Science · Drill 19

Science practice 19

87 questions ~9 min recommended

⏱ 00:00

Score

—

No passage text stored for this test yet.

1. A lab group investigated whether a caffeine solution increases heart rate in Daphnia (water fleas). Hypothesis: higher caffeine concentration increases Daphnia heart rate. Procedure: (1) Prepare caffeine solutions at 0.0% (control), 0.1%, and 0.5% (mass/volume) in pond water. (2) Place one Daphnia in a depression slide with 1 mL of solution and allow 2 minutes to acclimate. (3) Under a microscope, count heartbeats for 15 seconds and multiply by 4 to estimate beats/min. (4) Repeat for 10 Daphnia per concentration. (5) The same student performed all counts to reduce observer variation. The group compared mean beats/min among concentrations. A flaw in the experimental design is that:

A. Using one observer eliminates bias, so additional observers were required.

B. Different Daphnia were used at each concentration, preventing within-subject comparisons.

C. Heartbeats were counted for 15 seconds instead of a full minute.

D. Water temperature was not controlled or recorded during microscope observations.

2. A chemistry class tested whether the surface area of calcium carbonate affects reaction rate with hydrochloric acid. Hypothesis: powdered CaCO$_3$ reacts faster than a single large chunk of the same mass. Procedure: (1) Measure 2.00 g of CaCO$_3$ as either powder or one intact chip. (2) Add 50.0 mL of 1.0 M HCl to a 250 mL flask. (3) Add CaCO$_3$, immediately seal the flask with a stopper connected to a gas syringe, and start a timer. (4) Record CO$_2$ volume in the syringe every 10 s for 120 s. (5) Repeat 3 trials per CaCO$_3$ form, using fresh acid each time. The class compared CO$_2$ volume vs. time curves. Which hypothesis is being tested?

A. Powdered CaCO$_3$ produces CO$_2$ more rapidly than a single chip of equal mass.

B. CaCO$_3$ powder has a greater total mass than a CaCO$_3$ chip measured on a balance.

C. CO$_2$ gas dissolves in HCl less when the flask is sealed with a stopper.

D. Higher HCl concentration produces more CO$_2$ than lower HCl concentration for the same CaCO$_3$.

3. A student examined whether the angle of an inclined plane affects the acceleration of a rolling cart. Hypothesis: increasing ramp angle increases cart acceleration. Procedure: (1) Set a 1.00 m track on a lab bench and raise one end to create angles of 5°, 10°, and 15° (measured with a protractor). (2) Place a motion sensor at the bottom and align it with the cart’s path. (3) Release the cart from rest at the same marked starting line for each angle, without pushing. (4) Record velocity vs. time for 2.0 s and compute acceleration from the slope of the best-fit line. (5) Perform 5 trials per angle. The experiment could be improved by:

A. Replacing the motion sensor with a stopwatch to avoid electronic measurement errors.

B. Measuring and controlling wheel friction or using the same cart and wheels throughout.

C. Releasing the cart from different starting positions to sample more velocities.

D. Using a heavier cart at higher angles to prevent it from accelerating too quickly.

4. A researcher tested whether adding a commercial enzyme cleaner reduces protein-based stain mass on cotton fabric. Hypothesis: fabric treated with enzyme cleaner will lose more stain mass than fabric treated with water alone. Procedure: (1) Cut 24 identical 5 cm × 5 cm cotton squares and label them. (2) Apply 0.50 mL of egg-white solution to each square and dry for 2 hours. (3) Measure and record each square’s mass using a balance (±0.001 g). (4) Randomly assign squares to 3 groups (n=8): Enzyme Cleaner, Water Only, and No Wash. (5) For Enzyme Cleaner, soak in 100 mL cleaner diluted 1:10 for 10 min with gentle stirring; for Water Only, soak in 100 mL distilled water for 10 min; for No Wash, store dry for 10 min. (6) Rinse washed groups for 30 s under running distilled water, then air-dry all squares for 12 hours. (7) Re-measure mass and compute mass change for each square. Which hypothesis is being tested?

A. Enzyme cleaner causes a greater decrease in stained-fabric mass than water alone.

B. Egg-white stains increase fabric mass more on cotton than on synthetic fibers.

C. Rinsing under distilled water removes more stain than rinsing under tap water.

D. Air-drying for 12 hours removes a constant amount of water from all fabrics.

5. A researcher tested whether activated charcoal removes dye from water. Materials: 6 clear cups, blue dye solution, activated charcoal powder, coffee filters, and a balance. Procedure: (1) Add 100 mL of the same dye solution to each cup. (2) Add charcoal to reach 0.0 g, 0.5 g, or 1.0 g (2 cups per amount). (3) Stir each cup for exactly 30 s. (4) Filter each mixture through a coffee filter into a clean cup. (5) Measure the filtered liquid’s color intensity using a phone app that reports a “blue value” from 0 (no blue) to 255 (very blue). Lower blue values indicate more dye removal. Step 4 (filtering) was included in order to:

A. Standardize the amount of charcoal added, because filters absorb excess charcoal to a fixed level.

B. Remove charcoal particles so the color measurement reflects dissolved dye, not suspended black powder.

C. Chemically convert blue dye into a colorless form by exposing it to oxygen in the filter.

D. Increase dye concentration by evaporating water during filtration, making differences easier to detect.

6. A chemistry student tested whether activated charcoal removes dye from water. Materials: 6 flasks, 100 mL blue dye solution (same initial absorbance), activated charcoal, filter paper, spectrophotometer. Procedure: (1) Add 0 g, 0.5 g, or 1.0 g charcoal to flasks (2 flasks per amount). (2) Swirl for 60 s and let sit for 5 min. (3) Filter each mixture to remove charcoal particles. (4) Measure absorbance of the filtrate at the dye’s peak wavelength. Expected outcome: higher charcoal mass yields lower absorbance. Step 3 was included in order to:

