1. CHAPTER 10
Respiration in Humans

2. Chapter 10
Respiration in Humans
10.1 Why Do Living Things Respire?
10.2 Studying Respiration
10.3 Gas Exchange in Humans
10.4 How Does Inspired Air Differ from Expired Air?
10.5 Effects of Tobacco Smoke on Human Health

3. Why Do Living Things Respire?
10.1
Why Do Living Things Respire?
Learning Outcomes
After this section, you should be able to:
define and state the equations in words for aerobic and anaerobic respiration in humans;
describe the effect of lactic acid in muscles during exercise.

4. Why Do Living Things Respire?
10.1
Why Do Living Things Respire?
Energy that is needed for organisms to move, grow, excrete and reproduce, is obtained through the consumption of food.
To use the energy available in food, living organisms need to break down the food molecules through a process called oxidation.
The oxidation of food molecules to produce energy is called respiration.
Respiration occurs in the cell and although it involves the breakdown of food molecules, it is not digestion.
Digestion is the process in which food is broken down into simpler substances for absorption into the cells.
In respiration, organic compounds (food molecules) are converted into inorganic compounds (e.g. carbon dioxide and water) to produce energy.

5. Why Do Living Things Respire? What is aerobic respiration?
10.1
Why Do Living Things Respire?
What is aerobic respiration?
The oxidation of glucose in the presence of oxygen
Results in the production of a large amount of energy by giving off carbon dioxide and water as waste products
The word equation for aerobic respiration:
Notes:
Organic molecules other than glucose (e.g. amino acids and fatty acids) can be used in respiration. Glucose, however, is the most commonly used food molecule in respiration. The chemical energy stored in glucose cannot be used directly by cells and has to be broken down via cellular respiration to release energy in a form that can be used by the cells (i.e. adenosine triphosphate, ATP). +
glucose
oxygen
energy
carbon
dioxide
water

6. Why Do Living Things Respire?
10.1
Why Do Living Things Respire?
Aerobic respiration occurs in the mitochondria of all cells.
mitochondria
Note:
Mitochondria are like little factories which produces energy from the respiration of glucose.

7. What is anaerobic respiration?
10.1
Why Do Living Things Respire?
What is anaerobic respiration?
The oxidation of glucose in the absence of oxygen
Releases less energy than aerobic respiration
The word equation for anaerobic respiration in humans:
glucose +
energy
lactic acid
Notes:
The waste products of anaerobic respiration differs from species to species depending on what is used as an electron acceptor. (oxygen is used as an electron acceptor in aerobic respiration)
In humans, the waste product produced in anaerobic respiration is lactic acid.
In yeast, the waste product produced in anaerobic respiration is ethanol and carbon dioxide.
Equation for anaerobic respiration by yeast: glucose  ethanol + carbon dioxide + energy

8. What happens during exercise?
10.1
Why Do Living Things Respire?
What happens during exercise?
Muscles contract vigorously to enable movement.
Respiratory rate and heart rate increase to enable more oxygen to reach the muscles.
If the increased oxygen intake is not able to meet the oxygen demand, anaerobic respiration will take place to provide the energy required.
Start by asking a student to describe how he/she feels before, during and after running the 2.4km fitness test.
Notes:
By increasing the respiratory rate, the oxygen intake increases. Increased oxygen demand of the body can be met.
By increasing the heart rate, inhaled oxygen can be transported quickly to the relevant parts of the body (e.g. muscles).

9. What happens during exercise?
10.1
Why Do Living Things Respire?
What happens during exercise?
When anaerobic respiration occurs, lactic acid accumulates and the muscles incur an oxygen debt.
Lactic acid accumulation causes the soreness and tiredness in muscles.
Note:
An oxygen debt is the volume of oxygen required to remove the lactic acid that has been built up.

