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OCR AS/A Level Biology Context > module 3.1: exchange surfaces > Flashcards

module 3.1: exchange surfaces Flashcards

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1
Q

why do all living cell need to remove waste products

A

that these do not build up and become toxic

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2
Q

why do larger organisms need a specialised surface for exchange

A

more than two layers of cells, the body surface is no longer sufficient

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3
Q

what are the 3 main factors that affect the need for exchange system

A

size, surface area to volume ratio, and level of activity

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4
Q

describe how size affects the need for an exchange system

A

in very small organisms (i.e: single-celled organisms), all the cytoplasm is very close to the environment in which they live, so diffusion supplies enough oxygen and nutrients to keep the cells alive and active. multicellular organisms may have several layers of cells. so any oxygen or nutrients diffusing in from the outside have a longer diffusion pathway. diffusion is too slow to enable a sufficient supply to the innermost cells

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5
Q

how does surface area to volume ratio affect the need for an exchange system

A

small organisms have a small surface area, but they also have a small volume, so their surface area is large enough to supply all their cells with sufficient oxygen. as size increases, the volume rises more quickly than the surface area. so large organisms have a small surface area to volume ratio. organisms can increase their surface area by adopting a different shape. an animal such as a flatworm has a very thin, flat body, giving it a larger surface area to volume ratio (SA:V), but such a body form limits the overall size that the animal can reach

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6
Q

how does the level of activity affect the need for exchange system

A

metabolic activity uses energy from food and requires oxygen to release the energy in aerobic respiration. the cells of an active organism need good supplies of nutrients and oxygen to supply the energy for movement. this need for energy is increased in those animals, such as mammals, that keep themselves warm

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7
Q

what does all good exchange surfaces have

A
  • a large surface area to provide more space for molecules to pass through. this is often achieved by folding the walls and membranes involved. a good example is the root hairs in plants
  • a thin barrier to reduce the diffusion distance — and that barrier must be permeable to the substances being exchanged. this is shown well in the alveoli of the lungs
  • a good blood supply to bring fresh supplies of molecules to one side (supply side), keeping the concentration high, or it may remove molecules from the demand side to keep the concentration low. this is important to maintain a steep concentration gradient so that diffusion can occur rapidly. the gills in fish are a good example
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8
Q

what is alveoli

A

tiny folds of the lung epithelium to increase the surface area

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9
Q

what are bronchi and bronchioles

A

smaller airways leading into the lungs

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10
Q

what is the diaphragm

A

a layer of muscle beneath the lungs

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11
Q

what are the intercoastal muscles

A

muscles between the ribs. contraction of the external intercostal muscles raises the ribcage

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12
Q

what is tranchea

A

the main airway leading from the back of the mouth to the lungs

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13
Q

what is ventilation

A

the refreshing of the air in the lungs, so that there is a higher oxygen concentration than in the blood, and a lower carbon dioxide concentration

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14
Q

what does the gaseous exchange system in mammals consists of

A

the lungs and associated airways that carry air into and out of the lungs

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15
Q

describe what are the air goes through

A

the lungs are a pair of inflatable sacs lying in the chest cavity. air can pass into the lungs through the nose and along the trachea (windpipe), bronchi and bronchioles. finally, it reaches tiny air-filled sacs called alveoli. these are the surfaces where the exchange of gases takes place. the lungs are protected by the ribcage. the ribs are held together by the intercostal muscles. the action of these muscles and the diaphragm (a layer of muscular tissue beneath the lungs) helps to produce breathing movements (ventilation)

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16
Q

explain the gaseous exchange in the lungs

A

gases pass by diffusion through the thin walls of the alveoli. oxygen passes from the air in the alveoli to the blood in the capillaries. carbon dioxide passes from the blood to the air in the alveoli. the lungs must maintain a steep concentration gradient in each direction in order to ensure that diffusion can continue

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17
Q

what are some examples of adaptations to reduce the distance the gases have to diffuse

A
  • the alveolus wall is one cell thick
  • the capillary wall is one cell thick
  • both walls consist of squamous cells — this means flattened or very thin
  • the capillaries are in close contact with the alveolus walls
  • the capillaries are so narrow that the red blood cells are squeezed against the capillary wall — making them closer to the air in the alveoli and reducing their rate of flow. so, the total barrier to diffusion is only two flattened cells, and is less than 1µm thick
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18
Q

how does a good blood supply help with efficiency of diffusion

A

the blood supply helps to maintain a steep concentration gradient, so that the gases continue to diffuse
* the blood system transports carbon dioxide from the tissues to the lungs. this ensures that the concentration of carbon dioxide in the blood is higher than that in the air of the alveoli. therefore carbon dioxide diffuses into the alveoli. the blood also transports oxygen away from the lungs. this ensures that the concentration of oxygen in the blood is kept lower than that in the alveoli — so that oxygen diffuses into the blood

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19
Q

how does ventilation help with the efficiency of diffusion

A

the breathing movements ventilate the lungs. this replaces the used air with fresh air, bringing in more oxygen and removing carbon dioxide
ventilation ensures that:
* the concentration of oxygen in the air of the alveolus remains higher than that in the blood
* the concentration of carbon dioxide in the alveoli remains lower than that in the blood.