A. Increase dye concentration by evaporating water so absorbance readings are easier to compare.

B. Ensure the dye fully dissolves before measurement, preventing undissolved dye crystals from forming.

C. Remove charcoal solids that would scatter light and interfere with spectrophotometer absorbance readings.

D. Allow charcoal to chemically react with the dye to form a new colored compound in solution.

7. A scientist is testing the hypothesis that a new drug reduces blood pressure. Participants are given the drug, and their blood pressure is measured before and after. A flaw in the experimental design is that:

A. Blood pressure is not measured frequently.

B. Participants are not randomly selected.

C. The dosage of the drug is consistent.

D. There is no control group.

8. Students tested whether an antacid tablet neutralizes stomach acid faster when crushed. Materials: 6 beakers, 100 mL of 0.10 M HCl per beaker, antacid tablets (same brand), mortar and pestle, pH probe, stirrer. Procedure: (1) In 3 beakers, add one whole tablet; in 3 beakers, add one tablet crushed to powder. (2) Stir all beakers at 300 rpm. (3) Record pH every 15 s for 5 min. (4) Define “neutralized” as pH reaching 4.0. Results: crushed tablets reached pH 4.0 in 75 s; whole tablets in 180 s. The primary purpose of this experiment was to:

A. Compare how stirring speed changes pH over time during an acid-base reaction.

B. Determine whether crushed tablets contain more base than whole tablets of the same brand.

C. Measure the exact molarity of HCl using antacid tablets as a primary standard.

D. Test whether increasing tablet surface area increases the rate of acid neutralization.

9. A study investigates the effect of humidity on paper's tensile strength by varying humidity levels. Step 2 involves acclimating paper samples to each humidity level. This step was included to:

A. Test the paper's initial strength.

B. Measure the humidity levels accurately.

C. Prepare samples for cutting.

D. Ensure consistent exposure conditions.

10. Researchers examined whether running shoes with “energy return” foam reduce oxygen consumption at a fixed speed. Materials: treadmill, metabolic cart, 8 runners, Shoe A (standard foam), Shoe B (energy-return foam). Procedure: (1) Each runner completed two 10-min runs at 10 km/h on different days. (2) Order was randomized: half wore A first, half wore B first. (3) For each run, oxygen consumption ($\mathrm{VO_2}$) was recorded during minutes 8–10 and averaged. (4) Runners were instructed to eat the same breakfast before each session. Mean $\mathrm{VO_2}$: Shoe A = 38.2 mL/kg/min; Shoe B = 37.0 mL/kg/min. Which hypothesis is being tested?

A. Energy-return foam decreases oxygen consumption at a fixed speed relative to standard-foam shoes.

B. Runners who eat identical breakfasts will have identical oxygen consumption across all treadmill speeds.

C. Randomizing shoe order eliminates all physiological differences between runners during treadmill exercise.

D. Energy-return foam increases running speed at constant oxygen consumption compared with standard foam.

11. A scientist tested whether adding yeast increases CO$_2$ production in bread dough. Materials: flour, water, salt, sugar, yeast, 6 sealed bottles with balloons, balance. Procedure: (1) Prepare two dough mixtures: Mix Y contains yeast; Mix N is identical but without yeast. (2) Place 50.0 g of each mixture into 3 bottles each. (3) Stretch a balloon over each bottle opening to capture gas. (4) After 60 min at 30°C, measure balloon circumference as an estimate of gas produced. Results: Mix Y balloons were larger than Mix N. The primary purpose of this experiment was to:

A. Determine whether yeast produces CO$_2$ gas during dough fermentation compared with an otherwise identical mixture.

B. Measure the exact mass of CO$_2$ produced using balloon circumference as a direct mass measurement.

C. Compare how bottle size affects fermentation rate by changing the volume available for gas expansion.

D. Test whether salt is required for balloon inflation by preventing gas from escaping the bottle.

12. A group tested whether a smartphone’s battery drains faster at low temperature. Materials: 6 identical phones, freezer (0°C), room (22°C), battery logging app. Procedure: (1) Charge all phones to 100% and set screen brightness to 50%. (2) Place 3 phones in the freezer and 3 at room temperature. (3) Play the same 30-min video on loop with Wi‑Fi on for 3 hours. (4) Record battery percentage every 30 min. Result: freezer phones dropped to 40% after 3 h; room phones to 65%. A flaw in the experimental design is that:

A. Wi‑Fi was on, so battery drain cannot be measured at all under any temperature condition.

B. Recording battery percentage every 30 minutes provides too many data points for meaningful comparison.

C. Using identical phones prevents generalizing to other brands, so the hypothesis cannot be tested.

D. The freezer may reduce Wi‑Fi signal strength, changing power use independently of temperature effects.

13. A teacher tested whether rinsing rice reduces starch in the cooking water. Materials: 6 identical pots, 300 g uncooked white rice per pot, water, sieve, timer, colorimeter, iodine solution. Procedure: (1) For 3 pots, rinse rice under running water for 60 s, then drain. For 3 pots, do not rinse. (2) Add 600 mL water to each pot and boil for 12 min with lids on. (3) Collect 10 mL cooking water from each pot and add 2 mL iodine solution. (4) Measure absorbance at 620 nm; higher absorbance indicates more starch. Results: rinsed mean absorbance = 0.35; not rinsed = 0.62. The primary purpose of Step 3 was to:

A. Neutralize acids in the cooking water so boiling time is identical for all pots.

B. Convert starch into sugar so the colorimeter can measure sweetness of the cooking water.

C. Sterilize the cooking water sample to prevent microbial growth during colorimeter readings.

D. Create a colored complex with starch so starch amount can be estimated by absorbance.

14. Engineers tested whether a new biodegradable mulch film reduces soil water loss. Materials: 12 identical pots, potting soil, mulch film, plastic wrap, scale (±0.1 g), water. Procedure: (1) Add 500 g dry soil to each pot and water each with 200 g water. (2) Cover 6 pots with mulch film; cover 6 pots with plastic wrap (control cover). (3) Poke 6 identical holes (5 mm) in every cover to allow gas exchange. (4) Place all pots under the same lamp for 48 h. (5) Measure mass loss of each pot (soil + cover) after 48 h; assume mass loss is water evaporated. Mean mass loss: mulch = 62 g; plastic wrap = 40 g. A flaw in the experimental design is that:

