282 Science questions written for the HESI A2, 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: B — Osteoblasts Think of it this way: Osteoblasts are the 'builders' of bone, while osteoclasts are the 'breakers.' During healing, you need builders. Why B is right: Osteoblasts are bone-forming cells that synthesize new bone matrix and regulate mineralization. During fracture healing, they are activated to form new bone tissue at the fracture site. Why the others are wrong: - A (Osteoclasts): These cells resorb (break down) bone, not build it. - C (Chondrocytes): These form cartilage, not bone. - D (Osteocytes): These are mature bone cells that maintain existing bone tissue, but they don't form new bone. Remember: Osteoblasts build bone; osteoclasts break it down. Think 'blast' = 'build' and 'clast' = 'crush.'
The answer: B — Low blood pH due to accumulated acids Think of it this way: Metabolic acidosis is like the body's trash can overflowing with acid because the kidneys can't take out the garbage. Why B is right: In metabolic acidosis, the blood pH drops below 7.35 because acids build up. In chronic kidney disease, the kidneys can't excrete enough acid or reabsorb enough bicarbonate, leading to this condition. Why the others are wrong: - A (Primary respiratory alkalosis): This is a different condition involving low CO2, not related to kidney disease. - C (High blood bicarbonate levels): Metabolic acidosis actually has low bicarbonate levels, not high. - D (Compensated respiratory acidosis): This involves high CO2, not the primary problem in kidney disease. Remember: Metabolic acidosis = too much acid or too little bicarbonate. Kidneys are the main regulators of bicarbonate.
The answer: c — 480 Think of it this way: In Hardy-Weinberg, carriers are the middle group — 2pq — and you can find them once you know p and q. Why c is right: Given q² = 0.16, take the square root to get q = 0.4. Then p = 1 - q = 0.6. The carrier frequency is 2pq = 2 x 0.6 x 0.4 = 0.48. Multiply by the population: 0.48 x 1000 = 480 carriers. Why the others are wrong: - a (160): That's q² x 1000, which is the number of recessive individuals, not carriers. - b (320): That's 2q x 1000, which isn't the correct formula. - d (640): That's 2p x 1000 or p² x 1000, not the carrier frequency. Remember: Carriers = 2pq. First find q from q², then p = 1 - q, then calculate 2pq.
The answer: a — Excess nutrients from fertilizer runoff Think of it this way: Eutrophication is like overfeeding algae with too much fertilizer, causing an algae party that ends in a dead zone. Why a is right: Excess nutrients, especially nitrogen and phosphorus from agricultural fertilizers and wastewater, enter water bodies and cause excessive algae growth (algal blooms). When the algae die and decompose, oxygen levels drop, creating dead zones that cannot support aquatic life. Why the others are wrong: - b (Oil spills): Oil spills are toxic but do not cause nutrient-driven algal blooms. - c (Heavy metal contamination): Heavy metals poison organisms but do not cause eutrophication. - d (Ocean acidification): Ocean acidification is caused by CO2 absorption, not nutrient runoff. Remember: Eutrophication = too much fertilizer = algae bloom = dead zone. It is all about nutrients, not oil or metals.
The answer: A, B, C — NAD+ and NADP+, Coenzyme A, FAD Think of it this way: B vitamins are like the raw materials your body uses to build the tools (coenzymes) that run your energy factories. Why A, B, C are right: NAD+ and NADP+ come from niacin (B3) and carry electrons in reactions like glycolysis. Coenzyme A comes from pantothenic acid (B5) and shuttles acetyl groups into the Krebs cycle. FAD comes from riboflavin (B2) and also picks up electrons during metabolism. All are coenzymes from B vitamins. Why the others are wrong: - D (Insulin): Insulin is a protein hormone that regulates blood sugar, not a coenzyme from B vitamins. Remember: 'B vitamins build coenzymes' — think NAD+, CoA, and FAD as the 'B-team' for metabolism.
The answer: A — Nucleus Think of it this way: The nucleus is the 'brain' of the cell — it holds all the DNA instructions. Why A is right: In eukaryotic cells, DNA is contained within the membrane-bound nucleus, separate from the cytoplasm. Why the others are wrong: - B (Ribosome): Ribosomes are for protein synthesis, not DNA storage. - C (Cytoplasm): DNA is not in the cytoplasm of eukaryotes; it's in the nucleus. - D (Cell membrane): The cell membrane surrounds the cell but doesn't contain DNA. Remember: The nucleus is the 'DNA headquarters' — it's where the genetic material lives in eukaryotic cells.
The answer: B — Autosomal recessive Think of it this way: Cystic fibrosis requires two bad copies of the gene (one from each parent) to show the disease. If you have only one bad copy, you're a carrier but don't have symptoms. Why B is right: The CFTR gene is on chromosome 7 (an autosome). Autosomal recessive means you need two nonfunctional copies (one from each parent) to have the disease. Carriers have one normal and one mutated allele and don't show symptoms. Why the others are wrong: - A (Autosomal dominant): This would mean only one bad copy is needed to have the disease, but CF requires two. - C (X-linked dominant): This would mean the gene is on the X chromosome and one bad copy causes disease, but CF is on chromosome 7. - D (X-linked recessive): This would mean the gene is on the X chromosome and males are more affected, but CF is on an autosome. Remember: Autosomal recessive = two bad copies needed. Autosomal dominant = one bad copy is enough. X-linked = gene is on the X chromosome.
The answer: B — 4,000 N Think of it this way: The work done by the brakes to stop the car is equal to the car's kinetic energy that gets dissipated as heat. Why B is right: Use the work-energy theorem: Work = change in kinetic energy. The car's initial kinetic energy is ½mv² = ½(1000)(20)² = 200,000 J. This work is done over the braking distance of 50 meters. Since Work = Force × distance, the braking force = Work / distance = 200,000 / 50 = 4,000 N. Why the others are wrong: - A (10,000 N): This might come from a miscalculation of kinetic energy or distance. - C (20,000 N): This is another common miscalculation. - D (8,000 N): This might come from forgetting the ½ in the kinetic energy formula. Remember: Work = ΔKE = ½mv². Then, Force = Work / distance. The brakes do work to remove the car's kinetic energy.
The answer: B — Weathering Think of it this way: Weathering is what happens when nature "weathers" down rocks where they sit — like wind, rain, and ice chipping away at a mountain. Why B is right: Weathering is the natural breakdown of rocks and minerals at Earth's surface through exposure to water, air, and organisms. It happens in place, without moving the material. Why the others are wrong: - A (Erosion): Erosion is the movement of weathered material, not the breakdown itself. - C (Sedimentation): Sedimentation is the deposition of particles after they've been moved. - D (Leaching): Leaching is the dissolving of minerals by water moving through soil. Remember: Weathering breaks it down, erosion carries it away, sedimentation drops it off, and leaching dissolves it out.
The answer: A — Osmosis Think of it this way: Water moves to where there's more "stuff" dissolved, like a crowd moving to where the party is, without using energy. Why A is right: Osmosis is the passive movement of water across a selectively permeable membrane from an area of lower solute concentration (more water) to higher solute concentration (less water). No energy (ATP) is needed. Why the others are wrong: - B (Diffusion): This is the general movement of any molecule from high to low concentration, but osmosis specifically refers to water. - C (Active transport): This requires energy to move molecules against their gradient, but water moves passively here. - D (Facilitated diffusion): This uses protein channels for specific molecules, but water can move by simple osmosis without channels. Remember: Osmosis = water diffusion. Think "water follows salt" and remember it's passive — no energy required.
