Showing posts with label Gas exchange. Show all posts
Showing posts with label Gas exchange. Show all posts

#53 Summary of Smoking

AS , Gas exchange
#53 Summary of Smoking
1 Tobacco smoke contains tar, carbon monoxide and nicotine.

 2 Tar settles on the epithelium lining the bronchi and bronchioles and stimulates inflammation, an increase in the secretion of mucus and an accumulation of phagocytes from the blood.






 3 Damage to the airways and alveoli occurs in chronic obstructive pulmonary disease (COPD). In chronic bronchitis, the airways are obstructed by mucus and infection; in emphysema, alveoli are destroyed, reducing the surface area for gas exchange.

 4 Tar contains carcinogens, which cause changes in DNA in bronchial epithelial cells, leading to the development of a bronchial carcinoma. This is lung cancer.

5 Some of the signs and symptoms of COPD are breathlessness, wheezing and constant coughing; two of the symptoms of lung cancer are coughing up blood and chest pains.

 6 Carbon monoxide combines irreversibly with haemoglobin, reducing the oxygen-carrying capacity of the blood.

 7 Nicotine stimulates the nervous system, increasing heart rate and blood pressure, and stimulating vasoconstriction, which reduces blood fl ow to the extremities.

 8 Epidemiological evidence shows a strong correlation between smoking and lung diseases such as cancer; the link between smoking and lung cancer was confi rmed by experimental studies.

9 Smoking damages the cardiovascular system, increasing atherosclerosis and increasing the risk of coronary heart disease and stroke.

 10 Atherosclerosis is the development of fatty tissue within the walls of arteries. Th e fatty material, known as atheroma, forms plaques within the artery walls. These roughen the lining of arteries, which may lead to thrombosis (blood clotting).

 11 Coronary heart disease may be treated with drugs to lower blood cholesterol and blood pressure. Coronary artery by-pass surgery involves using a blood vessel from the leg, arm or chest to replace the part or parts of a coronary artery that are damaged. A heart transplant may be necessary, but it is an expensive operation and diffi cult to find donor
hearts, so very few are performed.

 12 Primary health care can reduce mortality from coronary heart disease and strokes. Screening people for risk factors of coronary heart disease and stroke allows early intervention. Advertising and education can promote the benefi ts of exercise, not smoking, avoiding an excessive consumption of alcohol and eating a diet low in saturated fat. These alternatives to treatment and surgery may be more cost-eff ective in the long term, but they
depend on people being willing and able to change their lifestyle.


1. Multiple-choice test

1 Tar in cigarette smoke contains carcinogens and is mostly deposited in the bronchi. 

What is the effect of these carcinogens? 

A   cause mutations in bronchial epithelial cells
B   destroy the cilia in the bronchi
C   stimulate goblet cells to produce more mucus
D   reduce the diameter of the bronchi

2 Which component of tobacco smoke binds with haemoglobin to form carboxyhaemoglobin?

A  carbon monoxide
B  carcinogens
C  nicotine
D tar

3 What is not a symptom of emphysema?

A  alveoli burst
B alveoli lose elastic fibres
C bronchi are blocked by tumours
D the total surface area of the alveoli is reduced

4 Two lifelong cigarette smokers, X and Y, both have persistent coughs. X also has difficulty breathing out and Y is getting much thinner. From these symptoms it is possible that: 

A  X has bronchitis and Y has emphysema.
B  X has emphysema and Y has chronic obstructive pulmonary disease.
C  X has chronic obstructive pulmonary disease and Y has lung cancer.
D  X has lung cancer and Y has bronchitis.

5 Both carbon monoxide and nicotine are absorbed into the blood from tobacco smoke.

What describes their effects on the body?


6 What is the sequence of events leading to atherosclerosis? 

1   blood clot forms at site of plaque
2    phagocytes attracted to site of damage
3   low density lipoproteins transport cholesterol to artery
4  damage to the lining of an artery
5  atheroma builds up and breaks through the endothelium

   A    1 → 2 → 3 → 4 → 5
   B    2 → 3 → 5 → 1 → 4
   C    4 → 2 → 3 → 5 → 1
   D    5 → 1 → 4 → 2 → 3


7   Which of the following explains the increased risk of stroke, caused by smoking tobacco? 

A   CO increases the blood pressure and increases the chance of a blood vessel in the brain bursting.
B   Carcinogens increase the blood pressure and increase the chance of a blood vessel in the brain bursting.
C  Nicotine increases the chance of a blood clot blocking a blood vessel in the brain.
D  Tars increase the chance of a blood clot blocking a blood vessel in the brain.

