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A-level Biology AQA > 3.1.5 Gas Exchange and the Transport of Oxygen in Living Organisms > Flashcards

3.1.5 Gas Exchange and the Transport of Oxygen in Living Organisms Flashcards

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1
Q

Why do organisms need to exchange substances with their environment?

A
  • Cells need to take in oxygen and nutrients
  • Cells need to excrete waste products (e.g. carbon dioxide and urea)
  • Most organisms need to stay same temperature = heat needs to exchanged
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2
Q

Smaller animals have a _____ SA : Volume Ratio

A

Higher

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3
Q

Why do multicellular organisms need exchange organs and mass transport systems?

A

∵ diffusion across the outer membrane would be too slow

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4
Q

Why don’t single-celled organisms need exchange organs or mass transport systems?

A

∵ Substances can diffuse directly into (or out of) cells across cell-surface membrane (diffusion rate is quick)

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5
Q

Name 2 things that cause diffusion across outer membrane to be too slow in multicellular organisms

A
  • Cells deep within body
    • Big distance between them & outside environment
  • Larger animals = low SA:volume ratio
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6
Q

What is tissue fluid?

A

Environment around cells of multicellular organisms

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7
Q

What is the mass transport system in mammals?

A

Circulatory system

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8
Q

What is the mass transport system in plants?

A

Transport of water and solutes in xylem and phloem

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9
Q

Name 2 factors that affect heat exchange

A
  • Shape
  • Size
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10
Q

Animals with compact shape have a ___ surface area relative to their volume which _____ heat loss from their surface

A

Animals with compact shape have a SMALL surface area relative to their volume which MINIMISIES heat loss from their surface

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11
Q

What do small animals (with a large surface area) need to stay warm and why?

A

High metabolic rate to generate enough heat to stay warm ∵ they lose heat easily

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12
Q

Name 3 gas exchange surfaces adaptations

A
  • Large SA
  • Thin = short diffusion pathway
  • Steep concentration gradient
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13
Q

Name 2 ways organisms maintain a steep concentration gradient

A
  1. Via movement of environmental medium e.g. air
  2. Via transport system = ensure movement of internal medium
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14
Q

Name 2 features that single-celled organisms have that allow gases to diffuse through their outer surface

A

Have large surface area, thin surface & short diffusion pathways

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15
Q

Name the main gas exchange surface in dicotyledonous plants

A

Surface of mesophyll cells in leaf

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16
Q

Dicotyledonous Plants

Gases move in and out through special pores in epidermis called _____

A

stomata

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17
Q

What do insects use for gas exchange?

A

Tracheae (microscopic air-filled pipes)

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18
Q

What are spiracles?

A

Pores on insects’ surface

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19
Q

Describe and explain the movement of oxygen into the gas exchange system of an insect when it is at rest

A
  1. Oxygen is used in aerobic respiration
  2. So oxygen concentration gradient established
  3. Oxygen diffuses in through spiracles, then tracheae & then through tracheoles which go into individual cells
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20
Q

How is carbon dioxide removed from insects?

A

Carbon dioxide from the cells diffuses (down its own concentration gradient) into tracheal tubes and through the spiracles

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21
Q

Why do insects have to be small in size?

A

∵ insects mainly rely on diffusion to exchange gases

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22
Q

What is tracheae supported by to prevent them from collapsing?

A

Strengthened rings

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23
Q

Name 4 adaptations of dicotyledonous plants that enable efficent gas exchange

A
  1. Many stomata
  2. Thin, flat shape = provides large SA:volume ratio
  3. Numerous interconnection air spaces throughout mesophyll
  4. Leaf is flattened so no living cell is far form external air
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24
Q

Exchanging gases ____ water

A

loses

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25
Q

Name 2 adaptations that insects have to minimise water loss (without reducing gas exchange too much)

A
  • If insects are losing too much water = close their spiracles using muscles
  • Have waterproof, waxy cuticle over their body & tiny hair around their spiracles = reduce evaporation
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26
Q

Name an adaptation of dicotyledonous plants to minimise water loss without reducing gas exchange too much

A

If plants gets dehydrated = guard cells lose water & become flaccid = closes stomata

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27
Q

How are plants’ stomata kept open during day (for gaseous exchange)?

A

Water enters guard cells = making them turgid = opens stomatal pore

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28
Q

What type of process is inspiration (breathing in)?

A

Active process – uses energy

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29
Q

What type of process is expiration (breathing out)?

A

Passive process

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30
Q

Describe the process of inspiration

A
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31
Q

Describe the process of expiration

A
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32
Q

Describe what happens during forced expiration (e.g. when you want to blow out candles)

A
  1. External intercostal muscles relax & internal intercostal muscles contract = pulling ribcage further down and in
  2. During this time, movement of 2 sets of intercostal muscles is said to be antagonistic (opposing)
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33
Q

What mainly causes the air to be forced out during normal quiet breathing (e.g. sleeping)?

