Transport Across Membrane Notes 2014
BIOLOGY – TRANSPORT ACROSS MEMBRANE
define diffusion and describe its role in nutrient uptake and gaseous exchange in plants and humans
define osmosis and describe the effects of osmosis on plant and animal tissues
define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi
.
A cell is surrounded by a layer of cell surface membrane. This phospholipid bilayer makes a very effective barrier, separating the cell interior from the exterior. This cell surface membrane prevents the movement of water-soluble molecules and ions, preventing the aqueous contents of the cell from escaping. Transport processes across the cell surface membrane are essential for the efficient exchange of molecules between the cell and its environment.
(A) Diffusion
Diffusion is the net movement of molecules (or ions) from a region of higher concentration to a region of lower concentration. The molecules move down its concentration gradient (high to low concentration). Diffusion is a passive process that does not require energy input from ATP.
1
Factors affecting the rate of diffusion:
‘steepness’ of the concentration- the greater the difference in concentrations between the two regions, the greater the difference in the number of molecules moving in the two direction and hence the faster the rate at which the substances diffuse.
Temperature – at higher temperatures, molecules and ions gain more kinetic energy than at lower temperature. Molecules moving at higher speed and enable diffusion to occur faster.
Surface area – the greater the surface area, the more molecules or ions can cross it at any one point in time, thereby increasing the rate of diffusion.
Size of molecules – large molecules require more energy to get them to move while smaller molecules require lesser energy.
Facilitated diffusion is a
define diffusion and describe its role in nutrient uptake and gaseous exchange in plants and humans
define osmosis and describe the effects of osmosis on plant and animal tissues
define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi
.
A cell is surrounded by a layer of cell surface membrane. This phospholipid bilayer makes a very effective barrier, separating the cell interior from the exterior. This cell surface membrane prevents the movement of water-soluble molecules and ions, preventing the aqueous contents of the cell from escaping. Transport processes across the cell surface membrane are essential for the efficient exchange of molecules between the cell and its environment.
(A) Diffusion
Diffusion is the net movement of molecules (or ions) from a region of higher concentration to a region of lower concentration. The molecules move down its concentration gradient (high to low concentration). Diffusion is a passive process that does not require energy input from ATP.
1
Factors affecting the rate of diffusion:
‘steepness’ of the concentration- the greater the difference in concentrations between the two regions, the greater the difference in the number of molecules moving in the two direction and hence the faster the rate at which the substances diffuse.
Temperature – at higher temperatures, molecules and ions gain more kinetic energy than at lower temperature. Molecules moving at higher speed and enable diffusion to occur faster.
Surface area – the greater the surface area, the more molecules or ions can cross it at any one point in time, thereby increasing the rate of diffusion.
Size of molecules – large molecules require more energy to get them to move while smaller molecules require lesser energy.
Facilitated diffusion is a