form 3 national book chapters 6-7

7/28/2019 Form 3 National Book Chapters 6-7

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6.0 BREATHING AND GAS EXCHANGE

Contents

6.1 The respiratory system

6.2 Gaseous exchange

6.3 Breathing mechanism

6.4 Common respiratory diseases

Learning outcomes

Students should be able to:

(a) Identify on diagrams and name the nostrils, pharynx, larynx, trachea, bronchi, bronchioles, alveoli and associated

capillaries:

(b) State the functions of the structures listed above in (a).

(c) Describe the role of hairs, cilia and mucus.

(d) Describe the sequence of events occurring during inspiration and expiration.

(e) Demonstrate an experiment to show a working model of chest and lungs.(f) State the differences in the percentages of the gases in inhaled air exhaled air.

(g) Investigate an experiment to compare carbon dioxide content between inspired and expired air.

(h) State the causes and health effects of common respiratory diseases.

6.1 The respiratory system

Lungs are the respiratory structures found in many terrestrial animals. Although lungs serve the same basic purpose as

other respiratory systems, they are structurally and functionally different.

Human bodies contain two lungs, both located in the chest cavity, one on each side of the body. They are surroundedby a ribcage and are situated above a large muscle, the diaphragm. Throughout the human lung are numerous tiny

grape-shaped sacs called alveoli, which give the lung its spongy texture. Alveoli provide a large surface area over which

gases can diffuse and are connected to a series of passages through which air passes during breathing.

Fig. 6.1 The respiratory system


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Breathing

Air moves into and out of the lungs via the process ofbreathing. The chest cavity expands as the diaphragm contracts

(moves downward), air is drawn in, orinhaled, into the lungs. When the diaphragm relaxes, the chest cavity decreases

in volume, causing air to be exhaled, or released from the body.

During the process of breathing, air moves through the structures of the respiratory system in the following order:

A. Nasal cavities

Air passes through two nostrils into the nasal cavities. The nasal cavities are guarded by hairs. Their inner surface is

lined with mucus-secreting cells, ciliated cells, blood capillaries and olfactory cells

Hairs filter the dust and germs in the inhaled air. The mucus traps dust and germs and moistens the inhaled air. The beating cilia move the trapped dust and germs to the back of the mouth where they are swallowed. The blood capillaries warm the inhaled air. The olfactory cells give the smell sensation of the inhaled air.

B. Pharynx

At the back of the mouth is the pharynx where the respiratory tract and the alimentary canal cross each other. It allows

for separation of food and air.

C. Larynx

The larynx is a box made of cartilage at the top of the trachea. It contains vocal cords which vibrate to produce sounds.

D. Trachea and bronchiTrachea

Trachea passes into the thoracic cavity where it divides into two tubes called bronchi. Each bronchus enters a lung.

Bronchi

1. Inside the lung the bronchus divides repeatedly into many tiny tubes celled bronchioles. Each bronchiole endsin tiny bags called air sacs.

2. Each air sac has many cup-shaped alveoli.Special structures of trachea and bronchi

Their walls are supported by C-shaped rings of cartilage, which prevents them from collapsing duringinspiration and swallowing.

Their inner lining is made up of smooth muscle, lined with ciliated epithelium, which possesses goblet cells.Goblet cells produce mucus that traps dust and germs. The cilia beat to move the mucus upwards to the

pharynx where it is swallowed or coughed out.


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(a) (b)

Fig. 6.2 (a) Transverse section of trachea seen with light microscope (b) diagram showing section of trachea

(a) (b)

Fig. 6.3 (a) Section of trachea showing cilia covered with pollen grains and dust breathed in (b) diagram

showing cilia and goblet cells

6.2 Gaseous exchange

The sites of gaseous exchange in mammals are the alveoli, minute air-sacs some 100-300 m in diameter and situated

in the lungs. The lungs are paired organs found in the thorax.

Alveoli

The two lungs of man are made of 700 million alveoli which provide very large surface area (80-90 m2) for gas

exchange to occur. The alveoli with the following features form an ideal respiratory surface.