8   Which observation is experimental evidence that smoking tobacco causes lung cancer? 

  A   Most people who develop cancer are smokers.
  B Death rates from lung cancer are highest in people who smoke more than 25 cigarettes per day.
  C Lung cancer was a rare disease until smoking became common in the 20th century.
  D When substances extracted from tar in cigarette smoke were painted onto the skin of mice, the mice developed tumours.

9 Which dietary factors increase the risk of coronary heart disease? 

  A   high intake of fruit and vegetables
  B  high intake of saturated fat and cholesterol
  C low intake of sodium chloride and alcohol
  D moderate intake of unsaturated fat

10 What would not form part of an effective screening programme for CHD?

 A  screening for high blood pressure
 B  screening for high cholesterol
 C monitoring heart rhythms
 D screening blood samples for bacterial infection a


Answers to Multiple choice test

1. A
2. A
3. C
4. C
5. A
6. C
7. C
8. D
9. B
10. D

2. End-of-chapter questions

1   Which  of the followingsubstances  in tobacco smokedamage the gas exchange system?
A  CO  and carcinogens
B   CO and nicotine
C   carcinogens  and tar
D  nicotine  and tar


2   What  are the symptoms  of lung cancer?
A   chestpain,  coughing  up blood,shortness  of breath
            B  difficulty breathing,  highblood pressure, smoker'scough
            C dizziness, high blood pressure, high sersting pulse rate
            D poor oxygenation of the blood, shortness of breath, smoker's cough


3 Which substance   in  tobacco   smoke   decreases   the  oxygen-carrying capacity   of haemoglobin? 
      A carbon dioxide
    Bcarbon monoxide

 4.  Which of the  following   is an  example   of an  epidemiological  investigation?

      A  carrying out  a clinical   trial  of a drug  for  heart   disease
  B   measuring  the  tar  content    of different   brands   of cigarettes
  Cresting substances    to  find  out  if they  are carcinogenic
  D  resting the  hypothesis    that  there  is a correlation    between   the  number    of people   who  smoke   and  the  number of cases oflung    disease

5. Cigarettesmoke  contains    tar,  nicotine    and  carbon   monoxide.

a  Describe the  effect  of tar  on  the  lining   of the  bronchi    in  the  lungs.
b    Describe the  effects  of nicotine and  carbon   monoxide    on  the  cardiovascular system.


6. The   figure shows  photomicrographs  of alveoli  from   

               1 a non-smoker     (x 200)         and                  2 a smoker   (x 50).



a Use the figure to describe how the lungs of smokers  differ from the lungs of non-smokers.  [4] 
b  Smokers with  lungs  similar   to  the  lungs  shown   in photomicrograph 2 have  poor  health. 
   i  Describe   the  symptoms    that  these  people   may  have.                                             [4] 
ii Explain  how  the  structure  of the  lungs  is responsible    for  this  poor  health.        [3] 

                                                                                                                               [Total:   11]
7   a   A person is diagnosed as having lungcancer. Describe how the lungcancer developed.[6] 
  
The figure shows  the  numbers    of deaths   from  lung  cancer   of men  and  women   aged  between   35  and  69 in the UK between    1950  and  2007.





b    i   Explain   the  advantage of calculating death rates as 'per 100000  of the  population'.[2] 
  ii   Use  the  information in  the  figure  to  compare   the  change   in  men's  death   rate  from  lung  cancer  between 1950 and  2007  with   that  in women.                                [4] 
  iii   Suggest   explanations   for  the  changes   in  death   rates  shown   in  the  figure.    [4] 
  [Total:   16]
  
8    Cardiovascular   diseases  such  as coronary   heart   disease  (CHD)    and  stroke  are major   causes  of illness  and  death throughout the  world.   People  diagnosed  with   these diseases  often  require   expensi   e treatments such  as surgery orlong-term drug treatment.
a    Explain   the  difference   between   CHD    and  stroke.                                                     [2]
b    Outline    how  coronary    by-pass  surgery   is used  in  the  treatment    of CHD.        [2]


