osmosis & active transport

Question 1

definition of osmosis?

Answer 1

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

Question 2

osmosis is a special type of diffusion. it’s only ever used to describe the ________ __ _____ _________ across a ________

Answer 2

osmosis is a special type of diffusion. it’s only ever used to describe the movement of water molecules across a membrane

Question 3

when are water molecules no longer considered free water molecules in the cup with sugar (pg 56 topic notes)?

Answer 3

• 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

Question 4

remember that we have to say overall movement, as particles move randomly, in all directions

Answer 4

ok

Question 5

what is ‘water potential’?

Answer 5

it’s a measure of the concentration of free water molecules in a solution

Question 6

what’s the water potential of pure water?

Answer 6

zero

Question 7

what happens to the water potential when a solute is added?

Answer 7

WP falls as there’ll be a lower concentration of free water molecules. concentrated solutions have very low WP

Question 8

what’s an isotonic solution?

Answer 8

where the solution outside the cell has same WP as inside cell - no net movement

Question 9

what’s a hypotonic solution?

Answer 9

where solution outside the cell has higher WP than inside cell - net movement of free water molecules into cell

Question 10

what’s a hypertonic solution?

Answer 10

where solution outside the cell has lower WP than inside cell - net movement of free water molecules out of the cell

Question 11

what happens if a plant cell is placed in a hypotonic solution, or water?

Answer 11

• 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

Question 12

what happens if an animal cell is placed in a hypotonic solution/water?

Answer 12

• water moves into cell by osmosis
• it bursts, doesn’t have cell wall which can withstand large amount of water pressure
• becomes lysed

Question 13

why do plants wilt?

Answer 13

because there’s not enough water to fill their cells, therefore the cytoplasm shrinks from the cell wall

Question 14

definition of active transport?

Answer 14

the movement of molecules from an area of low concentration to an area of high concentration using ATP (against concentration gradient)

Question 15

what is active transport used for?

Answer 15

• glucose absorbed by AT in small intestine
• plants use AT in root hair cells to absorb mineral ions

Question 16

what’s an experiment to investigate the factors affecting the rate of osmosis?

Answer 16

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

Question 17

how could you use the potato experiment to explore the effect of concentration gradient on the rate of osmosis?

Answer 17

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

Question 18

why do plant and animal cells react differently to being placed in different concentrations?

Answer 18

because plant cells have a cell wall which can withstand a large amount of water pressure - animal cells would burst

Question 19

what are the states of an animal cell in a hypotonic, isotonic, and hypertonic solution?

Answer 19

lysed (burst), normal, shrivelled

Question 20

what are the states of a plant cell in a hypotonic, isotonic, and hypertonic solution?

Answer 20

turgid, flaccid, plasmolyzed

Question 21

what’s a partially permeable membrane?

Answer 21

a membrane that only lets certain particles through

Question 22

what’s the definition for diffusion?

Answer 22

the random movement of particles from an area of high concentration to an area of low concentration

Question 23

2.16 what factors affect the rate of movement of substances into/out of cells?

Answer 23

1. temp
2. concentration gradient
3. distance
4. SA:vol ratio

Question 24

2.16 what effect does increasing the SA:vol ratio have on the rate of movement of substances into/out of cells and why?

Answer 24

• increases rate
• because an efficient exchange surface has a SA which is very large compared to the distance the molecules must travel

Question 25

2.16 what effect does decreasing the distance have on the rate of movement of substances into/out of cells and why?

Answer 25

• 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

Question 26

2.16 what effect does increasing the temperature have on the rate of movement of substances into/out of cells and why?

Answer 26

• increases the rate
• at higher temps, molecules have more kinetic energy and so move faster, therefore diffusion/osmosis/whatever occurs faster

Question 27

2.16 what effect does increasing the concentration gradient have on the rate of movement of substances into/out of cells and why?

Answer 27

• increases rate
• if there’s a very large difference in conc. between two areas, molecules will diffuse from higher to lower conc. quickly

Question 28

2.17 investigate diffusion using living and non-living systems

Answer 28

• 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