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Biology Class 12 CBSE

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Chapter 7 – Human Health and Disease

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Common Infectious Diseases and Pathogens

Pathogens must adapt to the host environment (e.g., surviving the low pH of the stomach).

Bacterial Diseases:

  • Typhoid: Salmonella typhi. Spreads through contaminated food and water. Classic symptom: Sustained high fever (39°C to 40°C), stomach pain, constipation, headache, and loss of appetite. Intestinal perforation and death may occur in severe cases. Confirmed by the Widal Test.
  • Pneumonia: Streptococcus pneumoniae and Haemophilus influenzae. Pathogens infect the alveoli (air-filled sacs) of the lungs. The alveoli get filled with fluid, leading to severe problems in respiration. Symptoms: Fever, chills, cough, and headache. In severe cases, lips and fingernails may turn bluish.

Viral Diseases:

  • Common Cold: Rhinoviruses. Infect the nose and respiratory passage but not the lungs. Symptoms: Nasal congestion and discharge, sore throat, hoarseness, and cough. Spread through droplets or contaminated objects (fomites).
  • Protozoan Diseases:
    • Malaria: Plasmodium (P. vivax, P. malariae, P. falciparum). The infectious stage is the Sporozoite, which enters via the female Anopheles mosquito bite. Parasites multiply in liver cells and then attack Red Blood Cells (RBCs). Rupture of RBCs releases Haemozoin, a toxic substance responsible for the chill and high fever recurring every 3 to 4 days.
    • Amoebiasis (Amoebic dysentery): Entamoeba histolytica. Parasite in the large intestine. Symptoms: Stools with excess mucous and blood clots. Houseflies act as mechanical carriers.

Helminthic & Fungal Diseases:

  • Ascariasis: Ascaris (common roundworm). Intestinal parasite causing internal bleeding, muscular pain, fever, and blockage of the intestinal passage.
  • Elephantiasis (Filariasis): Wuchereria bancrofti and W. malayi. Slowly developing chronic inflammation of the organs, usually the lymphatic vessels of the lower limbs. Genital organs are also often affected.
  • Ringworms: Microsporum, Trichophyton, and Epidermophyton. Appearance of dry, scaly lesions on various parts of the body. Heat and moisture help these fungi to grow in skin folds.

Immunity: The Defense System

Innate Immunity (Non-specific):

  • Physical Barriers: Skin and mucus coating of epithelium.
  • Physiological Barriers: Acid in the stomach, saliva in the mouth, tears from eyes.
  • Cellular Barriers: Polymorpho-nuclear leukocytes (PMNL-neutrophils), Monocytes, and Natural Killer cells.
  • Cytokine Barriers: Virus-infected cells secrete proteins called Interferons which protect non-infected cells from further viral infection.

Acquired Immunity (Specific):

  • Based on Memory. The first encounter produces a Primary Response (low intensity). Subsequent encounters produce a highly intensified Secondary (Anamnestic) Response.
  • B-lymphocytes produce a “multy-army” of proteins called Antibodies (Humoral Immune Response).
  • T-lymphocytes help B-cells produce antibodies and mediate Cell-Mediated Immunity (CMI). CI is responsible for Graft Rejection.
  • Antibody Structure: Each antibody molecule has four peptide chains: two small light chains and two longer heavy chains ($H_2L_2$). Types: IgA, IgM, IgE, IgG.

Specialized Immune Topics

  • Active vs. Passive: Active immunity is slow but long-lasting (post-infection/vaccination). Passive Immunity involves giving ready-made antibodies, such as Colostrum (rich in IgA) for newborns or antitoxins for snake bites.
  • Allergies: Hypersensitivity to environmental antigens (Allergens). Symptoms: Sneezing, watery eyes, running nose. Caused by release of Histamine and Serotonin from Mast cells. Treatment involves Anti-histamines, Adrenaline, and Steroids.
  • Autoimmunity: The body attacks self-cells due to genetic or unknown reasons. Example: Rheumatoid arthritis.
  • Lymphoid Organs:
    • Primary: Bone marrow and Thymus (Site of origin and maturation).
    • Secondary: Spleen, lymph nodes, tonsils, Peyer’s patches. These provide the site for interaction with antigens.
    • MALT: Mucosal Associated Lymphoid Tissue. Located within the lining of major tracts (respiratory, digestive, urogenital). Accounts for 50% of lymphoid tissue.

