binding to receptors on neighboring cells.

to enable the membrane to stay fluid more easily when the temperature drops.

Explanation:

The lipid bilayer is made of amphipathic phospholipids. The non-polar tails of phospholipids make the core of the membrane while the polar heads are exposed to the surrounding watery medium. At lower temperatures, tight packing of non-polar tails makes the membrane more rigid. Cholesterol is an amphipathic polar head group and non-polar steroid nucleus and hydrocarbon chain.

Interaction of non-polar part of cholesterol with non-polar tails of membrane phospholipids makes the membrane less rigid at lower temperatures. Thereby, cholesterol serves as an important structural component of membranes of some organisms such as animals and helps maintain the fluidity of the membrane at lower temperatures.

i have to report this, it doesn't relate to biology

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.