Biology Exam Revision Notes

ENERGY

  • Mesocosms

    • Controlled mini-ecosystems used for studying nutrient cycles and energy flow.
    • Contain producers, consumers, and decomposers in a balanced environment.
    • Useful for testing sustainability in ecological models.

  • Energy Flow

    • Source: Sunlight is converted by producers (plants) via photosynthesis.
    • Flow: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer
    • Loss: Approximately 90% of energy is lost at each trophic level, mainly as heat.

  • Pyramids of Energy

    • Show the energy available at each trophic level.
    • Units: kJm2⋅year\frac{kJ}{m^2 \cdot year}
    • The width of each level represents the energy content.

TRANSFORMATION

  • Macromolecules & Their Subunits

    • Carbohydrates:
      • Subunits: Monosaccharides (e.g., glucose)
    • Proteins:
      • Subunits: Amino acids form dipeptides that form polypeptides.
    • Lipids:
      • Subunits: Fatty acids and glycerol.
    • Nucleic Acids:
      • Subunits: Nucleotides (sugar, phosphate, base).
    • Enzymes
      • Biological catalysts.
      • The active site matches the substrate.
      • Affected by temperature, pH, and substrate concentration.
      • Denaturation occurs if conditions are extreme.

  • DNA Replication

    • Semi-conservative: Each new DNA molecule has one old strand and one new strand.
    • Helicase unwinds the DNA.
    • DNA polymerase adds new nucleotides.

  • Transcription (DNA → mRNA)

    • Occurs in the nucleus.
    • RNA polymerase reads the DNA and builds mRNA.

  • Translation (mRNA → Protein)

    • Occurs in the cytoplasm/ribosome.
    • tRNA matches codons with amino acids.
    • Ribosomes link amino acids to form polypeptides.

GENETICS

  • Chromosomes

    • Haploid (n): One set of chromosomes, found in gametes.
    • Diploid (2n): Two sets of chromosomes, found in body cells.

  • Genotype vs Phenotype

    • Genotype: Genetic makeup (e.g., Aa, BB).
    • Phenotype: Observable traits (e.g., blue eyes).

  • Punnett Squares

    • Used to predict genetic outcomes.
    • Alleles: Dominant (A), Recessive (a).
    • Codominance: A and B alleles are both expressed in AB blood type.
    • Multiple alleles: More than two alleles exist (e.g. IAI^A, IBI^B, i).

  • Mitosis vs Meiosis

    • Mitosis
      • Purpose: Growth, repair.
      • Number of Divisions: 1
      • Number of Cells Made: 2 identical cells (diploid)
      • Genetic Variation: No
    • Meiosis
      • Purpose: Gamete formation.
      • Number of Divisions: 2
      • Number of Cells Made: 4 varied cells (haploid)
      • Genetic Variation: Yes (crossing over, independent assortment)

FORM

  • Species

    • Organisms that can breed to produce fertile offspring.

  • Prokaryotes vs Eukaryotes

    • Prokaryote
      • Nucleus: No
      • Size: Small (approximately 1-5 μm)
      • Organelles: No membrane-bound organelles
      • DNA: Circular, free in cytoplasm
      • Cell Type: Usually unicellular
      • Example: Bacteria
    • Eukaryote
      • Nucleus: Yes
      • Size: Larger (approximately 10-100 μm)
      • Organelles: Membrane-bound organelles
      • DNA: Linear, inside nucleus
      • Cell Type: Usually multicellular
      • Example: Plants, animals, fungi, protists

MOVEMENT

  • Membrane Structure

    • Phospholipid bilayer: Hydrophilic heads, hydrophobic tails.
    • Proteins: Channels, carriers, enzymes, receptors.
    • Cholesterol: Maintains membrane fluidity.

  • Transpiration

    • Evaporation of water from stomata.
    • Creates suction that pulls water up through xylem from roots.

  • Leaf Cross-Section Layers (from top to bottom)

    1. Waxy Cuticle
    2. Upper Epidermis
    3. Palisade Mesophyll (photosynthesis)
    4. Spongy Mesophyll (gas exchange)
    5. Vascular Bundle (xylem & phloem)
    6. Lower Epidermis with Stomata

BALANCE

  • Homeostasis
    • Maintaining internal stability (e.g., body temperature, pH, glucose).
    • Controlled via negative feedback loops.