Is carbon dioxide dissolved in plasma same as carbonic acid?

Is carbon dioxide dissolved in plasma same as carbonic acid?

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Carbon dioxide is transported through blood via 3 methods : 1. Dissolved in plasma 2. As bicarbonate ion 3.through RBCs. The carbondioxide when transported as bicarbonate ion i.e HCO3- and H+. What i dont understand is that dissolved carbon dioxide in plasma should also yield H2CO3, so is writing co2(aq) the same thing as writing H2CO3? Further shouldnt this carbonic acid also dissociate and form bicarbonate ion and proton? Doesn't this make both the processes equivalent? What i found out is that H2CO3 has a low ionisation constant of the order 10-4, is this tbe reason why they are separate events? Implying that carbonic anhydrase catalyses the formation of bicarbonate ion while some part of H2CO3 is not ionised and that is what refers to co2(aq)

8.6: Transport of Gases

The other major activity in the lungs is the process of respiration, the process of gas exchange. The function of respiration is to provide oxygen for use by body cells during cellular respiration and to eliminate carbon dioxide, a waste product of cellular respiration, from the body. In order for the exchange of oxygen and carbon dioxide to occur, both gases must be transported between the external and internal respiration sites. Although carbon dioxide is more soluble than oxygen in blood, both gases require a specialized transport system for the majority of the gas molecules to be moved between the lungs and other tissues.

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Emmett M, Seldin DW (1989) Evaluation of acid-base disorders from plasma composition. In: Seldin DW, Giebisch H (eds) The regulation of acid-base. Raven Press, New York, pp 213–263

Lyons H (1977) Terminology of acid-base balance. In: Schwartz AB, Lyons H (eds) Acid-base and electrolyte balance-normal regulation and clinical disorders. Grune & Straton, New York, pp 9–15

Linden RJ, Norman J (1971) The imprecision arising from the application of the Henderson-Hasselbalch relation to the blood of anesthetized dogs. J Physiol 215:497–501.

Madias NE, Cohen JJ (1982) Acid-base chemistry and buffering. Ionization of carbonic acid. In: Cohen JJ, Kassirer JP (eds) Acid-base. Little, Brown and Company, Boston, p 13

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Regulation of the amount of carbon dioxide (CO2) in blood, or more precisely of the ratio of bicarbonate to dissolved carbon dioxide concentration, is essential for maintaining acid-base balance. CO2 is a major determinant of blood pH because of its conversion to carbonic acid. As CO2 concentration rises, so does hydrogen ion (H + ) concentration. Respiration rate, which is controlled bypCO2 sensitive chemoreceptors in the brain stem and carotid artery, is increased ifpCO2 is rising and decreased ifpCO2 is declining. Increased respiratory rate results in increased rate of CO2 elimination and decreased respiratory rate promotes CO2 retention. A low CO2 level may be associated with metabolic acidosis or compensated respiratory alkalosis. High CO2 content may be associated with metabolic alkalosis or compensated respiratory acidosis.

All cells depend on aerobic metabolism for generation of energy, in the form of ATP. During this process, mitochondria consume oxygen and produce carbon dioxide. Carbon dioxide diffuses from mitochondria into the cell cytoplasm, across the cell membrane and into the capillary network. It is transported by the blood to the lungs for excretion in expired air.

A little of the CO2 remains physically dissolved in blood plasma and an even smaller proportion binds to NH2 (amino) terminal groups of plasma proteins, forming carbamino compounds. However, most diffuses down a concentration gradient into red cells, where a small fraction remains dissolved in the cytoplasm and some is loosely bound to amino terminal groups of reduced hemoglobin forming carbamino-Hb. Most of the carbon dioxide arriving in red cells is rapidly hydrated to carbonic acid by the enzyme carbonic anhydrase. At physiological pH almost all (? 96 %) of this carbonic acid dissociates to bicarbonate and hydrogen ions:

When red blood cells reach the pulmonary circulation, carbon dioxide diffuses from the blood to alveoli. This loss of carbon dioxide from blood favors reversal of the red cell reaction described above. Bicarbonate passes from plasma to red cell, buffering hydrogen ions released from hemoglobin, as it is oxygenated. Reversal of the carbonic anhydrase reaction, results in production of CO2 that diffuses from red cells to plasma and ultimately to alveoli. Mixed venous blood arriving at the lungs has a total CO2 content of 23.5 mEq/L whereas arterial blood leaving the lungs has a total CO2 content of 21.5 mEq/L.

