3.3.2 Gas Exchange Flashcards
How does gas exchange in single celled organisms occur?
+ Oxygen is absorbed by diffusion across their body surface, carbon dioxide also diffuses across their body surface
+ small (large SA:V)
+ thin membrane only surrounding the entire organism
+ single celled organisms with an additional cell wall have walls that are permeable
What are the features of insects?
+ most are terrestrial
+ a problem for them is that water easily
evaporates from their body surface
+ however efficient gas exchange requires a thin,
permeable surface with a large area
+ have a small SA:V
What is the exoskeleton?
+ found in insects
+ composed of a hard fibrous material called
chitin (for protection)
+ covered by a lipid rich layer (to prevent water
loss)
What is the tracheae?
+internal network of tubes
+ supported by strengthened rings to prevent
them from collapsing
What are tracheoles?
+ smaller divisions from the trachea, which
extend throughout the body of the insect
+ tracheoles branch directly to the cells
What are air sacs?
+ temporary store of air within the insects body
(located at the end of the tracheoles)
What are spiracles?
+ tiny pores on the surface of the insects body
+ contain valves
Some smaller insects rely on simple diffusion of gases through the tracheal system. Why might this not be sufficient for larger insects?
+ longer diffusion distance
+ more active (require more energy)
+ therefore require more oxygen
How does gas exchange occur in insects?
- Valves in the spiracles open, to allow air to
enter into the trachea - From the trachea air is passed onto the
tracheoles ( thin walls) - From the tracheoles air is carried directly into t
the cells within the body of the insect
+ tracheoles also carry air into air sacs where it is
temporarily stored
What are the advantages of gas exchange in insects?
+ short diffusion pathway for gases (from air into
the respiring cells)
+ diffusion gradient maintained ( for both oxygen
and carbon dioxide)
What are the disadvantages of gas exchange in insects?
+ when spiracles are open, water can evaporate
from the insect causing it to dehydrate
+ relies on diffusion and for this to be effective
the pathway needs to be short
+ this limits the size that insects can get to
How do insects overcome these disadvantages in gas exchange?
+ for most of the time the spiracles are closed to
prevent water loss, only open to allow gas e
exchange
+ spiracles can be closed to conserve water in
hot conditions
+ in the mean time insects can use air stored
within their air sacs to require
+ being small has not hindered the survival of i
insects - they are the most successful
organisms on Earth
How do respiratory gases move in the tracheal system?
- Along a diffusion gradient:
+ low concentration of oxygen towards the end of the tracheoles
+ high concentration of oxygen outside of the insects body, in the atmosphere
+ oxygen diffuses along the trachea into the
tracheoles
+ opposite direction for carbon dioxide - Ventilation
+ rings of muscles within the insects body
contract and relax (rhythmic abdominal
movement) to allow mass movement of the air
in and out of the trachea
What happens when insects are rest?
+ water fills the end of the tracheoles
What happens when insects are flying?
- muscles cells respire anaerobically and
produce lactic acid - lowers the water potential in muscle cells
- water moves by osmosis from the tracheoles
into the muscles cells - this increases the exposed surface area to air
- as gases diffuse faster through air than water
this enables a greater volume of oxygen to be
supplied
Why can a fish not obtain oxygen in the same way as a single celled organism?
+ fish have a waterproof outer covering, which
will not allow gases to diffuse through
+ also they have a small SA:V, which means that
their body surface will not be able to supply
then with a sufficient supply of respiratory
gases
+ it is also much harder to obtain oxygen from
the environment because of the lower oxygen
concentration in water than in air
What are gills?
+ located behind the head of a fish
+ water enters through the mouth and is forced over these before leaving through the sides
What are gill filaments?
+ made from gill filaments (thin plates)
+these are stacked up in a pile
What are gill lamellae?
+ at right angle to gill filaments
How are the gills involved in diffusion?
