Unit 10: Applied Biology
10.1 Application of Zoology
Tissue and Organ Transplantation
Organ transplantation involves surgically transferring a functional organ from a donor to a recipient. Commonly transplanted organs include the kidney, heart, liver, and lung. Each organ has specific matching criteria (blood type, HLA antigens) and preservation techniques.
Tissue transplantation refers to the grafting of tissues such as cornea (for vision restoration), skin (for burn victims), and bone marrow (for hematological reconstitution). Corneal grafts have high success rates due to the avascular nature of the cornea, reducing immune rejection.
Immunosuppression is essential to prevent graft rejection. Drugs such as cyclosporine, tacrolimus, mycophenolate mofetil, and corticosteroids inhibit T‑cell activation. Monitoring drug levels and infection signs is crucial for long‑term graft survival.
Ethical issues encompass organ donation consent, fair allocation criteria (e.g., urgency, waiting time, geographic factors), and the prohibition of organ trade. Living donor transplantation raises concerns about donor coercion and postoperative morbidity.
In‑Vitro Fertilization (IVF)
The IVF process consists of several steps: egg collection (transvaginal ultrasound‑guided aspiration), fertilization in the lab (conventional insemination or intracytoplasmic sperm injection), embryo culture (3–5 days), and embryo transfer into the uterus.
Indications include tubal infertility, severe male factor infertility (low count/motility), endometriosis, ovulatory disorders, and unexplained infertility.
Success rates vary with maternal age: approximately 40% live birth per cycle for women < 35 years, decreasing to < 10% for women > 42 years. Factors influencing success include embryo quality, endometrial receptivity, and laboratory expertise.
Risks comprise ovarian hyperstimulation syndrome (OHSS), multiple gestations, ectopic pregnancy, and procedural complications (bleeding, infection). Long‑term follow‑up shows no major increase in congenital anomalies.
Ethical considerations involve embryo disposition (donation, research, cryopreservation), pre‑implantation genetic testing, and the use of donor gametes or surrogacy.
Test‑tube babies is a colloquial term for infants born via IVF. Surrogate mothers carry a pregnancy for another couple, either using the intended mother’s egg (traditional surrogacy) or a donor embryo (gestational surrogacy). Legal frameworks differ widely across countries.
Amniocentesis
Amniocentesis is a prenatal diagnostic technique performed typically between 15–20 weeks gestation. Under ultrasound guidance, a needle extracts ~15‑20 mL of amniotic fluid containing fetal cells and biochemical markers.
Detectable conditions include chromosomal abnormalities (e.g., Trisomy 21 Down syndrome, Trisomy 18 Edwards syndrome, Trisomy 13 Patau syndrome), single‑gene disorders (cystic fibrosis, sickle cell disease), and neural tube defects (via elevated alpha‑fetoprotein).
Legal restrictions: Many countries prohibit sex determination via amniocentesis to prevent gender‑based selective abortion. In India, the Pre‑Conception and Pre‑Natal Diagnostic Techniques (PCPNDT) Act bans such use.
Risks consist of procedure‑related miscarriage (≈0.5‑1 %), infection, amniotic fluid leakage, and fetal injury. Counseling and informed consent are mandatory before the procedure.
Genetically Modified Organisms (Transgenic Animals)
Definition: Transgenic animals are organisms whose genome has been altered by the stable integration of foreign DNA (transgene) using recombinant DNA technology.
Methods of transgene delivery include:
- Microinjection of DNA into the pronucleus of fertilized zygotes.
- Retroviral vectors** that infect embryos and integrate the transgene.
- Embryonic stem cell-mediated gene targeting** (knock‑in/knock‑out).
- CRISPR/Cas9** mediated genome editing for precise modifications.
Applications span basic research (gene function studies), pharmaceutical production (e.g., transgenic goats producing antithrombin III in milk), disease models (e.g., oncogene‑expressing mice for cancer research), and xenotransplantation (pigs expressing human complement regulatory proteins).
