D) Movement of substances into and out of cells

diffusion, active transport and osmosis

describe diffusion

net movement of particles (molecules/ions) from a region of high concentration to a region of low concentration

i.e. - down a concentration gradient

In respiration, is the CO₂ concentration higher or lower within the cell

so what direction will the CO₂ molecules be mainly moving

the molecules of CO₂ are constantly moving because of their _______ ______

higher - the cell produces CO₂ in respiration

the overall net movement is outside the cell, down the concentration gradient

kinetic energy

what 4 factors affect the rate of diffusion

• the concentration gradient - diffusion happens quicker w a steep concentration gradient (larger difference)

• surface area : volume ratio - larger surface area to the volume will increase the rate

• distance - rate = decreased when distance is larger

• temperature - rate is greater at high temperatures bc high temp = particles with more kinetic energy

describe active transport

the movement of substances against a concentration gradient, using energy from respiration

what is ATP

the energy-carrying molecule used in cells because it can release energy very quickly

during active transport, a cell will act like…

a pump which uses energy to move a liquid from one place to another

• bc the cell uses energy from respiration to take up substances (ions, molecules)

the ‘active transport pumps’ are located where in the cell?

what are they made of?

what are they driven by?

the pumps are large protein molecules located in the cell membrane

they are driven by the breakdown of ATP

an example of active transport

human small intestine

• some glucose in the gut is absorbed into the cells lining the small intestine by active transport

describe osmosis

the net movement of water from a dilute solution to a more concentrated solution across the partially permeable cell membrane