Cell must and in order to survive.
means that certain particles are allowed to pass through the membrane while others not.
diffusion always occurs a concentration gradient! rate of diffusion depends on and

Well let's see...cells have to maintain some sort of nutrition usually in the form of glucose. Cells also need to be able to dispose of wast products, so I think for 1 and 2 you could say eat and purge wastes. For the third blank, a membrane is said to be semipermeable meaning that it will let in some things and not others. For the fourth blank...diffusion occurs down a concentration gradient, and it does depend on temperature and concentration. Hope this helps!