AS-LEVEL AQA BIOLOGY NOTES 
TOPIC 1: surface area to volume ratio

< BACK TO TOPIC INDEX

Large organisms

• have a small surface area : volume ratio
  
• Rate of diffusion of substances from the body into the environment via skin is decreased
  
• This includes heat
  
• So large animals lose heat slowly
  
  • Advantageous in cold climates
    
• Less need to eat continuously
  

Small organisms

• Have a large surface area : volume ratio
  
• Rate of diffusion across skin is increased
  
• Small animals lose heat more rapidly
  
• This is advantageous in hot climates
  
• However small animals living in cold climates need a high calorie diet (relative to their size)
  
  • In order to maintain body warmth
    

Higher metabolic rate as more heat is generated and more heat is lost ​