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MTTC Integrated Science (Secondary) (094) study materials
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MTTC Integrated Science (Secondary) (094) practice questions

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Question 1Integrated Science (Secondary) - content domains not enumerated in source

In a controlled experiment testing how light intensity affects the rate of photosynthesis in Elodea, which variable should be deliberately varied by the investigator?

  1. The temperature of the water bath
  2. The distance of the light source from the plant Correct answer.
  3. The mass of the Elodea sprig used
  4. The concentration of carbon dioxide in the water

Explanation

The independent variable is the factor the experimenter intentionally changes, here the light intensity manipulated through distance. The other listed factors must be held constant so that any change in oxygen production can be attributed to light alone.

Question 2Integrated Science (Secondary) - content domains not enumerated in source

A rock sample contains equal numbers of parent and daughter atoms of a radioactive isotope with a half-life of 20 million years. Assuming no daughter atoms were present initially and none escaped, the rock is approximately how old?

  1. 40 million years
  2. 10 million years
  3. 80 million years
  4. 20 million years Correct answer.

Explanation

After one half-life, half of the parent atoms have decayed, leaving parent and daughter in a 1:1 ratio. Since the ratio is exactly 1:1, one half-life of 20 million years has elapsed.

Question 3Integrated Science (Secondary) - content domains not enumerated in source

Which statement best explains why a lunar eclipse can occur only at full moon?

  1. Earth's shadow falls on the Moon only when Earth lies between the Sun and the Moon Correct answer.
  2. Earth's atmosphere bends sunlight onto the Moon only during full phase
  3. The Moon reflects sunlight most strongly when fully illuminated
  4. The Moon's orbital plane is tilted so that it always faces Earth's night side at full moon

Explanation

A lunar eclipse requires Earth to pass directly between the Sun and the Moon so that Earth's shadow covers the lunar surface, which is geometrically possible only near full moon. The alignment must also occur near a node of the Moon's tilted orbit, which is why eclipses do not happen every month.

Question 4Integrated Science (Secondary) - content domains not enumerated in source

Which property of water most directly accounts for its unusually high specific heat compared with similar-sized molecules?

  1. Its ability to act as a solvent for ionic compounds
  2. Its bent molecular geometry
  3. Its extensive hydrogen bonding network Correct answer.
  4. Its low molar mass

Explanation

Hydrogen bonds between water molecules must be broken or distorted to raise the kinetic energy of the molecules, so a large amount of heat produces only a small temperature change. This network is the main reason water's specific heat is exceptionally high.

Question 5Integrated Science (Secondary) - content domains not enumerated in source

In a food web, a population of secondary consumers is suddenly removed. Which short-term change is most likely?

  1. Primary consumers will initially increase in number Correct answer.
  2. The number of trophic levels will increase
  3. Primary producer biomass will immediately decline
  4. Decomposers will stop recycling nutrients

Explanation

Removing secondary consumers releases primary consumers from predation pressure, so their population typically rises before resource limits or other feedbacks intervene. This is a top-down cascade effect in the short term.

Question 6Integrated Science (Secondary) - content domains not enumerated in source

Which observation provides the strongest evidence that a chemical reaction has occurred?

  1. A solid dissolves and the solution becomes clear
  2. A crystalline solid is ground into powder
  3. A liquid is heated and begins to boil
  4. A gas evolves and a new odor appears Correct answer.

Explanation

Formation of a gas with a new odor indicates new substances with different properties have formed, which is characteristic of a chemical change. Physical processes such as dissolving, boiling, and grinding change form but not composition.

Question 7Integrated Science (Secondary) - content domains not enumerated in source

A neutral atom of an element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴. Which element is it and how many valence electrons does it have?

  1. Selenium, with 6 valence electrons
  2. Silicon, with 4 valence electrons
  3. Oxygen, with 6 valence electrons
  4. Sulfur, with 6 valence electrons Correct answer.

Explanation

The configuration totals 16 electrons, identifying sulfur. The 3s² 3p⁴ outer shell contains six valence electrons, consistent with a Group 16 element.

Question 8Integrated Science (Secondary) - content domains not enumerated in source

According to Newton's third law, when a swimmer pushes backward against the water, what is the reaction force?

  1. Friction between the swimmer and the water
  2. The drag force opposing the swimmer's motion
  3. The swimmer's weight acting downward
  4. The water pushing forward on the swimmer Correct answer.

