UNIT 3: MOVEMENT IN AND OUT OF CELL
Diffusion: the net movement of molecules and ions from region of high
concentration to region of lower concentration, down a concentration gradient as
result of random movement
Factors that affect the rate of diffusion
o Higher temperature -> diffuse faster
o Larger surface area -> diffuse faster
o When the concentration gradient across which the diffusion is occurring is
greatest -> fastest
o Short distance -> diffuse faster
Energy for diffusion comes from the kinetic energy of random movement of
molecules and ions
Substances move into and out of cells by diffusion through the cell membrane
Importance of diffusion:
o Oxygen and carbon dioxide diffuse in and out through the stomata of the leaf
o Products of digestion are absorbed from the ileum of mammals by diffusion
o Flowering plant uses diffusion to attract pollinators
Osmosis: the net movement of water molecules from region of higher water
potential (dilute solution) to a region of lower water potential (concentrated
solution), through a partially permeable membrane
Osmosis and animal cell
If the solution inside the cell is more concentrated than the solution outside then
water diffuse in through the partially permeable membrane. The cell bursts
If the solution inside the cell is less concentrated, more dilute than the solution
outside then water diffuse out through the partially permeable membrane. The
cell shrinks
Osmosis and plant cell
If the solution inside the cell is more concentrated than the solution outside then
water diffuses in. The cell is turgid (tight and firm)
Plants are supported by the turgor pressure (water pressure acting against
inelastic cell wall) within cells
If the solution inside the cell is less concentrated than the solution outside then
water diffuses out. The cell becomes flaccid and eventually be plasmolysed
( cell membrane pull away from cell wall, leave spaces between)
Active transport: the movement of molecules and ions in or out of the cell through
the cell membrane against a concentration gradient, using energy from
respiration
Cells that undergo active transport have a large number of mitochondria
When the ions needed for a plant’s metabolism may be in very short supply in
the soil water, ions are absorbed by roots hair cells by active transport
Digested food is absorbed by epithelial cells of the villi by active transport in
small intestine
Diffusion: the net movement of molecules and ions from region of high
concentration to region of lower concentration, down a concentration gradient as
result of random movement
Factors that affect the rate of diffusion
o Higher temperature -> diffuse faster
o Larger surface area -> diffuse faster
o When the concentration gradient across which the diffusion is occurring is
greatest -> fastest
o Short distance -> diffuse faster
Energy for diffusion comes from the kinetic energy of random movement of
molecules and ions
Substances move into and out of cells by diffusion through the cell membrane
Importance of diffusion:
o Oxygen and carbon dioxide diffuse in and out through the stomata of the leaf
o Products of digestion are absorbed from the ileum of mammals by diffusion
o Flowering plant uses diffusion to attract pollinators
Osmosis: the net movement of water molecules from region of higher water
potential (dilute solution) to a region of lower water potential (concentrated
solution), through a partially permeable membrane
Osmosis and animal cell
If the solution inside the cell is more concentrated than the solution outside then
water diffuse in through the partially permeable membrane. The cell bursts
If the solution inside the cell is less concentrated, more dilute than the solution
outside then water diffuse out through the partially permeable membrane. The
cell shrinks
Osmosis and plant cell
If the solution inside the cell is more concentrated than the solution outside then
water diffuses in. The cell is turgid (tight and firm)
Plants are supported by the turgor pressure (water pressure acting against
inelastic cell wall) within cells
If the solution inside the cell is less concentrated than the solution outside then
water diffuses out. The cell becomes flaccid and eventually be plasmolysed
( cell membrane pull away from cell wall, leave spaces between)
Active transport: the movement of molecules and ions in or out of the cell through
the cell membrane against a concentration gradient, using energy from
respiration
Cells that undergo active transport have a large number of mitochondria
When the ions needed for a plant’s metabolism may be in very short supply in
the soil water, ions are absorbed by roots hair cells by active transport
Digested food is absorbed by epithelial cells of the villi by active transport in
small intestine
