Gas Exchange with the Gas Exchange with the environmentenvironment

Why do organisms need to Why do organisms need to exchange gases with their exchange gases with their

environments? environments? Carbon Dioxide and Oxygen levels must Carbon Dioxide and Oxygen levels must

be regulatedbe regulated Cellular respiration depends on the Cellular respiration depends on the raterate of of

oxygen entering the cellsoxygen entering the cells So why is this crucial?So why is this crucial? Because the amount of Because the amount of energyenergy released released

will be reduced if not enough oxygen is will be reduced if not enough oxygen is availableavailable

Carbon dioxide is a waste product for the Carbon dioxide is a waste product for the cells. What happens if this is allowed to cells. What happens if this is allowed to increase in cells and body tissues?increase in cells and body tissues?

When dissolved in water Carbon dioxide When dissolved in water Carbon dioxide forms carbonic acid and even though it is forms carbonic acid and even though it is weak, it changes the pH and that’s not a weak, it changes the pH and that’s not a good thing to do!!good thing to do!!

So how do animals exchange So how do animals exchange gases with their environmentgases with their environment

The answer is DIFFUSIONThe answer is DIFFUSION Remember that CO2 and O2 are small Remember that CO2 and O2 are small

molecules and so move easily across all molecules and so move easily across all membranes by diffusion. Does this process membranes by diffusion. Does this process involve energy and do they always move this involve energy and do they always move this way? way?

No energy involved and yes they always use No energy involved and yes they always use diffusion. diffusion.

Then how do they move?Then how do they move? Down the concentration gradient. High to Low.Down the concentration gradient. High to Low.

What properties do you think the What properties do you think the gas exchange surface should gas exchange surface should have? Think about the lungshave? Think about the lungs

Large Surface Area / Volume ratio ( I told you Large Surface Area / Volume ratio ( I told you this concept would be back!!)this concept would be back!!)

The barrier (membrane) to cross should be The barrier (membrane) to cross should be wafer thin. wafer thin.

An decent amount of gas to be transferred, this An decent amount of gas to be transferred, this maintains the concentration gradient and keeps maintains the concentration gradient and keeps the exchange rate goingthe exchange rate going

Some way of removing the substance after the Some way of removing the substance after the transfer has occurred. Eg: In the lungs, the O2 is transfer has occurred. Eg: In the lungs, the O2 is whisked away by the blood and the CO2 is whisked away by the blood and the CO2 is breathed out.breathed out.

There is a formula for this – for the There is a formula for this – for the Maths inclinedMaths inclined

Do you think the gas exchange surface Do you think the gas exchange surface should be moist, dry, or in-between?should be moist, dry, or in-between?

Definitely moist. In fact one of the biggest Definitely moist. In fact one of the biggest problems faced by terrestrial animals is problems faced by terrestrial animals is the evaporation of water from this surfacethe evaporation of water from this surface

The getting of oxygenThe getting of oxygen

Where you live and your size usually Where you live and your size usually determines what type of gas exchange determines what type of gas exchange mechanism you will usemechanism you will use

Smaller animals like amoeba and Smaller animals like amoeba and underwater molluscs can exchange gas underwater molluscs can exchange gas directly between their cells and the directly between their cells and the environment,environment,

Most animals however are way to big for Most animals however are way to big for this to be efficient and have devised this to be efficient and have devised ingenious ways to get around this problemingenious ways to get around this problem

Water Vs AirWater Vs Air

In which do you think Oxygen is more In which do you think Oxygen is more abundant? abundant?

Its air. Air is always about 21% oxygen. Its air. Air is always about 21% oxygen. Although at high altitude because it is less Although at high altitude because it is less dense, there are less oxygen moleculesdense, there are less oxygen molecules

Water generally has about 7ml (10mg) of Water generally has about 7ml (10mg) of O2 per litreO2 per litre

Air has 210ml (285mg) per litreAir has 210ml (285mg) per litre

The amount of O2 in water will also The amount of O2 in water will also decrease as:decrease as:

- The pressure increases (like in deep - The pressure increases (like in deep water)water)

- The Temperature increases- The Temperature increases

- The Salinity increases- The Salinity increases So basically it is a lot harder work to get So basically it is a lot harder work to get

oxygen out of water than air.oxygen out of water than air.

