Question

Ions are in low concentration outside a cell. They move rapidly into the cell via protein molecules. What term describes this action? Does it require energy?

Answer 1

there are 4 types of transport across the cell membrane
1. Diffusion- net movement of particles/molecules from HIGH concentration to LOW concentration, DOWN the concentration gradient. Does not require energy, its a PASSIVE type of transport.

2. Osmosis- net movement of WATER molecules from HIGH concentration to LOW concentration, DOWN the concentration gradient & through PARTIALLY PERMEABLE MEMBRANE. This one also is a passive type of transport which means no energy is required as movement of molecules is from high to low concentration. (REMEMBER! osmosis has to do with WATER molecules only!!!)

3. Active transport- movement of particles/molecules from LOW concentration to HIGH concentration, AGAINST the concentration gradient, using energy from respiration. As you can see this process DOES require energy (ATP) and reason is that molecules have to go from LOW to HIGH (against concentration gradient), thus need energy to do so.

ADDITIONAL (if you did learn about it)
Facilitated diffusion- same as normal diffusion accept this one requires a protein channel to go through, and each protein channel is specific to particular ions, BUT only difference is that in normal diffusion- no energy is used thus passive transport (in addition to the fact that it doesn't have to go through partially permeable membrane as when it comes to osmosis, think of when you spray perfume in one corner of the room and after some time you can smell it in the other corner of the room and whole room, so this is diffusion of perfume chemicals through air) , but in facilitated diffusion- it can be passive as well as active, so it'll require energy if active transport is needed. Example can be about roots of plant. Plants always require ions thus transport of ions has to always be there: if concentration of ions in the soil is more than in the root cells, it'll diffuse from high to low concentration into root cell and yes, through protein channels - process: facilitated diffusion. Now concentration of ions in the soil is LESS than in root cells, but plants always need ions, so it'll still need to take up that less amount of ions from the soil so this time it'll be using energy (active transport) to take up ions from low to high concentration into root cell.

Thats pretty much it, I hope you can figure it out now :)