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1. Microbes in Sewage Treatment (Activated Sludge)

• Primary treatment: Physical removal of large solid particles by sedimentation.
• Secondary (biological) treatment: Sewage is aerated and mixed with activated sludge — a mass of aerobic bacteria, fungi, and other microbes. These microbes break down organic matter (BOD — biological oxygen demand) through decomposition.
• The microbial mass forms flocs (aggregates) that settle out as sludge. Some sludge is recycled back ("activated"), and the rest is treated as biogas-generating waste via anaerobic digestion by methanogens (which produce biogas: CH₄ + CO₂).
• The clarified, treated water is then discharged. This is a key application of microbiology to public health and environmental management.

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2. Microbes in Food — Lactobacillus

• They carry out lactic acid fermentation — converting sugars (lactose, glucose) into lactic acid.
• This acidification preserves food and gives it characteristic flavors.
• Key applications:
  • Curd/Yogurt: Lactobacillus converts milk (lactose → lactic acid), causing it to coagulate.
  • Cheese: Along with other bacteria and fungi, Lactobacillus is essential for fermentation and ripening.
  • Bread (sourdough), pickles, and sauerkraut also involve bacterial fermentation.
• As probiotics, Lactobacillus species (along with Bifidobacterium) colonize the gut, suppress harmful bacteria, and support digestion and immunity. They are found in supplements and fermented foods like kefir and yogurt. — Medical Microbiology 9e

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3. Antibiotic — Penicillin Discovery

• In 1928, Scottish bacteriologist Alexander Fleming was studying Staphylococcus variants at St. Mary's Hospital, London.
• He noticed that a mold (Penicillium notatum) had contaminated a culture plate and created a clear zone of inhibition around it — meaning it was killing the bacteria.
• He identified the active substance as penicillin.
• Later, Howard Florey and Ernst Chain (1940s) purified and mass-produced it.
• Mechanism: Penicillin inhibits bacterial cell wall synthesis by blocking transpeptidase enzymes (penicillin-binding proteins), causing bacteria to lyse.
• It launched the antibiotic era, saving millions of lives from previously fatal bacterial infections. — Goodman & Gilman's Pharmacological Basis of Therapeutics; Medical Microbiology 9e

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4. Disease — Malaria (Plasmodium)

• P. falciparum — most dangerous, causes cerebral malaria
• P. vivax — most widespread
• P. malariae
• P. ovale (P. knowlesi causes zoonotic malaria in Southeast Asia)

1. Mosquito injects sporozoites → travel to the liver
2. Liver stage: sporozoites infect hepatocytes and multiply (exo-erythrocytic cycle)
3. Blood stage: merozoites released, enter RBCs, multiply → rupture RBCs → causes the classic fever cycles (every 48–72 hours depending on species)
4. Some develop into gametocytes → mosquito ingests these → sexual reproduction in mosquito gut → sporozoites form again

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5. Disease — AIDS (HIV)

• HIV-1 is the primary global cause; HIV-2 is less virulent and mainly in West Africa.
• HIV predominantly targets CD4+ T lymphocytes (helper T cells) by binding to CD4 receptors and co-receptors CCR5 or CXCR4.
• It uses reverse transcriptase to convert its RNA genome into DNA, which integrates into the host cell's genome.
• Progressive destruction of CD4+ T cells collapses cellular immunity.
• AIDS is diagnosed when CD4 count falls below 200 cells/µL or when AIDS-defining opportunistic infections/cancers appear (e.g., Pneumocystis jirovecii pneumonia, Kaposi's sarcoma).
• Transmission: unprotected sexual contact, contaminated blood/needles, mother-to-child (vertical).
• Treatment: Antiretroviral therapy (ART) — combinations of drugs targeting reverse transcriptase, protease, and integrase. — Washington Manual; Goldman-Cecil Medicine

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6. Cancer Cause — Uncontrolled Cell Division

• Normal cell division is regulated by:
  • Proto-oncogenes: promote cell growth (when mutated → oncogenes, they accelerate division)
  • Tumor suppressor genes (e.g., p53, Rb): apply brakes to the cell cycle (when mutated/deleted → brakes fail)
  • DNA repair genes: fix mutations (when defective → mutations accumulate)
• Carcinogenesis occurs when mutations accumulate in these regulatory genes (due to radiation, chemicals, viruses, or hereditary factors), causing:
  • Uncontrolled proliferation
  • Evasion of apoptosis (programmed cell death)
  • Invasion into surrounding tissue (malignancy)
  • Spread to distant sites (metastasis)
• Benign tumors: grow locally, do not invade or metastasize.
• Malignant tumors (cancer): invade and metastasize — this is what makes them life-threatening.
• Examples: carcinoma (epithelial origin), sarcoma (connective tissue), leukemia (blood cells), lymphoma (lymphatic tissue).

