NCERT Class 12 Books Biology Chapter 8- Human Health and Disease 

Safalta Expert Published by: Noor Fatima Updated Thu, 30 Jun 2022 11:54 PM IST


Here is the information about NCERT Class 12 Books Biology Chapter 8. You can give a read to this blog and get PDFs of the subject. 

NCERT Class 12 Books Biology Chapter 8- Human Health and Disease is accessible here for download purposes. You can download the PDF for and learn from the book anytime you want. Students who are studying in Class 12 and candidates who are preparing for competitive exams can download the PDF for NCERT Class 12 Books Biology Chapter 8- Human Health and Disease to learn from the reading material.  

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Here, you can learn the NCERT Class 12 Books Biology Chapter 8- Human Health and Disease. Moreover, you can get the links for other Chapter 8s to download the links. 


Health, for a long time, was considered as a state of body and mind where there was a balance of certain ‘humors’. This is what early Greeks like Hippocrates as well as Indian Ayurveda system of medicine asserted. It was thought that persons with ‘blackbile’ belonged to hot personality and would have fevers. This idea was arrived at by pure reflective thought. The discovery of blood circulation by William Harvey using experimental method and the demonstration of normal body temperature in persons with blackbile using thermometer disproved the ‘good humor’ hypothesis of health. In later years, biology stated that mind influences, through neural system and endocrine system, our immune system and that our immune system maintains our health. Hence, mind and mental state can affect our health. Of course, health is affected by –

(i) genetic disorders – deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth;

(ii) infections and

(iii) life style including food and water we take, rest and exercise we give to our bodies, habits that we have or lack etc.

The term health is very frequently used by everybody. How do we define it? Health does not simply mean ‘absence of disease’ or ‘physical fitness’. It could be defined as a state of complete physical, mental and social well-being. When people are healthy, they are more efficient at work. This increases productivity and brings economic prosperity. Health also increases longevity of people and reduces infant and maternal mortality.

Balanced diet, personal hygiene and regular exercise are very important to maintain good health. Yoga has been practised since time immemorial to achieve physical and mental health. Awareness about diseases and their effect on different bodily functions, vaccination (immunisation) against infectious diseases, proper disposal of wastes, control of vectors and maintenance of hygiene in food and water resources are necessary for achieving good health.

When the functioning of one or more organs or systems of the body is adversely affected, characterised by appearance of various signs and symptoms, we say that we are not healthy, i.e., we have a disease. Diseases can be broadly grouped into infectious and non-infectious. Diseases which are easily transmitted from one person to another, are called infectious diseases. Infectious diseases are very common and every one of us suffers from these at sometime or other. Some of the infectious diseases like AIDS are fatal. Among non-infectious diseases, cancer is the major cause of death. Drug and alcohol abuse also affect our health adversely. 


A wide range of organisms belonging to bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man. Such diseasecausing organisms are called pathogens. Most parasites are therefore pathogens as they cause harm to the host by living in (or on) them. The pathogens can enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage. Pathogens have to adapt to life within the environment of the host. For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes. A few representative members from different groups of pathogenic organisms are discussed here alongwith the diseases caused by them. Preventive and control measures against these diseases in general, are also briefly described.

Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings. These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite are some of the common symptoms of this disease. Intestinal perforation and death may occur in severe cases. Typhoid fever could be confirmed by 

Widal test : A classic case in medicine, that of Mary Mallon nicknamed Typhoid Mary, is worth mentioning here. She was a cook by profession and was a typhoid carrier who continued to spread typhoid for several years through the food she prepared.

Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration. The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and finger nails may turn gray to bluish in colour. A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person. Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man.

Many viruses also cause diseases in human beings. Rhino viruses represent one such group of viruses which cause one of the most infectious human ailments – the common cold. They infect the nose and respiratory passage but not the lungs. The common cold is characterised by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which usually last for 3-7 days. Droplets resulting from cough or sneezes of an infected person are either inhaled directly or transmitted through contaminated objects such as pens, books, cups, doorknobs, computer keyboard or mouse, etc., and cause infection in a healthy person. 

Some of the human diseases are caused by protozoans too. You might have heard about malaria, a disease man has been fighting since many years. Plasmodium, a tiny protozoan is responsible for this disease. Different species of Plasmodium (P. vivax, P. malaria and P. falciparum) are responsible for different types of malaria. Of these, malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal. Let us take a glance at the life cycle of Plasmodium (Figure 8.1). Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days. When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development. The parasites multiply within them to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into his/ her body, thereby initiating the events mentioned above. It is interesting to note that the malarial parasite requires two hosts – human and mosquitoes – to complete its life cycle (Figure 8.1); the female Anopheles mosquito is the vector (transmitting agent) too.

Entamoeba histolytica is a protozoan parasite in the large intestine of human which causes amoebiasis (amoebic dysentery). Symptoms of this disease include constipation, abdominal pain and cramps, stools with excess mucous and blood clots. Houseflies act as mechanical carriers and serve to transmit the parasite from faeces of infected person to food and food products, thereby contaminating them. Drinking water and food contaminated by the faecal matter are the main source of infection.

Here are the glimpses of the Chapter-

NCERT Class 12 Books Biology Chapter 8- Human Health and Disease- PDF Download

Chapter 8: Human Health and Diseases

अध्याय 8: मानव स्वास्थ्य तथा रोग

Where can you download NCERT Class 12 Books Biology Chapter 8 PDF?

Candidates can download NCERT Class 12 Books Biology Chapter 8- Human Health and Disease PDF for free on our page. Links are given below.

Chapter 8: Human Health and Diseases

अध्याय 8: मानव स्वास्थ्य तथा रोग

Why is NCERT Books Class 12 Biology the best study material?

The book can also help in clarifying doubts. Other benefits of studying from the NCERT Books Class 12 Biology are-
  • Students gain profound knowledge about Biology through the NCERT Books Class 12 Biology
  • The course books contain pictures that can help students in better understanding of the Chapter 8s
  • These books can help students in self-study

Why is NCERT Books Class 12 Biology so recommended for board exams?

Almost all the questions that appear in board exams are from NCERT Books Class 12 Science. Moreover, a team of professional teachers drafts these books, which become a reliable source of study for students.

Are CBSE Books for Class 12 Biology important from an examination perspective?

The Chapter 8 in CBSE Books for Class 12 Biology are vital for board exams and higher classes. Students should read the Unit given in the CBSE books for Class 12 Science. These stories and practice questions can help gain excellent marks.

To get outstanding marks, we provide mock test papers that can help gear-up your preparations for exams. Additionally, you can also download e-books to get yourself prepared even in a better way.

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