TASC Biology Level 3 cheat sheet

Cell theory: all living things are made of cells, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells by division.

Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells have a nucleus, mitochondria, and other membrane-bound compartments.

Surface-area-to-volume ratio decreases as a cell grows, so large cells must divide or develop folds to maintain adequate exchange with the environment.

Cell membrane is a phospholipid bilayer with embedded proteins; small nonpolar molecules diffuse freely, while ions and polar molecules need channels or carriers.

Osmosis moves water across a semipermeable membrane from low solute concentration to high solute concentration until equilibrium is reached.

Enzymes are proteins that lower activation energy; each has an active site specific to its substrate, and activity peaks at an optimal temperature and pH.

Photosynthesis converts light energy, carbon dioxide, and water into glucose and oxygen in chloroplasts; cellular respiration releases that energy as ATP in mitochondria.

DNA is a double helix of nucleotides paired by complementary bases (A-T, G-C), and its sequence encodes proteins through transcription and translation.

Mitosis produces two genetically identical diploid cells for growth and repair, while meiosis produces four genetically varied haploid gametes.

Mendel's law of segregation: two alleles for a gene separate during gamete formation, so each gamete carries only one allele.

Law of independent assortment: alleles of different genes are distributed to gametes independently when the genes are on different chromosomes.

Genotype is the allele combination (AA, Aa, aa); phenotype is the observable trait; a dominant allele masks a recessive allele in heterozygotes.

Punnett squares predict offspring genotype ratios; a cross of two heterozygotes (Aa x Aa) yields a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio.

A test cross with a homozygous recessive individual reveals whether a dominant-phenotype parent is homozygous or heterozygous.

Incomplete dominance produces an intermediate phenotype, and codominance expresses both alleles fully, as in AB blood type.

Sex-linked traits sit on sex chromosomes; X-linked recessive traits appear more often in males because they have only one X chromosome.

Mutations are changes in DNA sequence; point substitutions may be silent, missense, or nonsense, while insertions and deletions can cause frameshifts.

Pedigree analysis: a trait that skips generations and appears in unaffected parents' offspring is recessive; a trait in every generation with affected parents having affected children is likely dominant.

Natural selection requires heritable variation, differential reproductive success, and environmental pressure; individuals do not evolve, populations do.

Fitness is measured by relative reproductive success, not strength or lifespan, and it depends on the current environment.

Directional selection shifts a trait mean, stabilizing selection favors intermediates, and disruptive selection favors both extremes.

Genetic drift is random allele-frequency change, strongest in small populations; the bottleneck effect and founder effect are examples.

Gene flow (migration) and mutation both introduce new alleles or change allele frequencies within a population.

Homologous structures share ancestry despite different functions, analogous structures share function without ancestry, and vestigial structures are reduced remnants.

Speciation typically requires reproductive isolation, which can be geographic (allopatric) or arise within a range (sympatric, often via polyploidy in plants).

Binomial nomenclature gives each species a two-part Latin name (genus and species); the hierarchy runs domain, kingdom, phylum, class, order, family, genus, species.

The three domains are Bacteria, Archaea, and Eukarya; viruses are not classified as living cells because they lack cellular machinery and require hosts to replicate.

Homeostasis maintains internal stability through negative feedback, in which a deviation triggers a response that reverses the change.

Population size changes by births minus deaths plus immigration minus emigration; exponential growth occurs with unlimited resources.

Logistic growth produces an S-shaped curve that levels at carrying capacity (K) as resources become limiting.

Population density is individuals per unit area; mark-recapture estimates N as (marked in first sample x total in second sample) divided by recaptured marked individuals.

Life tables and survivorship curves describe mortality patterns; Type I has high early survival, Type II constant mortality, and Type III high early mortality.

A population's age structure predicts future growth: many young individuals indicate rapid growth, while an older-skewed structure indicates decline.

Organ systems divide labor: circulatory transports, respiratory exchanges gases, digestive absorbs nutrients, excretory removes wastes, and nervous and endocrine coordinate responses.

Photosynthesis and respiration link producers and consumers by moving carbon and energy through trophic levels, with about 10 percent of energy transferred between levels.

Symbiosis includes mutualism (both benefit), commensalism (one benefits, other unaffected), and parasitism (one benefits at the other's expense).

Energy flows one way through ecosystems and is lost as heat at each trophic level, while matter cycles repeatedly through biogeochemical pathways.

Food chains begin with producers; decomposers return nutrients to the soil and water, closing nutrient loops.

The carbon cycle moves carbon through photosynthesis, respiration, combustion, and decomposition; the nitrogen cycle relies on fixation, nitrification, and denitrification by microbes.

Primary succession begins on bare rock or lava with pioneer species such as lichens; secondary succession follows disturbance where soil remains.

Biodiversity includes genetic, species, and ecosystem diversity; greater diversity generally increases ecosystem resilience to disturbance.

Invasive species often lack natural predators, outcompete natives, and disrupt food webs, making them a leading cause of biodiversity loss.

Bioaccumulation is the buildup of a substance in an organism over its lifetime; biomagnification is its increasing concentration at higher trophic levels.

Abiotic factors include temperature, light, water, pH, and salinity; biotic factors include predation, competition, and disease.

Habitat fragmentation reduces gene flow and population size, increasing extinction risk for species with limited dispersal.

A hypothesis is a testable, falsifiable prediction; a theory is a well-supported explanation built from many tested hypotheses.

Independent variable is manipulated by the researcher, dependent variable is measured, and controlled variables are held constant across groups.

A control group receives no treatment or a placebo so the effect of the independent variable can be isolated.

Validity requires measuring what is intended; reliability requires consistent results across repeated trials, which larger samples and repetition improve.

Correlation does not establish causation; confounding variables can produce an apparent relationship between two factors.

Graph choice: line graphs show continuous change over time, bar graphs compare discrete categories, and scatter plots show relationships between two variables.

Metric conversions shift by powers of ten: 1 cm = 10 mm, 1 m = 100 cm, 1 kg = 1000 g, and 1 L = 1000 mL.

Microscopy: magnification equals ocular lens power times objective lens power; total magnification of a 10x ocular and 40x objective is 400x.

Significant figures and units must be reported consistently; a result should be stated with the appropriate precision and metric label.