Notes on Some Common Diseases in Humans- CBSE Class 12 Biolo - Study24x7
Social learning Network

Default error msg


New to Study24x7 ? Join Now
Already have an account? Login

Notes on Some Common Diseases in Humans- CBSE Class 12 Biology (Chapter 8)

Updated on 27 July 2022
Edubabble LLP
42 min read 55 views
Updated on 27 July 2022

What are diseases?

Definitions- “A disease is a condition that deteriorates the normal functioning of the cells, tissues, and organs.” 


“Any dangerous divergence from a functional or normal state of an entity.”

A disease is an undesirable condition that affects a living creature that is otherwise healthy. Infectious and non-infectious diseases are the two broad categories.

What are the Different Types of Diseases?

Infectious diseases- Diseases are caused by pathogenic microbes, such as bacteria, viruses, fungi, parasites, and can be easily transferred from one person to another, thus it is also known as an infectious or communicable disease. Infectious diseases include the common cold, tuberculosis, influenza, ringworm, and malaria.

Non-infectious diseases, also known as non-communicable diseases, are diseases that cannot be passed from one person to another. Genetic problems, bad diets, lack of physical activity, excessive use of tobacco, narcotics, or alcohol, and a few environmental variables can all contribute to these diseases.

Pathogens are bacteria that infect a host and infect humans. They include microorganisms such as bacteria, fungi, viruses, and so on.

Some Common Human Diseases

  1. Salmonella typhi, a pathogenic bacterium, is proven to cause typhoid in humans. The Widal test can detect this fever.

  1. Streptococcus pneumoniae and Hemophilus  influenza cause pneumonia.

  1. Rhinoviruses, a type of virus, are known to cause one of the most common infectious diseases in humans, the common cold.

  1. Malaria is a disease caused by Plasmodium, a small protozoan. Entamoeba histolytica is another protozoan that causes amoebiasis (amoebic dysentery)

  1. Ascariasis is caused by the intestinal parasite Ascaris.

  1. The filarial worm Wuchererta causes filariasis or elephantiasis.

Bacterial-caused Disease



Transmission Mode 



Salmonella typhi

Food and water contamination

Persistently high fever, stomach ache, Weakness, Constipation, Appetite loss (in serious forms, intestinal perforations and fatality).


Haemophilus influenzae/ Streptococcus pneumonia

Sharing cups and cutlery, as well as inhaling droplets from sick people

Lung alveoli become infected, resulting in respiratory problems, fever, chills, cough, and headache (lips and nails become grey in severe cases ).

Virus-Induced Disease



Transmission Mode


Common Cold


Air – passing through droplet nuclei and infected objects.

Nasal and respiratory system infection Wheezing, cough, headache, and tiredness are all symptoms of sinus problems and exhaustion.

Protozoa-caused disease



Mode of Transmission




By way of vector (Female Anopheles mosquito).

High fever and chills at regular intervals caused by the release of hemozoin after infected RBCs rupture.

Amoebiasis (amoebic dysentery)

Entamoeba histolytica

Houseflies act as mechanical carriers, transferring the parasite from an infected person's feces to food (fecal-oral transmission).

Constipation, abdominal pain and cramps, mucousy stools, and blood clots.

Worm-caused Diseases



Transmission Mode




Faeco-oral transmission.

Fever, anaemia, muscle pain, internal bleeding, and intestinal blockage.


Wuchereria bancrofti, W.malayi

Female mosquito vector bite

Chronic inflammation of lymphatic vessels in the lower extremities and genital organs, resulting in gross deformities.

Fungi-caused Diseases



Mode of Transmission



Epidermophyton, Microsporum, Trichophyton

Direct Contact with contaminated clothes, things, etc.

Itchiness from dry, scaly lesions on the skin, nails, and scalp. The symptoms worsen as the temperature and humidity rise.

Prevention and control include the following: 

  1. Maintain public hygiene and personal.
  2.  Prevent the transmission and isolate
  3. Getting rid of vectors and their breeding grounds
  4.  Anti-vector protection
  5. Immunization
  6. Antibiotics

AIDS (Acquired Immuno Deficiency Syndrome)

HIV-AIDS is caused by an Immunodeficiency Virus and negatively impacts the body's resistance to infection. This virus spreads through contact with infected blood, sperm, or vaginal secretions. AIDS was first confirmed in 1981, over the last twenty-five years, it has spread around the world, having killed over 25 million people.

  1. Flu-like signs, such as fever, fatigue, sore throat appear after a few weeks of being infected with an infectious disease.

  1. After that, the disease becomes clinically silent until it evolves into AIDS. AIDS symptoms include weight loss, fever or night sweats, tiredness, and frequent infections.

