We tracked how learners performed on every Science question in our TEAS practice course - between 18 and 20 learners per item. That is a small sample, so read these as direction rather than precise figures: one learner moves a ratio by about five points. But the pattern was hard to miss. Six Science items scored below the 25% that pure guessing would produce on a four-option question, and most of the weak spots came in related clusters rather than as one-off stumbles. Here are the six topics that caused the most trouble, the specific mistake behind each, and a fresh problem to fix it.
1. The two stages of protein synthesis
Both of those are well below the 25% that blind guessing would earn on a four-option item, which tells you learners were not guessing. They were confidently picking a wrong answer - almost always mixing up the two stages, or mixing up the three kinds of RNA.
Keep it to two words. Transcription copies DNA into mRNA, in the nucleus - same language, like transcribing notes. Translation turns the mRNA code into a chain of amino acids, at the ribosome - a new language. Then name the RNAs by job: mRNA is the message, tRNA transfers amino acids, and rRNA helps make up the ribosome itself.
1. tRNA molecules deliver amino acids to the ribosome
2. mRNA leaves the nucleus
3. RNA polymerase builds mRNA from a DNA template
4. Peptide bonds join the amino acids into a chain
- A. 3, 2, 1, 4
- B. 2, 3, 4, 1
- C. 1, 3, 2, 4
- D. 3, 1, 2, 4
Show the solution
Everything starts with the DNA, which never leaves the nucleus. So the first step must happen there: RNA polymerase reads the DNA and builds a matching mRNA strand. That is transcription - event 3.
The mRNA then carries that message out of the nucleus to a ribosome - event 2.
At the ribosome, translation begins. tRNA molecules arrive carrying amino acids, each matched to a codon on the mRNA - event 1 - and the amino acids are linked by peptide bonds into a chain - event 4.
Answer: A. 3, 2, 1, 4
Choice D puts tRNA at work before the mRNA has even left the nucleus. If the message has not reached the ribosome, there is nothing for tRNA to read.
2. The pH scale is not a ruler
The pull is to treat pH like a ruler - three units apart means three times as acidic. But the scale is logarithmic: each unit is ten times the last. A three-unit gap is a thousandfold difference, and a four-unit gap is ten thousandfold.
Two related facts fall out of the same idea. Blood pH is held near 7.4 mainly by the bicarbonate buffer system, which soaks up extra hydrogen ions or releases them as needed. And "strong" at the top end of the scale means close to 14 - a pH of 13 is a strong base, while 8 is only weakly basic.
- A. 4 times greater
- B. 40 times greater
- C. 400 times greater
- D. 10,000 times greater
Show the solution
Each whole step on the pH scale is a tenfold change in hydrogen ion concentration, and lower pH means more hydrogen ions.
From pH 6 down to pH 2 is 4 steps, so the change is 10 × 10 × 10 × 10 = 10,000.
Answer: D. 10,000 times greater
Choice A is subtraction and stop. Choice B treats each step as adding ten rather than multiplying by ten. Count the steps, then multiply ten by itself that many times.
3. What only meiosis does
Mitosis and meiosis share a vocabulary - prophase, metaphase, anaphase, telophase - so learners who know the phase names often assume the two processes are nearly the same. They differ in exactly the ways the TEAS likes to test: how many divisions, how many cells, how many chromosomes, and whether the cells come out identical.
Two memory hooks for the rest of the cluster: the S phase is synthesis, when the DNA is copied before division, and metaphase is when the chromosomes line up in the middle.
- A. The cell is undergoing meiosis and will produce haploid cells that are genetically different from each other.
- B. The cell is undergoing mitosis and will produce two identical body cells.
- C. The cell is in the S phase, copying its DNA.
- D. The cell is in metaphase of mitosis, lining its chromosomes up in the middle.
Show the solution
Homologous chromosomes pairing and swapping segments is crossing over, and it happens only in prophase I of meiosis.
Meiosis makes four cells, each with half the original chromosome number, and crossing over is one of the reasons no two are identical.
Mitosis never pairs homologous chromosomes, and neither the S phase nor metaphase involves swapping segments.
Answer: A. The cell is undergoing meiosis and will produce haploid cells that are genetically different from each other.
Mitosis: one division, two identical diploid cells, for growth and repair. Meiosis: two divisions, four unique haploid cells, for making eggs and sperm. Crossing over is the fingerprint of meiosis.