How the structure of the alveoli is related to its function

The 300 million alveoli in each lung of a human have a total surface area of around 70m 2. Their structure is shown

below. Each alveolus is lined mostly with squamous epithelial cells only 0.1-0.5m thick. Each alveolus has a diameter

of between 100 m and 300 m. Around each alveolus is a network of pulmonary capillaries, so narrow (7 -10 m) that

red blood cells are flattened against the thin capillary walls in order to squeeze through. These capillaries have walls

comprising only a single layer of endothelial cells.

1. the red blood cells are slowed as they pass through the pulmonary capillaries, allowing more time for diffusion2. the distance between alveolar air and red blood cells is reduced as the red blood cells are flattened against the

capillary walls

3. the walls of both alveoli and the capillaries are very thin and therefore the distance over which diffusion takesplace is very short

4. each alveolus is 0.1 to 0.2 mm in diameter - This small size maximizes surface area and allows for fasterexchange of gases.

5. A film of lipoprotein covers the alveoli. This lowers surface tension and prevents the alveoli from collapsing.


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6. the alveoli and blood capillaries have a very large total surface area of 70 m 2. This is about half the area of atennis court.

7. breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates bloodaround the alveoli. Together, these ensure that the steep concentration gradient of the gases to be exchanged

is maintained

Fig. 6.4 Structure of alveoli

Lungs

The lungs are spongy in nature and red in colour. They are present in pair and enclosed inside the thoracic basket.

Thoracic basket. (rib cage)

Lungs are protected by the thoracic basket which consists of sternum, ribs and vertebrae.

Pleural membranes, pleural cavity and pleural fluid

1. The outside surface of the lungs is covered with the inner pleural membrane. The inside surface of the thoracicwall is covered with the outer pleural membrane.

2. Between these membranes is the air-tight pleural cavity. If the pleura is punctured, air leaks in. The lungcollapse due to its own elasticity.

3. The pleural cavity is filled with pleural fluid which is secretd by the pleural membranes. The pleural fluidlubricates the pleurae to reduce friction between them during breathing movement.

Gas exchange in the alveoli

1. The pulmonary artery drains deoxygenated blood to the lungs. The deoxygenated blood has lower oxygenconcentration than that in the alveoli. Therefore oxygen diffuses from the alveolus through the alveolar wall and

the capillary wall into blood plasma.

2. Oxygen enters red blood cell by diffusion and forms oxy-haemoglobin. This is the form in which oxygen istransported in the blood.

Oxygen + haemoglobin oxyhaemoglobin


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Fig. 6.6 Diagram showing inspiration

Fig. 6.7 Diagram showing expiration

Model of lung

Fig. 6.8 Diagram showing lung model

Working of the lung model

Inspiration

When the rubber sheet (diaphragm) is pulled, the volume inside the bell jar (thoracic cavity) increases that will reduce

the pressure there. When the pressure inside the bell jar is lower than the atmospheric pressure, air rushes into the


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balloon (lungs) through the glass tube (trachea) and the side tubes (bronchi) to balance the pressure. The balloons are

inflated.

Expiration

When the rubber sheet is pushed back to the original position, the volume inside the bell jar decreases that will increase

the pressure there. The increased pressure allows the inflated balloons to return to its original shape under its elasticity.

Thus air inside the balloons is forced out though the Y-tube.

Comparison of the composition of inhaled and exhaled air

The table below shows the composition of inhaled and exhaled air

Composition of gases/ %

Inhaled air Exhaled air

Nitrogen

Oxygen

Carbon dioxide

Water vapour

Temperature

79.01

20.96

0.03

Variable

Variable

79.5

16.4

4.1

Fully saturated

Same as body

Reasons for the differences in gas composition between inhaled and exhaled air

After gaseous exchange has taken place in the lungs, the composition of gases in the exhaled air changes.

1. There is less oxygen because some of it diffuses from the alveoli into the deoxygenated blood.2. There is more carbon dioxide because those produced by cellular respiration diffuses from deoxygenated blood

into the alveoli.

3. There is no change in the nitrogen concentration because it is neither used nor produced by body tissues.4. There is more water vapour because the inhaled air is moistened by the mucus secreted by the nasal cavities,

trachea and the moist alveolar air.

5. The temperature is higher because the inhaled air is warmed by the heat released from the blood capillariesunderlying the nasal cavities and covering the alveoli.


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Experiment to compare carbon dioxide content of inhaled and exhaled air

In this experiment, a volunteer breathes in through one tube containing a CO2-detecting liquid, and out through another

tube containing the same CO2-detecting liquid.