The  treatment    of people  with   cardiovascular   diseases  costs  the  countries    of the  European    Union   (EU)  about  10%
of their   total  expenditure     on  health.
c     Describe   the  steps  that  health   authorities    and  governments   could  take  to prevent   people  requiring   this expensive   treatment.                                               [6]
d    Discuss   the  difficulties   in  reducing   the  number    of people  who  develop   cardiovascular   diseases.                                                                                                   [4]
  [Total:   14]

3. End-of-chapter answers

 1 C
 2 A
 3 B
 4 D

5  a  tar stimulates, goblet cells/mucous glands, to secrete more mucus; 
        paralyses/destroys, cilia;
        mucus not moved up the, bronchioles/bronchi, trachea/airways;
        mucus accumulates in the airways;
        bacteria multiply within the airways;
       (leads to) chronic bronchitis;
        tar contains, carcinogens/named carcinogen e.g. benzpyrene;
       (tar) settles on bronchial, epithelial cells/epithelium;
       mutation(s)/change to DNA;
      growth of tumour;
       bronchial carcinoma/lung cancer;

b   nicotine: increases heart rate;
    increases blood pressure;
    increases chance of blood clotting/promotes thrombosis;
    decreases fl ow of blood to, extremities/fi ngers/ toes;
    carbon monoxide: combines (irreversibly) with haemoglobin;
    forms carboxyhaemoglobin;
    reduces oxygen-carrying capacity of, haemoglobin/ blood;
   damages lining of arteries;
    promotes atherosclerosis;

Exam-style questions

6  a fewer alveoli;
       larger air spaces;
      fewer capillaries;
      scar tissue in bronchioles/bronchi;
      few/no cilia;
      few/no goblet cells;
      enlarged mucous glands;
      enlarged smooth muscle;
      may be pre-cancerous/cancerous cells;
      tumour/bronchial carcinoma; [max. 4]

b i difficulty breathing/breathlessness;
      wheezing;
      tiredness;
      not able to do (much) exercise; [max. 4]

 ii  small(er) surface area for gas exchange;
     less oxygen absorbed;
     poor oxygenation of the blood;
    bronchi/bronchioles/airways blocked by mucus;
    increased resistance to fl ow of air; [max. 3]
                                                        [Total: 11]

7 a (tar) settles on bronchial epithelial cells/epithelium;
      carcinogens/named carcinogen (in tar) e.g. benzpyrene;
      causes mutation(s)/change to DNA (in epithelial cells);
      in (proto onco)genes that control cell division/ mitosis;
     cancer cells do not respond to signals/growth factors/other cells;
     cancer cells divide uncontrollably;
     no programmed cell death/apoptosis;
    cells do not diff erentiate/become specialised;
    cells form tumour/bronchial carcinoma;
    tumour supplied with blood vessels/lymph vessels; [max. 6]

b i data are standardised;
     populations diff er from year to year;
     allows valid comparisons; [max. 2]

  ii death rate for men always higher than for women;
     use of the data to make a comparison between death rates for men and women;
     death rate for men rises to a maximum in 1966 and then decreases;
     death rate for women increases later than for men;
     death rate for women increases to a maximum in late 1980s/1990 and then decreases;
     decrease in death rate for women not as steep as for men;
     use of the data to show increase or decrease in death rate for men or women; [max. 4]

iii  men started smoking earlier than women;
     more men smoked than women;
     smoking became less popular among men from 1950s/1960s onwards;
     increase in number of women who smoked from the same time;
     link made between smoking and cancer;
    anti-smoking campaigns;
    lung cancer takes a long time to develop/be diagnosed;
    decrease in death rate did not happen until many years after decrease in popularity of smoking;                                                                                                                                                        [max. 4]
[Total: 16] 

