Cell Biology - Exchanging Substances 34-41

Question 1

define diffusion

Answer 1

the movement of particles from an area of higher concentration to an area of lower concentration

Question 2

in what substances does diffusion happen in and why
3 points

Answer 2

1) solutions
2) gases
3) because these particles are free to move about randomly

Question 3

what affects the rate of diffusion
3 points

Answer 3

1) concentration gradient - bigger = faster
2) temperature - higher = faster
3) large surface area - larger = faster

Question 4

what is concentration gradient

Answer 4

the difference in concentrations between 2 areas

Question 5

what substances can diffuse through a cell membrane
5 points

Answer 5

1) only very small molecules
2) oxygen
3) glucose
4) amino acids
5) water

Question 6

what substances can’t diffuse through a cell membrane
3 points

Answer 6

1) big molecules
2) protein
3) starch

Question 7

what direction do particles move across a cell membrane
2 points

Answer 7

1) they move in both directions
2) but there’s a net overall movement from an area of higher concentration

Question 8

define osmosis

Answer 8

the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration

Question 9

what is a partially permeable membrane

Answer 9

a membrane with very small holes in it that only lets small molecules through

Question 10

how can you observe the effect of sugar solutions in plant tissue
4 points

Answer 10

1) cut up a potato into identical cylinders
2) set up beakers with different concentrations of sugar solutions, one should be pure water and one very concentrated sugar solution
3) measure the mass of the cylinders then leave one in each beaker for about 24hr
4) take them out, dry them with a paper towel and measure their masses again

Question 11

what would you expect the results to be when observing the effect of sugar solutions on plant tissue
3 points

Answer 11

1) if the cylinders have drawn in water by osmosis they’ll have an increased mass
2) if water has been drawn out, they’ll have a decreased mass
3) calculate %change so you can plot graphs

Question 12

what is the dependent variable when observing the effect of sugar solutions on plant tissue

Answer 12

the change in mass

Question 13

what is the independent variable when observing the effect of sugar solutions on plant tissue

Answer 13

the concentration of the sugar concentration

Question 14

what are some control variables when observing the effect of sugar solutions on plant tissue
4 points

Answer 14

1) temperature
2) type of sugar
3) volume of solution
4) the time potato left in solution

Question 15

what are sources of error when observing the effect of sugar solutions on plant tissue and how do you reduce them
3 points

Answer 15

1) not drying potato properly
2) water evaporating
3) reduce these errors by repeating the experiment and calculation a mean

Question 16

how are plants adapted for absorbing water and mineral ions

Answer 16

each branch of the root covered in microscopic hairs which gives them a large surface area

Question 17

what type of transport do root hair cells use for absorbing water and mineral ions and why
2 points

Answer 17

1) active transport
2) because the concentration of of minerals is usually higher in the root hair cell than in the soil so can’t use diffusion

Question 18

what is active transport
2 points

Answer 18

1) active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient)
2) this requires energy from respiration

Question 19

what are the uses of active transport
2 points

Answer 19

1) allows mineral ions to be absorbed into plant root hairs
from very dilute solutions in the soil - plants require ions for healthy growth
2) allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration - sugar molecules are used for cell respiration.

Question 20

does the gut always used active transport
2 points

Answer 20

1) no because sometimes there is a higher concentration of nutrients in the gut than in the blood
2) but active transport allows nutrients to be taken into the bloodstream even when the concentration gradient is the wrong way

Question 21

give examples of when cells exchange substances
2 points

Answer 21

1) oxygen and carbon dioxide are transferred between cells and the environment during gas exchange
2) urea diffuses from cells into the blood plasma for removal from the body by the kidneys

Question 22

what affects the rate of substance exchange by an organism
2 points

Answer 22

1) surface area to volume ratio
2) a larger SA:V is better because a larger SA means larger area for substances to diffuse across and it means less V to travel round

Question 23

describe exchange in single celled organisms
2 points

Answer 23

1) gases and dissolved substances can diffuse directly into (or out of) the cell across the cell membrane
2) because they a large SA:V so enough substances can be exchanges across the membrane to supply the volume of the cell

Question 24

describe exchange in multicellular organisms
2 points

Answer 24

1) they have a smaller SA:V so not enough substances can diffuse from their outside surface to supply their volume
2) so they need some sort of exchange surface for efficient diffusion

Question 25

how are exchange surfaces adapted to maximise diffusion effectiveness
4 points

Answer 25

1) thin membranes - so short distance to diffuse
2) large SA - lots of substances can diffuse at once
3) lots of blood vessels in animals - so gets stuff in and out quickly
4) gas exchange surfaces are often ventilated -

Question 26

describe gas exchange in the lungs
3 points

Answer 26

1) needs to transfer O2 to the blood and remove waste CO2
2) the lungs contain millions of little air sacs called alveoli
3) alveoli are specialised to maximise diffusion of O2 and CO2

Question 27

how are alveoli are specialised to maximise diffusion of O2 and CO2
4 points

Answer 27

1) an enormous surface area (about 75m^2 in humans)
2) a moist lining for dissolving gases
3) very thin walls
4) a good blood supply

Question 28

what are villi
2 points

Answer 28

1) inside the small intestine there are millions of tiny projections called villi
2) they increase surface area so digested food is absorbed much more quickly

Question 29

how are villi adapted for efficient exchange
2 points

Answer 29

1) single layer of surface cells
2) very good supply

Question 30

how is the leaf structure adapted to let gases diffuse in and out of cells
5 points

Answer 30

1) stomata
2) guard cells
3) flattened shape of the leaf
4) air spaces inside the leaf

Question 31

how does stomata help gases diffuse
3 points

Answer 31

1) the underneath of the leaf is an exchange surface and covered in little holes called stomata
2) CO2 diffuses into the leaf through them
3) O2 and water vapour diffuse out of the stomata

Question 32

how do guard cells help diffuse gases in and out
3 points

Answer 32

1) they control the size of stomata
2) they close the stomata if the plant is losing water faster than is being replaced by the roots
3) without the plant would wilt

Question 33

how does the flattened shape help diffusion of gases in and out

Answer 33

increases the area of the exchange surface

Question 34

how does the air spaces help diffusion of gases in and out
3 points

Answer 34

1) the wall of the cells form another exchange surface
2) the air spaces inside the leaf increase the area of this surface
3) so more chance CO2 will get into the cells

Question 35

what is the exchange surface in a fish

Answer 35

its gills

Question 36

describe exchange in gills
3 points

Answer 36

1) water (containing O2) enter the fish through its mouth and pass out through its gills
2) as this happens O2 diffuses from the water into the blood and the gills
3) CO2 diffuses from the blood into the water

Question 37

how are gills adapted for exchange
4 points

Answer 37

1) each gill is made up of thin plates called gill filaments - gives a big SA
2) gill filaments are covered in lots of tiny structures called lamellae - increase SA more
3) lamellae have lots of blood capillaries - to speed up diffusion
4) lamellae have thin surface area of cells - minimise distance gases have to diffuse

Question 38

describe how a large concentration gradient is maintained in the gas exchange of a fish
3 points

Answer 38

1) blood flows through the lamellae in one direction and water flows in the opposite
2) the concentration of O2 in the water is always higher than that in the blood
3) so as much O2 as possible diffuses from the water into blood