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Biology AS > 3.2 Gas Exchange > Flashcards

3.2 Gas Exchange Flashcards

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1
Q

Where does gas exchange happen?

A
  • In single celled organisms
  • In plants
  • In fish
  • In insects
  • In humans
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2
Q

What are the characteristics of a gas exchange surface?

A
  • Large surface area
  • Very thin (short diffusion pathway) - one cell thick
  • Permeable
  • Highly vascularised (good blood supply)
  • Moist
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3
Q

What factors affect diffusion?

A
  • Fick’s Law
  • Diffusion ∝ SA x Difference in concentration/Length of diffusion pathway
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4
Q

What is gas exchange in single celled organisms?

A
  • Single celled organisms such as amoeba have large surface area to volume ratios
  • Oxygen is absorbed across their cell membrane and can reach all cell organelles
  • Carbon dioxide is able to diffuse out of the cell in the same way
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5
Q

What is gas exchange in plants?

A
  • All living parts of a plant must respire and therefore need to exchange respiratory gases, gas exchange takes place through the leaves, plants have to balance gas exchange with water loss
  • Stomata are pores through which gases exchange, if they are open the plant is subject to losing water, particularly if it’s a hot day
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6
Q

What is the structure of leaves?

A
  • Leaves are typically flat, offering a large surface area for gas exchange, the inside of the leaf has a large internal surface area for gas exchange. These surfaces are moist.
  • Leaves are thin in cross section to allow a short diffusion pathway
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7
Q

What is a counter current?

A
  • A counter current means that the blood and water flow in opposite directions
  • The concentration of oxygen in the blood reaching the gills is lower than that of the water. Oxygen diffuses from the water to the blood. The counter-current mechanism maintains an optimal diffusion gradient over the full length of the capillary
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8
Q

How do fish get oxygen out of water?

A
  • A given volume of air contains about 30 times more oxygen than the same volume of water
  • Oxygen does not readily dissolve in water and its solubility is proportional to the temperature
  • Unlike aquatic mammals fish are adapted to extract oxygen directly from water
  • The gas exchange surface of a fish is their gills
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9
Q

What is ventilation?

A

The passage of oxygen over a gas exchange surface (mechanism of breathing)

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10
Q

What is inspiration in fish?

A

Inspiration (breathing in)
- The fish has its mouth open
- The gills cover (operculum) is closed
- Water enters the buccal cavity (mouth area)

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11
Q

What is expiration in fish?

A

Expiration (breathing out)
- The mouth of the fish will close, the floor of the buccal cavity moves upwards
- This decreases the volume of the buccal cavity and increases the pressure
- The pressure opens the operculum and water is forced over the gills and out through the gill opening

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12
Q

What is the structure of the gills?

A
  • The gills are located within the body of the fish, behind the head
  • They are made up of gill filaments
  • The gill filaments are stacked up in a pile
  • At right angles to the filaments are gill lamellae which increase the surface area of the gills
  • Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body
  • The flow of water over the gill lamellae and the flow of blood within them are in opposite directions is know as the counter current flow
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13
Q

What is the structure of the gas exchange system in insects?

A
  • Holes which lead from the outside to inside the insects body are called spiracles
  • The tubes into the body is known as the tracheae
  • These tubes divide to tracheoles
  • The tracheoles are directly embedded in muscle, oxygen is not transported to muscles by a circulatory system
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14
Q

What is ventilation in insects?

A
  • When the insect is at rest the tracheoles are filled with a watery fluid, simple diffusion of oxygen and carbon dioxide satisfy the insects needs
  • Insects rely on diffusion for gas exchange, oxygen is delivered directly to muscles and carbon dioxide is removed in the same way
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15
Q

When does the insect use oxygen for flight?

A
  • During exercise such as flight, increased metabolic activity of the muscles leads to lactic acid accumulation which decreases the water potential of the cells, this draws the fluid into the tissues, this in turn pulls more oxygen into the trachea
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16
Q

What is the structure of the alveoli?

