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Exchange surfaces Flashcards

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1
Q

Why is diffusion alone enough to supply the needs of single-celled organisms?

A
  • The metabolic activity of a single-celled organism is usually low, so their oxygen demands are relatively low
  • The SA:V ratio is large
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2
Q

Why is diffusion alone not enough to supply the needs of complex organisms (e.g. mammals)?

A
  • High metabolic activity
  • Low SA:V ratio
  • Large diffusion distance
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3
Q

What features do all effective exchange surfaces have?

A
  • Large surface area
  • Thin layers
  • Good blood supply/ventilation (to maintain steep concentration gradient)
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4
Q

Example of large surface area exchange surface

A

Root hair cells

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5
Q

Example of thin layer exchange surface

A

Alveoli

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6
Q

Example of good blood supply exchange surface

A

Alveoli

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7
Q

Example of ventilation exchange surface

A

Gills

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8
Q

What is the trachea?

A

The main large airway which carries air from the nose down the chest, leading into the bronchi

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9
Q

What is the structure of the trachea?

A

The trachea is a wide tube supported by incomplete rings of strong, flexible cartilage.

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10
Q

Why do trachea have incomplete rings of cartilage?

A

Rings of cartilage are present to stop the trachea from collapsing. They are incomplete rings to allow food to travel down the oesophagus behind

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11
Q

What are the trachea and its branches lined with?

A

Ciliated epithelial cells and goblet cells

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12
Q

What do ciliated epithelial cells do in the trachea?

A

They have hair-like structures called cilia, which move in a rhythmic manner and beat away mucus from entering the lungs

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13
Q

What do goblet cells do in the trachea?

A

They secrete mucus, which traps and prevents dust and possibly harmful microorganisms from entering the lungs

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14
Q

Where does the trachea divide and into what?

A

In the chest cavity, the trachea divides into the left and right bronchus. The right bronchus leads to the right lung, and the left bronchus to the left lung

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15
Q

What is the structure of bronchi?

A

They are similar in structure to the trachea, with the same supporting cartilage rings, but are smaller

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16
Q

Where do bronchi divide and into what?

A

In the lungs, bronchi divide to form many small bronchioles

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17
Q

What is the structure of brochioles?

A

The smaller bronchioles have no cartilage rings, and their walls contain smooth muscle

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18
Q

What are bronchioles lined with, and what does this allow for?

A

Bronchioles are lined with a thin layer of flattened epithelial cells; this allows for a small level of gaseous exchange

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19
Q

What is the purpose of the smooth muscle in the walls of bronchioles?

A

Constriction and relaxation of the smooth muscle can control the amount of air reaching the lungs

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20
Q

What are alveoli?

A

Tiny air sacs which are the main site of gaseous exchange in the body

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21
Q

What is the structure of alveoli?

A

Made up of a single layer of flattened epithelial cells, along with some elastic fibres

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22
Q

What is the function of elastic fibres in the alveoli?

A

They allow for elastic recoil

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23
Q

What is elastic recoil?

A

Where the elastic tissues in the alveoli stretch as air is drawn in, and when they return to the their resting size they help squeeze air back out

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24
Q

Where is lung surfactant found, and what does it do?

A

Lung surfactant is found on the inner walls of alveoli, and it makes it possible for alveoli to remain inflated, stopping them from collapsing and sticking together

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25
Q

How are alveoli adapted for their function?

A
  • High SA:V ratio
  • Thin layers
  • Good blood supply
  • Good ventilation
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26
Q

Why is a good blood supply and ventilation important in alveoli?

A

Maintains a steep concentration gradient of O2 and CO2

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27
Q

Why do insects need a different way of exchanging gases?

A
  • Tough exoskeleton through which little to no gaseous exchange can take place
  • Do not have blood pigments that can carry oxygen
28
Q

How does gaseous exchange work in insects?

A

Insects have evolved to deliver oxygen directly to the cells and to remove the carbon dioxide the same way

29
Q

What are the small openings found on insects known as?

A

Spiracles

30
Q

Where are spiracles found?

A

Along the thorax and abdomen

31
Q

What enters and leaves through spiracles?

A

Air enters and leaves through spiracles, but water is also lost

32
Q

How do insects control the loss of water through spiracles?

A

Spiracles can be opened and closed by spiracle sphincters.

33
Q

When will spiracles be closed?

A

When an insect is inactive and oxygen demands are very low, spiracles will all be closed most of the time

34
Q

When will spiracles be open?

A

When the oxygen demand is raised or the carbon dioxide levels build up, more spiracles open

35
Q

What structure leads away from spiracles?

A

Tracheae

36
Q

What are tracheae?

A

The largest tubes of the insect respiratory system, they carry air into the body

37
Q

What are tracheae lined with and what is the effect of this?

A

Tracheae are lined with spirals of chitin, which keep them open. This chitin cuticle is relatively impermeable to gases so little gaseous exchange occurs in the tracheae

38
Q

What leads on from tracheae?

A

Tracheae branch to form narrower tubes until they divide into tracheoles

39
Q

What is the structure of tracheoles?

