HSC Biology Modules 5-8 Practice Flashcards

Mechanisms of Reproduction and Species Continuity

Asexual Reproduction

• Requires only one organism to reproduce and form genetically identical offspring.

• Budding: A type of asexual reproduction where an organism (e.g., a fungus) grows a genetically identical version of itself on its surface, which eventually separates to form a new individual.

• Binary Fission: A process where a single-celled organism splits into two, creating two new organisms.

Sexual Reproduction

• Requires the joining of haploid ($n$) gametes from a male and female parent to form genetically varied offspring.

• Continuity of a Species: Dependent on cell division ensuring daughter cells have the same type and number of genes as the parent cell, maintaining the species despite individual genetic variation.

• Animal Reproduction:

  • Process: Haploid gametes produced in gonads (testes and ovaries) combine to form a diploid ($2n$) zygote. This guarantees variation through meiosis (crossing over and independent segregation) and random fertilization.

  • Advantages: Increased diversity allows survival against selective pressures.

  • Disadvantages: High energy expenditure and time-consuming processes (finding mates, mating).

External vs. Internal Fertilization

• External Fertilization: Gametes combine outside the female's body, typically in aquatic environments.

  • Example: Broadcast spawning (multiple males and females releasing gametes simultaneously).

  • Advantages: No parental care required (females can reproduce again quickly); greater genetic diversity (one organism can fertilize many others); high frequency/rate of breeding.

  • Disadvantages: No guarantee of fertilization; high loss of gametes; requires wet environments to prevent desiccation; high exposure to predation and infection.

• Internal Fertilization: Gametes combine inside the female's body.

  • Advantages: Higher chance of survival for offspring due to protection in a moist environment; higher chance of fertilization in a closed vicinity; parental care; wider selection of mates.

  • Disadvantages: Fewer offspring; requires specialized reproductive structures; high energy cost for mating and lengthy parental care.

Reproduction in Other Organisms

• Plants:

  • Sexual: Involves the Carpel (female: ovary, style, stigma) and Stamen (male: filament, anther). Pollen (male gamete) travels from the anther to the stigma (pollination). After fertilization, the ovule becomes a seed and the ovary becomes a fruit. Germination involves the radical (first root) and plumule (young stem).

  • Asexual: Includes methods like vegetative propagation.

• Fungi:

  • Budding: Used widely by yeasts; involves mitosis to create a DNA copy in a new bud.

  • Spores: Haploid cells replicated via mitosis; light for wind dispersal.

• Bacteria: Reproduce via Binary Fission.

• Protists: Reproduce via Binary Fission and Budding.

Cell Replication and Genetic Material

Key Definitions

• Mitosis: Cell replication creating two identical diploid ($2n$) daughter cells for growth and repair.

• Meiosis: Cell replication producing four unique haploid ($n$) gametes.

• Nucleotide: The building block of DNA, consisting of a deoxyribose sugar, a phosphate molecule, and a nitrogenous base.

Mitosis Process

1. Interphase: DNA replication occurs; chromosomes exist as chromatin.

2. Prophase: Chromosomes condense; nuclear membrane breaks down; spindle fibers form.

3. Metaphase: Chromosomes line up at the equator; spindle fibers attach to centromeres.

4. Anaphase: Sister chromatids are pulled to opposite poles (now called daughter chromosomes).

5. Telophase: Nuclear membranes reappear at opposite ends.

6. Cytokinesis: Division of the cytoplasm into two identical cells.

Meiosis and Genetic Variation

• Meiosis I: Homologous pairs separate. Includes Prophase I (crossing over), Metaphase I (independent assortment), and Anaphase I (random segregation).

• Meiosis II: Sister chromatids separate (similar to mitosis), resulting in four non-identical haploid cells.

• Crossing Over: Exchange of genetic info between inner chromatids of homologous pairs.

• Independent Assortment: Random alignment of homologous pairs at the equator.

• Random Segregation: Alleles separate so each gamete receives only one; they never end up in the same gamete.

DNA Structure (Watson and Crick Model)

• Structure is a double helix with a sugar-phosphate backbone and nitrogenous base rungs.

• Complementary Base Pairing: Adenine (A) pairs with Thymine (T) via $2\text{ hydrogen bonds}$; Guanine (G) pairs with Cytosine (C) via $3\text{ hydrogen bonds}$.

• Antiparallel Strands: Strands run in opposite directions: $3' \rightarrow 5'$ and $5' \rightarrow 3'$.

DNA Replication Process

1. Initiation: Helicase unzips DNA; SSB proteins keep strands apart; Topoisomerase prevents supercoiling.

2. Elongation: Primase adds RNA primers.

   • Leading Strand ($3' \rightarrow 5'$): DNA Polymerase III adds nucleotides continuously toward the fork.

   • Lagging Strand ($5' \rightarrow 3'$): DNA Polymerase III adds nucleotides away from the fork in Okazaki fragments.

   • Ligase: Seals gaps between fragments.

3. Termination: Two semi-conservative strands are formed (each has one original and one new strand).

Polypeptide Synthesis and Genetic Change

Transcription (DNA to mRNA)

• Occurs in the nucleus.

• RNA Polymerase binds to the Promoter Region, separates strands, and builds a complementary mRNA strand using Uracil (U) instead of Thymine (T).

