Metabolic Rate and Surface Area

• Surface area refers to the total area of the organisms that is exposed to the external environment
• What is the surface area of an organism?

  The total area of the organisms that is exposed to the external environment
• The volume refers to the total internal volume of the organism
• As the overall size of an organism increases, the surface area to volume ratio decreases, this is because volume increases much more rapidly than surface area as size increases
• What is an objects surface area to volume ratio?

  How close every internal part of it is to its surface
• Area is measured in units squared
• Volume is measure in units cubed
• How is volume calculated?

  Length x width x depth of object
• All organisms need to exchange substances with the environment to survive
• Organisms need to take in oxygen and nutrients and remove carbon dioxide and urea
• Temperature and water levels within an organism needs to be kept constant, so heat and water also needs to be exchanged
• In terms of organisms, the larger the organisms mass, the lower its surface area to volume ratio becomes
• Small objects have a high surface area to volume ratio, which shows that every part of the object is quite close to its surface
• Having a high SA:V ratio means that there is only a short distance from the edge to the middle so things can move in and out quickly (short diffusion pathway)
• Small objects have a high surface area to volume ratio
• Large objects have a low surface area to volume ratio
• Large objects have a low SA:V ratio, which means that there are parts of the object that are a far distance from the surface
• Large objects have a low SA:V ratio, meaning that there is a longer distance from the edge to the middle, so things take longer to get in and out (large diffusion pathway).
• What is metabolic rate?

  The amount of energy expended by that organism in a specific time period, typically daily
• What is metabolic demand?

  How much oxygen and nutrients an organism needs to take in daily to respire enough to maintain the metabolic rate
• What is the basal metabolic rate (BMR)?


  The metabolic rate of an organism when at rest
• The basal metabolic rate is significantly lower than the metabolic rate when an organism is actively moving
• During periods of rest, the body of an organism only requires energy for the functioning of vital organs such as the lungs, heart and brain
• How can the metabolic rate of an organism be measured?

  • Oxygen consumption
  • Carbon dioxide production
  • Heat production
• Typically, the greater the mass of an organism, the higher taht organisms metabolic rate
• Why does an animal with greater mass have a higher metabolic rate?

  They require more efficient delivery of oxygen to cells as more respiration is needed
• Why have multicellular organisms evolved more complex exchnage systems?

  The need for more efficient delivery of oxygen and nutrients to cells
• The rate of exchange of substances depends on the surface area in contact with the surroundings
• As organisms get bigger, their surface area to volume ratio gets smaller, so larger organisms have more difficulty in getting the oxygen and nutrients they need from the environment.
• Why do larger organisms have more difficulty getting the oxygen and nutrients they need from the environment?

  Their surface area to volume ratio gets smaller
• The greater the mass of an organism, the higher the metabolic rate
• What happens to the metabolic rate as an organisms mass increases?


  Gets higher
• When metabolic rate is higher, the oxygen consumed in a given period of time is higher
• Why have multicellular organisms evolved more complex mass transport and exchange systems?

  To have efficient delivery of oxygen and nutrients to cells
• The rate of exchange of substances depends on the surface area in contact with the surroundings
• As organisms get bigger, their surface area to volume ratio gets smaller
• Why do larger organisms have less efficient oxygen and nutrient exchange?

  They have a smaller surface area to volume ratio than smaller organisms
• The greater the mass of an organism, the higher the metabolic rate
• The BMR per unit of body mass is higher in smaller animals than in larger animals
• Why is the BMR of smaller animals greater than in larger animals?

  They have a greater surface area to volume ratio, so they lose more heat, meaning that they need more energy and a higher metabolic rate per unit of body mass to maintain a constant internal temperature