Surface area and diffusion

how do small and single-celled organisms exchange materials?

by diffusion across their cell membranes

what is diffusion?

movement of molecules from a region of high concentration to region of lower concentration

what is the SA:V of small organisms

small organisms have a small SA:V

how does having a large SA:V help small organisms?

the exchange surface is adequate to exchange material by diffusion as they have a short diffusion distance

what happens to SA:V if you double the size?

• surface area increases by 4

• volume increases by 8

• SA:V halves

what happens to the SA:V as the organism increases in size?

smaller SA:V ratio

why is a specialised system need for larger organisms?

outer SA:V is too small and there is not enough exchange surface for a short diffusion to exchange materials so a specialised exchange system is necessary

what does a mammal’s complex gas exchange system do?

• absorbs oxygen needed for respiration

• to get rid of CO2 waste from the body

why can’t multi-cellular organisms do gas exchange via diffusion on the surface area?

• cells too far away from oxygen to reach through diffusion

• need specialised exchange surface

when does diffusions stop?

when particles are distributed evenly throughout the system and a uniform concentration is achieved so no further net movement

what is the formula for rate of diffusion?

rate of diffusion = (surface area x difference in concentration) / length of diffusion path

what is passive diffusion?

simple diffusion of a substance in or out of a cell which does not require energy

what affects diffusion through a membrane?

• nature of membrane

• size of molecule

• type of moelcule