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🧫 BIOLOGY IN HUMAN WELFARE — NCERT (Class 12)

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1. Microbes in Sewage Treatment (Activated Sludge)

Treatment Process:

• Sewage passed through sequential filtration (removes large floating materials)
• Then through sedimentation tanks where grit (soil, small pebbles) settles
• The primary sludge settles at bottom; the supernatant is called primary effluent

• Primary effluent is passed into large aeration tanks
• It is constantly agitated and air is pumped in
• This allows aerobic bacteria to grow rapidly and form flocs
• Flocs = masses of bacteria associated with fungal filaments forming mesh-like structures
• Bacteria digest the organic matter → BOD (Biological Oxygen Demand) is significantly reduced
• After BOD reduction, effluent goes to a settling tank
• Flocs settle → called activated sludge
• A small part of activated sludge is pumped back into the aeration tank (as inoculum)
• Remaining sludge is pumped into large anaerobic sludge digesters

• Anaerobic bacteria digest the organic matter and microbes in the sludge
• Produce a mixture of gases: methane + CO₂ + H₂S → called biogas
• Treated water is released into rivers/streams

🔑 NEET Key Point: BOD = amount of oxygen consumed by bacteria to oxidize organic matter in 1 litre of water. Higher BOD = more polluted water.

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2. Microbes in Food — Lactobacillus

Lactobacillus and Curd:

• Lactobacillus and other Lactic Acid Bacteria (LAB) are present in curd
• When a small amount of curd (inoculum) is added to fresh milk and kept warm:
  • LAB multiply in milk
  • They convert lactose → lactic acid
  • Lactic acid causes coagulation and partial digestion of milk protein (casein)
  • Milk sets into curd
• LAB produce vitamins especially Vitamin B₁₂
• LAB in our stomach keep harmful microbes in check

Other Microbe-based Foods:

🔑 NEET Key Point: LAB = good example of microbes in food; they produce lactic acid and Vitamin B₁₂. Saccharomyces cerevisiae = used in bread, beer, wine.

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3. Antibiotic — Penicillin Discovery

What are Antibiotics?

• Chemical substances produced by microbes that can kill or inhibit the growth of other (pathogenic) microbes
• The word comes from Greek: anti = against, bios = life

Discovery of Penicillin — Alexander Fleming (1928):

• Alexander Fleming was working with Staphylococcus bacteria
• He observed that a mould (Penicillium notatum) had contaminated his culture plate
• Around the mould, there was a clear zone — the Staphylococcus colonies had been killed
• He realized the mould was producing something that killed the bacteria → named it Penicillin
• Ernest Chain and Howard Florey later established the full potential of penicillin as an antibiotic (Nobel Prize 1945)

🔑 NEET Key Point: Fleming discovered penicillin in 1928 from Penicillium notatum. Chain and Florey developed it for medical use. Penicillin is effective against gram-positive bacteria.

Other Important Antibiotics (NCERT mentions):

• Streptomycin → from Streptomyces griseus
• Chloramphenicol → from Streptomyces venezuelae
• Tetracycline, erythromycin → also from Streptomyces

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4. Disease — Malaria (Plasmodium)

Causative Organism:

• Plasmodium — a protozoan parasite
• Different species cause different types of malaria:

Vector:

• Female Anopheles mosquito is the vector (transmits the parasite)
• Mosquito = definitive host (sexual reproduction occurs here)
• Human = intermediate host (asexual reproduction occurs here)

Life Cycle (NCERT):