Gills Vs LungsGills Vs Lungs

Which do you think extracts the greater Which do you think extracts the greater percentage of oxygen, Gills or Lungs?percentage of oxygen, Gills or Lungs?

Actually it is Gills. They can get a massive Actually it is Gills. They can get a massive 90% out of water. Lungs can only get 90% out of water. Lungs can only get 25%. So which is the most efficient?25%. So which is the most efficient?

The lungs. 25% of 210ml is more than The lungs. 25% of 210ml is more than 90% of 7ml90% of 7ml

However, both are designed to give the However, both are designed to give the animal enough 02 for maximum energy animal enough 02 for maximum energy efficiencyefficiency

GillsGills Gills are basically wafer thin membranes Gills are basically wafer thin membranes

surrounded by heaps of blood vessels. surrounded by heaps of blood vessels. What would the surface are be like?What would the surface are be like?

As the fish swims around with its mouth As the fish swims around with its mouth open, water rushes past the gills and the open, water rushes past the gills and the oxygen diffuses out of the wateroxygen diffuses out of the water

Blood flows around the gills in opposite Blood flows around the gills in opposite directions a process called Counter directions a process called Counter current flow. This basically keeps the current flow. This basically keeps the concentration gradient really high so it concentration gradient really high so it allows the maximum amount of O2 to get allows the maximum amount of O2 to get absorbed from the waterabsorbed from the water

Counter current flow in the gillsCounter current flow in the gills

InsectsInsects Breathe through holes in their skin called Breathe through holes in their skin called

spiraclesspiracles These connect direct to the trachea and These connect direct to the trachea and

branch into tracheolesbranch into tracheoles

http://evolution.berkeley.edu/evolibrary/artihttp://evolution.berkeley.edu/evolibrary/article/_0_0/constraint_14cle/_0_0/constraint_14

Transporting gasesTransporting gases Oxygen does not actually dissolve that well in Oxygen does not actually dissolve that well in

the plasma and so the amount that can be the plasma and so the amount that can be carried is very small. carried is very small.

So how do animals get the large amount of O2 So how do animals get the large amount of O2 from the lungs to the tissues?from the lungs to the tissues?

By using oxygen carrier moleculesBy using oxygen carrier molecules These are usually proteins with a metal in the These are usually proteins with a metal in the

middle of the moleculemiddle of the molecule Mammals have haemoglobin as the oxygen Mammals have haemoglobin as the oxygen

carrier and it has which metal in the middle?carrier and it has which metal in the middle? IronIron

Mammals have haemoglobin for two Mammals have haemoglobin for two reasons, what are they?reasons, what are they?

It has the ability to bind 4 molecules of It has the ability to bind 4 molecules of oxygen at a time and can easily release it oxygen at a time and can easily release it to the tissuesto the tissues

It increases the oxygen carrying capacity It increases the oxygen carrying capacity of the blood so the animal can have less of the blood so the animal can have less blood to pump around and still meet its blood to pump around and still meet its energy needsenergy needs

Getting rid of CO2Getting rid of CO2 It all ends up in the bloodstreamIt all ends up in the bloodstream 7% dissolved in plasma7% dissolved in plasma 23% carried by Haemoglobin23% carried by Haemoglobin 70% converted into Hydrogen carbonate 70% converted into Hydrogen carbonate

and carried in the red blood cellsand carried in the red blood cells When the blood gets to the alveoli the When the blood gets to the alveoli the

CO2 diffuses across the walls into the CO2 diffuses across the walls into the alveloar spaces, where it will be breathed alveloar spaces, where it will be breathed out by the lungsout by the lungs

Consider the following diseasesConsider the following diseases

Emphysema, Iron deficiency anaemia, Emphysema, Iron deficiency anaemia, Asthma and pneumoniaAsthma and pneumonia

All of these give very similar symptoms. All of these give very similar symptoms. Tiredness, inability to exercise, shortness Tiredness, inability to exercise, shortness of breath. Explain why.of breath. Explain why.

Tip: It has something to do with how they Tip: It has something to do with how they affect the respiratory surfaceaffect the respiratory surface