diffusion, osmosis, active transport large 4.1.3.1, 4.1.3.2, 4.1.3.3

what is diffusion

the net movement of particles from an area of high concentration to an area of low concentration

osmosis

the net movement of water particles from an area of high water concentration to an area of low water concentration through a partially permeable membrane

active transport

the net movement of particles from an area of low concentration to an area of high concentration using energy from respiration

why can unicellular organisms rely on diffusion

they have large surface area to volume ratios so the distance from the surface of the organism to the centre is small. Diffusion works out a sufficient rate to exchange substances.

why do multicellular organisms need transport systems

they have small surface area to volume ratio so the distance from the surface to the centre is large so diffusion cannot occur at a sufficient rate to meet the needs of the organism

exchange surfaces in animals

lungs and alveoli for gas exchange, small intestine and villi for absorption for digested food

transport systems in animals

the blood and circulatory system that carries necessary substances around the body

exchange surfaces in plants

roots and root hairs where mineral ions and water are absorbed, leaves for gas exchange

transport systems in plants

xylem which moves water and mineral ions from roots to shoots, phloem which moves sugars and amino acids to where they are needed in plants