In summary, most carbon dioxide is transported as bicarbonate plasma, but there are three other modes of CO2 transport:

  • 90 % is transported as bicarbonate in plasma (65 %) and red cells (25 %)
  • 5 % is transported physically dissolved in plasma and red cell cytoplasm
  • 5 % is transported loosely bound to hemoglobin and plasma proteins
  • < 0.1 % is transported as carbonic acid

Total carbon dioxide blood content is the sum of these four components.

Arterial blood gas analysis includes three parameters related to the carbon dioxide content of blood.

  • Partial pressure of carbon dioxide (pCO2)
  • Plasma bicarbonate concentration (HCO3 - )
  • Plasma total concentration carbon dioxide (ctCO2)

Of the three, only bloodpCO2 is actually measured during blood gas analysis, the other two are calculated from pCO2 and pH. Total concentration of carbon dioxide can also be measured in plasma or serum by chemical methods and is included in all chemistry panels containing electrolytes.

Partial pressure of carbon dioxide (pCO2) is a measure of the pressure exerted by that small portion (? 5 %) of total carbon dioxide in blood that is dissolved in the aqueous phase of plasma and blood cell cytoplasm. The measurement is made using a CO2 specific pH electrode. In health, pCO2 of arterial blood is maintained within the range of 35-45 mm Hg pCO2 of venous blood is a little higher, 41-51 mmHg.

Most of the carbon dioxide (90%) is transported in blood as plasma bicarbonate. This parameter is calculated. In health, arterial plasma bicarbonate is maintained between 21-28 mEq/L. Venous bicarbonate is slightly higher at 24-30 mEq/L.

Total carbon dioxide content is calculated during blood gas analysis as the sum of all forms of carbon dioxide. Dissolved CO2 contributes approximately 1.2 mEq/L to the total CO2 in the plasma of arterial blood, explaining why ctCO2 is usually this much higher than plasma bicarbonate. The ctCO2 reference range is 23-29 mEq/L in arterial blood. Critical values are <10 mEq/L and >40 mEq/L.

AlthoughctCO2 and bicarbonate provide essentially equivalent information, bicarbonate is invariably used in conjunction with pH andpCO2 to evaluate acid-base status.The clinical value of calculated ctCO2 generated during blood gas analysis is limited.

Unlike bicarbonate, which cannot be measured,ctCO2 can be measured chemically and this parameter is routinely included with electrolytes. Since electrolytes are ordered much more frequently than arterial blood gases, measuredctCO2 is often the first indication of a disturbance in acid-base balance. For all practical purposes, ctCO2 and bicarbonate are equivalent, but a difference of 2-3 mEq/L may be observed. The major difference is that electrolytes are usually measured on venous blood and blood gases on arterial blood so there is a 1-2 mEq/L due to the arterial-venous difference. There is an additional potential difference of 1.5 mEq/L due to the inclusion of dissolved CO2 and carbonic acid in measuredctCO2. However, this difference presupposes that no dissolved carbon dioxide is lost to the atmosphere prior to analysis, but this is often not case because electrolyte samples are not handled anaerobically. Since ambient air contains less CO2 than blood, there is a tendency for dissolved CO2 to be lost from the sample if tubes are left uncapped. If this occurs, measured CO2 can decrease at a rate of 6 mEq/h. By contrast calculated bicarbonate is not associated with the same risk of pre-analytic variation because blood gas analyses are sampled anaerobically with minimal delay.

Synthesis and Structure-Activity Studies of Lissoclinum Peptide Alkaloids


In the previous chapter, a possible link between metal ion chelation properties of lissoclinum peptide alkaloids, carbon dioxide transport and biological function was already mentioned. However, to date the most extensively documented biological effect of these marine natural products is cytotoxicity.

