FY12CE Biology cheat sheet

Water: polar covalent O–H bonds, hydrogen bonding between molecules; high specific heat, high heat of vaporization, cohesion/adhesion, and lower density as a solid (ice floats) because the crystal lattice is less tightly packed.

Monomers to polymers by condensation (dehydration) synthesis, releasing one water per bond formed; hydrolysis reverses it by adding water. Bonds: glycosidic (carbohydrates), ester (triglycerides, phospholipids), peptide (proteins), phosphodiester (nucleic acids).

Enzyme kinetics: rate rises with substrate concentration to Vmax; Michaelis constant Km equals the substrate concentration at half Vmax, so a low Km means high affinity. Temperature and pH above optimum denature by disrupting hydrogen bonds and ionic interactions, not peptide bonds.

Competitive inhibitors raise apparent Km with Vmax unchanged; non-competitive (allosteric) inhibitors lower Vmax with Km unchanged.

Membrane transport: simple diffusion and osmosis are passive; facilitated diffusion uses channels or carriers down a gradient; primary active transport (Na+/K+ ATPase, 3 Na+ out per 2 K+ in) and secondary active transport (cotransport) require energy input.

Osmosis rule: water moves toward higher solute concentration (lower water potential). Animal cells lyse in hypotonic solution and shrivel in hypertonic; plant cells become turgid in hypotonic solution because the cell wall resists expansion.

Photosynthesis: light reactions in thylakoid membranes split water, release O2, and produce ATP and NADPH; the Calvin cycle in the stroma fixes CO2 with rubisco. Net equation: 6CO2 + 6H2O + light -> C6H12O6 + 6O2.

Cellular respiration: glycolysis (cytosol, net 2 ATP, 2 NADH), pyruvate oxidation and the Krebs cycle (mitochondrial matrix, 2 ATP, 6 NADH, 2 FADH2 per glucose), oxidative phosphorylation on the inner membrane (about 26-28 ATP). Fermentation regenerates NAD+ without oxygen.

Cell cycle checkpoints (G1, G2, spindle/M) halt the cycle on DNA damage or failed spindle attachment; uncontrolled progression from mutated proto-oncogenes or inactivated tumour-suppressor genes (e.g. p53) promotes cancer.

Mendel's law of segregation: two alleles per gene separate during meiosis, one per gamete. Law of independent assortment: alleles of unlinked genes assort independently during metaphase I.

Monohybrid cross Aa x Aa gives 1 AA : 2 Aa : 1 aa genotypes and 3 : 1 phenotypes for complete dominance; a testcross with a homozygous recessive reveals an unknown genotype.

Dihybrid cross AaBb x AaBb gives a 9 : 3 : 3 : 1 phenotype ratio when genes are unlinked and show complete dominance.

Codominance (both alleles expressed, e.g. AB blood type) differs from incomplete dominance (blended intermediate phenotype). Multiple alleles: ABO has IA, IB, i.

Sex-linked traits: X-linked recessive alleles affect males more often because males are hemizygous (XY). An affected father cannot pass an X-linked allele to sons but passes it to all daughters as carriers.

DNA structure: antiparallel double helix, A pairs with T (2 hydrogen bonds), G pairs with C (3 hydrogen bonds); purines A and G, pyrimidines T and C.

Replication is semiconservative: helicase unwinds, primase lays RNA primers, DNA polymerase III extends 5' to 3' (leading strand continuous, lagging strand in Okazaki fragments), ligase seals nicks.

Transcription in the nucleus uses RNA polymerase to make mRNA (U replaces T); translation at ribosomes reads codons 5' to 3' against anticodons, AUG starts and UAA/UAG/UGA stop.

Mutation types: substitution (silent, missense, nonsense), insertion or deletion causing frameshift; non-disjunction in meiosis gives aneuploidy such as trisomy 21. Pedigree symbols: square male, circle female, filled affected.

Natural selection requires heritable variation, differential reproductive success, and a selective pressure; it acts on phenotypes and changes allele frequencies in populations, not individuals.

Hardy-Weinberg equilibrium: p + q = 1 and p^2 + 2pq + q^2 = 1. Conditions are no mutation, no migration, random mating, infinite population size, and no selection; deviation indicates evolution.

Five mechanisms of microevolution: mutation, gene flow (migration), genetic drift (bottleneck and founder effects), non-random mating, and natural selection.

