surface area to volume ratio

If the surface area of an organism is 6cm3 and the volume is 1cm3 what is the sa:v ratio? is a bigger sa:v better?

sa:v = 6

a bigger value is better because that means theres more surface area in comparison to volume

benefits of a large sa:v ratio

• there is a big surface for the exchange of

  substances

• a smaller distance from the outside of

  the organism to the middle of it so diffusion occurs more efficiently

relationship between size of an organism and sa:v

small organisms (like bacteria) have a large SA:V ratio → exchange with their environment (oxygen, CO₂, heat, nutrients) is easy.
Larger organisms (like mammals) have a small SA:V ratio → diffusion across the body surface is too slow.

what are some features of effective exchange surface

• Large surface area (e.g. alveoli, villi)

• Thin (short diffusion pathway)

• Steep concentration gradient (maintained by ventilation or blood flow)

what is metabolic rate?

Metabolic rate = rate of all chemical reactions in the body (esp. those generating heat).

A mouse has a higher metabolic rate than an elephant, explain why

• the mouse is a small organism (large SA:V ratio) so it loses heat quickly to the environment.
  → They need a high metabolic rate (burn more food/respire faster) to maintain body temperature.

• Large organisms like the elephant (small SA:V ratio) lose heat slowly.
  → Lower metabolic rate per gram of tissue.