306 Science questions written for the TEAS 7, each with a rationale explaining why the correct answer is correct and why the others are not. Free, no account required. 10 examples are shown below.
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The answer: C (aortic semilunar valve) Think of it this way: each heart valve is a one-way door. After the left ventricle (the heart's main pumping chamber) squeezes blood out into the aorta, the door behind it has to slam shut — otherwise, during diastole (when the heart relaxes between beats), blood would fall right back in. The door between the left ventricle and the aorta is the aortic valve. Why C is right: The aortic semilunar valve sits at the exit from the left ventricle into the aorta. When the heart relaxes (diastole), this valve closes so blood can't drain back into the ventricle. Why the others are wrong: - A (mitral valve): This door is one step earlier — between the left atrium and the left ventricle. - B (tricuspid valve): This is the matching door on the right side — between the right atrium and the right ventricle. - D (pulmonic valve): This is the exit door toward the lungs — between the right ventricle and the pulmonary artery. Remember: "Aortic" has the aorta in its name — it's the door guarding the aorta from backflow. Technical note: The aortic semilunar valve closes during diastole to prevent regurgitation from the aorta into the left ventricle. Mitral guards LV→LA, tricuspid guards RV→RA, pulmonic guards pulmonary artery→RV.
The answer: D — Oxidation-reduction (redox) reaction Think of it this way: Rusting involves iron LOSING electrons (oxidation) and oxygen GAINING electrons (reduction). Any reaction involving transfer of electrons is a redox reaction. Why D is right: Rusting (iron corrosion) is a redox reaction: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃. Iron (Fe) is oxidized from Fe⁰ to Fe³⁺ (loses electrons). Oxygen (O₂) is reduced from 0 to -2 (gains electrons). The water facilitates the electron transfer. Why the others are wrong: - A (Synthesis reaction): While rusting could superficially be called a synthesis (iron + oxygen → iron oxide), the key characteristic of the reaction is the electron transfer, making it specifically redox. - B (Decomposition reaction): Decomposition is when one compound breaks down into simpler substances (AB → A + B). Rusting combines substances, not decompose them. - C (Single replacement reaction): Single replacement is when one element displaces another in a compound (A + BC → AC + B). Rusting does not fit this pattern. Remember: Redox = any reaction involving transfer of electrons. OIL RIG: Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons). Rusting, burning, and combustion are all redox reactions. Corrosion of metals is always a redox process.
The answer: B, C, D — Carrier female (XᴰXᵈ); Color-blind female (XᵈXᵈ); Normal vision male (XᴰY) Think of it this way: Color blindness is X-linked recessive. The mother (XᴰXᵈ) can pass either her dominant Xᴰ or recessive Xᵈ. The father (XᵈY) can only pass either his Xᵈ or his Y (no Xᴰ at all). Why B, C, and D are right: - B (XᴰXᵈ, carrier female): Mother passes Xᴰ + father passes Xᵈ = XᴰXᵈ. Normal vision (one dominant allele) but a carrier. - C (XᵈXᵈ, color-blind female): Mother passes Xᵈ + father passes Xᵈ = XᵈXᵈ. Both X chromosomes carry the recessive allele → color blind. - D (XᴰY, normal vision male): Mother passes Xᴰ + father passes Y = XᴰY. Has the dominant allele → normal vision. Why A is wrong: A homozygous dominant female (XᴰXᴰ) would require BOTH X chromosomes to carry the dominant Xᴰ allele. The father (XᵈY) has NO Xᴰ allele to contribute — he can only pass Xᵈ or Y. So XᴰXᴰ is impossible from this cross. Remember: With X-linked traits, the father's X chromosome determines daughters' second X. A color-blind father (XᵈY) cannot have normal-vision (XᴰXᴰ) daughters because he has no Xᴰ to give. Also note: daughters get X from each parent; sons get X from mother and Y from father.