Materials

2 boiling tubes delivery tubes to fit the apparatus below 50 cm3 of lime water or bicarbonate indicator

Fig. 6.9 Apparatus used to compare amount of carbon dioxide in inhaled and exhaled air.

Procedure

1. Check that the apparatus is assembled correctly.2. Add same volume of lime water or bicarbonate indicator to both boiling tubes, and insert the tip each long

delivery tube at about the same level in the liquid.3. Securely insert the bungs in the both tubes.4. Breathe in very gently.5. Without removing your mouth from the apparatus, breathe out gently.6. Continue to breathe in and out without removing the tube from the mouth. This should ensure that the same

amount of air passes through both tubes.

Results

The hydrogen bicarbonate indicator remains orange (limewater clear) in tubeY while the bicarbonate indicator in tube X

turns yellow (limewater cloudy/milky).

Interpretation

The carbon dioxide concentration in inhaled air is less thus it could not change the colour of the indicator while in tube X

exhaled contains a higher percentage of carbon dioxide which cause the colour change in the indicator.

Conclusion

Exhaled air contains more carbon dioxide then inhaled air.


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6.4 Common respiratory diseases

Since the respiratory system is in direct contact with air, it is prone to be infected with bacteria and viruses and affected

by pollutants in air. Some of the most common respiratory disease are: common cold, bronchitis, emphysema, lung

cancer, asthma, pneumonia and tuberculosis. Every year thousands of people die due to several respiratory

diseases, the most common being emphysema and tuberculosis.

Common cold

This is caused by viruses which infect the upper respiratory tract. Symptoms include: influenza, runny nose and

headache.

Bronchitis

Bronchitis is characterized by redness and swelling of the lining of the air passages, and the destruction of cilia. As a

result, dust and harmful chemicals or disease causing organisms (pathogens) are able to move past the bronchi and

invade the alveoli. The air passages then become irritated and clogged with mucus and dust, resulting in infections in

the lungs. Patients suffering from bronchitis have a lot of phlegm and are always coughing.

Asthma

The irritants that are found in air e.g. pollen, dust , ash from cigarette smoke, chill air etc. may cause allergic reactions in

the respiratory tract. A sensitive respiratory tract suddenly constrict. An sudden asthma attack may lead to suffocation

and death.

Emphysema

As a result of pathogens and dust invading the alveoli, numerous alveolar sacs may be destroyed while others becomeless elastic. This inhibits gaseous exchange and many patients with emphysema have difficulty breathing. Any slight

physical exertion will result in shortness of breath. A wheezing sound occurs during breathing and the chest becomes

barrel shaped. Some patients become dependent on respirators to help them breathe.

Lung cancer

Lung cancer occurs when the lung tissue cells start to divide without any control to form a mass of undifferentiated cells

known as a tumour. Tobacco smoke is the leading cause of death due to cancer. One compound called benzopyrene

found in tar in cigarette smoke, is a powerful carcinogen (cancer causing compound). Symptoms include: weight loss,coughing up blood and extreme chest pain leading to death.

Pneumonia

Pneumonia is an infection of the lungs that is caused by bacteria, viruses, fungi, or parasites. It is characterized

primarily by inflammation of the alveoli in the lungs or by alveoli that are filled with fluid. At times in very serious

condition, pneumonia can make a person very sick or even cause death. Although the disease can occur in young and

healthy people, it is most dangerous for older adults, babies, and people with other diseases such as AIDS.

Tuberculosis

Tuberculosis (TB) is an infectious disease that is caused by a bacterium called Mycobacterium tuberculosis. TB

primarily affects the lungs, but it can also affect organs in the central nervous system and circulatory system among

others. Talking, laughing, spitting and coughing cause spread of TB. Symptoms include coughing blood, chest pain,


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shortness of breath, fever, sweating and weight loss.

Causes of respiratory diseases

Although there is broad range of respiratory diseases, their causes, which are also large in number, have similarities.

Among the most common causes are accidents, inhalation of toxic materials and harmful lifestyle habits like incessant

smoking. Smoking is the leading cause of respiratory disease such as bronchitis, emphysema and lung cancer.

