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AQA A Level Biology > 3.3.1 Exchange Surfaces and 3.3.2 Gas Exchange > Flashcards

3.3.1 Exchange Surfaces and 3.3.2 Gas Exchange Flashcards

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1
Q

What is the rate of exchange affected by?

A
  • Size of organism (SA:V ratio)
  • Metabolic rate
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2
Q

What is diffusion directly proportional to?

A

surface area x diff in concentration / length of diffusion pathway

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3
Q

What are the 5 features of an exchange surface?

A
  1. Large Surface Area
  2. Thin
  3. Selectively Permeable
  4. Movement of external medium
  5. Movement of internal medium
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4
Q

Why is a large SA:V ratio beneficial?

A

Increases the rate of exchange

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5
Q

Why is a thin exchange surface beneficial?

A

Decreases diffusion distance, allowing quicker diffusion

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6
Q

Why is the movement of internal and external medium beneficial?

A

maintains concentration gradient

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7
Q

Explain the process of gas exchange in insects (2)

A
  1. Gases enter and leave the tracheae through the spiracles via diffusion
  2. Spiracles are opened and closed through valves
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8
Q

Why might it be a problem to have the spiracles open for a long time?​

A

water loss

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9
Q

What are spiracles?

A

tiny pores in which gases leave and enter.

Can be opened and closed through valves

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10
Q

What is tracheae?

A

internal network of tubes in insects

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11
Q

What are tracheoles?

A

tracheae divided into smaller dead-end tubes

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12
Q

What 3 ways do respiratory gases move in and out of the tracheae?

A
  1. Along a diffusion gradient (insect at rest)
  2. By mass transport (high activity)
  3. Ends of tracheoles are filed with water (high activity)
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13
Q

How do respiratory gases move in out the tracheae along a diffusion gradient?

A

Muscle cells use up oxygen in aerobic respiration

Muscle cells produce carbon dioxide

This creates a diffusion gradient

So ocygen diffuses in via spiracles

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14
Q

How do respiratory gases move in out the tracheae by mass transport?

A

The contraction of muscles in insects can squeeze the trachea allowing large amounts of gas to move in and out. (abdominal pumping)

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15
Q

How do respiratory gases move in out the tracheae through the ends of tracheoles (5)

A
  1. Muscle cells at the end of tracheoles respire anaerobically during major activity​
  2. This produces lactic acid (lactate)​
  3. Lactic acid is soluble and so dissolves in cells, lowering their water potential​
  4. Water moves into the cells by osmosis (from the tracheoles)​
  5. There is now a lower volume of water in the tracheoles, and so space for more air to be drawn further into the tracheal system
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16
Q

Why is simple diffusion not suitable for gas exchange in fish? (3)

A
  • multicellular organism, so diffusion would take too long
  • small SA:V ratio
  • Waterproof outer covering
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17
Q

What is a gill arch?

A

rigid curved structure made from cartilage which supports one or two rows of gill filaments​

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18
Q

What are gill filaments?

A

threadlike projections covered by lamellae

Each filament contains two blood vessels, one carrying deoxygenated blood, the other oxygenated

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19
Q

What is lamellae?

A

a thin piece of tissue covered by capillary network

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20
Q

Explain the process of exchange in fish(3)

A
  1. Water is taken in through the mouth
  2. Water is forced over the gills and out through the opening on each side of the body​
  3. The flow of blood is opposite to the flow of water (counter current flow)​
21
Q

What is meant by counter current flow?

A

blood and water that flow over the lamella flow in opposite directions

22
Q

Why is a counter current flow system beneficial?

A

it maintains a diffusion gradient across the whole length of the lamellae

23
Q

What exchange features does a fish have?

A
  1. Many filaments and lamellae = a large surface area​
  2. Lamellae are very thin = short diffusion pathway​
  3. Endothelial cells of the capillary walls are selectively permeable to oxygen and carbon dioxide​
  4. Movement of blood (internal medium) and movement of water (external medium) = maintains a steep concentration gradient
24
Q

Another name for gill cover is..

A

Operculum

25
Q

What factors affect the rate of transpiration? (4)

A

Temperature
Wind
Light Intensity
Humidity ( conc. of water vapour)

26
Q

What is the site of gas exchange in plants?

A

Leaves

27
Q

Why do leaves have no specific transport system and are reliant on passive diffusion? (2)

A

Thin - short distance between phosynthesising cells and air spaces​

Large surface area due to the many air spaces

28
Q

What are stomata?

