2.2 gas exchange Flashcards
what do all living organisms require to survive?
a source of energy
How is energy obtained?
through respiration
what occurs in every cell
respiration
generates ATP
using oxygen and releasing carbon dioxide as a waste product and in order to keep this process going, we need to do this continously
what is gas exchange?
the diffusion of these gases in opposite directions across an exchange surface
what does gas exchange involve?
the rapid and efficient exxchanfe of oxygen and carbon dioixde across the respiratory surface
in order to achieve the maximum gas exchange, a respiratory must have :
a large surface area - relative to the volume of the organisms to satidfy the needs of the organisms
be thin - so that the length of diffusion pathway is short
permeable - to allow the gases to pass through
moist - to allow a medium in which the gases dissolve before diffusion
maintain a concentration gradient
what is the surface area to volume relationship?
as the size of an organism is increased, its surface area to volume ratio decreases
why does the relationship have important consequences for organisms?
some processes such as rate of diffusion depend on surface area whilst others such as metabolic rate depend on volume
consequently, a small organism such as amoeba can satisfy its need for oxygen by simple diffusion. however, simple diffusion cannot supply sufficient quantities of oxygen for larger organisms.
therefore larger organisms have evolved respiratory exchange surfaces such as lungs,gills and trachae
what are the problems associated with gas exchange in air and water?
the highest metabolic rtes are airbreathers
for example mammals and birds are air breathers
they cant obtain the amount of oxygen they need from water
but the problem w breathing air = the loss of water. the combination of a large surface area + moist membrane means that exhaled air = saturated with water vapour
gas exchange single celled organisms
as the organisms are so small, they have a very large surface are to volume ratio. their external surfaces can therefore be used to exchange gases, as the large surface area = able to supply sufficient oxygen to small volume
for example amoeba?
they live in water.
the water has a higher conc of oxygen than found in the organisms . oxygen therefore diffuses through the plasma membrane in the cell where oxygen is at a lower concentration and can reach every part of its small volume.
gas exchange in simple multicellular animals?
simple multicellular animals - worms have modest oxygen requirements because they are slow moving + so have a very slow metabolic rate. oxygen and carbon dioxide diffuse across the skin surface so dont have any special exchange organs
Flatworms?
= aquatic animals that have a flattened shape
this increases the surface are to volume ratio , ensuring that no part of the body is far from the surface (maintaining a short diffusion pathway)
Earthworms?
terrestial orgaisms that have a tubular shape and are restricted to the damp environment of the soil. its elonagated shape provides it with a large surface area to volume ratio compared to a compact organism of the same volume.
doesnt require a special surface for gas exchange, it doesnt need to keep its skin moist by excreting mucus onto the surface
earthworm has a closed circulatory system.
blood also contains a respiratory pigement for oxygen transport.
oxygen diffuses into the blood cappilaries beneath the skin surface and carried in vessels to the cells with carbon dioixde being transported in the opposite direction.
blood system maintains a diffusion gradient atthe respiratory surface.
How are amphibians adapted to gas exchange?
amphibians = frogs, toads and newts.
frogs live in moist habitats as they require water for fertilisation.
tadpoles also live in water and have gills
inactive adult uses the moist skin as a respiratory surface and this provides sufficient oxygen for its needs
when active as in mating, frog uses lungs as a respiratory surface.
reptiles?
include crocodiles, lizards and snakes
better suited to life on land than amphibins
reptiles can move on all 4 limbs without the truck of the body touching the ground
pairs of the ribs project from the vertebrae
ribs provide support and protection to the lungs
the lungs also has a more complex internal structure than that of amphibians with the in - growth of tissues increasing the surface area for gas exchange.
Birds?
lungs of birds have an internal structure to similar to that of animals.
however, large volumes of oxygen = needed to provide the energy for flight
ventilation of the lungs in birds = far moreefficient than that in vertebrates
structure of insects?
insects have a segmented body with a rigid exoskeleton made of chitin. the outside of the exoskeleton = covered with a layer of wax, making it impermeable to water and gases
an insect has a trachael system consisting of tubes leading from the outside to the inside of the body.
on the outside of the insect’s body there are small hoes on each side of the segments, through which gases can diffuse. the holes - spiracles can open and close to the level of ventilation.
gas exchange in small insects?
transport is entirely by diffusion
gas exchange in a large insect or when it is active
these insects compress their abdomen and squeeze air from the tracheal tubes. fresh air moves into the tubes when the body = very active
what is happening when an insect is very active?
lactic acid accumulates in the cells, decreasing the water potential. by osmosi, water in the tracheoles drawn into the cells, causing more air to enter the tracheoles. this means that more oxygen comes into close contact with the tissues at the time when it is required.
some of the moisture in the tracheoles will inevitably evaporate and diffuse out through the spiracles.
in hot dry windy conditions, insects can reduce water loss through their spiracles by closing them by means of a muscular valve
hairs around the spiracles can trap most air also reducing water loss
respiratory systems in animals
land animals skin adapted to conserve water and is an unsuitable surface for gas exchange. furthermore, mammals are too large to rely solely on diffusion to gas exchanges, it would take too long for oxygen to reach the cenral cells from the skin.mammals have evolved specalised internal organs, to enable them to exchange gases without losing too much water.
where does gas exchange take place?
the alveoli
