Diffusion can be defined as the net movement of molecules (or ions) from a region of their higher concentration to a region of their lower concentration. The molecules move down a concentration gradient.
Example: CO2 for photosynthesis
Osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
Animal cells burst in pure water, because water molecules will osmosis into the cell makes the cell swells and the cell getting bigger and bigger and finally will burst
Animal cells shrink in concentrated solutions, because water molecules will osmosis out of the cell makes the cell shrink
Plant cells do not burst in a pure water, because plant cells have a strong cell wall that keeps the cell in shape
Plant cells plasmolyse in concentrated solutions
Active Transport can be defined as the energy consuming transport of molecules or ion across the membrane against a concentration gradient (from a lower concentration to a higher concentration)