Ethical concerns involve animal welfare (potential pain, abnormal phenotypes), environmental impact (gene flow to wild populations), and societal issues (consumption of transgenic animal products, patenting of life forms). Regulatory frameworks require rigorous containment and phenotypic assessment.
Poultry Farming
Types based on purpose:
- Broiler – raised for meat production, fast‑growing (≈5‑6 weeks to market weight).
- Layer – kept for egg production, longer productive life (≈72 weeks).
Common Breeds:
- White Leghorn – high egg‑laying efficiency, white eggs.
- Rhode Island Red – dual‑purpose, brown eggs, good meat quality.
- Broiler hybrids (e.g., Cobb 500, Ross 308) – optimized for rapid growth and feed conversion.
Management Practices:
- Housing: controlled‑environment sheds with ventilation, lighting, and litter management.
- Feeding: nutritionally balanced diets (starter, grower, finisher phases) containing proteins, carbohydrates, vitamins, and minerals.
- Disease control: vaccination (Newcastle disease, infectious bronchitis), biosecurity (restricted access, disinfection), and prompt treatment of bacterial infections (e.g., colibacillosis).
Economic importance: Poultry provides a cheap source of high‑quality protein and essential amino acids, generates employment in farming, processing, and distribution, and contributes significantly to national GDP and export earnings.
Fish Farming (Aquaculture)
Types by water salinity:
- Freshwater – ponds, tanks, raceways.
- Marine – sea cages, offshore pens.
- Brackish water – estuarine ponds, integrated mangrove systems.
Common Species:
- Carp (Cyprinus carpio) – tolerant, omnivorous.
- Tilapia (Oreochromis spp.) – fast‑growing, warm‑water.
- Salmon (Salmo salar) – high‑value, cold‑water marine.
- Shrimp (Litopenaeus vannamei, Penaeus monodon) – high‑value crustacean.
Culture Methods:
- Pond culture – earthen ponds, fertilization, supplemental feeding.
- Cage culture – floating net cages in lakes, reservoirs, or seas.
- Rice‑fish culture – simultaneous rice cultivation and fish stocking, enhancing land‑use efficiency.
- Recirculating aquaculture systems (RAS) – closed‑loop water treatment for intensive production.
Economic importance: Aquaculture supplies > 50 % of global fish consumption, improves food security, provides livelihoods for coastal and rural communities, and contributes to foreign exchange through export of high‑value species (e.g., shrimp, salmon). Sustainable practices focus on reducing feed fish dependence, managing effluents, and preventing disease outbreaks.
10.2 Microbial Diseases and Application of Microbiology
Risk and Hazard Groups
Microorganisms are classified into four risk groups based on pathogenicity, transmissibility, and availability of effective prophylaxis or treatment.
| Risk Group | Description | Example Organisms | |
|---|---|---|---|
| RG > | Risk Group 1 | Low risk – unlikely to cause disease in healthy adults. | Non‑pathogenic Escherichia coli K‑12, Bacillus subtilis |
| Risk Group 2 | Moderate risk – can cause disease but limited spread; effective prophylaxis/treatment available. | Salmonella spp., Hepatitis B virus, Staphylococcus aureus | |
| Risk Group 3 | High risk – may cause serious disease; potential for aerosol transmission; limited vaccines/treatment. | Mycobacterium tuberculosis, HIV, Bacillus anthracis | |
| Risk Group 4 | Extreme risk – causes lethal disease; high aerosol transmission; no effective vaccines/treatment. | Ebola virus, Variola (smallpox) virus, Marburg virus |
Selected Human Diseases
The following table summarizes key aspects of important bacterial, viral, and fungal diseases.
