The cell membrane is selectively permeable, meaning only certain substances can pass through it. The cell membrane is made up of proteins and phospholipids.
High concentration to a Low concentration requires no energy. This is passive transport.
Low concentration to High concentration requires energy. This is active transport.
Diffusion is the movement of molecules from an area of of High concentration to a area of Low concentration. This is a passive process and does NOT require energy,
Active transport is the movement of molecules or ions against a concentration gradient. This uses membrane proteins. This is an active process and requires energy.
Proteins in the cell membrane are responsible for moving molecules through active transport.
When you place an animal cell into a water concentration that is higher than outside the cell, water will enter the cell and the cell will swell up and burst due to Osmosis.
If you place an animal cell into a water concentration that is lower than inside the cell, water will exit the cell and it will shrink.
If you place a plant cell into a water concentration that is higher outside, water will move into the cell and the cell will become turgid.
If you place a plant cell into a water concentration that is lower outside, water will exit the cell and the cell will become plasmoyed.
Osmosis is the movement of molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane.