Praxis Elem CKT Science cheat sheet

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

Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂; occurs in chloroplasts, where chlorophyll absorbs light.

Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP; occurs in mitochondria, and plants respire as well as photosynthesize.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically unique haploid gametes; fertilization restores the diploid number.

Punnett square rule: Aa × Aa yields 1 AA : 2 Aa : 1 aa genotypes and a 3 dominant : 1 recessive phenotype ratio.

Natural selection requires heritable variation, overproduction of offspring, differential survival and reproduction, and change in trait frequency across generations.

Energy flow: only about 10% of energy transfers between trophic levels, so food chains rarely exceed four or five links; decomposers recycle nutrients, not energy.

Xylem transports water and dissolved minerals upward from roots; phloem transports sugars from leaves to roots and growing tissue; stomata regulate gas exchange.

Classification hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Newton's first law: an object maintains constant velocity unless a net force acts; inertia increases with mass; third-law pairs are equal, opposite, and act on different objects.

Newton's second law: F = ma; weight = mg with g ≈ 9.8 N/kg, so mass stays constant while weight changes with gravitational field strength.

Speed = distance ÷ time; acceleration = change in velocity ÷ time; velocity is speed with a stated direction.

KE = ½mv²; GPE = mgh; energy is conserved but transforms among motion, heat, light, sound, chemical, and electrical forms.

Density = mass ÷ volume; an object floats in water when its density is less than 1 g/cm³; phase changes (melting, freezing, evaporation, condensation, sublimation, deposition) conserve mass.

Atomic number = protons; mass number = protons + neutrons; a neutral atom has equal protons and electrons; elements in the same group share valence electron count.

Series circuits have one current path, the same current everywhere, and resistances that add; parallel circuits have multiple paths, equal voltage across branches, and keep working when one branch breaks.

Waves: v = fλ, so at a fixed speed higher frequency means shorter wavelength; sound requires a medium, light does not; reflection, refraction, and absorption describe wave interactions.

pH scale 0–14: below 7 acidic, 7 neutral, above 7 basic; each whole step is a tenfold change in hydrogen ion concentration, and acid-base reactions neutralize.

Earth's layers from outside in: thin rocky crust, solid mantle that flows very slowly, liquid iron-nickel outer core, solid inner core; seismic wave behavior reveals the boundaries.

Igneous rock forms from cooling magma or lava, sedimentary rock from compacted and cemented sediments, metamorphic rock from heat and pressure; the rock cycle links all three.

Divergent boundaries create new crust at mid-ocean ridges, convergent boundaries produce subduction zones, volcanoes, and mountains, and transform boundaries generate earthquakes.

Weathering breaks rock in place, erosion transports sediment by water, wind, ice, or gravity, and deposition lays sediment down in new locations.

Water cycle: evaporation and transpiration add vapor, condensation forms clouds, precipitation returns water, and runoff or infiltration moves it to streams, oceans, and groundwater.

Rotation on Earth's axis takes about 24 hours and causes day and night; revolution takes about 365.25 days and, combined with the 23.5° tilt, causes seasons.

Seasons come from the axial tilt changing sunlight angle and day length, not from changing distance to the sun; moon phases cycle in about 29.5 days and are not Earth's shadow.

Solar system order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune; the first four are rocky, the outer four are gas or ice giants, and the sun's energy comes from hydrogen fusion.

Weather is the short-term atmospheric state, climate is the long-term average; the troposphere holds most weather; renewable resources replenish while nonrenewable resources do not.

5E sequence: Engage, Explore, Explain, Elaborate, Evaluate; students investigate a phenomenon during Explore before the teacher formalizes the explanation in Explain.

NGSS three dimensions: disciplinary core ideas, science and engineering practices, and crosscutting concepts must be integrated, not taught separately.

Practices: asking questions, developing models, planning investigations, analyzing data, using mathematics, constructing explanations, arguing from evidence, and obtaining and communicating information.

Crosscutting concepts: patterns, cause and effect, scale and proportion, systems and system models, energy and matter, structure and function, stability and change.

Fair-test design: one independent variable, one measurable dependent variable, all other conditions held constant as controlled variables, plus a comparison or control group.

Formative assessment occurs during instruction to shape feedback and next steps; summative assessment occurs at the end to judge achievement against standards; rubrics score performance tasks.

Common misconceptions to probe: heavier objects fall faster, seasons caused by distance to the sun, plants getting food from soil, moon phases caused by Earth's shadow.

Safety rules: goggles on, waft odors instead of sniffing directly, never taste materials, wash hands after activities, use teacher-approved materials, and dispose of chemicals as directed.

Models and representations should be debriefed for what they show and what they simplify; ELLs benefit from visuals, sentence frames, word walls, and paired discussion.