| Disease | Causative Agent | Transmission | Key Clinical Features | Prevention / Control |
|---|---|---|---|---|
| Typhoid fever | Salmonella typhi | Fecal‑oral; contaminated water/food | Prolonged fever, headache, abdominal pain, rose‑spot rash, relative bradycardia | Safe water, sanitation, hand hygiene, Typhoid Vi polysaccharide vaccine |
| Tuberculosis (TB) | Mycobacterium tuberculosis | Airborne droplet nuclei | Chronic cough > 2 weeks, night sweats, weight loss, hemoptysis, cavitary lesions on CXR | BCG vaccine, DOTS (Directly Observed Treatment, Short‑course), infection control |
| HIV Infection | Human Immunodeficiency Virus (HIV‑1/2) | Sexual contact, blood transfusion, needle sharing, mother‑to‑child | Progressive CD4⁺ T‑cell loss, opportunistic infections, AIDS‑defining illnesses | Safe sex, condom use, needle exchange programs, ART (antiretroviral therapy), PrEP |
| Cholera | Vibrio cholerae O1/O139 | Contaminated water/food | Profuse watery diarrhea (“rice‑water stools”), vomiting, rapid dehydration, electrolyte loss | Safe water, oral rehydration salts (ORS), cholera vaccine (WC‑rBS) |
| Influenza | Influenza virus A, B, C | Respiratory droplets, aerosols | Sudden fever, myalgia, sore throat, cough, fatigue; can lead to pneumonia | Annual inactivated or live‑attenuated vaccine, antiviral neuraminidase inhibitors (oseltamivir) |
| Hepatitis (A‑E) | HAV, HBV, HCV, HDV, HEV | HAV/HEV – fecal‑oral; HBV/HCV/HDV – blood, sexual, perinatal | Jaundice, fatigue, anorexia, elevated transaminases; chronic HBV/HCV → cirrhosis, HCC | Vaccines for HAV & HBV; safe blood products, harm reduction for HCV; HEV – safe water |
| Candidiasis | Candida albicans (yeast) | Endogenous overgrowth; risk factors: antibiotics, immunosuppression, diabetes | Oral thrush (white plaques), vulvovaginal itching/discharge, cutaneous intertrigo, systemic candidiasis in immunocompromised | Good glycemic control, prudent antibiotic use, topical/systemic antifungals (fluconazole, amphotericin B) |
Basic Concepts of Immunology
The immune system operates in three overlapping lines of defense.
- First line – physical and chemical barriers: skin, mucous membranes, lysozyme, gastric acid, normal flora.
- Second line – innate cellular responses: phagocytes (neutrophils, macrophages), natural killer cells, inflammation, fever, complement system.
- Third line – adaptive immunity: antigen‑specific lymphocytes (B cells produce antibodies; T cells mediate cellular immunity), immunological memory.
Vaccines stimulate adaptive immunity without causing disease. Major types:
- Live attenuated – weakened but replicating pathogens (e.g., MMR, oral polio).
- Killed (inactivated) – chemically/physically inactivated pathogens (e.g., IPV, hepatitis A).
- Subunit/recombinant – purified antigens (e.g., Hepatitis B surface antigen, HPV VLPs).
- Toxoid – inactivated toxins (e.g., diphtheria, tetanus toxoids).
- mRNA vaccines** – lipid‑nanoparticle‑encapsulated mRNA encoding antigen (e.g., Pfizer‑BioNTech, Moderna COVID‑19 vaccines).
Herd immunity occurs when a sufficient proportion of the population is immune, reducing the probability of pathogen transmission and protecting susceptible individuals. The threshold depends on the basic reproduction number (R₀): Herd‑immunity threshold = 1 − 1/R₀.
