So it deserves the largest share of your study time — but spent on reasoning, not recall. Almost every item below hands you data and asks what it supports.
The official study guide is blunt about this: the science test is not a memory test, and you do not need to know the entire periodic table or the number of bones in the human body. What you need is the ability to read a scenario and reason from it.
That reframes how to study each topic below. Learn the concept well enough to recognize it in a new situation, then practice pulling conclusions from data. Definitions alone will not get you there. So every section here pairs the concept with the question type it shows up in.
There is a practical upside to this. Life science has a lot of vocabulary, and trying to hold all of it costs weeks. You need far less than you think — enough to follow a passage, plus the skill of reading data carefully. Spend the saved time on practice questions instead.
Start with the two cell types. Prokaryotic cells have no nucleus; eukaryotic cells do. Then the structures that keep appearing in questions:
Structure | Role |
|---|
Nucleus | Contains genetic material and directs cell activities |
Cell membrane | Selectively controls what enters and leaves |
Mitochondria | Site of cellular energy production |
Ribosomes | Build proteins |
Chloroplasts | Carry out photosynthesis in plant cells |
Osmosis is the movement of water across a selectively permeable membrane toward the side with greater solute concentration. That single sentence answers a lot of cell questions.
A researcher places identical cells into solutions of different salt concentration. Cells in the most concentrated solution lose the most water. What explains it?
Answer: osmosis. Water moved out of the cells toward the higher solute concentration outside them. Note the direction — water moves toward more solute, not away from it, which is the detail these items check.
Two processes, two purposes. Mitosis supports growth and repair. Meiosis produces gametes and adds genetic variation. Tie each to its purpose rather than its mechanism, because that is how the GED asks about them.
Two paired processes sit at the center of this sub-area.
Process | Equation | What it does with energy |
|---|
Photosynthesis | Carbon dioxide + water + light → glucose + oxygen | Stores energy in glucose |
Cellular respiration | Glucose + oxygen → carbon dioxide + water + usable energy | Releases usable energy from food |
They are not opposites so much as counterparts. One stores energy, the other releases it, and the products of each are the reactants of the other.
A study measures oxygen consumption at rest, then at light, moderate and vigorous exercise, and the values rise at each stage. Which conclusion is best supported?
Answer: oxygen consumption increased as exercise intensity increased. That is the observation, stated plainly. Options claiming the participant is unfit, or calculating total energy produced, go beyond what was measured.
Human Body and Health
Learn the systems as a connected set rather than in isolation, because questions almost always involve two of them working together.
System | What it does |
|---|
Circulatory | Transports blood, oxygen, nutrients and waste |
Respiratory | Exchanges oxygen and carbon dioxide, at the alveoli |
Digestive | Breaks down food and absorbs nutrients |
Nervous | Carries signals and coordinates responses |
Endocrine | Releases hormones that regulate body processes |
Immune | Defends against pathogens |
Skeletal and muscular | Provide structure, protection and movement |
Homeostasis is the thread connecting them — the body maintaining stable internal conditions as the outside changes. Most body-system questions are really homeostasis questions with a different label.
A table shows heart rate before, during and after exercise: it rises during activity and falls back toward the resting value afterwards. Which statement is supported?
Answer: heart rate increased during exercise and moved toward the resting rate during recovery. It describes exactly what the table shows and claims nothing more. That restraint is the pattern to learn — you will meet it in the free GED science practice test repeatedly.
Three terms people mix up, and the GED does not. DNA is the genetic material. Genes are segments of DNA. Chromosomes package DNA into packaged structures. A question can hinge on nothing more than that hierarchy.
Genotype is the genetic makeup; phenotype is the observable trait. Keep them separate, because the numbers differ.
The four equally likely outcomes give 25% AA, 50% Aa and 25% aa. If A is dominant, 75% show the dominant phenotype.
Worked question: two parents both have genotype Aa. A recessive condition appears only in aa offspring. What is the probability their child inherits it? 25% — one aa outcome among four equally likely combinations. Note that the genotype split is 25/50/25 while the phenotype split is 75/25, and items often offer both.
Mutations introduce new genetic variation. Not every mutation is harmful — effects can be harmful, neutral or beneficial depending on where the mutation sits and what the environment is like. Answers describing all mutations as damaging are wrong.
Ecology questions ask you to interpret food webs, population data and environmental change, not just to name producers and consumers.