Explanation

For every action there is an equal and opposite reaction acting on a different object. The swimmer pushes the water backward, so the water pushes the swimmer forward with equal magnitude.

Question 9Integrated Science (Secondary) - content domains not enumerated in source

A 4 kg cart moving at 3 m/s collides with and sticks to a stationary 2 kg cart on a frictionless track. What is the velocity of the combined carts after the collision?

  1. 1.0 m/s
  2. 2.0 m/s Correct answer.
  3. 1.5 m/s
  4. 3.0 m/s

Explanation

Momentum is conserved in an inelastic collision: (4 kg)(3 m/s) = (6 kg)(v), giving v = 2.0 m/s. Kinetic energy is not conserved, but total momentum is.

Question 10Integrated Science (Secondary) - content domains not enumerated in source

A wave has a frequency of 250 Hz and a wavelength of 1.2 m. What is its speed?

  1. 120 m/s
  2. 208 m/s
  3. 360 m/s
  4. 300 m/s Correct answer.

Explanation

Wave speed equals frequency multiplied by wavelength: 250 Hz × 1.2 m = 300 m/s. This relationship applies to all periodic waves in a uniform medium.

Question 11Integrated Science (Secondary) - content domains not enumerated in source

Which cellular structure is directly responsible for synthesizing proteins destined for secretion from the cell?

  1. Smooth endoplasmic reticulum
  2. Golgi apparatus
  3. Rough endoplasmic reticulum Correct answer.
  4. Lysosome

Explanation

Ribosomes bound to the rough endoplasmic reticulum synthesize proteins that enter the secretory pathway. The Golgi apparatus later modifies and packages these proteins but does not synthesize them.

Question 12Integrated Science (Secondary) - content domains not enumerated in source

In a dihybrid cross between two heterozygous individuals (AaBb × AaBb) with independent assortment, what fraction of offspring is expected to show both recessive traits?

  1. 1/8
  2. 3/16
  3. 1/16 Correct answer.
  4. 9/16

Explanation

Each recessive trait appears in 1/4 of offspring from a heterozygous monohybrid cross. Multiplying the independent probabilities gives 1/4 × 1/4 = 1/16 for the double recessive phenotype.

Question 13Integrated Science (Secondary) - content domains not enumerated in source

Which process most directly increases genetic variation within a population of sexually reproducing organisms?

  1. Crossing over during meiosis Correct answer.
  2. Mitotic cell division
  3. DNA replication during interphase
  4. Cytokinesis following mitosis

Explanation

Crossing over between homologous chromosomes during prophase I of meiosis creates new combinations of alleles on chromosomes. This recombination, along with independent assortment, generates genetic variation in gametes.

Question 14Integrated Science (Secondary) - content domains not enumerated in source

A population of insects develops resistance to an insecticide over several generations. Which mechanism best explains this outcome?

  1. The insecticide becomes less potent as it degrades in the environment
  2. Insects learn to avoid the insecticide and pass the behavior to offspring
  3. Individuals with pre-existing resistance survive and reproduce more successfully Correct answer.
  4. The insecticide induces mutations that make individual insects resistant

Explanation

Natural selection acts on variation already present in the population; resistant individuals survive and leave more offspring, increasing resistance allele frequency. The insecticide selects rather than creates resistance.

Question 15Integrated Science (Secondary) - content domains not enumerated in source

Which statement correctly describes the role of ATP in cellular metabolism?

  1. It serves as a structural component of the plasma membrane
  2. It stores genetic information for protein synthesis
  3. It transfers energy from exergonic reactions to endergonic reactions Correct answer.
  4. It catalyzes the hydrolysis of macromolecules in the lysosome

Explanation

ATP couples energy-releasing reactions to energy-requiring ones by capturing energy in its phosphate bonds and releasing it upon hydrolysis. This makes it the cell's universal energy currency.

Question 16Integrated Science (Secondary) - content domains not enumerated in source

Which layer of Earth's atmosphere contains the ozone layer that absorbs most ultraviolet radiation?

  1. Troposphere
  2. Mesosphere
  3. Thermosphere
  4. Stratosphere Correct answer.

Explanation

The ozone layer resides in the stratosphere, where ozone molecules absorb ultraviolet radiation and protect surface life. This absorption also warms the stratosphere.

