Class 11 Biology ch 17 breathing and exchange of gases.


Class 11 Biology ch 17 breathing and exchange of gases

Breathing:- The process of exchange of oxygen from the atmosphere with carbon dioxide produced by the cells.


Inspiration:- Oxygen from fresh air taken by the lungs and diffuses into the blood.

Expiration:- Co2 given up by venous blood in the lungs is sent out to exteriers.

Respiration:- The sum total of physical and chemical processes by which oxygen and carbohydrates are assimilated into the system and oxidation products like co2 and h2o are given off.


Question. Difference between Breathing and Respiration.

Solution: Breathing: It is simply an intake of fresh air and removal of foul air. It is a physical process. No energy is released. It is an extracellular process.

Respiration: It is the oxidation of food to form co2.h2o and energy. It is a bio chemical process. Energy is released in form of A.T.P. It is an intracellular process.


Human Respiratory system

Human respiratory system consists of a pair of nostrils, pharynx, larynx, bronchi and bronchioles that finally terminate into alveoli.

Nasal chamber opens into pharynx that leads to larynx. It contains voice box that help in sound production.

The trachea, primary, secondary and tertiary bronchi and intial bronchioles are supported by an complete cartilaginous rings to prevent collapsing in absence of air.

each bronchiole terminate into an irregular walled, vascularized bg like structure called alveoli.

Respiratory system

Conducting part:- Include nostrils, pharynx, larynx and trachea. main functions include

  1. Transport of atmospheric air to alveoli.
  2. Removing foreign particles from air humidifying it and bringing it to body temperature.

Exchange parts:- they are alveoli. It is the site of actual diffusion of oxygen and carbon dioxide between blood and atmospheric air.

Steps of respiration

Breathing in which oxygen rich atmospheric air is diffused in and carbon dioxide rich alveolar air is diffused out.

Diffusion of gases across alveolar membrane.

Transport of gases by blood. diffusion of oxygen and carbon dioxide between blood and tissue. utilization of oxygen by cells to obtain energy and release of carbon dioxide.

Mechanism of breathing:-

Breathing involves inspiration and expiration during inspiration air is drawn in and during expiration, alveolar air is released out.

Class 11 Biology ch 17 breathing and exchange of gases.

Movement of air in and out take place due to difference in pressure gradient.

Inspiration occurs when pressure inside the lungs is less and expiration occur when pressure is more in the lungs than outside.

The diaphragm and external and internal intercostal muscles between the ribs help in developing pressure gradient due to change in volume.

The contraction of intercostal muscles lifts the ribs and sternum causing an increase in volume of thoracic cavity that result in decrease in pressure than the atmospheric pressure. This causes inspiration.

Class 11 Biology ch 17 breathing and exchange of gases.

Relaxation of the diaphragm and intercostal muscles reduce the thoracic volume and increase the pressure causing expiration.

The volume of air involved in breathing movement is estimated by using spirometer for clinical assessment of pulmonary functions.

Respiratory volume and capacities:-

Tidal volume- Volume of air inspired or expired during a normal respiration. It is about 500ml in healthy volume.

Inspiratory reserve volume- Additional volume of air a person can inspire by forceful inspiration. It is about 2500ml to 3000ml.

Total lung capacity- Total volume of air accommodated in lung at the end of forced inspiration RV+ERV+TV+IRV+ vital capacity.

Expiratory reserve volume- Additional volume of air a person can expire by forceful expiration. It is about 1000 ml to 1100ml.

Residual volume- Volume of air remaining in lung even after a forceful expiration. It is about 1100ml to 1200ml.

Vital capacity- Maximum volume of air a person can breath in after a forceful expiration. ERV+TV+IRV.

Exchange of gases:-

Exchange of gases take plcae at two sets.

  1. Alveoli to blood
  2. Between blood and tissue

Exchange of gasses occur by simple diffusion due to pressure gradient, solubility of the gases and thickness of membrane. Pressure contributed by individual gas in a mixture of gas is called partial pressure represent by pO2 and pCO2.

Partial pressure of o2 and co2 at different part involved in diffusion varies from one part to another and moves from higher partial pressure to lower pressure.

Solubility of co2 is 20-25 times more than the solubility of o2, so co2 diffuse , much fast through membrane.

Diffusion membrane is three layered thick that is alveolar squamous epithelium, endothelium of alveolar capillaries and basement substance between them.

Transport of gases:-

Blood is the medium of transpport for co2 and o2, most of the oxygen (97%) is transported through RBC and remaining 3% by blood plasma.

20-25% of co2 is transported by RBC, 70% as bicarbonate and rest 7% is dissolved state by blood plasma.

Transport of oxygen:-

Hemoglobin in RBC combines with o2 to form oxyhemoglobin. Each o2 hemoglobin combines with four oxygen molecules. Binding of o2 released with partial pressure of o2 and co2, hydrogen ion concentration and temperature.

Percentage saturation of hemoglobin and partial pressure of o2 form sigmoid curve. In the alveoli, pO2 is more and pCO2 is less. Less hydrogen ions concentration and lower temperature favour the binding of O2 with hemoglobin where opposite condition in tissues favour the dissociation of oxyhemoglobin.

Regulation of respiration:-

Huan beings have the ability to maintain and moderate the rate of respiration to fulfill the demand of body tissue by normal system. Respiratory rhythm center is located in medulla region in hind brain and pneumotoxic center in pons to moderate the function of respiratory rhythm center.

Chemo sensitive area near rhythm center highly sensitive to C and H+ ions, that ultimately control the respiratory rate. O2 do not play major role in controlling rate of respiration.

Functions of respiration:-

  1. Energy production
  2. Maintenance of acid – base balance
  3. Maintenance of temperature
  4. Return of blood and lymph

Mountain sickness- Is the condition characterized by the ill effect of hyparia (shortage of o2) in the tissues at high altitude commonly to person going to high altitude for first time.

Class 11 Biology ch 17 breathing and exchange of gases.
Class 11 Biology ch 17 breathing and exchange of gases.


  1. Loss of appetite, nausea and vomiting occurs due to expansion of gasses in digestive system.
  2. Breathlessness occurs because of pulmonary oedema.
  3. Headache, depression, disorientation, lack of sleep, weakness and fatigue.

Disorders of respiratory system:-

Asthma- It is due to allergic to foreign particles that affect the respiratory tract. The symptoms include coughing, wheezing and difficulty in breathing. This is de to excess of mucus in wall of respiratory tract.

Emphysema- Is the inflation or abnormal distension of the bronchioles or alveolar sacs of lungs. This occur due to destroying of septa between alveoli because of smoking and inhalation of other smokes. the exhalation becomes difficult and lungs remains infated.

Occupational respiratory disorder- Occur due to occupation of individual. This id caused by inhalation of gas, fumes present in surrounding of work place. This include silicasis, asbestases due to exposer of silica and asbestos. The symptom include proliferation of fibrous connective tissue of upper part of lungs causing inflammation.

Pneumonia- It is acute infection of the alveoli of the lungs due to to bacterieum streptococcus pneumonia. Alveoli became acutely inflamed and most of air space of the alveoli is filled with fluid and dead white blood corpuses limited gaseous exchange.


Leave a Comment

Your email address will not be published. Required fields are marked *