Movement of Substances

Question 1

what is diffusion?

Answer 1

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

Question 2

what is net movement?

Answer 2

overall movement of particles when the movement of particles in one direction is greater than the movement of particles in the opposite direction

Question 3

what is equilibrium?

Answer 3

when both regions being compared have the same concentration

Question 4

what is a concentration gradient?

Answer 4

difference in concentration between two regions

Question 5

what is diffusion distance?

Answer 5

distance through which a substance has to pass

Question 6

what happens to particles when diffusion is complete (i.e. concentration in both regions are the same)?

Answer 6

even at equilibrium, particles are moving, just no net movement

Question 7

what are 5 factors affecting the rate of diffusion?

Answer 7

1) concentration gradient
2) diffusion distance
3) surface-area-to-volume ratio
4) temperature
5) particle size

Question 8

how does the concentration gradient affect the rate of diffusion?

Answer 8

the steeper the concentration gradient, the faster the rate of diffusion (directly proportional)

Question 9

how does the diffusion distance affect the rate of diffusion?

Answer 9

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

Question 10

how does the surface-area-to-volume ratio affect the rate of diffusion?

Answer 10

the higher the surface-area-to-volume ratio, the faster the rate of diffusion (directly proportional)

*smaller cell = increased surface-area-to-volume ratio

Question 11

how does the temperature affect the rate of diffusion?

Answer 11

the higher the temperature, the faster the rate of diffusion (directly proportional)

Question 12

how does the (diffusing) particle size affect the rate of diffusion?

Answer 12

the smaller the size of the diffusing particle, the faster the rate of diffusion (inversely proportional)

Question 13

how does diffusion play a part in gaseous exchange in human lungs?

Answer 13

oxygen diffuses down a concentration gradient from air spaces in the lungs across the one-cell thick capillary walls into the red blood cells

Question 14

how does diffusion play a part in gaseous exchange in plant roots?

Answer 14

oxygen diffuses down a concentration gradient from soil directly into root hair cell

Question 15

how does diffusion play a part in absorption in the human small intestine?

Answer 15

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

Question 16

what is osmosis?

Answer 16

net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

Question 17

what does a partially permeable membrane do?

Answer 17

allows some substances to pass through it but not others

Question 18

what is water potential?

Answer 18

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

Question 19

what are the 4 factors affecting osmosis?

Answer 19

1) water potential gradient
2) distance
3) surface-area-to-volume ratio
4) temperature

Question 20

how does the concentration gradient affect the rate of diffusion?

Answer 20

the steeper the concentration gradient, the faster the rate of osmosis (directly proportional)

Question 21

how does the distance (i.e. thickness of PPM) affect the rate of osmosis?

Answer 21

the shorter the distance, the faster the rate of osmosis (inversely proportional)

Question 22

how does the surface area of the PPM affect the rate of osmosis?

Answer 22

the greater the surface area of the PPM, the faster the rate of osmosis (directly proportional)

Question 23

how does the temperature affect the rate of osmosis?

Answer 23

the higher the temperature, the faster the rate of osmosis (directly proportional)

Question 24

what happens to a plant cell in a hypotonic (higher water potential) solution?

Answer 24

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

Question 25

what happens to a red blood cell in a hypotonic (higher water potential) solution?

Answer 25

cytoplasm has a lower water potential than surrounding solution and water enters cell by osmosis

cell expands and bursts (lyses)

Question 26

what happens to a plant cell in a hypertonic (lower water potential) solution?

Answer 26

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

Question 27

what happens to a red blood cell in a hypertonic (lower water potential) solution?

Answer 27

cytoplasm has a higher water potential than surrounding solution and water leaves cell by osmosis

cell shrinks in size and is crenated

Question 28

what is the importance of turgor pressure especially in herbaceous (non-woody) plants?

Answer 28

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

Question 29

what are 3 differences between diffusion and osmosis?

Answer 29

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

Question 30

what is active transport?

Answer 30

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

Question 31

how does active transport play a role in plant cells?

Answer 31

dissolved mineral salts are taken up by root hair cells via active transport and diffusion

Question 32

what are 3 differences between diffusion and active transport?

Answer 32

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