A
  • Pressure + volume changes ensure air arrives at the alveolus and air is then expelled
  • Folded alveoli walls give a large surface area
  • Constant movement of blood maintains the concentration gradient as deoxygenated blood is always arriving at the alveolus
  • Mucus lines alveoli making the surfaces moist
  • The walls of the capillary and alveoli are 1 cell thick making a short diffusion pathway
  • These are almost the diameter of the capillary, so passage is slowed allowing more time for diffusion. Flexible membranes allow them to squeeze through
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17
Q

What is the process of breathing in?

A
  • The ribs move upwards and outwards
  • The rib cage moves up and out because the external intercostal muscles contract
  • The diaphragm moves downwards
  • This increases the volume of the chest cavity (thorax)
  • The pressure in the thorax is now lower than the external pressure
  • So air moves into the lungs
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18
Q

What type of muscles are internal and external intercostal muscles?

A

The internal and external intercostal muscles are antagonistic muscles

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19
Q

What is the process of breathing out?

A
  • The ribs move downwards and inwards
  • The ribs move down and in because the external intercostal muscles relax
  • The diaphragm moves upwards
  • This decreases the volume of the thorax
  • This means the pressure is now increased
  • Air is forced out of the lungs
  • If we force out the last of our breath the internal intercostal muscles contract more strongly
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20
Q

How do respiratory gases move in and out of the tracheal system?

A
  • Along a diffusion gradient
  • Mass transport
  • The ends of the tracheoles are filled with water
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21
Q

How do respiratory gases move in and out of the tracheal system along a diffusion pathway?

A
  • When cells are respiring, oxygen is used up and so its concentration towards the ends of the tracheoles falls.
  • This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells.
  • Carbon dioxide is produced by cells during respiration
  • This creates a diffusion gradient in the opposite direction
  • This causes gaseous carbon dioxide to diffuse along the tracheoles and tracheae from the cells to the atmosphere
  • As diffusion in air is much more rapid than in water, respiratory gases are exchanged quickly by this method
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22
Q

How do respiratory gases move in and out of the tracheal system by mass transport?

A

The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases

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23
Q

How do respiratory gases move in and out of the tracheal system by the end of the tracheoles being filled with water?

A
  • During periods of major activity, the muscle cells around the tracheoles respire carry out some anaerobic respiration
  • This produces lactate, which is soluble and lowers the water potential of the muscle cells
  • Water therefore moves into the cells from the tracheoles by osmosis
  • The water in the ends of the tracheoles decreases in volume and in doing so draws air further into them
  • This means the final diffusion pathway is in a gas rather than a liquid phase, and therefore diffusion is more rapid
  • This increases the rate at which air is moved in the tracheoles but leads to greater water evaporation
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24
Q

How do spiracles work?

A
  • Gases enter and leave the tracheae through tiny pores, called spiracles, on the body surface
  • When the spiracles are open, water vapour can evaporate from the insect
  • For much of the time insects keep their spiracles closed to prevent this water loss
  • Periodically they open the spiracles to allow gas exchange
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25
Q

What are the limitations of the tracheal system?

A
  • It relies mostly on diffusion to exchange gases between the environment and the cells
  • For diffusion to be effective, the diffusion pathway needs to be short which is why insects are of a small size
  • As a result the length of the diffusion pathway limits the size that insects can attain
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26
Q

What is inspiration?

A

When the air pressure of the atmosphere is greater than the air pressure inside the lungs, air is forced into the lungs

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27
Q

What is expiration?

A

When the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs

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28
Q

Why will the diffusion of gases between the alveoli and the blood be very rapid?

A
  • Red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
  • 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 and therefore the distance over which diffusion takes place is very short
  • Alveoli and pulmonary capillaries have a very large total surface area
  • Breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained
  • Blood flow through the pulmonary capillaries maintains a concentration gradient
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29
Q

What are the main parts of the human gas-exchange system?

A
  • The lungs
  • The trachea
  • The bronchi
  • The bronchioles
  • The alveoli
30
Q

What is the structure and function of the lungs?

A
  • The lungs are a pair of lobed structures made up of a series of highly branched tubules, called bronchioles, which end in tiny air sacs called alveoli
31
Q

What is the structure and function of the trachea?

A
  • The trachea is a flexible airway that is supported by rings of cartilage
  • The cartilage prevents the trachea collapsing as the air pressure inside falls when breathing in
  • The tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells which move mucus towards the throat to be swallowed, preventing lung infections
  • carries air to the bronchi
32
Q

What is the structure and function of the bronchi?

