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ADAPTIONS FOR GAS EXCHANGE - Coggle Diagram
ADAPTIONS FOR GAS EXCHANGE
Aerobic respiration involves oxygen absorption
Organisms that respire aerobically absorb oxygen and release carbon dioxide.
Absorption of oxygen and release of carbon dioxide is known as gas exchange.
Oxygen must reach the cells of an organism fast enough to maintain respiration and therefore meet its metabolic needs.
The route through which is gases diffuse is known as the
diffusion pathways.
Longer diffusion pathways = Slower diffusion of gases.
As organisms increase in size their surface are-to-volume ratio decreases
A
small surface area-to-volume ratio
means that
larger organisms require specialised gas exchange surfaces in order to meet the organisms metabolic needs.
Larger organisms are also often metabolically active
, meaning that they have a
higher oxygen demand.
Single celled organisms such as amoeba have a large surface are-to-volume ratio
Single-celled organisms so not require specialised surfaces because diffusion pathways are very short.
Diffusion of gases across the cell surface membrane is s
ufficient to meet the metabolic needs of an organisms
.
Some multicellular organisms can also exchange gases through the body surface.
Flatworms:
Because of large size,
flatworms have a much smaller surface area-to-volume ratio than amoebae.
They are
flattened
, which
maximises their surface area-to-volume and ensures that the diffusion pathways for gases are short enough to diffuse gases to be fast enough to meet their metabolic need.
-
Gas exhange can occur through the flatworms' body surface and they do not require a specialised respiratory surface.
Earthworms:
Are also multicellular organism that use their body surface for gas exchange.
However, their
body shape means that their surface are-to-volume ratio is too small and diffusion pathways are too long, so they are unable to rely on diffusion. alone to supply their cells fast enough to meet their metabolic needs.
Earthworms therefore have a
circulatory system that transports gases to the respiring tissues
.
Gases diffuse through their body surface and into cappilaries in the skin.
Contractions of
pseudohearts then pump the blood around the body.
Insects have a tracheal system
Insects are adapted to terrestrial life by having tracheal system.
Insects have an impermeable cuticle, which reduces water loss by evaporation
An insects impermeable cuticle means that gases cannot be exchanged over the body surface.
Instead,
air enters the insects body
through
small, paired holes called
'spiracles' on the thorax and the abdomen.
Air enters the 'spiracles
' and then
travels through a system of tubes called tracheae and then tracheoles.
The
tracheoles come into direct contact with repiring cells in all tissues
; the
ends of the tracheoles are the gas exchange surface and gases diffuse directly into and out of the cells.
-
Contractions
of the insect's body
speed up the movement of air through the spiracles
. The spiracles are able to open and close to conserve water.
Larger animals have specialised respiratory surfaces.
Respiratory surfaces in larger animas are adapted to environmental conditions - for example, fish have gills for aquatic environments and mammals have lungs for terrestrial environments.
A number of features are required for efficient exchange of gases
Specialised respiratory surfaces:
A large surface area
- to maximise the absorption of gases.
To be moist
- to ensure the efficient diffusions of gases.
To be thin
- to provide a short diffusion pathways for gases.
A good blood supply
- to transport gases to and from the gas exchange surface and maintain the concentration.
Large, active animals with high metabolic rates have mechanisms to allow
ventilation
.
These mechanisms maintain diffusion gradients across respiratory surfaces.
Bony fish use internal fills as a gas exchange surface
Bony fish
have internal gills
, which
they ventilate by drawing water in and then pushing it out and over the gills.
Gills have a large surface area for gases to diffuse
due to the gill filaments and gill plates.
When water flows over the gills it separates them, maximising the surface are for gas exchange.
Capillaries
in the gill filaments
ensure there is a good blood supply and fish ventilate the gills to maintain the concentration gradient between the blood and the water.
This process of ventilation in fish:
1) - The fish's mouth opens and the floor of the buccal cavity lowers; the operculum is closed.
2) - The lowers the pressure in the buccal cavity and draws water in
3) - The mouth closes, the floor of the buccal cavity raises and the operculum opens; this increases the pressure in the buccal cavity and forces water over the gills and out of the operculum.
Bony fish have a countercurrent system of blood flow over their gills
Countercurrent flow:
That
blood flows in the opposite direction from the water flowing over the gills.
This e
nsures that water is always in contact with blood,
which has a l
ower oxygen concentration.
This
maintains a concentrations gradient for diffusion of oxygen from the water into the blood across the whole length of the gill.
This
allows the blood to become highly saturated with oxygen.
Countercurrent flow:
Water and blood flowing in the opposite direction.
Parallel flow:
Where
water and blood flow in the same direction over the gill.
In parallel flow equilibrium is reached and after that point there is no net diffusion of oxygen from water into the blood.
This means that the
blood has a lower oxygen saturation than in countercurrent flow.
Parallel flow:
Water and blood are flowing in the same direction.
Amphibians have lungs but are also able to carry out gas exchange through their skin.
Amphibians
Have a
lower metabolic rate than mammals because they do not need to maintain their body temperature.
Meaning diffusion of oxygen through their skin is fast enough to meet their metabolic needs of the amphibian, particularly if the amphibian is not hunting and remaining particularly unactive.
Humans have an internal gas exchange surface to reduce water and heat loss
The gas exchange surface is in the
alveoli.
Gases diffuse through the wall of the capillary into and out of the blood.
Ventilation ensures that a concentration gradient for oxygen and carbon dioxide is maintained
Humans ventilate their lungs using negative pressure breathing:
Inspiration:
External intercostal muscles contract - ribs move upwards and outwards, and the diaphrgm down.
Diaphragm muscles contract.
Expiration:
External intercostal muscles relax - ribs more downwards and inwards. and the diaphragm muscles relax.
Process:
The external intercostal muscles contract, which raises the ribcage, pulling on the outer pleural membrane; this reduces the pressure the pleural cavity.
The diaphragm contracts and flattens; the inner pleural membrane moves outwards.
The inner pleural membrane pulls on the surface of the ling and causes on volume of the alveoli to increase; this decreases the alveolar pressure below atmospheric pressure and air is drawn into the lungs.
Leaves are adapted for photosynthesis and gas exchange
The leaf is the photosynthetic organ of a plant
Adaptions of leaves for photosynthesis:
Adaptations:
The cuticle and epidermis are transparent.
Palisade mesophyll cells contain many chloroplasts, which are able to move within the cells.
Well-developed xylem.
Well-developed phloem.
Benefit:
Allows light to pass through to the photosynthetic mesophyll tissue.
Maximises the absoption of light for photosynthesis.
Provides water, which is a reactant for photosynthesis.
Transports the products of photosynthesis.
For photosynthesis to occur, the leaf also needs to adapted for exchange of gases. For photosynthesis plants needs to take in carbon dioxide and the oxygen produced is either used in respiration or released.
Stomata can open and close to reduce water loss
In the light,
chloroplasts
in the guard cells surrounding the stomata
produce ATP during photosynthesis.
The
ATP is used to actively transport potassium ions (k+) into guard cells.
Starch, which is insoluble and therefore osmotically inactive, is converted into malate, which is soluble and therefore osmotically active
The presence of the
malate and the k+ lowers the water potential of the guard cells.
This leads to
water moving into the guard cells by osmosis down a water potential gradient.
The outer walls of the guard cells are thinner than the inner walls of the guard cell.
This means that as
water moves into the guard cells and they become turgid the outer walls of the guard cells bend more than the inner walls. This causes the stomatal pore to open.
The reverse of this process occurs in the dark, causing the guard cells to close.