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OCR Biology Paper 1 > 3.1 - Exchange Surfaces > Flashcards

3.1 - Exchange Surfaces Flashcards

1
Q

Why do single-celled organisms not need exchange surfaces?

A
  • Metabolic activity is low - low demand for oxygen for respiration
  • Large surface area to volume ratio
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2
Q

Why are exchange surfaces necessary for larger organisms?

A
  • High metabolic activity
  • Smaller surface area to volume ratio
  • Larger distances between cells where oxygen is needed and the supply of oxygen
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3
Q

How is the surface area to volume ratio calculated?

A

Ratio = surface area / volume

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4
Q

How does the size of an organism correlate it its SA:V?

A

The bigger the organism, the smaller its SA:V

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5
Q

Describe and explain the features of efficient exchange surfaces

A

Large surface area
- Provides more surface for diffusion to take place through
- e.g. root hair cells

Thin
- Short diffusion pathway
- e.g. epithelial cells of alveoli

Good blood supply
- Maintains steep concentration gradient
- e.g. dense capillary network around alveoli

Good ventilation
- Maintains steep concentration gradient
- e.g. fish gills maintain steady flow of water over exchange surfaces

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6
Q

Define gas exchange in mammals

A

Process whereby oxygen enters the blood capillaries in the alveoli and carbon dioxide leaves

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7
Q

Outline the structure and function of the nasal cavity

A
  • Good blood supply - warms air to body temperature
  • Hairy lining - traps dust and bacteria
  • Moist surfaces - increases humidity of oncoming air
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8
Q

Outline the structure and function of the trachea

A
  • Carries clean, warm air from nose to chest
  • Supported by C-shaped rings of cartilage - stop trachea from collapsing (but allow food to move down neighbouring oesophagus)
  • Smooth muscle contracts to narrow lumen
  • Elastic fibres allow lumen to dilate
  • Lined with goblet cells and ciliated epithelium - produce mucus to trap
    pathogens and move it to throat
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9
Q

Outline the structure and function of the bronchus

A
  • Lead to left and right lungs
  • Supported by smaller C-shaped rings of cartilage
  • Smooth muscle contracts to narrow lumen
  • Elastic fibres allow lumen to dilate
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10
Q

Outline the structure and function of the bronchioles

A
  • Narrow tubes leading from bronchi to alveoli - Made from smooth muscle and elastic fibres - can contract and relax to
    control air flow
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11
Q

Outline the structure and function of the alveoli

A
  • Site of gas exchange
  • Elastic fibres allow alveoli to stretch and recoil to return to original shape
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12
Q

Describe what happens in alveoli

A
  • Gas exchange
  • Oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air
  • Oxygen binds to haemoglobin in red blood cells
  • Volume of alveoli increases during inspiration
  • Concentration gradients of gases maintained
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13
Q

How are the alveoli adapted for gas exchange?

A
  • Very large surface area
  • Large surface area to volume ratio
  • Thin walls (single cell thick) - short diffusion distance
  • Moist - lined with lung surfactant - allows gases to dissolve and keeps alveoli inflated
  • Good blood supply from capillaries - maintains steep concentration gradient
  • Good ventilation - breathing maintains steep diffusion gradient
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14
Q

Define ventilation

A

Inhalation and exhalation of air between the lungs and the outside

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15
Q

What is the role of ventilation?

