General Science: mixed review

Independent (manipulated): the factor the experimenter deliberately changes, usually on the x-axis. Dependent (responding): the outcome measured, usually on the y-axis.

A control group gets no treatment and serves as the baseline (plants given plain water). Controlled variables are factors held the same for all groups (soil, light, pot size).

A hypothesis is a proposed, testable explanation of why something happens. A prediction is the specific result expected if the hypothesis is right, often written as if-then.

$\rho =\frac{m}{V}$, where $\rho$ is density, m is mass (g) and V is volume (${\text{cm}}^3$ or mL). Example: 54 g in 20 ${\text{cm}}^3$ gives 2.7 g/${\text{cm}}^3$. Water is about 1 g/mL; denser objects sink.

Accuracy: how close a measurement is to the true value. Precision: how close repeated measurements are to each other. A scale reading 105 g three times for a 100 g mass is precise but not accurate.

Systematic error shifts every reading the same way (a scale always 5 g high); fix it by recalibrating, not averaging. Random error scatters readings both ways; repeat and average to reduce it.

$\text{percent change}=\frac{\text{new}-\text{original}}{\text{original}}\times 100$. 50 to 40 is a 20% decrease; 40 to 50 is a 25% increase. The original value is the reference.

Square or cube the conversion factor too. Since 1 m = 100 cm, 1 ${\text{m}}^2$ = 10,000 ${\text{cm}}^2$ and 1 ${\text{m}}^3$ = 1,000,000 ${\text{cm}}^3$, not 100.

All living things are made of one or more cells; the cell is the smallest unit that carries out all life activities; new cells arise only from existing cells by division.

Prokaryotes (bacteria, archaea) keep DNA in a nucleoid with no membrane and lack membrane-bound organelles. Eukaryotes (animals, plants, fungi, protists) have a true nucleus and organelles such as mitochondria.

Nucleus stores DNA; ribosome builds proteins; mitochondrion releases energy as ATP; Golgi modifies, sorts and packages products; lysosome digests worn-out parts and engulfed material.

Osmosis is diffusion of water across a selectively permeable membrane, toward the side with more dissolved solute. Water follows solute.

Hypotonic (less solute outside): water enters, cell swells and may burst. Hypertonic (more solute outside): water leaves, cell shrinks. Isotonic: no net change in volume.

Passive (diffusion, facilitated diffusion) moves substances down a concentration gradient with no ATP. Active transport moves them against the gradient using ATP and a pump, e.g. the sodium-potassium pump.

Photosynthesis (chloroplasts, needs light): $6{\text{CO}}_2+6{\text{H}}_2\text{O}\to {\text{C}}_6{\text{H}}_{12}{\text{O}}_6+6{\text{O}}_2$. Respiration (cytosol and mitochondria) runs the reverse and stores energy in ATP.

Yes. Plant cells have mitochondria and respire day and night using sugar they made. In the dark, respiration is their only ATP source. Plants do both processes; animals only respire.

In DNA, A pairs with T and G pairs with C. RNA uses uracil (U) in place of thymine, so a DNA A is matched by U in messenger RNA.

Genotype is the pair of alleles an organism carries (e.g. Ff). Phenotype is the observable trait (e.g. freckles). Different genotypes like FF and Ff can share a phenotype, and environment also shapes phenotype.

Homozygous: two identical alleles (RR or rr). Heterozygous: two different alleles (Rr). Homo means same, hetero means different.

Genotypes 1 AA : 2 Aa : 1 aa. Phenotypes 3 dominant : 1 recessive, so each offspring has a $\frac{1}{4}$ (25%) chance of showing the recessive trait.

Multiply: $P(A\text{ and }B)=P(A)\times P(B)$. Example from two Bb parents: first child bb and second not bb is $\frac{1}{4}\times \frac{3}{4}=\frac{3}{16}$. Each birth is independent.

Mitosis: two identical diploid cells for growth and repair. Meiosis: two divisions giving four genetically different haploid cells (gametes). In humans, 46 chromosomes become 23 in each gamete.

Selection: heritable variation that affects survival or reproduction makes favored alleles more common. Drift: allele frequencies change by chance, strongest in small populations (founder and bottleneck effects).

A father gives his Y chromosome to every son and his X to every daughter. So sons get their X from the mother; every daughter of an affected father receives his allele.

Body veins to the venae cavae, right atrium, right ventricle, pulmonary artery, lungs, pulmonary vein, left atrium, left ventricle, then out the aorta. The left ventricle has the thickest wall because it pumps to the whole body.

