Cell Biology - Exchanging Substances 34-41 Flashcards
define diffusion
the movement of particles from an area of higher concentration to an area of lower concentration
in what substances does diffusion happen in and why
3 points
1) solutions
2) gases
3) because these particles are free to move about randomly
what affects the rate of diffusion
3 points
1) concentration gradient - bigger = faster
2) temperature - higher = faster
3) large surface area - larger = faster
what is concentration gradient
the difference in concentrations between 2 areas
what substances can diffuse through a cell membrane
5 points
1) only very small molecules
2) oxygen
3) glucose
4) amino acids
5) water
what substances can’t diffuse through a cell membrane
3 points
1) big molecules
2) protein
3) starch
what direction do particles move across a cell membrane
2 points
1) they move in both directions
2) but there’s a net overall movement from an area of higher concentration
define osmosis
the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
what is a partially permeable membrane
a membrane with very small holes in it that only lets small molecules through
how can you observe the effect of sugar solutions in plant tissue
4 points
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
what would you expect the results to be when observing the effect of sugar solutions on plant tissue
3 points
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
what is the dependent variable when observing the effect of sugar solutions on plant tissue
the change in mass
what is the independent variable when observing the effect of sugar solutions on plant tissue
the concentration of the sugar concentration
what are some control variables when observing the effect of sugar solutions on plant tissue
4 points
1) temperature
2) type of sugar
3) volume of solution
4) the time potato left in solution
what are sources of error when observing the effect of sugar solutions on plant tissue and how do you reduce them
3 points
1) not drying potato properly
2) water evaporating
3) reduce these errors by repeating the experiment and calculation a mean
how are plants adapted for absorbing water and mineral ions
each branch of the root covered in microscopic hairs which gives them a large surface area
what type of transport do root hair cells use for absorbing water and mineral ions and why
2 points
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
what is active transport
2 points
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
what are the uses of active transport
2 points
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.
does the gut always used active transport
2 points
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
give examples of when cells exchange substances
2 points
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
what affects the rate of substance exchange by an organism
2 points
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
describe exchange in single celled organisms
2 points
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
describe exchange in multicellular organisms
2 points
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
how are exchange surfaces adapted to maximise diffusion effectiveness
4 points
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 -
describe gas exchange in the lungs
3 points
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
how are alveoli are specialised to maximise diffusion of O2 and CO2
4 points
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
what are villi
2 points
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
how are villi adapted for efficient exchange
2 points
1) single layer of surface cells
2) very good supply
how is the leaf structure adapted to let gases diffuse in and out of cells
5 points
1) stomata
2) guard cells
3) flattened shape of the leaf
4) air spaces inside the leaf
how does stomata help gases diffuse
3 points
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
how do guard cells help diffuse gases in and out
3 points
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
how does the flattened shape help diffusion of gases in and out
increases the area of the exchange surface
how does the air spaces help diffusion of gases in and out
3 points
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
what is the exchange surface in a fish
its gills
describe exchange in gills
3 points
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
how are gills adapted for exchange
4 points
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
describe how a large concentration gradient is maintained in the gas exchange of a fish
3 points
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
