Overview
This study guide covers the four core science domains tested on the GED: Life Science, Physical Science, Earth and Space Science, and Scientific Reasoning. Mastering these concepts requires understanding not just definitions but how ideas connect across topics. Use this guide alongside practice questions to build both knowledge and test-taking confidence.
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Life Science
Summary
Life science on the GED focuses on how living organisms function, interact, and change over time — from the molecular level (DNA, cells) to ecosystem-wide processes (food chains, decomposition). Understanding the relationships between structure and function is key.
Cell Biology
• Mitochondria — The "powerhouse of the cell"; converts glucose and oxygen into ATP (usable energy) through cellular respiration
• Chloroplasts — Site of photosynthesis in plant cells; converts sunlight, water, and CO₂ into glucose and oxygen
• Cell Membrane — Selectively permeable barrier that controls what enters and exits the cell, maintaining internal stability (homeostasis)
> Photosynthesis equation (know this!):
> CO₂ + H₂O + sunlight → Glucose + O₂
Key Terms: Cell Biology
• ATP — Adenosine triphosphate; the cell's primary energy currency
• Selectively permeable — Allows only certain substances to pass through
• Cellular respiration — Process of converting glucose to ATP using oxygen
• Organelle — Specialized structure within a cell that performs a specific function
Genetics
• DNA — Carries genetic instructions for growth, development, and reproduction; determines inherited traits
• Dominant gene — Trait is expressed whenever the allele is present (even one copy is enough)
• Recessive gene — Trait is only expressed when two copies of the recessive allele are present
• Traits are passed from parents to offspring through inherited alleles
Key Terms: Genetics
• Allele — A version of a gene
• Trait — An observable characteristic determined by genes
• Heredity — The passing of traits from parent to offspring
• Genotype — Genetic makeup; Phenotype — Physical expression of genes
Ecosystems and Evolution
• Producers (Autotrophs) — Make their own food using sunlight; examples: plants, algae; base of every food chain
• Consumers (Heterotrophs) — Obtain energy by eating other organisms
• Decomposers — Break down dead organic matter; return nutrients to the soil; examples: bacteria and fungi; essential for nutrient cycling
• Natural Selection — Organisms with traits better suited to their environment survive and reproduce more successfully; drives evolutionary change over generations
Key Terms: Ecosystems
• Food chain — Linear sequence showing energy flow between organisms
• Ecosystem — Community of organisms interacting with their environment
• Nutrient cycling — The recycling of chemical elements through an ecosystem
• Adaptation — A trait that improves an organism's survival in its environment
⚠️ Watch Out For: Life Science
• Photosynthesis ≠ Cellular Respiration — They are nearly opposite processes. Plants do both; only plants (and some bacteria) do photosynthesis.
• Dominant does NOT mean "more common" — A dominant trait can be rare in a population; it only means it's expressed over a recessive allele.
• Decomposers are often forgotten in food chain questions — remember they are critical to ecosystem health, not just "cleanup crews."
• Natural selection acts on populations, not individuals — Individuals don't evolve; populations do over many generations.
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Physical Science
Summary
Physical science covers the laws governing matter, energy, and motion. GED questions frequently test your ability to apply formulas conceptually (especially F = ma), distinguish types of changes and energy, and understand atomic structure and chemical properties.
Forces and Motion
• Newton's Second Law: F = ma (Force = mass × acceleration)
- Greater force → greater acceleration (for the same mass)
- Greater mass → less acceleration (for the same force)
• Potential Energy — Stored energy based on position or condition (e.g., a ball held up high, a compressed spring)
• Kinetic Energy — Energy of motion; any moving object possesses it
• Law of Conservation of Energy — Energy cannot be created or destroyed; it can only be converted from one form to another; total energy in a closed system is constant
Key Terms: Forces and Motion
• Force — A push or pull measured in Newtons (N)
• Mass — Amount of matter in an object (kg)
• Acceleration — Change in velocity over time
• Closed system — A system with no exchange of matter or energy with its surroundings
Matter and Chemical Properties
| Concept | Definition | Example |
|---|---|---|
| Physical change | Alters form/appearance; no new substance | Cutting paper, melting ice |
| Chemical change | Produces a new substance with different properties | Burning wood, rusting iron |
| Atom | Smallest unit of an element retaining its properties | A single carbon atom |
| Molecule | Two or more atoms chemically bonded | H₂O, O₂ |
• States of matter and particle behavior:
- Liquid → Gas: Particles gain energy, overcome intermolecular forces, spread far apart, and move faster and freely
• Periodic Table Groups (columns): Elements share similar chemical properties because they have the same number of valence electrons
Acids and Bases
• pH Scale: Ranges from 0–14
- Acid — pH below 7; donates hydrogen ions (H⁺)
- Neutral — pH of exactly 7 (e.g., pure water)
- Base — pH above 7; accepts hydrogen ions (H⁺)
Key Terms: Matter and Chemistry
• Valence electrons — Electrons in an atom's outermost shell; determine chemical behavior
• Element — A pure substance made of only one type of atom
• Compound — A substance formed from two or more elements chemically bonded
• Intermolecular forces — Attractive forces between molecules
• pH — Measure of hydrogen ion concentration in a solution
⚠️ Watch Out For: Physical Science
• Chemical vs. Physical Change — Dissolving sugar in water is a physical change (you can get the sugar back); burning sugar is chemical (you cannot).