Arteries carry blood away from the heart; veins carry it back. They are named for direction, not oxygen content: pulmonary arteries carry oxygen-poor blood, pulmonary veins oxygen-rich blood.

In the alveoli, tiny air sacs wrapped in capillaries. Oxygen diffuses from air into blood and carbon dioxide diffuses from blood into air, across very thin walls with huge surface area.

The small intestine. Folds, finger-like villi and microvilli greatly increase surface area; sugars and amino acids enter capillaries, and most fats enter lacteals.

The liver makes bile; the gallbladder only stores and concentrates it. Bile is not an enzyme; it breaks fat into small droplets so lipase can work.

Kidney (makes urine), ureter, urinary bladder (stores it), urethra, outside. A common trap swaps ureter and urethra.

Both come from pancreatic islets. Insulin (beta cells) lowers blood glucose after a meal; glucagon (alpha cells) raises it during fasting by releasing glucose from liver glycogen.

A tendon connects muscle to bone and passes the muscle's pull to the skeleton. A ligament connects bone to bone and stabilizes a joint.

Count species. One species in an area is a population; several species together form a community; a community plus its nonliving conditions (water, light, soil) is an ecosystem.

From the food to the eater, showing where energy and matter go. Read each arrow as 'is eaten by'. Grass to rabbit means the rabbit eats the grass.

Start at the producer and count feeding steps: primary consumers eat producers, secondary eat primary, tertiary eat secondary. Do not just pick the top predator.

Each level gets about one-tenth of the level below: move the decimal one place left per step. 20,000 kcal of producers gives 2,000, then 200, then 20 kcal. Use a different percentage if the question states one.

Matter (carbon, nitrogen, phosphorus) is recycled again and again. Energy flows one way: in as sunlight, up the food chain, out as heat that producers cannot reuse.

$\Delta N=(B+I)-(D+E)$, where B is births, I immigrants, D deaths and E emigrants over the same period. Example: 400 elk with 60 B, 12 I, 45 D, 7 E end at 420.

Mutualism: both benefit (+/+), like bees and flowers. Commensalism: one benefits, the other unaffected (+/0), like barnacles on a whale. Parasitism: one benefits, the host is harmed (+/-), like a tapeworm.

Eutrophication: excess nitrogen and phosphorus cause algal blooms whose decay uses up oxygen, creating dead zones. Biomagnification: a toxin such as DDT or mercury becomes more concentrated at each higher trophic level.

Melting: solid to liquid. Freezing: liquid to solid. Vaporization: liquid to gas. Condensation: gas to liquid. Sublimation: solid to gas. Deposition: gas to solid (frost).

Ask whether a new substance forms. Changes of state, cutting and dissolving keep the same substance (physical). Rusting, burning and cooking make new substances (chemical).

Element: one kind of atom. Compound: two or more elements chemically bonded in a fixed ratio. Mixture: substances combined physically, not bonded, in any ratio and separable by physical methods.

$D=\frac{m}{V}$: density equals mass divided by volume, in g/cm³ or g/mL (1 mL = 1 cm³). Objects less dense than a fluid (water is about 1.0 g/mL) float in it.

Protons = atomic number Z. Neutrons = mass number A minus Z. Electrons = protons minus charge. Example: ${\text{Al}}^{3+}$ (Z = 13) has 10 electrons.

Isotopes of an element differ in neutrons, changing mass but not charge. Ions differ in electrons, changing charge. The proton count stays the same in both.

The decimal is a weighted average of the element's natural isotopes, not one atom's mass number. Use the isotope's mass number: copper-65 has 65 - 29 = 36 neutrons.

Group 1 alkali metals: +1. Group 2 alkaline earth metals: +2. Group 17 halogens: -1. Group 18 noble gases: full outer shells, so they rarely form ions or react.

Only the coefficients in front of formulas. Changing a subscript changes the substance (H2O to H2O2 turns water into hydrogen peroxide). Balanced: $2{\text{H}}_2+{\text{O}}_2\to 2{\text{H}}_2\text{O}$.

Total mass of products equals total mass of reactants because atoms are only rearranged. In an open container a gas product can escape, so the reading drops; in a sealed one it stays the same.

$\text{ratio}=10^{\Delta \text{pH}}$. Each pH unit is a tenfold change, so pH 3 has $10^2=100$ times the hydrogen-ion level of pH 5. The lower pH is more acidic.

