Semester Two: Biology Lecture 24

Front 1

Air composition and altitude

Back 1

Air is 78% nitrogen and 21% oxygen
The percentage composition of air does not change with increased altitude
As you climb a mountain, the total amount of air falls

Front 2

Partial Pressure of a Gas

Back 2

Depends on the relationship between surface area to volume
Bacteria have a SA to volume ratio of 6 000 000:1....They can rely on diffusion alone for gas exchange because the surface area is large in respect to volume, and the distance the gases must diffuse is small

Front 3

Formula for Calculating the Partial Pressure of a Gas

Back 3

PP = (% of gas)(atmospheric pressure at a given height)

Front 4

Direction of Movement of a Gas

Back 4

Gases move spontaneously down a partial pressure gradient, from regions of high partial pressure to low partial pressure

Front 5

The Role of Diffusion in the Movement of Gas Molecules

Back 5

Gas exchange occurs by diffusion, no active transport
If distances are short (mitochondrial membrane) there is no issue and diffusion time is fast

Front 6

Ficks Equation

Back 6

Q = D x A x (P1-P2)/L
Q = rate of gas movement
D = diffusion coefficient
A = area across which diffusion takes place
L = path length, how far the diffusion has to move

Front 7

How do we maximize the rate of gas movement? Q!?

Back 7

1) Respiratory Surfaces
-An organism exchanges gases with the environment across the respiratory surface
-Flatworms
-All respiratory surfaces must be wet: because gases are in a solution when they pass into or out of the organism

Front 8

Leaves and Gas Exchange

Back 8

Most leaves are covered by a waxy cuticle so gases cant move in or out whenever they want
Stomata: The only area where gases can move in or out

Front 9

What drives CO2 uptakes into a leaf? Why does water always escape from the leaf?
Why is leaf gas exchange so fast?

Back 9

PP of CO2 is very low in the leaf because rubisco is carboxylating the CO2
CO2 is being consumed by the calvin cycle so the partial pressure is lower on the inside
Water always escapes from the leaf because the partial pressure of water outside the leaf is greater then inside the leaf
Leaf gas exchange is so fast because the SA for gas exchange is inside the leaf and large with short diffusion distances

Front 10

Animal Gas Exchange

Back 10

Animals can get big because of circulatory systems
Respiratory system is all PP, no ATP
THE SURFACE
Oxygen diffuses down the PP gradient - more oxygen is outside of the lung then on the blood vessels
CO2 diffuses out because the blood vessels have a lot of CO2 and there is less in the air
MITOCHONDRIA
Consumes oxygen and produces carbon dioxide
Oxygen moves down the PP gradient into the mitochondria
Carbon dioxide diffuses out of the mitochondria

Front 11

Fish Gills

Back 11

Water flows through the gills and oxygen diffuses into the blood
Fish always have to move because diffusion of a gas in an aqueous environment is slower than air
Counter Current: Oxygen diffuses from water into the blood
Co-current System: Net diffusion falls to zero, diffusion eventually stops when PP are the same

Front 12

Hemoglobin and Oxygen

Back 12

Obvs carries oxygen
If hemoglobin is in an area where the PP is high, you'll have lots of binding
**Graph of hemoglobin has an S shaped curve because under low PP, one molecules of oxygen will bind to one globin and it changes conformation of the other 3 sub units, so it has a higher affinity for binding the other three
When exercising, you consume a lot of oxygen, so PP of tissue is lower so 75% of oxygen is released

Front 13

pH and Oxygen Transport

Back 13

At a lower pH the affinity of hemoglobin for oxygen is lower
This occurs in blood vessels close to heavily active cells
pH in muscle cells is lower because heavily active mitochondria are producing a lot of CO2, Co2 produces carbonic acid so the pH drops
In the lungs there is a lot of hemoglobin binding, when the pH drops it releases more oxygen then it normally would so it delivers more oxygen to the mitochondria that require it