  • therefore, the concentration gradient necessary for diffusion is maintained. the air we breathe in is not oxygen — it is rich in oxygen. the air we breathe out is not carbon dioxide — it is rich in carbon dioxide
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20
Q

what happens in inspiration (inhaling)

A
  • the diaphragm contracts to move down and become flatter — this displaces the digestive organs downwards
  • the external intercostal muscles contract to raise the ribs
  • the volume of the chest cavity is increased
  • the pressure in the chest cavity drops below the atmospheric pressure
  • air is moved into of the lungs
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21
Q

what happens in expiration (exhaling)

A
  • the diaphragm relaxes and is pushed up by the displaced organs underneath
  • the external intercostal muscles relax and the ribs fall; the internal intercostal muscles can contract to help push air out more forcefully — this usually only happens during exercise or coughing and sneezing
  • the volume of the chest cavity is decreased
  • the pressure in the lungs increases and rises above the pressure in the surrounding atmosphere
  • air is moved out of the lungs
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22
Q

what is cartilage

A

a form of connective tissue

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23
Q

what is ciliated epithelium

A

a layer of cells that have many hair-like extensions called cilia

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24
Q

what are elastic fibres

A

protein fibres that can deform and then recoil to their original size

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25
Q

what are goblet cells

A

cells that secrete mucus

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26
Q

what are smooth muscles

A

involuntary muscle that contracts without the need for conscious thought

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27
Q

what is the alveoli comprised of

A

squamous epithelium and are surrounded by blood capillaries, so that the distance that gases must diffuse is very short

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28
Q

what does the alveolus walls contain

A

elastic fibres that stretch during inspiration but then recoil to help push air out during expiration

29
Q

the alveolus walls are so thin. what does this mean

A

may not be possible to distinguish separate cells under a light microscope

30
Q

for the airways to be effective, what requirements must it meet

A
  • be large enough to allow sufficient air to flow without obstruction
  • be supported to prevent collapse when the air pressure inside is low during inspiration
  • be flexible in order to allow movement.
  • the airways are lined by ciliated epithelium, which contributes to keeping the lungs healthy. Goblet cells in the epithelium release mucus, which traps pathogens. The cilia then move the mucus up to the top of the airway, where it is swallowed
31
Q

what is narrower the trachea or the bronchi

A

bronchi

32
Q

what are the airways trachea and bronchi supported by

A

rings of cartilage which prevent collapse during inspiration

33
Q

why are the rings of the cartilage in the trachea C shaped rather than a complete ring

A

allows flexibility and space for food to pass down the oesophagus

34
Q

what is narrower, bronchioles or bronchi

A

bronchioles

35
Q

larger bronchioles may have some cartilage but the smaller ones do not

A
36
Q

what does the bronchioles wall comprised of

A

mostly of smooth muscle and elastic fibres

37
Q

smooth muscle in the airways does not contribute to the breathing movements

A
38
Q

what will the action of the smooth muscle do

A

constrict the airway and therefore make the lumen of the airway narrower

39
Q

what can the constriction of the lumen cause

A

can restrict the flow of air to and from the alveoli. controlling the flow of air to the alveoli might be important if there are harmful substances in the air

40
Q

what can smooth muscles not do after being contracted

A

it cannot reverse this effect on its own

41
Q

is the contraction of smooth muscles voluntary or involutary and what can it be caused by

A

involuntary and may occur as a result of an allergic reaction

42
Q

what are the smooth muscles elongated by

A

by the elastic fibres

43
Q

what happens when the smooth muscles contract

A

it deforms the elastic fibres

44
Q

what happens as the smooth muscles relax

A

the elastic fibres recoil to their original size and shape. this acts to dilate the airway

45
Q

what is the cause of asthma

A

some people overreact to certain substances in the air and their bronchioles constrict unnecessarily

46
Q

what is the breathing rate

A

the number of breaths per minute

47
Q

what is the oxygen uptake

A

the volume of oxygen absorbed by the lungs in one minute

48
Q

what is tidal volume

A

the volume of air inhaled or exhaled in one breath, usually measured at rest

49
Q

what is a spirometer

A

a device that can measure the movement of air into and out of the lungs

50
Q

what is vital capacity

A

the greatest volume of air that can be expelled from the lungs after taking the deepest possible breath