A. The plastic wrap control blocks water loss differently than bare soil, confounding mulch effectiveness.

B. Mass loss measures only soil erosion, not evaporation, so results cannot relate to water loss.

C. Using identical soil mass prevents detecting evaporation differences between cover types.

D. Poking holes in both covers ensures gas exchange, which invalidates evaporation measurements.

15. A physics class tested whether a parachute’s canopy area affects fall time. Materials: 9 identical toy figures (same mass), plastic bags, string, scissors, meter stick, stopwatch, 3 m drop height. Procedure: (1) Build parachutes with canopy areas 100 cm$^2$, 200 cm$^2$, and 400 cm$^2$ (3 parachutes each). (2) Attach each parachute to a toy with equal string length. (3) Drop each toy from 3 m indoors and time from release to floor contact. (4) Repeat each drop twice and average times. Results: larger canopy area produced longer fall times. What is the independent variable in this experiment?

A. The drop height, because it determines the distance the toy falls before landing.

B. The average time it takes the toy to reach the floor after being dropped.

C. The number of repeated drops, because repetition changes the final average time.

D. The canopy area of the parachute, changed across three designed size conditions.

16. In an experiment to see if sugar affects yeast fermentation, yeast cultures were grown with 5%, 10%, and 15% sugar concentrations. The amount of carbon dioxide produced was measured. The dependent variable is:

A. Fermentation temperature

B. Amount of carbon dioxide produced

C. Sugar concentration in the cultures

D. Type of yeast used

17. A researcher designs an experiment to test the effect of sound on sleep quality by exposing subjects to different noise levels. What is the independent variable?

A. Duration of sleep

B. Noise level

C. Number of subjects

D. Sleep quality

18. A biologist conducted an experiment to test the effect of different fertilizer types on crop yield. Three types of fertilizers were used on three separate fields, and the crop yield was measured after 3 months. Which hypothesis is being tested?

A. Different fertilizers affect the crop yield differently.

B. Fertilizers decrease the growth rate of crops.

C. Crop yield is unaffected by fertilizer type.

D. All fertilizers increase crop yield equally.

19. Researchers investigated whether a disinfectant reduces bacterial growth on countertops. Materials: 15 identical sterile tiles, a nonpathogenic bacterial culture, sterile swabs, nutrient agar plates, and two spray bottles labeled Solution A and Solution B. Procedure: (1) Add the same volume of bacterial culture to each tile and spread evenly. (2) After 5 min, spray tiles: 5 tiles with Solution A, 5 tiles with Solution B, and 5 tiles with sterile water. (3) Wait 10 min. (4) Swab each tile using the same swabbing pattern and pressure, then streak each swab onto an agar plate. (5) Incubate plates at 37°C for 24 hr and count colonies (CFUs). The team concluded Solution A was best because its plates had the fewest colonies. The experiment could be improved by:

A. Using different bacterial species on each tile to ensure results generalize to all bacteria.

B. Incubating plates at different temperatures for each solution to match each disinfectant’s optimal conditions.

C. Randomly assigning tiles to treatments and blinding the colony counter to reduce bias and confounding.

D. Removing the water-sprayed tiles, because controls reduce the ability to detect disinfectant differences.

20. A student investigated whether salt concentration affects the boiling point of water. Materials: 4 identical 250-mL beakers, hot plate, thermometer probe, table salt (NaCl), balance, and 200 mL distilled water per beaker. Procedure: (1) Add 200 mL distilled water to each beaker. (2) Add NaCl to reach 0 g, 5 g, 10 g, or 15 g per beaker; stir for 60 s. (3) Heat each beaker on the same hot plate setting until vigorous boiling occurs. (4) Record the highest stable temperature over 30 s as the boiling point. (5) Repeat Steps 1–4 three times for each salt amount. The student expected boiling point to increase as more NaCl was added. Step 2 (stirring for 60 s) was included in order to:

A. Calibrate the thermometer probe by exposing it repeatedly to changing salt concentrations.

B. Raise the water temperature by friction so less heating is needed to reach boiling.

C. Prevent evaporation by creating a surface vortex that blocks water molecules from escaping.

D. Ensure NaCl dissolves evenly so the intended salt concentration is consistent throughout the beaker.

21. A class tested whether music tempo affects typing speed. Materials: computer typing test, headphones, and two playlists: slow (60 beats/min) and fast (140 beats/min). Procedure: (1) Each student completed a 2-min typing test in silence to obtain a baseline words-per-minute (WPM). (2) Students then completed a second 2-min test while listening to either slow or fast music. (3) The teacher compared the change in WPM between the slow-music group and the fast-music group. However, students chose which playlist to use, and many students who reported frequent gaming selected the fast playlist. A flaw in the experimental design is that:

A. Students self-selected the tempo condition, so prior typing skill or gaming habits could confound results.

B. Using headphones prevents accurate WPM measurement because sound interferes with keyboard input signals.

C. Comparing change in WPM is invalid because only absolute WPM, not change, can be analyzed.

D. The baseline typing test should be longer than 2 minutes to prevent students from learning to type.

22. A student tested the effect of different soil types on plant growth. They planted seeds in clay, sandy, and loamy soils and measured plant height after 6 weeks. The primary purpose of this experiment was to:

A. Test the nutrient content of the soils.

B. Determine the water retention of each soil.

C. Compare plant species growth rates.

D. Find the best soil for plant growth.

23. An environmental science class tested whether pH affects the corrosion rate of iron nails. Materials: 12 identical iron nails, 4 beakers, vinegar (pH ~3), distilled water (pH ~7), baking soda solution (pH ~9), saltwater (pH ~7 with NaCl), balance, sandpaper. Procedure: (1) Sand and rinse all nails, then record initial mass. (2) Place 3 nails in each solution: vinegar, distilled water, baking soda solution, and saltwater. (3) Leave beakers uncovered at room temperature for 7 days. (4) Remove nails, rinse, dry, and record final mass. Results: vinegar and saltwater nails lost the most mass. The experiment could be improved by:

A. Including a pH 7 solution with salt removed and a pH 7 solution with salt added to separate pH from salinity.

B. Skipping the sanding step, because oxide layers ensure all nails start with identical surfaces.

C. Leaving beakers uncovered to maximize evaporation, because corrosion requires changing concentrations over time.

D. Using different nail sizes in each beaker so surface area varies widely and corrosion is easier to observe.

24. An experiment tests if plant species affects soil nitrogen levels. Different species are planted, and nitrogen levels measured. What is the independent variable?