Evidence for evolution: fossil record, homologous structures (common ancestry), analogous structures (convergent evolution), vestigial structures, embryology, biogeography, and molecular (DNA/protein) comparisons.

Speciation: allopatric requires geographic isolation; sympatric occurs without it, often via polyploidy or behavioural isolation. Reproductive isolating mechanisms (prezygotic and postzygotic) maintain species boundaries.

Three domains: Bacteria, Archaea (extremophiles, ether-linked membrane lipids), Eukarya. Kingdom-level classification of eukaryotes includes Protista, Fungi, Plantae, Animalia.

Binomial nomenclature: genus capitalized, species lowercase, both italicized (e.g. Homo sapiens); hierarchical ranks from domain down to species.

Viruses are acellular obligate intracellular parasites with a nucleic acid core and protein capsid; they are not classified in the three domains and reproduce only inside host cells.

Endosymbiotic theory: mitochondria and chloroplasts descend from engulfed bacteria, evidenced by their own circular DNA, 70S ribosomes, and double membranes.

Circulatory systems: fish have a single circuit and two-chambered heart; amphibians and reptiles have a three-chambered heart (crocodilians four); mammals and birds have a four-chambered heart with complete separation of oxygenated and deoxygenated blood.

Blood flow through the mammalian heart: vena cava -> right atrium -> right ventricle -> pulmonary artery -> lungs -> pulmonary vein -> left atrium -> left ventricle -> aorta. Arteries carry blood away from the heart; veins return it; capillaries allow exchange.

Gas exchange: fish use countercurrent gills; insects use tracheae; mammals use alveoli with large surface area and thin walls. Breathing is driven by the diaphragm and rib cage changing thoracic volume and pressure.

Neurons: resting potential about -70 mV maintained by the Na+/K+ pump; depolarization opens Na+ channels, repolarization opens K+ channels; the signal travels as an action potential and crosses synapses via neurotransmitters.

Hormones: insulin lowers blood glucose, glucagon raises it; adrenaline raises heart rate and glucose; thyroxine controls metabolic rate; negative feedback restores homeostasis.

Plant transport: xylem carries water and minerals upward driven by transpiration pull and cohesion-tension; phloem carries sugars bidirectionally by pressure flow. Stomata, controlled by guard cells, regulate gas exchange and water loss.

Tissues: epithelial (covering), connective (blood, bone, cartilage), muscle (skeletal, smooth, cardiac), nervous. Organs combine tissues for a function; organ systems coordinate whole-body activity.

Immune defence: barriers, then innate responses (inflammation, phagocytes), then adaptive responses. B cells produce antibodies (humoral); T cells mediate cell-mediated immunity and helper T cells activate other lymphocytes.

Digestion: mechanical and chemical breakdown; amylase digests starch in the mouth, pepsin digests protein in the acidic stomach, lipase and bile act in the small intestine, and villi absorb nutrients into blood and lymph.

Population growth: exponential model dN/dt = rN applies to unlimited resources; logistic model dN/dt = rN(K - N)/K levels off at carrying capacity K.

Population size estimates use mark-recapture: N ≈ (number marked in first sample x total in second sample) / number of recaptures.

Trophic levels: producers (autotrophs) -> primary consumers -> secondary consumers -> tertiary consumers; decomposers recycle nutrients. Only about 10% of energy passes to the next level (10% rule).

Species interactions: mutualism (+,+), commensalism (+,0), parasitism (+,−), predation (+,−), competition (−,−). Competitive exclusion occurs when two species need the same limiting resource.

Symbiosis and succession: primary succession begins on bare rock (lichens, mosses), secondary succession follows a disturbance that leaves soil. Pioneer species alter conditions for later species.

Biogeochemical cycles: carbon (photosynthesis, respiration, combustion), nitrogen (fixation by bacteria, nitrification, denitrification), water (evaporation, transpiration, condensation, precipitation).

Food webs show interconnected food chains; removing a keystone species causes disproportionate change. Bioaccumulation increases persistent toxin concentration up the food chain.

Human impacts: greenhouse gases (CO2, CH4) raise mean temperature; eutrophication from nutrient runoff causes algal blooms and oxygen depletion; habitat fragmentation reduces biodiversity.

Biodiversity has genetic, species, and ecosystem components; conservation strategies include protected areas, corridors, captive breeding, and reducing invasive species.