The answer: C — Osteoclasts Think of it this way: The word root "clast" means "to break." Osteoclasts break down bone. Think: oSTEOclasts = DESTROY bone, just as "iconoclast" means someone who destroys icons. Why C is right: Osteoclasts are large, multinucleated cells derived from monocytes/macrophages that resorb bone matrix. They secrete acids (HCl) to dissolve the mineral component (hydroxyapatite) and enzymes (cathepsin K) to break down the organic matrix (collagen). This releases calcium and phosphate into the bloodstream. Osteoclast activity is essential for bone remodeling, calcium homeostasis, and fracture healing. Why the others are wrong: - A (Osteoblasts): Osteoblasts BUILD bone — they secrete collagen and the proteins of the bone matrix (osteoid) and regulate its mineralization. "Blast" = to form/build. They become osteocytes when surrounded by bone matrix. - B (Osteocytes): Mature bone cells trapped within the bone matrix — they maintain the surrounding bone tissue and mechanosense bone stress, but are not the primary resorptive cells. - D (Chondrocytes): Cartilage cells — they produce and maintain cartilage matrix. They have nothing to do with bone resorption. Remember: Bone cell memory — Osteoblasts BLAST bone into existence (build). Osteocytes are OLDER blasts that got trapped (maintain). Osteoclasts CRUSH and remove bone (resorb). Balance: osteoblast > osteoclast = bone gain (young adults). Osteoclast > osteoblast = bone loss (osteoporosis). Bisphosphonates (alendronate) work by inhibiting osteoclasts.
The answer: A, C — NaCl and HCl Think of it this way: Strong electrolytes are substances that COMPLETELY dissociate into ions in water, producing a solution that conducts electricity well. The two categories of strong electrolytes are: (1) soluble ionic compounds (like NaCl) and (2) strong acids/bases. Why A and C are right: - A (NaCl): Sodium chloride is a soluble ionic compound — in water it completely dissociates: NaCl → Na⁺(aq) + Cl⁻(aq). 100% ionization → strong electrolyte. This is why IV saline conducts electricity and why it serves as an electrolyte replacement. - C (HCl): Hydrochloric acid is a strong acid — it completely dissociates in water: HCl → H⁺(aq) + Cl⁻(aq). 100% ionization → strong electrolyte. Strong acids (HCl, H₂SO₄, HNO₃, HBr, HI, HClO₄) are strong electrolytes. Why B and D are wrong: - B (CH₃COOH — acetic acid): A WEAK acid — only partially dissociates (~1% at typical concentrations): CH₃COOH ⇌ CH₃COO⁻ + H⁺. Partial ionization = weak electrolyte. This is why vinegar (acetic acid) tastes sour but conducts electricity poorly. - D (NH₃ — ammonia): A WEAK base — partially dissociates: NH₃ + H₂O ⇌ NH₄⁺ + OH⁻. Partial ionization = weak electrolyte. Remember: Strong electrolytes: soluble ionic compounds + strong acids (HCl, H₂SO₄, HNO₃, HBr, HI, HClO₄) + strong bases (NaOH, KOH, Ca(OH)₂). Weak electrolytes: weak acids (CH₃COOH, HF, H₂CO₃), weak bases (NH₃). Non-electrolytes: molecular compounds that don't ionize (sugar/C₆H₁₂O₆, ethanol). Clinical note: serum electrolytes (Na⁺, K⁺, Cl⁻, HCO₃⁻) are essential for cell function, nerve conduction, and fluid balance.
The answer: C — Melting of ice Think of it this way: Ask: does a NEW substance form? Physical changes change the form or phase of matter without creating new molecules. Chemical changes break and form chemical bonds, creating new substances. Why C is right: Melting ice is a phase change — solid H₂O becomes liquid H₂O. The chemical formula remains H₂O throughout. No new bonds are formed or broken; intermolecular forces (hydrogen bonds) weaken to allow the liquid phase. This is a physical change. Why the others are wrong: - A (Rusting of iron): Rusting is the reaction of iron with oxygen and water to form iron oxides (Fe₂O₃, Fe₃O₄). New chemical substances are created = chemical change. - B (Burning of wood): Combustion breaks the carbon-carbon and carbon-hydrogen bonds in wood, reacting with oxygen to form CO₂ and H₂O — entirely new molecules = chemical change. The ash left behind is chemically different from wood. - D (Souring of milk): Souring is caused by bacteria converting lactose to lactic acid — a chemical change that alters the composition of the milk. Remember: Physical changes: phase changes (melting, freezing, boiling), dissolving, cutting, bending. Chemical changes: combustion, rusting, digestion, fermentation, photosynthesis, souring. Clues to chemical changes: color change, gas produced, precipitate forms, energy released/absorbed, new smell. Clue to physical change: the substance can be returned to its original form (ice → water → ice).
