Exchange between organisms and their environment

• Size and metabolic rate affect the rate of exchange
• 4 things exchanged by an organism with their environment = respiratory gases, nutrients, excretory products, heat
• Exchanges takes place through diffusion, facilitated diffusion, osmosis, active transport and co-transport
• Large organisms have a smaller surface area to volume ratio
• Large organisms have a smaller metabolic rate
• Small organisms have higher surface area to volume ratio
• Small organisms have a higher metabolic rate
• The greater the surface area to volume ratio, the more efficient gas exchange will be
• Specialised exchange surfaces have a high surface area to volume ratio to maximise rate of diffusion
• Specialised exchange surfaces are very thin to have a short diffusion pathway
• Exchange surfaces are selectively permeable to only allow certain molecules through
• Fick's Law states that rate of diffusion across unit area is proportional to concentration gradient
• Single celled organisms have a large surface area to volume ratio and have a short diffusion distance