3.3.1 SA:Volume ratio Flashcards
What is an exchange surface
Surface over which an organism exchanges materials with the external environment
2 types of transport
Passive (diffusion)
Active
Examples of exchanging substances
Respiratory gases
Nutrients - products of digestion (glucose,amino acids,vitamins)
Waste products (urea)
2 things the amount of materials that need to be exchanged depends on
Size of organism Metabolic rate (rate of chemical reactions)
How does size of organism effect amount of materials needed to be exchanged
The bigger the organism, the more materials needed
How does metabolic rate effect amount of materials needed to be exchanged
Higher metabolic rate, more materials exchanged
4 factors that effect diffusion
Concentration gradient
Thickness of diffusion surface (thin membrane)
Surface area (bigger-faster)
Temperature (warmer-faster as more kinetic energy)
What does Fick’s law express
The relationship between 3 factors that effect diffusion
Rate of diffusion= surface area(C2-C1)/thickness of exchange surface
C2-C1 = difference in concentration gradient
What is the quantity of material exchanged dependent on
Why
The volume of the organism (how much tissue)
As exchange is proportional to surface area
What does SA:volume tell us
How close internal parts are to the surface
What happens to an organism as their SA:volume decreases
Get bigger
What’s its SA:volume ratio if it’s smaller
Larger SA:volume ratio
What type of organisms can’t rely on exchange across their surface
Why
What do they need instead
Large complex organisms
As their cells are bathed in tissue fluid + most are too far away from an exchange surface
So they need a mass transport system to deliver oxygen
How do u work out volume
Length x width x height
What should you always make the ratio to
1