A. Plant species

B. Soil nitrogen levels

C. Plant size

D. Measurement method

25. In a study measuring the effect of study duration on test performance, students study various lengths of time and take the same test. What is the independent variable?

A. Student age

B. Test difficulty

C. Study duration

D. Test performance

26. In an experiment, researchers wanted to determine the effect of sunlight on plant growth. They placed 20 plants in a greenhouse, with 10 plants receiving 6 hours of sunlight per day and the other 10 receiving no sunlight. At the end of four weeks, they measured the height of each plant. What is the independent variable in this experiment?

A. Duration of the experiment

B. Height of the plants

C. Amount of sunlight received

D. Type of plant used

27. Scientists are testing whether a new fertilizer increases crop yield compared to no fertilizer. A flaw in this experimental design is that:

A. There is no measurement of yield.

B. There is no randomization of plots.

C. Fertilizer amount is not varied.

D. The control group is unaccounted for.

28. In a study testing whether temperature affects bacterial growth, cultures are grown at varying temperatures. Which hypothesis is being tested?

A. Nutrient variation affects growth.

B. Temperature influences bacterial growth.

C. Bacterial growth is independent of temperature.

D. Temperature affects bacterial color.

29. Researchers are studying the effect of music on concentration. Participants performed a task in silence or with background music, and their performance was measured. The independent variable is:

A. Type of task performed

B. Participants' task performance

C. Presence of background music

D. Duration of the task

30. A chemist wants to find out if temperature affects the rate of a reaction. In a series of experiments, the chemist conducted reactions at 20°C, 30°C, and 40°C and recorded the time taken for each reaction to complete. What is the dependent variable in this experiment?

A. Time taken for reaction to complete

B. Amount of reactants

C. Chemicals used in the reaction

D. Temperature of the reaction

31. A scientist wants to test the effect of pH on enzyme activity. They perform reactions at pH 4, 7, and 9, measuring enzyme activity. What improvement could be made to this experiment?

A. Increase the sample size for each pH level.

B. Conduct tests at constant temperature.

C. Use a different enzyme for each pH level.

D. Include more pH levels in the test range.

32. In an experiment to assess the effect of food coloring on taste perception, participants tasted identical drinks with different colors and reported their taste. What is a potential design flaw?

A. Participants were not told about the colors.

B. Taste was self-reported by participants.

C. The same drink was used for all colors.

D. All drinks were served at the same temperature.

33. In an experiment to test how different cleaning agents affect bacterial growth, petri dishes were treated with vinegar, bleach, and soap, and bacterial colonies were counted. What is an independent variable?

A. Temperature of incubation

B. Number of bacterial colonies

C. Type of cleaning agent used

D. Size of the petri dishes

34. In a study on the impact of diet on cholesterol levels, participants followed different diets for 6 months, and cholesterol levels were measured. What is a possible improvement?

A. Measure cholesterol levels weekly.

B. Shorten the study duration to 3 months.

C. Include a diverse participant demographic.

D. Use a single diet type for all participants.

35. An educational researcher tested the effect of study breaks on test performance. Students took a test with or without breaks, and scores were compared. Which hypothesis is being tested?

A. Study breaks lead to increased stress.

B. Breaks improve test performance.

C. Breaks decrease focus during tests.

D. Breaks have no impact on test scores.

36. A biologist conducted an experiment to see if humidity affects seed germination. Seeds were placed in environments with 30%, 50%, and 70% humidity, and germination rates were recorded. The dependent variable is:

A. Size of the seeds

B. Type of seeds used

C. Germination rates of the seeds

D. Humidity levels in the environments

37. A researcher is testing a new drug to see if it lowers blood pressure. They give the drug to 50 participants and measure their blood pressure before and after the treatment. A flaw in the experimental design is that:

A. There is no control group for comparison.

B. The sample size is too large.

C. Participants were not randomly selected.

D. Blood pressure is measured too frequently.

38. A nutritionist conducted an experiment to test if a high-protein diet affects muscle gain. Participants followed a high-protein diet for 12 weeks, and muscle mass was measured. What is the independent variable?

A. Amount of muscle gain

B. Type of diet followed

C. Duration of the experiment

D. Participants' initial muscle mass

39. A study examined the effect of noise level on concentration. Participants completed tasks under quiet and noisy conditions, and task accuracy was measured. What is the independent variable?

A. Noise level during task performance

B. Type of tasks completed

C. Duration of tasks

D. Task accuracy of participants

40. An experiment was designed to test the effect of soil pH on bacterial growth. Bacteria were grown in soils with pH levels of 5, 7, and 9. Bacterial growth was measured. What is the independent variable?

A. Moisture content of the soil

B. pH level of the soil

C. Type of bacteria used

D. Amount of bacterial growth

41. A physicist measured the effect of air pressure on sound speed. Sound was transmitted through air at different pressures, and speed was recorded. What is the dependent variable?