Tobacco smoke contains three toxic components among others: nicotine, carbon monoxide and tar. Genetic factors,

infections as well as anything else that are known to affect the development of the lungs are also believed to indirectly

or directly cause the symptoms of respiratory disorders.

Smoking. Smoke from cigarettes, cigars, and pipes is the number one cause of

lung disease. Don't start smoking, or quit if you already smoke. If you live or

work with a smoker, avoid secondhand smoke. Ask smokers to smoke outdoors.

Secondhand smoke is especially bad for babies and young children.

Air pollution. Recent studies suggest that some air pollutants like car exhaust may

contribute to asthma, COPD, lung cancer, and other lung diseases.

Some diseases that affect the lungs, like the flu, are caused by germs (bacteria,

viruses, and fungi).

Chapter summary

The organs and structures involved in gaseous exchange in humans are the pair oflungs and the airpassages that lead to them.

Breathing through nose is advantageous because:o Harmful chemicals and substances can be detectedo The air is warmed and moistenedo Dust particles and germs are trapped in the nasal hairs and mucus produced by goblet cells.

Air passes through the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and eventually to thealveoli.

The trachea is supported by a ring of cartilage. Nasal hairs, cilia and mucus help to trap bacteria and dust particles in inspired air. Breathing consists ofinspiration and expiration. During inspiration, the diaphragm and external intercostal muscles contract and enlarge the thoracic cavity. During expiration, the diaphragm and internal intercostal muscles contract. Gas exchange occurs between the capillary network surrounding the alveoli and the air in the alveolar cavity. Common respiratory disease include common cold, bronchitis, emphysema, lung cancer, asthma,

pneumonia and tuberculosis.

The leading causes of respiratory disease are : a persons genetic background, lifestyle and exposure toenvironmental factors.

Concept map

Air


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End of chapter Questions

Multiple choice question 1 Which air sample has just been breathed out?

nostril

nasal cavity

pharynx

trachea

bronchus

bronchioles

lungs

alveoli

Breathing

expiration

inspiration

Gas exchange


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Air

sample

Percentage

of oxygen

Percentage

of carbon

dioxide

Percentage

humidity

A

B

C

D

21

16

4

20

0.04

4.04

0.40

4.00

20

100

80

60

2 The diagram shows someone blowing up a balloon.

What percentage of the gas in the balloon is carbon

dioxide?

A 0.04 % B 0.4 %

C 4.0 % D 40 %

3 The diagram shows the breathing system and a

section of an alveolus surrounded by a capillary.

Which label shows a cell?

4 What are the effects of smoking on the gas exchange

system?

Mucus in the

airways

Chance of lung

infection

A

B

C

D

Decreased

Decreased

Increased

Increased

Decreased

Increased

Decreased

Increased

5 Which route is taken by air passing into the lungs of a

human?

Aalveolus trachea bronchus

Bbronchus trachea alveolus

Ctrachea alveolus bronchus

Dtrachea bronchus alveolus

6 The diagram shows some cells from the lining of the

trachea (windpipe) in the respiratory tract.

What is the function of the structures labelled X?

A absorbing oxygen

B killing micro-organisms

C moving mucusD trapping bacteria

7 The table shows the composition of inspired and

expired air.

Inspired air% Expired air %

Oxygen

Carbon dioxide

Nitrogen and inert

gases

20

0.04

79.96

16

X

Y

What are the likely percentages at X and Y?

X Y

A

B

0.04

4

83.96

80


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C

D

20

83.96

64

0.04

8 What happens to the diaphragm when breathing in?

Muscle action Shape becomes

A

B

C

D

Contraction

Relaxation

Contraction

relaxation

Domed

Domed

Flattened

Flattened

9 When breathing out, which changes occur in the

volume of the thorax, the rib cage and the diaphragm?

Volume of

thorax

Rib cage diaphragm

A

B

C

D

Decreases

Decreases

Increases

Increases

Lowered

Raised

Lowered

Raised

Rises

Pulled down

Rises

Pulled down

10 The diagram shows part of the human gas exchange

system.

What are W, X, Y and Z?

bronchus bronchiole larynx trachea

A

B

C

W

X

Y

X

Z

W

Z

Y

X

Y

W

Z

D Z Y W X

Structured questions

Question 1

Fig. 1.1 shows an alveolus in which gaseous exchange

takes place.

Fig. 1.1

(a) (i) Define the term diffusion.

