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class 10th biology chapter 1 gaseous exchange | the mechanism of breathing | the lungs | bad effects of smoking

This chapter covers the concept of gaseous exchange in organisms. Animals use specialized respiratory systems for this gaseous exchange. Plants lack specialized respiratory systems for,


Gaseous Exchange

Cellular Respiration and Gaseous Exchange

Organisms get energy from food. For this purpose, they carry out a chemical process known as cellular respiration During it, the food molecules are oxidized. The C-H bonds present in food molecules are broken. It results in the release of energy. In most organisms, cellular respiration occurs in the presence of oxygen And in the process, Carbon Dioxide can be produced.For cellular respiration, organisms get oxygen from their environment (air or water). They also release carbon dioxide to the environment.


Breathing is a physical process in Which Animals Move Air In And out of their Bodies!!This is done to the get Oxygen from the air and release carbon dioxide into it.Breathing and respiration are not the same processes.

10.1-Gaseous Exchange in Plants

During the day time, all plant cells are carrying out cellular respiration while their green parts are carrying out photosynthesis.

. For respiration (plants use oxygen which is produced during photosynthesis. During respiration, they release carbon dioxide to the environment.

So, during day time leaves are releasing oxygen and taking carbon dioxide from the environment. At night, all  the cells are Breathing While There is no photosynthesis.

Process of Gaseous Exchange

In plants, the gaseous exchange between body and the environment occurs through the surface. The outer surface of root, stem and leaves is epidermis. It also allows the exchange of gasest In leaves and young stems, the epidermis has small pores called stomatal Air moves in and out through stomata. Inside body, gaseous exchange occurs between cells and air.

In Wanden Trunks, The entire surface is covered with bark,gas can not be exchanged through the bark.the bark has special holes called lenticels, which allow the exchange of gasses with the atmosphere.

10.2-Gaseous Exchange in Humans

In humans, gaseous exchange is done by a specialized system called the respiratory system, it is responsible for breathing and gaseous exchange.

The Air Passageway

 When air enters the body, it passes through the tubes  the attached the lungs. After gaseous exchange, air moves from the lungs to outside through the same tubes. These connected tubes are collectively called air passageway. it consist of the following parts.

1:- Nostrils and Nasal cavity: Air enters the cavity of nose, called nasal cavity, through nostrils The nasal cavity is present between nostrils and pharynx. It is made of two narrow cavities. There are fine hairs and mucus on the walls of nasal cavity. The hairs filter the incoming air by trapping large dust particles. The small dust particles stick with mucus. Mucus also warms the air and keeps its temperature nearly equal to the temperature of the body.

2:- Pharynx: The nasal cavity opens into pharynx. At the floor of pharynx there is an opening called glottiesit open  in larynx. The glottis is protected by a flap called epiglottis.

3. Larynx: It is a box present between pharynx and trachea.

4:- Trachea and Bronchi:

A trachea (windpipe) is a tube that is about 12 cm long. It starts after the larynx and ends at two branches called bronchi).

The inner walls of trachea and bronchi are lined with mucus and cilia. Mucus traps fine particles of dust or bacteria from the air. Cilia move these particles and mucus upwards to the oral cavity.

5. Bronchioles and Alveoli:inside lungs, both bronchi continue to divide into very small tubes called bronchioles. Each bronchiole ends at a duct (The duct opens into a cluster of pouches. These pouches are called alveoli (singular: alveolus). Each alveolus is thin-walled. It is also surrounded by blood capillaries. When air reaches alveoli, gaseous exchange takes place. Oxygen moves from the air into the blood, and carbon dioxide passes out of the blood into the air in the alveoli.

The Lungs

The Breast cavity contains a pair of lungs.From above the top and sides,  the lungs are closed to chest wall. While, there is a thick muscular structure, called diaphragm below lungs.

Lungs are spongy and elastic organs. The left lungs is smaller then decades.There are two lobes in the left lung while right lung has three lobes. Lungs are enclosed in a double membrane called pleural It contains a pleural fluid for reducing friction between lungs and the chest wall.

Blood Circulation in Lungs:

Pulmonary Arteries carry blood from the heart to the lungs.Inside each lung, it divides into arterioles. The arterioles divide further and make capillaries around the alveoli. After surrounding the alveoli, the capillaries join to form venules. The venules join to form pulmonary vein which carries the oxygenated blood back to the heart.

The Mechanism of Breathing

Physical movements to take air to the lungs and then remove air from the lungs are called breathing.  There are two stages of exhalation and exhalation.

Mechanism of Breathing

1. Inhalation (inspiration): 

Inhalation means intake of air to the lungs. The following events occur during inhalation;

The inter-coastal muscles contract. Due to this contraction, ribcage expands. At the same time, diaphragm also contracts and moves down. These two contractions (of inter-coastal muscles and diaphragm) increase the volume of the chest. So air pressure inside the chest is reduced and the outside air is moves into the lungs.

2. Exhalation (expiration): 

Exhaling means expelling air from the lungs. The following events occur during exhalation:

Ben shore muscles relax. This causes the rib cage to move inward. At the same time the diaphragm relaxes and moves upwards. Both of these movements reduce the volume of the chest. So the air pressure inside the chest increases and the air inside goes out.