Question 17Integrated Science (Secondary) - content domains not enumerated in source

A weather station records a steady drop in atmospheric pressure over 12 hours. Which interpretation is most reasonable?

  1. A low-pressure system is approaching and unsettled weather is likely Correct answer.
  2. Wind speed is decreasing and conditions are stabilizing
  3. A high-pressure system is moving in and clear skies are likely
  4. A cold front has already passed and pressure is rising

Explanation

Falling pressure indicates that air is being removed aloft faster than it is replaced near the surface, typical of an approaching low-pressure system. Rising air in lows favors cloud formation and precipitation.

Question 18Integrated Science (Secondary) - content domains not enumerated in source

Which feature forms at a divergent boundary between two oceanic plates?

  1. A mid-ocean ridge with new crust Correct answer.
  2. A transform fault with lateral offset
  3. A continental volcanic arc
  4. A deep ocean trench

Explanation

At a divergent boundary, magma rises between separating plates and solidifies to form new oceanic crust, building a mid-ocean ridge. Seafloor spreading moves the plates apart.

Question 19Integrated Science (Secondary) - content domains not enumerated in source

In a sample of gas at constant temperature, the volume is halved. According to Boyle's law, what happens to the pressure?

  1. It is halved
  2. It is doubled Correct answer.
  3. It increases fourfold
  4. It remains unchanged

Explanation

Boyle's law states that pressure and volume are inversely proportional at constant temperature, so halving the volume doubles the pressure. The product PV remains constant.

Question 20Integrated Science (Secondary) - content domains not enumerated in source

Which type of chemical bond involves the transfer of electrons from a metal to a nonmetal?

  1. Ionic bond Correct answer.
  2. Metallic bond
  3. Covalent bond
  4. Hydrogen bond

Explanation

Ionic bonding occurs when one atom donates electrons and another accepts them, producing oppositely charged ions held together by electrostatic attraction. This typically occurs between metals and nonmetals.

Question 21Integrated Science (Secondary) - content domains not enumerated in source

A solution has a hydrogen ion concentration of 1 × 10⁻⁴ M. What is its pH, and is it acidic or basic?

  1. pH 10, acidic
  2. pH 4, acidic Correct answer.
  3. pH 10, basic
  4. pH 4, basic

Explanation

pH is the negative base-10 logarithm of the hydrogen ion concentration, so pH = 4. A pH below 7 indicates an acidic solution.

Question 22Integrated Science (Secondary) - content domains not enumerated in source

An object is placed beyond twice the focal length of a converging lens. Which image is formed?

  1. Virtual, upright, and reduced
  2. Real, inverted, and enlarged
  3. Virtual, upright, and enlarged
  4. Real, inverted, and reduced Correct answer.

Explanation

For a converging lens, an object beyond 2f produces a real, inverted image between f and 2f on the far side, which is smaller than the object. This is the principle behind a camera's optics.

Question 23Integrated Science (Secondary) - content domains not enumerated in source

A block slides down a frictionless incline from rest. If the vertical height of the incline is doubled while the angle stays the same, what happens to the block's speed at the bottom?

  1. It remains the same
  2. It increases by a factor of 4
  3. It increases by a factor of √2 Correct answer.
  4. It doubles

Explanation

Conservation of energy gives mgh = ½mv², so v = √(2gh). Doubling h multiplies the speed by the square root of 2, not by 2.

Question 24Integrated Science (Secondary) - content domains not enumerated in source

In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is 0.2. What is the expected frequency of heterozygotes?

  1. 0.16
  2. 0.04
  3. 0.32 Correct answer.
  4. 0.64

Explanation

With q = 0.2, p = 0.8, and the heterozygote frequency is 2pq = 2(0.8)(0.2) = 0.32. The equilibrium model assumes no selection, mutation, migration, or genetic drift and random mating.

Question 25Integrated Science (Secondary) - content domains not enumerated in source

A researcher measures plant growth under five light intensities and finds a strong positive correlation. Which conclusion is most defensible?

  1. Increased light intensity causes increased growth in this experiment Correct answer.
  2. Light intensity has no effect on plant growth
  3. The correlation proves that light is the only factor affecting growth
  4. Plant growth determines the light intensity

Explanation

In a controlled experiment where light intensity is the manipulated variable and other factors are held constant, a consistent response supports a causal inference within the tested range. Correlation alone would be weaker, but experimental control strengthens the causal claim.

