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MPW biology > 3.1.1 Exchange and Transport > Flashcards

3.1.1 Exchange and Transport Flashcards

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1
Q

What is an exchange surface?

A

a surface or barrier across which materials are exchanged between one area (usually the organism’s body) and another (usually the environment).

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2
Q

Do small organsisms need a specialised exchange surface?

A

NO

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3
Q

Why dont small organsisms need a specialised exchange surface? 3 marks

A
  1. Small size means that they have a high enough surface area to volume (SA:V)
  2. The distances that molecules and ions will need to move will always be short. This means that diffusion (which is too slow over long distances) is an adequate method of transport
  3. Their demand for oxygen uptake and CO2 removal are not too high due to the low metabolic rate, and respiration rates
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4
Q

Do larger organsisms need a specialised exchange surface?

A

YES

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5
Q

Why do large organsisms need a specialised exchange surface? 4 marks

A
  1. Large size means they have a low surface area to volume ratio (SA:V), this makess it difficult for enough substances to be exchanged across the outer body surface to meet the needs of allcells in the organism
  2. Many body cells are a great distance from the body surface, therfore diffusion would be too SLOW
  3. Their demand for oxygen uptake and CO2 removal are very high respiration rate in the muscles during movement, requiring high rates of oxygen supply.
  4. Endotherms, must maintain a constant body
    temperature, usually higher than that of their surroundings, using physiological mechanisms. Therfore high metabolic rates, including a high rate of respiration, hence they need high rates of oxygen uptake
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6
Q

is the SA:V ratio high or low in small organsims?

A

High

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7
Q

is the SA:V ratio high or low in large small organsims?

A

Low

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8
Q

Finish this statement, ‘The larger the organism…’

A

‘…the lower its surface area to volume (SA:V) ratio’

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9
Q

In biology how do we write SA:V ratios?

A

SA:V ratios are usually written so that they all have a ‘1’ on the right‐hand side, and it must be in decimal form

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10
Q

Why do we write the 1 on the righ-hand side for SA:V ratios?

A

This is useful because different ratios can then be compared very easily

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11
Q

How to work out the surface area of a cube?

A

6 x side of length x side of length

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12
Q

What are some key common features of exchange surfaces? 3 main points + 2 sub points

A
  1. Very high surface area - more space for diffusion so that more molecules can be taken up (or removed)
  2. Thin barrier for diffusion - Provides short diffusion pathway. This means that the molecules/ions being exchanged can cross the barrier at a higher rate.
  3. Mechanisms to maintain steep concentration gradients - A steep concentration gradient occurs when there is a greater difference inthe concentration of a molecule/ion between the two sides of the exchange surface. The steeper the concentration gradient, the faster the rate of diffusion
    a) Good blood supply - exchange surfaces in animals contain dense networks of capillaries in close contact with the barrier itself. The flowing blood delivers molecules to the surface and/or carries other molecules away from the surface, maintaining steep concentration gradients
    b) Ventilation (Breathing in and out) - Ventilation refreshes the air in the lungs (or water in contact with the gills) and so brings more oxygen and takes away carbon dioxide, maintaining steep concentration gradients for both gases.
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13
Q

How thick are exchange surfaces normally?

A

A single layer of thin/flat cells.

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14
Q

What is a gaseous exchange system?

A

A complex system (containing several tissues and organs) which enables the respiratory gases oxygen and carbon dioxide to be exchanged between the environment and the organism.

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15
Q

What is the trachea and what is its function?

A

What :
The main airways w/ incomplete C-shaped cartilage rings

Function:
In inspiration - the trachea carries warm moist air down from the nasal cavity to the bronchi

In expiration - the trachea carries the air back from the bronchi up to the nasal cavity

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16
Q

What is the bronchus and what is its function?

A

What :
There are two bronchi, formed where the base of the trachea divides w/ smaller irregular pieces of cartilage. Each bronchi then further divides within each lung into more numerous bronchioles.

Function:
An airway that carries air into each lung

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17
Q

What are the bronchioles and what are its function?

