MTTC Biology (017) cheat sheet

Hierarchy of organization: atom → molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere. Each level has emergent properties not present at lower levels.

Four macromolecule classes: carbohydrates (monosaccharides, energy and structure), lipids (glycerol plus fatty acids, nonpolar, membranes and long-term energy), proteins (amino acids joined by peptide bonds, enzymes and structure), nucleic acids (nucleotides, information storage).

Dehydration synthesis bonds monomers by removing water; hydrolysis splits polymers by adding water. Peptide bonds form between the amino group of one amino acid and the carboxyl group of the next.

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; they have a nucleoid, 70S ribosomes, and often a cell wall. Eukaryotic cells have a true nucleus, 80S ribosomes, and membrane-bound organelles.

Endosymbiotic theory: mitochondria and chloroplasts derive from engulfed prokaryotes, supported by their own circular DNA, 70S-like ribosomes, double membranes, and independent division.

Surface-area-to-volume ratio limits cell size: as a cell enlarges, volume grows faster than surface area, so exchange across the membrane becomes insufficient and the cell divides or stays small.

Enzyme kinetics: enzymes lower activation energy, are not consumed, and are specific by active-site shape. Rate rises with substrate until saturation (Vmax); excess heat or extreme pH denatures enzymes by disrupting tertiary structure.

Water properties that support life: high specific heat and heat of vaporization, cohesion and adhesion (capillary action), universal solvent behavior due to polarity, and lower density as a solid.

DNA structure: two antiparallel strands, sugar-phosphate backbone, complementary base pairing A-T (two hydrogen bonds) and G-C (three hydrogen bonds), major and minor grooves, 5' to 3' directionality.

Semiconservative replication: helicase unwinds, primase lays RNA primer, DNA polymerase III adds nucleotides 5'→3' and proofreads, ligase seals Okazaki fragments on the lagging strand.

Central dogma: DNA → RNA (transcription, RNA polymerase, promoter and terminator) → protein (translation at the ribosome; mRNA codons read 5'→3', tRNA anticodons pair, start codon AUG, stop codons UAA, UAG, UGA).

Mutations: substitution (missense, nonsense, silent), insertion or deletion causing frameshift. Only germline mutations are heritable; somatic mutations affect only the individual.

Mendelian ratios: monohybrid F2 phenotype 3:1, genotype 1:2:1; dihybrid F2 9:3:3:1 with independent assortment. Testcross reveals an unknown dominant genotype.

Non-Mendelian patterns: incomplete dominance (blended heterozygote), codominance (both alleles expressed), multiple alleles (ABO blood groups), polygenic traits (continuous variation), sex-linked traits (X-linked recessive affects males more).

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, large population, and no selection; p + q = 1 and p² + 2pq + q² = 1.

Biotechnology tools: restriction enzymes cut at palindromic recognition sites, gel electrophoresis separates DNA by size (smaller fragments migrate farther), PCR amplifies DNA through denaturation, annealing, and extension cycles, and CRISPR-Cas9 uses guide RNA to target cleavage.

Natural selection requires heritable variation, differential reproductive success, and environmental pressure. It acts on phenotypes and changes allele frequencies in populations, not individuals.

Evidence for evolution: fossil record with transitional forms, homologous structures (common ancestry), analogous structures (convergent evolution), vestigial structures, biogeography, and molecular sequence similarity.

Five mechanisms of microevolution: mutation, gene flow (migration), genetic drift (bottleneck and founder effects), nonrandom mating, and natural selection. Drift is strongest in small populations.

Species concepts: biological (interbreeding and viable fertile offspring), morphological, ecological, and phylogenetic. Reproductive isolation is prezygotic (temporal, behavioral, habitat, mechanical, gametic) or postzygotic (hybrid inviability or sterility).

Speciation modes: allopatric (geographic separation), sympatric (polyploidy, habitat shifts, sexual selection within one area). Adaptive radiation follows new niche availability, as with Darwin's finches.

Taxonomic hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Three domains are Bacteria, Archaea, and Eukarya; binomial nomenclature italicizes genus and species.

Six-kingdom survey: Bacteria and Archaea (prokaryotic), Protista (mostly unicellular eukaryotic), Fungi (chitin walls, absorptive heterotrophs), Plantae (cellulose walls, photosynthesis), Animalia (no cell walls, ingestive heterotrophs).

Patterns of selection: directional shifts the mean, stabilizing favors intermediates, disruptive favors extremes. Sexual selection and coevolution (predator-prey, host-parasite) also drive change.

Plant tissues: dermal (epidermis, cuticle), ground (parenchyma, collenchyma, sclerenchyma), and vascular (xylem transports water and minerals upward; phloem transports sugars bidirectionally).

Transpiration-cohesion-tension mechanism moves water through xylem; stomata regulated by guard cells balance gas exchange with water loss. Photosynthesis occurs in chloroplasts (light reactions in thylakoids, Calvin cycle in stroma).

Plant hormones: auxin (phototropism, apical dominance), gibberellin (stem elongation, seed germination), cytokinin (cell division), abscisic acid (stomatal closure, dormancy), ethylene (fruit ripening, senescence).

