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Flashcards in Gas Exchange Deck (89):

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:-

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.



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:-



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?



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.


Up to percentage of O2 in water does the system enable bony fish to remove?



What 3 things maintain steep concentration gradient in bony fish?

-dense capillary network ehich circulates oxygenated blood away from and deoxygenated towards the lamallae.
-blood contains haemoglobin with high O2 affinity which increased oxygen carriage efficiency.


What is GE medium for land vertebrates?



Internal lungs:-

Provide large SA reduce water and heat loss as are within the body cavity.


Amphibiam habitat:-

Typically live in moist habitats as they require water for fertilisation


Amphibian larvae (tadpoles):-

Live in water and have gills.
Transition from larvae to adult frog involves changes in body form (metamorphosis).
Adult frog develops lungs.


Frog GE (4 points):-

-cold blooded so don't have a high metabolic rate at rest as don't have to maintain body temperature.
-when inactive can use moist skin as a resp surface + it provides enough oxygen to satisfy its needs.
-when active, the adult frog use its lungs as a resp surface.
-also use buccal cavity as a GE surf.


Reptile GE:-

Their lungs have a more complex internal structure than that of amphibians w/ ribs assisting in ventilation of the lungs and the in-growth of tissues increasing the SA for GE.


4 points for bird GE:-

-the lungs of birds have an internal structure similar to that of mammals.
-require large oxygen vol to provide energy for flight. Also have high metabolic rate as are warm-blooded.
-ventilation of the lungs in birds is far more efficient than in other vertebrates and is assisted by a system of air sacs.
-although no GE occurs in the sacs, they act as a reservoir moving air.


Insect exoskeleton:-

Rigid, made of chitin, reduced water loss water loss.


Why do insects need a specialised gas exchange system?

Relatively small SA:vol ratio


What does insect GE occur through?

Paired holes called spiracles, running along the side of the body.


Insect tracheal system structure (6 points):-

-hairs covering spiracles help prevent water loss and solid particles getting in.
-spiracles lead into system of chitin lined air tubes called tracheae.
-spiracles can open and close like valves.
-this allows GE to take place but reduces water loss.
-ends of tracheal branches are called tracheoles.
-every cell in an insect is only a short distance from tracheoles =short diffusion pathway.


Insect GE at rest:-

Simply passive diffusion via the spiracles.


Insect GE during activity:-

Muscles in the thorax and abdomen contract and relax, helping draw air in through the thoracic spiracles and out through the abdominal spiracles.


What does insect ventilation mechanism ensure?

A fresh supply of air is constantly passed from front to back segments over the GE surfaces and a conc grad is maintained.


Insect GE imto muscles 3 points:-

-the ends of the tracheoles are filled with fluid and are close to muscle fibres.
-interface between the tracheoles and the muscles= wherr GE takes place.
-oxygen dissolves in the fluid and diffuses directly into the muscle cells, so no resp pigment or blood circulation is needed.


How does CO2 diffues out insects?

Reverse process.


3 advantages of insect adaptations:-

-every tissue directly supplied with O = fast GE system.
-no haemoglobin needed.
-reduced water loss.


8Components of human resp system (area =thorax, have a labelled diagram):-

Pleural membrane



A flexible airway bringing air to the lungs. Strengthened by rings of cartilage that keep airway open.


Ribs/intercostal muscles:-

Ribs surround the thorax. Intercostal muscles are located between. They can alter thoracic cavity size to change vol/pressure during inspiration and expiration.


Pleural membranes:-

Line thorax and cover each lung. Fluid between the membranes prevents friction between the lungs and the chest cavity when the lungs move.



Two bronchi which are bramches of the trachea. They carry air to and from each lung.



Branching network of tubes which branch off from the bronchi.



Air sacs located at ends of bronchioles. Provide surface for GE.



Alters size of thoracic cavity to change volume/pressuring inspiration and expiration.


2 human respiratory system functions:-

Ventilation and gaseous exchange.


3 advs of internal lungs:-

-infolding reduces heat loss.
-infolding reduces water loss.
-protected by ribcage.


Human ventilation purpose:-

To move gases over the GE surf to maintain a conc grad between blood capillaries and blood in the alveoli.


How do mammals ventilate their lungs?

By negative pressure breathing, forcing air down into the lungs. In order for air to enter the lungs, the pressure inside must be lower than the atmospheric pressure outside.