Question 26Integrated Science (Secondary) - content domains not enumerated in source

In an integrated science investigation, students measure the mass of a sealed flask containing vinegar and baking soda before and after mixing. The total mass stays the same even though gas is produced. Which principle best explains this result?

  1. Definite proportions, because compounds combine in fixed mass ratios
  2. Conservation of mass, because matter is neither created nor destroyed in a closed system Correct answer.
  3. Conservation of energy, because the reaction releases heat to the surroundings
  4. Ideal gas behavior, because the gas produced exerts pressure on the flask

Explanation

In a closed system, the total mass before and after a chemical reaction remains constant because atoms are rearranged, not created or destroyed. The gas produced stays inside the sealed flask, so its mass is still counted.

Question 27Integrated Science (Secondary) - content domains not enumerated in source

A scientist wants to determine whether a new fertilizer increases crop yield. Which experimental design best supports a valid causal conclusion?

  1. Measure yield in fields where farmers already use the fertilizer
  2. Randomly assign plants to fertilized and unfertilized groups and keep other conditions identical Correct answer.
  3. Compare yields from two different crop species grown in different soils
  4. Apply fertilizer to all plants and compare yields across seasons

Explanation

A controlled experiment with random assignment and a comparison group isolates the fertilizer as the only variable. Holding other conditions constant allows a causal inference about the treatment.

Question 28Integrated Science (Secondary) - content domains not enumerated in source

A student observes that a rock sample scratches glass but is scratched by a steel nail. Which property is being used to identify the mineral?

  1. Hardness Correct answer.
  2. Luster
  3. Cleavage
  4. Streak

Explanation

Hardness is a mineral's resistance to being scratched, ranked on the Mohs scale. Comparing the mineral's ability to scratch or be scratched by reference materials identifies relative hardness.

Question 29Integrated Science (Secondary) - content domains not enumerated in source

Which statement best describes the role of decomposers in an ecosystem's matter cycling?

  1. They break down dead organic matter and release nutrients into the soil Correct answer.
  2. They fix carbon into glucose using sunlight
  3. They transfer energy directly to primary consumers
  4. They convert atmospheric nitrogen into forms plants can use

Explanation

Decomposers such as bacteria and fungi break down dead organisms and wastes, releasing nutrients like nitrogen and phosphorus back to the environment. This returns matter to producers for reuse.

Question 30Integrated Science (Secondary) - content domains not enumerated in source

An igneous rock with very large crystals most likely formed under which conditions?

  1. Rapid cooling at Earth's surface
  2. Slow cooling deep underground Correct answer.
  3. Rapid cooling underwater
  4. Cooling after being ejected into the air

Explanation

Large crystals require slow cooling, which gives mineral grains time to grow. Slow cooling typically occurs deep underground in intrusive igneous settings.

Question 31Integrated Science (Secondary) - content domains not enumerated in source

Which statement correctly distinguishes a scientific hypothesis from a scientific theory?

  1. A hypothesis applies only to physics, while a theory applies to all sciences
  2. A hypothesis is a well-supported explanation, while a theory is an initial guess
  3. A hypothesis is always correct, while a theory remains unproven
  4. A hypothesis is a testable prediction, while a theory is a broad explanation supported by extensive evidence Correct answer.

Explanation

A hypothesis is a testable prediction or proposed explanation for a specific observation. A scientific theory is a broad, well-supported explanation built from many lines of evidence.

Question 32Integrated Science (Secondary) - content domains not enumerated in source

Which human activity most directly increases the concentration of atmospheric carbon dioxide?

  1. Discharging heated water from power plants into rivers
  2. Releasing chlorofluorocarbons from refrigerants
  3. Adding excess nitrogen fertilizer to farmland
  4. Burning fossil fuels for electricity and transportation Correct answer.

Explanation

Combustion of fossil fuels releases carbon that was stored underground into the atmosphere as carbon dioxide. This directly raises atmospheric CO2 concentrations.

Question 33Integrated Science (Secondary) - content domains not enumerated in source

A car travels 150 meters east in 10 seconds. What is its average velocity?