The Rate of Breathing

It sends messages to the muscles of ribs and diaphragm at greater speed. The speed of contraction and relaxation of these muscles increases, So, the breathing rate increases up to 30-40 times per minute.

10.3-Respiratory Disorders

1. Bronchitis jo

The inflammation in bronchi or bronchioles is called bronchitis. In bronchitis, the walls of bronchi or bronchioles swell. The inner space of these tubes decreases. Bronchitis may be short term i.e. acute (two weeks) or long term i.e. chronic (years). In long-term bronchitis, mucus-producing cells in the walls of bronchi increase in number. Thus there is thick mucus in bronchi. It obstructs the inhaled and exhaled air.

Causes:  This inflammation may be due to infections by viruses or bacteria. It may also be due to chemical irritants (e.g. tobacco smoke).

Symptoms:  Patient suffers from coughing, wheezing, fever, chills and shortness of breath.

Treatment: Short-term bronchitis cures without treatment in two weeks. If conditions do not improve, and thw patient is given medication. Antibiotics are used. when bronchitis is caused to  the bacterial infection. When bronchitis is due to viral infection, anti-viral medicines are used. Coughing helps to remove irritants from bronchi.

2. Emphysema 

(in emphysema, the walls of alveoli become weak and then rupture. Thus one larger air space is created instead of many small ones. Due to it, there is less surface for gaseous exchange. Moreover, air is trapped inside alveoli and the patient cannot inhale properly.

Causes: The main cause of emphysema is long-term exposure to irritants present in air e.g. tobacco smoke, manufactured fumes and other air pollutants.

Symptoms: Patient of emphysema feels difficulty in breathing (shortness of breath).

Treatment: Emphysema cannot be cured completely.However, Disease progressions can be slowed down. Patients are given drugs that help relieve coughing and shortness of breath.

3. Pneumonia

Pneumonia is an inflammation in the lungs, due to infection in alveoli. Alveoli are filed with pus due to the pneumonia.

Causes: Pneumonia may be caused by bacteria (bacterial pneumonia), viruses (viral pneumonia) or fungi (fungal pneumonia).

Symptoms: The pneumonia patient suffers from high fever, chills, shortness of breath, and cough with sputum.

Treatment: Vaccines are available to prevent bacterial pneumonia. Bacterial pneumonia is treated by using antibiotics. The viral and fungal pneumonia are treated by using antiviral and antifungal drugs.

4. Asthma

Asthma is a chronic (long-term) inflammation of the bronchi in which bronchi and bronchioles swell and are constricted.

Symptoms: The patient experiences recurring attacks of shortness of breath, wheezing (whistling sound when breathing), coughing and chest tightness.

Causes: The reasons of asthma may be genetic or environmental.

Environmental causes include allergen sensitivities (allergens such as pollen, cold, smoke or other chemicals in the air). When asthma sufferers inhale such allergens, they may develop an asthma attack.

Treatment: Asthma patients are given short-term treatments. They use medicines which contain chemicals to dilate the bronchi and bronchioles. Such "bronchodilators" are given in the form of Inhalers.

5. Lung Cancer

Cancer means uncontrolled increase in the number of cell in any part of the body. When a combination of dysfunctional cells forms in the lungs, it is called lung cancer.

Causes: The main causes of any cancer are carcinogens (cancer causing chemicals), ionizing radiation and viral infection.Smoking plays an important role in lung Cancer.Cigarette smoke contains more than 69 known carcinogens.

Passive smoking i.e the inhalation of smoke from another's smoking is also a cause of lung cancer. The smoke from the upper burning portion of cigarette is more dangerous than smoke exhaled by the smoker. If a smoker stops smoking, the damage to his lungs is repaired.

Symptoms: The most cammon symptoms are Difficulty breathing, coughing ( including coughing up blood) and the weight loss.

Treatment: One Or more Treatments are given to lungs cancer patients, including surgery. Chemotherapy, or radiation therapy.

Bad Effects of Smoking

Smokers Have a Much Deadly disease.The important risks of smoking are the cancers in lungs, kidneys, oral cavity, larynx, breast, bladder, oesophagus, pancreas and stomach. These cancers do claim a lot of lives. Cigarette Smoke affects  the whole  body.

Smoking is harmful due to the chemicals in tobacco. Tobacco smoke contains over 4,000 different chemicals. Of these,more than 69 are known carcinogens. The effects of some chemicals found in cigarettes are given below.

. Nicotine (addictive drug) is the major component of cigarettes. It is a powerful poison and damages many organs including brain. It also hardens the walls of arteries and results in heart problem.

• Carbon monoxide is produced when tobacco is burnt during smoking. It is a poisonous gas. It combines with red blood cells and prevents oxygen transport.

When it is inhaled along with cigarette smoke, it is deposited in the lungs. It reduces the surface for gaseous exchange.

. Ammonia (toilet cleaner) frees nicotine from tobacco turning it into a gasiti poisonous for the body.

. There are many other irritants in cigarettes. These damage the air passageway and cause many respiratory diseases, including cancer.

Other Effects of Smoking:

Smoking also increases blood cholesterol levels. It also increases blood pressure and weakens blood vessels.

Smoking is an important factor in the staining of teeth. Bad breath is common among smokers.

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