Animal tissue types: epithelial (covering and lining), connective (matrix-rich; blood, bone, cartilage, adipose), muscle (skeletal striated voluntary, cardiac striated involuntary, smooth nonstriated involuntary), nervous (neurons and glia).

Homeostasis via negative feedback (thermoregulation, blood glucose via insulin and glucagon, osmoregulation) and positive feedback in rare amplifying loops such as childbirth and blood clotting.

Vertebrate circulation: fish two-chambered heart, amphibians three-chambered, reptiles three-chambered with partial septum, mammals and birds four-chambered with complete separation of oxygenated and deoxygenated blood.

Gas exchange surfaces must be thin, moist, and highly vascular: alveoli in mammals, gills in fish with countercurrent flow, tracheae in insects, stomata and lenticels in plants.

Nervous signaling: resting potential maintained by Na⁺/K⁺ pump; action potential depolarizes via Na⁺ influx and repolarizes via K⁺ efflux; neurotransmitters cross synapses. Hormones act more slowly through the bloodstream.

Population growth: exponential model dN/dt = rN applies to unlimited resources; logistic model dN/dt = rN(K − N)/K adds carrying capacity K. r-selected species favor rapid reproduction; K-selected favor competitive ability.

Population density factors: birth rate, death rate, immigration, and emigration. Age-structure pyramids predict growth (broad base) or decline (narrow base).

Species interactions: competition (−/−, competitive exclusion or resource partitioning), predation and parasitism (+/−), mutualism (+/+), commensalism (+/0).

Trophic levels: producers, primary consumers, secondary consumers, decomposers. Energy transfer is about 10% per level (the rest lost as heat), so food chains rarely exceed four or five links.

Biogeochemical cycles: carbon (photosynthesis, respiration, combustion, fossil fuels), nitrogen (fixation by bacteria and lightning, nitrification, assimilation, denitrification), phosphorus (no atmospheric phase; weathering and runoff), water cycle.

Primary succession begins on bare substrate (lichens, pioneer species) and proceeds to a climax community; secondary succession follows disturbance where soil remains (fire, abandoned field).

Biomes keyed to temperature and precipitation: tropical rainforest, savanna, desert, temperate deciduous forest, grassland, taiga, tundra, freshwater, marine, and estuary (high productivity, brackish).

Biodiversity threats: habitat loss and fragmentation, invasive species, overexploitation, pollution, and climate change. Conservation tools include corridors, protected areas, and captive breeding.

Scientific method sequence: observation, question, hypothesis, prediction, controlled experiment or field study, data analysis, conclusion, and peer review. A hypothesis must be testable and falsifiable.

Variables: independent variable is manipulated, dependent variable is measured, controlled variables are held constant, and a control group provides baseline comparison. Random assignment and replication reduce bias.

Data quality: accuracy is closeness to the true value; precision is repeatability. Reliability increases with sample size and repetition; validity means the experiment measures what it claims.

Graph choice: line graphs for continuous change over time, bar graphs for categorical comparisons, scatter plots for correlation. Report mean with standard deviation or standard error and identify outliers.

Ethical standards in biology: informed consent, Institutional Review Board approval for human subjects, Institutional Animal Care and Use Committee oversight for animals, biosafety levels for pathogens, and environmental impact review.

Applied biotechnology: gene therapy, genetically modified crops, recombinant insulin, DNA fingerprinting in forensics, and stem cell research each raise distinct ethical and regulatory questions.

Public health and epidemiology: incidence versus prevalence, herd immunity thresholds, vaccination, antibiotic resistance from selection and misuse, and outbreak investigation through case tracing.

Science literacy: distinguish correlation from causation, recognize bias in funding or sampling, evaluate source credibility, and understand that scientific theories are well-supported explanations, not guesses.

Personal protective equipment: goggles, lab coat, and gloves for all wet-lab work; tie back hair, secure loose clothing, and wear closed-toe shoes. No food, drink, or gum in the lab.

Chemical safety: read the Safety Data Sheet (SDS) for hazards; know the location of the eyewash station, safety shower, fire extinguisher, and spill kit. Never return unused chemicals to stock bottles.

Handling glassware: check for chips or cracks before use; heat only borosilicate glass; never heat a closed system; use tongs for hot glass and allow it to cool before washing.

Bunsen burner protocol: clear the area, keep flame away from flammable liquids, never leave a lit burner unattended, and turn off the gas at the source if a flame goes out.

Biological safety: treat all body fluids and cultures as potentially infectious; disinfect benches before and after work; dispose of biohazard waste in designated containers; autoclave contaminated materials.

Microscope use: carry with two hands, start on low power, focus with the coarse knob on low power only, use the fine knob at high power, use lens paper only, and never use the coarse adjustment while viewing with the oil-immersion objective.

Measurement rules: use the correct graduated cylinder size for volume, read the meniscus at eye level, record to the precision of the instrument plus one estimated digit, and use metric units (SI).

Emergency response: report all spills and injuries to the instructor immediately; flush chemical splashes with water for at least 15 minutes; know evacuation routes, and never attempt to clean up a hazardous spill unassisted.