NCERT Class 9 Science Chapter 13 Notes Why Do We Fall ill- Download PDF Notes

NCERT Class 9 Chapter 13 Class Notes

Why do we fall ill?

• Health and disease are very crucial issues in the human population.
• The cell is regarded as the basic unit in the life of an organism. The process of developing new cells is a continuous one. Cells form tissues and organs. The activities which take place inside a cell are interconnected. This requires some raw materials and energy. Food is the basic requirement for the functioning of cells and tissues.

Health and its Failure

The Health:

A state of complete well-being to function well physically, mentally, and socially is called health.

Personal And Community Issues Both Matter For Health

• An organism's health is dependent on its surroundings and physical environment.
• The physical environment in which we live is decided by our social environment. Thus, it plays an important role in an individual's health.
• Poor health is caused by throwing garbage and open-drain water around. It causes a significant amount of damage to an individual's health. Thus, the cleanliness of public areas like the neighbourhood is of utmost importance.
• Consumption of healthy food is very important for us to remain healthy. Happiness also comes as a factor in one's health. Therefore, social equality and harmony are important for the health of an individual.

The Difference Between Healthy and Disease-Free:

• The disease is defined as a disturbed state of body and mind.
• Health and disease-free are not the same. We can suffer from poor health without being in a diseased state. Thus, when we think about health, automatically the thought of our society and community come to mind.

Disease and Its Causes:

What Does Disease Look Like?

• Cells form tissues, which in turn form organ systems. An organ system comprises different organs and their particular functions. E.g., the digestive system has many organs like the stomach, buccal cavity, pharynx, etc.
• When the disease develops in the body, several changes appear in our body. These are called the symptoms and signs of the disease. Symptoms of the disease can be defined by some unusual changes in the body, while signs give a definite indication of the presence of a disease.

Chronic And Acute Diseases:

• The diseases which last for only a short period of time are known as acute diseases.

E.g., Common cold

• Diseases that last for a long time are known as chronic diseases.

E.g.- Elephantiasis

Effects of Chronic Disease:

• Acute and chronic diseases affect our health in different ways. Acute diseases do not cause threatening effects on our body, while chronic disease are very harmful to our body. Chronic diseases have prolonged poor health in the body of an infected individual.
• Let us take an example. Cough and colds do not last for a long time. We feel better within a week or so. But if we encounter chronic diseases such as tuberculosis, it makes us ill and tired for a longer time.

Causes of Diseases:

1. When a person is unhealthy, his/her body is unable to fight infections, which leads to the development of diseases.

2. Lack of good nourishment.

3. The genetic makeup of an organism.

4. Lack of public services in the surroundings.

Infectious and Non-Infectious Causes:

• There are two major causes of diseases, namely infectious and noninfectious causes. The diseases where microbes or microorganisms become the immediate cause are known as infectious diseases.
• The diseases which are not caused by any infection but spread in the community are known as non-infectious diseases.

Infectious Diseases

Infectious agents:

These include viruses, bacteria, fungi, protozoans, or worms of different kinds.

Figure: Photograph of SARS virus coming out of the surface of an infected cell.

Figure: Photograph of an adult roundworm (Ascaris lumbricoides) from the small intestine.

The diseases that are caused by these infectious agents include:

• Viruses are the major cause of common cold, influenza, dengue fever, and AIDS.
• Bacteria are the major cause of typhoid fever, cholera, tuberculosis and anthrax.
• Fungi are the major cause of common skin infections
• Protozoans cause malaria and kala-azar.

The infectious agents need to be categorised to decide what kind of treatment should be used to cure the infection. The drug or medicine effective for curing bacterial infections is not suitable for curing viral infections.

Let us take the example of antibiotics:

Antibiotics are substances that prevent bacterial infections. The antibiotic penicillin blocks the bacterial processes that build the cell wall. Show that the bacteria does not invade the cell wall, which ultimately leads to its death. The cells of human beings do not develop a cell wall, so penicillin will not be able to affect humans. But penicillin will affect any type of bacteria that tries to invade a cell wall. Thus, it is concluded that penicillin works against many species of bacteria but does not work for other infections, such as viral infections.

Viruses do not use the cell wall pathway, so antibiotics do not work against these infections. For example, if we have a common cold, taking antibiotics won't help. But if we get a viral cold along with a bacterial infection, the antibiotics will come in effect only against the bacterial part of the infection.

Means of Spread

• Infectious diseases are also known as communicable diseases because they are usually spread by microbial agents from one person to another.
• These microbial agents generally spread through the air. When an infected person coughs or sneezes, the microbes come out and enter a healthy person standing close.

Eg., Common cold, COVID- 19, pneumonia, and tuberculosis.

Fig. Air transmission

• Water is also one of the means of spreading communicable diseases. This happens when the excreta of an infected person gets mixed with drinking water, which the healthy person consumes. The microbes enter a healthy person and cause disease in them.
• Sexual intercourse is also one of the major causes of microbial infections like syphilis or AIDS. These infections are not spread by physical contact like handshakes, sports like wrestling, etc.
• HIV-causing AIDS spread through blood-to-blood contact with an infected person or from an infected mother to her baby.
• Animals are a major cause of the spread of infectious diseases. These animals transport the infectious agents from an infected person to a healthy person. Thus, these animals are referred to as vectors. Mosquitoes are the most common vector.

Organ-Specific and Tissue-Specific Manifestations:

• When a microbe enters a healthy person, it goes to many different parts of the body. The destination is decided by their point of entry. If a microbe enters from the atmospheric air, reaching the nose, its destination is the lungs. This is a common case seen in the bacteria causing tuberculosis.
• However, when a microbe enters through the mouth, it stays in the gut lining. It is seen in typhoid-causing bacteria. They may also go to the liver and cause jaundice.
• HIV enters the body through the sexual organs. It spreads to the lymph nodes of the body.
• Microbes that cause malaria enter through a mosquito bite. They go to the liver and then to RBCs. The same mechanism is followed by viruses causing Japanese encephalitis or brain fever.
• The signs or symptoms of any disease depend on the organ or tissue that is targeted by the microbe. If the microbe's destination is the lungs, cough and breathlessness become the common symptoms, while if any microbe enters the brain, headaches, vomiting, and unconsciousness become the common symptoms. These effects are termed the tissue-specific effects of infectious diseases.
• When an infection develops in the body, the immune system of the body is activated. This immune system causes many cells of the affected tissue to kill the damage-causing microbes. This process is known as inflammation, which causes local effects such as swelling and pain.
• Sometimes the tissue specificity of the infection causes general effects. For example, in HIV infection, the virus reaches the immune system and damages its function. Show that the effects of HIV/AIDS can no longer kill the microbes causing the infection.
• The severity of diseases depends on the number of microbes present in the body. If the microbes are present in small amounts, the manifestation will be minor or unnoticed, while if the number is increased, the disease can be life-threatening. The immune system plays a major role in determining the number of microbes present in the body.

Principles of Treatment:

There are two major ways of curing infectious diseases:

1. By lowering the effects of the disease.

• It can be done by providing treatment that will lower the symptoms of the disease. The symptoms usually appear because of the process of inflammation.
• The drawback of this symptom-directed treatment is that the infection does not go away and the disease is still uncured.

2. By killing the microbes causing the disease.

To kill the microbe, medicine or drug is taken which can block the pathway without affecting our own body system. This task can be done by consuming antibiotics.

Principles of Prevention:

General ways of preventing infections:

• Prevention of airborne diseases is done by preventing ourselves from being exposed to overcrowded surroundings.
• For the prevention of water-borne diseases, we can prevent our shelf by ensuring safe drinking water. This can be achieved by providing water sump treatments to kill microbial agents present in the water.
• Infections due to vectors can be avoided by ensuring a clean environment. This will prevent the breeding of mosquitoes and other vectors.

Specific ways of preventing infections:

Our immune system has a peculiar property to fight microbial infection. Let us take an example to understand this. Today there is no case of smallpox in the world. But in the past few hundred years, this infection has been regarded as an epidemic. There was everyone around who was afraid of catching this infectious disease. However, one group of people was fearless. They were the people who provided nursing care for the infected. They had encountered smallpox earlier and survived it. Thus, it was proven that when a person encountered smallpox once, there was no chance of this person suffering from the same disease again. So having smallpox once was a means of preventing subsequent attacks of smallpox.

When our immune system first encounters an infectious microbe agent, it responds against it and remembers it specifically. So the next time our body is confronted with the same infectious agent, the immune system will respond more vigorously. This will prevent the infection even faster than the first time. This formed the basic principle of immunisation.

Currently, vaccines are available against tetanus, diphtheria, whooping cough, polio, and many others. There are many public health programmes organised for childhood immunisation. All these aim to prevent these infectious diseases.

Chapter-Wise NCERT Class 9 Notes Science

Significance of NCERT notes for class 9 Science chapter 13

Why do we fall ill? Class 9th notes will assist you in revising the chapter and gaining an understanding of the main concepts addressed. These Notes for Class 9 Science Chapter 13 are also not complicated, and they thoroughly explain step-by-step approaches to guarantee that students understand the concepts of this chapter, which is part of the CBSE Science syllabus for class 9. Why do we fall ill Class 9 notes PDF downloads can be used for offline preparation.

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