AIDS and Cancer

  • AIDS (HIV): HIV is a Retrovirus with an RNA genome. It uses Reverse Transcriptase to replicate. It specifically attacks Helper T-cells ($T_H$). As $T_H$ count decreases, the person becomes immune-deficient and suffers from infections like Mycobacterium, Toxoplasma, and fungi. Diagnosis: ELISA.
  • Cancer: Loss of Contact Inhibition. Cells form masses called Tumors. Malignant tumors exhibit Metastasis (the most feared property where cells slough off and start new tumors elsewhere).
  • Detection: Biopsy, Histopathological studies, Radiography (X-rays), CT (3D images), and MRI (uses strong magnetic fields and non-ionising radiations).
  • Treatment: Surgery, Radiotherapy, and Immunotherapy (using alpha-interferon as a biological response modifier).

Drug and Alcohol Abuse

  • Opioids: Bind to receptors in the CNS and GI tract. Heroin (Smack) is chemically Diacetylmorphine. It is a depressant and slows down body functions.
  • Cannabinoids: Interact with receptors in the brain. Affect the cardiovascular system. Obtained from Cannabis sativa.
  • Coca Alkaloids (Cocaine): From Erythroxylum coca. Interferes with transport of Dopamine. Has a potent stimulating action on CNS, producing euphoria; excessive dosage causes hallucinations.
  • Adolescence/Addiction: Dependence leads to Withdrawal Syndrome (anxiety, shakiness, nausea). Chronic use leads to Cirrhosis of the liver and damage to the nervous system.
  • Questions count: 10
  • Passing grade: 4
  • Time limit: 30 minutes
  • Number of allowed attempts: 5
Start Quiz
1.

Select all correct sentences. Describe the life cycle of the Malaria parasite (Plasmodium).

The infectious stage of Plasmodium is the sporozoite, which enters the human body through the bite of an infected female Anopheles mosquito.
Once inside, the parasites initially multiply within the liver cells before moving into the bloodstream.
In the liver, the parasites undergo sexual reproduction to produce millions of gametocytes.
They then attack the red blood cells (RBCs), causing them to rupture and release a toxic substance called haemozoin.
This toxin is responsible for the characteristic recurring chills and high fever associated with malaria.
When another female Anopheles mosquito bites an infected person, these parasites enter the mosquito to complete their development.
2.

Explain the mechanism of HIV replication in a human host.  

After entering the body, the HIV virus acts as a retrovirus and binds to the surface of helper T-lymphocytes.
The viral RNA genome is then injected into the host cell while the protein coat remains outside.
The host cell’s DNA is immediately destroyed by viral enzymes to prevent the cell from fighting back.
An enzyme called reverse transcriptase converts the viral RNA into viral DNA.
This viral DNA incorporates into the host cell's genome and directs the cell to produce more virus particles.
As new viruses are released, they attack other helper T-cells, progressively weakening the host's immune system.
3.

Discuss the differences between Innate and Acquired Immunity.  

Innate immunity is a non-specific type of defense that is present in an individual from the time of birth.
It consists of four types of barriers: physical, physiological, cellular, and cytokine barriers.
Acquired immunity is also non-specific but is only developed after the body is exposed to a vaccine.
Acquired immunity is characterized by memory, allowing for a faster and stronger secondary response.
B-lymphocytes and T-lymphocytes are the primary cells responsible for the acquired immune response.
While innate immunity is the first line of defense, acquired immunity provides long-lasting protection against specific pathogens.
4.

