osmosis & active transport Flashcards
2.15 definition of osmosis?
osmosis is the net diffusion of free water molecules from an area of high water concentration to an area of low water concentration, across a partially permeable membrane
osmosis is a special type of diffusion. it’s only ever used to describe the ________ __ _____ _________ across a ________
osmosis is a special type of diffusion. it’s only ever used to describe the movement of water molecules across a membrane
when are water molecules no longer considered free water molecules in the cup with sugar (pg 56 topic notes)?
- when the sugar dissolves, water molecules attracted to sugar molecules
- they’re now not considered free
- therefore there are less free water molecules in that beaker
remember that we have to say overall movement, as particles move randomly, in all directions
ok
what is ‘water potential’?
it’s a measure of the concentration of free water molecules in a solution
what’s the water potential of pure water?
zero
what happens to the water potential when a solute is added?
WP falls as there’ll be a lower concentration of free water molecules. concentrated solutions have very low WP
what’s an isotonic solution?
where the solution outside the cell has same WP as inside cell - no net movement
what’s a hypotonic solution?
where solution outside the cell has higher WP than inside cell - net movement of free water molecules into cell
what’s a hypertonic solution?
where solution outside the cell has lower WP than inside cell - net movement of free water molecules out of the cell
what happens if a plant cell is placed in a hypotonic solution, or water?
- water moves into cell by osmosis
- it becomes turgid
- doesn’t burst, because it has a cell wall which can withstand large amount of water pressure
what happens if an animal cell is placed in a hypotonic solution/water?
- water moves into cell by osmosis
- it bursts, doesn’t have cell wall which can withstand large amount of water pressure
- becomes lysed
why do plants wilt?
because there’s not enough water to fill their cells, therefore the cytoplasm shrinks from the cell wall
2.15 definition of active transport?
the movement of molecules from an area of low concentration to an area of high concentration using ATP (against concentration gradient)
what is active transport used for?
- glucose absorbed by AT in small intestine
- plants use AT in root hair cells to absorb mineral ions
what’s an experiment to investigate the factors affecting the rate of osmosis?
potato chips can be placed in sucrose/salt solutions of diff. concentrations
osmosis will occur until WP of tissue & solution =, this causes a mass change
- if solution has higher water conc., water moves into potato chip & mass increases
- if solution has lower water conc., water moves out of potato chip & mass decreases
this method can be used to determine the WP of the potato. if there’s no change in mass, the conc. of solution is same as conc. of the cytoplasm
how could you use the potato experiment to explore the effect of concentration gradient on the rate of osmosis?
by leaving it for a short time (e.g. 20 mins), the potato chips in solutions where the conc. has biggest difference to the cytoplasm will experience biggest mass changes
why do plant and animal cells react differently to being placed in different concentrations?
because plant cells have a cell wall which can withstand a large amount of water pressure - animal cells would burst
what are the states of an animal cell in a hypotonic, isotonic, and hypertonic solution?
lysed (burst), normal, shrivelled
what are the states of a plant cell in a hypotonic, isotonic, and hypertonic solution?
turgid, flaccid, plasmolyzed
what’s a partially permeable membrane?
a membrane that only lets certain particles through
2.15 what’s the definition for diffusion?
the random movement of particles from an area of high concentration to an area of low concentration
2.16 what factors affect the rate of movement of substances into/out of cells?
- temp
- concentration gradient
- distance
- SA:vol ratio
2.16 what effect does increasing the SA:vol ratio have on the rate of movement of substances into/out of cells and why?
- increases rate
- because an efficient exchange surface has a SA which is very large compared to the distance the molecules must travel
2.16 what effect does decreasing the distance have on the rate of movement of substances into/out of cells and why?
- increases rate
- because the molecules don’t have to travel as far
- also molecules don’t travel in a straight line, so a large distance would be really slow
2.16 what effect does increasing the temperature have on the rate of movement of substances into/out of cells and why?
- increases the rate
- at higher temps, molecules have more kinetic energy and so move faster, therefore diffusion/osmosis/whatever occurs faster
2.16 what effect does increasing the concentration gradient have on the rate of movement of substances into/out of cells and why?
- increases rate
- if there’s a very large difference in conc. between two areas, molecules will diffuse from higher to lower conc. quickly
2.17 investigate diffusion using living and non-living systems
- agar cubes of diff. sizes can be used to demonstrate relationship between SA:vol ratio & rate of diffusion
- cubes contain alkali & an indicator, they’re then placed in an acid
- as acid diffuses into cube it reacts w alkali, this neutralisation turns the indicator colourless
- the smallest (0.5cm length) cube becomes colourless quickest