Tables 1-3 summarize the reported cytotoxic activity for 18-, 21-, and 24-membered lissoclinum peptide alkaloids, respectively. Quite frequently, mouse leukemia cells (L1210), SV40 transformed fibroblasts (MRC5CV1), transitional bladder carcinoma cells (T24), and human colon cancer cells (HCT-116) were used in these evaluations. The most active compounds appear to be lissoclinamide 7 and ulithiacyclamide however, cell types and assay conditions have been widely varied for different natural products and research groups. The presence of contaminating cytotoxic impurities is a major concern with natural product samples. In the absence of any information on the biological mechanism of action of lissoclinum peptides, any conclusions as to the actual potency of these compounds are preliminary at best. The only pharmacological studies that are currently available focus on ulithiacyclamide and ulicyclamide. Ulithiacyclamide was found to have a strong inhibitory effect on protein synthesis and can potentiate the cytotoxicity of anticancer drugs such as bleomycin [102] . Interestingly, ulithiacyclamide self-distructs in the process of inhibiting cell growth. Ulicyclamide, in contrast, was shown to inhibit DNA and RNA syntheses [103] .

Table 1 . Cytotoxic activity of 18-membered lissoclinum peptides (IC50 [mg/mL]).

T24 cellsMRC5CV1 cellsHCT-116 cellsother cell linesreference
Bistratamide A5050 [3]
Bistratamide B&gt 100&gt 100 [3]
Bistratamide C 125 [4]
Bistratamide D 125 [4]
Cycloxazoline0.50.5 2 [5, 6]
Dolastatin E 22-40 [8]
Nostocyclamide 12 [10]
Raocyclamide A &lt 30[H]

Table 2 . Cytotoxic activity of 21-membered lissoclinum peptides (IC50[mg/mL).

L1210 cellsT24 cellsMRC5CV1 cellsHCT-116 cellsLympho-cytesreference
Lissoclinamide 1&gt 10 [12]
Lissoclinamide 2&gt 10 [12]
Lissoclinamide 3&gt 10 [12]
Lissoclinamide 4 11 12 [13, 14]
Lissoclinamide 5 1015 10, 20 [14, 17]
Lissoclinamide 6 7 [14]
Lissoclinamide 7 0.060.04 0.08 [17]
Lissoclinamide 8 61 8 [17]
Ulicyclamide7 [19]
Cyclodidemnamide 16 [20]

Table 3 . Cytotoxic activity of 24-membered lissoclinum peptides (IC [mg/mL]).

L1210 cellsT24 cellsMRC5CV1 cellsHCT-116 cellsother cell linesreference
Ascidiacyclamide &lt 10 [22]
Patellamide A3.9 [19]
Patellamide B2.0 [19]
Patellamide C3.2 [19]
Patellamide D 11 [13, 14]
Ulithiacyclamide0.350.150.2 0.01 [13, 19]
Tawicyclamide A 31 [32]
Tawicyclamide B 31 [32]

Several lissoclinum peptides show only moderate levels of cytotoxicity in cell assays. In spite of sub-micromolar activity against bladder carcinoma and SV40 transformed fibroblast cells, cycloxazoline (westiellamide) had no activity in solid tumor assays [6] .

Nostocyclamide (10) was shown to exhibit growth inhibitory activity against diatoms, chlorophyceae, and cyanobacteria (Anabaena P-9 and others) at 0.1 μM concentration [10] . These data support the notion that chemical defense directed against predators or competitors is a potential biological function of these secondary metabolites. Dendroamide A (but not B and C) was active in reversing multidrug-resistance due to inhibition of drug transport by P-glycoprotein [7] . Patellamide D (26) has also been reported to reverse multidrug-resistance in a human leukemia cell line [104] .

A comparison of the cytotoxic effects of naturally occurring lissoclinum peptides, synthetic cyclic peptides and relatively short linear segments served as the basis for the hypothesis that the oxazoline function is essential for cytotoxicity and that a cyclic skeleton might not be needed [105] . While this hypothesis has found considerable support [32] , no conclusive evidence for or against it, and no molecular rationalization for an oxazoline-induced cytotoxicity is available to date [106] .

Xx.4 Gas Transport in the Blood

The other major activity in the lungs is the process of respiration, the process of gas exchange. The function of respiration is to provide oxygen for use by body cells during cellular respiration and to eliminate carbon dioxide, a waste product of cellular respiration, from the body. In order for the exchange of oxygen and carbon dioxide to occur, both gases must be transported between the external and internal respiration sites. Both gases require a specialized transport system for the majority of the gas molecules to be moved between the lungs and other tissues.