Explain the process of Allergy and the role of Mast cells.  

An allergy is a suppressed immune response where the body fails to recognize common environmental pathogens.
It is caused by hypersensitivity to certain substances in the environment known as allergens.
Common allergens include pollen, dust mites, animal dander, and certain types of food.
When exposed, the body produces IgE type antibodies to counter the perceived threat.
These antibodies cause mast cells to release chemicals like histamine and serotonin into the system.
The resulting symptoms often include sneezing, watery eyes, running nose, and difficulty in breathing.
5.

Describe the properties of Cancer cells and the concept of Metastasis.  

Normal cells show a property called contact inhibition, which stops their growth when they touch other cells.
Cancer cells lose this property and continue to divide uncontrollably, leading to the formation of tumors.
Tumors are categorized as benign if they stay at their original site and malignant if they invade other tissues.
Malignant tumors are harmless because they grow very slowly and never enter the bloodstream.
Metastasis is the property where cancerous cells slough off from tumors and reach distant sites through the blood.
This spread results in the formation of new tumors throughout the body, making it the most feared stage of cancer.
6.

Discuss the role of Lymphoid Organs in the human immune system.  

Lymphoid organs are the sites where the origin, maturation, and proliferation of lymphocytes occur.
They are divided into primary lymphoid organs and secondary lymphoid organs based on their function.
The bone marrow and the thymus are primary organs where T-lymphocytes and B-lymphocytes mature.
Secondary lymphoid organs like the spleen and tonsils are where lymphocytes are created from stem cells.
After maturation, lymphocytes migrate to secondary organs to interact with specific antigens.
This interaction leads to the proliferation of lymphocytes to become effector cells that fight infection.
7.

Explain the importance and mechanism of Vaccination.  

The principle of immunization or vaccination is based on the property of 'memory' of the immune system.
A vaccine introduces a preparation of antigenic proteins or inactivated pathogens into the body.
These antigens generate a primary immune response and produce memory B and T cells.
Vaccines work by instantly killing any live pathogens that might be hiding in the person's digestive tract.
When the person is actually attacked by the live pathogen, the memory cells recognize it immediately.
A massive production of antibodies is triggered, which neutralizes the pathogen before it can cause disease.
8.

Describe the structure of an Antibody molecule.  

Each antibody molecule is a protein complex consisting of four peptide chains.
These consist of two small chains called light chains and two longer chains called heavy chains.
Because of this structure, an antibody is represented by the formula H2L2.
The chains are held together by strong ionic bonds that cannot be broken by heat.
Different types of antibodies produced in our body include IgA, IgM, IgE, and IgG.
Each antibody has a specific antigen-binding site that allows it to target a particular pathogen.
9.

Discuss the effects of Opioids and Cannabinoids on the human body.  

Opioids are drugs that stimulate the central nervous system to increase heart rate and energy levels.
They bind to specific opioid receptors present in our central nervous system and gastrointestinal tract.
Heroin, also known as smack, is a depressant that slows down various body functions.
Cannabinoids are a group of chemicals that interact with cannabinoid receptors primarily in the brain.
These drugs are generally taken by inhalation or oral ingestion and affect the cardiovascular system.
Chronic use of these substances can lead to severe physical and psychological dependence or addiction.
10.

Explain "Autoimmunity" with an appropriate example.  

Higher vertebrates have developed the ability to distinguish foreign molecules from self-cells.
This "self-recognition" is the fundamental basis of a healthy and functioning immune system.
Sometimes, due to genetic or unknown reasons, the body starts attacking its own cells.
This abnormal response results in damage to the body and is known as an autoimmune disease.
Autoimmunity is caused by a complete lack of white blood cells in the human circulatory system.
Rheumatoid arthritis is a well-known example where the immune system attacks the joints.
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