Gas exchange in fish

• How does concurrent flow affect the concentration gradient of oxygen in water and blood?

  + parallel/ concurrent flow

  + concentration of oxygen in water and blood equalises

  + no more oxygen exchange takes place
• Why is there still a diffusion gradient to allow diffusion of oxygen from water into blood?

  + even when O2 concentration in water is low at end of lamella

  + deoxygenated blood has just entered the lamella, so even lower in oxygen concentration

  + still a diffusion gradient present
• What challenges must aquatic organisms face for gas exchange?

  + lower oxygen content in lakes/ oceans

  + higher density and viscosity

  + slower rate of diffusion

  + scales prohibit gas exchange

  + inhaling and exhaling water requires too much energy to be efficient
• How have fish evolved a more energy efficient form of ventilation?

  + moving water in one direction is simpler and more economical in energy terms

  + evolved gills as an internal gas exchange surface
• Where are the gills found?

  found within the body of the fish, behind the head
• What is the purpose of the operculum in most bony fish?

  covers five pairs of gills
• How can swimming fish keep a current of water flowing over their gills?

  by keeping their mouth open
• What do primitive cartilaginous fish need to do for gas exchange?

  continually swim
• What are cartilaginous fish?

  fish with skeletons made of cartilage instead of bone
• What process keeps the water flowing into the mouth and out of the gills?

  coordinating changing the volume of the buccal cavity and movements of the operculum
• What are the steps for coordinating inspiration in fish (water flowing to the gills)?

  + mouth opens, buccal floor lowers and operculum closes

  + volume of buccal cavity increases

  + pressure inside mouth now lower than outside

  + water enters mouth down a pressure gradient
• What are the steps for coordinating expiration ( water flows out over the gills) in fish?

  + mouth remains closed, buccal floor risen

  + operculum opens

  + pressure in opercular cavity decreases

  + water forced out of the operculum, over the gills, down a pressure gradient

  + water gets rid of CO2
• Which four features make fish gills a good gas exchange surface?

  + large SA

  + thin ( to reduce diffusion distance)

  + good blood supply/ large network of capillaries ( maintain concentration gradient)

  + well-ventilated; fresh water constantly passes over ( maintain concentration gradient)
• How are the gills structured?

  + composed of gill filaments ( primary lamellae)

  + primary lamellae stacked together and attached to bony arch

  + overlapping tip reduces water flow speed

  + more time for gas exchange
• What other structures are on the gill filaments ( primary lamellae)?


  + many protrusions positioned at right angles

  + called secondary lamellae ( gill plates)
• How are the gills adapted for their function?

  + gill filaments (primary lamellae) and (gill plates) secondary lamellae provide a large SA

  + lamellae have many capillaries i.e. good blood supply

  + lamellae have thin walls i.e. short diffusion distance

  + gills well-ventilated with fresh water ( maintaining a steep concentration gradient of O2)
• What is the gill arch?

  bone or cartilage to connect paired gill filaments with lamellae
• How would a concurrent flow system in fish work?

  + water and blood flow in the same direction

  + most oxygenated meets least oxygenated blood

  + starts favourable due to steep concentration gradient

  + concentration gradient lose across gills

  + efficiency of gas exchange drops
• What is the counter-current flow system in fish?

  + water and blood flow in opposite directions

  + deoxygenated blood flows to gills

  + initially meets water with some oxygen removed

  + efficiency maintained across length of gill plate -> steep concentration gradient maintained
• Why is the counter-current flow system most efficient than the mammalian gas exchange system?

  gills can extract oxygen at rate 3x greater than humans using lungs
• What safety precautions should be taken to dissect a bony fish?

  + wear gloves to prevent contamination with biological material/ potential microbes

  + place instruments in disinfectant to kills microbes

  + dispose biological material appropriately to avoid contamination of bins

  + thoroughly disinfect surfaces to kill microbes
• Why do the tips of gill filaments overlap?

  + this increases resistance to the flow of water over the gills

  + slows water down

  + more time for gas exchange
• What kind of circulatory system do fish have?

  single circulatory system
• What is ram ventilation?

  + fish in high activity keep their mouths open while swimming

  + this allows constant ventilation while moving and going through aerobic respiration