A
  • The bronchi are two divisions of the trachea, each leading to one lung
  • They are similar in structure to the trachea and , like the trachea, they also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat
  • The larger bronchi are supported by cartilage, although the amount of cartilage is reduced as the bronchi get smaller
33
Q

What is the structure and function of the bronchioles?

A
  • The bronchioles are a series of branching subdivisions of the bronchi
  • Their walls are made of muscle lined with epithelial cells so that they can contract and relax easily during ventilation
  • This muscle allows them to constrict so that they can control the flow of air in and out of the alveoli
34
Q

What is the structure and function of the alveoli?

A
  • The alveoli are mini air-sacs, with a diameter of between 100μm and 300μm, at the end of the bronchioles
  • Between the alveoli there are some collagen and elastic fibres
  • The alveoli are lined with epithelium
  • The elastic fibres allow the alveoli to stretch as they fill with air when breathing in
  • They then spring back during breathing out in order to expel the carbon dioxide-rich air
  • The alveolar membrane is the gas-exchange surface
35
Q

Why are lungs located in the body?

A
  • Air is not dense enough to support and protect these delicate structures
  • The body as a whole otherwise lose a great deal of water and dry out
36
Q

What do aerobic organisms require?

A
  • All aerobic organisms require a constant supply of oxygen to release energy in the form of ATP during respiration.
  • The carbon dioxide produced in the process needs to be removed as its build-up could be harmful to the body
37
Q

Why is the volume of oxygen that has to be absorbed and the volume of carbon dioxide that must be removed large in mammals?

A
  • They are relatively large organisms with a large volume of living cells
  • They maintain a high body temperature which is related to them having high metabolic and respiratory rates
38
Q

What modifications do leaves have to prevent water loss?

A
  • A thick cuticle
  • Rolling up of leaves
  • Hairy leaves
  • Stomata in pits or grooves
  • A reduced surface area to volume ratio of the leaves
39
Q

Why do leaves have a thick cuticle?

A

Although the waxy cuticle on leaves forms a waterproof barrier, up to 10% of water loss can still occur by this route. The thicker the cuticle, the less water can escape by this means, for example holly

40
Q

How does the rolling up of leaves prevent water loss?

A
  • Most leaves have their stomata largely or entirely confined to the lower epidermis
  • The rolling of leaves in a way that protects the lower epidermis from the outside helps to trap a region of still air within the rolled leaf
  • This region become saturated with water vapour and so has a very high water potential
  • There is no water potential gradient between the inside and outside of the leaf and therefore no water loss
  • Marram grass rolls its leaves
41
Q

How does hairy leaves prevent water loss?

A
  • A thick layer of hairs on leaves, especially on the lower epidermis, traps still, moist air next to the leaf surface
  • The water potential gradient between the inside and the outside of the leaves is reduced and therefore less water is lost by evaporation
  • One type of heather plant has this modification
42
Q

How does stomata in pits or grooves prevent water loss?

A
  • These trap still, moist air next to the leaf and reduce the water potential gradient
  • Examples of plants using this mechanism include pine trees
43
Q

How does having a reduced surface area to volume ratio of the leaves prevent water loss?

A
  • The smaller the surface area to volume ratio the slower the rate of diffusion
  • By having leaves that are small and roughly circular in cross-section, as in pine needles, rather than leaves that are broad and flat, the rate of water loss can be reduced
  • This reduction in surface area is balanced against the need for a sufficient area for photosynthesis to meet the requirement of the plant
44
Q

How do plant survive in habitants?

A

The main way of surviving in habitants where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation. As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications

45
Q

Why can’t plants have a small surface area?

A

Because they photosynthesise and photosynthesis requires a large leaf surface area for the capture of light and for the gas exchange of gases

46
Q

What do terrestrial plants have to prevent water loss?

A

They have a waterproof covering over parts of the leaves and the ability to close stomata when necessary

47
Q

What are xerophytes?

A
  • Plants that are adapted to living in areas where water is in short supply
  • They have a restricted supply of water so have evolved a range of other adaptations to limit water loss through transpiration
  • Without these the plants would become desiccated and die
48
Q

What is the problem with terrestrial organisms?