Oxygen Transport in the Blood

The majority of oxygen molecules are carried from the lungs to the body’s tissues by a specialized transport system, which relies on the erythrocyte—the red blood cell. Erythrocytes contain hemoglobin, which serves to bind oxygen molecules to the erythrocyte (Figure). Heme is the portion of hemoglobin that contains iron, and it is heme that binds oxygen. One erythrocyte contains four iron ions, and because of this, each erythrocyte is capable of carrying up to four molecules of oxygen. As oxygen diffuses across the respiratory membrane from the alveolus to the capillary, it also diffuses into the red blood cell and is bound by hemoglobin. The following reversible chemical reaction describes the production of the final product, oxyhemoglobin (Hb–O2), which is formed when oxygen binds to hemoglobin. Oxyhemoglobin is a bright red-colored molecule that contributes to the bright red color of oxygenated blood.

Hemoglobin consists of four subunits, each of which contains one molecule of iron.

Function of Hemoglobin

Hemoglobin is composed of subunits, a protein structure that is referred to as a quaternary structure. Each of the four subunits that make up hemoglobin is arranged in a ring-like fashion, with an iron atom covalently bound to the heme in the center of each subunit. When all four heme sites are occupied, the hemoglobin is said to be saturated. Hemoglobin saturation of 100 percent means that every heme unit in all of the erythrocytes of the body is bound to oxygen. In a healthy individual with normal hemoglobin levels, hemoglobin saturation generally ranges from 95 percent to 99 percent.

Carbon Dioxide Transport in the Blood

Carbon dioxide is transported by three major mechanisms. The first mechanism of carbon dioxide transport is by blood plasma, as some carbon dioxide molecules dissolve in the blood. The second mechanism is transport in the form of bicarbonate (HCO3 – ), which also dissolves in plasma. The third mechanism of carbon dioxide transport is similar to the transport of oxygen by erythrocytes (Figure).

Carbon dioxide is transported by three different methods: (a) in erythrocytes (b) after forming carbonic acid (H2CO3 ), which is dissolved in plasma (c) and in plasma.

Dissolved Carbon Dioxide

Although carbon dioxide is not considered to be highly soluble in blood, a small fraction—about 7 to 10 percent—of the carbon dioxide that diffuses into the blood from the tissues dissolves in plasma. The dissolved carbon dioxide then travels in the bloodstream and when the blood reaches the pulmonary capillaries, the dissolved carbon dioxide diffuses across the respiratory membrane into the alveoli, where it is then exhaled during pulmonary ventilation.

Bicarbonate Buffer

A large fraction—about 70 percent—of the carbon dioxide molecules that diffuse into the blood is transported to the lungs as bicarbonate. Most bicarbonate is produced in erythrocytes after carbon dioxide diffuses into the capillaries, and subsequently into red blood cells. Carbonic anhydrase (CA) causes carbon dioxide and water to form carbonic acid (H2CO3), which dissociates into two ions: bicarbonate (HCO3 – ) and hydrogen (H + ). The following formula depicts this reaction:

At the pulmonary capillaries, the chemical reaction that produced bicarbonate (shown above) is reversed, and carbon dioxide and water are the products. Hydrogen ions and bicarbonate ions join to form carbonic acid, which is converted into carbon dioxide and water by carbonic anhydrase. Carbon dioxide diffuses out of the erythrocytes and into the plasma, where it can further diffuse across the respiratory membrane into the alveoli to be exhaled during pulmonary ventilation.