  1. Currently there is no cure for AIDS, but anti - retroviral treatments can slow the disease's progression and prevent communicable disease and other complications from occurring.

Causative Agent- It is caused by Human Immunodeficiency and is an associate of a virus family known as a retrovirus. Their genome is made up of RNA wrapped in an enclosure, as well as the reverse transcriptase gene.

HIV infection transmission

(a) Sexual contact with an infected individual: people who have several sexual partners.

(b) Individuals who require repeated blood transfusions, may be exposed to infected blood and blood products through transfusion (certain cancers, anemia, and thalassemia).

(c) By sharing highly contagious syringes, as in the case of injectable druggies: drug addicts who use drugs recreationally.

(d) Viral transmission from a contaminated mother to her child via the placenta: children born to an HIV-infected mother. HIV/AIDS does not spread through physical touch. It is primarily transmitted through sexual contact, but it can also be transmitted through infected blood from shared intravenous needles and other means.

Detection of AIDS in human body:

A biochemical test is used to detect the involvement of an antibody or enzyme in a sample. A Western Blot test is also performed to confirm the results of the ELISA test.

Treatment of AIDS: 

AIDS is treated with antiretroviral drugs, which increase a person's lifespan but can not prevent death.

Prevention from AIDS:

Because there is no cure for AIDS, it is advisable to prevent it from happening. The main thing to remember when trying to prevent AIDS is blood transfusion and transmission from mother to newborn.

The function of government and non-governmental organisations in containing the spread of this infection.

To raise public awareness and education about AIDS, with the assistance of the National AIDS Control Organization (NACO) and other non-governmental organisations (NGOs). WHO runs a lot of programs to reduce the spread of AIDS.


Cell growth is carefully regulated and coordinated in our bodies, but when these mechanisms fail, it results in uncontrolled cell differentiation, which helps in the growth of cancerous cells, leading to unmanageable growth. These cancerous cells will continue to divide, resulting in the formation of mature cells known as tumor cells.

Tumors are classified into two types:

1. A benign tumor has been differentiated and encapsulated. Benign tumors typically grow at a slower rate, remain localized, and do not spread to other parts of the body, resulting in less damage.

2. They form when cells proliferate uncontrollably. If the cells continue to grow and spread, the disease can become fatal. Malignant tumors can spread to other parts of the body quickly, a process known as metastasis.

Cause of Cancer:

Cancer is caused by the transformation of normal cells into cancerous cells by physical, chemical, or biological agents. These substances are known as carcinogens.

Common Carcinogens

  1. Ionizing radiations such as X-rays and gamma rays are common carcinogens.
  2. UV rays are non-ionizing radiations. Ionizing and non-ionizing radiations cause DNA damage, which leads to neoplastic transformation.
  3. Tobacco smoke contains chemical carcinogens, which are the leading cause of lung cancer.
  4. Oncogenic viruses are cancer-causing viruses that contain genes known as viral oncogenes. Several genes known as cellular oncogenes (c-onc) or proto-oncogenes have been identified in normal cells that can be stimulated under certain conditions, resulting in oncogenic transformation of the cells.

Cancer Detection and Diagnosis: 

When cancer is diagnosed, it can be effectively treated. Cancer detection is based on the following factors:

Biopsy: In this procedure, a small amount of suspected tissue is removed and spattered, resulting in Histopathological studies of the tissue (thin sections are examined under the microscope).

Blood and bone marrow tests: These are used to detect leukemia and to count the increase in cell counts.

Radiography: Uses X-Rays

CT (computed tomography): The use of X-rays to generate the three-dimensional structure of the organ.

MRI (magnetic resonance imaging): This technique detects changes in living tissues by using a powerful magnetic field and non-ionizing radiation.

Antibodies against cancer-specific antibodies: These are used to detect specific cancers.

Methods of molecular biology: It is used to detect different types of cancer as well as to identify genes that help in cancer prevention. Individuals who have these identified are advised to discontinue the use of carcinogens that are dangerous to them, such as alcohol and cigarettes in the case of lung cancer.

Cancer Treatment:

Cancer can be treated using one or a combination of different approaches. Cancer treatments available include surgery, radiotherapy, chemotherapy, and immunotherapy.

The tumor cells are irradiated lethally while the normal cells surrounding them are protected.

Chemotherapeutics are drugs that are used to kill cancer cells and may be specific for specialized tumors. These drugs will cause certain side effects such as hair loss, anemia, and so on.


Biology students who want to pursue a career in medicine should learn some core points in the Class 12 syllabus and prepare thoroughly for both Boards and competitive exams. Because Human Health and Disease is a wide topic with a high weightage in all examinations, it is essential to keep it handy. 

Prepare Well, Good Luck!

Write a comment...
Related Posts