3.3.2 gas exchange Flashcards
what is a gas exchange surface
boundary between outside and inside environment that gas exchange occurs over
what do organisms need to diffuse across gas exchange surfaces as quickly as possible?
oxygen and carbon dioxide
what do most gas exchange surfaces have to increase the rate of diffusion?
large surface area
thin - often 1 layer of epithelial cells (short diffusion pathway)
what do most organisms often do to help with rate of diffusion in gas exchange?
organism maintains steep concentration gradient of gases across the exchange surface, increases rate of diffusion
gas exchange in single celled organism
single celled organisms absorb/release gases by diffusion through their cell surface membranes
do single celled organisms have a specialised gas exchange system?
large surface area, thin surface, short diffusion pathway so no need for specialised gas exchange system
what is the gas exchange surface in fishes?
the gills
do fish have special adaptions to get enough oxygen?
there’s a lower concentration of oxygen in water than in air so fish have special adaptations to get enough of it
structure of the gills: how does water enter and leave the fish
water, containing oxygen, enters the fish through its mouth and passes out through the gills
structure of the gills: what is each gill made of
each gill is made of lots of thin plates (gill filaments)
structure of the gills: what do gill filaments give?
gill filaments give a large surface area for exchange of gases so increase rate of diffusion
structure of the gills: what are gill filaments covered in?
gill filaments are covered in lots of lamellae which increase surface area even more
structure of the gills: what features do lamellae have?
lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and the blood
the counter current system in fish: what is it?
in fishes’ gills blood flows through the lamellae in 1 direction and water flows over them in the opposite direction (counter current system)
the counter current system in fish: what does it do?
the cc system means the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen
the counter current system in fish: what does this do to the concentration gradient?
means that steep concentration gradient is maintained between the water and the blood over the whole length of the gill so as much oxygen as possible diffuses from the water into the blood
gas exchange in dicotyledonous plants:
what do plants need carbon dioxide for?
plants need carbon dioxide for photosynthesis which produces O2 as a waste gas
gas exchange in dicotyledonous plants:
what do plants need O2 for?
plants need O2 for respiration , which produces CO2 as a waste gas
gas exchange in dicotyledonous plants: what is the main gas exchange surface in the leaves?
the main gas exchange surface is the surface of the mesophyll cells in the leaf
gas exchange in dicotyledonous plants:
how are mesophyll cells well adapated to their function?
mesophyll cells are well adapted to their function by having a large surface area
gas exchange in dicotyledonous plants:
where would you find the mesophyll cells?
the mesophyll cells are inside the leaf
gas exchange in dicotyledonous plants:
how do gases move in and out
gases move in and out through pores in the epidermis (mostly the lower epidermis) called stomata
gas exchange in dicotyledonous plants:
what do stomato do
the stomata can open to allow exchange of gases, and close if the plant is losing too much water
gas exchange in dicotyledonous plants:
what do guard cells do
guard cells control the opening and closing of the stomata
gas exchange in insects:
what do terrestrial insects use for gas exchange
terrestrial insects have microscopic air filled pipes (tracheae) which they use for gas exchange
gas exchange in insects (1):
how does air move into the tracheae?
air moves into the tracheae through pores on the surface (spiracles).
gas exchange in insects (2):
where does oxygen travel?
oxygen travels down the concentration gradient towards the cells.
gas exchange in insects (3):
what do the tracheae branch off into
tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells so oxygen diffuses directly into the respiring cells - insect’s circulatory system doesn’t transport O2
gas exchange in insects (4):
what does carbon dioxide do
CO2 from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
gas exchange in insects (5):
what do insects do to move air in/out of the spiracles
insects use rhythmic abdominal movements to move air in and out of the spiracles
control of water loss:
what does exchanging gases often result in
exchanging gases tends to make you lose water
control of water loss in insects:
spiracles
if insects are losing too much water they close their spiracles using muscles
control of water loss in insects:
cuticles/hairs
insects have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles = reduce evaporation
control of water loss in plants:
how are plant’s stomata usually in the day
plant’s stomata usually kept open during day to allow gaseous exchange
control of water loss in plants:
guard cells
water enters the guard cells so they become turgid = opens stomatal pore. if plant starts to get dehydrated , guard cells lose water and become flaccid which closes the pore
what are xerophytes
plants specially adapted for warm/dry/windy environments where water loss is a problem
examples of xerophytic adaptations
sunken stomata
stomata sunk in pits to trap water vapour, reducing concentration gradient of water between the leaf and the air, reduces evaporation of water from the leaf
examples of xerophytic adaptations
epidermal hairs
layer of ‘hairs’ on the epidermis to trap water vapour around the stomata
examples of xerophytic adaptations
curled leaves
curled leaves within the stomata inside, protecting them from the wind - windy conditions increase rate of diffusion/evaporation
examples of xerophytic adaptations
number of stomata
a reduced number of stomata = fewer places for water to escape
examples of xerophytic adaptations
cuticles
thick waxy, waterproof cuticles on leaves and stems to reduce evaporation
what is the role of the gas exchange system in humans?