 8  a  CHD: narrowing of coronary arteries that supply oxygenated blood to heart muscle; 
        stroke: interruption of blood supply to part of the brain as a result of blockage or bursting of an            artery (or arteries), leading to death of brain cells; [2] 

    b  vein taken from the chest, arm or leg;
        attached to coronary artery either side of blockage;
        may be one or more by-passes if there are several blockages in the coronary arteries; [max. 2]

    c   health promotion campaigns/publicity/leafl ets/ advertising;
        provide information about maintaining fitness/ healthy eating/stopping smoking/reducing                      alcohol intake;
        increase tax on tobacco/alcohol to reduce consumption;
       provide health warnings on foods that are high in saturated fat;
       print health warnings on tobacco products;
      ban smoking in public places;
      provide drugs for, hypertension/high blood cholesterol;
      provide screening for, risk factors/high blood pressure/high blood cholesterol;
      in people at greatest risk;
      provide, leisure facilities/fi tness centres; [max. 6]

d   many risk factors involved;
    some of which are genetic factors;
    factors that cannot be modifi ed (e.g. sex, age, genes);
     people are resistant to advice about changing lifestyle/diet;
    cardiovasular disease most common in lower income groups;
    who may not be able to aff ord to buy healthier food/use leisure facilities;
    people at most risk may not be screened for risk factors; [max. 4]
                                                                                            [Total: 14]



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#52 Cigarette smoking and health

AS , Gas exchange
#52 Cigarette smoking and health
Smoking  is one of the major avoidable  risk factors of chronic,  life-threatening diseases of the gas exchange and circulatory systems.











The smoke from cigarettes contains several substances that affect the gas exchange system and the cardiovascular system. These include:

• tar, a mixture of substances including various chemicals that act as carcinogens.
• nicotine, an addictive substance that affects the nervous system by binding to receptors on neurones (nerve cells) in the brain and other parts of the body. It increases the release of a neurotransmitter called dopamine in the brain, which gives feelings of pleasure. It increases the release of adrenaline into the blood, which in turn increases breathing rate and heart rate. There is also some evidence that nicotine increases the likelihood of blood clots forming.
• CO, which combines irreversibly with Hb, forming carboxyhaemoglobin. This reduces the amount of Hb available to combine with O2, and so reduces the amount of O2 that is transported to body tissues.

Effects of smoking on the gas exchange system

Chronic obstructive pulmonary disease (COPD)

This is a condition in which a person has chronic bronchitis and emphysema. It can be extremely disabling.


Chronic bronchitis

Various components of cigarette smoke, including tar, cause goblet cells to increase mucus production and cilia to beat less strongly. This causes mucus to build up, which may partially block alveoli. This makes gas exchange more difficult, as the diffusion distance between the air in the alveoli and the blood in the capillaries is greater. The mucus may become infected with bacteria, causing bronchitis. Smokers often have chronic (long-lasting) bronchitis.

The mucus stimulates persistent coughing, which can damage the tissues in the walls of the airways, making them stiffer and the airways narrower.


Emphysema

Smoking causes inflammation in the lungs. This involves the presence of increased numbers of white blood cells, some of which secrete chemicals that damage elastic fibres. This makes the alveoli less elastic. They may burst, resulting in larger air spaces. This reduces the surface area available for gas exchange. This is called emphysema. A person with emphysema has shortness of breath, meaning they struggle to breathe as deeply as they need to, especially when exercising.



Lung cancer

Various components of tar can cause changes in the DNA in body cells, including the genes that control cell division, which can cause cancer. These substances are therefore carcinogens. Cancers caused by cigarette smoke are most likely to form in the lungs but may form anywhere in the gas exchange system, and also in other parts of the body. Smoking increases the risk of developing all types of cancer. Symptoms of lung cancer include shortness of breath, a chronic cough - which may
bring up blood - chest pain, fatigue and weight loss.



Effects of smoking on the cardiovascular system

The nicotine and CO in tobacco smoke increase the risk of developing atherosclerosis. Atherosclerosis is a thickening and loss of elasticity in the walls of arteries. It is caused by build-up of plaques in the blood vessel wall. The plaques contain cholesterol and fibres. They produce a rough surface lining the artery, which stimulates the formation of blood clots.



A blood clot may break away from the artery wall and get stuck in a narrow vessel elsewhere in the blood system, for example in the lungs or in the brain. This prevents blood passing through so cells are not supplied with O2 and die. If this happens in the brain it is called a stroke.

The loss of elasticity In an artery or arteriole also makes it more likely that the vessel will burst when high-pressure blood pulses through. This is another cause of stroke.

If atherosclerosis happens in the coronary arteries that supply the heart muscle with oxygenated blood, the person has coronary heart disease (CHD). Parts of the muscle may be unable to function properly as they do not have enough O2 for aerobic respiration. The muscle may die. Eventually, this part of the heart may stop beating, causing a heart attack.