About 20 percent of carbon dioxide is bound by hemoglobin and is transported to the lungs. Carbon dioxide does not bind to iron as oxygen does instead, carbon dioxide binds amino acids on the globin portions of hemoglobin to form carbaminohemoglobin , which forms when hemoglobin and carbon dioxide bind. When hemoglobin is not transporting oxygen, it tends to have a bluish-purple tone to it, creating the darker maroon color typical of deoxygenated blood. The following formula depicts this reversible reaction:

Similar to the transport of oxygen by heme, the binding and dissociation of carbon dioxide to and from hemoglobin is dependent on the partial pressure of carbon dioxide. Because carbon dioxide is released from the lungs, blood that leaves the lungs and reaches body tissues has a lower partial pressure of carbon dioxide than is found in the tissues. As a result, carbon dioxide leaves the tissues because of its higher partial pressure, enters the blood, and then moves into red blood cells, binding to hemoglobin. In contrast, in the pulmonary capillaries, the partial pressure of carbon dioxide is high compared to within the alveoli. As a result, carbon dioxide dissociates readily from hemoglobin and diffuses across the respiratory membrane into the air.

Chapter Review

Oxygen is primarily transported through the blood by erythrocytes. These cells contain a protein molecule called hemoglobin, which is composed of four subunits with a ring-like structure. Each subunit contains one atom of iron bound to a molecule of heme. Heme binds oxygen so that each hemoglobin molecule can bind up to four oxygen molecules. When all of the heme units in the blood are bound to oxygen, hemoglobin is considered to be saturated.

Carbon dioxide is transported in blood by three different mechanisms: as dissolved carbon dioxide, as bicarbonate, or as carbaminohemoglobin. A small portion of carbon dioxide remains. The largest amount of transported carbon dioxide is as bicarbonate, formed in erythrocytes. For this conversion, carbon dioxide is combined with water with the aid of an enzyme called carbonic anhydrase. This combination forms carbonic acid, which spontaneously dissociates into bicarbonate and hydrogen ions. As bicarbonate builds up in erythrocytes, it is moved across the membrane into the plasma. At the pulmonary capillaries, bicarbonate re-enters erythrocytes and the reaction with carbonic anhydrase is reversed, recreating carbon dioxide and water. Carbon dioxide then diffuses out of the erythrocyte and across the respiratory membrane into the air. An intermediate amount of carbon dioxide binds directly to hemoglobin to form carbaminohemoglobin.

Carbon Monoxide Poisoning

While carbon dioxide can readily associate and dissociate from hemoglobin, other molecules such as carbon monoxide (CO) cannot. Carbon monoxide has a greater affinity for hemoglobin than oxygen. Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported through the body (see the figure below). Carbon monoxide is a colorless, odorless gas and is therefore difficult to detect. It is produced by gas-powered vehicles and tools. Carbon monoxide can cause headaches, confusion, and nausea long-term exposure can cause brain damage or death. Administering 100 percent (pure) oxygen is the usual treatment for carbon monoxide poisoning. Administration of pure oxygen speeds up the separation of carbon monoxide from hemoglobin.

Regulation of Blood Acidity

What Happens to the Breathing System When We Exercise?

Because the release of carbon dioxide into the blood shifts the carbonate buffer equilibrium, the body needs to remove the excess carbon dioxide in order to regulate the pH level 3. Therefore, blood carries the carbon dioxide to the lungs where it is exhaled 3. The speed and depth of breathing regulates the amount of carbon dioxide that is exhaled 23. Faster, deeper breathing exhales more carbon dioxide 3.


1. LARGE SURFACE AREA-human lungs consists of million of alveolus.
2. THIN-wall of alveolus consists of one layer of thin squamous epithelial cells to facilitate diffusion of gaseous such as o2 and co2.
3. MOIST-inner surface of alveolus is lined with fluid and its surface tension is lowered by secretion of surfactant from special septal cells in the alveolus . This fluid dissolve respiratory gaseous for diffusion and speed up gas exchange.
4. Each alveolus is covered by a dense of network capillaries which carries away the oxygen and keep the partial pressure low.


-The haemoglobin in red blood cells is responsible in transporting oxygen and carbon dioxide.
-Breathing allows the inspired air to come in contact with the blood vessel that cover the alveoli.



