ORELA Biology (NT316) cheat sheet

Biology: Core Principles and Exam Reference

• Cell theory: all living things are made of one or more cells; the cell is the basic unit of structure and function; new cells arise only from pre-existing cells by division.

• Prokaryotes lack a membrane-bound nucleus and membrane-bound organelles; they have a nucleoid, 70S ribosomes, and usually a peptidoglycan cell wall (bacteria) - archaea lack peptidoglycan.

• Eukaryotic organelles and functions: mitochondrion (aerobic ATP via Krebs cycle and oxidative phosphorylation), chloroplast (photosynthesis), rough ER (protein synthesis and folding), smooth ER (lipid synthesis, detoxification), Golgi (modification, sorting, packaging), lysosome (acid hydrolase digestion), peroxisome (fatty acid oxidation, catalase).

• Endosymbiotic theory evidence: mitochondria and chloroplasts have double membranes, circular DNA, their own 70S ribosomes, and divide independently of the cell cycle.

• Membrane transport decision rule: small nonpolar molecules diffuse freely; polar molecules and ions need channels or carriers; movement down a gradient uses passive transport (no ATP); movement against a gradient uses active transport (ATP or an electrochemical gradient).

• Osmosis: water moves from low solute concentration (high water potential) to high solute concentration (low water potential). Hypertonic solution causes animal cell shrinkage (crenation) and plant plasmolysis; hypotonic causes animal cell lysis and plant cell turgor.

• Enzyme kinetics: enzymes lower activation energy, are not consumed, and are sensitive to pH and temperature; competitive inhibitors raise apparent Km while noncompetitive inhibitors lower Vmax; allosteric regulation changes enzyme shape at a site other than the active site.

• Central dogma: DNA → RNA → protein. Transcription occurs in the nucleus (eukaryotes); translation occurs on ribosomes. DNA replication is semiconservative and uses DNA polymerase (5′→3′ synthesis) with leading and lagging (Okazaki) strands.

• Mendelian ratios: monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; dihybrid cross of heterozygotes with independent assortment gives 9:3:3:1. Test cross uses a homozygous recessive to reveal an unknown genotype.

• Hardy-Weinberg equilibrium conditions: no mutation, no migration, no selection, random mating, and large population size. Allele frequencies p + q = 1 and genotype frequencies p² + 2pq + q² = 1.

• Natural selection requires heritable variation in a population and differential reproductive success. Genetic drift (bottleneck, founder effect) is random and strongest in small populations; gene flow reduces differences between populations.

• Ecological hierarchy and energy flow: organism → population → community → ecosystem → biosphere. Only about 10% of energy transfers between trophic levels; energy flows one way while nutrients cycle.

• Taxonomy hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Binomial nomenclature italicizes or underlines the genus and species; the species epithet is lowercase.

• Homeostasis and feedback: negative feedback opposes a change (e.g., insulin lowering blood glucose); positive feedback amplifies a change (e.g., oxytocin in childbirth, action potential depolarization).