Solved Exercise, Bio-11, Ch-13


(i) ________ is the most abundant protein in the world. (Rubisco)

(ii) Haemoglobin is a complex molecule which contains 9512 atoms and _______ amino acids. (574)

(iii) The opening of larynx is called ________. (glottis)

(iv) When the smaller bronchi attain the diameter of _______ mm or less they are called bronchioles. (1 mm)

(v) There are about ________ stomata per square centimeter of leaf surface of tobacco plant. (12000)


(i) ATP is generated during organismic respiration. (FALSE)

CORRECT: ATP is generated during cellular respiration.

(ii) Water is a better respiratory medium than air. (FALSE)

CORRECT: Air is a better respiratory medium than water.

(iii) The earthworm does not possess specialized organs for respiration. (TRUE)

(iv) In parabronchi of birds, the blood flows in the opposite direction of air flow. (TRUE)

(v) Ring shaped cartilages are present in trachea of man. (FALSE)

CORRECT: C shaped cartilage rings are present in trachea of man.


(i) Air spaces between mesophyll cells of a leaf comprise _______ of the total volume.

(a)   20%

(b)   30%

(c)   40%

(d)   50%

EXPLANATION: The air spaces between mesophyll cells in a leaf play constitute about 40% of the total volume, allow for the movement of gases like carbon dioxide and oxygen. This facilitates efficient photosynthesis by providing a pathway for carbon dioxide to reach the chloroplasts where it is used to produce sugars, and for oxygen to be released as a byproduct.

(ii) The respiratory system is most efficient in:                                     

(a)   Snake

(b)   Man

(c)   Bird

(d)   Fish

EXPLANATION: The avian respiratory system is highly efficient due to features like unidirectional airflow, air sacs, and crosscurrent exchange, enabling optimal oxygen uptake and carbon dioxide removal during both inhalation and exhalation.

(iii) Respiratory pigment present in muscles is called:

(a)   Myoglobin

(b)   Globin

(c)   Hemoglobin

(d)   Hemocyanin

EXPLANATION: Myoglobin is haemoglobin-like iron-containing protein pigment occurring in muscle fibers. Myoglobin is also known as muscle haemoglobin. It serves as an intermediate compound for the transfer of oxygen from haemoglobin to aerobic metabolic processes of the muscle cells. It can also store some oxygen. Myoglobin consists of just one polypeptide chain associated with an iron containing ring structure which can bind with one molecule of oxygen. The affinity of myoglobin to combine with oxygen is much higher as compared to haemoglobin.

(iv) Blood contains _______ oxygen when hemoglobin is 98% saturated per 100 ml of blood: 

(a)   19.6 ml

(b)   18.6 ml

(c)   17.6 ml

(d)   16.6 ml

EXPLANATION: The maximum amount of oxygen which normal human blood absorbs and carries at the sea-level is about 20ml/100ml of blood. When an oxygen tension is 115 mm mercury, haemoglobin is 98 percent saturated and, therefore, contains 19.6 ml of oxygen per 100 ml of blood.

(v) How much air lungs can hold when they are fully inflated?             

(a)   5 liter

(b)   4 liter

(c)   4.5 liter

(d)   3.5 liter

EXPLANATION: In an adult human being when the lungs are fully inflated the total inside capacity of lungs is about 5 liters.



Breathing or Organismic respiration or ventilation is the exchange of gases between the organism and the environment.


Cellular respiration is the process by which cell utilizes oxygen, produces carbon dioxide, extracts and conserves the energy from food molecules in biologically useful form, such as, ATP.

Concentration of CO2 in Blood:

Arterial blood contains about 50 ml of carbon dioxide per 100 ml of blood whereas venous blood has 54 ml of carbon dioxide per 100 ml of blood. So, the percentage of CO2 in arterial blood is 50% and in venous blood is 54%.

In an adult human being when the lungs are fully inflated, the total inside capacity of lungs is about 5 liters. 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. In other words, there is a residual volume of 1.5 liters even during exercise which cannot be expelled.

The products formed during photorespiration are:

RuBP ⟶ Glycolate ⟶ Glycine ⟶ Serine + CO2

Water is 8000 times denser than air.


Air is better respiratory medium than water because oxygen can be obtained more easily from air than from water because of many reasons:

(1) Oxygen content of air is much higher than that of equal volume of water. A liter of water cannot contain even 10 ml of oxygen, whereas oxygen content of fresh air is about 200 ml per liter.

(2) Oxygen diffuses about 8000 times more quickly in air than in water.


Photorespiration may be defined as: “The respiratory activity occurring in plants during day-time is called photorespiration.” & “Photorespiration is the process in which ribulose bisphosphate carboxylase/oxygenase (rubisco) fixes oxygen instead of carbon dioxide which results in lowering the overall rate of carbon dioxide fixation and plant growth.” & “The pathway in which RuBP is converted into serine, is called photorespiration.”

Photorespiration is the reverse of Calvin cycle because here carbon dioxide is released, instead of fixation into carbohydrates, and oxygen is absorbed. In most plants, photorespiration reduces the amount of carbon fixed into carbohydrates by 25%.

Organelles Involved in Photorespiration: The organelles involved in photorespiration are:

(1) Chloroplasts (2) Peroxisomes (3) Mitochondria.

Products of Photorespiration: The products formed during photorespiration are:

RuBP ⟶ Glycolate ⟶ Glycine ⟶ Serine + CO2

Cockroaches have a network of tiny air tubules or tracheoles in cockroach end into blind ducts partly filled with fluid, in which the oxygen dissolves. These surround the organs and the tissues and directly supply oxygen to the living cells. A concentration gradient is set up between them and the spiracular openings and oxygen diffuses into the trachea from the outside air. This respiratory system facilitates the exchange of gases without the need for specialized respiratory organs like lungs.

The respiratory system of birds is highly efficient and elaborate due to several key adaptations:

(1) Air Sacs: Birds have a system of air sacs in addition to lungs. These air sacs allow for a unidirectional flow of air through the respiratory system, ensuring a continuous supply of oxygen. This is in contrast to mammals, where air moves bidirectionally in and out of the lungs.

(2) Crosscurrent Exchange: As the air moves through the avian lungs, it flows in the opposite direction to the blood flow. This creates a crosscurrent exchange, maximizing the efficiency of oxygen uptake and carbon dioxide removal.

(3) High Metabolic Rate: Birds, especially those engaged in flight, have high metabolic rates. The avian respiratory system meets these demands by efficiently extracting oxygen from the air, enabling sustained energy production.

(4) Reduced Dead Space: The avian respiratory system minimizes dead space, ensuring that a higher percentage of the inhaled air participates in gas exchange, contributing to greater respiratory efficiency.

These adaptations collectively make the respiratory system of birds one of the most efficient and sophisticated among vertebrates.

Consult textbook at page 269 —270.

Consult textbook at page 274.

Consult textbook at page 267 — 268.

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