A
  • Maintains concentration gradients of oxygen and carbon dioxide
  • Concentration of oxygen remains higher in alveoli than in blood
  • Concentration of carbon dioxide remains higher in blood than alveoli
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16
Q

Outline the mechanism of ventilation in the lungs during inhalation

A

During inhalation:
- External intercostal muscles contract moving rib cage up and out
- Diaphragm contracts and becomes flatter
- Increase in volume in thorax
- Decrease in pressure in thorax
- Air flows into lungs as atmospheric pressure is higher than pressure in thorax

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17
Q

Outline the mechanism of ventilation in the lungs during exhalation

A

During exhalation:
- Internal intercostal muscles contract so ribs move in and down
- Diaphragm relaxes and becomes domed in shape
- Decrease in volume in thorax
- Increase in pressure in thorax
- Air moves out until pressure in lungs falls
- Abdominal muscles can be used to make a stronger exhalation

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18
Q

Define antagonistic muscles

A
  • Muscles that oppose the action of each other
  • e.g. internal and external intercostal muscles
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19
Q

Define breathing rate

A

Number of inhalations or exhalations per minute

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20
Q

Define ventilation rate

A

Total volume of air inhaled per minute

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21
Q

Define tidal volume

A

The volume of air moved into or out of the lungs during a normal breath

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22
Q

Define vital capacity

A

Maximum volume of air that can be breathed in

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23
Q

Define inspiratory reserve volume

A

Maximum volume of air that can be breathed in over and above normal inhalation

24
Q

Define expiratory reserve volume

A

Maximum volume of air that can be breathed out over and above normal tidal volume

25
Q

Define residual volume

A

Volume of air left in lungs after largest possible exhale

26
Q

How is total lung capacity calculated?

A

Vital capacity + residual volume

27
Q

How is ventilation rate calculated?

A

Ventilation rate = tidal volume x breathing rate (per minute)

28
Q

How is ventilation rate monitored?

A
  • Simple observation
  • Data logging with a spirometer
29
Q

How is tidal volume determined?

A

Spirometer (tube used to measure the volume of exhaled air)

30
Q

Describe how a spirometer would be used to measure tidal volume

A
  • Subject breathes evenly into spirometer
  • Subject wears nose clip so as not to breathe through nose
  • Measure height of waves from the spirometer trace
  • Measure at least three waves and calculate mean
31
Q

Explain the change in tidal volume during exercise

A
  • Exercise increases rate of respiration
  • Produces more carbon dioxide
  • Requires more oxygen
  • Increased tidal volume excretes more carbon dioxide
  • Increased tidal volume increases gas exchange
  • Concentration gradients of gases is maintained
32
Q

What features of an insect requires them to have a different gas exchange system to mammals?

A
  • Larger surface area : volume
  • Tough exoskeleton - no gas exchange can take place through it
  • Blood pigments do not carry oxygen
33
Q

What are spiracles?

A
  • Small openings along thorax and abdomen of insects
  • Allow air to enter and leave tracheal system
  • Water lost through open spiracles
34
Q

What are tracheae?
How are they opened/closed?
How are they supported?

A
  • Network of air filled pipes that run into body of insect
  • Spiracles at end control opening and closing
  • Supported by rings of chitin
35
Q

What are tracheoles?

A

Narrower tubes formed from branching of tracheae

36
Q

Where does most of the gas exchange occur in an insect?

A

In the tracheoles

37
Q

What is the role of tracheal fluid?

A
  • Lactic acid causes tracheal fluid to leave tracheoles by osmosis
  • Occurs when oxygen demand is high
  • More surface area exposed for gas exchange
38
Q

How does oxygen reach the cells in an insect?

A
  • Tracheoles run past each cell
  • Oxygen diffuses from tracheoles into cells
39
Q

How is gas exchanged controlled in insects?

A
  • Opening and closing of spiracles
  • Sphincters open and close to minimise water loss
  • When oxygen demand is low, spiracles are closed
  • When oxygen demand is high, spiracles are open
40
Q

Describe how gas exchange takes place in insects

A

Oxygen used up by cells during respiration
- O2 concentration towards ends of tracheoles falls
- Diffusion gradient established - O2 diffuses from atmosphere through tracheae and
tracheoles into cells

CO2 produced by cells during respiration
- Diffusion gradient established in opposite direction

CO2 diffuses along tracheoles and tracheae to atmosphere
- Diffuses into atmosphere through open spiracles

41
Q

How do larger insects increase the level of gas exchange?

