Which molecules dramatically increases the rate of diffusion of water across cell membranes?

AQUAPORINS dramatically increases the rate of diffusion of water across cell membranes.

Explanation:

Aquaporins are integral membrane proteins also called water channels that forms pores in the membrane mainly for facilitating diffusion of water molecules in and out of the cell. Aquaporins selectively allow the passage of water molecules while preventing the passage of ions and other solutes through it as they are impermeable to protons, and large solutes. These proteins therefore increases the permeability of the membrane to water molecules and the rate of diffusion of water increases through them. Flow of water molecules in aquaporins follows the direction of osmotic pressure across the membrane. Aquaporins in some organisms have been modified to voltage gated aquaporins which helps them to close the water channels in unfavorable conditions such as drought and flooding. This is to prevent excessive loss of water to the surrounding or intake of water into the cells.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.