  1. 15 m/s east Correct answer.
  2. 150 m/s east
  3. 1.5 m/s east
  4. 1500 m/s east

Explanation

Average velocity equals displacement divided by time, so 150 m divided by 10 s equals 15 m/s east. Velocity includes direction, which is stated as east.

Question 34Integrated Science (Secondary) - content domains not enumerated in source

A student dissolves table salt in water until no more will dissolve at room temperature. What happens if the solution is gently warmed?

  1. The solubility decreases, so salt precipitates out
  2. The salt chemically reacts with the water
  3. The salt's solubility is unaffected by temperature
  4. The solubility of most solid solutes increases, so more salt can dissolve Correct answer.

Explanation

For most solids, solubility in water increases with temperature because dissolving is often endothermic. Warming the saturated solution allows additional solute to dissolve.

Question 35Integrated Science (Secondary) - content domains not enumerated in source

A 2 kg block is pushed across a horizontal surface with a constant horizontal force of 10 N while a friction force of 4 N opposes the motion. What is the block's acceleration?

  1. 5 m/s²
  2. 3 m/s² Correct answer.
  3. 2 m/s²
  4. 7 m/s²

Explanation

The net force is 10 N minus 4 N, or 6 N. Using Newton's second law, a = F_net / m = 6 N / 2 kg = 3 m/s².

Question 36Integrated Science (Secondary) - content domains not enumerated in source

Which change to a simple pendulum will double its period?

  1. Doubling the amplitude for small angles
  2. Doubling the mass of the bob
  3. Doubling the length of the pendulum Correct answer.
  4. Doubling the acceleration due to gravity

Explanation

The period of a simple pendulum is proportional to the square root of its length. Increasing length by a factor of four doubles the period, while mass and small amplitude do not affect it.

Question 37Integrated Science (Secondary) - content domains not enumerated in source

Which statement best explains why water has a higher boiling point than hydrogen sulfide, despite both being bent molecules?

  1. Water molecules form hydrogen bonds with one another Correct answer.
  2. Water has a lower molar mass than hydrogen sulfide
  3. Water molecules are larger and have more electrons
  4. Hydrogen sulfide molecules are nonpolar

Explanation

Oxygen is much more electronegative than sulfur, so water molecules engage in strong hydrogen bonding. These stronger intermolecular forces require more energy to overcome during boiling.

Question 38Integrated Science (Secondary) - content domains not enumerated in source

A cell is placed in a hypertonic solution. What is the most likely immediate result?

  1. Solutes move into the cell until concentrations equalize
  2. Water leaves the cell and it shrinks Correct answer.
  3. Water enters the cell and it swells
  4. The cell membrane dissolves

Explanation

In a hypertonic solution, the surrounding solute concentration is higher than inside the cell, so water moves out by osmosis. The cell loses water and shrinks.

Question 39Integrated Science (Secondary) - content domains not enumerated in source

In a food web, a hawk eats snakes, snakes eat mice, and mice eat seeds. If the hawk population declines sharply, which short-term change is most likely?

  1. The mouse population will decrease immediately
  2. The snake population will decrease
  3. The seed population will decrease
  4. The snake population will increase Correct answer.

Explanation

Fewer hawks means less predation on snakes, so the snake population can increase in the short term. This illustrates top-down control in a food web.

Question 40Integrated Science (Secondary) - content domains not enumerated in source

Which process explains how a single fertilized egg can develop into many specialized cell types?

  1. Random mutation
  2. Selective gene expression Correct answer.
  3. Crossing over
  4. Independent assortment

Explanation

All cells in an organism generally contain the same DNA, but different genes are activated in different tissues. Selective gene expression produces specialized cell types during development.

Question 41Integrated Science (Secondary) - content domains not enumerated in source

A mutation changes a codon from UAC to UAA in the middle of an mRNA sequence. What is the most likely effect on the protein?

  1. A single amino acid substitution
  2. No change because the code is degenerate
  3. Premature termination of translation Correct answer.
  4. A frameshift affecting all later codons

Explanation

UAA is a stop codon, so the ribosome will terminate translation early. This produces a shortened protein that may not function normally.

Question 42Integrated Science (Secondary) - content domains not enumerated in source

Which evidence best supports the claim that two continents were once joined?