Acids: pH below 7, turn blue litmus red, donate protons (H+). Bases: pH above 7, turn red litmus blue, accept protons or add OH-. pH 7 is neutral.

A salt plus water: ${\text{H}}^{+}+{\text{OH}}^{-}\to {\text{H}}_2\text{O}$. The salt combines the base's metal ion with the acid's negative ion, e.g. HNO3 + KOH gives KNO3 + H2O.

Exothermic reactions release energy, so surroundings warm (burning, hand warmers). Endothermic reactions absorb energy, so surroundings cool (instant cold packs, photosynthesis). Neither label says how fast a reaction goes.

A substance that speeds a reaction by lowering activation energy and is not used up (enzymes are biological catalysts). It does not change the overall energy released or the final amount of product.

Strength is how completely the acid ionizes in water (HCl is strong, acetic acid is weak). Concentration is how much acid is dissolved per volume. A dilute strong acid can have a higher pH than a concentrated weak one.

Distance is the total path length traveled (a scalar, never negative). Displacement is the straight-line change from start to finish with a direction (a vector). One full lap: 400 m distance, zero displacement.

$a=\frac{\Delta v}{\Delta t}=\frac{v_f-v_i}{t}$, the change in velocity (m/s) divided by time (s), in ${\text{m/s}}^2$. From 2 to 8 m/s in 3 s gives $2{\text{m/s}}^2$.

$v=v_0+at$ and $\Delta x=v_{0}t+\frac{1}{2}a{t}^2$, with $v_0$ the initial velocity (m/s), a the acceleration (${\text{m/s}}^2$) and t the time (s). From rest at $4{\text{m/s}}^2$ for 3 s: 12 m/s and 18 m.

$F_{net}=ma$: net force in newtons equals mass in kg times acceleration in ${\text{m/s}}^2$. Subtract opposing forces first: 40 N forward minus 16 N friction on 8 kg gives $3{\text{m/s}}^2$.

No. Constant velocity (even at high speed) means zero acceleration, so the net force is zero; forces are balanced. A net force is needed only to change speed or direction (Newton's first law, inertia).

They are equal and opposite but act on two different objects. Only forces on the same object can cancel. A book's weight and the table's normal force balance, but they are not a third-law pair.

$W=mg$, with m in kg and g about $9.8{\text{m/s}}^2$ on Earth (often rounded to 10), giving newtons. Mass never changes with location; a 12 kg toolbox weighs about 118 N on Earth and 19 N on the Moon.

Equal distances at different speeds take unequal times, so use total distance over total time. 6 km out at 12 km/h (0.5 h) and back at 4 km/h (1.5 h) averages 12 km in 2 h = 6 km/h, not 8.

$KE=\frac{1}{2}m{v}^2$ and $PE=mgh$, with m in kg, v in m/s, g about $9.8{\text{m/s}}^2$ and h in m; both in joules. Doubling speed makes KE four times larger; doubling height doubles PE.

$P=\frac{E}{t}$: power in watts (1 W = 1 J/s) equals energy in joules over time in seconds. Energy = power x time; 1 kWh = 3,600,000 J. A 1,500 W heater for 2 h uses 3 kWh.

Efficiency = useful output energy / total input energy x 100%. A pump using 5,000 J to give 3,500 J useful is 70% efficient. It is always below 100%; the rest becomes waste heat or sound, not destroyed.

$K={}^{\circ }C+273.15$ and ${}^{\circ }F=\frac{9}{5}{}^{\circ }C+32$. So 37 °C is 98.6 °F and 310.15 K. Kelvin has no degree sign and is never negative.

Conduction: direct contact, mostly in solids (hot spoon handle). Convection: bulk flow of a liquid or gas as warm fluid rises (boiling pot, sea breeze). Radiation: electromagnetic waves, crosses a vacuum (sunlight, campfire warmth).

$v=f\lambda$: speed (m/s) equals frequency (Hz) times wavelength (m). Period $T=\frac{1}{f}$. A 170 Hz sound at 340 m/s has a 2 m wavelength.

The echo travels out and back, so halve the round trip: $d=\frac{vt}{2}$. Sonar echo after 0.8 s in seawater at 1,500 m/s: 1,200 m round trip, so the floor is 600 m down.

Amplitude (displacement from rest) sets energy, loudness and brightness. Frequency (cycles per second) sets pitch and light color. Frequency stays the same when a wave enters a new medium; speed and wavelength change.