• Splicing (Eukaryotes): Introns (non-coding) are removed, and exons (coding) are joined. A $5'$ cap (Guanine) and $3'$ poly-A tail are added to create mature mRNA.

Translation (mRNA to Protein)

• Occurs at the ribosome.

• mRNA attaches to the ribosome; tRNA with specific anticodons carries amino acids to matching codons.

• Start codon is AUG (Methionine).

• Successive amino acids are linked by peptide bonds until a Stop Codon triggers a release factor, freeing the polypeptide chain.

Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Folding into Alpha Helices or Beta-pleated sheets.

• Tertiary: 3D shape determined by R-group interactions.

• Quaternary: Multiple polypeptide chains folded together.

Mutations

• Mutagens: Environmental factors altering DNA. Includes Physical (ionizing radiation: UV, X-ray, Gamma), Chemical (nicotine, pesticides), and Biological (viruses, bacteria).

• Point Mutations: Alter single nucleotides. Includes Substitution (Silent, Missense, Nonsense) and Frameshift (Insertion/Deletion).

• Chromosomal Mutations: Affect large sections. Includes Deletion, Duplication, Inversion, Translocation, and Aneuploidy (e.g., Down Syndrome: $47\text{ chromosomes}$).

• Somatic vs. Germline: Somatic mutations occur in body cells and are not inherited; Germline mutations occur in gametes and are passed to offspring.

Genetic Technologies and Agriculture

Manipulating Reproduction

• Selective Breeding: Choosing parents with desirable traits for intraspecific or interspecific breeding. Disadvantage: Reduces gene pool.

• Artificial Insemination: Collection and transport of semen. Highly efficient but reduces genetic variation.

• Artificial Pollination: Manual transfer of pollen. Increases yield but can lead to monocultures.

• Cloning:

  • Whole Organism: Techniques like Somatic Cell Nuclear Transfer (SCNT) (e.g., Dolly the sheep).

  • Gene Cloning: Inserting a gene into a bacterial plasmid to produce large quantities of proteins (e.g., insulin).

• Recombinant DNA Technology: Joining DNA from different species to create transgenic organisms (e.g., cows producing human-like milk).

Infectious Disease: Causes and Responses

Pathogen Classification

• Prions: Abnormally folded proteins; cause neurodegeneration (e.g., CJD, Kuru).

• Viruses: Non-cellular; hijack host machinery (e.g., Ebola, Rhinovirus).

• Bacteria: Prokaryotic; release toxins (e.g., Cholera/$Vibrio cholerae$, Bubonic plague/$Yersinia pestis$).

• Protozoans: Eukaryotic, unicellular; often vector-born (e.g., Malaria/$Plasmodium falciparum$).

• Fungi: Eukaryotic heterotrophs; secrete digestive enzymes (e.g., Thrush).

• Macroparasites: Visible multicellular organisms (e.g., Ticks, Liver flukes).

Historical Contributions

• Robert Koch: Formulated Koch's Postulates to link specific microbes to specific diseases.

• Louis Pasteur: Disproved spontaneous generation with the Swan-necked flask experiment; developed pasteurization and vaccines.

Plant and Animal Diseases in Agriculture

• Panama Disease: Caused by the fungus $Fusarium oxysporum$ in Cavendish bananas; threatens total crop wipeout due to lack of genetic variation in clones.

• Sheep Lice: Caused by $Bovicola ovis$; damages wool and irritates sheep, leading to significant economic loss ($>\text{ }100\text{ million per year in NSW}$).

Immune System Responses

• Innate Immunity (1st Line): Physical (Skin, Cilia) and Chemical (Stomach acid, Lysozymes in tears) barriers.

• Innate Immunity (2nd Line): Non-specific responses including the Inflammatory response (histamine release, vasodilation), Phagocytosis (neutrophils/macrophages engulfing pathogens), and Fever.

• Adaptive Immunity (3rd Line):

  • Humoral Response (B Cells): Produce specific antibodies to deactivate antigens; form B memory cells.

  • Cell-Mediated Response (T Cells): Cytotoxic T cells destroy infected cells; Helper T cells coordinate the response; Suppressor T cells stop the response.

Non-Infectious Disease and Homeostasis

Homeostasis

• Maintenance of a stable internal environment. Controlled via negative feedback loops.

• Temperature Regulation: Managed by the hypothalamus; involves vasodilation/vasoconstriction.

• Glucose Regulation: Alpha cells in the pancreas release glucagon when BGL is low (optimal range: $70\text{--}100\text{ mg/dL}$); Beta cells release insulin when BGL is high.

Epidemiology and Management

• Epidemiology: Study of disease distribution. Requires large sample sizes, long durations, and lack of bias for validity and reliability.

• Nutritional Diseases: Include Rickets (Vitamin D deficiency) and Scurvy (Vitamin C deficiency).

• Environmental Diseases: Included Melanoma (UV exposure) and Asbestosis (asbestos fibers).

Assistive Technologies

• Hearing: Hearing Aids (amplify sound), Bone Conduction Implants (vibrations to cochlea), and Cochlear Implants (electrical signals to auditory nerve).

• Vision: Spectacles (Concave for Myopia, Convex for Hyperopia) and Laser Surgery (LASIK).

• Kidney: Dialysis (external removal of waste) and Kidney Transplants.