A

many small pores that have guard cells which control the rate of gaseous exchange

29
Q

How does the stomata open? (3)

A
  1. Water moves into guard cell via osmosis, down a water potential gradient ​
  2. Causes cell to become turgid ​
  3. Due to their inner cell wall being thicker and more rigid, the guard cells bend away from each other when they fill with water, opening the stomatal pore.
30
Q

How does the stomata close? (3)

A
  1. Water moves out of guard cell by osmosis, down a water potential gradient
  2. This causes the cell to become flaccid ​
  3. The guard cells no longer bend away from each other causing the stoma to close
31
Q

What is meant by transpiration?

A

the movement of water through a plant from roots to leaves, caused by the evaporation of water out of the leaf.​

32
Q

What are plants that are adapted for very dry /extreme conditions called?

A

xerophytes

33
Q

What adaptations do plants have to prevent water loss? (5)

A
  1. Thick waxy cuticle – waterproof layer​
  2. Rolling up leaves – traps air (containing water vapour)​
  3. Hairy leaves – traps air (containing water vapour)​
  4. Stomata in pits or grooves – traps air (containing water vapour)​
  5. Reduced SA:V for some leaves – e.g. pine needles,
34
Q

How are the lungs adapted for efficient gas exchange? (4)

A
  1. Many alveoli and many capillaries provide a large surface area, which increases the SA:V = fast diffusion​
  2. Alveolar epithelium and capillary walls are only one cell thick so short diffusion gradient between alveoli and blood = fast diffusion​

​3. Alveolar wall made of squamous (flattened) epithelial cells ​

​4. Ventilation and circulation maintain a diffusion gradient = fast diffusion

35
Q

What tissues allow the alveoli to stretch and recoil?

A

collagen and elastic

36
Q

List the correct sequence of all the structures that are part of the journey of mammalian gas exchange.

A

trachea, bronchus, bronchioles, alveoli, alveolus

37
Q

Describe how gas exchange occurs in the alveolus (5)

A
  1. Oxygen diffuses from a high concentration through the alveolar epithelium and capillary endothelium into the blood.
  2. This is because there is higher concentration of oxygen inside the alveoli.​
  3. Carbon dioxide diffuses through the capillary endothelium and alveolar epithelium into the alveoli.
  4. This is because there is higher concentration of carbon dioxide in the blood.
38
Q

Explain the adaptations of the alveolus for rapid diffusion (5)

Hint: constant ventilation and circulation (1)

A
  1. Constant ventilation and circulation, maintaining a diffusion gradient ​
  2. Thin alveolar epithelium and capillary endothelium are only one cell thick so diffusion pathway is short​
  3. Many alveoli and capillaries = large SA = increasing SA: V​
  4. Alveolar surface is moist so gases dissolve​
  5. RBC’s are compressed against capillary wall so reduces diffusion pathway
39
Q

Describe how oxygen in the air reaches surrounding capillaries surrounding the alveoli in the lungs (4)

A
  1. Trachea and bronchi and bronchioles
  2. Down pressure gradient
  3. Down diffusion gradient
  4. Across alveolar epithelium
  5. Across capillary endothelium
40
Q

Limiting water loss in insects (3)

A
  • Small SA:V ratio
  • Waterproof coverings
  • Spiracles
41
Q

Breathing in =

A

inspiration

42
Q

Breathing out =

A

expiration

43
Q

Explain the Process of Inspiration (5)

A
  1. External intercostal muscles contract, internal intercostals relax​
  2. Ribs are pulled up and out which increases volume​
  3. Diaphragm contracts (flattens) which further increases volume​
  4. Increased volume in thorax leads to decreased pressure.​
  5. Atmospheric pressure > pulmonary pressure, so air is forced into lungs down a pressure gradient
43
Q

Explain the process of Expiration (5)

A
  1. Internal intercostal muscles contract, external intercostals relax​
  2. Ribs move down and in which decreases volume​
  3. Diaphragm relaxes (pushed up) which further decreases volume​
  4. Decreased volume leads to increased pressure ​
  5. Pulmonary pressure > atmospheric pressure, so air is forced out of lungs down a pressure gradient
44
Q

pulmonary ventilation rate =

A

tidal volume x breathing rate

45
Q

Tidal volume

A

volume of air taken in each breath (at rest)

46
Q

Breathing rate

A

number of breaths per minute

47
Q

What does a spirometer do?

A

measures tidal volume and breathing rate.​

The top of the chamber of air is attached to a position sensor, which records movement of the chamber and displays the results on a computer screen.​

48
Q

Diffusion of gases between the alveoli and
the blood will be very rapid because:

A
  • the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
  • the walls of both alveoli and capillaries are very thin = short diffusion pathway

AQA A Level Biology (8 decks)

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