Divergent: plates separate, making new crust at mid-ocean ridges and rift valleys. Convergent: plates move together, causing subduction trenches, volcanic arcs or mountains. Transform: plates slide sideways past each other (San Andreas).

No. The mantle is mostly solid rock that deforms and flows very slowly. The rigid lithosphere (crust plus uppermost mantle) moves over the weak but solid asthenosphere. Only the outer core is liquid.

Igneous: magma or lava cools and solidifies. Sedimentary: sediment is deposited, compacted and cemented. Metamorphic: existing rock changes under heat and pressure without melting (limestone to marble).

Weathering breaks rock down in place (frost wedging, dissolving). Erosion carries the loose material away by water, wind, ice or gravity. Deposition is where the material settles, such as a delta at a river mouth.

The focus (hypocenter) is the underground point where rupture begins. The epicenter is the spot on the surface directly above the focus. Neither is automatically where shaking is strongest.

P (primary) waves are compressional, arrive first and travel through solids and liquids. S (secondary) waves are shear waves that cannot pass through liquids, which is evidence for a liquid outer core.

Earth's axial tilt of about 23.4 degrees, which changes the Sun's angle and day length. It is not the changing Earth-Sun distance. The two hemispheres have opposite seasons.

Halve the amount once per half-life: remaining = start x $(\frac{1}{2}{)}^n$ for n half-lives. 80 units become 40, then 20 (25%) after two half-lives; the sample never simply drops to zero.

Mercury, Venus, Earth, Mars (rocky terrestrial planets), then Jupiter, Saturn (gas giants), Uranus, Neptune (ice giants). Pluto is a dwarf planet in the Kuiper Belt, not a ninth planet.

Rotation is Earth spinning on its axis about once a day, causing day and night. Revolution is Earth orbiting the Sun in about 365.25 days; together with axial tilt it produces the seasons.

Solar eclipse: Sun, Moon, Earth, at new moon; the Moon's shadow falls on Earth. Lunar eclipse: Sun, Earth, Moon, at full moon; Earth's shadow falls on the Moon. The Moon's 5 degree orbital tilt prevents monthly eclipses.

Seeing different fractions of the Moon's sunlit half as it orbits Earth (cycle about 29.5 days). Phases are not caused by Earth's shadow; that happens only in a lunar eclipse.

A meteoroid is a small rock in space. A meteor is the bright streak it makes burning through the atmosphere. A meteorite is a piece that survives and lands on the ground.

Distance: how far light travels in one year, about 9.46 trillion km (light moves about 300,000 km/s). A star 6 light-years away is seen as it was 6 years ago.

time = distance / speed = 150,000,000 km / 300,000 km/s = 500 s, about 8 minutes 20 seconds. The Earth-Sun distance of about 150 million km is 1 astronomical unit (AU).

Blue-white stars are hotter than red stars. A Sun-like star becomes a red giant, then a white dwarf; a much more massive star can explode as a supernova, leaving a neutron star or black hole.

Independent: the factor the experimenter deliberately changes (fertilizer amount). Dependent: the outcome measured (plant height). Controlled: everything kept the same (seed type, light, water). A measuring tool is not a variable.

Two things can change together because a hidden confounder drives both (hot weather raises ice cream sales and sunburns) or because the direction is reversed. Causation needs a controlled experiment, a mechanism and repeatable results.

Accuracy is closeness to the true value; precision is closeness of repeated readings to each other. A scale reading 251, 251, 252 g for a 200 g weight is precise but not accurate. Averaging trials cannot fix a constant offset.

Diffusion: particles spread from higher to lower concentration with no energy needed. Osmosis: water diffuses across a membrane toward the side with more dissolved solute. A cell in a hypertonic (saltier) solution loses water.

AA, Aa, Aa, aa: 1/4 chance of aa (recessive trait) and 3/4 chance of showing the dominant trait. Each offspring is independent, so two aa in a row is $\frac{1}{4}\times \frac{1}{4}=\frac{1}{16}$.

No. Natural selection acts on inherited variation already present; variants that help survival and reproduction become more common over generations. Populations evolve, individuals do not. Antibiotic resistance spreads this way.

Compare rates, not totals: always ask 'per what?' 50 cases in a town of 1,000 is 5 percent, while 200 cases in a town of 100,000 is only 0.2 percent.

A necessary condition must be present but may not be enough; a sufficient one guarantees the outcome. Oxygen is necessary for a wood fire but not sufficient, since fuel and heat are also needed.