Antibody classes (immunoglobulins)** and their primary functions:
| Isotype | Key Features | Principal Roles |
|---|---|---|
| IgG | Most abundant in serum; crosses placenta | Neutralization, opsonization, complement activation, long‑term immunity |
| IgM | Pentamer; first responder in primary response | Agglutination, complement activation, early infection marker |
| IgA | Dimeric in secretions (gut, respiratory tract) | Mucosal immunity, pathogen exclusion |
| IgE | Binds FcεRI on mast cells & basophils | Allergic reactions, defense against helminths |
| IgD | Surface marker on naïve B cells | B‑cell activation and antigen receptor signaling |
Application of Microorganisms
Microbes are harnessed across industries for food production, beverage fermentation, environmental management, and agricultural productivity.
Dairy Industries
- Lactobacillus spp. – ferment lactose to lactic acid, producing yogurt, curd, and buttermilk.
- Streptococcus thermophilus – synergistic with Lactobacillus in yogurt; contributes to flavor and texture.
- Propionibacterium freudenreichii – produces propionic acid and CO₂, creating characteristic “eyes” in Swiss cheese.
- Lactococcus lactis – used in cheese starter cultures; facilitates curd formation.
Beverage Industries
- Saccharomyces cerevisiae – ferments sugars to ethanol and CO₂ in beer, wine, and bread making.
- Saccharomyces pastorianus – lager yeast, ferments at lower temperatures.
- Various fungi and bacteria** – involved in tea (e.g., Acetobacter for kombucha) and coffee fermentation, influencing aroma and acidity.
Microbial Contamination of Water
- Saccharomyces cerevisiae – ferments sugars to ethanol and CO₂ in beer, wine, and bread making.
- Saccharomyces pastorianus – lager yeast, ferments at lower temperatures.
- Various fungi and bacteria** – involved in tea (e.g., Acetobacter for kombucha) and coffee fermentation, influencing aroma and acidity.
Microbial Contamination of Water
Coliform bacteria (total coliforms, fecal coliforms, Escherichia coli) serve as indicators of fecal contamination and potential presence of pathogens. Regulatory limits: < 1 CFU/100 mL for drinking water.
Sewage Treatment
- Primary treatment – physical processes: screening, grit removal, sedimentation (primary sludge).
- Secondary treatment – biological processes: activated sludge, trickling filters, rotating biological contactors; microbes oxidize organic matter (BOD removal).
- Tertiary treatment – advanced polishing: filtration (sand, membrane), nutrient removal (nitrification/denitrification), disinfection (chlorination, UV, ozonation).
Drinking Water Treatment
- Coagulation – addition of alum or ferric chloride to neutralize colloidal charges.
- Sedimentation – flocs settle in clarifiers.
- Filtration – rapid sand or dual‑media filters remove remaining particles.
- Disinfection – chlorine, chloramine, ozone, or UV to inactivate pathogens.
Bio‑control Agents
- Coagulation – addition of alum or ferric chloride to neutralize colloidal charges.
- Sedimentation – flocs settle in clarifiers.
- Filtration – rapid sand or dual‑media filters remove remaining particles.
- Disinfection – chlorine, chloramine, ozone, or UV to inactivate pathogens.
Bio‑control Agents
Microorganisms used to suppress pests and diseases, reducing chemical pesticide reliance.
- Trichoderma spp. – antagonistic fungi that parasitize plant pathogenic fungi; promote plant growth.
- Bacillus thuringiensis (Bt) – produces Cry toxins lethal to specific insect larvae (Lepidoptera, Diptera, Coleoptera).
- Nucleopolyhedrovirus (NPV)** – baculoviruses infecting insect hosts; species‑specific, environmentally safe.
Bio‑fertilizers
Beneficial microbes that enhance nutrient availability to plants.
- Rhizobium – forms nodules on legume roots, fixing atmospheric N₂.
- Azotobacter – free‑living aerobic nitrogen fixer in soil.
- Anabaena – filamentous cyanobacterium, fixes N₂, used in rice paddies.
- Mycorrhizal fungi** (e.g., Glomus) – form symbiotic associations with plant roots, improving phosphorus uptake and water relations.
These applications demonstrate the profound impact of microbiology on human welfare, food security, and environmental sustainability.