Respiration

Question 1

What happens when O2 pressure is below 60 mm of Hg?

Answer 1

In many cells and tissues, the oxygen pressure is below 60 mm of mercury. Now the reaction becomes reversible. HbO2 → Hb + O This results in the liberation of large quantities of oxygen from haemoglobin. In this way in the tissue where oxygen pressure is low oxyhaemoglobin dissociates rapidly.

Question 2

Carbon Dioxide Concentration in Arterial and Venous Blood:

Answer 2

-The arterial blood contains about 50 ml of carbon dioxide per 100 ml of blood.
-The venous blood has 54 ml of carbon dioxide per 100 ml of blood.
-Each 100 ml of blood takes up 4 ml of CO2 as it passes through the tissues and gives off 4 ml of CO2 per 100 ml of blood as it passes through the lungs.

Question 3

CO2 as a Ventilation (Breathing) Regulator:

Answer 3

Carbon dioxide is much more important than oxygen as a regulator of normal alveolar
Breathing. However under certain conditions a reduced PO2 (partial pressure of O2) in the
arterial blood plays an important stimulatory role especially during conditions of shock.

Question 4

Gaseous Exchange Respiration occurs at two levels:

Answer 4

1. Organismic Respiration:
   Cellular respiration is the process by which cell utilizes oxygen produces carbon dioxide extracts and conserve the energy from food molecules in biologically useful from such as ATP.

Question 5

respiration in man

Answer 5

In man respiratory system includes lungs and air passages which carry fresh air to the respiratory sites.
1. Nasal Cavities: Nasal cavities are lined by mucous membrane of the ciliated epithelium. Each nasal cavity is subdivided into three passage ways by the projection of bones from the walls of the internal nose.

Question 6

Functions of the Nasal Cavities:

Answer 6

(i) Filtration: When the air enters the nasal cavity through nostril, the larger dust particles are trapped by the hair and mucus in the nostrils. (ii) Moistening: When the air passes through the nasal cavity, it becomes moist. (iii) Temperature Regulation: While passing through the nasal cavities, the temperature is regulated and becomes closer to the body temperature. In the above functions, mucous membrane is actively involved. 2. Pharynx: The nasal cavity leads into the throat or pharynx by two internal openings. Pharynx is a muscular passage lined with mucous membrane. 3. Larynx: The air enters from the pharynx into the larynx. The larynx or voice box is a complex cartilaginous structure surrounding the upper end of the trachea. The opening of larynx is called glottis. It is also lined by mucous membrane. (i) Epiglottis:
It is a lid which automatically covers the opening of the larynx during swallowing. Therefore, food
or liquids cannot enter into the larynx. The properties of epiglottis are as follows:
* Epiglottis is a cartilaginous structure
* It is muscularly controlled
* It has a hinge like action
(ii) Vocal Cords:
In the glottis, the mucous membrane is stretched across into two thin edged
fibrous bands called vocal cords. These help in voice production, when vibrated by
air.

Question 7

4. Trachea and Bronchi:

Answer 7

The trachea or wind pipe is a tubular structure. It is ventral to the oesophagus and extends
to the chest cavity or thorax where it is divided into right and left branches. In the wall of
trachea there are a series of’ C shaped cartilage rings. These prevent the trachea from
collapsing and keep the passage of air open. Bronchi have the same cartilage rings as the
trachea. However, the rings are progressively replaced by irregularly placed cartilage
plates.

Question 8

5. Bronchioles:

Answer 8

Each bronchus on entering the lung divides and subdivides progressively into smaller and
smaller bronchi. When the smaller bronchi attain a diameter of one mm or less, then they
are called bronchioles. The bronchioles totally lack cartilages. Bronchioles are made up of
mainly circular smooth muscles.

Question 9

6. Air Sacs:

Answer 9

The bronchioles continue to divide and subdivide deep into the lungs and finally open into
a large number of air-sacs. Air-sac is the functional unit of the lungs. Each air-sac consists
of several microscopic single layered structures called alveoli. Overlying the alveoli, there
is a rich network of blood capillaries. It is an excellent site for the exchange of gases.