A

Recoil of the elastic lungs

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34
Q

Describe how oxygen gets from the alveoli to the blood

A

O2 diffuses out of alveoli, across the alveolar epithelium and capillary endothelium (type of epithelium that forms the capillary wall) & into haemoglobin in blood

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35
Q

Oxygen from the air moves down the trachea, bronchi and bronchioles into the alveoli down a ______ _______

A

pressure gradient

36
Q

Once in alveoli, oxyegn diffuses across alveolar epithelium, then capillary endothelium, into the capillary, down a ____ _______

A

diffusion gradient

37
Q

Name 3 adaptations alveoli have for gaseous exchange

A
  1. Thin exchange surface
    1. Alveolar epithelium = one cell thick
    2. Short diffusion pathway
  2. Large SA
    1. Large no. of alveoli = large SA for gas exchange
  3. Steep concentration gradient
    1. (of O2 & CO2 between alveoli and capillaries)
    2. Maintained by flow of blood and ventilation
38
Q

Name 2 things red blood cells do to enable efficent gas exchange

A
  • RBC are slowed as they pass through pulmonary capillaries = allow more time for diffusion
  • RBCS are flattened against capillary walls = reduces diffusion distance
39
Q

Describe the structure of haemoglobin

A
  1. Haemoglobin = large protein with quaternary structure
    1. Made up of 4 polypeptide chains
    2. Coiled into a helix
    3. Chains linked together to form spherical molecule
  2. Each chain contains a haem group
    1. Which contains a iron ion (Fe2+)
40
Q

How many oxygen molecules can each haem group combine with?

A

1 oxygen molecule

41
Q

How many molecules of oxygen can each haemoglobin carry?

A

4 oxygen molecules

42
Q

What happens to haemoglobin in the lungs?

A

Oxygen joins to haemoglobin in RBCs to form oxyhaemoglobin

43
Q

What happens to oxyhaemoglobin when it nears body cells?

A

Oxygen leaves oxyhaemoglobin (dissociates from it) & turns back to haemoglobin

44
Q

What is partial pressure of oxygen (pO2)?

A

A measure of oxygen concentration

45
Q

The greater the concentration of dissolved oxygen in the cells are, the _____ the partial pressure is

A

Higher

46
Q

Haemoglobin’s affinity for oxygen varies depending on…

A

The partial pressure of oxygen (pO2)

47
Q

What happens to haemoglobin when there is low pO2?

A
  1. Oxyhaemoglobin unloads its oxygen
  2. ∵ Haemoglobin = low affinity for oxygen
    • Means it releases oxygen rather than combines with it
48
Q

What happens to haemoglobin when there is high pO2?

A
  1. Oxygen loads onto haemoglobin to form oxyhaemoglobin
  2. ∵ Haemoglobin = high affinity for oxygen
    • Means it will readily combine with oxygen rather than release it
49
Q

Haemoglobin

What happens to oxygen when it enters the blood capillaries at the alveoli in the lungs & why?

A

Alveoli = have high pO2 ∴ oxygen loads onto haemoglobin to form oxyhaemoglobin

50
Q

Haemoglobin

What happens to oxygen at respiring cells & why?

A
  • When cells respire, use up oxygen = pO2 decreases
  • RBCs deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen
51
Q

What do dissociation curves show?

A

How saturated haemoglobin is with oxygen at any given partial pressure

52
Q

Why is that when the pO2 is high, haemoglobin has a high saturation of oxygen?

A

∵ haemoglobin has a high affinity for oxygen so it’ll readily combine with oxygen

53
Q

Why is that when the pO2 is low, haemoglobin has a low saturation of oxygen?

A

∵ haemoglobin has a low affinity for oxygen so it releases oxygen rather than combine with it

54
Q

Why is it difficult for the haemoglobin to absorb the 1st oxygen
molecule?

A

∵ 4 polypeptides of haemoglobin molecule are closely united

55
Q

Why is the dissociation curve ‘S-shaped’?

A
  1. ∵ when haemoglobin combines with 1st O2 molecule → conformational change occurs
    • Its shape alters, exposing more subunits to oxygen ∴ makes it easier for other O2 molecules to join
  2. But as Hb becomes saturated = harder for more oxygen molecules to join
  3. ∴ curve has steep bit in middle where it’s really easy for oxygen molecules to join & shadows bits at each end where it’s harder
56
Q

Dissociation Curves

When the curve is steep, a small change in pO2 can cause a…

A

big change in amount of oxygen carried by Hb

(e.g. very small decrease in partial pressure of oxygen = lot of oxygen becoming dissociated from haemoglobin)

57
Q

Why does haemoglobin rarely achieves 100% saturation of oxygen?

A

∵ it’s very difficult for 4th oxygen molecule to bind

58
Q

Why do different haemoglobin molecules have different affinities for oxygen? (structure wise)

A

∵ different haemoglobin molecules have slightly different sequences of amino acids & ∴ slightly different shapes

59
Q

Haemoglobin gives up its oxygen more readily at _____ partial pressures of carbon dioxide (pCO2)

A

HIGHER

60
Q

What is the purpose of haemoglobin having a lower affinity for O2 at higher pCO2?

