Adaptations for gas exchange

• Surface area and volume are important factors in the exchange of materials in organisms
• As the surface area and volume of an organism increase, the surface area : volume ratio decreases because volume increases much more rapidly than surface area as size increases
• Calculation of surface area to volume ratio varies for different shapes, reflecting different cells or organisms
• In the investigation of the effect of changing surface area to volume ratio on diffusion, measurements can be taken of the time taken for acid to change the color of indicator in agar blocks or the distance traveled into the block by the acid in a given time
• The greater the surface area to volume ratio, the faster the rate of diffusion in organisms like agar cubes or biological cells
• Single-celled organisms have a high surface area to volume ratio allowing for substance exchange via simple diffusion, while large organisms have evolved adaptations like specialized cells, tissues, organs, and systems to facilitate substance exchange
• The metabolic rate of an organism is the amount of energy expended within a given period, with experiments showing that metabolic rate increases with body mass
• Experiments have shown that the greater the mass of an organism, the higher the metabolic rate, but the basal metabolic rate per unit of body mass is higher in smaller animals than in larger animals
• Metabolic rate increases with body mass, but the Basal Metabolic Rate (BMR) per unit of body mass is higher in smaller animals than in larger animals
• Smaller animals have a greater Surface Area to Volume (SA:V) ratio, leading to more heat loss and requiring more energy to maintain body temperature
• Different apparatus used for investigating metabolic rates in organisms include:

  • Respirometers
  • Oxygen/carbon dioxide probes
  • Calorimeters
• Plants have lower metabolic rates than animals as they do not move around their habitat and do not have to maintain a high body temperature
• Effective gas exchange surfaces in organisms have:

  • Large surface area
  • Short diffusion distance
  • Maintained concentration gradient
• Chlamydomonas, a single-celled organism found in fresh-water ponds, demonstrates efficient gas exchange through oxygen diffusion across its cell wall and surface membrane
• Insects possess a tracheal system for breathing, with spiracles as openings in the exoskeleton connected to tracheae that lead to tracheoles for gas exchange
• Fish gills have a counter-current system where blood flow is opposite to water flow, maintaining a concentration gradient for efficient oxygen extraction from water
• Leaves of dicotyledonous plants have adaptations like stomata, guard cells, and air spaces in mesophyll layers to facilitate efficient gas exchange for photosynthesis
• Compromises between gas exchange and water loss in organisms are observed, with adaptations like waterproof exoskeletons and tracheal systems in insects, and xerophytic adaptations in plants