CBSE Class 12 Biology Chapter 8 Revision Notes Part 2

Chapter 8: Human Health and Diseases Revision Notes Part 2

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Multiple Choice Questions

  1. Which type of tumors can invade adjacent tissues and cause harm? _______

  2. Plasmodium, the parasite that causes malaria, is spread from person to person by the bite of the female Anopheles mosquito. __________

  3. The HIV virus uses __________ to generate viral DNA in the host.

  4. Which of these impacts the cardiovascular system? ___________

  5. Ringworm is caused by _________.

Human Health and Disease

  • A state of complete physical, mental, and social well-being is characterized as health.
  • A pathogen is a disease-causing organism, such as bacteria, viruses, protozoans, fungus, or worms.
  • A pathogen can enter our bodies in a variety of ways.

Pathogen-related Disease

Typhoid: caused by a bacteria, Salmonella typhi.

  • One can contract this disease through contaminated food and water.
  • Symptoms include high fever, headache, constipation, and loss of appetite.
  • This disease can be diagnosed by performing a Widal test, and intestinal perforations can be seen In some extreme cases.

Pneumonia: a lung infection that causes the air sacs in one or both lungs to become inflamed.

  • Cough with phlegm or pus, fever, chills, and trouble breathing can occur when the air sacs fill with fluid or pus (purulent material).
  • Streptococcus pneumoniae is the most prevalent cause of bacterial pneumonia.
  • This form of pneumonia can develop independently or as a result of a cold or virus.

Ascariasis: a parasitic illness of the small intestine.

  • Caused by the roundworm Ascaris lumbricoides.
  • Roundworms are parasitic worms, and Roundworm infections are rather frequent.
  • The most prevalent roundworm infection is ascariasis.

Ringworm: A fungus causes ringworm, which is a common skin illness.

  • Because it can create a circular rash (formed like a ring) that is generally red and itchy, it’s nicknamed “ringworm.”
  • Ringworms may affect anyone.

Malaria: Malaria is an infectious illness spread by mosquitoes that affect people and other animals.

  • Malaria is characterized by fever, exhaustion, vomiting, and headaches.

  • In extreme cases, it can cause yellow skin, convulsions, coma in extreme cases, or death.

  • Lifecycle of Plasmodium

    • Plasmodium is spread from person to person by female Anopheles mosquito bites.
    • Sporozoites, which are formed by female anopheles saliva after they bite, are the infectious form.
    • Before attacking RBCs, it replicates in liver cells, leading RBCs to explode.
    • Haemozoin, a harmful toxin, is secreted.
    • The infected person’s gametocyte is transferred to the mosquito whenever a mosquito bites an infected person.
    • Macro and micro gametocytes get fertilized, converted, and sporogenesis happens in the mosquito’s stomach, culminating in the formation of sporozoites.
    • The cycle is restarted when sporozoites reach a mosquito’s salivary gland.
    • Plasmodium sp. needs both humans and female Anopheles mosquitoes to finish its life cycle.

Plasmodium lifecycle

Source: Plasmodium lifecycle

AIDS (Acquired Immunodeficiency Syndrome)

  • Caused by HIV (Human Immunodeficiency Virus)
  • The virus uses the reverse transcriptase enzyme to generate viral DNA in the host.
  • The viral DNA is integrated into the host genome, resulting in numerous copies of the virus.
  • The virus targets helper T-cells, where it replicates and multiplies, resulting in a significant reduction in T lymphocyte numbers.
  • After the virus targets T-helper cells, the infected person develops immunodeficiency.
  • AIDS patients are vulnerable to infections such as mycobacterium, toxoplasma, fungal, and viral infections.
  • The ELISA test is a commonly used AIDS diagnostic test.
  • AIDS can be passed down from mother to fetus through the placenta, contaminated blood transfusions, or using an infected syringe.

HIV Replication Cycle

Source: HIV


  • Cancer is caused by unregulated cell division, which results in tumor development.


  • Cancerous cells cannot stop future cell proliferation when they touch other cells.
  • Non-invading benign tumors stay in their original position and do not spread.
  • Malignant tumors can invade adjacent tissues and cause harm.
  • Metastasis is a feature of malignant tumors in which sloughed-off cells travel to distant areas and establish tumors in various sections of the body.
  • Cancer is caused by DNA damage or genetic mutations that result in improper cell cycle control.
  • Under some conditions, cancer can also be triggered by the activation of proto-oncogenes found in normal cells.
  • Ionizing radiation (e.g., X-rays, gamma rays), non-ionizing radiation (UV rays), chemical agents (e.g., tobacco), viral oncogenes of oncogenic viruses are all examples of carcinogens.
  • A CT scan, MRI, X-ray, PET scan, or histological investigations of tissue and blood can all be used to identify cancer.
  • Molecular biology approaches can also diagnose cancer by identifying inherited cancer-prone genes.
  • Surgery, transplantation, immunotherapy, and radiation therapy are all options for cancer treatment.
  • 𝛂 -interferon acts as a biological response modifier, activating the immune system and causing it to attack the tumor.

Alcohol and Drug Abuse

Commonly misused drugs include opioids, cannabinoids, and coca alkaloids.

  • Opioids bind to opioid receptors in our central nervous system and gastrointestinal tract.
  • Diacetylmorphine is sometimes known as smack or heroin.
  • It’s made from the latex of the Papaver somniferum poppy plant, and the acetylation of morphine produces it.
  • Cannabinoids interact with the brain’s cannabinoid receptors, and they have an impact on the cardiovascular system.
  • Cannabis, hashish, charas, ganja, and other cannabinoids are extracted from the plant’s flower tops, leaves, and resins, Cannabis sativa.
  • Cocaine, also known as coca alkaloid, is derived from the Erythroxylum coca plant.
  • Cocaine works by interfering with dopamine transport, a neurotransmitter.
  • Cannabinoids are also used by athletes to improve their performance, muscle relaxation, and anxiety reduction.
  • Morphine is a sedative and a pain reliever.
  • Depression, sleeplessness, and other mental illnesses are treated with barbiturates, amphetamines, and benzodiazepines, among other drugs.
  • Tobacco’s nicotine (alkaloid) promotes the adrenal gland’s secretion of adrenalin and nor-adrenalin hormones. It raises blood pressure and heart rate.
  • Smoking causes oxygen deficit by raising carbon monoxide levels in the blood, lowering the concentration of oxygen bound to hemoglobin.
  • Excessive drug and alcohol use harms the nervous system and leads to liver cirrhosis.

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