Study notes Biology and human welfare Class 12 Biology CBSE and CHSE

1. Common Diseases and Pathogens

Understanding the causal organism, transmission, and symptoms is key:

Disease	Pathogen Type	Pathogen Name	Transmission	Symptoms
Typhoid	Bacteria	Salmonella typhi	Contaminated food/water	High sustained fever, stomach pain, headache, constipation. Confirmed by the Widal Test.
Pneumonia	Bacteria/Virus	Streptococcus pneumoniae or Hemophilus influenzae	Droplets/aerosols	Alveoli fill with fluid, leading to breathing problems, chills, cough. Lips/fingers may turn blue/grey.
Malaria	Protozoan	Plasmodium species	Female Anopheles mosquito (Vector)	Recurrent high fever cycles (every 3-4 days), chills, and rigor due to the rupture of RBCs.
Amoebiasis	Protozoan	Entamoeba histolytica	Contaminated food/water (Houseflies are mechanical carriers)	Constipation, abdominal pain, bloody stools, mucus in stool.
Ascariasis	Helminth (Worm)	Ascaris lumbricoides	Contaminated food/water (eggs)	Internal bleeding, muscular pain, blockage of the intestinal passage.
Ringworm	Fungi	Microsporum, Trichophyton, Epidermophyton	Soil or infected towels/clothing	Dry, scaly lesions on the skin, nails, and scalp accompanied by intense itching.

2. Detailed Mechanism of Immunity

The immune response is the coordinated action of different cells.

A. Antibody Structure and Function

Antibodies, or Immunoglobulins (Ig), are Y-shaped protein molecules produced by Plasma B-cells.

Each antibody molecule has four peptide chains: two identical Heavy (H) chains and two identical Light (L) chains, hence represented as H2L2.

They have a variable region that binds specifically to the antigen and a constant region.

The five major types are IgG (most abundant), IgA (in secretions like colostrum), IgM (first produced), IgE (involved in allergies), and IgD.

B. Cell-Mediated Immunity (CMI)

Mediated by T-lymphocytes, CMI is responsible for distinguishing 'self' from 'non-self'. Its main function is:

Graft Rejection: The immune system recognizes a transplanted organ (graft) as non-self and attempts to reject it. This is why patients need to take immunosuppressive agents lifelong.

3. Cancer

Cancer is characterized by the uncontrolled and abnormal proliferation of cells, known as neoplastic transformation.

Normal cells exhibit contact inhibition, meaning they stop dividing when they come in contact with other cells. Cancer cells lose this property.

The mass of cells formed is called a tumour.

Benign Tumours: Confined to their original location; do not spread.

Malignant Tumours: The dangerous type; cells proliferate rapidly, invading and damaging surrounding tissues. Malignant cells may travel through the blood to distant sites and form secondary tumours (a process called metastasis).

Detection and Diagnosis: Biopsy, Histopathological studies, CT scans, MRI, and using antibodies against cancer-specific antigens.

Treatment: Surgery, Radiation Therapy (where tumour cells are killed), Chemotherapy (using drugs, often with side effects like hair loss), and Immunotherapy (using α-Interferons to activate the immune system).

Microbes in Human Welfare (Descriptive Notes)

1. Industrial Products

The large-scale cultivation of microbes is done in large vessels called fermenters.

Product Type	Example	Microbe Used	Role/Application
Antibiotics	Penicillin	Penicillium notatum	Kills a wide range of harmful bacteria.
Organic Acid	Citric Acid	Fungus: Aspergillus niger	Used as a food additive and preservative.
Organic Acid	Acetic Acid	Bacterium: Acetobacter aceti	Used to produce vinegar.
Enzyme	Lipase	Bacteria/Yeast/Fungi	Used in detergent formulations for removing oily stains.
Enzyme	Streptokinase	Bacterium: Streptococcus	Modified and used as a "clot-buster" for patients with myocardial infarction (heart attack).
Bioactive Molecule	Cyclosporin A	Fungus: Trichoderma polysporum	Used as an immunosuppressive agent in organ transplant patients.
Bioactive Molecule	Statins	Yeast: Monascus purpureus	Used as blood cholesterol-lowering agents by competitively inhibiting the enzyme responsible for cholesterol synthesis.

2. Sewage Treatment Plant (STP)

This process involves treating urban wastewater (sewage) before discharge into natural water bodies. The goal is to reduce its Biochemical Oxygen Demand (BOD).

Primary Treatment (Physical):

Filtration: Large and small particles (floating debris) are removed.

Sedimentation: Grit (soil and small pebbles) settles down in settling tanks. The settled material is the primary sludge, and the supernatant is the primary effluent.

 

Secondary Treatment (Biological):

The primary effluent is passed into large aeration tanks where it is vigorously mixed and air is pumped in.

This promotes the growth of aerobic microbes into masses called flocs (masses of bacteria associated with fungal filaments).

These microbes consume the major part of the organic matter in the effluent, significantly reducing the BOD.

The effluent is then passed into a settling tank where the bacterial flocs settle, forming activated sludge. A small part of this is pumped back to the aeration tank as an inoculum.

The remaining activated sludge is pumped into an Anaerobic Sludge Digestor, where anaerobic bacteria digest the remaining organic matter and produce biogas.

3. Biofertilizers

These are living organisms that enrich the nutrient quality of the soil.

Bacteria (e.g., Rhizobium): Form a symbiotic association with the roots of leguminous plants, fixing atmospheric nitrogen (N2) into usable nitrogenous compounds.

Free-living Bacteria (e.g., Azotobacter, Azospirillum): Fix N2 without forming a symbiotic relationship, making it available to plants.

Fungi (Mycorrhiza): The fungus (Glomus genus) forms a symbiotic association with plant roots. The fungal partner absorbs phosphorus from the soil and passes it to the plant, while the plant provides sugars to the fungus.

Cyanobacteria (Blue-Green Algae): Autotrophic microbes (e.g., Anabaena, Nostoc) that fix atmospheric nitrogen, particularly useful in paddy fields.