Question 10

7. Lungs:

Answer 10

The lungs are closed sacs that are connected to the outside by the way of the trachea end
the nostrils or mouth.
Note: The human gas exchanging organ, the lung, is located in the thorax, where it’s
delicate tissues are protected by the bony and muscular thoracic cage.
Note: The trachea is a tube about 10 to 12 centimeters long and two centimeters wide.
Note: The larynx is an organ of dual function: as an air canal to the lungs and as the organ
of phonation.
Note: On average, an adult human lung as about 300,000,000 alveoli. They are
polyhedral structures, with a diameter of about 250 to 300 micrometers.
Lungs are spongy because of the presence of millions of alveoli.
Lungs are placed in the chest cavity. Chest cavity is bounded by ribs
and muscles on the sides.
The floor of the chest is called diaphragm. Diaphragm is a sheet of
skeletal muscles.
Lungs are covered with double layered thin membranous sacs
called pleura.

Question 11

Breathing and its mechanism

Answer 11

Breathing is a process in which fresh air containing more oxygen is pumped into the lungs
and air with more carbon dioxide is pumped out of the lungs. In other words breathing is
a mechanical process consisting of two phases, Inspiration and expiration. During
inspiration, fresh air moves in while during expiration the consumed air moves out of the
lungs.
Breathing rate:
During rest, breathing occurs rhythmically at the frequency of 15 to 20 times per minute
in humans. This is sufficient to remove CO2 from the blood.

Question 12

Breathing and its mechanism

Answer 12

Breathing is a process in which fresh air containing more oxygen is pumped into the lungs
and air with more carbon dioxide is pumped out of the lungs. In other words breathing is
a mechanical process consisting of two phases, Inspiration and expiration. During
inspiration, fresh air moves in while during expiration the consumed air moves out of the
lungs.
Breathing rate:
During rest, breathing occurs rhythmically at the frequency of 15 to 20 times per minute
in humans. This is sufficient to remove CO2 from the blood.

Question 13

1. Inspiration:

Answer 13

During inspiration the space inside the chest cavity is increased by two was the muscles
of ribs contract and elevate the ribs upwards and forwards. The muscles of the diaphragm
also contract and diaphragm becomes less domelike.
This downward movement of diaphragm and outward and upward movement of the ribs,
causes increase in the chest cavity and reduces internal pressure.
When the pressure from the lungs is removed, they expand. With the expansion of the
lungs vacuum is created inside the lungs. The air rushes into the lungs from the outside
due to the higher atmospheric pressure. This is called inspiration.

Question 14

2. Expiration:

Answer 14

During expiration the muscles of the ribs are relaxed and the ribs move downward and
inward. In this way from the side of chest cavity the space becomes less. At the same time
the muscles of diaphragm also relax, becoming more domes like chest cavity is also
reduced from the floor as well. The chest cavity is reduced and a pre-exerted on the lungs.
The air inside the lungs moves out. This is called expiration.

Question 15

Respiratory Distress Syndrome:

Answer 15

It is common in premature infants especially in infants with a gestation age of less than 7
months. This occurs because enough surfactant is not produced to reduce the tendency
of the lungs to collapse.
Surfactant is a mixture of lipoprotein molecules produced by the secretary cells of the
alveolar epithelium. This mixture forms a layer over the surface of the fluid within the
alveoli to reduce the surface tension.

Question 16

Factors Causing Gaseous Exchange:

Answer 16

Following factors bring about gaseous exchange (Intake of oxygen and release of carbon
dioxide) between blood and the alveolar air.
(i) Diffusion of oxygen in and carbon dioxide out occurs because of difference in p
artial pressure of these gases.
(ii) The alveoli are surrounded by a network of capillaries. The blood is distributed in
thin layers and therefore exposed to large alveolar surface.
(iii) Blood in the lungs is separated from the alveolar air by extremely thin membranes
of the capillaries and alveoli.

Question 17

Transport of Oxygen:

Answer 17

In human beings the respiratory pigment is haemoglobin. It is contained in the red blood corpuscles (R.B.C.). Haemoglobin combines with oxygen to form bright red oxyhaemoglobin. At low oxygen concentration and less pressure, the reaction becomes reversible. Now oxyhaemoglobin (which is unstable) splits back to its normal purple-red coloured haemoglobin after giving out most of its oxygen. This reaction occurs with the help of an enzyme carbonicanhydrase present in R.B.C. In this way haemoglobin acts as an efficient oxygen carrier. A small proportion of oxygen also dissolved in blood plasma. Hb + O2 = HbO2

Question 18

Maximum Absorption Capacity:

Answer 18

Haemoglobin can absorb maximum oxygen at the sea level. The maximum amount of oxygen which normal human blood absorbs and carries at the sea-level is about 20 ml/100 ml of blood. This is the maximum capacity of haemoglobin for oxygen when it is fully oxygenated. Under normal conditions blood of alveoli of the lungs, is not completely oxygenated. When an oxygen tension is 100 mm mercury then haemoglobin is 98 percent oxygenated. Therefore, loo ml of blood contains 19.6 ml of oxygen. This means that haemoglobin can be almost completely oxygenated by an oxygen pressure of 100 mm mercury which is present in the lungs. Any higher oxygen pressure would have the same result. What happens when O2 pressure is below 60 mm of Hg? In many cells and tissues, the oxygen pressure is below 60 mm of mercury. Now the reaction becomes reversible. HbO2 → Hb + O This results in the liberation of large quantities of oxygen from haemoglobin. In this way in the tissue where oxygen pressure is low oxyhaemoglobin dissociates rapidly.

Question 19

Factors affecting the capacity of haemoglobin to combine with oxygen:

Answer 19

Three important factors affect the capacity of haemoglobin to combine with oxygen: 1. Carbon Dioxide: When CO2 pressure increases, the O2 pressure decreases. As a result the capacity of haemoglobin to hold oxygen becomes less. In this way increased CO2 pressure favours the greater liberation of oxygen from theblood to the tissue. 2. Temperature: Rise in temperature also decreases the oxygen-carrying capacity of blood. For example when muscular activity is increased, 02 is released from the blood and is supplied to the muscles. 3. pH: When the pH of the blood declines, the amount of oxygen bound to haemoglobin also declines. This occurs because decreased pH results from an increase in hydrogenions. The hydrogen ions combine with the protein part of the haemoglohin. As a result, the ability of haemoglobin to bind oxygen is decreased. An increase in blood pH results in an
increased ability of haemoglobin to bind oxygen.

Question 20

Transport of carbon dioxide:

Answer 20

Carbon dioxide is more soluble than oxygen and dissolves freely in the tissue fluid
surrounding the cells.
From the tissue fluid, dissolved carbon dioxide passes to the plasma with in the blood
capillaries.
Carbon dioxide is transported in the blood in several different states.
1. As Carboxyhaemoglobin:
Some of the CO2 (about 20%) is carried as carboxyhaemoglobin. Carboxyhaernoglohin is
formed when carbon dioxide combines with amino group of hemoglobin.
2. In Combination with Plasma Proteins:
The plasma proteins also carry about 5% carbon dioxide from the body fluids to the
capillaries of lungs.
3. In Combination with Potassium:
Small amount of carbon dioxide is also carried by corpuscles combined with potassium.
4. As Bicarbonate:
About 70% carbon dioxide is carried as bicarbonate ion combined with sodium in the
plasma. As carbon dioxide from tissue fluid enters in the capillaries, it combines to form
carbonic acid.
CO2+ H2O → H2CO3
The carbonic acid splits quickly and ionizes to produce hydrogen ions and bicarbonate
ions.
H2CO3 → H++ HCO3
–
When blood leaves the capillaries most of the carbon dioxide is in the form of bicarbonate
ions.
All these reactions are reversible.
In the lungs bicarbonate ions combine with hydrogen ions to form carbonic acid which
splits into water and carbon dioxide.
The carbon dioxide diffuses out from the capillaries of the lungs into the space of alveolar
sac.
HCO3
–+ H + → H2CO3 CO2 + H2O

Question 21

Carbon Dioxide Concentration in Arterial and Venous Blood:

Answer 21

The arterial blood contains about 50 ml of carbon dioxide per 100 ml of blood. The venous
blood has 54 ml of carbon dioxide per 100 ml of blood. Each 100 ml of blood takes up 4
ml of CO2 as it passes through the tissues and gives off 4 ml of CO2 per 100 ml of blood as
it passes through the lungs.

Question 22

CO2 as a Ventilation (Breathing) Regulator:

Answer 22

Carbon dioxide is much more important than oxygen as a regulator of normal alveolar
Breathing. However under certain conditions a reduced PO2 (partial pressure of O2) in the
arterial blood plays an important stimulatory role especially during conditions of shock.

