HSC Biology Summary Notes - Modules 5 to 8

Pathogen Classification and Transmission

• Pathogens are classified into six categories:

  • Prion: Non-living, abnormally folded proteins (e.g., Mad cow disease).

  • Virus: Non-living, non-cellular DNA/RNA packages (e.g., $HIV$, Ebola, Influenza).

  • Bacteria: Unicellular prokaryotes reproducing via binary fission (e.g., Tuberculosis, Tetanus).

  • Protozoa: Unicellular eukaryotes (e.g., Malaria).

  • Fungi: Eukaryotic organisms reproducing via spores (e.g., Tinea, Black spot).

  • Macroparasite: Multicellular organisms (e.g., Ticks, Tapeworms).

• Modes of transmission include direct contact, indirect contact, and vector transmission.

• Case Study: Ebola Virus Epidemic (West Africa, $2014-2016$):

  • Source: Guinea (wild bats).

  • Statistics: $28,000$ cases and $11,500$ deaths.

  • Management: Isolation for $21$ days, screening at airports, and the ban of burial practices.

Historical Foundations of Microbiology

• $Koch's$ Postulates: A four-step criteria to determine if a specific microorganism causes a specific disease.

• $Pasteur's$ Experiments: Disproved spontaneous generation using swan-neck flasks; established the germ theory of disease and the process of Pasteurisation.

• Agricultural Impact:

  • Plant Diseases: Potato Blight (fungus) leading to Irish starvation.

  • Animal Diseases: Flystrike (parasite) impacting livestock productivity.

Immune Responses in Plants and Animals

• Plant Response: Includes basal resistance, gene-for-gene resistance, hypersensitive response (programmed cell death), and systemic acquired resistance.

• Animal Innate Immunity ($1^{st}$ and $2^{nd}$ Lines of Defence):

  • Physical/Chemical Barriers: Skin, stomach acid, and mucous membranes.

  • Inflammatory Response: Triggered by cytokines and histamines; involves phagocytosis by neutrophils and macrophages.

• Adaptive Immunity ($3^{rd}$ Line of Defence):

  • Humoral Immunity: Helper $T$ cells activate $B$ cells to differentiate into plasma cells that secrete antibodies.

  • Cell-mediated Immunity: Cytotoxic $T$ cells destroy infected cells.

Heredity and Cell Replication

• Reproduction Mechanisms:

  • Animals: Internal vs. external fertilisation.

  • Plants: Sexual (pollination) and asexual (runners, tubers).

  • Microbes: Budding, binary fission, and spore formation.

• Cell Replication:

  • Mitosis: Produces two identical somatic daughter cells for growth and repair.

  • Meiosis: Produces four non-identical haploid gametes through crossing over and independent assortment.

• DNA Replication: Involves Helicase (unwinding), DNA Polymerase (adding nucleotides), and Ligase (sealing).

Polypeptide Synthesis and Genetic Variation

• Polypeptide Synthesis:

  • Transcription: RNA polymerase creates an $mRNA$ copy of a DNA template.

  • Translation: Ribosomes read $mRNA$ codons to assemble amino acids via $tRNA$ anticodons.

• Variation Sources: Crossing over (Prophase $I$), independent assortment (Metaphase $I$), random fertilisation, and mutations.

• Inheritance Patterns:

  • Autosomal: Dominant and recessive traits.

  • Sex-linkage: Traits located on $X$ or $Y$ chromosomes (e.g., Haemophilia).

  • Co-dominance: Both alleles expressed (e.g., Roan cattle, $AB$ blood type).

  • Incomplete Dominance: Blending of traits (e.g., Pink snapdragons).

Genetic Change and Biotechnology

• Mutagens: Electromagnetic radiation ($UV$, $X$-rays, $Gamma$), chemicals, and biological agents (viruses).

• Mutation Types: Point (substitution, insertion, deletion), Frameshift, and Chromosomal (deletion, duplication, inversion, translocation).

• Biotechnology Applications:

  • Past: Fermentation and selective breeding.

  • Modern: Recombinant DNA (e.g., $BT$ Cotton, Golden Rice), $IVF$, and cloning.

  • Medical: Mass production of insulin and mRNA vaccines.

Homeostasis and Non-Infectious Disease

• Homeostasis: Maintenance of a stable internal environment via negative feedback loops for temperature and blood glucose levels.

• Disease Categories:

  • Genetic: E.g., Haemophilia ($X$-linked).

  • Environmental: E.g., Melanoma (caused by $UV$ radiation) and Lead poisoning.

  • Nutritional: E.g., Scurvy (Vitamin $C$ deficiency) and Anaemia (iron deficiency).

  • Cancer: Uncontrolled cell division (e.g., Lung cancer, Breast cancer).

• Epidemiology: Use of incidence (new cases) and prevalence (total cases) data to establish links between disease and cause.

Assistive Technologies for Human Disorders

• Hearing Loss: Treated via hearing aids (amplification), bone conduction implants (vibration), or cochlear implants (direct nerve stimulation).

• Visual Disorders:

  • Myopia: Short-sightedness corrected with concave lenses.

  • Hyperopia: Long-sightedness corrected with convex lenses.

  • Cataracts: Corrected via phacoemulsification surgery to replace the lens.

• Kidney Failure: Treated via haemodialysis (filtering blood through a machine) or organ transplantation.