  1. Both continents currently have similar average temperatures
  2. Matching fossil species and rock formations occur along their facing coastlines Correct answer.
  3. Both continents have high population densities
  4. Both continents contain large deserts

Explanation

Matching fossils and rock sequences across separated coastlines indicate the landmasses were once connected. This is classic evidence for continental drift and plate tectonics.

Question 43Integrated Science (Secondary) - content domains not enumerated in source

A sample of an unknown element has an atomic number of 19. Which statement about its neutral atom is correct?

  1. It has 19 protons and 39 electrons
  2. It has 19 neutrons and 39 protons
  3. It has 19 protons and 19 electrons Correct answer.
  4. It has 19 neutrons and 19 electrons

Explanation

The atomic number equals the number of protons, and a neutral atom has an equal number of electrons. Therefore the atom has 19 protons and 19 electrons.

Question 44Integrated Science (Secondary) - content domains not enumerated in source

An object is moving in a straight line at constant speed. Which statement about the forces acting on it must be true?

  1. A single force acts in the direction of motion
  2. No forces are acting on the object
  3. The net force is constant but nonzero
  4. The net force on the object is zero Correct answer.

Explanation

Constant velocity means acceleration is zero, so by Newton's second law the net force must be zero. Individual forces may act, but they balance.

Question 45Integrated Science (Secondary) - content domains not enumerated in source

A sample of gas occupies 3.0 L at 300 K. If the pressure is held constant and the temperature is raised to 600 K, what is the new volume?

  1. 6.0 L Correct answer.
  2. 9.0 L
  3. 1.5 L
  4. 3.0 L

Explanation

Charles's law states that volume is directly proportional to absolute temperature at constant pressure. Doubling the temperature from 300 K to 600 K doubles the volume to 6.0 L.

Question 46Integrated Science (Secondary) - content domains not enumerated in source

A student adds a strong acid to a buffer solution. Which best explains why the pH changes only slightly?

  1. The buffer neutralizes the acid by releasing hydroxide ions equal to the acid added
  2. The buffer contains a weak acid and its conjugate base that consume added H⁺ and OH⁻ Correct answer.
  3. The buffer prevents any reaction from occurring
  4. The buffer raises the temperature to decompose the acid

Explanation

A buffer consists of a weak acid and its conjugate base, which react with added acid or base. This pairing absorbs excess H⁺ or OH⁻ and limits pH change.

Question 47Integrated Science (Secondary) - content domains not enumerated in source

Two identical resistors are connected in parallel across a battery. Compared with connecting them in series, what happens to the total resistance and total current?

  1. Resistance halves and current halves
  2. Resistance doubles and current halves
  3. Resistance halves and current doubles Correct answer.
  4. Resistance doubles and current doubles

Explanation

For two equal resistors, the parallel equivalent resistance is half of one resistor, while the series value is double. Lower resistance across the same voltage draws more current, doubling it relative to series.

Question 48Integrated Science (Secondary) - content domains not enumerated in source

A reaction reaches equilibrium in a closed container. Which statement correctly describes the system at equilibrium?

  1. The reaction has stopped completely
  2. Forward and reverse reaction rates are equal, and concentrations remain constant Correct answer.
  3. All reactants have been converted to products
  4. The equilibrium constant changes as concentrations fluctuate

Explanation

At equilibrium, the rates of the forward and reverse reactions are equal, so concentrations remain constant. This is dynamic equilibrium, with both reactions still occurring.

Question 49Integrated Science (Secondary) - content domains not enumerated in source

A population of birds shows a bimodal distribution of beak size, with large and small beaks favored but intermediate beaks selected against. Which type of selection is occurring?

  1. Disruptive selection Correct answer.
  2. Artificial selection
  3. Directional selection
  4. Stabilizing selection

Explanation

Disruptive selection favors extreme phenotypes at both ends of a range and selects against intermediates, producing a bimodal distribution. This can eventually contribute to speciation.

Question 50Integrated Science (Secondary) - content domains not enumerated in source

A scientist measures a correlation between ice cream sales and drowning rates across a summer. Which conclusion is most scientifically defensible?

  1. Drowning causes increased ice cream sales
  2. Both variables are likely influenced by warm weather, a confounding variable Correct answer.
  3. The correlation proves a direct causal link between the variables
  4. Eating ice cream causes drowning

Explanation

Correlation does not establish causation; a third variable such as warm weather can drive both increases. A confounding variable can create a spurious association between the measured variables.