A

What:
narrow airways formed from the division of the bronchi, becoming increasingly numerous (but narrower in lumen diameter), each terminating in a cluster of alveoli.

Function:
An airway that carries air into each alveoli

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18
Q

What are the intercostal muscles and what are its function?

A

What:
short skeletal muscles located between the ribs.

Function:
In inspiration - The external intercostal muscles contract, and internal intercostal muscles relax, pulling the ribcage upwards and outwards.

In forced expiration - The internal intercostal muscles contract, and external intercostal muscles relax, pulling the ribcage inwards and downwards. Much faster and greater than quiet breathing.

REMEMBER THAT:
inSPIRATION = inTERNAL RELAX
exPIRATION = exTERNAL RELAX

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19
Q

What is the diaphragm and what is its function?

A

What:
A large sheet of skeletal muscle found just below the ribcage, forming the boundary between the thorax and abdomen. It plays a key role in ventilation.

Function:
In inspiration: the diaphragm contracts, becoming flatter and moving lower in the body; this increases the volume of the thorax and decreases the pressure of the air in the lungs below atmospheric air pressure, so that air flows in to the lungs from the atmosphere down the pressure gradient

In expiration: During expiration, the diaphragm relaxes (eXpiration = relaXes), becoming more dome‐shaped and moving higher in the body; this decreases the volume of the thorax and increases the pressure of the air in the lungs above atmospheric air pressure, so the air flows out of the lungs into the atmosphere.

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20
Q

What are the alveoli and what are its function?

A

What:
numerous tiny air sacs found in clusters in the mammalian lungs

Function:
The alveolar walls provide the gas exchange surfaces between the air and the blood (which flows in the numerous and capillaries which form a net around each alveolus.
Oxygen diffuses from the air in the alveolus into the blood (specifically, into the erythrocytes, where it combines with ,haemoglobin); meanwhile carbon dioxide diffuses from the blood plasma into the air in the alveolus. Both gases are moving passively down their own concentration gradient and have to pass through just two thin layers of cells: the squamous epithelium of the alveolar wall and the capillary wall endothelium.

elastic recoil - The ability to stretch when air is drawn in, and return to their resting size passively when air is drawn out.

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21
Q

what word do we use to describe the intercostal muscles, and what does it mean?

A

Antagonistic (have opposing actions)

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22
Q

What is the order oxygen takes in inspiration

A

nasal cavity, trachea, bronchus, bronchiole, alveoli

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23
Q

What is the order carbon dioxide takes in expiration

A

alveoli, bronchiole, bronchus, trachea, nasal cavity

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24
Q

What is the nasal cavity, and what is its features?

A

What:
The area when air first enters the body

Features:
Large surface area, w/ a good blood supply, which warms the air
A hairy lining, w/ mucis to trap dust and bacteria
Moist surface, increases humidity of incoming air, reducing evaportaion from exchange surfaces.

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25
Q

What are the key features of the alveoli? 5 marks

A
  1. high surface area to volume ratio
  2. Numerous - their total surface area available for gas exchange is huge
  3. ONE epithelial cell thick - short diffusion
  4. Good blood supply - maintains a steep concentration gradient, increases the rate of diffusion
  5. Good ventialtion - maintains a steep concentration gradient, increases the rate of diffusion
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26
Q

what cells are the walls of the alveoli called?

A

squamous epithelium cells

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27
Q

What is the Ciliated epithelium and what is its function, and how is it specialised?

A

What:
Ciliated epithelial cells are found in the lining of the trachea, bronchi and bronchioles

Function:
The hair‐like projections called cilia carry out beating or wafting movements in order to propel mucus (which contains trapped dust, pollen and pathogens).

Specialiasations of Cilitaed epithelial cells:
Cilia, hair like projection which make a wafting motion to propel mucus

many mitochondra, to supply ATP for the movement of the cilia Basement membrane, made of collagen, holds the cells in a single layer without any gaps between them creating a continuous surface of cells

Mucus, provided by the goblet cells, it sticky and traps bacteria, dust, pollen etc

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28
Q

What are squamous epithelial cells, what is its functions, and how is it specialised?

A

What:
Squamous epithelial cells are flattened, smooth cells.