10. Chapter 10
Respiration in Humans
10.1 Why Do Living Things Respire?
10.2 Studying Respiration
10.3 Gas Exchange in Humans
10.4 How Does Inspired Air Differ from Expired Air
10.5 Effects of Tobacco Smoke on Human Health

11. 10.2 Studying Respiration Learning Outcome
After this section, you should be able to:
carry out simple experiments to determine the products of respiration.

12. Carbon dioxide is a product of aerobic respiration
10.2
Studying Respiration
Carbon dioxide is a product of aerobic respiration
The potassium hydroxide solution in flask A removes carbon dioxide from the air.
The air entering flask B and C does not contain carbon dioxide. Hence, any carbon dioxide detected in flask D would be due to respiration by the snails.
Limewater turns chalky when carbon dioxide is dissolved into it.
The limewater in flask B should not turn chalky because the carbon dioxide in the air entering flask B should have been removed in flask A.
Carbon dioxide is released during respiration. Therefore, the limewater in D should turn chalky.
potassium hydroxide solution
limewater A B
limewater
snails C D

13. Carbon dioxide is a product of anaerobic respiration
10.2
Studying Respiration
Carbon dioxide is a product of anaerobic respiration
The glucose solution is first boiled and cooled to:
remove dissolved oxygen
kill microorganisms
Due to limited oxygen availability, the yeast undergoes anaerobic respiration.
If carbon dioxide is released during the anaerobic respiration of yeast, the limewater will turn chalky.
The limewater should turn chalky as anaerobic respiration of yeast produces ethanol and carbon dioxide.
Highlight to students that carbon dioxide is not always released in anaerobic respiration. (e.g. Anaerobic respiration in muscle cells does not produce carbon dioxide.)
Note:
Yeast suspension is prepared using distilled water and dry yeast.
glucose and yeast suspension
limewater

14. Heat is a product of respiration
10.2
Studying Respiration
Heat is a product of respiration
The vacuum flask insulates the experimental set-up.
The cotton wool plug allows gaseous exchange between the seeds and the environment.
The antiseptic solution prevents growth of microorganisms.
If heat is produced during respiration, the thermometer would register a temperature higher than the surrounding temperature.
vacuum flask
pea seeds
in antiseptic
solution
cotton wool plug
thermometer
The thermometer should register a higher temperature than the surrounding temperature as respiration releases heat energy.
Note:
Germinating (actively growing) seeds are used because they have higher rate of respiration as compared to dormant seeds.

15. Chapter 10
Respiration in Humans
10.1 Why Do Living Things Respire?
10.2 Studying Respiration
10.3 Gas Exchange in Humans
10.4 How Does Inspired Air Differ from Expired Air
10.5 Effects of Tobacco Smoke on Human Health

16. 10.3 Gas Exchange in Humans Learning Outcomes
After this section, you should be able to:
identify the organs involved in the human gaseous exchange system;
describe the role of the alveoli in gaseous exchange.

17. Why the need for a respiratory system?
10.3
Gas Exchange in Humans
Why the need for a respiratory system?
Humans are large organisms that are made up of millions of cells.
We have a small surface area to volume ratio, unlike unicellular microorganisms.
This mechanism of exchange is called external respiration and it involves a process called breathing.
Emphasise to students the difference between external respiration and cellular respiration.
External respiration refers to the breathing process. It is the process where oxygen is taken into and carbon dioxide is removed from the body.
Cellular respiration refers to the oxidation of glucose to release energy in cells. Aerobic respiration requires oxygen which is obtained through breathing (external respiration).

18. Gas exchange system in humans
10.3
Gas Exchange in Humans
Gas exchange system in humans
nasal cavity
larynx
pharynx
The fringe of hair and the mucous layer on the walls of the nasal cavity trap dust and foreign particles.
The air is warmed and moistened as it passes through the nasal passages.