-Haemoglobin is a complex conjugated protein
-Quaternary in nature
-Protein consists of four polypeptide chains , two alpha and two beta
-These polypeptide chains are globular in nature and called globin
-Each haem group can associate with one molecule of oxygen that gives blood its bright red colour
-Process of associating oxygen with the haem group is called oxygenation
-Its a loose combination which allows dissociation occurs easily


-RBC are round disc , concave on each side(biconcave) and do not contain nucleus. Gives it an extremely high surface area to volume ratio for more efficient gaseous exchange.
-In the blood , only small portion of oxygen can dissolve in plasma as the solubility of o2 to plasma is very low.
-Haemoglobin in RBC increase the ability of blood to transport o2 by about 65 to 70 times.
-The main function of haemoglobin is to carry oxygen but it can help to transport c02.
-It can do so efficiently because it can bind with oxygen at very low partial pressure of oxygen.
[email protected] the first o2 bind with the first haem group, the haemoglobin molecule changes shape slightly. This facilitates the binding of the next oxygen.
-When there is a drop in partial pressure of oxygen, haemoglobin will release oxygen.
-In the tissue, the partial pressure of oxygen is lower that at the alveoli , the tissues are continuously supplied with oxygen.
-CARBON DIOXIDE is more soluble in blood than oxygen.

Question 1.
Which one of the following mammalian cells is not capable of metabolising glucose to carbon-dioxide aerobically?
(a) unstraited muscle cells
(b) liver cells
(c) red blood cells
(d) white blood

Question 2.
The process of migration of chloride ions from plasma to RBC and of carbonate ions from RBC to plasma is:
(a) chloride shift
(b) ionic shift
(c) atomic shift
(d) Na+ pump

Question 3.
When CO2 concentration in blood increases, breathing becomes:
(a) shallower and slow
(b) there is no effect on breathing
(c) slow and deep
(d) faster and deeper

Answer: (d) faster and deeper

Question 4.
Intercostal muscles occur in:
(a) abdomen
(b) thigh
(c) ribs
(d) diaphragm

Question 5.
Very high number of alveoli present in a lung is meant for
(a) More space for increasing volume of inspired air
(b) More area for diffusion
(c) Making the organ spongy
(d) Increasing nerve supply

Answer: (b) More area for diffusion

Question 6.
Azygous lobe is part of
(a) Lung
(b) Kidney
(c) Larynx
(d) Palate

Question 7.
The alveolar epithelium in the lungs is:
(a) nonciliated columnar
(b) nonciliated squamous
(c) ciliated columnar
(d) ciliated squamous

Answer: (b) nonciliated squamous

Question 8.
How much oxygen, blood supplies to tissues in one circulation
(a) 75%
(b) 1.34%
(c) 25%
(d) 7%

Question 9.
How oxygen enters in blood from alveoli of lungs
(a) Pressure of CO2
(b) Simple diffusion
(c) By Hb
(d) None of the Above

Answer: (b) Simple diffusion

Question 10.
The carbon dioxide is transported via blood to lungs as:
(a) dissolved in blood plasma
(b) in the form of carbonic acid only
(c) in combination with haemoglobin only
(d) carbaminohaemoglobin and as carbonic acid

Answer: (d) carbaminohaemoglobin and as carbonic acid

Question 11.
Thoracic cavity is enlarged by contraction of
(a) Internal Intercostal muscles
(b) Diaphragm
(c) Lungs
(d) All of above

Question 12.
The two organisms which breath only through their moist skin are
(a) Frog and earthworm
(b) Fish and frog
(c) Leech and earthworm
(d) Fish and earthworm

Answer: (c) Leech and earthworm

Question 13.
Chloride shift for the transport of
(a) O2
(b) CO2
(c) CO
(d) Ozone

Question 14.
Increased asthmatic attacks in certain seasons are related to
(a) Inhalation of seasonal pollen
(b) Hot and humid environment
(c) Low temperature
(d) Eating fruits preserved in containers

Answer: (a) Inhalation of seasonal pollen

Question 15.
The lungs are enclosed in a covering called
(a) Perichondrium
(b) Pleural membrane
(c) Pericardium
(d) Peritoneum

Answer: (b) Pleural membrane

Question 16.
The exchange of gases in the alveoli of the lungs takes place by:
(a) simple diffusion
(b) osmosis
(c) active transport
(d) passive transport

Answer: (a) simple diffusion

Question 17.
Oxygen dissociation curve of haemoglobin is:
(a) Sigmoid
(b) Hyperbolic
(c) Linear
(d) Hypobolic

Question 18.
A film of _____ lines lung alveoli that lowers _____ of the alveoli and makes breathing _____
(a) Lecithin, surface tension, easier.
(b) Pleuron, surface tension, easier.
(c) Cuticle, bacterial inflammation, difficult.
(d) Cuticle, inflating, difficult.

