Scio NSZ Biology cheat sheet

Cell theory: all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

Hierarchy of biological organization: molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere.

Homeostasis is the maintenance of a stable internal environment through negative feedback loops that counteract deviations from a set point.

Prokaryotes lack a membrane-bound nucleus and organelles; eukaryotes possess a nucleus and membrane-bound compartments.

Viruses are acellular obligate intracellular parasites consisting of nucleic acid (DNA or RNA) enclosed in a protein capsid, sometimes with a lipid envelope.

ATP is the universal energy currency; energy is released when its terminal phosphate bond is hydrolyzed to ADP and inorganic phosphate.

Enzymes are biological catalysts that lower activation energy; they are not consumed in the reaction and are sensitive to temperature and pH.

Autotrophs fix inorganic carbon into organic compounds; heterotrophs obtain carbon by consuming other organisms.

Plasma membrane follows the fluid mosaic model: a phospholipid bilayer with embedded and peripheral proteins, cholesterol, and glycoproteins.

Passive transport (simple and facilitated diffusion, osmosis) moves substances down a concentration gradient without ATP; active transport moves them against the gradient using ATP.

Mitochondria perform aerobic cellular respiration and are the main site of ATP production; they contain their own circular DNA and ribosomes.

Chloroplasts carry out photosynthesis; thylakoid membranes host the light reactions and the stroma hosts the Calvin cycle.

Ribosomes synthesize proteins; free ribosomes produce cytosolic proteins while rough ER ribosomes produce proteins for secretion or membranes.

The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum.

Lysosomes contain hydrolytic enzymes for intracellular digestion; peroxisomes detoxify substances and break down fatty acids.

Mitosis produces two genetically identical diploid daughter cells; meiosis produces four genetically distinct haploid gametes.

Osmosis is diffusion of water across a semipermeable membrane from low to high solute concentration; plant cells become turgid in hypotonic solutions.

DNA is a double helix of nucleotides (adenine pairs with thymine via 2 hydrogen bonds; guanine pairs with cytosine via 3).

Semiconservative replication: each new DNA molecule retains one parental strand and one newly synthesized strand.

Transcription copies DNA into mRNA; translation at the ribosome assembles amino acids according to mRNA codons.

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

Mendel's law of independent assortment applies to genes on different chromosomes or far apart on the same chromosome.

A monohybrid cross of two heterozygotes (Aa × Aa) yields a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio.

Sex-linked traits are carried on sex chromosomes (usually X); affected fathers pass X-linked alleles to all daughters, not to sons.

Mutations are heritable changes in DNA sequence; point substitutions, insertions, and deletions can alter protein structure or function.

The Hardy-Weinberg equation p² + 2pq + q² = 1 predicts allele and genotype frequencies in a non-evolving population.

Blood flows through the heart: right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta.

The left ventricle has the thickest myocardium because it pumps blood at high pressure into the systemic circulation.

Arteries carry blood away from the heart under high pressure; veins return blood to the heart and contain valves preventing backflow.

Gas exchange occurs in alveoli, thin-walled sacs with a large surface area and rich capillary supply.

The nephron is the functional unit of the kidney; filtration occurs in the glomerulus and reabsorption mainly in the proximal tubule.

Neurons transmit impulses; depolarization results from sodium influx and repolarization from potassium efflux, with conduction accelerated by myelin.

Hormones are secreted by endocrine glands into the bloodstream; insulin lowers blood glucose and glucagon raises it.

The small intestine absorbs most nutrients via villi and microvilli; the large intestine reabsorbs water and forms feces.

Red blood cells contain hemoglobin, which binds oxygen in the lungs and releases it in tissues; they lack a nucleus in mammals.

Photosynthesis equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂, occurring in chloroplasts.

Light reactions split water to release oxygen, produce ATP, and reduce NADP⁺ to NADPH; the Calvin cycle fixes CO₂ using ATP and NADPH.

Xylem transports water and dissolved minerals upward from roots; phloem transports sugars bidirectionally from sources to sinks.

Transpiration is water loss through stomata; it drives the upward pull of water in the xylem and is regulated by guard cells.

Root hairs increase surface area for water and mineral absorption; root pressure and cohesion-tension move water upward.

Vascular plants have true roots, stems, and leaves with vascular tissue; bryophytes lack vascular tissue and are restricted to moist habitats.

Flowers are reproductive structures; pollination transfers pollen to the stigma, followed by fertilization and seed development in the ovary.

Plant hormones include auxin (cell elongation and phototropism), gibberellin (stem growth), cytokinin (cell division), and ethylene (fruit ripening).

Alternation of generations: a diploid sporophyte produces haploid spores by meiosis, which grow into a haploid gametophyte.

Animals are multicellular heterotrophs with cells lacking cell walls; most have specialized tissues and a nervous system.

Body symmetry: asymmetrical (sponges), radial (cnidarians), and bilateral (most animals) with cephalization.

Invertebrate phyla include Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, and Echinodermata.

Arthropods are the most species-rich phylum, characterized by an exoskeleton of chitin, segmented bodies, and jointed appendages.

Vertebrates comprise fish, amphibians, reptiles, birds, and mammals; mammals have hair and mammary glands.

Body temperature regulation: ectotherms rely on external heat, endotherms generate metabolic heat internally.

Closed circulatory systems keep blood within vessels (vertebrates, annelids); open systems bathe organs in hemolymph (arthropods, mollusks).

Metamorphosis transforms larvae into adults; complete metamorphosis includes egg, larva, pupa, and adult stages.

Excretion of nitrogenous waste: ammonia in aquatic animals, urea in mammals, uric acid in birds and reptiles to conserve water.

A population is a group of one species in one area; a community includes all species; an ecosystem adds abiotic factors.

Population growth is exponential when resources are unlimited and logistic when limited by carrying capacity (K).

Carrying capacity is the maximum population size an environment can sustain indefinitely given available resources.

Trophic levels: producers → primary consumers → secondary consumers → tertiary consumers, with energy lost as heat at each transfer.

The 10% rule: only about 10% of energy is transferred between trophic levels; biomass pyramids reflect this loss.

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

The carbon cycle moves carbon through photosynthesis, respiration, decomposition, combustion, and fossilization.

The nitrogen cycle involves nitrogen fixation by bacteria, nitrification, assimilation, and denitrification back to atmospheric N₂.

Primary succession begins on bare substrate without soil; secondary succession follows disturbance where soil remains.

Natural selection requires heritable variation, differential reproductive success, and a struggle for existence.

Fitness is measured as relative reproductive success; traits increasing fitness tend to increase in frequency in a population.

Homologous structures share common ancestry despite different functions; analogous structures share function but not ancestry (convergent evolution).

Directional, stabilizing, and disruptive selection describe how trait distributions shift under different environmental pressures.

Speciation occurs when populations become reproductively isolated; allopatric speciation involves geographic separation.

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

Mutation, gene flow, genetic drift, and natural selection are the main mechanisms of evolutionary change.

The Hardy-Weinberg equilibrium holds only if there is no mutation, no migration, no selection, random mating, and large population size.

Evidence for evolution includes the fossil record, comparative anatomy, embryology, biogeography, and molecular sequence similarity.