• F = ma requires correct unit thinking — If mass doubles and force stays the same, acceleration is halved, not doubled.
• Conservation of Energy ≠ Energy stays the same form — Energy transforms (e.g., potential → kinetic), but the total amount doesn't change.
• Atoms vs. Molecules — Oxygen gas (O₂) is a molecule made of oxygen atoms; don't confuse the two.
• pH is a reverse scale for concentration — A pH of 2 is more acidic (and has more H⁺ ions) than a pH of 5.
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Earth and Space Science
Summary
Earth and space science covers Earth's systems — atmosphere, geosphere, hydrosphere — and how they interact and change over time. Key themes include cycles, large-scale processes (plate tectonics), and Earth's place in space.
Earth's Atmosphere and Climate
• Weather — Short-term atmospheric conditions at a specific location (today's rain, temperature)
• Climate — Average weather patterns over 30+ years for a region
• Greenhouse Effect — CO₂, water vapor, and other gases trap heat in Earth's atmosphere, warming the surface; essential for life, but enhanced by human activity leads to global warming
• Seasons — Caused by Earth's 23.5° axial tilt, not distance from the sun
- Hemisphere tilted toward the sun → summer (more direct sunlight)
- Hemisphere tilted away from the sun → winter
Earth's Structure and Processes
• Plate Tectonics — Earth's crust is divided into large plates that move due to convection currents in the mantle
- Plate interactions cause: earthquakes, volcanoes, and mountain formation
The Three Types of Rocks
| Rock Type | How It Forms | Example |
|---|---|---|
| Igneous | Cooled magma (underground) or lava (surface) | Granite, Basalt |
| Sedimentary | Compressed layers of sediment over time | Sandstone, Limestone |
| Metamorphic | Existing rocks transformed by heat and pressure | Marble, Slate |
The Water Cycle
Key stages (in order):
1. Evaporation — Water turns to vapor, rises into atmosphere
2. Condensation — Water vapor cools and forms clouds
3. Precipitation — Water falls as rain, snow, sleet
4. Collection — Water gathers in oceans, lakes, rivers, groundwater
Key Terms: Earth and Space Science
• Convection currents — Circular movement of fluid (or magma) driven by heat; drives plate movement
• Axial tilt — The 23.5° angle of Earth's rotational axis relative to its orbital plane
• Greenhouse gases — Gases (CO₂, methane, water vapor) that trap heat in the atmosphere
• Sediment — Small particles of rock, mineral, or organic material
• Mantle — The layer of Earth between the crust and the core
⚠️ Watch Out For: Earth and Space Science
• Seasons are caused by TILT, not distance — Earth is actually slightly closer to the sun in winter (in the Northern Hemisphere). Tilt determines seasons.
• Weather vs. Climate — "It's cold today" is weather; "This region has cold winters" is climate. Think: weather is your mood, climate is your personality.
• Greenhouse effect is natural AND necessary — The GED may test whether you understand the difference between the natural greenhouse effect (beneficial) and the enhanced greenhouse effect from human emissions (problematic).
• Rock cycle flows in all directions — Any rock type can become any other type; it's not a strict one-way sequence.
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Scientific Reasoning
Summary
Scientific reasoning questions test your ability to understand how science is done — designing experiments, interpreting data, and evaluating claims. These skills apply across all three science content areas on the GED.
