3.2 Gas exchange Flashcards
what gives a leaf a large surface area
mesophyll cells with air spaces between them
what gives a leaf a large concentration gradient (4 things)
- constant use and removal of gases
- air spaces continuous with air
- huge number of stomata
- leaves help of to let breeze renew the air
what gives a leaf a short diffusion distance (2 things)
- thin cell walls
- mesophyll cells close to stomata
xerophytes adaptions to reduce water loss (5 things)
reduced leaf area - through needles
thick waxy cuticle - reduce evaporation
hairy leaves - hairs trap a layer of saturated air
sunken stomata - the pits above the stomata become saturated
rolled leaves - this reduces the area exposed to the air and keep the stomata on the inside so increasing the water vapour inside the roll
3 xerophyte adaptions to increase water intake
deep extensive root system - to maximise water uptake
accumulation of solutes in the root system - to reduce the ψ so making the ψ gradient from the soil to the root cells steeper
some very shallow roots to absorb dew which condenses on the soil at night
why do plants close their stomata
as at night there is no sun to carry out photosynthesis so they want to close their stomata to reduce water loss as there is no need to absorb CO2. The stomata are also closed around midday as there is more heat so they want to hold water and reduce loss through transpiration as there would be a shallower concentration gradient.
3 features of single celled organisms for efficient exchange
- large surface area to volume ratio
- small diffusion distance - only pass through one membrane
- large concentration difference - oxygen is continually being used in respiration and CO2 produced so there is always a concentration gradient
5 features of specialised exchange
- a large surface area to volume ratio - increases the rate of exchange
- very thin - so that the diffusion distance is short and therefore materials cross exchange surface rapidly
- selectively permeable - to allow selected materials to cross
- movement of the environmental medium - air to maintain diffusion gradient
- a transport system - to ensure the movement of the internal medium such as blood in order to maintain a diffusion gradient
why are insects not bigger
as if they were bigger they would have more cells which means more demand for oxygen and the tracheal system could not provide for the respiratory demands
order of exchange systems in insect
spiracles > trachea > thracheols > muscle fibres
how do muscular contractions help an insect during exercise
muscular contractions help maintain a concentration gradient during exercise by increasing ventilation rate allowing a higher rate of oxygen for the insect
why is there moisture at the end of tracheoles in an insect
so oxygen can dissolve and then diffuse easier
three steps of inspiration in insects
increase volume from relaxing muscles
decreases pressure
air force in
three steps of expiration in insects
decrease volume from contracting muscles
increase pressure
Air forced out
three insect adaptations to reduce water loss
small surface area to volume ratio to minimise area over which water is lost
waterproof coverings over the body
spiracles can be closed to reduce water loss with trapping humid air with hairs around spiracles
steps of water flow in gills
water enters the mouth > buccal floor closes shutting mouth increasing pressure forcing it over the gills > over the lamellae > oxygen moves into blood in blood vessels
why counter currant
water passes over gill plates in opposite direction to the flow of blood so the blood meats water with a higher oxygen concentration than its own. This increases the efficiency of oxygen extraction by ensuring there is a diffusion gradient along the whole gill plate so the blood absorbs more oxygen. this is because if the blood flowed the same way they will both quickly reach equilibrium and the blood would extract less of the available oxygen from the water.
6 steps of counter current flow
- as the blood flows in the opposite direction to the water, to always flows next to the water that has given up less of its oxygen
- this way the blood is absorbing more and more oxygen as it moves along
- even as the blood reaches the end of the lamella and is 80% or so saturated with oxygen, it is flowing past water which is at the beginning of the lamella and is 90-100% saturated
- this means hat even when the blood is highly saturated having flowed past most of the length of the lamellae
- there is still a concentration gradient and it can continue to absorb oxygen from the water
- meaning oxygen can diffuse over the whole length of the gill.
3 ways the gills have a large surface area
- each gill has 2 rows of lamellae
- each lamellae has a series of gill plates at right angles
- each gill plate has a mass of capillaries
3 ways the gill has a short diffusion distance
- lamellae walls are only one cell thick
- capillary walls are only one cell think
- blood close to surface gradient
3 ways the gill maintains a diffusion gradient
- ventilation ensures continual flow of water
- circulation of blood
- counter currant flow
describe the trachea
a flexible airway that is supported by rings of cartilage. this cartilage prevents the trachea collapsing and the tracheal walls are made of muscles lined with ciliated epithelium and goblet cells producing mucus
describe the bronchi
are two divisions of the trachea each leading to one lungs. similar in structure to the trachea
describe bronchioles
are a series of branching subdivisions of the bronchi, their walls are made of muscles lined with epithelial cells, this muscle allows them to constrict so that they can control the flow of air in and out of the alveoli