Question 23

Important points to remember:

Answer 23

Respiratory distress syndrome occurs because enough surfactant is not produced to reduce the tendency of
the lungs to collapse. It is common in premature infants especially in infants with a gestation age of
less than 7 months.
2. Alveolar Breathing is regulated by CO2 and O2.
3. Normally, at rest we inhale and exhale 15 – 20 times per minutes. During exercise the breathing rate
may rise to 30 times per minute.
4. Lung cancer is one of the most serious diseases of respiratory system. 90% of lung cancer is caused
by smoking.
5. More than ten compounds of tar of tobacco smoke are involved to cause cancer.
6. Cancer or carcinoma is basically malignant tumor of potentially unlimited growth. It expands locally
by invasion and systemically by metastasis.
7. Tuberculosis is the general name of a group of diseases caused by Mycobacterium tuberculosis.
8. Asthma is an allergic reaction to pollen, spores, cold, humidity, pollution etc. This allergic reaction
causes sudden contraction of small bronchioles.
9. Emphysema is a breakdown of alveoli due to “smoker’s cough”.
10. Haemogiobin is the most important protein present in many animals including man.

Question 24

Important points to remember:

Answer 24

11. Haemoglobin in man increases the oxygen carrying capacity of the blood to about 75 times.
12. Myoglobin is haemoglobin like iron containing protein pigment present in the muscle fibers.
13. Myoglobin is also known as muscle haemoglobin. It is an intermediate compound for the transfer of
    oxygen from haemoglobin to aerobic metabolic processes of the muscle cells. Myoglobin can also
    store some oxygen.
14. Myoglobin consists of one polypeptide chain associated with an iron containing ring structure which
    can bind with the molecule of oxygen. The affinity of myoglobin to combine with oxygen is much
    higher as compared to haemoglobin.
15. Aquatic mammals especially the Cetaceans can stay in the depth of the ocean for about two hours
    without coming up for air. Diving mammals have almost twice the volume of the blood in relation to
    their body weight as compared to the non-divers. Most of the diving mammals have high
    concentration of myoglobin in their muscles. Myoglobinbinds extra oxygen.
16. When a mammal dives to its limit, the diving reflex is activated. Now the breathing stops, rate of
    heart beat slows down to 1/10th of the normal, most of the blood goes to the brain and heart which
    can least withstand anoxia, Muscles shift from aerobic to an aerobic respiration.
17. In an adult human being when the lungs are fully inflated, the total inside capacity of the lungs is
    about 5 liters.
18. Normally when we are at rest or asleep, the exchange is only about half a liter. The volume of air
    taken inside the lungs and expelled during exercise is about 3.5 liters. It means, there is a residual
    volume of 1.5 liters even during exercise which cannot be expelled.

Question 25

ADDITIONAL / RELATED READINGS

Answer 25

1. Respiration is the most important metabolic activity of all living organisms.
2. Respiration occurs at two levels:
   (i) Organismic level
   (ii) Cellular level.
3. Organismic respiration is also known as breathing or ventilation.
4. Cellular respiration is the process by which cell utilizes oxygen, produces carbon dioxide,
   extracts and conserve the energy from food molecules in biologically useful form such as ATP.
5. Respiratory gases are exchanged between body fluid and outside medium. The outside
   medium may be water or air.
6. Exchange of gases occurs only by diffusion.
7. Air is better respiratory medium than water. In the equal volumes of air and water, oxygen is
   higher in the air. A liter of air has about 200 ml oxygen while one-liter water cannot contain
   even 10 ml oxygen.
8. Oxygen diffuses about 8000 times more quickly in air than in water. Water is 8000 times
   denser than air.
9. Water is 50 times more viscous than the air.
10. The transport system of plants (xylem and phloem) is not involved in the transport of gases.
    This is because that in plants there is no special organ or system for gaseous exchange.

