Movement of Substances Flashcards
what is diffusion?
net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is reached
*diffusion is only for fluids (at this level of syllabus)
*movement of particles are random
what is net movement?
overall movement of particles when the movement of particles in one direction is greater than the movement of particles in the opposite direction
what is equilibrium?
when both regions being compared have the same concentration
what is a concentration gradient?
difference in concentration between two regions
what is diffusion distance?
distance through which a substance has to pass
what happens to particles when diffusion is complete (i.e. concentration in both regions are the same)?
even at equilibrium, particles are moving, just no net movement
what are 5 factors affecting the rate of diffusion?
1) concentration gradient
2) diffusion distance
3) surface-area-to-volume ratio
4) temperature
5) particle size
how does the concentration gradient affect the rate of diffusion?
the steeper the concentration gradient, the faster the rate of diffusion (directly proportional)
how does the diffusion distance affect the rate of diffusion?
the shorter the diffusion distance, the faster the rate of diffusion (inversely proportional)
*kept short in living organisms by having a one-cell thick area for exchange of substances
how does the surface-area-to-volume ratio affect the rate of diffusion?
the higher the surface-area-to-volume ratio, the faster the rate of diffusion (directly proportional)
*smaller cell = increased surface-area-to-volume ratio
how does the temperature affect the rate of diffusion?
the higher the temperature, the faster the rate of diffusion (directly proportional)
how does the (diffusing) particle size affect the rate of diffusion?
the smaller the size of the diffusing particle, the faster the rate of diffusion (inversely proportional)
how does diffusion play a part in gaseous exchange in human lungs?
oxygen diffuses down a concentration gradient from air spaces in the lungs across the one-cell thick capillary walls into the red blood cells
how does diffusion play a part in gaseous exchange in plant roots?
oxygen diffuses down a concentration gradient from soil directly into root hair cell
how does diffusion play a part in absorption in the human small intestine?
epithelial cells lining small intestine have folds in their membranes which increase surface-area-to-volume ratio for faster rate of absorption of substances from lumen of small intestine
what is osmosis?
net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
what does a partially permeable membrane do?
allows some substances to pass through it but not others
what is water potential?
tendency of water to move from one place to another
*distilled water has the highest water potential
*a water potential gradient is established when there is a partially permeable membrane separating two solutions of different water potentials
what are the 4 factors affecting osmosis?
1) water potential gradient
2) distance
3) surface-area-to-volume ratio
4) temperature
how does the concentration gradient affect the rate of diffusion?
the steeper the concentration gradient, the faster the rate of osmosis (directly proportional)
how does the distance (i.e. thickness of PPM) affect the rate of osmosis?
the shorter the distance, the faster the rate of osmosis (inversely proportional)
how does the surface area of the PPM affect the rate of osmosis?
the greater the surface area of the PPM, the faster the rate of osmosis (directly proportional)
how does the temperature affect the rate of osmosis?
the higher the temperature, the faster the rate of osmosis (directly proportional)
what happens to a plant cell in a hypotonic (higher water potential) solution?
cell sap in vacuole has a lower water potential than surrounding solution and water enters cell by osmosis
cell expands and becomes turgid (cell wall prevents bursting)
*turgidity only applies to plant cells as animal cells lyse
what happens to a red blood cell in a hypotonic (higher water potential) solution?
cytoplasm has a lower water potential than surrounding solution and water enters cell by osmosis
cell expands and bursts (lyses)
what happens to a plant cell in a hypertonic (lower water potential) solution?
cell sap in vacuole has a higher water potential than surrounding solution and water leaves cell by osmosis
cell becomes flaccid and as cytoplasm and cell membrane shrink away from cell wall, cell becomes plasmolysed
*plasmolysis only applies to plant cells as animal cells crenate
what happens to a red blood cell in a hypertonic (lower water potential) solution?
cytoplasm has a higher water potential than surrounding solution and water leaves cell by osmosis
cell shrinks in size and is crenated
what is the importance of turgor pressure especially in herbaceous (non-woody) plants?
plasmolysis causes plant tissue to become limp or flaccid and plant wilts
water can be added to soil to dilute the soil solution, causing water molecules to enter plant cells, making them turgid and keeps the plant firm and upright
what are 3 differences between diffusion and osmosis?
diffusion:
1) movement of particles
2) PPM not required
3) down concentration gradient
osmosis:
1) movement of water molecules
2) PPM required
3) down water potential gradient
what is active transport?
movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration against a concentration gradient using energy from respiration
*requires energy from respiration; only occurs in living cells
how does active transport play a role in plant cells?
dissolved mineral salts are taken up by root hair cells via active transport and diffusion
what are 3 differences between diffusion and active transport?
diffusion:
1) cell membrane not required
2) down concentration gradient
3) energy from respiration not required (passive transport)
active transport:
1) cell membrane required
2) against concentration gradient
3) energy from respiration required
