Question

How do substances like carbon dioxide and water move in and out of the cell?

Answer 1

Movement of carbon dioxide:

1. ${CO}_2$ is gaseous molecule and hence it moves in and out of the cell freely by simple diffusion.
2. Diffusion is a process in which the molecules interact and move from a region of higher concentration to a region of lower concentration.
3. This process does not involve any requirement of energy since carbon dioxide can freely move through the cell membrane.​

Movement of water:

1. $H_{2}O$ moves in and out of the cell by osmosis which is a form of diffusion.
2. In osmosis, the water molecules move from lower solute concentration to higher solute concentration through the cell membrane. i,e. the water molecules move from the region of their higher concentration to lower concentration.
3. Therefore, movement of water requires a concentration gradient but no energy.​