4.2 Gas exchange Flashcards
why can single celled organisms have oxygen and nutrients diffuse directly into their cells?
- the diffusion distances are very small
- they have a large surface area to volume ratio
- their metabolic demands are low, so they don’t need much oxygen supplied to them
why don’t single celled organisms not need complex gas exchange systems
- diffusion supplies them with enough oxygen to supply their needs
why do larger organisms need complex gas exchange systems
because if it all worked by simple diffusion then oxygen and nutrients wouldn’t be supplied to their cells fast enough because:
1. the diffusion distance is too long
2. they maintain their own body temperature so have greater metabolic needs and require more oxygen
name and explain the factors that affect diffusion rate
- surface area, the bigger the surface area, the faster the diffusion rate
- conc. gradient, the bigger the concentration gradient, the faster the diffusion rate
- diffusion distance, the shorter the distance, the faster the diffusion rate
what are the features of an effective gas exchange system
- a large surface area
- thin layers to minimise diffusion distances
- rich blood supply to respiratory surfaces to maintain the concentration gradient
- most surfaces
- permeable surfaces
hoe is the nasal cavity adapted for its function
- The lining of the nasal cavity secretes mucus and is covered in hairs, to prepare external air for internal system
- the hairs and mucus filter out a lot of the particles and pathogens
what are alveoli made of
a single layer of epithelial cells
lung surfactant to stop them collapsing
what’s the elastic recoil of the lungs
the elastic tissue in the lungs helps force air out of the lungs, which stretch when you breathe in
how is the site of gas exchange adapted for gas exchange
- alveoli are folded single layers of epithelial cells and capillaries are one cell thick, provide a large SA and short diff. distance
- capillaries have a very good blood supply, so maintains a steep concentration gradient
define ventilation
the process of moving air between the lungs and the external environment
what is the chest cavity
a sealed unit of air, air can only enter or leave through the trachea
what happens during inhalation
- active process
- muscles around diaphragm contract, lowered and flattened
- intercostal muscles contract, raises rib cage, expands chest cavity volume
- cavity pressure < outside air, so air moves into lungs to equalise pressure
what happens during normal exhalation
- passive process
- muscles around diaphragm relax, so it moves up
- intercostal muscles relax
- ribs move down and in
- elastic fibres around lungs and alveoli return to normal length so volume of chest cavity decreases
- chest cavity pressure > outside air, so air leaves lungs to equalise pressure
what happens when you actively force air out of your lungs
- intercostal muscles contract, pulling ribs down and in
- abdominal muscles contract which force diaphragm upwards
- increases pressure in chest cavity and forces exhalation
how does the respiratory system protect the lungs
it produces a lot of mucus that lines the airways and traps tiny particles and organisms, it is moved upwards by the cilia towards the back of the throat where its swallowed and digested by stomach acid
what are spiracles
the site of entry and exit of respiratory gases, found along the abdomen and opened or closed by sphincters (which also control water loss)
what are tracheae
largest tubes that carry air directly into the body for gas exchange
supported of spirals of chitin that hold them open, but also makes it impermeable to gases
what are tracheoles
minute tubes made from single elongated cells, permeable to gases, spread throughout tissue and penetrate individual cells
how does insect respiratory system work
- air enters through spiracles, sphincters keep them closes as much as possible to minimise water loss
2.air moves along trachea then tracheoles by diffusion - air moves into cells
how do spiracles know when to open and close
- it is a response from the insects nervous system
- nervous system stimulated by increasing CO2 levels or built up lactic acid
what are the features of the gas exchange system in very active insects
- mechanical ventilation
- air is pumped actively into tracheal system, spiracles open, insect makes pumping movements of the thorax/ abdomen
- these movements change the volume and pressure inside the body and draw air in and out of trachea and tracheoles - collapsible trachea and air sacs that act as reservoirs
- increase volume of air moving through respiratory system
- ventilating movements of the thorax inflate and deflate air sacs
how is the gas exchange system in fish adapted for their environment
- they have a large surface area for diffusion
- they have a good blood supply to maintain concentration gradients
- they have thin walls for short diffusion distances
describe the structure of gills
- the fragile gill filaments occur in large stacks
- they need water to keep them apart to expose the large surface area
- gill lamellae is the main site of gas exchange and they have a very rich blood supply
- blood leaving the gills leaves in the opposite direction of incoming water, ensuring the most effective exchange of gases
describe the ventilation of the gills in fish
- most fish have evolved a system of ensuring the constant flow of water in the mouth and gills even when they’re not moving / their mouths are closed
- when the mouth is open, buccal chamber expands and operculum cavity is closed
- when the mouth is closed the buccal chamber contracts and the operculum cavity is open, water flows out
how is gas exchange maximised in gills
- countercurrent exchange system
- blood in the gill filaments and water moving over the gills flow in different directions
- this maintains a steeper conc. gradient for the diffusion of gases than if they were flowing in the same direction, more gas exchange can occur - overlapping gill filaments
- diffusion in water tends to be slow, so if water passes over gills too quickly, it limits gas exchange.
- the tips of the adjacent gill filaments overlap, increasing the resistance of water flow, slowing it down and giving more time for gas exchange to occur
what is the main site of gas exchange in plants
- the leaves
what are the adaptations of the leaf for gas exchange
- leaves provide a large surface area
- spongy mesophyll cells have irregular shapes, increasing their surface area and leaving gaps between the cells, this also allows for the flow of gases between cells and air spaces
- surfaces of spongy mesophyll cells are moist
- waxy cuticle acts as a barrier to water evaporation through the leaf’s surface
how is gas exchange controlled in plants
- pores on the underside of the leaf called stomata, surrounded by two guard cells
- when conditions are favourable for photosynthesis, water moves into guard cells from surrounding epidermal cells and by osmosis and stomata open
- when conditions are less favourable, active pumping of potassium ions into the cells stops and water leaves the cells by osmosis and turgor is reduced and the stomata closes