1. Infected female Anopheles bites human → injects sporozoites (infective form) into blood
2. Sporozoites reach the liver → enter liver cells (hepatocytes)
3. Liver stage (exo-erythrocytic cycle): sporozoites multiply asexually → form merozoites
4. Merozoites released into blood → enter Red Blood Cells (RBCs)
5. Blood stage (erythrocytic cycle): multiply inside RBCs → RBCs burst → more merozoites released
6. Bursting of RBCs → releases toxins → causes chills and high fever (every 48–72 hrs)
7. Some merozoites develop into gametocytes (male & female)
8. Mosquito bites infected person → ingests gametocytes → fertilization occurs in mosquito gut → sporozoites form in salivary glands → cycle continues

Symptoms:

• Recurring fever with chills, headache, muscle pain
• Anaemia (due to RBC destruction)
• Enlargement of spleen

Treatment:

• Quinine (from Cinchona bark) — classical drug
• Chloroquine — common antimalarial

🔑 NEET Key Points:

• P. falciparum = most dangerous
• Female Anopheles = vector
• Sporozoites = infective stage injected into humans
• Merozoites = form that infects RBCs
• Fever is due to bursting of RBCs

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5. Disease — AIDS (HIV)

Full Form:

• AIDS = Acquired Immuno Deficiency Syndrome
• HIV = Human Immunodeficiency Virus

Nature of HIV:

• HIV is a retrovirus — has RNA as its genetic material
• Contains the enzyme reverse transcriptase (converts RNA → DNA inside host cell)
• Belongs to the family Retroviridae

How HIV Causes AIDS (NCERT):

1. HIV enters the body through infected blood/sexual contact/mother to child
2. Virus enters macrophages first → RNA replicates using reverse transcriptase → viral DNA formed → new viruses bud off
3. HIV then attacks Helper T-lymphocytes (TH / CD4+ cells)
4. Viral DNA integrates into host cell's DNA
5. New HIV particles produced → infect more TH cells
6. Over time, TH cell count drops drastically
7. Person loses immunity → becomes susceptible to opportunistic infections (infections by normally harmless microbes)

Transmission:

• Sexual contact with infected person
• Contaminated needles/syringes (IV drug users)
• Transfusion of infected blood
• Infected mother to child (during birth or breast feeding)
• NOT transmitted by: casual contact, hugging, handshakes, toilet seats, mosquitoes

Symptoms:

• Rapid weight loss, prolonged fever, diarrhoea
• Recurrent infections (TB, fungal infections, etc.)
• Window period: time between HIV infection and appearance of antibodies (~3 weeks to 3 months; person is infectious but tests may be negative)

Diagnosis:

• ELISA (Enzyme-Linked ImmunoSorbent Assay) — detects HIV antibodies
• Western Blot — confirmatory test

Prevention:

• Safe sex (use of condoms)
• Use of sterilized needles
• Screening of blood before transfusion
• No vaccine available till date

🔑 NEET Key Points:

• HIV = retrovirus, RNA virus
• Attacks CD4+ T-helper lymphocytes
• Reverse transcriptase converts RNA → DNA
• ELISA = diagnostic test
• AIDS = loss of immune function → opportunistic infections

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6. Cancer — Uncontrolled Cell Division

Definition (NCERT):

Normal Cells vs Cancer Cells:

Types of Tumours:

• Benign tumour: Cells remain confined in their original location. Do not invade other tissues. Generally not life-threatening.
• Malignant tumour (Cancer): Cells grow rapidly, invade neighbouring tissues, and spread to distant sites.

Metastasis:

• Process by which cancerous cells break away from the original tumour, enter blood/lymph, travel to distant organs, and form new tumours
• This is what makes cancer dangerous and hard to treat

Causes of Cancer — Carcinogens:

Proto-oncogenes:

• Normal genes that control cell division
• When mutated → become oncogenes → cause uncontrolled division → cancer

Diagnosis:

• Biopsy — tissue sample examined histologically
• MRI, CT scan, X-ray — imaging to detect tumours
• Blood tests — for leukemia (blood cancer)

Treatment:

🔑 NEET Key Points:

• Cancer = loss of contact inhibition
• Malignant > Benign (in terms of danger)
• Metastasis = spread to distant organs (characteristic of malignant tumours)
• Tobacco = most common chemical carcinogen
• α-interferon = used in biological response modifier therapy

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Quick Revision Table for NEET