A

Mechanical ventilation - air actively pumped into system by muscular contraction of thorax
and abdomen
- Changes pressure in tracheae, drawing air in and forcing it out

Collapsible air sacs in tracheae - act as air reservoirs
- Increase amount of air moved through gas exchange system
- Inflated and deflated by movements of thorax and abdomen

42
Q

Give the advantage of the tracheal system

A

Direct delivery of oxygen to the tissues and direct removal of carbon dioxide

43
Q

Give the disadvantage of the tracheal system

A
  • System limits size of the organism
  • Tracheoles can only successfully deliver enough oxygen if diffusion distance is short and pumping mechanism of abdomen keeps the air flowing
  • This can only occur over a relatively short distance
44
Q

Describe the similarities between the gas exchange of an insect and that of a
mammal

A
  • Large surface area
  • Moist gas exchange surface
  • Thin gas exchange surface
  • Concentration gradient maintained by ventilation
45
Q

Describe the differences between the gas exchange of an insect and that of a mammal

A
  • Oxygen transported to cells via circulatory system in mammals
  • Alveoli are gas exchange surface in mammals, in insects it is the junction between
    tracheoles and respiring tissues
46
Q

What are the issues with carrying out gas exchange in water?

A
  • Water is denser and more viscous than air
  • Water has much lower oxygen content than air
47
Q

What are the issues with carrying out gas exchange in water?

A
  • Water is denser and more viscous than air
  • Water has much lower oxygen content than air
48
Q

Describe the respiratory system of a bony fish

A
  • Buccal cavity - mouth of the fish - floor can lower and raise to change volume
  • Operculum - bony flap that covers gills
  • Gill filaments - occur in stacks (gill plates) - separated by flowing water to provide large
    surface area - Ends overlap to slow down water flow
  • Gill lamellae - organs of gas exchange - rich blood supply and large surface area
49
Q

How are the gill filaments adapted for gas exchange?

A

Covered in lamella
- Increase surface area

Tips overlap
- Increases resistance to flow of water
- Slows water down for more effective gas exchange

50
Q

How are the gill lamellae adapted for gas exchange?

A
  • Rich blood supply to maintain concentration gradient
  • Large surface area
  • Very thin - short diffusion pathway
51
Q

Describe how a constant flow of water is maintained by bony fish

A
  • Mouth opens and floor of buccal cavity lowered
  • Volume of buccal cavity increases
  • Pressure decreases
  • Water moves into buccal cavity
  • Mouth closes and floor of buccal cavity raised
  • Forces water over gills and out of operculum
52
Q

What is the countercurrent flow system?

A
  • Blood flows through the lamella in one direction
  • Water flows over lamellae in the opposite direction
53
Q

How does the countercurrent flow system mean that gas exchange is more efficient?

A
  • Water and blood flow in opposite directions
  • Maintains constant concentration gradient along length of gill
  • Water always next to blood with a lower concentration of oxygen
54
Q

Explain how the structure of the gas exchange system of bony fish maximises the amount of oxygen than can be absorbed from water

A

Gills have large stacks of gill filaments carrying gill lamellae
- Gill lamellae adapted for successful gaseous exchange
- Large surface area
- Good blood supply
- Thin layers

Constant flow of water maintained over gills
- Maximises diffusion gradient for respiratory gases

Tips of gill filaments overlap
- Increases resistance to flow of water
- Slows water down for more effective gaseous exchange

Countercurrent exchange system maximises the potential exchange of gases

55
Q

Outline the mechanism of ventilation in the lungs during exhalation

A

During exhalation:
- Internal intercostal muscles contract so ribs move in and down
- Diaphragm relaxes and becomes domed in shape
- Decrease in volume in thorax
- Increase in pressure in thorax
- Air moves out until pressure in lungs falls
- Abdominal muscles can be used to make a stronger exhalation

OCR Biology Paper 1 (20 decks)

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