19. Gas exchange system in humans
10.3
Gas Exchange in Humans
Gas exchange system in humans
C-shaped rings of cartilage support the trachea.
They keep the lumen of the trachea open.
nasal cavity
larynx
pharynx
trachea
bronchus
C-shaped ring of cartilage
Transverse section of a trachea
Highlight to students that the trachea branches out into two bronchi (singular: bronchus).

20. Gas exchange system in humans
10.3
Gas Exchange in Humans
Gas exchange system in humans
On the inner walls of the trachea and bronchi are:
gland cell
epithelial cell
cilia
mucus produced by gland cell
gland cells
epithelial cells
Gland cells secrete mucus that trap dust particles and bacteria in the air that is channelled to the lungs.
Epithelial cells have cilia that sweep trapped particles and bacteria up the bronchi and trachea, to the pharynx.

21. Gas exchange system in humans
10.3
Gas Exchange in Humans
Gas exchange system in humans
nasal cavity
larynx
pharynx
trachea
lung
The lungs lie in the thoracic cavity.
Within the lungs, the bronchial tubes divide repeatedly to form bronchioles.
Bronchioles end in clusters of air sacs called alveoli.
bronchiole
a cluster of alveoli
bronchus
URL
Bronchial tubes refer to the tubes of the bronchi (singular: bronchus)
Highlight to students that each bronchiole ends in a cluster of grape-like structures called alveoli (singular: alveolus). The alveoli are the site of gaseous exchange.
Click on the Video-URL button to be directed to a website where a video summary (length = 1:46 minutes) on the human gaseous exchange system can be found. This video introduces the passage of air into the trachea, bronchi, bronchiole and alveoli. It also covers the features of the trachea (C-shaped cartilage) and explains how the large surface area to volume ratio is achieved for efficient gaseous exchange.

22. How are the alveoli adapted for efficient gaseous exchange?
10.3
Gas Exchange in Humans
How are the alveoli adapted for efficient gaseous exchange?
capillary network
The numerous alveoli in the lungs increase the surface area for gaseous exchange.
The alveoli are well-supplied with blood capillaries to maintain a steep concentration gradient of gases.

23. How are the alveoli adapted for efficient gaseous exchange?
10.3
Gas Exchange in Humans
How are the alveoli adapted for efficient gaseous exchange?
The alveolar surface is coated with a thin film of moisture to allow oxygen to dissolve.
The wall of each alveolus and its surrounding capillaries are one-cell thick, ensuring faster rate of diffusion.
capillary wall
thin film of water
alveolar wall

24. Gaseous exchange in the alveolus
10.3
Gas Exchange in Humans
CO2 O2
inhaled oxygen
carbon dioxide to be exhaled
capillary
alveolus
Gaseous exchange in the alveolus
deoxygenated blood (carbon dioxide rich)
oxygenated blood (transported to the heart)
URL
Highlight to students that the alveolus is the site of gaseous exchange and that this gaseous exchange occurs via diffusion.
Blood entering the lungs has lower concentration of oxygen and higher concentration of carbon dioxide than the air in the alveolus (the inhaled air).
Carbon dioxide from the blood diffuses into the alveolus and this carbon dioxide will be channelled out of the lungs via expiration.
The air in the alveolus contains a higher concentration of oxygen than the blood entering the lungs.
The oxygen in the alveolus diffuses into the blood in the capillary vessels and is transported to the heart where it is pumped throughout the body.
Click on the Video-URL button to be directed to a website with a video (length = 1:22 minutes) that shows how gaseous exchange occurs at the alveoli.