Function:
gives a short diffusion distance to gases by forming the thin walls of the alveoli and capillary walls

Specialisations:
Smooth surface, (in blood vesssels, it reduces friction to blood cells)

Flat and thin, (in the alveoli walls it allows for a short diffusion diustance for gases). Provides a short diffusion distance and high permeability

Basement membrane, made of collagen, holds the cells in a single layer without any gaps between them creating a continuous surface of cells

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29
Q

What are goblet cells, and what is its function, and how is it specialised?

A

What:
Differentiated cells found in ciliated epithelial tissue specialised to produce and secrete mucus

function:
specialised to produce and secrete mucus by exocytosis

specialisations:
basement membrane, made of collagen, holds the cells in a single layer without any gaps between them creating a continuous surface of cells
Mucus, provided by the goblet cells, it sticky and traps bacteria, dust, pollen etc

Specialiasations of goblet cells:
Mucus, provided by the goblet cells, it sticky and traps bacteria, dust, pollen etc
many mitochondra
Many RER and golgi apparatus - glycoproteins (to make mucus)

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30
Q

what is mucus?

A

Mucus is a sticky solution of glycoproteins and salt ions in water, ideal for trapping bacteria and particles of dust, pollen

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31
Q

what is cartilage, and what is its function, and how is it specilaised?

A

What:
A strong, flexible connective tissue found in C‐shaped incomplete rings in the walls of the trachea and in smaller irregular pieces in the walls of the bronchi.

Funcition:
keeping the airways open

specialisations:
Contains many Chondrocytes - embedded in a extracellular matrix which they have secreted themselves, rich in structural proteins such as collagen (providing mechanical strength) and elastin (providing springiness and flexibility).

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32
Q

what are elestic fibres, and what are its function, and what is it made of?

A

What:
Fibres made of elastin found in the walls of the trachea, bronchi, bronchioles and alveoli

Function:
elastic recoil: The ability to stretch when air is drawn in, and return to their resting size passively when air is drawn out.

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33
Q

How does elastic recoil work in inspiration?

A

thay are stretched as the structure containing them expands, as occurs to the walls of the airways and alveoli during inspiration

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34
Q

How does elastic recoil work in expiration?

A

the fibres then recoil during expiration, shortening back to their original length

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35
Q

why is it important the alveoli have the ability to recoil with elastic fibres?

A

This elastic recoil of the elastic fibres helps to expel more air from the lungs during expiration.

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36
Q

What is smooth muscle, and what is its function?

A

What:
A type of muscle tissue found in the walls of the trachea, bronchi, and larger bronchioles

Function:
It control airway diameter, particularly that of the bronchi

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37
Q

How do irritant affect the smooth muscle?

A

If irritants (e.g. smoke particles) are present in the air, the smooth muscle contracts and so constricts the airways, decreasing the potential for damage to the alveoli or the likelihood of harmful particles entering the bloodstream

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38
Q

How does exercise affect the smooth muscle?

A

During exercise, the smooth muscle relaxes, dilating (widening) the airways; this reduces resistance to air flow.

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39
Q

what is ventilation?

A

Ventilation is the complete process of breathing in and breathing out; inspiration followed by expiration.

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40
Q

where is ventilation necessary?

A

in animals that have specialised gaseous exchange surfaces.

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41
Q

what in inspiration/inhilation?

A

the process of breathing in during ventilation, an active process, requiring muscle contraction and hence energy from ATP

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42
Q

what are the 6 steps of inspiration?

A
  1. The external intercostal muscles contract, pulling the ribcage upwards and outwards
  2. Meanwhile the diaphragm also contracts, becoming flatter and moving lower in the body
  3. These changes cause an increase in the volume of the thorax
  4. Due to the increased thoracic volume, there is a decrease in the pressure of the air within the lungs, to below atmospheric air pressure
  5. Air therefore moves into the lungs down the pressure gradient from the atmosphere
  6. Gaseous exchange occurs across the alveolar walls.
43
Q

what is expiration/ exhalation

A

the process of breathing out during ventilation. This
process is usually passive (‘quiet breathing’) in that no muscle contraction is necessary and occurs simply due to muscle relaxation and elastic recoil (therefore no ATP is required as an energy provider).

