DC CAPE 2.0 Science Biology cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells have both, plus linear chromosomes.

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

Mitochondria carry out aerobic respiration: glycolysis (cytoplasm) → Krebs cycle (matrix) → electron transport chain (inner membrane), yielding about 30-32 ATP per glucose.

Chloroplast thylakoid membranes run the light reactions (ATP and NADPH); the stroma runs the Calvin cycle (glucose synthesis from CO2).

Enzymes are catalysts that lower activation energy; activity peaks at an optimum pH and temperature and drops sharply when the enzyme denatures.

Osmosis is net water movement across a semipermeable membrane from low to high solute concentration; cells shrink in hypertonic and swell in hypotonic solutions.

DNA replication is semiconservative; transcription makes mRNA from DNA, and translation at ribosomes builds polypeptide chains from codons.

Photosynthesis and cellular respiration are complementary: photosynthesis stores energy in glucose and releases O2; respiration oxidizes glucose and releases CO2.

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

Law of independent assortment applies to genes on different chromosomes or far apart; linked genes tend to be inherited together.

Monohybrid cross of two heterozygotes (Aa × Aa) gives a 3:1 phenotype ratio and 1:2:1 genotype ratio; a test cross with a homozygous recessive reveals an unknown genotype.

Incomplete dominance blends phenotypes (red × white → pink); codominance expresses both alleles fully (AB blood type).

Sex-linked traits sit on the X chromosome; recessive X-linked disorders appear more often in males, who have only one X.

A Punnett square predicts offspring genotype probabilities, not guaranteed outcomes; multiply independent event probabilities.

DNA is a double helix with complementary base pairing (A-T, G-C); RNA substitutes uracil for thymine and is usually single-stranded.

Mutations include substitutions (point), insertions, and deletions; frameshift mutations alter every downstream codon and usually cause greater harm.

Nondisjunction produces gametes with extra or missing chromosomes, causing conditions such as trisomy 21.

Natural selection requires heritable variation, differential reproductive success, and environmental pressure; it acts on phenotypes, not genotypes directly.

Fitness means reproductive success in a given environment, not strength or longevity.

Directional selection shifts a trait's mean; stabilizing selection favors intermediates; disruptive selection favors both extremes.

Allele frequencies in a population change through mutation, gene flow (migration), genetic drift (random, strongest in small populations), and selection.

Hardy-Weinberg equilibrium (p² + 2pq + q² = 1, p + q = 1) holds only with no mutation, no migration, no selection, random mating, and large population.

Homologous structures share ancestry (human arm and bat wing); analogous structures share function but not ancestry (bird and insect wings).

Speciation typically requires reproductive isolation, often following geographic separation (allopatric) or polyploidy/habitat shifts (sympatric).

Fossils, biogeography, comparative anatomy, embryology, and molecular sequence similarity all support common descent.

Linnaean hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species; binomial names use capitalized genus and lowercase species.

Three domains: Bacteria and Archaea (prokaryotic) and Eukarya (protists, fungi, plants, animals); Archaea differ biochemically from Bacteria.

Viruses are acellular, obligate intracellular parasites with nucleic acid and a protein capsid; they are not classified in the three domains.

Fungi are heterotrophic eukaryotes with chitin cell walls that absorb nutrients externally; they reproduce by spores.

Plants: nonvascular (bryophytes), seedless vascular (ferns), gymnosperms (naked seeds, cones), angiosperms (flowers and enclosed seeds).

Animal phyla are distinguished by symmetry, body cavity, segmentation, and developmental patterns; chordates share a notochord, dorsal nerve cord, and pharyngeal slits.

Dichotomous keys classify by a series of paired contrasting traits, each choice narrowing the identification.

Biological species concept: members interbreed and produce fertile offspring; it fails for asexual organisms and fossils.

Trophic levels: producers → primary consumers → secondary consumers → tertiary consumers; only about 10% of energy transfers to the next level.

Food webs are more realistic than food chains because most organisms eat and are eaten by multiple species.

Symbiosis types: mutualism (both benefit), commensalism (one benefits, other unaffected), parasitism (one benefits, host harmed).

Carrying capacity is the maximum population an environment sustains; logistic growth levels off at it, exponential growth does not.

Density-dependent limits include food, disease, and predation; density-independent limits include fire, drought, and storms.

Carbon, nitrogen, and water cycles move matter between organisms and abiotic reservoirs; decomposers return nutrients to soil.

Primary succession starts on bare rock or lava with pioneer species; secondary succession follows disturbance where soil remains.

Invasive species often lack natural predators and can outcompete natives, reducing biodiversity.

Negative feedback reverses a change (e.g., insulin lowers high blood glucose); positive feedback amplifies it (e.g., oxytocin in childbirth).

Levels of organization: cell → tissue → organ → organ system → organism.

Digestion: mechanical breakdown in mouth and stomach, chemical breakdown by enzymes (amylase, pepsin, lipase), absorption mainly in the small intestine villi.

Blood flow: right heart → lungs (pulmonary circuit) → left heart → body (systemic); arteries carry blood away, veins return it.

Nephron filtration in kidneys removes wastes and regulates water and salt balance; urine formation supports blood pressure and pH homeostasis.

Neurons transmit electrochemical impulses; synapses release neurotransmitters across a gap to the next cell.

Immune defenses: barrier (skin, mucus), innate (inflammation, phagocytes), adaptive (B cells make antibodies, T cells destroy infected cells).

Hormones from endocrine glands travel in blood and act on target cells with matching receptors; insulin and glucagon regulate blood glucose.

Vaccination exposes the body to antigens, prompting memory cells that speed the response to later infection.