Adaptions for gas exchange

• what does surface area refer to in organisms

  total area of organisms exposed to external environment
• what does volume refer to in organisms

  refers to total internal volume of organisms
• what happens to surface area and volume ratio as both increase

  ratio decreases as volume increases more rapidly than surface area
• benefits of single celled organisms having high SA:V ratio

  large SA allows for maximum absorption of nutrients and gases and secretion of waste products

  small volume means diffusion distance to all organelles short
• what does large volume mean for diffusion

  greater volume results in longer diffusion distance to cells and tissues of organisms
• how have large multicellular animals and plants evolved to facilitate exchange of substances between environment 


  large variety of specialised cells, tissues ,organs and organ systems.

  examples involve gas exchange system, circulatory system ,urinary system ,Xylem and phloem and lymphatic system
• why do larger organisms need specialised system for exchange of oxygen

  organisms require atp for metabolic reactions and atp produced through aerobic respiration with oxygen
• Need for a Specialised System for Gas Exchange of carbon dioxide 


  carbon dioxide is toxic and a waste product of aerobic respiration , if it accumulates in cells and tissues can alter ph
• why do single celled organisms not need a gas exchange system

  small SA:Volume ratio

  short diffusion distance between cells and environment

  substances can diffuse across cell membranes into environment by simple diffusion
• what is metabolic rate of an organism

  The metabolic rate of an organism is the amount of energy expended by that organism within a given period of time
• what is basal metabolic rate

   is the metabolic rate of an organism when at rest. The BMR is significantly lower than when an organism is actively moving
• methods to measure metabolic rate of organisms

  oxygen consumption

  carbon dioxide production

  Heat production
• how does mass of organisms correlate to metabolic rate

  Greater mass of organism higher metabolic rate
• SA:V ratio correlation to organisms BMR

  BMR per unit of body mass is higher in smaller animals as they have greater SA:V ratio so lose more heat and have to use more energy to maintain body temp
• Apparatus to measure metabolic rate

  respirometer

  oxygen/ carbon dioxide probes

  calorimeters
• what do effective exchange surfaces in organisms have

  Large surface area

  short Diffusion distance

  concentration gradient maintained
• Features of insect gas exchange system

  Spiracles

  exoskeleton

  Trachea

  air sac

  tracheoles

  muscle cells
• feature of insect exoskeleton

  rigid with a waxy coating impermeable to gases
• Features of spiracles in insects

  Has valves

  allows air to enter insect and flow into system of trachea

  can close to reduce water loss
• Features of trachea in insects

  leads into tracheoles (narrower tubes)

  trachea walls have reinforcement that keeps them open as air pressure fluctuates

  large number of tracheoles run between cells and into muscle fibres for gas exchange.
• how is concentration gradient created in insects

  oxygen is used by respiring tissues so more can move into spiracles for diffusion

  CO2 produced by respiring tissue moves out through spiracles down concentration gradient
• how do active insects create mass flow of air for rapid gas exchange

  closing spiracles

  using muscles to create pumping movement for ventilation to maintain concentration gradient
• how does production of lactic acid in insects affect gas exchange

  lactic acid lowers water potential of muscle cells

  water found at narrow ends of trachea drawn into respiring muscles by osmosis

  allows gases to diffuse across more quickly
• how does oxygen diffuse in water

  oxygen diffuses less readily in water
• structure of fish gas exchange

  series of gills on each side of head

  each gill has gill arch attached to filaments

  on surface of each filament there are rows of lamellae

  lamellae surface consists of single layer of flattened cells covering capillaries
• what is counter current system

  water flowing through gills goes in opposite direction to blood flow to
• benefits of counter current system

  ensures concentration gradient is maintained along capillaries water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood
• how are plants adapted for gas exchange

  have small holes called stomata which allow gases to eter and exit leaves . large number so reduces diffusion distance . Also have air spaces to allow gases to easily move and come into contact with photosynthesising mesophyll cells