A. Air pressure in the environment

B. Frequency of the sound

C. Type of sound used

D. Speed of sound recorded

42. A physicist tested the effect of wire length on electrical resistance. Wires of 1m, 2m, and 3m were used, and resistance was measured. The primary purpose of this experiment was to:

A. Determine how wire length affects resistance.

B. Find the best wire material for resistance.

C. Measure the current in different wires.

D. Test the durability of the wires.

43. In an experiment testing the effect of sugar concentration on yeast fermentation rate, the sugar concentration serves as:

A. The dependent variable.

B. The independent variable.

C. An irrelevant factor.

D. A control variable.

44. A biologist observes bird feeding patterns at different times of day. What is the dependent variable in this study?

A. Time of day

B. Weather conditions

C. Feeding patterns

D. Bird species

45. Researchers tested whether a new fertilizer increases plant growth. They used 12 identical pots filled with the same mass of potting soil and planted one bean seed in each pot. Pots were placed on a bench under the same grow lights. Procedure: (1) Water all pots with 50 mL daily. (2) Apply fertilizer solution weekly: 6 pots received Fertilizer X (as directed), and 6 pots received plain water. (3) Measure plant height from soil surface to the highest leaf tip every 3 days for 30 days. (4) Calculate mean height increase for each group. However, the 6 Fertilizer X pots were all placed on the left side of the bench, and the 6 control pots were all placed on the right side. The researchers concluded Fertilizer X increased growth. A flaw in the experimental design is that:

A. The fertilizer and control pots were not randomized, so bench position could confound the results.

B. Plant height was measured too often, which can cause plants to grow differently from disturbance.

C. Using identical pots prevents detecting growth differences because all plants experience the same container.

D. Watering all pots daily removes the independent variable, so fertilizer concentration cannot differ.

46. In Study 1, the independent variable (the factor intentionally changed by the student) was:

A. the surface material.

B. the force measured by the spring scale.

C. the angle of the incline.

D. the mass of the block.

47. In Study 3, the students included Trial 6 (0.0% NaHCO₃) primarily to:

A. measure the amount of oxygen dissolved in the water before the experiment began.

B. determine the maximum possible rate of photosynthesis.

C. serve as a control to verify that CO₂ is necessary for photosynthesis.

D. prove that Elodea can produce oxygen without carbon dioxide.

48. In Study 1, the animals were kept "at rest." This was an important experimental control because:

A. it ensured that the environmental temperature remained stable.

B. measuring oxygen consumption is impossible while animals are moving.

C. lizards cannot run at temperatures below 10°C.

D. activity level significantly affects metabolic rate, as shown in Study 2.

49. Researchers tested the effect of light intensity on plant growth using three groups of plants exposed to low, medium, and high light. What is the independent variable in this experiment?

A. Watering frequency

B. Light intensity

C. Number of plants

D. Plant growth

50. In an experiment to measure the effect of temperature on the solubility of a salt, a student dissolves the same amount of salt in 100 mL of water at 5°C, 25°C, and 50°C. The primary purpose of this experiment was to:

A. Examine the effect of salt concentration on water temperature.

B. Determine how temperature affects salt solubility.

C. Find the best temperature for salt preservation.

D. Test the effect of water volume on temperature.

51. An experiment tests the effect of water salinity on fish respiration rate by altering salinity levels. What is the independent variable?

A. Water salinity

B. Fish respiration rate

C. Type of fish

D. Water temperature

52. To evaluate the effect of caffeine on alertness, participants consumed either a regular coffee or a decaf coffee. Their alertness was tested using a reaction time task. Which hypothesis is being tested?

A. Caffeine consumption increases alertness.

B. Decaf coffee improves reaction time.

C. No difference in alertness between groups.

D. All coffee types reduce alertness.

53. A researcher investigated the effect of light color on plant photosynthesis rates. Plants were exposed to red, blue, and green light, and oxygen production was measured. Which hypothesis is being tested?

A. Different light colors affect photosynthesis rates.

B. Light color has no impact on photosynthesis.

C. Green light is most effective for photosynthesis.

D. All colors of light reduce photosynthesis.

54. An experiment was conducted to determine if a special coating on cookware affects heat distribution. Cookware with and without coating was heated, and surface temperatures were measured. What is a potential design flaw?

A. Surface temperature should be measured at multiple points.

B. Coated and uncoated cookware should differ in size.

C. Cookware should be made of different materials.

D. Lack of measurement of heat source temperature.

55. In a study testing the effect of color on mood, subjects' moods are assessed after exposure to different colors. What is the independent variable?

A. Color

B. Duration of exposure

C. Mood

D. Number of subjects

56. Researchers are testing if a new teaching method improves student test scores. Student scores are recorded before and after the new method. What is the dependent variable?

A. Class size

B. Teacher experience

C. Teaching method

D. Student test scores

57. In a study testing whether caffeine affects reaction time, participants' reaction times are measured before and after consuming caffeine. Which hypothesis is being tested?

A. Caffeine reduces reaction time.

B. Reaction time depends on sleep quality.

C. Caffeine increases blood pressure.

D. Reaction time is unaffected by caffeine.

58. In an experiment to determine if music affects concentration, participants complete tasks with and without music. Which hypothesis is being tested?

A. Music increases task completion speed.

B. Concentration is unaffected by music.

C. Task difficulty affects concentration.

D. Music impacts task concentration.

59. Students conducted an experiment to test the effect of pH on enzyme activity by measuring reaction rates at pH 4, 7, and 9. Which hypothesis is being tested?

A. Enzyme activity is consistent across pH levels.

B. pH affects the temperature of the solution.

C. Enzyme activity varies with pH levels.

D. Reaction rate is independent of pH.

60. In an experiment to determine if exercise affects memory, participants' memory is tested before and after exercise sessions. What is the dependent variable?

A. Participant age

B. Exercise duration

C. Type of exercise

D. Memory test results

61. In a test of the effect of sunlight on algae growth, samples were exposed to full sunlight, partial shade, or complete darkness, and growth rates were measured. Which hypothesis is being tested?

A. Partial shade inhibits algae growth.

B. Sunlight exposure affects algae growth rates.

C. Algae grow faster in darkness.

D. All light conditions promote algae growth equally.

62. To test whether a new detergent removes grease better than water alone, a student used 8 identical glass slides. Materials: cooking oil, detergent solution (2%), distilled water, pipette, drying rack, balance (±0.001 g). Procedure: (1) Clean and dry all slides, then record initial mass. (2) Add 0.50 g oil to each slide and record mass again. (3) Wash 4 slides with 50 mL detergent solution for 30 s; wash 4 slides with 50 mL water for 30 s. (4) Rinse all slides with 50 mL distilled water and air-dry 24 h. (5) Record final mass; grease removed is decrease from oily mass to final mass. Which hypothesis is being tested?

