Gas Exchange Flashcards
5 properties GE surfaces of all living organisms share:-
- Large surface area:volume ratio so rate of GE satisfies organism’s needs.
- Thin = short diffusion pathway.
- Permeable to gases.
- moist because gases must dissolve before they can diffuse across membranes.
- have ventilating mechanism to maintain steep conc grad across GE surface.
3 ways of increasing diffusion rate:-
- increasing SA
- decreasing diffusion pathway
- increasing gradient steepness
Surface area:Vol ratio:-
Supply:Demand
All organisms need O2 for resp.
Demand is proportional to organism volume.
Rate of uptake is proportional to surface area.
What has a larger SA:Vol ratio?
Smaller animals.
5 points about GE in unicellular (amoeba):-
- thin membrane = short pathway.
- large SA:VOL (0.1mm length).
- unicellular (thin) = short diffusion distances inside.
- lives in water =moist surface.
- no specialised systems = low O2 demand.
Unicellular (amoeba) therefore summary:-
Therefore unicellular organisms can absorb enough O2 to satisfy their needs for resp and remove CO2 fast enough to prevent it building up, lowering pH and causing harm
What are the 3 specialised resp surfaces of multicellular organisms?
- gills for aquatic organisms.
- lungs for terrestrial environments.
- trachea in insects
3 things multicellular also need for efficient GE:-
- ventilation mechanism to maintain steep conc grad across resp surfaces by moving GE medium (air/water) or in larger animals, blood.
- internal transp system (circulatory system) to move gases between resp surf + respiring cells.
- resp pigment in blood (e.g. Haemoglobin) to increase its O carrying capacity.
Annelids:-
There are some simple multicellular animals that have evolved to enable GE to take place across their body surface.
5 earthworm GE adaptations:-
- elongated body shape = increased SA:Vol.
- live in damp area + secrete mucus = skin remains moist.
- well developed capillary network close to skin surface provides short diffusion pathway.
- blood contains haemoglobin which has high O2 affinity = increased GE efficiency.
- low metabolic rate = low O2 demand.
Flatworm description:-
Aquatic animals which have evolved a flattened shape.
Flatworm length:-
15mm
3 flatworm adaptations:-
- low metabolic rate.
- short diffusion pathway (0.2mm thick body).
- increased SA:Vol due to flattened body.
Why do fish have have higher O2 demand than invertebrates?
More active.
What is the fish gas exchange medium?
Water.
Why is diffusion rate lower for fish?
Water contains less O2 and is more dense than air.
What is the effect of gills’ many folds?
Increases SA over which water can flow and gases can be exchanged.
How is GE efficiency increased in fish?
Water is forced over the gills by pressure changes in the body which maintains a continuous, unidirectional flow.
Two groups of fish based on skeletal structure:-
Cartilaginous fish
Bony fish
Examples of cartilaginous fish and skeleton:-
Sharks and rays
Skeleton made of cartilage.
3 points of cartilaginous fish GE:-
- 5 gill slits which open into gill clefts (pouches) just behind head on each side.
- water enters mouth and is forced out through the gill slits when the roof of the mouth is raised.
- don’t have a specialised ventilation mechanism to force water over the gills so they must keep swimming for ventilation to happen.
Parallel flow:-
Blood flows through the gill capillaries in the same direction as the water flows over the gills.
Why is parallel flow GE inefficient?
Equilibrium is reached halfway across gill (lamallae) so it doesn’t occur across the whole lamallae as O2 diffuses from where it is more concentrated.
Effect of bony fish ventilation mechanism:-
Allows blood to flow through the gill capillaries in the opposite direction to the water passing over them (counter current flow).
3 bony fish GE structural adaptations:-
- gills found just behind head, in the pharynx.
- 4 pairs of gills.
- flap called the operculum covers + protects gills on each side.
Gill structure:-
3 points
- each gill is supported by a gill arch.
- along each arch are many pairs of gill filaments and on these are the GE surfs, the gill lamellae.
- lamallae are formed by numerous thin folds lying in top of each other.
Gills in and out of water:-
In:- filaments are supported and lamallae provide a large SA.
Out:- the gill collapsed as the gill filaments lie on top of each other and stick together.
Purpose of many blood capillaries on lamallae:-
Take up O2 from the water and co2 passes out.
Fish blood:-
Contains Haemoglobin, increases transport efficiency in blood.
Flow for bony fish ventilation mechanism:-
Unidirectional because water is too dense to move in 2 directions.
Water is forced over filaments by pressure differences which maintain a continuous unidirectional flow.
6 components of bony fish water intake:-
- mouth opens.
- operculum closes.
- floor of mouth (buccal cavity) lowers.
- volume inside mouth increases.
- pressure inside mouth decreases.
- water flows in down a pressure gradient as the external pressure is higher than the pressure inside the mouth.
6 components of bony fish forcing water out over the gills (essentially opposite of intake):-
- mouth closes.
- operculum opens.
- floor of mouth raised.
- volume inside decreases.
- pressure increases.
- water flows out over the gills because the pressure in the mouth is higher than in the opercular and outside.
Gas exchange definition:-
The diffusion of gases down a concentration gradient across a respiratory surface, between an organism and its environment.
Counter current flow:-
Water containing O2 flows in the opposite direction to that of the blood in the capillaries of the gill filament.
Why is counter current flow more efficient for GE that parallel?
- there is always a higher O2 conc in the water than the blood it meets so equilibrium is never reached.
- this enables O2 to diffuse into the boood along the whole length of the gill lamallae.