.........................................................................................

.........................................................................................

.........................................................................................

(ii) State what causes oxygen to diffuse into the blood

from the alveoli.

.........................................................................................

.........................................................................................

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Question 2

(a) The air which is inhaled is different from that which

is exhaled. Complete the following sentences about

these differences.

(i) Inhaled air has more than

exhaled air.

(ii) Exhaled air has more ..and

than inhaled air.

(iii) Inhaled air usually has a ..


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temperature than exhaled air.

(b) One of the gases present in inhaled and exhaled air

is carbon dioxide.

Describe how you could test exhaled air for carbon

dioxide and describe the result if carbon dioxide ispresent.

test

..

result

(c) Gases enter and leave the blood by diffusion. Define

diffusion.

.........................................................................................

.........................................................................................

.........................................................................................

Question 3

The apparatus below can be used as a model to

demonstrate the functioning of the diaphragm.

(a) Name the structures found in the human thorax that

are represented by the following parts of the model.

A......................................................................................

B......................................................................................

C......................................................................................

(b) Explain the effect of pulling down the rubber sheet.

.........................................................................................

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(c) Other structures, not shown in the model, are also

involved in ventilation. Explain how they help in thisprocess.

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(d) Explain how a short period of exercise can affect

breathing rate.

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Question 4


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Adam used the apparatus below to compare the

concentration of carbon dioxide in inhaled and exhaled

air. He breathed in and out through the apparatus

several times for 2 minutes.

(a) Through which tube would the inhaled air pass?

Give a reason for your answer.

.........................................................................................

.........................................................................................

.........................................................................................

.........................................................................................

.........................................................................................

.........................................................................................

(b) (i) Suggest a suitable indicator that could be used to

compare the carbon dioxide content of the inhaled and

exhaled gases.

.........................................................................................

(ii) Describe the changes you would expect in eachflask during the two minute period.

.........................................................................................

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(c) (i) Explain why the air exhaled from the lungs differs

in composition from inhaled air.

.........................................................................................

.........................................................................................

.........................................................................................

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.........................................................................................

.........................................................................................

(ii) Other than changes in percentage composition, give

two ways that exhaled air differs from inhaled air.

1.......................................................................................

.........................................................................................

.........................................................................................

2.......................................................................................

.........................................................................................

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(d) Describe the mechanism of inspiration.

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(e) State two conditions affecting the human breathing

system that are caused by smoking cigarettes.

1.......................................................................................

2.......................................................................................


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Question 5

The diagram below shows the human lungs and related

structures.

(a) Name the parts labelled X andY.

X......................................................................................

Y......................................................................................

(b) The table below shows the concentration of oxygen

and of carbon dioxide in blood entering and leaving the

lungs.

GasConcentration of the gas in cm3

per 100 cm3 of blood

Blood entering

lungs

Blood leaving

lungs

Oxygen 10.6 19.0

Carbon

dioxide

58.0 50.0

(i) How many cm3 of oxygen per 100 cm3 of blood arecollected in the lungs?

.........................................................................................

(ii) Name the cells in blood that collect oxygen in the

lungs.

.........................................................................................

(iii) Name the blood vessel that takes blood to the lungs

from the heart.

.........................................................................................

(c) Describe and explain how a carbon dioxide

molecule passes from the blood into the lungs and how

it is then breathed out.

.........................................................................................

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Question 6

The diagram shows part of the human respiratory

system.

(ii) Name parts A, B, C and D.

A.

B.


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C.

D.

The diagram shows some cells from the respiratory

system.

Healthy cells

Cells from a smoker

(iii) Name the type of cells shown and describe their

function.

.........................................................................................

.........................................................................................

.........................................................................................

(iv) Describe one difference between the healthy cells

and those of the smoker.

.........................................................................................

.........................................................................................

.........................................................................................

(v) Name a disease caused by smoking.

.........................................................................................

(b) (i) Complete the diagram of expiration by drawing in

the diaphragm and complete boxes X and Y to describe

the changes

(ii) What effect do the changes which occur during

expiration have on the volume and pressure in the

lungs?

.........................................................................................

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Question 77 (a) (i) Define the term organ.

.........................................................................................

.........................................................................................

(ii) Name two organs found in the respiratory tract.

1.......................................................................................

2.......................................................................................

