3 major routes by which substances can cross membranes?

What can pass through pores and channels in the lipid layer?

Polar molecules are those with an.........charge distribution. They have positive and negative ends.

Pore size is about ......in diameter?

What substances diffuse through the lipid membrane?

With simple diffusion and dissolving in the lipid membrane the rate of movement is in ........proportion to the concentration gradient across the membrane.

However, with carrier mediated (facilitated) diffusion there is ........increase in rate of movement at a higher concentration gradient.

There are ......molecules which become saturated at higher concentrations.

What process maintains the concentration difference across the membrane?

The active transport systems are known as...

What does the active transport system need in order to work?