A. Detergent removes more oil than water alone when wash volume and time are held constant.

B. Detergent increases the mass of glass slides by depositing surfactants that bond permanently to glass.

C. Air-drying for 24 hours causes oil to evaporate completely from slides regardless of washing method.

D. Distilled water rinsing removes all remaining oil, making detergent unnecessary for grease removal.

63. A researcher tested whether caffeine increases heart rate in Daphnia (water fleas). Materials: microscope, cavity slides, Daphnia culture, spring water, caffeine solutions (0%, 0.1%, 0.2% w/v), pipettes, timer. Procedure: (1) Place one Daphnia in 0% caffeine for 2 min to acclimate. (2) Count heartbeats for 15 s under the microscope; multiply by 4 to estimate beats/min. (3) Transfer the same Daphnia to 0.1% caffeine for 2 min, then repeat the 15 s count. (4) Transfer to 0.2% caffeine for 2 min, then repeat. (5) Repeat Steps 1–4 for 10 different Daphnia. Mean estimated heart rates: 0% = 180 bpm; 0.1% = 210 bpm; 0.2% = 240 bpm. Step 1 was included in order to:

A. Increase the Daphnia’s temperature to match the microscope light intensity during later trials.

B. Provide a baseline heart rate and reduce handling stress before measuring caffeine’s effect.

C. Ensure each Daphnia is exposed to oxygen, preventing hypoxia from lowering heartbeat counts.

D. Allow caffeine to fully dissolve in spring water so concentration remains constant during counting.

64. A medical intern tested whether hand sanitizer reduces bacterial growth on hands. Materials: agar plates, sterile swabs, hand sanitizer (70% ethanol), soap and water, incubator. Procedure: (1) Swab one hand before cleaning and streak onto Plate B (before). (2) Wash both hands with soap and water for 20 s. (3) Apply sanitizer to one hand only; let dry 30 s. (4) Swab the sanitized hand and streak onto Plate S; swab the non-sanitized hand and streak onto Plate W. (5) Incubate 48 h and count colonies. Result: Plate S had fewer colonies than Plate W. A flaw in the experimental design is that:

A. Incubating plates for 48 hours prevents bacteria from forming colonies, so counts are meaningless.

B. Swabbing different hands makes results invalid because hands can never have different initial bacteria levels.

C. Only one person was tested, so individual variability could limit conclusions about sanitizer effectiveness.

D. Using soap and water before sanitizer guarantees no bacteria remain, so sanitizer cannot show differences.

65. A biology club tested whether fertilizer concentration affects radish seed germination. Materials: 12 petri dishes, filter paper, 240 radish seeds, fertilizer solutions (0%, 1%, 2%, 4%), pipettes, incubator at 25°C. Procedure: (1) Place 20 seeds on filter paper in each dish. (2) Add 5.0 mL of one fertilizer solution to each dish; use 3 dishes per concentration. (3) Seal dishes with parafilm to reduce evaporation. (4) After 72 h, count seeds with visible radicles as germinated. Results: mean germination: 0% = 90%; 1% = 88%; 2% = 70%; 4% = 20%. What is the independent variable in this experiment?

A. The fertilizer concentration applied to the seeds, expressed as percent solution.

B. The number of petri dishes used per treatment, which determines replication.

C. The percentage of seeds germinated after 72 hours in each petri dish.

D. The incubator temperature maintained during the 72-hour germination period.

66. A lab group tested whether a copper wire coil increases the rate of hydrogen peroxide decomposition. Materials: 6 flasks, 50 mL of 3% $\mathrm{H_2O_2}$ per flask, copper wire coils, rubber stoppers with gas syringe, stopwatch. Procedure: (1) Place a copper coil in 3 flasks; leave 3 flasks without copper. (2) Seal each flask to a gas syringe to measure oxygen volume. (3) Start timing immediately after sealing. (4) Record gas syringe volume every minute for 10 min. Results: copper flasks produced more gas per minute than no-copper flasks. Step 2 was included in order to:

A. Maintain constant temperature by trapping heat inside the flask and syringe.

B. Measure oxygen production as an indicator of decomposition rate under different conditions.

C. Ensure hydrogen peroxide concentration stays constant by preventing evaporation of water.

D. Prevent copper from oxidizing by isolating it from air during the reaction.

67. A class investigated whether increasing light intensity increases the rate of photosynthesis in Elodea by measuring oxygen bubbles. Materials: 4 beakers, sodium bicarbonate solution (0.2%), 4 equal-length Elodea sprigs, lamp, ruler, thermometer. Procedure: (1) Place one sprig in each beaker with 200 mL bicarbonate solution. (2) Position a lamp at 10 cm, 20 cm, 30 cm, and 40 cm from the beakers. (3) After 5 min acclimation, count bubbles produced in 2 min for each sprig. (4) Record water temperature in each beaker after counting. Results: bubble counts decreased with distance; temperatures were 29°C at 10 cm and 23°C at 40 cm. The experiment could be improved by:

A. Replacing bicarbonate with distilled water so oxygen bubbles come only from photosynthesis.

B. Turning off room lights to eliminate all light so only the lamp affects photosynthesis.

C. Using different plant species at each distance to ensure results apply broadly.

D. Keeping water temperature constant across distances, such as using a water bath or heat filter.

68. A researcher tested whether stirring affects how fast sugar dissolves in water. Materials: 9 beakers, 200 mL water per beaker, granulated sugar, balance, stir plates, thermometers. Procedure: (1) Heat all water to 25°C and verify with thermometers. (2) Add 10.0 g sugar to each beaker. (3) Stir 3 beakers at 0 rpm (no stirring), 3 at 200 rpm, and 3 at 600 rpm. (4) Every 30 s, remove a 5 mL sample, filter out undissolved crystals, and measure dissolved sugar concentration using a refractometer. (5) Continue until concentration stops increasing. What is the independent variable in this experiment?