(b) Fig. 7.1 shows some cells lining parts of the

respiratory tract.

Fig. 7.1

(ii) Name two parts of the of the respiratory tract where


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this tissue is present.

1.......................................................................................

2.......................................................................................

(iii) Suggest the function of this tissue.

.........................................................................................

.........................................................................................

.........................................................................................

(iv) Which respiratory disease develops when this

tissue is destroyed?

.........................................................................................

(v) Name one cause of this disease.

.........................................................................................

Question 8

Smoking cigarettes has many harmful effects on the

body.

(a) Give two diseases of the lungs caused by smoking

cigarettes.

1.......................................................................................

2.......................................................................................

(b) Explain why some countries have banned smoking

in public places.

.........................................................................................

.........................................................................................

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Question 9

Gaseous exchange takes place while air flows in and

out of the lungs.

(a) State three ways in which inspired air is different

from expired air.

1.......................................................................................

.........................................................................................

2.......................................................................................

.........................................................................................

3.......................................................................................

.........................................................................................

Question 10(a) Explain how the following are involved in the

process of breathing.

(i) the diaphragm

.........................................................................................

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.........................................................................................(ii) intercostal muscles

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7.0 RESPIRATION

Contents

7.1 The need for energy

7.2 Aerobic respiration

7.3 Anaerobic respiration

Learning outcomes

Students should be able to:

(a) State the need for energy in humans.

(b) Define respiration.

(c) Define aerobic respiration.

(d) State the equation (in word) for aerobic respiration.

(e) Define anaerobic respiration.

(f) State the equation (in word) for anaerobic respiration in humans and in yeast.(g) Describe the effect of lactic acid production in muscles during exercise.

(h) Demonstrate an experiment to find out whether carbon dioxide is given off during respiration.

7.1 The need for energy

Respiration is the oxidation of food substances (mainly glucose) with the release of energy in living cells. It is necessary

to supply organisms with energy, which help them to maintain themselves, move, excrete, grow and reproduce. The

main source of energy for organisms is the radiant energy from sunlight. During photosynthesis, green plants transform

this energy into chemical energy, which is stored in the organic foods (products of photosynthesis). This stored chemicalenergy is obtained by organisms (animals) by feeding on green plants or on other animals.

Since the energy is locked up in the organic food molecules, an organism will have to oxidise them. This process of

oxidation which occurs within every living cells of animals (aw well as plants) is called respiration.

7.1.1 Uses of energy in humans

1. Synthesis of proteins from amino acids2. Cell division and therefore growth3. Heartbeat4. Respiratory movements5. Muscular contractions6. Active transport (absorption of glucose and amino acids by the villi in the small intestine is by active transport.

(So does absorption of mineral salts by the root hair cells)

7. Transmission of nerve impulses8. Keeping warm (homeostasis)
http://aunibazilahbiologynotes.blogspot.com/2009/01/respiration.htmlhttp://aunibazilahbiologynotes.blogspot.com/2009/01/respiration.html


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Fig. 7.1 Uses of energy in the human body

Respiration can be of two forms: AEROBIC RESPIRATION and ANAEROBIC RESPIRATION.

7.2 Aerobic respiration

Aerobic respiration is defined as the release of a relatively large amount of energy by the breakdown of food substances

in the presence of oxygen. Carbon dioxide and water are produced as wastes. The energy is stored as ATP (adenosine

triphosphate). The body uses this ATP for fuelling all activities of the body. Hence, ATP is known as the energy currency

as it is the immediate source of energy.

Fig. 7.2 Aerobic session in a fitness centre

Need for

energy in

humans

Muscle

contraction

Protein

synthesis

Nerve

impulsetransmission

Keep warm

Cell dision

and Growth

Activetransport

Heartbeat

Respiratory

movements


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Aerobic respiration can be represented by the following word equation.

Glucose + oxygencarbon dioxide + water + large amount of energy (28 ATP)

7.3 Anaerobic respiration

Anaerobic respiration is defined as the release of a relatively small amount of energy by the breakdown of food

substances in the in the absence of oxygen.

There are two types of anaerobic respiration: one occurring in plants and yeast and one occurring in animals and

bacteria.

7.3.1 Anaerobic respiration in plants yeast (fermentation)

Yeast is a kind of fungi (one class of organism which feed on dead organic matter), which is used in bread making.