+ as the water passes through the gills, gas
exchange occurs in the lamellae
+ in the lamellae, the distance between the water
and the blood cells is approx 5µm
+ the distance between two lamellae is approx
50µm (short diffusion pathway)
+ gills provide a large SA
+ gills have an extensive network of blood
capillaries to maintain a concentration gradient
What is the counter current system?
+ flow of blood and water over the gill lamellae
occur in opposite directions
+ this is done to maintain a concentration
gradient of oxygen and carbon dioxide
throughout the gill lamellae
What are the stages of parallel flow?
- At the start: high concentration gradient
present so oxygen from the water diffuses into
the blood - Towards the end: concentration gradient no
longer available. Only approx 50% of oxygen
available has been observed. Problem: a
sufficient amount of oxygen is not being taken
out of the water and into the blood - because
diffusion isn’t happening across the whole of
the lamellae
What are the stages of counter flow?
- At the start: blood already loaded with oxygen meets water with an even higher concentration of oxygen and diffusion can take place
- Towards the end:
+ blood with slightly less/no oxygen meets
water that has had some oxygen removed
already
+ BUT still has enough oxygen left for diffusion
to take place
+ therefore, at all points through the gill
lamellae diffusion of oxygen into the blood
occurs
How does ventilation happen in fish?
- When the fish open their mouth they lower the
floor of the buccal cavity - This causes the volume inside the buccal cavity
to increase, which causes a decrease in
pressure within the cavity - The pressure is higher outisde the mouth of
the fish and so water flows into the buccal
cavity - This fish then raises the floor if the buccal
cavity to close its mouth, increasing the
pressure within the buccal cavity - Water flows from the buccal cavity (high
pressure) into the gill cavity (low pressure) - As water enters pressure begins to build up in
the gill cavity and causes the operculum to be
forced open and water to exit the fish
Compare and contrast the methods by which insects and bony fish exchange oxygen and
carbon dioxide with the environment
Insects
Spiracles - location and function
Trachea - structure (chitin rings) and function
Tracheoles - thin walls & end at body cells, large number
Ability of some insects to compress air sacs with abdominal pumping
Removal of water from tracheoles when insect is active
Fish
Filaments – location, function, many of them
Lamellae – many of them, thin walls
Blood supply – many capillaries in lamellae
Counter-current system
Similarities
Short distance for diffusion
Large surface area
Possibility of ventilation
Simple diffusion of gases (or dissolved gases) into/out of cells
Differences
Blood supply in fish – due to small SA:vol ratio
Water flows through fish (in one direction), air moved in and out of insec
Describe two adaptions of the structure of alveoli for efficient gas exchange
+ large surface area
+ thin walls
People who are fire-breathers for many years often find they cannot breathe out properly. Explain why.
+ fibrosis reduces elasticity of
alveoli
+ due to scar tissue
Destruction of phagocytes causes the lungs to be more susceptible to infections. Explain why.
+ phagocytes destroy/engulf
pathogens
+ lung diseases are caused by
pathogens
The reduced elasticity of the lungs causes breathing difficulty. Explain how.
+ lungs can no longer expand to their maximum capacity
+ breathing out particularly affected
explain how the elastic tissue in the wall helps to even out the pressure of blood flowing through the artery
+ stretches as a result of high pressure
+ then recoils
Describe and explain how ventilation occurs in a ladybird
- Diffusion gradient maintained by spiracles
- Gases passively move down their concentration gradient along trachea
- Ladybird pumps abdomen
- Air is forced in and out of the tracheole
Explain how the rate of gas exchange increases when a ladybird is in flight
- Muscle cells in ladybird respire anaerobically and produce lactate
- Lactate lowers water potential
- Water moves via osmosis from tracheoles into muscle cells
- More air is drawn into muscle cells
Describe and explain how a terrestrial insect is adapted to reduce water loss
- Waxy cuticle (made up of chitin)
- Is impermeable to gases
- Spiracles
- Close during the day
- Hairs around spiracles
- Reduce evaporation