A
  • So more oxygen will dissociate into respiring tissues
  • Rapid respiration
61
Q

Describe the Bohr Effect

A
  1. Respiring tissues produce CO2
  2. CO2 dissociates into many H+ ions
  3. H+ ions bind to haemoglobin & changes its shape causing more oxygen to be released = lowers affinity for oxygen

∴ the dissociation curve ‘shifts’ to right

62
Q

Left of the dissociation curve = …

A

Greater affinity of haemoglobin for oxygen

63
Q

Right of the dissociation curve = …

A

lower affinity of haemoglobin for oxygen

64
Q

When haemoglobin reaches a tissue with low respiratory rate, ___ oxygen molecule is released

A

1

65
Q

When haemoglobin reaches a tissue with high respiratory rate, ___ oxygen molecule is released

A

3

66
Q

What does the Bohr effect ensure?

A

Haemoglobin will load with oxygen more easily in pulmonary capillaries (low CO2 = high O2 affinity) and unload easily in tissue capillaries (high CO2 = low O2 affinity)

67
Q

What type of haemoglobin does organisms that live in environments with low concentration of oxygen have?

A

Haemoglobin with higher affinity for oxygen than human haemoglobin

(Dissociation curve is to the left of ours)

68
Q

What type of haemoglobin do organisms who are very active & have a high oxygen demand have?

A

Haemoglobin with a lower affinity for oxygen than human haemoglobin

(Curve is to right of human one)

69
Q

Name the type of curve at C

A

Human dissociation curve

70
Q

Describe the type of animal at curve A

A

Animal living in depleted oxygen environment e.g. lugworm

71
Q

Describe the type of animal at curve B

A

Animal living at high altitude where the pO2 is lower e.g. a llama in the Andes

72
Q

Describe the type of animal at curve D

A

Active animal with a high respiratory rate living where there’s plenty of available oxygen e.g. hawk

73
Q

Name 2 factors other than pCO2 or pO2 that affect the affinity of Hb for O2

A
  • Increasing temperature
  • Decrease in pH (more acidic solution)
74
Q

What happens to Hb’s affinity for O2 when there’s an increase in temperature and why is this benefical?

A
  • Lowers affinity of Hb for O2
  • Beneficial ∵ temp. increases during exercise, when you need more O2 for respiration
75
Q

What happens to Hb’s affinity for O2 when there’s a decrease in pH and why does this occur?

A
  • Lowers affinity of Hb for O2
  • ∵ more acidic solution = more H+ ions there will be to bind with Hb
76
Q

When there is CO2 present, why does it causes Hb to release its O2?

A

CO2 and H+ wants to take its (O2) place

77
Q

Why is the pO2 in the placenta low?

A
  • ∵ mother’s blood travels from the lungs around to the body then to the placenta
  • So blood loses oxygen along the way
78
Q

What is foetal Hb like (i.e. its affinity for O2)?

A

Has higher affinity for oxygen than adult haemoglobin

79
Q

At high altitude the pO2 in air decreases. This lowers pO2 breathed into lungs.

What will be the effect of a low pO2 in the percentage saturation of the Hb?

A

It will be lower

80
Q

At high altitude the pO2 in air decreases. This lowers pO2 breathed into lungs.

What would your body do in the short term to overcome this?

A
  • Heart rate increases
  • Breathing rate increases
  • Deeper breaths
81
Q

At high altitude the pO2 in air decreases. This lowers pO2 breathed into lungs.

What would your body do in the long term to overcome this?

A

Body will produce more red blood cells

82
Q

Why do many elite athletes choose to spend part of of their training season at high altitude?

A

To have more red blood cells so they can respire longer

83
Q

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf

A
  • CO2 enters via stomata
  • Stomata opened by guard cells
  • Diffuses through air spaces
  • Down diffusion gradient
84
Q

Common Question

Suggest how the control groups should have been treated in this investigation (2)

A
  • Give Placebo
  • (Otherwise) treated the same way
85
Q

Describe and explain how the countercurrent system leads to efficient gas exchanges across the gills of a fish (3)

A
  • Water and blood flow in opposite directions
  • Maintains concentration gradient
  • Along whole of gill/lamellae
86
Q

Name 4 common symptoms of lung disease

A
  1. Less elastic recoil
  2. Harder to remove air from the alveoli (when breathing out)
  3. (The walls of the alveoli are damaged) so reduced surface area (for gas exchange)
  4. (Inflammation of alveoli/thicker walls) so increased diffusion distance
  5. (More carbon dioxide/less oxygen in the alveoli) so reduced concentration gradients (for diffusion/gas exchange)
87
Q

Pulmonary fibrosis is a lung disease that causes the epithelium of the lungs to become irreversibly thickened. It also leads to reduced elasticity of lungs. One symptom of the disease is shortness of breath, especially when exercising.

Suggest why this symptom arises. (3)

A
  • Thickened epithelium of the alveoli = increases diffusion distance
    • Descreases rate of diffusion of oxygen into blood
  • More air space within lungs is occupied by fibrous tissue
    • Less air/oxygen is taken into lungs at each breath
  • Loss of elasticity makes ventilating very difficult
    • Makes it hard to maintain diffusion gradients
    • So patient becomes breathless in attempt to compensate by breathing faster

A-level Biology AQA (41 decks)

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