A

Each tracheole is a single, greatly elongated cell with no chitin lining

40
Q

What does the lack of chitin lining mean in tracheoles?

A

It means they are freely permeable to gases, and so the tracheoles are where most gaseous exchange take place

41
Q

What does the small size of tracheoles allow for?

A

Tracheoles spread throughout the tissue of the insect, running between individual cells

42
Q

What is tracheal fluid?

A

Towards the end of tracheoles, there is often a build up of water known as tracheal fluid. This fluid prevents gaseous penetration, lowering the surface area available for gaseous exchange

43
Q

What happens to tracheal fluid when oxygen demands build up?

A

When oxygen demands build up, there is also a build up of lactic acid in the tissues, which causes tracheal fluid to leave the tracheoles via osmosis.

44
Q

What is the effect of tracheal fluid leaving the tracheoles?

A

It exposes more area for gaseous exchange, increasing the rate of diffusion

45
Q

What other methods do insects with higher energy demands have to supply them with the oxygen they need?

A
  • Mechanical ventilation of the tracheal system

- Air sacs

46
Q

How does mechanical ventilation of the tracheal system work to increase oxygen supply?

A

Air is actively pumped into the system by the muscular pumping movements of the thorax and/or abdomen. This results in changes in the pressure, causing air to be move quickly drawn in and pumped out

47
Q

How do air sacs work to increase oxygen supply?

A

They act as air reservoirs, and increase the amount of air that can be moved through the gas exchange system

48
Q

Why must bony fish have a different and specialised gaseous exchange system?

A
  • Diffusion alone would not be enough to supply the oxygen they need
  • They have a scaly outer covering which is not permeable enough to allow gaseous exchange
  • The density, viscosity and lower oxygen content of water would make conventional diffusion impossible
49
Q

Why do bony fish need a specialised exchange system?

A
  • Low SA:V ratio

- Scaly impermeable outer covering

50
Q

How does the respiratory system of bony fish work?

A

They maintain a flow of water in one direction over the gills, and the gills take oxygen from the water and get rid of carbon dioxide into the water

51
Q

What are gills contained in and covered by?

A

Gills are contained in the opercular cavity, and covered by a protective operculum (a bony flap that covers the gills)

52
Q

What is the structure of gills?

A

Gills consist of a series of bony gill arches, each with two stacks of gill filaments. Gill arches act as the backbone for gill filaments to come out of

53
Q

What is found on gill filaments?

A

Gill filaments have protruding rows of gill lamellae, which are the main site of gaseous exchange

54
Q

Why do gills need a constant supply of water?

A

In order to keep gill filaments apart and expose the surface area of gaseous exchange, a constant supply of flowing water is needed

55
Q

Why are gill lamellae well adapted to be the main sites of gaseous exchange?

A

Each lamellae consists of a network of capillaries covered by a single thin layer of flattened epithelial cells. This means lamellae have a good blood supply, low diffusion distance and high SA:V ratio

56
Q

What is ram ventilation in fishes?

A

More primitive fish such as sharks rely on continual movement to keep a continuous flow of water to ventilate the gills. This is known as ram ventilation

57
Q

Do all fish use ram ventilation?

A

No, most bony fish have evolved a sophisticated system of ventilation, which allows a constant flow of water over the gills even without movement

58
Q

What is step one of water flowing over the gills?

A

The mouth is opened and the floor of the buccal cavity is lowered; this increases the volume and lowers the pressure of the buccal cavity, causing water to enter

59
Q

What happens after water enters the buccal cavity?

A

The opercular valve is closed and the opercular cavity containing the gills expands, lowering the pressure in the opercular cavity containing the gills.

60
Q

What happens after the pressure in the opercular cavity is lowered?

A

The floor of the buccal cavity moves up, increasing the pressure in the buccal cavity, causing water to move into the opercular cavity down the pressure gradient

61
Q

What happens after water enters the opercular cavity?

A

The opercular valve is opened, the mouth is closed and the sides of the opercular cavity move inwards. All these actions cause the pressure in the opercular cavity to increase, forcing water over the gills and out of the fish

62
Q

What other adaptions do gills have to ensure the most effect possible gaseous exchange?

A
  • Tips of adjacent gill filaments overlap

- Counter current system

63
Q

Why does the tips of adjacent gill filaments overlap make for more efficient gaseous exchange?

A

It increases the resistance to the flow of water over the gill surfaces, increasing the amount of time available for gaseous exchange to take place

64
Q

What does a counter current system mean in bony fish?

A

Water and blood flow in different directions

65
Q

What does a counter current system allow for in bony fish?

A

It means there is always a greater oxygen concentration in the water than in the blood, allowing for continuous diffusion and hence more efficient gaseous exchange

66
Q

How do parallel systems work in bony fish?

A

Water and blood flow in the same direction, which gives an initial steep oxygen concentration gradient, however equilibrium between the blood and water will soon be reached, resulting in no further net diffusion of oxygen into the blood

Biology Exams (28 decks)

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