44
Q

what are the 6 steps of passive expiration?

A
  1. The external intercostal muscles relax, allowing the ribcage to fall downwards and inwards due to gravity
  2. Meanwhile the diaphragm also relaxes, becoming more dome‐shaped and moving higher in the body
  3. These changes cause a decrease in the volume of the thorax
  4. Due to the decreased thoracic volume, there is an increase in the pressure of the air in the lungs, to above atmospheric air pressure
  5. Air therefore moves out of the lungs down the pressure gradient into the atmosphere
  6. Occurring simultaneously with the above, the elastic recoil of elastic fibres in the alveolar walls and airways helps push more air out of the lungs
45
Q

What is forced expiration?

A

an active process as it does require muscle contraction (and hence use of ATP as a provider of energy). To carry out forced expiration, the internal intercostal muscles contract, pulling the ribcage inwards and
downwards more quickly and to a greater extent than
in quiet breathing. Thus an air pressure gradient is established more quickly and is steeper than usual; hence more air is forced out of the lungs more quickly.

46
Q

How does asthma work?

A

smooth muscle in the walls of the bronchi and bronchioles contracts inappropriately, decreasing the lumen diameter of these airways. This increases the resistance to air flow during both inspiration and expiration, meaning that ventilation becomes more difficult. Tidal volume is likely to decrease (i.e. a smaller volume of air is inhaled/exhaled in each breath) and the breathing rate (number of breaths per minute) increases in an attempt to compensate for this.

47
Q

What is breathing rate?

A

The number of breaths (complete cycles of inhalation plus exhalation) taken per minute. Units: min‐1.

48
Q

What is a spirometer?

A

A spirometer is a piece of equipment used to make measurements of various aspects of breathing, including breathing rate, tidal volume, vital capacity and oxygen consumption rate.

49
Q

How does a spirometer work?

A

Inhale - air is drawn into the lungs through the upper tube from the air chamber; the lid (float) will fall, dragging the pen downwards so it makes a downward sloping trace on the graph paper that covers the kymograph.

Exhale - air is forced into the air chamber from their lungs via the lower tube; the lid (float) will rise, pulling the pen upwards so it makes an upward sloping trace on the graph paper.

50
Q

What are the precautions we must take when using a spirometer? 7 marks

A
  1. Check health of subject – if the subject has asthma, the equipment could trigger an attack
  2. Check correction functioning of equipment – do the valves work, is the water level not too high
  3. Sterilise the mouthpiece – minimises risk of infection
  4. Use medical grade oxygen to fill the air chamber – this reduces infection risk and decreases the possibility that oxygen will run out whilst the subject is using the equipment
  5. Use fresh soda lime to absorb carbon dioxide from the exhaled air – especially important if oxygen uptake rate is to be measured (see below);
  6. Subject should wear nose clip – important in order to get valid readings of tidalvolume and vital capacity as all air must be inhaled from the air chamber and exhaled into the air chamber, not from/into the atmosphere;
  7. Subject should be at rest and breathing normally for readings of tidal volume.
51
Q

How do we measure oxygen consumption rate without soda lime?

A

the total volume of air in the air chamber plus lungs would actually remain constant over time. This is because the body is using up oxygen in respiration but is producing carbon dioxide at (approximately) the same rate.

This carbon dioxide is excreted via the lungs and leaves the body when air is exhaled into the air chamber.

52
Q

How do we measure oxygen consumption rate with soda lime?

A

fresh soda lime will absorb all the carbon dioxide in exhaled air, the spirometer can be used to determine a subject’s rate of oxygen uptake. If the subject’s body is using up oxygen in respiration and if the (equivalent volume of) carbon dioxide produced by the body is removed by the soda lime, the total volume of air in the air chamber plus lungs will fall steadily over time. The spirometer trace will have a downward slope over time

53
Q

How do we measure the oxygen concentraion rate from a graph?

A

draw a straight line joining all the peaks (or all the toughs) on the trace. Calculate the gradient

54
Q

What are the units for a spirometer graph?