7 components of inspiration (active process because muscle contraction requires energy):-

-diaphragm contracts and flattens.
-external intercostal muscles contract, moving the rib cage up and out.
-outer pleural membrane pulled out.
-this increases the volume of the thoracic cavity.
-decreases pressure in pleural cavity and inner pleural membrane moves outwards.
-this pulls on the surface of the lungs and causes the alveoli to expand.
-atmospheric air pressure now greater than in the lungs air moves down pressure grad into lungs.


7 components of expiration (mainly passive process):-
*essentially opposite of inspiration.

-diaphragm relaxes and domes upwards.
-external intercostal muscles relax. Rib cage moves down and in.
-outer pleural membrane pulled in.
-this decreases the thoracic cavity vol.
-increases pressure in pleural cavity and inner pleural membrane moves inwards.
-this reduces the pull on the surface of the lungs so the alveoli relax.
-air pressure in the lungs greater than atmospheric so air moves down pressure gradient from lungs to outside.


How do lungs have a large SA?

-millions of alveoli.
-extensive capillary network surrounding each alveolus.


How do lungs have a moist surface?

Tissue fluid, known as surfactant, lining the alveolus allows gases to dissolve and diffuse across.


How do lungs have a short diffusion pathway?

-alveolar wall is a single layer of flattened squamous epithelial cells.
-the capillary is a single layer of flattened endothelial cells.


How do lungs maintain a steep concentration gradient?

-ventilation ensures O2 conc in the alveolus is high.
-a dense capillary network surrounding the alveoli maintains diffusion gradients as O2 is rapidly carried away from the alveoli and CO2 is rapidly brought to the alveoli.


Role of surfactant (5 points):-

-coats the inside surfaces of the alveoli:-
-made of moist secretions containing phospholipid and protein.
-has a low surface tension so acts as an anti-sticking mixture.
-prevents the alveoli collapsing during expiration when the air pressure inside them is low.
-allowa gases to dissolve before they diffuse in or out.


Where does human GE take place?

In the alveoli


Respiration equation:-

Glucose + oxygen -> carbon dioxide + water + ATP


Photosynthesis equation:-

Carbon dioxide + water -> glucose + oxygen

->= light energy and chlorophyll


Plant CO2 source:-

Some of the CO2 they need for photosynthesis is produced by respiration, but most diffuses into the leaves from the atmosphere.


Use of O2 produced by photosynthesis:-

Some is used in resp, but most diffuses out of the leaves.


Which processes do plants do both of during the day?

Resp and photosynthesis


Plant GE at night:-

-only respire so need more O from the atmosphere.
-some O enters the stem and roots by diffusion but most GE occurs at the leaves.
-at night, photosynthesis doesn't happen so no O is produced, so the gas released is CO2.


Plant GE during day:-

-rate of photosynthesis is faster than rate of respiration.
-more oxygen is produced in photosynthesis than is used in respiration so overall the gas released is oxygen.


What do plants rely on entirely for exchange of CO2 and O2?



What are plant leaves structurally adapted to do?

Maximise GE and light absorption and prevent dehydration due to excess water loss.


Diffusion in leaves:-
(3 points)

-gases diffues throught the stomata (s. Stoma) down a conc grad.
-once inside the leaf, the gases in the sub-stomatal air chambers diffues through the intercellular spaces between the spongy mesophyll cells and into cells.
-the direction of diffusion depends on the conc of gases in the atmosphere and the needs of the plant.


Structure of leaf, top to bottom:-

-Wax cuticle.
-Upper epidermis.
-Palisade mesophyll.
-Spongy mesophyll.
-Lower epidermis W/ stomata.
-Wax cuticle.
-Air space throughout.
*mesophyll cells and stomata guard cells have chloroplasts.


5 leaf adaptations for CO2 absorption (inc 3 of spongy mesophyll):-

-thin leaves to reduce absorption difference.
-stomatal pores allow the entry of gas into the small spaces.
•Spongy mesophyll:-
- large SA for GE.
-contains air spaces to allow circulation of gases and reduce diff pathway of CO2.


How do stomata open in light?

Chloroplasts photosynthesise in guard cells, producing ATP which fuels pumping of K+ into guard cells. These stimulate conversion of starch by enzymes from insoluble starch to soluble malate, lowering water pot. Water therefore flows in, the cells expand and become turgid. Inner wall thicker than outer so the cells curve away from each other, pore opens.


Why are stomata open in the day and closed at night?

Day- increases rate of CO2 diffusion into spongy mesophyll cells. Close at night as no photosynthesis and to reduce water vapour loss via transpiration.


Why do Xerophytes open their stomata at night instead of in the day?

Adapted to dry/desert habitats- conserves water