A. The stirring speed applied to the beakers, measured in revolutions per minute.

B. The dissolved sugar concentration measured by refractometer at each sampling time.

C. The initial mass of sugar added to each beaker before stirring begins.

D. The time required for the sugar concentration to stop increasing in each beaker.

69. A chemist tested how salt concentration affects the freezing point of water. Solutions with 2%, 5%, and 10% salt were cooled, and freezing points were noted. What is the primary purpose of this experiment?

A. Determine how salt affects water's freezing point.

B. Test the purity of the salt used.

C. Measure cooling rates of different solutions.

D. Find the ideal salt concentration for freezing.

70. A student investigated whether stretching a rubber band changes its electrical resistance when coated with graphite. Hypothesis: increasing stretch length increases resistance. Procedure: (1) Rub a soft graphite pencil along a 6 cm section of a rubber band until the surface appears uniformly gray. (2) Attach two alligator clips 4.0 cm apart along the coated section; connect to a digital multimeter set to ohms. (3) Measure resistance with the band unstretched. (4) Stretch the band to lengths of 7 cm, 8 cm, and 9 cm (measured with a ruler) while keeping clip spacing fixed at 4.0 cm, and record resistance at each length. (5) Repeat the entire procedure with 5 rubber bands and average results. What is the independent variable in this experiment?

A. The total stretched length of the rubber band measured with the ruler.

B. The number of rubber bands used to compute the average resistance.

C. The distance between the alligator clips along the graphite-coated section.

D. The resistance reading displayed on the multimeter for each rubber band length.

71. A student tested whether light color affects photosynthesis rate in an aquatic plant (Elodea). The student hypothesized that red light produces a higher photosynthesis rate than green light at the same intensity. Procedure: (1) Place a 10 cm Elodea sprig in a test tube containing 40 mL of 0.2% sodium bicarbonate solution. (2) Position an LED lamp 20 cm from the tube; use a light meter to adjust lamp settings so intensity is 500 lux at the tube for each color. (3) Cover the tube with a clear plastic wrap to minimize gas exchange with air. (4) Illuminate for 10 minutes using either red, green, or white LEDs. (5) Count oxygen bubbles released from the cut stem for the final 5 minutes; record bubbles/min. (6) Repeat 5 trials per light color, using a new sprig each trial. Results were compared among colors. Step 3 was included in order to:

A. Ensure sodium bicarbonate does not dissolve, keeping CO$_2$ concentration constant.

B. Reduce exchange of gases with air so measured bubbles reflect plant oxygen production.

C. Increase light intensity at the tube by reducing reflection from the water surface.

D. Prevent oxygen bubbles from forming so counting is more accurate.

72. A researcher tested whether adding fertilizer increases the growth rate of duckweed (Lemna). Hypothesis: higher fertilizer concentration increases duckweed growth. Procedure: (1) Place 10 duckweed fronds into each of 12 identical cups containing 100 mL pond water. (2) Add fertilizer to reach concentrations of 0, 1, 2, or 4 g/L (3 cups per concentration). (3) Place all cups on the same windowsill for 7 days. (4) Count fronds in each cup on day 0 and day 7; compute growth as fronds gained. (5) Compare mean growth among fertilizer concentrations. A flaw in the experimental design is that:

A. Counting fronds is qualitative and cannot be used to measure growth.

B. Including a 0 g/L fertilizer group prevents detecting differences among fertilized groups.

C. Using 3 cups per concentration provides replication, which weakens conclusions.

D. Light intensity and temperature may vary across the windowsill and were not controlled.

73. A researcher tested whether soil pH affects seed germination of radish plants. Hypothesis: radish seeds germinate best at near-neutral pH. Procedure: (1) Fill 15 identical pots with 200 g of the same potting soil. (2) Adjust soil pH by adding buffered solutions to reach pH 4, pH 7, or pH 10 (5 pots per pH). (3) Plant 20 radish seeds in each pot at 1 cm depth. (4) Add 30 mL distilled water to each pot daily for 7 days. (5) Keep all pots under the same grow light for 12 h/day at 25°C. (6) After 7 days, count germinated seeds (emerged seedlings) per pot and compute percent germination. The primary purpose of this experiment was to:

A. Test whether soil pH changes the percentage of radish seeds that germinate.

B. Compare germination of radish seeds planted at different depths in the same soil.

C. Determine whether buffered solutions increase radish growth compared with distilled water.

D. Identify which grow-light schedule produces the fastest radish seedling emergence.

74. A student tested whether washing hands with soap reduces bacterial growth compared with rinsing with water. Hypothesis: soap washing reduces bacterial colonies on skin more than water rinsing. Procedure: (1) Before washing, press the fingertips of the right hand onto a sterile agar plate for 5 s (Pre plate). (2) Wash hands for 20 s using either liquid soap and water (Soap group) or water only (Water group). (3) After washing, press the same fingertips onto a second agar plate for 5 s (Post plate). (4) Incubate plates at 37°C for 24 hours. (5) Count the number of visible colonies on each plate. (6) Use 12 volunteers, randomly assigned to Soap or Water groups. Step 1 was included in order to:

A. Sterilize the fingertips so only new bacteria appear after washing.

B. Ensure the agar plates are contaminated equally before incubation begins.

C. Increase bacterial growth by warming the plate with body heat during contact.

D. Provide each volunteer’s baseline bacterial level for comparison with their post-wash result.

75. Researchers asked whether caffeine increases the heart rate of freshwater fish (zebrafish). They prepared 4 aquariums (10 fish each) with identical volume (20 L), temperature (25°C), light cycle, and feeding schedule. Step 1: Fish were acclimated for 24 hr in plain water. Step 2: Baseline heart rate was measured for each fish by recording a 15-s microscope video and counting beats, then converting to beats/min. Step 3: Each aquarium received caffeine dissolved in water to reach 0, 10, 20, or 40 mg/L; fish remained in the solution for 30 min. Step 4: Heart rate was measured again using the same 15-s video method. The independent variable was caffeine concentration; the dependent variable was change in heart rate from baseline. Each aquarium’s mean change was calculated. The researchers expected higher caffeine concentrations to produce larger increases in heart rate. Which hypothesis is being tested?