role of the gas exchange system is to supply your blood with oxygen, and remove CO2 from your body
structure of the human gas exchange system:
step one
as you breathe in, air enters the trachea (windpipe).
structure of the human gas exchange system:
step two
the trachea splits into 2 bronchi, one bronchus leading to each lung
structure of the human gas exchange system:
step three
each bronchus then branches off into smaller tubes called bronchioles
structure of the human gas exchange system:
step four
the bronchioles end in small ‘air sacs’ called alveoli where gases are exchanged
structure of the human gas exchange system:
step five
the ribcage, intercostal muscles and diaphragm all work together to move air in and out
intercostal muscles
where are they found
the intercostal muscles are found between the ribs, there are 3 layers of intercostal muscles
intercostal muscles
what layers of intercostal muscles do you need to be aware of
the internal and external intercostal muscles
intercostal muscles
where are the internal intercostal muscles found
on the inside of the external intercostal muscles
ventilation
what does ventilation consist of
ventilation consists of inspiration (breathing in) and expiration (breathing out)
ventilation
what is it controlled by
it’s controlled by the movements of the diaphragm, internal/external intercostal muscles and ribcage
inspiration
step one
during inspiration the external intercostal and diaphragm muscles contract
inspiration
step two
this causes the ribcage to move upwards/outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity (space where lungs are)
inspiration
step three
as the volume of the thoracic cavity increases, lung pressure decreases to below atmospheric pressure
inspiration
step four
air will always flow from an area of higher pressure to an area of lower pressure (down a pressure gradient) so air flows down the trachea and into the lungs
inspiration
what type of process is it?
inspiration is an active process as it requires energy
expiration
step one
during expiration the external intercostal and diaphragm muscles relax
expiration
step two
the ribcage moves downwards and inwards , and the diaphragm curves upwards again so it becomes dome shaped
expiration
step three
volume of the thoracic cavity decreases, causing the air pressure to increase to above atmospheric presssure
expiration
step four
air is forced down the pressure gradient and out of the lungs
expiration
what type of process is it?
normal expiration is a passive process as it doesn’t require any energy
what other type of expiration is there?
forced expiration, e.g. blowing out candles
what happens in forced expiration
the external intercostal muscles relax and internal intercostal muscles contract, pulling the ribcage further down and in. the movement of the 2 sets of intercostal muscles is antagonistic (opposing)
alveoli and gas exchange
where does gas exchange
happen
in microscopic air sacs called alveoli found in the lungs in large numbers
alveoli and gas exchange
what are the alveoli surrounded by?
the alveoli are surrounded by a network of capillaries
alveoli structure
walls of alveolus
the walls of each alveolus is made from a single layer of thin, flat cells called alveolar epithelium
alveoli structure
walls of capillaries
walls of the capillaries are made from capillary endothelium
alveoli structure
what do the walls of alveoli contain
the walls of the alveoli contain the protein elastin which is elastic so helps the alveoli to return to their normal shape after inhaling/exhaling air
movement of carbon dioxide and oxygen through the gas exchange system:
where does oxygen move first?
air (containing oxygen) moves down the trachea, bronchi and bronchioles into the alveoli (down a pressure gradient)
movement of carbon dioxide and oxygen through the gas exchange system:
where does oxygen move second
oxygen then moves into the blood where it can be transported round the body (happens down a diffusion gradient)
movement of carbon dioxide and oxygen through the gas exchange system:
where does carbon dioxide move?
carbon dioxide moves down its own diffusion and pressure gradients, but in the opposite direction to oxygen so it can be breathed out
gas exchange in the alveoli:
oxygen
oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into haemoglobin in the blood
gas exchange in the alveoli:
carbon dioxide
carbon dioxide diffuses into the alveoli from the blood
factors affecting the rate of diffusion
how are alveoli adapted?
alveoli have features that speed up the rate of diffusion so gases can be exchanged quickly
factors affecting the rate of diffusion
how are alveoli’s exchange surface adapted
thin exchange surface - alveolar epithelium is one cell thick so there is a shorter diffusion pathway which speeds up diffusion
factors affecting the rate of diffusion
how are alveoli’s surface area adapted
a large surface area - are millions of alveoli so there is a large surface area for gas exchange
factors affecting the rate of diffusion
concentration gradient
steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries = increases rate of diffusion
factors affecting the rate of diffusion
what is the concentration gradient maintained by?