The answer: A, B, D — Redness (rubor), Swelling (tumor), Heat (calor) Think of it this way: The four cardinal signs of inflammation were identified by Celsus in the 1st century CE and are remembered by their Latin terms: rubor (redness), tumor (swelling), calor (heat), and dolor (pain). Fatigue is a systemic symptom, not one of the four classical local signs. Why A, B, and D are right: - A (Redness/rubor): ✓ Caused by vasodilation — increased blood flow to the injured area makes it appear red. - B (Swelling/tumor): ✓ Caused by increased vascular permeability — fluid (including proteins and white blood cells) leaks from blood vessels into the surrounding tissue. - D (Heat/calor): ✓ Caused by increased blood flow (vasodilation brings warm blood from the body's core to the periphery, raising local temperature) and by metabolic activity of immune cells. Why C is wrong: Fatigue is a GENERAL SYSTEMIC symptom associated with many conditions including infection and chronic inflammation — but it is NOT one of the four cardinal local signs of inflammation. The classical four are all localized signs at the site of injury: redness, swelling, heat, and PAIN (dolor). Pain is the fourth cardinal sign not listed as an option here. Remember: Five signs of inflammation (Celsus + Virchow): Rubor = Redness (vasodilation). Calor = Heat (vasodilation + metabolic activity). Tumor = Swelling (increased permeability → edema). Dolor = Pain (prostaglandins + kinins stimulate nociceptors). Functio laesa = Loss of function (5th sign, added by Rudolf Virchow in the 19th century). Inflammation vs. Infection: Inflammation = the body's RESPONSE (can occur without infection — e.g., sprained ankle, allergic reaction). Infection = presence of a pathogen that MAY cause inflammation.
The answer: B — The group that received the placebo Think of it this way: The control group is the one that does not receive the treatment, providing a baseline for comparison. Why B is right: The control group does not receive the experimental treatment (the drug). Instead, they receive a placebo, which allows the scientist to compare the effects of the drug against no treatment. Why the others are wrong: - A (The group that received the drug): This is the experimental group, which receives the treatment being tested. - C (Both groups together): Only one group serves as the control; both groups cannot be the control. - D (The group with the highest blood pressure at the start): This is not a defined group in the experiment; the control is determined by treatment assignment, not baseline measurements. Remember: The control group is the untreated group used as a benchmark. It helps ensure that any observed effect is due to the treatment and not other factors.
The answer: B — The amount of sunlight Think of it this way: The independent variable is what the experimenter deliberately changes or manipulates. Why B is right: The student is purposefully exposing one group to full sunlight and the other to no sunlight. This change in light exposure is what she is testing, making sunlight the independent variable. Why the others are wrong: - A (The height of the bean plants): This is the dependent variable — it is what is measured as a result of the change. - C (The type of soil): The soil is the same for all pots, so it is a controlled variable, not something being changed. - D (The number of bean seeds): The number of seeds is constant (20 total, 10 per group), so it is also a controlled variable. Remember: Independent variable = what you change; dependent variable = what you measure. Controlled variables are kept constant to ensure a fair test.
The answer: C — There is only one room per condition, so other factors could affect the results Think of it this way: With only one room per condition, any difference could be due to the light bulbs or to an uncontrolled difference between the rooms (like how often the lights were used or the number of windows). Why C is right: Using only one room per treatment group means there is no replication. Any uncontrolled variable unique to that room (e.g., more frequent use, different room size) could confound the results, making it impossible to attribute the difference solely to the light bulbs. Why the others are wrong: - A (The experiment lacks a control group): The room with standard bulbs serves as a control group, so this is not a flaw. - B (The researcher did not measure the dependent variable correctly): The measurement of electricity use is straightforward and likely accurate; the flaw is in the design, not the measurement. - D (The experiment was not blinded): Blinding is less critical for an objective outcome like electricity use; it is not the most significant flaw here. Remember: Replication (using multiple subjects or samples per condition) is a key element of good experimental design. It helps ensure that observed effects are due to the treatment and not to chance or uncontrolled variables.