Answer: (a) Lecithin, surface tension, easier.

Question 19.
Opening to the trachea is covered by a small flap of tissues termed as the ______.
(a) Glottis
(b) Trachea
(c) Epiglottis
(d) Larynx

Question 20.
Which one of the following mammalian cells is not capable of metabolising glucose to carbon dioxide aerobically?
(a) Unstriated muscle cells
(b) White blood cells
(c) Liver cells
(d) Red blood cells

Question 21.
The regulatory centres for respiration are located in :
(a) Diencephalon and pons
(b) medulla oblongata & pons
(c) pons & cerebellum
(d) cerebellum and medulla oblongata

Answer: (b) medulla oblongata & pons

Question 22.
The pneumotaxic centre is present in
(a) Medulla
(b) Cerebrum
(c) Cerebellum
(d) Pons varolii

Question 23.
In alveoli of the lungs, the air at the site of gas exchange, is separated from the blood by
(a) alveolar epithelium only
(b) alveolar epithelium and capillary endothelium
(c) alveolar epithelium, capillary endothelium and tunica adventitia
(d) alveolar epithelium, capillary endothelium, a thin layer of tunica media and tunica adventitia

Answer: (b) alveolar epithelium and capillary endothelium

Question 24.
Habit of Cigarette smoking can lead to :
(a) loss of cilia lining the respiratory tract
(b) emphysema
(c) coughing
(d) All of the Above

Answer: (d) All of the Above

Question 25.
During inspiration muscles of diaphragm
(a) Contracts
(b) Expands
(c) No effect
(d) Coiled like string

Question 26.
If TLC is 5500ml, IRV is 2950ml, ERV is 900ml and TV is 500ml then what will be value of RV?
(a) 2550ml
(b) 1100ml
(c) 1200ml
(d) 1150ml

Question 27.
Respiration in insects is direct due to exchange of gases
(a) Directly with the air outside through body surface
(b) By tracheal tubes directly with haemocoel which then exchange with tissues.
(c) Directly with coelomic fluid
(d) Directly with the air in tubes

Answer: (b) By tracheal tubes directly with hemocoel which then exchange with tissues.

Question 28.
Book lungs are respiratory organs of
(a) Mammals
(b) Mollusca
(c) Earthworm
(d) Arachnida

Question 29.
Expiration involves
(a) Relaxation of diaphragm and intercostal muscles
(b) Contraction of diaphragm and intercostal muscles
(c) Contraction of diaphragm muscles
(d) Contraction of intercostal muscles

Answer: (a) Relaxation of diaphragm and intercostal muscles

Question 30.
Cartilaginous rings in trachea are incomplete at which surface.
(a) Dorsal
(b) Ventral
(c) Lateral
(d) Ventrolateral

Question 31.
What percentage of CO2 flows in blood in form of bicarbonates
(a) 7%
(b) 23%
(c) 50%
(d) 70%

Question 32.
People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude of 5400 metres have around 8 million. This is because at high altitude
(a) atmospheric O2 level is less and hence more RBCs are needed to absorb the required amount of O2 to survive
(b) there is more UV radiation which enhances RBC production
(c) people eat more nutritive food, therefore more RBCs are formed
(d) people get pollution-free air to breathe and more oxygen is available

Answer: (a) atmospheric O2 level is less and hence more RBCs are needed to absorb the required amount of O2 to survive

Question 33.
Wall of alveoli is composed of
(a) Simple squamous epithelium
(b) Simple cuboidal epithelium
(c) Pseudostratified epithelium
(d) Simple columnar epithelium

Answer: (a) Simple squamous epithelium

Question 34.
Air is breathed through:
(a) Trachea — lungs — larynx — pharynx — alveoli
(b) Nose — larynx — pharynx — bronchus — alveoli — bronchioles
(c) Nostrils — pharynx — larynx — trachea — bronchi — bronchioles — alveoli
(d) Nose — mouth — lungs

Answer: (c) Nostrils — pharynx — larynx — trachea — bronchi — bronchioles — alveoli

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