the concentration gradient is constantly maintained by the flow of blood and ventilation
what does lung disease affect?
ventilation and gas exchange in the lungs
what is tidal volume
volume of air in each breath
what is the tidal volume usually for adults
between 0.4 and 0.5 dm^3
what is ventilation rate
the number of breaths per minute
what is the ventilation rate for a healthy person
15 breaths
what is forced expiratory volume
(FEV1)
maximum volume of air that can be breathed out in 1 second
what is forced vital capacity (FVC)
maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in
give some examples of lung diseases
tuberculosis, fibrosis, asthma, emphysema
lung disease example: tuberculosis
what is tuberculosis caused by?
pulmonary tuberculosis (TB)
is a lung disease caused by bacteria
lung disease example: tuberculosis
what happens when some becomes infected with tuberculosis bacteria?
immune system cells build a wall around the bacteria in the lungs which forms small, hard lumps called tubercles
lung disease example: tuberculosis
what happens to infected tissue within the tubercles
infected tissue within the tubercles dies and the gaseous exchange surface is damaged, so tidal volume is decreased
lung disease example: tuberculosis
what additional lung disease can TB also cause
TB also causes fibrosis, which reduces the tidal volume further
lung disease example: tuberculosis
how does TB affect tidal volume/ventilation rate
reduced tidal volume means less air is inhaled with each breath so take in enough oxygen patients have to breathe faster (increased ventilation rate)
lung disease example: tuberculosis
symptoms of TB
persistent cough, coughing up blood/mucus, chest pains, shortness of breath, fatigue
lung disease example: fibrosis
what is fibrosis?
fibrosis is the formation of scar tissue in the lungs
lung disease example: fibrosis
what can cause fibrosis?
can be the result of an infection or exposure to substances e.g. asbestos or dust
lung disease example: fibrosis
how and why does fibrosis affect tidal volume and FVC?
scar tissue is thicker/less elastic than normal lung tissue = lungs less able to expand/hold less air = tidal volume/FVC reduced
lung disease example: fibrosis
how does fibrosis affect rate of gas exchange
there is a reduction in the rate of gas exchange, diffusion is slower across a thicker scarred membrane
lung disease example: fibrosis
how does fibrosis affect someone’s ventilation rate
those with fibrosis have a faster ventilation rate than normal to get enough air into their lungs to oxygenate their blood
lung disease example: fibrosis
symptoms of fibrosis
shortness of breath, a dry cough, chest pain, fatigue and weakness
lung disease example: asthma
what is asthma
asthma is a respiratory condition where the airways become inflamed and irritated
lung disease example: asthma
what is the cause of asthma?
usually because of an allergic reaction to substances e.g. pollen or dust
lung disease example: asthma
what happens in an asthma attack, stage 1
during an asthma attack, the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced
lung disease example: asthma
what happens in an asthma attack, stage 2
this causes constriction of the airways, making it difficult to breathe properly
lung disease example: asthma
what happens in an asthma attack, stage 3
air flow in and out of the lungs is severely reduced, so less oxygen enters the alveoli and moves into the blood
lung disease example: asthma
how does an asthma attack affect forced expiratory volume
reduced air flow means forced expiratory volume is severely reduced
lung disease example: asthma
symptoms
wheezing, tight chest, shortness of breath
lung disease example: asthma
how do the symptoms come on during an attack
during an attack, symptoms come on very suddenly
lung disease example: asthma
how are the symptoms treated?
they can be relieved by drugs, often inhalers, which cause the muscle in the bronchioles to relax, opening up the airways
lung disease example: emphysema
what is emphysema
emphysema is a lung disease caused by smoking/long term exposure to air pollution
lung disease example: emphysema
how is emphysema caused
foreign particles in the smoke/air become trapped in the alveoli, causing inflammation which attracts phagocytes to the area
lung disease example: emphysema
what do the phagocytes produce?
the phagocytes produce an enzyme that breaks down elastin (protein found in the walls of alveoli)
lung disease example: emphysema
what does elastin do
elastin is elastic so helps the alveoli return to their normal shape after inhaling/exhaling air
lung disease example: emphysema
how does loss of elastin affect the alveoli
loss of elastin means the alveoli can’t recoil to expel air as well (it remains trapped in the alveoli)
lung disease example: emphysema
how does loss of elastin affect the alveoli walls/rate of gas exchange
loss of elastin also leads to destruction of the alveoli walls, reducing the alveoli’s surface area, reducing the rate of gaseous exchange
lung disease example: emphysema
symptoms
shortness of breath, wheezing
lung disease example: emphysema
how does emphysema affect ventilation rate
people with emphysema have increased ventilation rate as they try to increase the amount of air (containing oxygen) reaching their lungs