The Scientific Method
• Hypothesis — A testable, specific, falsifiable prediction; typically written as an "if-then" statement
- Must be testable and capable of being proven wrong
• Scientific Theory — A well-substantiated explanation supported by extensive evidence, repeated testing, and broad scientific consensus
- Far stronger than a hypothesis; not just a "guess"
> Hierarchy of confidence:
> Observation → Hypothesis → Experiment → (repeated testing) → Theory
Experimental Design
| Term | Definition |
|---|---|
| Independent variable | The factor deliberately changed by the researcher |
| Dependent variable | What is measured or observed in response to the change |
| Control group | The group that does not receive the experimental treatment; provides a baseline for comparison |
| Reproducibility | Other scientists obtain the same results under the same conditions; validates findings |
Data Interpretation
• Positive correlation — As one variable increases, the other also increases (upward slope on a graph)
• Negative correlation — As one variable increases, the other decreases
• No correlation — No consistent relationship between the two variables
• Critical rule: Correlation does NOT equal causation — Two things happening together doesn't mean one causes the other
Key Terms: Scientific Reasoning
• Falsifiable — A hypothesis that can be tested and potentially proven wrong
• Variable — Any factor that can change in an experiment
• Controlled experiment — An experiment where all variables except the independent variable are kept constant
• Causation — A direct cause-and-effect relationship between variables
• Bias — A systematic error that skews results in a particular direction
• Sample size — The number of subjects/trials in a study; larger = more reliable results
⚠️ Watch Out For: Scientific Reasoning
• Theory ≠ Guess — In everyday language, "theory" means a guess. In science, a theory is the highest level of explanation supported by overwhelming evidence (e.g., the Theory of Evolution, Germ Theory).
• Correlation ≠ Causation — This is one of the most commonly tested reasoning traps on the GED. Always ask: could a third factor explain both variables?
• Control group vs. control variables — A control group receives no treatment. Control variables are factors kept constant throughout the experiment. These are different things.
• The dependent variable "depends" on the independent variable — Use this memory trick: the dependent variable is what you measure, the independent variable is what you change.
• Reproducibility requires same conditions — If another lab gets different results, it may mean conditions varied — not necessarily that the original experiment was wrong.
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Cross-Domain Connections to Know
Understanding how topics link across domains strengthens GED performance:
• Photosynthesis ↔ Carbon Cycle ↔ Greenhouse Effect — Plants absorb CO₂ (Life Science); CO₂ is a greenhouse gas affecting climate (Earth Science)
• Energy Conservation ↔ Food Chains — Energy flows through ecosystems following physical laws; only ~10% transfers between trophic levels
• Plate Tectonics ↔ Rock Cycle — Volcanic activity (plate tectonics) creates igneous rock; heat and pressure (from tectonic forces) create metamorphic rock
• DNA ↔ Natural Selection — Genetic variation encoded in DNA provides the raw material for natural selection to act upon
• Scientific Method ↔ All Science — Every content area may include questions asking you to analyze experimental design or interpret data
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Quick Review Checklist
Use this checklist before your GED test. Check off each item as you feel confident:
Life Science
• [ ] I can explain the functions of mitochondria, chloroplasts, and the cell membrane
• [ ] I know the photosynthesis equation and where it occurs
• [ ] I can distinguish dominant from recessive traits and explain how they are expressed
• [ ] I can describe the role of producers, consumers, and decomposers in a food chain
• [ ] I can explain natural selection and how it drives evolution
Physical Science
• [ ] I can apply F = ma to predict changes in force, mass, or acceleration
• [ ] I can tell the difference between physical and chemical changes with examples
• [ ] I can distinguish potential energy from kinetic energy
• [ ] I can explain the Law of Conservation of Energy
• [ ] I know where acids, bases, and neutral substances fall on the pH scale
• [ ] I understand why elements in the same group share similar properties
Earth and Space Science
• [ ] I know that Earth's seasons are caused by axial tilt, not distance from the sun
• [ ] I can distinguish weather from climate
• [ ] I can explain the greenhouse effect and name key greenhouse gases
• [ ] I can identify how igneous, sedimentary, and metamorphic rocks form
• [ ] I can describe each stage of the water cycle
• [ ] I understand how plate tectonics explains earthquakes, volcanoes, and mountains
Scientific Reasoning
• [ ] I can write a proper hypothesis and identify independent/dependent variables
• [ ] I know the purpose of a control group
• [ ] I understand why scientific theories are stronger than hypotheses
• [ ] I can read a graph showing positive or negative correlation
• [ ] I know that correlation does not prove causation
• [ ] I understand why reproducibility matters in science
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Tip: Focus extra attention on any box above that you cannot check with confidence — those are your highest-priority review areas before test day.