A

dm^3min^‐1, cm^3min^‐1 or mm^3s^‐1

55
Q

what is tidal volume?

A

The volume of air which moves into or out of the lungs with each normal breath

56
Q

what is ventilation rate?

A

The total volume of air inhaled in one minute. Ventilation rate = tidal volume × breathing rate.

57
Q

what is the tidal volume of an average adult?

A

500cm3

58
Q

what happens to ventialtion rate during exercise and why?

A

Ventilation rate will increase significantly, due to increases both in tidal volume (deeper breaths) and breathing rate (more breaths per minute).

59
Q

What is Inspiratory reserve volume (IRV)?

A

The maximum extra volume of air that can be breathed in, beyond a normal inhalation (tidal volume).

60
Q

what is Expiratory reserve volume (ERV)?

A

The maximum extra volume of air that can be forced out of the lungs, beyond the normal exhalation (tidal volume).

61
Q

What is Vital capacity (VC)?

A

The largest volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath. Or, the largest volume of air that can be breathed out when the deepest possible intake of breath is followed by the strongest possible exhalation.

62
Q

What is Residual volume (RV)?

A

The volume of air that is still left in the lungs after forced expiration

63
Q

can residual volume be measured directly?

A

It cannot be measured directly,

64
Q

why do we have residual volume? 3 marks

A

not all air can be expelled from the lungs, for
example because elastic fibres prevent the alveoli completely collapsing, and also the C-rings of cartilage in the trachea prevent complete collapse of the airways

air can only be expelled as long as the air pressure in the lungs is higher than the atmosphere, i.e. as long as there is a pressure gradient.

once the air pressures equalise, no more air will
be pushed out of the lungs no matter how much remains.

65
Q

what is Total lung capacity?

A

The sum of the vital capacity and the residual volume; the maximum volume of air that the lungs can contain at one time. Since residual volume cannot be measured directly, total lung capacity of living individuals may only be estimated.

66
Q

What is Oxygen consumption rate?

A

The rate at which the subject’s body is using up oxygen, i.e. the volume of oxygen used in a given time period. Oxygen is absorbed into the blood, from the
air that has been inhaled into the lungs. Oxygen diffuses from the blood into body cells and is used in the mitochondria for aerobic respiration

67
Q

what happens to the oxygen consumption rate during exercise?

A

During exercise, oxygen consumption rate increases, since muscles have increased aerobic respiration rate to provide more energy for muscle contraction.

68
Q

what are the units for oxygen consumption rate?

A

Units: cm3min‐1.

69
Q

Draw a spirometer graph

A

look in notes :(

70
Q

What do insects have instead of a internal bone skeleton?

A

Insects have an exoskeleton made of strong, insoluble chitin

71
Q

why do insects need a specisalised exchange surface?

A

chitin is impermeable to gases, insects cannot use their outer body surface for gas exchange

72
Q

what is a spircale of an insect?

A

Spiracles are the small openings along the thorax and abdomen of an insect that open and close (using valves) to control the amount of air moving in and out of the tracheal (gas exchange) system; they also control the level of water vapour loss from the exchange surfaces.

73
Q

what is a tracheal system?

A

the system of airways called tracheae and tracheoles which penetrate throughout an insect’s body

74
Q

what is the tracheae of an insect made of?

A

Tracheae have rings or spirals of chitin in their walls, supporting the walls against inward collapse. This is similar in principle to the role of cartilage in the walls of a mammal’s trachea. Little gas exchange occurs across the tracheal walls, due to the impermeability of the chitin.

75
Q

what are the tracheoles of an insect?

A

narrower airways that branch off from the trachea. Each tracheole is a single differentiated cell that forms a cylinder with highly permeable walls. The walls of the tracheoles form the gas exchange surface.

76
Q

how does O2 enter an insect?

A

Oxygen is at a higher concentration in the atmosphere than in the tracheal system, and is at the lowest concentration in body cells (where oxygen is being used up in aerobic respiration). Hence oxygen diffuses down its concentration gradient from the atmosphere
through open spiracles into tracheae. From here the oxygen diffuses via tracheoles into body cells.