Yeast cells oxidise glucose during fermentation. The products are ethanol, which is an alcohol. For this reason,

anaerobic respiration is yeast is also called alcoholic fermentation. Anaerobic respiration is yeast can be represented by

the following word equation:

Glucose (alcohol) carbon dioxide + small amount of energy (2 ATP)

Less energy is released because the alcohol molecule is relatively large and still contains a considerable amount of

chemical energy. The small amount of energy released is only enough for the yeast to survive.

(Note: the carbon dioxide produced as the waste products actually helps in raising the bread dough thus making the

bread fluffy. It is also used in the production of wine by the fermentation of grape juice)

7.3.2 Anaerobic respiration in human muscles

Normally muscle cells respire aerobically (using oxygen gas). But in certain circumstances, where oxygen is not

available for a very short period of time, these cells need to respire anaerobically (without oxygen gas). This usually

occurs during a vigorous or strenuous exercise such as sprinting in a 100 m race.

Fig. 7.3 Anaerobic respiration taking place in muscles


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What actually happens during exercise?

At the beginning of an exercise, the muscle cells first respire aerobically Soon the amount of oxygen available in the muscle cells becomes depleted Despite the increased breathing rate and heart beat, oxygen cannot be transported to the muscles fast enough

to be used for respiration

Under this circumstance, the muscle cells then respire anaerobically to continue producing energy (though onlya small amount is produced)

In the absence of oxygen in the muscle cells, the glucose is converted to lactic acid together with acomparatively small amount of energy

Glucose l small amount of energy (2 ATP)

1. During the exercise period the muscles are said to incur an oxygen debt (more oxygen is used up than can besupplied by the blood)

2. This "debt" is "paid" by fast and deep breathing in the recovery period after the exercise3. During the recovery period, 1/6 of the lactic acid produced during the exercise is oxidised aerobically into

carbon dioxide and water to produce enough energy to convert 5/6 of the lactic acid back into glucose

4. The glucose formed this way is then used in the normal aerobic respiration to release a large amount of energyNote: Sometimes, individual experiences muscle cramp. This is due to an accumulation of lactic acid in their muscles. If

the level of lactic acid exceeds the individual tolerance level (depending on how fit the individual is), muscles stop

contracting and cramp occurs). Muscle fatigue is also the result of the accumulation of lactic acid.

This type of anaerobic respiration also takes place in bacteria. The lactic acid produced by these bacteria is used in theproduction of yoghurt and cheese.

7.3.3 Differences between aerobic and anaerobic respiration

1. Aerobic respiration occurs in the presence of oxygen whereas anaerobic respiration occurs in the absence ofoxygen.

2. Aerobic respiration releases a large amount of energy (efficient in terms of energy yield) whereas anaerobicrespiration only releases a small amount of energy (less efficient in terms of energy yield)

3.

Aerobic respiration always produces carbon dioxide and water as the waste products whereas anaerobicrespiration produces lactic acid (as in the case of anaerobic respiration in muscle cells) and ethanol and carbon

dioxide (as in the case of anaerobic respiration in yeast)


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Experiment to find out whether carbon dioxide is given off during respiration

Requirements

Three boiling tubes 5 pieces of curved delivery tubes potassium or sodium hydroxide solution (5%)

One conical flask 4 Rubber bungs lime water

Germinated mung beans or grasshoppers (or any easily available animal)

Filter pump (an aquarium pump can also be used)

Procedure

1. Set up the apparatus as shown in fig. 7.4.2. Use the filter pump to draw water through the apparatus.3. The concentrated potassium hydroxide solution in the first boiling tube is used to absorb carbon dioxide from the

incoming air.

4. The lime water in flask 1 is used to show that there is no carbon dioxide in the air entering the conical flask wherethe living organisms are found.

5. The lime water in flask 2 is used to detect for the presence of carbon dioxide in the air leaving the conical flask.

Fig. 7.4 Apparatus used to show release of carbon dioxide during respiration

Observation

(a) What is the colour of lime water in(i) flask 1?

.

(ii) flask 2?

.

Interpretation

(b) Suggest an explanation for the results obtained.

.......................................................................................................................................................

..............................................................................................................................................................................................


