Biology 3602A/B Lecture Notes - Lecture 4: Lake Huron, Lake Titicaca, Gas Exchange

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5 Aug 2016
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Animals breathe air and water
Breathing is movement of gas exchange medium over the gas exchange surface
Breathing is ventilation
Active process of moving stuff over gas exchange surface, but all the exchange
happens via diffusion
All these things happen passively; you can change the conditions in which they happen
but you can’t alter physics
Many ways to define Dalton’s Law – total atmospheric pressure is the sum of the PPs of
the individual gases making up the atmosphere
Most useful way of using Dalton’s law: Px=FxPtot
Total atmospheric P at sea level is 760 mmHg; if you put that into Dalton’s law, you get
PO2 of 159; at the top of Everest PO2 is 49 b/c atmospheric pressure is much lower
PO2 is going to affect the passive process of diffusion, that’s why we have to know it
Some animals breathe water (salt or freshwater)
We have to know the relationship of the gases of interest in diff mediums
To calculate the conc of any gas in air, we can use Henry’s law: Cx = A (or solubility) *
Px
Solubility in water, similar to absorption coefficient, differs in all gases
Oxygen not very soluble in water; Water cannot hold a lot of oxygen; can hold a lot more
CO2 than O2; nitrogen is not very soluble in water either
What affects solubility?
Salinity; if you add a grain of salt in beer, more bubbles will go up; higher salinity, less
soluble CO2 or O2 is in the water
Temperature; if you take a bottle of water from a cold creek and sit it in a warm room;
warm water cannot take in as much oxygen as cold water, so oxygen previously
dissolved in the water comes out of the sol’n and forms bubbles
As you warm up water, conc of O2 goes lower
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Breathing in a freshwater environment
Atmospheric P is around 750 mmHg; 0.2095 O2
Conc of O2 in Lake Huron is pretty low, but animals still live in it
Enough animals live in it that there’s a good fishery
Highest navigable lake in the world
Atm P is around 550 mmHg
PO2 in the air around is 150 mmHg; a lot less than Lake Huron
Freshwater env in higher altitude not much O2 in air and water
But there’s still a lot of fish in Lake Titicaca
Diffusion of gases into and out of animals is described by the Fick equation; gases can
only be exchanged by the env by diffusion
J can be referred to as flux, or rate of gas exchange (how much gas is exchanged per
unit time)
K is the Krogh coefficient
P1-P2 is the partial pressure difference between the animal and the outside
If we’re thinking of O2, high PP outside, low PP inside; positive flux
In CO2, more CO2 inside than outside, so negative flux
X is distance separating inside and outside of animal; surface over which that gas must
diffuse like the alveoli in lungs
Krogh constant depends on type of gas
Depends on diffusability of the gas
Diffusion coefficient is part of Krogh constant and is faster in air than it is in water
So diffusion is quicker in air
K also depends on the material across which gas diffuses
If we think about gases diffusing across a damp frog, there are a lot of gases
exchanged across the skin
compared to tires, not much gas will diffuse across tires
K also depends on area of material
Thus K = D*A
To maximize rate of diffusion, increase A, D, sum of P1 and P2; minimize by decreasing
X
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