77
Q

how does CO2 leave an insect?

A

Carbon dioxide is produced in respiration and so is at highest concentration in body cells, lower in the tracheal system and lowest in the atmosphere. Hence carbon dioxide diffuses down its concentration gradient from body cells into tracheoles, then through tracheae and out to the atmosphere through open spiracles.

78
Q

What is mechanical ventilation?

A

similar to principles to breathing in mammals, requiring muscle contraction that leads to volume and therefore pressure changes. The aim is to increase the steepness of the concentration gradients for each gas and hence speed up diffusion.

79
Q

Are all insects able to do mechanical ventialtion?

A

no, in larger insects, diffusion alone may be too slow to meet the needs of respiring muscle cells.

80
Q

What is the process of mechanical ventialtion?

A

Drawing air in - specific muscles contract and cause an increase in the volume of the thorax and abdomen, including increasing the volume of the tracheal system. The pressure of the air in the tracheal system decreases to below atmospheric air pressure, hence air flows into the tracheal system from the atmosphere down the air pressure gradient.

Expeling air out - other muscles contract and cause a decrease in the volume of the thorax and abdomen, including decreasing the volume of the tracheal system. The pressure of the air in the tracheal system increases to above atmospheric air pressure, hence air flows out of the tracheal system into the atmosphere down the air pressure gradient.

81
Q

what is tracheal fluid?

A

The fluid found at the ends of each tracheole called tracheal fluid. This helps control the surface area available for gas exchange according to the insect’s activity level and regulates the loss of water vapour from the tracheal system to the atmosphere.

82
Q

how does tracheal fluid work when the insect is inactive?

A

When the insect is inactive, there is more tracheal fluid present at the ends of the tracheoles, limiting the exposed surface area of the tracheole walls available for gas exchange. Gas exchange occurs at a lower rate, in line with the lower respiration rate in the surrounding cells.

83
Q

how does tracheal fluid work when the insect is active?

A

the higher rate of (initially anaerobic) respiration in the surrounding muscles causes them to accumulate lactic acid. The increasing concentration of lactic acid decreases the water potential in the muscle cells and so tracheal fluid (mostly water) moves out of the tracheoles down a water potential gradient into those muscle cells, leaving a greater exposed surface area of tracheole walls. This increases the rate of exchange of oxygen and carbon dioxide by diffusion between the air in the tracheoles and the muscle cells (across the tracheole walls), supporting the higher activity level of the insect.

84
Q

How do we view the insect tracheal system?

A

To view the tracheal system of an insect, carry out the dissection under water. First cut open the exoskeleton with a sharp scalpel, making a longitudinal cut down the abdomen. Carefully peel back the exoskeleton and pin in place. The tracheoles will appear pearly white under water and should appear as fine, branching threads.

85
Q

where do fish get their oxygen from?

A

THE WATER

86
Q

What is the challenge for fish absorbing O2 from water? 2 marks

A
  1. the concentration of oxygen in water is much lower than in atmospheric air
  2. water is a great deal more viscous than air (requiring more energy expenditure to move it past the
    exchange surface)
87
Q

What are the adaptations of fish gills? 4 marks

A
  1. Very large surface area so more gases can be exchanged by diffusion - crucial to compensate for the low concentration of oxygen in water. The large
    surface area is achieved by the presence of multiple gill plates, each made up of numerous long, thin gill filaments; each gill filament can a large number of tiny folds on their surfaces called lamellae.
  2. Thin barrier providing short diffusion distance - the gill surface is a single layer of epithelial cells, beyond which is immediately found a dense network of capillaries, whose walls are similarly made of a single layer of endothelium. Oxygen and carbon dioxide only have a short distance to diffuse between the blood and the water.
  3. Good blood supply: the dense network of capillaries inside the gills brings carbon dioxide to the exchange surface and carries oxygen away from it. This maintains concentration gradients for both gases and hence increases rates of diffusion. The effectiveness of this aspect of the gills is maximised by the presence of a countercurrent system the blood in the gill capillaries flows in the opposite direction to the water flowing past the gills, enabling as much oxygen as possible to be extracted from this water.
  4. Ventilation: to increase the steepness of the concentration gradients for oxygen and carbon dioxide (and thus achieve high enough rates of diffusion), a flow of water over the gills must be maintained. This is achieved via active movements of the floor of the buccal cavity and the operculum.
88
Q

order of sizes of fish ventialtion systems?

