Cell biology - Transport in cells Flashcards
what is diffusion
the spreading out of particles from an area of high concentration to an area of low concentration ( through the cell membane )
where does diffusion happen
it happens in solutions and gases as the particles in these substances are free to move about randomly
things affecting the rate of diffusion
- temperature
- concentration gradient ( difference in concentration)
- surface area - as more particles can pass through at once
examples of diffusion
- oxygen moving out of a leaf and carbon dioxide moving in
- carbon dioxide and oxygen moving in the blood to the alveolus in the lungs
- liver cells, urea moving out of the kidneys
what kind of molecules can pass through a cell membrane
small molecules like oxygen, not large molecules like starch and proteins
what is osmosis
- the movement of water molecules across a PARTIALLY PEMEABLE MEMBRANE from a region of high water concentration to a region of lower water concentration
what is a partially permeable membrane
a membrane with very small holes in, only allows small molecules past
why do water molecules pass both ways through the membrane during osmosis
because the water molecules move about randomly all the time
difference between dilute and concentrated
A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.
what is net flow
overall movement
describe what happens during osmosis
- because there are more water molecules on one side of the membrane than the other, there’s a steady net flow of water into the region with fewer water molecules, meaning the solution becomes DILUTE
examples of osmosis
- Root hair cells, if the soil is wet or moist, will also take up water by osmosis
-red blood cells could:
lose water and shrink, gain water, swell and burst in a more dilute solution
what is active transport
Active transport is the net movement of particles against a concentration gradient from a area of low concetration to a high concentration
describe active transport in plants
Active transport allows mineral ions to be absorbed into plant root hairs
from very dilute solutions in the soil. Plants require ions for healthy
growth.
describe active transport in humans
Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed from the gut and into the blood from the gut, even when the sugar concentration of the blood is higher.
- 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.
what are exchange surfaces
Exchange surfaces are surfaces that are adapted to maximise the efficiency of gas and solute (a substance dissolved in a liquid) exchange across them
how are exchange surfaces adapted
- thin membrane so substances have a short diffusion path
- large surface area so lots of substances can diffuse at once
- efficient blood supply
- ventilation to maintain a high concentration gradient
examples of exchange surfaces
small intestine - adapted for exchanging nutrients between digested food in the small intestine and blood
lungs - The lungs are adapted for exchanging carbon dioxide and oxygen between the blood and air.
Gills - The gills are adapted for exchanging oxygen that is dissolved in water, with the carbon dioxide in a fish’s bloodstream.
Roots - Roots are adapted for taking up both water and minerals from the soil around them.
Leaves - Leaves are adapted for exchanging carbon dioxide and oxygen between the leaves and the surrounding air.
describe how glucose from the small intestine is moved to a muscle cell
- glucose absorbed by diffusion into the bloodstream
- blood delivers glucose to muscles using capillaries
why does a higher temperature increase the rate of diffusion
higher temperature gives particles more energy to move around faster
how are single celled organisms adapted for diffusion
A single-celled organism has a relatively large surface area to volume
ratio. This allows sufficient transport of molecules into and out of the cell
to meet the needs of the organism.
explain why plants are not able to rely in diffusion to absorb mineral ions from the soil
- the concentration of minerals is higher in the plant than in the soul
- so the minerals will move out of the plant by diffusion
how does active transport differ to diffusion
- active transport occurs along a concentration gradient but diffusion occurs down a concentration gradient
- active transport needs energy from respiration but diffusion doesnt