Question 26

ADDITIONAL / RELATED READINGS

Answer 26

11. Land plants get their oxygen from air through stomata. Therefore, stomata are the main
    source of exchange of gases in plants. Stomata are largely present in the leaves and in young
    stem.
12. There are about 12000 stomata per square centimeter of leaf surface in Tobacco plant.
13. The stomata lead to the intercellular spaces between mesophyll cells.
14. The air spaces in the leaf are similar to honey comb. The air spaces cover up to 40% of the
    total volume of the leaf.
15. In the older stems, cork tissue is present which is formed of dead cells. The cork tissue has
    special pores called lenticels which are involved in gaseous exchange.
16. The roots of the land plants get their oxygen from the air present in the spaces between the
    soil particles.
17. Respiratory activity which occurs in plants during daytime is called photorespiration.
    OR
    The pathway in which RuBP is converted into serine is called photorespiration.
18. Photorespiration starts in hot dry weather when temperature above 40° C. Now ABA is
    released and stomata close. But light reaction will continue. As a result the level of oxygen
    inside the leaf rises while the level of carbon dioxide falls due to its consumption. Now
    photorespiration starts.
19. The process of photorespiration uses ATP and NADPH produced in the light reactions just like
    Calvin-Benson cycle. However photorespiration is reverse of the Calvin cycle. In this process carbon dioxide is released and oxygen is absorbed. This oxygen is produced in the light reactions.
20. Three main reactions in the photorespiration:
    (i) RuBP + O2 → Glycolate (in the Chloroplast)
    (ii) Glycolate → Glycine (in the Peroxisomes)
    (iii) 2 glycine → Serine + CO2 (in the Mitochondria)

Question 27

ADDITIONAL / RELATED READINGS

Answer 27

21. The rubisco is carboxylase as well as oxygenase. When the rubisco acts as carboxylase it adds
    carbon dioxide to RuBP, which is an accepter molecule. On the other hand when rubisco is
    oxygenase it adds oxygen to RuBP. Both these reactions compete with each other.
22. The photorespiration reduces the photosynthetic process. In most plants, by photorespiration,
    the carbohydrate production is reduced up to 25%.
23. The distance across which diffusion of gases has to take place should be little. In most animals
    the epithelium which separates air and blood is only two cells thick.
    Therefore, the distance for diffusion is very short.
24. Blood in the lungs is separated from the alveolar air by extremely thin membranes of the
    capillaries and alveoli.
25. Organismic respiration/breathing/Ventilation maintains a steep diffusion gradient.
26. Hydra has no specialized organs for respiration. Exchange of gases (intake of 02 and removal of
    CO2) occurs through the entire surface of the body by diffusion.
27. Earthworm has no specialized organs for respiration. The exchange of gases occurs mainly
    through the skin.
28. The respiratory system of the cockroach consists of branching systems of air tubules called
    tracheae lined by chitin.
29. In the cockroach the main tracheal trunk communicates with exterior by 10 pairs of apertures
    called spiracles. These are present on the lateral sides of the body. Two pairs are in the thorax
    while eight pairs in the first eight abdominal segments.
30. In the cockroach Air is pumped in and out of the tracheae by the expansion and contraction of
    the abdominal muscles (Dorsoventral muscles). When abdomen expands the first four pairs of
    spiracles open, the air rushes in through these spiracles into the tracheoles. When the abdomen
    contracts, the anterior four pairs of spiracles close and posterior six pairs of spiracles open. The
    air is forced out of the body through these spiracles.

Question 28

ADDITIONAL / RELATED READINGS

Answer 28

31. Fish respires through the gills Gills are paired structures present on the either side of the body
    almost at the junction of head and trunk. There are four to five pairs of gills which may be visible
    on the surface of the pharynx (in the cartilaginous fishes) or placed in the branchial cavities (in
    bony fishes).
32. In frog, the gaseous exchange occurs through the lungs, by skin and the buccal chamber. The
    gaseous exchange through the skin is known as cutaneous respiration. Gaseous exchange through
    the lungs is called pulmonary respiration.
33. Respiratory system in birds is the most efficient and complicated. The birds are very active
    animals with high metabolic rate. Therefore, they need large amount of oxygen.

Question 29

ADDITIONAL / RELATED READINGS

Answer 29

34. In birds there is one-way flow of the air through the lungs and the air is renewed after inspiration.
35. The lungs of birds have parabronchi instead of alveoli. These are tiny thin walled ducts. These
    parabronchi are opened at both ends and the air is constantly ventilated. The walls of the
    parabronchi are chief sites of gaseous exchange. The direction of the blood flow in the lungs is
    opposes to the air flow through the parabronchi. This counter current exchange increases the
    amount of oxygen which enters the blood.
36. In birds the lungs have also developed several extensions known as air sacs. These reach into all
    parts of the body and even penetrate some of the bones. In most birds the air sacs are nine in
    number. The air sacs send air into the parabronchi. Photo respiration is a process which is reverse
    of: