Question

can someone explain to me the magic of osmosis in layman's terms? :D

Answer 1

Basically what you need to know is that if you have a semi-permeable membrane (e.g. a cell membrane) in between an area with a high concentration of things dissolved in water (e.g. salt or sugar or whatever else) and an area with a lower concentration of things dissolved in water, water will flow from the area with the low solute concentration to the high solute concentration in order to get the same concentration of solutes (those are the things dissolved) on both sides.

In a cell, this can be either good or bad. If you have an animal cell and put it in water with a low concentration of solutes, the cell will burst because water will rush through the membrane: cells always have lots of things dissolved inside them and water goes from an area of low solute concentration to high solute concentration to try and balance things out. A lot of single-celled organisms have contractile vacuoles to pump excess water out so they don't burst when they're swimming around in fresh water.

Plant cells, however, have cell walls, so if water rushes in, that isn't necessarily a bad thing. As long as it's not TOO much, the cell wall can deal with the pressure from the extra water inside the cell and this can actually give the plant more rigidity.

On the other hand, if you put a cell in water with a LOT of things dissolved in it, e.g. salt water, the cell might shrivel up because water rushes out of the cell.

Here I've drawn a cell in different types of solutions (Isotonic is the ideal and basically means there's the same solute concentration inside and outside the cell) with the direction of water flow.