A
  • Most organisms are terrestrial (live on land)
  • Water easily evaporates from the surface of their bodies and they can become dehydrated
  • They have evolved adaptations to conserve water
  • The insects have to balance the opposing needs of exchanging respiratory gases with limiting water loss
49
Q

What adaptations do insects have that reduce water loss?

A
  • Small surface area to volume ratio
  • Waterproof coverings
  • Spiracles
50
Q

Why do insects have a small surface area to volume ratio?

A

To minimise the area over which water is lost

51
Q

Why do insects have waterproof coverings?

A

They have waterproof coverings over their body surfaces. In the case of insects this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle

52
Q

Why do insects have spiracles?

A

Spiracles are the opening of the tracheae at the body surface and these can be closed to reduce water loss. This conflicts with the need for oxygen and so occurs largely when the insect is at rest

53
Q

How do insects carry air?

A
  • Insects cannot use their body surface to diffuse respiratory gases in the way a single-celled organism does
  • Instead they have an internal network of tubes called tracheae that carry air containing oxygen directly to the tissues
54
Q

Why is gas exchange in plants different to in animals?

A
  • Some plant cells carry out photosynthesis
  • During photosynthesis, plant cells take in carbon dioxide and produce oxygen
  • At times the gases produced in one process can be used for the other
  • This reduces gas exchange with the external air
  • Overall, this means that the volumes and types of gases that are being exchanged by a plant leaf changes
  • This depends on the balance between rates of photosynthesis and respiration
55
Q

What happens when photosynthesis is taking place?

A
  • When photosynthesis is taking place, although some carbon dioxide comes from respiration of cells, most of it is obtained from the external air. In the same way, some oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant
56
Q

What happens when photosynthesis is not occurring?

A
  • When photosynthesis is not occurring, for example, in the dark, oxygen diffuses into the leaf because it is constantly being used by cells during respiration
  • In the same way, carbon dioxide produced during respiration diffuses out
57
Q

Why can’t insects use their bodies as an exchange surface?

A

They have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water

58
Q

What are the three main features of an insects gas transport system?

A
  • Spiracles = holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
  • Tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
  • Tracheoles = smaller branches dividing off the tracheae
59
Q

Explain the process of gas exchange in insects.

A
  • Gases move in and out of the tracheae through the spiracles
  • A diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out
  • Contraction of muscles in the tracheae allows mass movement of air in and out
60
Q

Why cant fish use their bodies as an exchange surface?

A

They have a waterproof, impermeable outer membrane and a small surface area to volume ratio

61
Q

Name and describe the 2 main features of a fish’s gas transport system

A

Gills = located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles
Lamellae = at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (counter current exchange system)

62
Q

Explain the process of gas exchange in fish

A
  • the fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure
  • the water passes over the lamellae and the oxygen diffuses into the bloodstream
  • waste carbon dioxide diffuses into the water and flows back and out of the gills
63
Q

How does the counter current exchange system maximise oxygen absorbed by the fish?

A

Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed

64
Q

Name and describe 3 adaptations of a leaf that allow efficient gas exchange

A
  1. thin and flat to provide short diffusion pathway and large surface area to volume ratio
  2. Many minute pores in the underside of the leaf allow gasses to easily enter
  3. Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis
65
Q

How do plants limit their water loss while still allowing gases to be exchanged?

A

Stomata regulated by guard cells which allows them to open and close as needed. Most stay closed to prevent water loss while some stay open to let oxygen in

66
Q

Describe the pathway taken by air as it enters the mammalian gaseous echange system

A

nasal cavity, trachea, bronchi, bronchioles, alveoli

67
Q

Describe the function of the nasal cavity in the mammalian gaseous exchange system.

A

A good blood supply warms and moistens the air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria

68
Q

What is tidal volume?

A

the volume of air we breathe in and out during each breath at rest

69
Q

What is breathing rate?

A

the number of breaths we take per minute

70
Q

How do you calculate pulmonary ventilation rate?

A

tidal volume x breathing rate. These can be measured using a spirometer, a device which records volume changes onto a graph as a person breaths

Biology AS (36 decks)

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