Transport in cells
Diffusion
Diffusion is the spreading of the particles of a gas or substances in solution, resulting in a net movement of particles from a region where they are of a higher concentration to an area of a lower concentration.
Diffusion can occur in:
Air
Smells from perfume
Solution
Tea from a tea bag, dye in water
Through membranes
Small intestines, blood cells
Factors which affect the rate of diffusion.
The concentration gradient
A difference in concentration between two areas next to each other. Particles will move down the concentration gradient from high to low.
The temperature
As the temperature increases the particles in a gas or liquid gain more energy so they move faster. The hotter it is the faster the rate of diffusion.
The surface area of the membrane
A single-celled organism has a large surface area compared to its volume. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.
Adaptations in animals
Adaptations in plants
Adaptations of the small intestines
Internal surface is covered in millions of folds called villi.
Villi increase the surface area.
Villi have very good blood supply. This maintains the concentration gradient.
Membrane of the villi are very thin to allow for a short diffusion distance.
Adaptations of the lungs
Lungs contain millions of tiny air sacs called alveoli.
Alveoli increase the surface area.
Alveoli have a very good blood supply. This maintains the concentration gradient.
Membranes of the alveoli are very thin to allows for a short diffusion distance.
Adaptations of the roots
The root surface is covered in millions of root hair cells.
Root hair cells increase the surface area.
Present on the mature parts of the root.
Absorb water and minerals from the soil.
Adaptations of the leaves
Large surface area to absorb more light.
Thin so short distance for carbon dioxide to diffuse into leaf cells.
Chlorophyll absorbs sunlight for photosynthesis.
Xylem and phloem to support the leaf and transport water and glucose.
Stomata on the lower side of the leaf to allow gases to diffuse into and out of the leaf.
Osmosis
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
The rate of osmosis changes depending on the concentration gradient and temperature. Partially permeable membrane - a membrane that lets some but not all substances through.
Hypertonic, isotonic, hypotonic.
Hyper tonic - more concentrated solution than in the cells.
Isotonic - same concentration as the solution in the cell.
Hypotonic - more dilute than the solution in the cells.
Active Transport
Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). The energy is provided by respiration.
Active transport occurs in root hair cells.
The minerals are at a higher concentration in the root hair cell than in the soil. So the minerals move into the cell against the concentration gradient. :
Active transport also occurs in the gut (small intestines) sugar (glucose) molecules are absorbed from lower concentrations in the gut into the blood which has a higher sugar concentrations. The glucose is used for respiration.