A

Gills are made of gill arches, each gill arch supports a pair of gill plates, each gill plate is made up of gill filaments, then each gill filament has lamellae

89
Q

why do gill plates overlap?

A

it slows down the flow of water over the gills in order to allow more time for gas exchange

90
Q

what are gill arches made of?

A

bone

91
Q

what are the function of gill arches?

A

they support the soft tissues of the gills

92
Q

what is a gill plate?

A

a stack of parallel, long, thin gill filaments

93
Q

what are the specialisations of gill filaments?

A

ndividually have a large surface area and are numerous to further increase the area available for gas exchange

94
Q

what are the specialisations of the lamellae?

A

increasing surface area yet further o further increase the area available for gas exchange

95
Q

Why do gills apear to be red?

A

due to the thin layer of epithelial tissue that covers the rich network of blood capillaries (which thin walls of endothelium) inside the gills. This arrangement decreases the diffusion distance for the gases and so increases rate of gas exchange.

96
Q

What is the countercurrent exchange system?

A

an efficient mechanism for exchanging materials when two different components flow in opposite directions past each other.

97
Q

How does the countercurrent exchange system work in fish?

A

the blood in the gill capillaries flows in the opposite direction to the water that is flowing over the gills. This maintains a concentration gradient along the whole length of the gills, extracting the most oxygen possible from the water (and releasing as much carbon dioxide as possible to the water). Overall, this countercurrent system is therefore much more effective than a parallel (i.e. concurrent) system. If the fluids on both sides of the barrier were flowing in the same direction, the result would be a steep concentration gradient at one end of the system that is then quickly lost further along. This would not transfer anywhere near as much oxygen from the water to the blood as the countercurren system can achieve.

98
Q

Draw the counter current flow graph vs the parallel flow graph

A

look in notes :(

99
Q

What is the role of the buccal cavity in ventilation

A

The buccal cavity is the water‐filled space within the fish’s mouth. Water is able to flow into the buccal cavity when the mouth is open and flow from the buccal cavity through and out over the gills when the operculum is open.

100
Q

What is the role of the operculum in ventilation

A

The operculum is a bony flap found covering the gills of bony fish. The opening and closing of the operculum (or specifically the opercular valve) is part of the mechanism that maintains a constant flow of water over the gas exchange surfaces of the gills (in the opposite direction to the flow of blood in the gill capillaries).

101
Q

can a bony fish maintain the flow of water when not moving?

A

A bony fish is able to maintain a flow of water (in a single direction) over the gills, even if the fish is not moving forwards through the water

102
Q

What is the mechanism for ventulating the gills in bony fish? 10 marks

A
  1. While the opercular valve is closed, the fish’s mouth opens
  2. The floor of buccal cavity moves downwards (due to muscle contraction)
  3. This increases the volume of buccal cavity
  4. Hence there is a decreased pressure of the water inside the buccal cavity
  5. Water enters the buccal cavity through the mouth, down the pressure gradient
  6. Then the mouth closes and the opercular valve opens
  7. The floor of buccal cavity moves upwards
  8. The pressure in buccal cavity increases and is now higher than in opercular cavity (the space in which the gills are located)
  9. Water moves down the pressure gradient from the buccal cavity over the gills (where gas exchange occurs) and out through the open opercular valve
  10. The opercular valve now closes and the whole process repeats.
103
Q

How do we view the gills of a fish?

A

To view the gills of a bony fish, first use a sharp scalpel to remove the operculum (since this will be obscuring the view of the gills). Place a pencil (or similar) into the buccal cavity, pushing it through the opening at the back of the gills. The pencil lifts and supports the gill arches, allowing a clear view of the interleaved gill plates with their numerous gill filaments.

MPW biology (26 decks)

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