4. What holds the two strands of DNA together
Learners who can build a complementary strand still miss this, which suggests the pairing rules are memorized as letters rather than as chemistry. Covalent is the bond type most people reach for, because it is the one they know is strong.
Attach the rule to the letters you already know: adenine pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. If you can say that sentence, you have the bond type and the pairing in one line.
- A. Heat strengthens the covalent bonds between the two strands.
- B. The strands are joined by relatively weak hydrogen bonds between bases, while each strand's backbone is held by stronger covalent bonds.
- C. Ionic bonds between phosphate groups on opposite strands dissolve in heat.
- D. Peptide bonds link the bases on opposite strands.
Show the solution
Heat breaks weak bonds before strong ones. If the strands come apart while each strand survives, the bonds between strands must be weaker than the bonds within a strand.
That is exactly the structure of DNA: hydrogen bonds between paired bases hold the two strands together, and strong covalent bonds link the sugar-phosphate backbone of each strand.
Peptide bonds join amino acids in proteins, not bases in DNA.
Answer: B. The strands are joined by relatively weak hydrogen bonds between bases, while each strand's backbone is held by stronger covalent bonds.
The weakness of those hydrogen bonds is the point. DNA has to unzip to be copied and transcribed, and a molecule glued together with covalent bonds could not.
5. Cellular respiration, forward and backward
This is the clearest case in the data of two processes being swapped. Photosynthesis and cellular respiration use the same molecules pointing in opposite directions, so a learner who half-remembers one will confidently give the other.
Anchor it with the equation and the location. Respiration takes in glucose and oxygen, releases carbon dioxide and water, and captures the energy as ATP. Glycolysis starts in the cytoplasm, but most of the ATP is made in the mitochondria, which is why they are called the powerhouse of the cell.
- A. Glucose and oxygen
- B. Carbon dioxide and water
- C. Oxygen and ATP
- D. Carbon dioxide and glucose
Show the solution
Write the equation: glucose + oxygen → carbon dioxide + water + ATP.
Glucose and oxygen are what goes in. Carbon dioxide, water and ATP are what comes out.
Only B contains nothing but products. C is half right - ATP is a product - but oxygen is consumed, not produced.
Answer: B. Carbon dioxide and water
Cellular respiration is photosynthesis run in reverse. If a choice lists glucose or oxygen as a product, it has described the plant side of the cycle.
6. Which part of the brain does what
Anatomy and physiology is the heaviest-weighted area of TEAS Science, and the nervous system produced the largest cluster of misses among the body systems in our data - four separate items between 39% and 56%. The misses were not random: the wrong answers point to regions being swapped with each other, especially the cerebellum and the medulla, which sit next to each other at the back of the brain.
One job per structure is enough. Medulla oblongata: breathing and heart rate. Cerebellum: balance and coordination. Corpus callosum: the bridge between the left and right hemispheres. Sympathetic nervous system: fight or flight.
- A. Cerebellum
- B. Medulla oblongata
- C. Corpus callosum
- D. Frontal lobe
Show the solution
Breathing and heart rate are involuntary functions controlled from the brainstem, and the medulla oblongata is the region most directly responsible for them.
Balance and coordination are intact, which points away from the cerebellum. The corpus callosum connects the two hemispheres, and the frontal lobe handles planning, judgment and voluntary movement.
Answer: B. Medulla oblongata
Sort brain questions by whether the action is voluntary. Automatic survival functions sit low, in the brainstem. Coordination sits just behind it, in the cerebellum. Thinking and choosing sit up top, in the cerebrum.
What this data is telling you
Five of these six clusters are biology and chemistry, not anatomy - protein synthesis, pH, cell division, DNA structure and cellular respiration. That matters because the TEAS 7 split biology and chemistry out as their own scored areas, and they are exactly where learners who studied mainly body systems get caught. The other pattern is below-chance scoring: when a question lands under 25%, learners are not guessing, they are confidently choosing a specific wrong answer, and a single corrected idea usually fixes the whole cluster. One smaller signal is worth passing on. Two questions about where sweat glands sit in the skin scored 28% without a diagram and 61% with a labeled one - different wording and small samples, but consistent with the advice to sketch a structure when you are unsure. Next in line in our data: how a food web responds to losing its primary consumers (33%), the kidney's filtering unit (39%) and the structure connecting muscle to bone (40%). Our TEAS Science practice set covers the nephron and heart blood flow step by step.
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The success ratios on this page come from the ATI TEAS practice course that produced them - all four sections, with a worked explanation behind every question.