AQA Biology A-Level cheat sheet
ORGANISMS EXCHANGE SUBSTANCES WI
THEIR ENVIRONMENT
, Surface area and exchange
• Smaller organisms have larger surface area : volume ratio, so more energy/heat is lost (per gram etc…), so higher rate of aerobic
respiration/metabolic reactions carried out to replace heat lost/release more heat…
• Increasing rate of diffusion: large surface area, thin/flattened/single layer of cells – allows for shorter diffusion pathway.
• Larger organisms have a smaller surface area to volume ratio, specialized systems (e.g., in humans) overcomes long diffusion pathwa
allows for faster diffusion
• Water also has a lower oxygen concentration/partial pressure compared to air so fish have larger surface area (due to gills) to maxim
diffusion of oxygen when in contact with water
Diffusion of water/oxygen in fish, VENTILATION:
• Fish opens mouth, floor of buccal cavity lowered.
• Volume inside buccal cavity increases, pressure decreases.
• Pressure higher outside fish mouth so water flows into buccal cavity.
• Fish raises floor of buccal cavity to close mouth, increased pressure in mouth.
• Water flows from buccal cavity into the gill cavity.
• Pressure builds up inside gill cavity and causes operculum to force open and forces water to exist.
• Operculum forced shut when floor of buccal cavity lowered.
Gill lamellae – increases surface area for diffusion + very thin – short diffusion distance
Lots of gill filaments – large surface area : volume ratio
Diffusion and counter current in fish:
• Blood and water flow in opposite directions through lamellae
• Maintains steep concentration gradient
• Water with a relatively high oxygen concentration always flowing next to blood with lower concentration of oxygen
• Allows for diffusion across whole length of the lamellae/filaments
ORGANISMS EXCHANGE SUBSTANCES WI
THEIR ENVIRONMENT
, Surface area and exchange
• Smaller organisms have larger surface area : volume ratio, so more energy/heat is lost (per gram etc…), so higher rate of aerobic
respiration/metabolic reactions carried out to replace heat lost/release more heat…
• Increasing rate of diffusion: large surface area, thin/flattened/single layer of cells – allows for shorter diffusion pathway.
• Larger organisms have a smaller surface area to volume ratio, specialized systems (e.g., in humans) overcomes long diffusion pathwa
allows for faster diffusion
• Water also has a lower oxygen concentration/partial pressure compared to air so fish have larger surface area (due to gills) to maxim
diffusion of oxygen when in contact with water
Diffusion of water/oxygen in fish, VENTILATION:
• Fish opens mouth, floor of buccal cavity lowered.
• Volume inside buccal cavity increases, pressure decreases.
• Pressure higher outside fish mouth so water flows into buccal cavity.
• Fish raises floor of buccal cavity to close mouth, increased pressure in mouth.
• Water flows from buccal cavity into the gill cavity.
• Pressure builds up inside gill cavity and causes operculum to force open and forces water to exist.
• Operculum forced shut when floor of buccal cavity lowered.
Gill lamellae – increases surface area for diffusion + very thin – short diffusion distance
Lots of gill filaments – large surface area : volume ratio
Diffusion and counter current in fish:
• Blood and water flow in opposite directions through lamellae
• Maintains steep concentration gradient
• Water with a relatively high oxygen concentration always flowing next to blood with lower concentration of oxygen
• Allows for diffusion across whole length of the lamellae/filaments