Evidence for effects of smoking on health

There are two ways in which the effects of smoking on health can be investigated.

Epidemiological evidence

This consists of data collected about people's smoking habits and their health. Large numbers of people should be involved in the study. The researchers then look for correlations between smoking and particular diseases. Although this approach does not provide any definite evidence about a causal link between smoking and the disease, it can at least show whether there could be a causal relationship. If we then have physiological evidence to show how smoking might cause the disease, then this adds up to strong evidence that smoking does indeed cause the disease.

Experimental evidence

This consists of carrying out controlled experiments. For example, the independent variable could be whether or not a subject smokes (or how much they smoke) and the dependent variable could be some aspect of physiology. All other variables should be kept constant. This is not possible with humans, as it would be unethical to make people smoke. In the 1960s, dogs and other animals were used in such experiments. The results showed conclusively that smoking tobacco greatly increases the risk of developing lung cancer. Experiments can also be carried out using cells grown in
tissue culture. Exposure of these cells to chemicals found in tar shows that these chemicals can damage DNA.

Preventing and treating CHD

The risk of developing CHD is increased by:

• inheriting particular alleles of genes
• eating a diet rich in saturated fats and cholesterol
• not taking sufficient exercise
• being obese
• smoking

Severe CHD can be treated with a coronary bypass, in which a piece of blood vessel is taken from another part of the body and sewn into place to provide an alternative route for oxygenated blood to flow from the aorta to the heart muscle.

If the heart is damaged beyond repair, either by CHD or other conditions, then the only long-term option may be a heart transplant. The heart must come from a person who has just died (often in an accident) and has a tissue type that is similar to the recipient. Even so, the recipient will still have to take immunosuppressant drugs for the rest of their life, to prevent their immune system from attacking the donor tissues and rejecting the transplant.



Prevention of CHD and other forms of heart disease is clearly much better than having to carry out complex surgery. Lifestyle choices can be made that reduce the risks listed above (apart, of course, from the genes a person has). However, research shows that slightly obese people are more likely to recover well after heart surgery than thinner people.


 

Syllabus 2015

(e) describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system;

(f) describe the signs and symptoms that enable diagnosis of lung cancer and chronic obstructive pulmonary disease (COPD) (emphysema and chronic bronchitis);

(g) describe the effects of nicotine and carbon monoxide on the cardiovascular system;

(h) explain how tobacco smoking contributes to atherosclerosis and coronary heart disease (CHD);

(i) evaluate the epidemiological and experimental evidence linking cigarette smoking to disease and early death;

(j) discuss the difficulties in achieving a balance between preventions and cure with reference to coronary heart disease, coronary by-pass surgery and heart transplant surgery;


Syllabus 2016-2018

9.2    Smoking

Smoking  is one of the major avoidable  risk factors of chronic,  life-threatening diseases of the gas exchange and circulatory systems.

 a)   describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system with reference to lung cancer and chronic obstructive pulmonary disease (COPD)


b)   describe the short-term effects of nicotine  and carbon monoxide on the cardiovascular system

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#51 Summary of Gas exchange

AS , Gas exchange
#51 Summary of Gas exchange
1 Multicellular organisms often have surfaces that are specialised to allow exchange of gases to take place between their bodies and the environment. Alveoli in the lungs form the gas exchange surface in mammals.








 2 In the human lungs, air passes down the trachea and through a branching system of airways to reach the alveoli. The airways are lined by a ciliated epithelium with mucus-secreting goblet cells. The epithelium protects the alveoli by moving a carpet of mucus
towards the throat, where it can be swallowed.

 3 There are C-shaped rings of cartilage in the trachea and irregularly shaped blocks of cartilage in the bronchus to keep the large airways open and so reduce resistance to the fl ow of air. Smooth muscle in the airways contracts and relaxes to adjust the diameter of the airway.

4 The alveoli are lined by a squamous epithelium that gives a short diff usion distance for the exchange of oxygen and carbon dioxide. The alveoli are well supplied with blood by the many capillaries surrounding the gas exchange surface.

 5 The constant flow of blood and the continuous ventilation of the lungs maintain concentration gradients between blood and air for oxygen and carbon dioxide.

 6 Recoil of the elastic fi bres surrounding the alveoli helps to move air out during expiration.


1. Multiple-choice test

1  A large, thick-walled blood vessel lies alongside a bronchus. 

Which row names the vessel and describes its contents?