Producers make organic food molecules, usually using sunlight through photosynthesis.
Consumers get energy by eating other organisms.
Decomposers break down dead material and return nutrients to the ecosystem.
A food chain is one pathway of energy transfer, such as grass → grasshopper → frog → snake. A food web shows many connected feeding relationships. The arrows point from the food to the organism eating it — that is, in the direction energy travels.
Available energy generally falls at higher trophic levels, because organisms spend energy on metabolism and other life functions. Biomass usually follows the same pattern.
A grassland holds 1,800 kg of plant biomass, 320 kg of herbivore biomass and 45 kg of carnivore biomass. Which conclusion fits?
Answer: biomass decreases at higher trophic levels. The figures describe this ecosystem. They do not establish that every ecosystem must show the same distribution, and an option claiming that goes too far.
A fish population falls from 8,000 to 5,600 after a pollution event. The decrease is 8,000 − 5,600 = 2,400, so the percentage decrease is 2,400 ÷ 8,000 × 100 = 30%.
A follow-up may ask whether the pollution caused the decline. It probably did — but the study shows timing and a link, not a controlled comparison. The strongest available answer stops short of asserting cause.
Evolution is change in inherited traits within populations across generations. Natural selection needs three ingredients: variation among individuals, differences in survival or breeding tied to that variation, and inheritance of the relevant traits.
The current framework includes common ancestry, cladograms, natural and artificial selection, adaptation, selection pressure and speciation.
An adaptation is an inherited trait that improves survival or reproductive success in a given environment. Organisms do not develop adaptations because they need them. Existing variation is acted on by selection pressure.
Worked question: a bacterial population contains a few antibiotic-resistant individuals. After repeated treatment, resistant bacteria make up a much larger share. What explains it? Antibiotic treatment created a selection pressure under which resistant bacteria were more likely to survive and reproduce. The antibiotic did not create resistance on demand — the variation was already there.
Cladograms show proposed family trees. Shared derived traits indicate which organisms are more closely related. Read the branching points, not how near two organisms sit on the page. How close they look in the drawing means nothing.
Most life science questions are data questions in a biology costume. Work them in a fixed sequence and they get much easier.
Identify what is being measured.
Find the independent and dependent variables.
Check the units and scale.
Compare the experimental and control groups.
Identify the trend.
Decide whether the evidence supports the conclusion.
Reject any claim that extends beyond the data.
Take a study of plant growth at three fertiliser concentrations plus a control:
Fertiliser | Average growth |
|---|
0 g/L | 14 cm |
2 g/L | 21 cm |
4 g/L | 26 cm |
8 g/L | 19 cm |
Growth rises to 4 g/L then falls at 8 g/L. So "more fertiliser means more growth" is not supported, even though it is true across the first three rows. Step 7 is what catches that.
Trap | The distinction that matters |
|---|
DNA, genes and chromosomes used interchangeably | DNA is the material, genes are segments of it, chromosomes package it |
Mitosis confused with meiosis | Mitosis for growth and repair; meiosis for gametes and variation |
Photosynthesis confused with respiration | Photosynthesis stores energy in glucose; respiration releases usable energy |
Energy treated like matter | Energy flows through and disperses as heat; matter cycles and is reused |
Correlation read as causation | A link plus timing is not a controlled comparison |
Adaptation seen as a conscious response | Selection acts on variation that already exists |
Five of the six are pairs of things that sound alike. If you only revise one thing from this page, revise the distinctions rather than the definitions — the GED tests the boundary between two concepts far more often than either concept alone.
Five quick checks. Answer each before reading on.
Question | Answer |
|---|
Cells in the most concentrated salt solution lose the most water. What process? | Osmosis — water moves toward greater solute concentration |
Reduced oxygen and carbon dioxide exchange between lungs and blood. Which structure? | Alveoli — the gas-exchange surface |
Bb × Bb. Probability of bb offspring? | 25% — one of four equally likely combinations |
A plant decline is followed by herbivore declines. What relationship? | Reduced plant availability lowers the herbivores’ food supply |
Bacteria become resistant after repeated antibiotic exposure. What process? | Natural selection favoured inherited resistance |
Notice how few of these needed a memorised fact. Each rewarded recognizing a process from a description, which is exactly what the reporting categories weight. To build the same habit across all three content areas, work through the GED science study guide and keep the GED science cheat sheet beside you. The official GED Science Study Guide confirms the reasoning-first approach.
