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Gas Exchange Essay, Research Paper

Gas Exchange 3.1 Ø Surface

area to volume ratio Ø Exchange

of gases occurs by diffusion at surface Whereas Ø Production

of wastes and use of resources occurs in the volume Ø Therefore,

as organisms increase in size they have proportionately less surface area compared

to volume Ø Adaptations

? flat, thin , ribbed bodies increase exchange surfaces 3.2 Ø As

organisms get larger ? they must have exchange surfaces within them Ø all

are moist, thin permeable, large surface area Plants Spongy/Palisade Mesophyll Air directly contacts cells Insects Ends of tracheoles Air directly contacts cells Fish Gill Lamellae O2 absorbed by blood pigments then delivered to

cells Mammals Alveoli O2 absorbed by blood pigments then delivered to

cells Ventilation Ø Aim

? maintain concentration gradient Ø Remove

CO2 rich O2 poor air Ø Supply

O2 rich CO2 poor air Ø Move

respiratory medium over exchange surfaceØ Insects

? larger insects make pumping movements of the abdomen, which crushes the air

sacs and helps to move air Ø Fish

? move operculum out, buccal cavity up ? therefore one way flow of water over

the gill lamellae ? counter current flow of water against the direction of

blood flowØ Mammal

? Tidal flow of air ? movement of diaphragm and ribs Control of Breathing Ø Involuntary Ø Respiratory

centre is bundle of nerves in medulla oblongata Ø Impulses

are sent to the diaphragm and external intercostal muscles causing them to

contract Ø As

lungs expand stretch receptors in airway sense and send back infoØ Meeting Demand Ø CO2

levels vary according to exerciseØ As

CO2 goes up ? pH goes down Ø Chemoreceptors

sense this Ø

Receptors in the medulla oblongata Ø

Carotid bodies in the carotid arteries Ø

Aortic bodies in the aortic arch Ø

As chemoreceptors sense increase in CO2 or decrease in

pH, impulses are sent to the respiratory centre, this sends impulses to the

diaphragm and intercostal muscles increase the rate of ventilation. Oxygen/Haemoglobin

Dissociation Curves 3.7 (part)·

Red blood cells contain haemoglobin (Hb) which transports all of the oxygen around your body

and most of the CO2·

Each Hb molecule can carry up to four O2 molecules.However, ·

The relationship between O2? concentration (partial pressure of O2

- p O2 ) and how much is taken up by Hb (% saturation) is not linear, it is ‘S’ shaped (sigmoid) ·

This is because a completely ‘empty’ Hb molecule takes

up the first O2 rather ‘reluctantly’, then takes up the remaining

three rapidly, and finally it is ‘full’ and won’t take up any more. ·

Loading: In

the lungs the pO2 is very

high, so Hb is ‘filled up’ (saturated) with O2 , represented by the

flat ‘top’ of the curve·

Carrying: As

the Hb travels through arteries and arterioles, pO2 drops, but not

enough for the Hb to give up any oxygen, we are still in the flat region at the top.·

Unloading: When

the Hb reaches capillaries which are next to actively respiring cells, pO2 is much lower, due to

oxygen being consumed to make ATP. Here, Hb is ‘emptied’ of its oxygen, which

diffuses to the cells. This is represented by the steep part of the curve in

the middle of the ‘S’.·

The relationship between p O2 and Hb

saturation is not fixed, the shape of the curve alters in response to various

conditions: Condition Effect on curve Overall result Increased pCO2 Shifts to the right

(Bohr shift) At any given pO2, Hb will be less saturated, so oxygen will be

given up more easily Increased temperature Shifts to the right At any given pO2, Hb will be less saturated, so oxygen will be

given up more easily Increased pH (alkaline) Shifts to the left At any given pO2, Hb will be more saturated, so oxygen will be

given up less easily ·

This makes good sense, if cells are actively respiring

they produce CO2, heat up and become more acidic (due to dissolved

CO2, and production of lactic acid), all these things cause the

curve to move to the right, so

oxygen is given up easily. This oxygen is precisely what actively respiring

cells need!·

Other examples: Foetal Hb is to the left of its mother’s (so it can ’steal’

oxygen from her blood via the placenta). Myoglobin, in muscles has a curve to

the left of Hb (it also ’steals’

oxygen from Hb, and retains it as a store and only gives it up at very low pO2).·

Finally, Hb carries CO2 by means of a series

of reactions (catalysed by carbonic anhydrase) which result in the production

of hydrogen ions and hydrogencarbonate ions. The hydrogen ions are taken up by

Hb, meaning that Hb acts as a buffer,

absorbing excess acid. The hydrogencarbonate diffuses into the plasma, in

exchange for chloride ions (the chloride shift).CARDIAC CYCLE AND ITS CONTROL·

The heart muscle is?

myogenic ( contracts without stimulation) ·

The sino-atrial node coordinates the heart beat so that

the muscle cells contract together. ·

The SAN is in the right atrium next to the vena cava ·

Specialised muscle (Purkinje) fibres radiate out from

the node and cause atrial contracton (systole) ·

These stimulate the AVN, on the septum at the junction

of the atria & ventricles ·

The AVN causes a time delay which ensures the ventricle

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