51
Q

what are some precautions that should be taken when using a spirometer

A
  • the subject should be healthy and, in particular, free from asthma
  • the soda lime should be fresh and functioning
  • there should be no air leaks in the apparatus, as this would give invalid or inaccurate results
  • the mouthpiece should be sterilised
  • the water chamber must not be overfilled (or water may enter the air tubes)
52
Q

what happens to the spirometer during inspiration

A

air is drawn from the chamber so that the lid moves down

53
Q

what happens to the spirometer during expiration

A

the air returns to the chamber, raising the lid

54
Q

where are the movement in a spirometer recorded on

A

a data logger

55
Q

what does the total lung volume consist of

A

vital capacity, which can be measured, and the residual volume, which cannot be measured using the spirometer

56
Q

what are the factors affecting the vital capacity

A
  • the size of a person (particularly their height)
  • their age and gender
  • their level of regular exercise
57
Q

what is residue capacity

A

the volume of air that remains in the lungs even after forced expiration

58
Q

what is the approximate amount of residual volume left in the airways and alveoli

A

1.5dm3

59
Q

what is the typical value of the tidal volume

A

0.5 dm3

60
Q

what happens as the CO2 is removed using soda lime

A

the volume of air in the chamber decreases

61
Q

how do you calculate the oxygen uptake from a spirometer trace

A
  • on trace, draw a line from the initial oxygen volume (A) down to the horizontal axis, and another line from the final oxygen volume (B) to the horizontal axis. measure the length of time between these points
  • measure the difference in volume between points A and B
  • divide by the time taken for this decrease
  • the unit will be dm3s-1
62
Q

what would increased O2 uptake result in

A
  • increased breathing rate
  • deeper breaths
63
Q

describe the respiratory system of bony fish

A

bony fish must exchange gases with the water in which they live. they use gills in order to absorb oxygen dissolved in the water and release carbon dioxide into the water. the oxygen concentration will be typically much lower than is found in air. most bony fish have five pairs of gills (see Figure 1) which are covered by a bony plate called the operculum. each gill consists of two rows of gill filaments (primary lamellae) attached to a bony arch. the filaments are very thin, and their surface is folded into many secondary lamellae (or gill plates). this provides a very large surface area. blood capillaries carry deoxygenated blood close to the surface of the secondary lamellae where exchange takes place

64
Q

describe the concept of countercurrent flow

A

blood flows along the gill arch and out along the filaments to the secondary lamellae. the blood then flows through capillaries in the opposite direction to the flow of water over the lamellae. this arrangement creates a countercurrent flow that absorbs the maximum amount of oxygen from the water

65
Q

describe ventilation in bony fish

A

bony fish can keep water flowing over the gills by using a buccal—opercular pump. the buccal cavity (mouth) can change volume. the floor of the mouth moves downwards, drawing water into the buccal cavity. the mouth closes and the floor is raised again pushing water through the gills. movements of the operculum are coordinated with the movements of the buccal cavity. as water is pushed from the buccal cavity, the operculum moves outwards. this movement reduces the pressure in the opercular cavity (the space under the operculum), helping water to flow through the gills

66
Q

describe the respiratory system of insects

A
  • insects do not transport oxygen in blood. insects have an open circulatory system in which the body fluid acts as both blood and tissue fluid. circulation is slow and can be affected by body movements
  • insects possess an air-filled tracheal system, which supplies air directly to all the respiring tissues. air enters the system via a pore in each segment, called a spiracle. the air is transported into the body through a series of tubes called tracheae (singular `trachea’). these divide into smaller and smaller tubes, called tracheoles. the ends of the tracheoles are open and filled with fluid called tracheal fluid. gaseous exchange occurs between the air in the tracheole and the tracheal fluid. some exchange can also occur across the thin walls of the tracheoles
67
Q

describe ventilation in insects

A
  • in many insects, sections of the tracheal system are expanded and have flexible walls. these act as air sacs which can be squeezed by the action of the flight muscles. repetitive expansion and contraction of these sacs ventilate the tracheal system
  • in some insects, movements of the wings alter the volume of the thorax. as the thorax volume decreases, air in the tracheal system is put under pressure and is pushed out of the tracheal system. when the thorax increases in volume, the pressure inside drops and air is pushed into the tracheal system from outside
  • some insects have developed this ventilation even further. locusts can alter the volume of their abdomen by specialised breathing movements. these are coordinated with opening and closing valves in the spiracles. as the abdomen expands, spiracles at the front end of the body open and air enters the tracheal system. as the abdomen reduces in volume, the spiracles at the rear end of the body open and air can leave the tracheal system
68
Q

in insects, as there is an increase in the volume of the body cavity reduces pressure…….

A

so that air enters the tracheal system; a decrease in volume raises the pressure to push air out again

OCR AS/A Level Biology Context (24 decks)

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