- Movemet of water from high concentration of water (dilute) to low concentration of water (concentrated) through a partially permeable membrane.
- Partially permeable means some substance can pass through while other's can't. This is because molecules are different sizes, water is relatively very small.
- Used in root hair cells.
Key point: ONLY WITH WATER!
- Spreading particles of gas (or any substance in solution).
- Movement is random but Net movemet is from High concentration to low concentration.
- Used in respiration for oxygen to enter cells.
- Substances move against concentration gradient (from low to high concentration).
- To do this cell use energy from respiration.
- Used by plants to absorb ions when they are in a very dilute solution.
- Used so sugar and ions can pass through cell membranes.
- Sugar absorbed from the intestine and from the kidney tubules this way.
Exchanging Materials in humans
Humans have organ systems which are specialised to help the exhange of materials, E.G.
Villi in small intestine
- Massive surface area
- Extensive network of capillaries
- Uses diffusion AND active transport
Alveoli in lungs
- Large moiste surface area
- Excellent blood supply
- Carbon dioxide diffuses from your blood to your alveoli
- Oxygens diffused from your alveoli into your blood.
The breathing system
Ribcage: Protects heart and lungs
Diaphragm: Muscular sheet which divides your thorax (heart and lungs) and your abdomen (tummy area).
Trachea: Air comes down your trachea to your lungs. It has rings ("C" shaped) of cartilage to prevent it from collapsing but allowig room for stretch.
Your trachea splites into two bronchi then lots and lots of bronchioles. Brionchioles split into alveoli.
Exchanging materials in plants.
- Leaves broad and thin and flat with lots of internal air spaces. This means they have a large surface area therefore efficient at photosynthesis.
- Stomata on the bottom of leaves let carbon dioxide in and oxygen out (by diffusion) during photosynthesis.
- Opening stomata lets water vapour out (via evaporation) which is bad for the plant. This is transpiration.
- Transpiration is quicker when it's hot, dry and/or windy, so guard cells carefully choose how much to open the stomata in these conditions.