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Chapter summary

Organisms require energy to fuel various processes which take place in the body such muscle contraction, celldivision and growth, protein synthesis, nerve impulse transmission, keeping warm among others.

Aerobic respiration is the release of a relatively large amount of energy in the presence of oxygen. Energy is stored in the form ofATP. Anaerobic respiration is the release of a relatively small amount of energy in the absence of oxygen. Anaerobic respiration in humans releases lactic acid. The accumulation of lactic acid results in oxygen debt and muscle fatigue. Anaerobic respiration in yeasts produces alcohol and carbon dioxide. It is also known as fermentation used in

the production ofwine (brewing) and making ofbread.

Concept map

Respiration

Aerobic

respiration

Anaerobic

respiration

Presence of oxygen Absence of oxygen

HumanYeast

Large amount

of energy

Water vapour

Lactic

acid

Carbon dioxide

Small amount

of energy

Muscle

fatigue

Alcohol

produces

produces produces

causesMuscle contraction

Nerve impulse transmission

Cell division and growth

Keeping warm (homeostasis)

Protein synthesis

Used for


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yeast?

A glucose + oxygen water + carbon dioxide

B glucose + oxygen alcohol + water

Cglucose water + carbon dioxide

Dglucose lactic acid + water

8 What do all living things release during respiration?

energy oxygen Carbon

dioxide

A

B

C

D

9 An athlete produces lactic acid in the leg muscles

while running a race. After the race he is seen to

breathe faster and deeper.

How does this help to remove the lactic acid?

A More carbon dioxide is used up.

B More energy is needed.C More lactic acid is breathed out.

D More oxygen is breathed in.

10 The flow diagram shows what happens to food in

humans.

Which stage shows human respiration?

Structured questions

Question 1

Athletes often have a sports drink when they are

exercising.

(a) The drink contains water and sugar.

Explain how each substance is used in the athletes

body.

(i) water

.........................................................................................

.........................................................................................

.........................................................................................

(ii) sugar

.........................................................................................

.........................................................................................

........................................................................................

(b) When the athlete exercises, his muscles respire

anaerobically and make lactic acid.

(i) What is meant by anaerobic respiration?

.........................................................................................

.........................................................................................

(ii) What is the effect of lactic acid in the muscles?

.........................................................................................

.........................................................................................

Question 2

(a) (i) In the box, state the word equation for aerobic

respiration.

(ii) Complete Table 2.1 to show three differences

between aerobic respiration and anaerobic respiration

in humans.


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3. Transmission of nerve ...4. Keeping the body ..5. . transport in the

absorption of food substances by the small

intestine.

6. . contractions e.g.heartbeat & respiratory movements.

Question 6

Fill in the spaces to with correct word to show what

happens during exercise.

a. During vigorous muscular contraction, musclesfirst use . to respire.

b. Rapid . occurs toremove carbon dioxide and take in more

oxygen.

c. Heart beats .so thatmore oxygen can be brought to the muscles.

d. Muscle cells carry out .respiration.

e. Lactic acid slowly builds up in the

f. Muscle has an OXYGEN .Lactic acid causes muscle ..

Question 7

Select the most appropriate word from the list below to

complete the following paragraph.

cells, food, carbon dioxide, muscles, aerobic,

oxygen, water, vitamin, protein, energy, anaerobic.

Respiration is the release of .. from

the breakdown of and takes place

in all of the body. If oxygen is used for

this process, the respiration is called

If oxygen is not used in the process, the respiration is

called ............................

Question 8

Complete the following equation which summarises

aerobic and anaerobic respirations of glucose:

(i) Glucose + ...

water + large amount of energy

(ii) Glucose .. + small amount of

energy (in human)

(iii) Glucose. +

+ small amount of energy (in yeast)

Question 9

Which two of the following statements are incorrect?

(a) Anaerobic respiration uses oxygen to release

energy from food. Ans.

(b) Aerobic respiration releases oxygen from food

during oxidation. Ans.

(c) Aerobic respiration converts food to carbon dioxide

and water. Ans.

(d) Anaerobic respiration releases energy from food

without using oxygen. Ans.


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Question 10

(a) What chemical is normally used to test for the

presence of carbon dioxide?

(b) What is the result of the test if carbon dioxide is

present?

(c) Suggest why carbon dioxide need to be removed

from the body:

form 3 national book chapters 6-7

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