2 The diagram shows part of the wall of a bronchus in cross-section.

























3 The table shows the presence or absence of ciliated epithelium and goblet cells in airways. 

Which row describes a bronchiole?












4 Two airways each have smooth muscle in their walls, but only one has cartilage.

What are the airways?

A  alveolus and bronchus
B  alveolus and trachea
C  bronchiole and bronchus
D  bronchus and trachea

5 The mucus secreted into the airways is a solution of the glycoprotein mucin.

Which statement about mucin contains a mistake?

A  Carbohydrate chains make mucus sticky enough to trap dust particles.
B  Mucus is secreted by goblet cells by the process of endocytosis.
C  Carbohydrate chains are added to protein in the Golgi apparatus of goblet cells.
D  Mucus is moved over the surface of the airways by the action of ciliated cells.

6 A carbon dioxide molecule dissociates from haemoglobin and diffuses along the shortest path into an alveolus.

Assuming that the molecule diffuses through a gap in a capillary wall, how many phospholipid bilayers did the molecule pass through?

A  2
B  3
C  4
D  5

7 What maintains the diffusion gradient for the diffusion of oxygen out of an alveolus?

1  binding of oxygen with haemoglobin to form oxyhaemoglobin
2  blood flow bringing a new supply of red blood cells
3  increased surface area of red blood cells as they are forced through narrow capillaries
4  complete replacement of the air in the alveolus with each breath

A  1, 2 and 3 only
B  1, 2 and 4 only
C  2 and 3 only
D  3 and 4 only

8 What are the adaptations of an alveolus for its role in gas exchange?

1  very thin epithelial walls
2  close contact of walls and capillaries
3  walls with elastic fibres which recoil after stretching, to help force air out
4  stiff walls to prevent collapse of the alveolus when breathing out

A  1, 2 and 3 only
B  1, 2 and 4 only
C  1 and 2 only
D  3 and 4 only

9 Which event occurring at an alveolus does not require a red blood cell? 

A  carbon dioxide dissociates from carbaminohaemoglobin
B  carbon dioxide is formed from hydrogencarbonate ions
C  carbon dioxide diffuses from the blood into an air space
D  oxygen binds with haemoglobin to form oxyhaemoglobin

10 Measurements of an adult’s breathing show that at rest:

  • the volume of air in a single breath is 500cm3
  • 350 cm3  of each breath reaches the alveoli
  • 2500 cm3 of air remain in the lungs after breathing out.

Which is not a correct conclusion from these measurements?

A  About one sixth of the air in the lungs is replaced by breathing out and then in.
B  Almost one third of each breath does not reach a gas exchange surface.
C Large changes in the composition of the air in the alveoli do not occur.

D The volume of air in the alveoli after breathing in is 3.0dm3

Answers to Multiple choice test

1. A
2. B
3. C
4. C
5. B
6. B
7. A
8. A
9. C
10. D

2. End-of-chapter questions

1   The following structures  are found  in the walls of the gas exchange system.
1   capillaries
2  cilia
3  elastic fibres
4   goblet cells
5  smooth  muscle cells

Which  would  be found  in the lining of an alveolus?

A   1 and 3
B   1,2  and 3
C  2 and 5
D 4 and 5

2  Cartilage is found   in which   structure?

A  alveolus
B  bronchiole
C  capillary
D  trachea

3  Which of the  following   is not  a role  of elastic  fibres  in  the  gas exchange   system?

A   contract   to  decrease   the  volume   of the  alveoli  during   expiration
B   recoil  to force  air out  of the  alveoli  during   expiration
C  stretch  to accommodate     more  air in  the  alveoli  during   deep  breathing
Dstretch  to increase   the  surface   area  of the  alveoli  for  gas exchange

4  Which  of the  following   best  describes   the  process   of gas exchange   in  the  lungs?

    A   Air moves  in  and  out  of the  alveoli  during   breathing.
    B   CO2  diffuses  from  deoxygenated  blood in  capillaries   into  the  alveolar  air.
    C   O2   and  CO2   diffuse  down   their  concentrations gradients between blood and alveolar  air.
    D  O2  diffuses  from  alveolar   air into  deoxygenated  blood.