A. Caffeine decreases zebrafish heart rate by slowing metabolism during the 24-hr acclimation period.

B. Zebrafish heart rate changes only with temperature, so caffeine should have no measurable effect.

C. Caffeine increases zebrafish heart rate, and the increase becomes larger at higher caffeine concentrations.

D. Zebrafish heart rate is determined mainly by aquarium size, regardless of caffeine concentration.

76. A psychologist tested whether time of day affects cognitive performance. Tasks were performed in the morning and afternoon, and results were compared. What is a potential improvement?

A. Reduce the number of tasks performed.

B. Use different tasks for morning and afternoon.

C. Test participants at multiple times throughout the day.

D. Include a third time point in the evening.

77. A study was conducted to examine the effect of water temperature on fish activity. Fish were placed in tanks at 15°C, 20°C, and 25°C, and activity levels were recorded. What is the dependent variable?

A. Water temperature in each tank

B. Size of the fish

C. Volume of water in tanks

D. Fish activity levels

78. Students tested whether adding salt to ice water lowers the temperature enough to cool a soda faster. They used 12 identical 355 mL cans of room-temperature soda (22°C), 2 insulated beakers (2 L), crushed ice, water, table salt, a digital thermometer (±0.1°C), and a stopwatch. Procedure: (1) Fill each beaker with 1.0 L ice and 0.5 L water. (2) Add 200 g salt to Beaker S; add 200 g sugar to Beaker U to keep added mass similar. Stir each beaker 30 s. (3) Place 6 cans in each beaker, fully submerged, and start timing. (4) After 5, 10, and 15 min, remove one can from each beaker and immediately measure soda temperature by inserting a probe through a small puncture in the can. (5) Record temperatures and discard punctured cans. Results (mean soda temperature at 10 min): Beaker S = 6.8°C; Beaker U = 10.9°C. Which hypothesis is being tested?

A. Salt increases heat transfer by increasing water viscosity, causing faster cooling than pure ice water.

B. Adding any solid to ice water increases cooling equally by increasing the mixture’s thermal mass.

C. Salt lowers the ice-water mixture temperature, cooling submerged soda cans faster than a non-salt additive.

D. Sugar chemically reacts with aluminum cans, creating holes that allow faster temperature equilibration.

79. A botanist studied the effect of water frequency on plant health. Plants were watered daily, weekly, or not at all, and health was assessed. The primary purpose of this experiment was to:

A. Find drought-resistant plant species.

B. Test the impact of water quality on growth.

C. Determine optimal watering frequency for plant health.

D. Measure water absorption by plants.

80. During an experiment to determine if a specific diet affects weight loss, participants' weights are recorded weekly. What is the dependent variable?

A. Weight loss

B. Weekly recording

C. Participant age

D. Diet type

81. A student tested whether a magnetic stir bar affects the measured conductivity of salt solutions. Materials: conductivity probe, 6 beakers, 0.50 M NaCl solution, stir plate, stir bar. Procedure: (1) Pour 100 mL NaCl into each beaker. (2) Place a stir bar in 3 beakers; leave 3 without a bar. (3) Put all beakers on the same stir plate set to 300 rpm; beakers without bars do not spin. (4) After 2 min, measure conductivity in each beaker. Mean conductivity: with bar = 52 mS/cm; without bar = 47 mS/cm. A flaw in the experimental design is that:

A. Using NaCl prevents conductivity measurements because NaCl is not an electrolyte in water.

B. The beakers without stir bars were not stirred, so mixing differs from the stir-bar condition.

C. Measuring after 2 minutes guarantees identical ion concentration, eliminating any possible difference.

D. Conductivity probes only work in distilled water, so the reported values cannot be compared.

82. A student investigated whether the concentration of dissolved salt affects the boiling point of water. The student hypothesized that increasing NaCl concentration increases boiling point. Procedure: (1) Prepare four 250 mL beakers, each with 200.0 mL distilled water. (2) Add NaCl to make solutions of 0.0 g (control), 5.0 g, 10.0 g, and 15.0 g NaCl; stir 60 s. (3) Place each beaker on the same hot plate set to a fixed power level; cover each beaker with identical watch glasses to reduce evaporation. (4) Insert a digital thermometer probe 2 cm below the surface, not touching glass. (5) Heat until vigorous boiling persists for 30 s; record temperature every 5 s during that 30 s and compute the average “boiling temperature.” (6) Repeat steps 1–5 three times for each salt mass, using fresh water each time. The student compared average boiling temperatures across salt masses. What is the independent variable in this experiment?

A. The average temperature recorded during 30 s of vigorous boiling.

B. The hot plate power level used to heat each beaker.

C. The depth of the thermometer probe below the water surface.

D. The mass of NaCl added to 200.0 mL of water for each trial.

83. In an experiment to determine the boiling point of water at different altitudes, water samples were boiled at sea level, 1,000 meters, and 2,000 meters. Which step is crucial for this experiment?

A. Ensure all samples are boiled simultaneously.

B. Use the same type of pot for all samples.

C. Measure ambient temperature at each location.

D. Maintain constant water volume across samples.

84. In a study on the effect of screen time on sleep quality, participants reported screen usage and sleep quality over a month. A flaw in the experimental design is that:

A. Screen time was measured in hours.

B. Participants self-reported their sleep quality.

C. The sample size was too large.

D. There is no control group.

85. In Study 1, the independent variable (the factor intentionally changed by the student) was:

A. the mass of the block.

B. the force measured by the spring scale.

C. the surface material.

D. the angle of the incline.

86. In Study 1, the animals were kept "at rest." This was an important experimental control because:

A. it ensured that the environmental temperature remained stable.

B. lizards cannot run at temperatures below 10°C.

C. activity level significantly affects metabolic rate, as shown in Study 2.

D. measuring oxygen consumption is impossible while animals are moving.

87. In Study 3, the students included Trial 6 (0.0% NaHCO₃) primarily to:

A. serve as a control to verify that CO₂ is necessary for photosynthesis.

B. measure the amount of oxygen dissolved in the water before the experiment began.

C. prove that Elodea can produce oxygen without carbon dioxide.

D. determine the maximum possible rate of photosynthesis.

Next test →