25. How is oxygen transported?
10.3
Gas Exchange in Humans
How is oxygen transported?
Oxygen molecules bind to haemoglobin in red blood cells to form oxyhaemoglobin.
This process is reversible.
Notes:
Oxygen is transported by haemoglobin in red blood cells. When haemoglobin binds to oxygen, it becomes bright red in colour and when it loses oxygen, it becomes purplish-red in color. The binding of oxygen is a reversible reaction.
The binding of oxygen to haemoglobin (Hb) molecules is dependent on the concentration of oxygen in the surroundings. In oxygen-rich areas (such as in the lungs), oxygen binds to Hb to form oxyhaemoglobin. In places where oxygen concentration is low (e.g. muscles), the process is reversed and oxygen molecules are released. This allows efficient transportation and distribution of oxygen.
+ oxygen molecules
haemoglobin
oxyhaemoglobin
- oxygen molecules

26. How is carbon dioxide transported?
10.3
Gas Exchange in Humans
How is carbon dioxide transported?
Carbon dioxide molecules produced by tissue cells are converted to hydrogen carbonate ions which diffuse into the blood plasma.
In the lungs, the hydrogen carbonate ions are converted back into carbon dioxide.
In blood, converted to
Hydrogen carbonate ions
Carbon dioxide
In the lungs, converted to

27. Chapter 10
Respiration in Humans
10.1 Why Do Living Things Respire?
10.2 Studying Respiration
10.3 Gas Exchange in Humans
10.4 How Does Inspired Air Differ from Expired Air?
10.5 Effects of Tobacco Smoke on Human Health

28. How Does Inspired Air Differ from Expired Air?
10.4
Learning Outcome
After this section, you should be able to:
state the difference in composition between inspired air and expired air.

29. How Does Inspired Air Differ from Expired Air?
10.4
Breathing is the muscular contractions and movements of the ribs, which result in air moving in and out of the lungs.
The taking in of air is called inspiration (or inhalation).
 The giving out of air is called expiration (or exhalation).

30. How Does Inspired Air Differ from Expired Air?
10.4

31. Chapter 10
Respiration in Humans
10.1 Why Do Living Things Respire?
10.2 Studying Respiration
10.3 Gas Exchange in Humans
10.4 How Does Inspired Air Differ from Expired Air
10.5 Effects of Tobacco Smoke on Human Health

32. Effects of Tobacco Smoke on Human Health
10.5
Learning Outcome
After this section, you should be able to:
describe the effects of the major toxic components of tobacco smoke on human health.

33. Effects of Tobacco Smoke on Human Health
10.5
Carbon monoxide
Nicotine
addictive
increases risk of blood clot in blood vessels
increases the risk of heart diseases
decreases the ability of red blood cells to transport oxygen
increases the rate at which fats are deposited on the inner arterial walls (leads to artherosclerosis)
Irritants
(e.g. formaldehyde, hydrogen cyanide)
Tar
paralyse the cilia lining in air passages
increase the risk of chronic bronchitis and emphysema
carcinogenic
paralyses the cilia lining in air passages
reduces the efficiency of gaseous exchange

34. Effects of Tobacco Smoke on Human Health
10.5
Chronic bronchitis
In chronic bronchitis,
the epithelium lining the airways is inflamed
there is excessive mucus secretion
the cilia lining the airways are paralysed
Symptoms:
Breathing difficulties due to blocked airways
Persistent cough (body’s response to clear the blocked airways)
over secretion of mucus
Notes:
Tobacco smoking is the most common cause of chronic bronchitis. The components of tobacco smoke that contribute to the development of this disease are the irritants and tar.
Persistent and prolonged coughing can lead to emphysema.
cilia paralysed and unable to remove mucus

35. Effects of Tobacco Smoke on Human Health
10.5
Emphysema
In emphysema,
the partition walls between alveoli break down due to violent coughs. (This reduces the surface area available for gaseous exchange.)
the lungs lose their elasticity and become inflated with air
Symptoms
Breathing difficulties
Wheezing
healthy lungs
partition walls between alveoli
diseased lungs
damaged partition walls
A person that suffers from both chronic bronchitis and emphysema, has chronic (meaning recurrent, persistent) obstructive (due to the blockage in the airways) lung disease.
Note:
Tobacco smoking is also the most common cause of emphysema.

36. Chapter 10
Respiration in Humans