5    The  figure  shows  an alveolus.

a   Name:


i  cells A, B and  C                                                                                                         [3]
ii  the  fluid  at  D.                                                                                                         [1]

b  Calculate   the  actual  distance   indicated  by X- Y. Show  your  working.          [2]


c   Explain   how  alveoli  are adapted   for  the  exchange   of gases.                        [4]
                                                                                                                                    Total  [10]

6    The  figure  shows  two  cells from  the  lining   of the  trachea.



a    Name:
i  cells  P and  R                                                                                                                      [2]
ii  structures  S, T, U  and  W                                                                                                [4]
b    Explain:
i  why  cell  P contains  many   of the  structures  labelled  T                                          [2]
ii  the  role  of structure U  in cell  R.                                                                                   [2]
c    Calculate  the  actual   length   of cell  P.  Show  your  working.                                      [2]
d    Describe   the  roles  of cell P and  cell R in  the  gas exchange  system.                       [4]
                                                                                                                                          [Total:   16]
7    a    Copy   and  complete   the  table  to  compare   the  trachea   with  a respiratory  bronchiole.   Use  a tick  (v)   to indicate   that  the  structure    is present   and  a cross  (x)  to  indicate   that  it is not.

[5]
     b    Describe   how  the  alveoli  are protected    against   infection.                                                   [5] 
                                                                                                                                                             [Total:   10]

8  The composition  of alveolar   air  remains   fairly  constant    even  though   gases  are exchanged   with   the  blood   in  the capillaries  that  surround    the  alveoli.

a   Describe   the  process   of gas exchange   between   alveolar  air and  blood.                          [4]
b   Explain  why  the  composition     of alveolar   air remains   fairly  constant.                              [3]
c   Suggest  3 ways  in which  the  gas exchange system responds  to the demands of exercise. [3]
                                                                                                                                                                [Total:   10]

3. End-of-chapter answers

 1 A
 2 D
 3 A
 4 C


5 a   i A squamous epithelial cell;
          B red blood cell;
          C endothelial cell; [3]
 
      ii) D plasma;             [1]

  b distance of scale bar is 15mm 15mm = 10μm X–Y distance measured on page is 47mm 47 ÷ 15 ×      10 = 31μm                     [2]

  c  (very) large number forming a large surface area;
       squamous epithelial cells are very thin to give short diff usion distance;
       surrounded by capillaries so well supplied with blood;
       capillaries are very close so short diff usion distance; 
      well ventilated so air constantly refreshed;
      maintains concentration gradients for oxygen and carbon dioxide; [max. 4]
                                                                                                             [Total: 10]

6 a i   P ciliated epithelial cell;
         R goblet cell; [2]
      ii S cilium/cilia;
        T mitochondrion;
        U Golgi apparatus;
       W nucleolus; [4]

 b i  T/mitochondria provide energy/ATP;
         for movement of cilia; [2]

   ii  U/Golgi apparatus packages proteins into vesicles;
       for secretion; [2]

c   length of cell P on page is 80mm 80 ÷ 750 × 0.107mm or 107μm [2]

d  cell P: cilia beat/move back and forth;
              move mucus;
              upwards/towards throat;

     cell R: secretes mucus;
                mucus traps dust/bacteria/viruses/pollen;
                prevents entry to alveoli/gas exchange surface; [max. 4]
                                                                                         [Total: 16]


b   mucus secreted; 
     by mucous glands (in the trachea)/goblet cells (in trachea and bronchi);
     bacteria/viruses/pathogens, stick to mucus;
     cilia move mucus, upwards/towards throat;
     mucus and pathogens swallowed;
     destroyed by acid in stomach;
     macrophages/phagocytes, in the alveoli;
    engulf and digest any pathogens;                                              [max. 5]
                                                                                                      [Total: 10]

8  a  oxygen diff uses down its concentration gradient;
        from alveolar air into red blood cell; 
        carbon dioxide diff uses down its concentration gradient;
       from red blood cells/plasma to alveolar air;
       across epithelial cells of alveolus and endothelium of capillary; [max. 4] 

   b  breathing/ventilation;
      introduces fresh air/atmospheric air;
      removes stale air/air rich in carbon dioxide;                                       [3]

   c  increase in:
       • depth of breathing;
       • rate of breathing;
       • expansion of alveoli to give a larger surface area;
      • diameter of airways;                                                                     [max. 3]
                                                                                                        [Total: 10]




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