We tracked how test-takers performed on every Science question in our GED practice course, roughly 40 learners per item. That is a small sample - enough to spot a pattern, not enough to quote to the decimal - but the pattern was consistent and worth acting on. Two items sat at a 21% success ratio, which is below what random guessing on four choices would produce. Here are the six that caused the most trouble, the specific mistake behind each, and a fresh problem to fix it.
1. Why astronauts float in orbit
Almost everyone reaches for the same answer: there is no gravity up there. There is. At the altitude of the International Space Station, Earth's gravity is still around 90% as strong as it is at the surface. If it weren't, the station would fly off into space instead of circling us.
What is actually happening is continuous free fall. The station is falling toward Earth the whole time, but it is also moving sideways so fast that it keeps missing. Everything inside falls at exactly the same rate, so nothing presses against anything else - and that sensation of not being pressed is what we call weightlessness.
- A. Gravity does not reach that far from Earth.
- B. The satellite and everything in it are in continuous free fall around Earth.
- C. The satellite's speed cancels out Earth's mass.
- D. There is no air at that altitude to hold objects down.
Show the solution
Gravity is still strong at 400 km - it is what curves the satellite's path into an orbit in the first place, so A is out.
The satellite is falling toward Earth continuously while moving sideways fast enough that it never reaches the ground. Everything inside falls at the same rate, so nothing has any apparent weight.
Speed does not cancel mass, and air was never what held objects down - gravity did.
Answer: B. The satellite and everything in it are in continuous free fall around Earth.
Weightlessness means free fall, not zero gravity. If a question offers you 'no gravity in space', that is the trap.
2. What Earth's atmosphere is actually made of
The pull toward oxygen is almost irresistible. It is the gas we breathe, the one we talk about, the one we die without. But dry air is roughly 78% nitrogen and only about 21% oxygen, with argon near 0.9% and carbon dioxide around 0.04%.
Importance and abundance are two different things. Nitrogen dominates the atmosphere by volume even though your body cannot use it directly from the air. Learn the four numbers - 78, 21, 0.9, 0.04 - and this whole family of questions becomes free points.
- A. Oxygen, nitrogen, carbon dioxide
- B. Nitrogen, oxygen, argon
- C. Carbon dioxide, oxygen, nitrogen
- D. Oxygen, argon, nitrogen
Show the solution
Nitrogen comes first at about 78% of dry air. Oxygen is second at about 21%. Argon is a distant third at roughly 0.9%.
Carbon dioxide, despite how much attention it gets in climate questions, is only about 0.04% - far too little to appear in a top-three list.
Answer: B. Nitrogen, oxygen, argon
Carbon dioxide matters enormously to the greenhouse effect and is still a trace gas by volume. Those two facts are not in conflict.
3. Which system moves things around the body
The stem names oxygen, nutrients and wastes, and each of those words drags learners toward a different system: oxygen pulls toward respiratory, nutrients toward digestive, wastes toward excretory. Every one of those systems is involved somewhere in the chain - which is exactly why the question feels ambiguous when it isn't.
Sort them by verb. The respiratory system brings oxygen in. The digestive system breaks food down. The excretory system filters waste out. Only the circulatory system moves material between them. If the question says transport, carry, deliver or distribute, the answer is circulatory.
- A. Digestive
- B. Respiratory
- C. Circulatory
- D. Endocrine
Show the solution
The digestive system did its job by breaking the food down and absorbing the glucose - but absorption is where its work ends.
From the intestinal wall onward, the glucose travels in the bloodstream. Blood vessels carry it to the muscle. That is the circulatory system.
The respiratory system handles gas exchange, and the endocrine system sends chemical signals such as insulin - it regulates glucose rather than transporting it.
Answer: C. Circulatory
Every organ-system question is really asking about a verb. Match the verb in the stem to the system that performs it.
4. What an open switch actually does
That 30-point gap is the most useful thing in this data. Learners understand that closing a switch turns a bulb on. They stumble on the mirror image, and the likely reason is the word itself: in everyday English, open means available, working, ready. In a circuit it means the opposite - open is a gap, and a gap stops everything.
Current needs an unbroken loop from one battery terminal, through the components, and back to the other. Break the loop anywhere - an open switch, a removed bulb, a cut wire - and no current flows anywhere in that loop.
- A. It stays exactly as bright as before.
- B. It becomes brighter, because it now receives all the current.
- C. It goes out, because the loop is no longer complete.
- D. It dims but stays lit.
Show the solution
The bulbs are in a single loop, so the same current has to pass through both. Removing one leaves a gap in that loop.
With the loop broken, no current flows anywhere in it, and the remaining bulb goes out.
Choice B describes what would happen in a parallel circuit, where each bulb sits on its own branch. Read whether the components share one path or have separate paths.
Answer: C. It goes out, because the loop is no longer complete.
Open switch, removed bulb, cut wire - three phrasings, one meaning: the loop is broken and nothing flows.
5. What ribosomes do
Long time plus low accuracy is a different signal from fast and wrong. It means people were reading the choices carefully, weighing them, and still could not separate the organelles.
The fix is a production line. Ribosomes build proteins by linking amino acids together. The endoplasmic reticulum transports them. The Golgi apparatus packages and ships them. Lysosomes break down waste. Mitochondria supply the energy for all of it. Learn the sequence, not five isolated definitions.
- A. Lysosomes
- B. Ribosomes
- C. Golgi apparatus
- D. Vacuoles
Show the solution
Making more protein means assembling more amino acid chains, and that assembly happens at the ribosomes. They are the first step in the line.
The Golgi apparatus will get busier too, but only after the protein exists - it packages and ships, it does not build.
Lysosomes handle breakdown and vacuoles handle storage. Neither produces protein.
Answer: B. Ribosomes
If a question uses the words make, build, produce or synthesize about a protein, ribosomes are almost always the answer.
6. Telling the dependent variable from the independent one
This is the cleanest pattern in the whole data set. Learners can identify what the researcher changed. They lose the thread when asked for what the researcher measured.
One sentence fixes it. Write out: Does changing [blank] affect [blank]? The first blank is the independent variable - the thing you set. The second blank is the dependent variable - the outcome you record. It is called dependent because its value depends on the first one.
Everything else in the setup is a controlled variable: the things deliberately held the same so the comparison is fair. Those are never the answer to either question.
- A. The amount of fertilizer given each week
- B. The mass of tomatoes produced
- C. The amount of water given to each plant
- D. The eight-week growing period
Show the solution
Say the sentence: does changing the amount of fertilizer affect the mass of tomatoes produced?
Fertilizer fills the first blank, so it is the independent variable - what the class deliberately set. Tomato mass fills the second blank, so it is the dependent variable - the outcome measured at the end.
Water was held constant, making it a controlled variable, and the eight weeks is simply how long the study ran.
Answer: B. The mass of tomatoes produced
Independent goes on the horizontal axis, dependent on the vertical. If you can picture the graph, you can name both.
What this data is telling you
Five of these six misses are vocabulary problems wearing a science costume. Open does not mean available. Abundant does not mean important. Transport does not mean respiratory. Weightless does not mean gravity-free. Dependent does not mean the thing you changed. The underlying science in each case is something most learners already understand once the word is unpacked - which means these are fast points to recover, not months of study. Read the stem for the exact word being tested before you look at the answer choices.
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The success ratios on this page come from the GED practice course that produced them - all four subjects, with worked visuals for every question.