3.3.2 Gas Exchange Flashcards

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1
Q

How does gas exchange in single celled organisms occur?

A

+ 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

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2
Q

What are the features of insects?

A

+ 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

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3
Q

What is the exoskeleton?

A

+ found in insects
+ composed of a hard fibrous material called
chitin (for protection)
+ covered by a lipid rich layer (to prevent water
loss)

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4
Q

What is the tracheae?

A

+internal network of tubes
+ supported by strengthened rings to prevent
them from collapsing

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5
Q

What are tracheoles?

A

+ smaller divisions from the trachea, which
extend throughout the body of the insect
+ tracheoles branch directly to the cells

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5
Q

What are air sacs?

A

+ temporary store of air within the insects body
(located at the end of the tracheoles)

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5
Q

What are spiracles?

A

+ tiny pores on the surface of the insects body
+ contain valves

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6
Q

Some smaller insects rely on simple diffusion of gases through the tracheal system. Why might this not be sufficient for larger insects?

A

+ longer diffusion distance
+ more active (require more energy)
+ therefore require more oxygen

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7
Q

How does gas exchange occur in insects?

A
  1. Valves in the spiracles open, to allow air to
    enter into the trachea
  2. From the trachea air is passed onto the
    tracheoles ( thin walls)
  3. 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
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8
Q

What are the advantages of gas exchange in insects?

A

+ short diffusion pathway for gases (from air into
the respiring cells)
+ diffusion gradient maintained ( for both oxygen
and carbon dioxide)

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9
Q

What are the disadvantages of gas exchange in insects?

A

+ 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

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10
Q

How do insects overcome these disadvantages in gas exchange?

A

+ 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

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11
Q

How do respiratory gases move in the tracheal system?

A
  1. 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
  2. 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
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12
Q

What happens when insects are rest?

A

+ water fills the end of the tracheoles

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13
Q

What happens when insects are flying?

A
  1. muscles cells respire anaerobically and
    produce lactic acid
  2. lowers the water potential in muscle cells
  3. water moves by osmosis from the tracheoles
    into the muscles cells
  4. this increases the exposed surface area to air
  5. as gases diffuse faster through air than water
    this enables a greater volume of oxygen to be
    supplied
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14
Q

Why can a fish not obtain oxygen in the same way as a single celled organism?

A

+ 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

15
Q

What are gills?

A

+ located behind the head of a fish
+ water enters through the mouth and is forced over these before leaving through the sides

16
Q

What are gill filaments?

A

+ made from gill filaments (thin plates)
+these are stacked up in a pile

17
Q

What are gill lamellae?

A

+ at right angle to gill filaments

18
Q

How are the gills involved in diffusion?

A

+ 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

19
Q

What is the counter current system?

A

+ 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

20
Q

What are the stages of parallel flow?

A
  1. At the start: high concentration gradient
    present so oxygen from the water diffuses into
    the blood
  2. 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
21
Q

What are the stages of counter flow?

A
  1. At the start: blood already loaded with oxygen meets water with an even higher concentration of oxygen and diffusion can take place
  2. 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
22
Q

How does ventilation happen in fish?

A
  1. When the fish open their mouth they lower the
    floor of the buccal cavity
  2. This causes the volume inside the buccal cavity
    to increase, which causes a decrease in
    pressure within the cavity
  3. The pressure is higher outisde the mouth of
    the fish and so water flows into the buccal
    cavity
  4. This fish then raises the floor if the buccal
    cavity to close its mouth, increasing the
    pressure within the buccal cavity
  5. Water flows from the buccal cavity (high
    pressure) into the gill cavity (low pressure)
  6. 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
23
Q

Compare and contrast the methods by which insects and bony fish exchange oxygen and
carbon dioxide with the environment

A

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

24
Q

Describe two adaptions of the structure of alveoli for efficient gas exchange

A

+ large surface area
+ thin walls

25
Q

People who are fire-breathers for many years often find they cannot breathe out properly. Explain why.

A

+ fibrosis reduces elasticity of
alveoli
+ due to scar tissue

26
Q

Destruction of phagocytes causes the lungs to be more susceptible to infections. Explain why.

A

+ phagocytes destroy/engulf
pathogens
+ lung diseases are caused by
pathogens

27
Q

The reduced elasticity of the lungs causes breathing difficulty. Explain how.

A

+ lungs can no longer expand to their maximum capacity
+ breathing out particularly affected

28
Q

explain how the elastic tissue in the wall helps to even out the pressure of blood flowing through the artery

A

+ stretches as a result of high pressure
+ then recoils