# HiSET Science Practice Test

Our HiSET Science practice test will help you prepare for this section of the test. There are 50 multiple choice questions on the HiSET Science test which must be answered within 80 minutes. Most of the questions include an exhibit with an image, chart, or text passage. Be sure to review the exhibit carefully before selecting your answer.

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 Question 1
As part of a study on how skin type and redness correlate when exposed to different amounts of UV light, a scientist set up an experiment to see how much redness occurred on various skin types. The scientist classified 100 people into six different categories of skin type, then exposed them to increasingly higher doses of UV light and recorded the level of redness that appeared on the skin.

### Which is an independent variable and which is a dependent variable in this experiment?

 A An independent variable is the skin type; a dependent variable is the amount of UV light. B An independent variable is the redness; a dependent variable is the amount of UV light. C An independent variable is the amount of UV light; a dependent variable is the skin type. D An independent variable is the skin type; a dependent variable is the redness.
Question 1 Explanation:
The correct answer is (D). In an experiment, scientists use both independent and dependent variables. An independent variable is the variable that is changed by the scientists in an experiment to test the effects on the dependent variable. A dependent variable is the variable being measured. In this study, the scientist controls two independent variables: the skin type and the UV light. The dependent variable is the level of redness on the skin.
 Question 2

### Questions 2–5 are based on the following table.

This table contains data from the National Centers for Environmental Information. It displays the average temperature in the United States at five-year intervals from 1920 to 2015.

A change of 0.2°F or more in a 5-year period is considered significant. A change of 1.0°F or more in a 5-year period is considered extreme.

### Which of the following statements best describes the trends in the data above?

 A Temperatures increase steadily throughout the century. B Temperatures increase, then decrease, then increase again. C Temperatures fluctuate throughout the century, with a general trend toward increasing. D Temperatures don’t change by a significant amount throughout the century.
Question 2 Explanation:
The correct answer is (C). Though it is technically correct to answer that the temperatures simply increase over time, the response that also mentions fluctuation over the century is more precise, and thus the best answer.
 Question 3
This table contains data from the National Centers for Environmental Information. It displays the average temperature in the United States at five-year intervals from 1920 to 2015.

A change of 0.2°F or more in a 5-year period is considered significant. A change of 1.0°F or more in a 5-year period is considered extreme.

### Which pair of years were most similar, according to this data?

 A 1930 and 1935 B 2010 and 2015 C 1935 and 1940 D 1965 and 1970
Question 3 Explanation:
The correct answer is (C). These two years have the smallest difference of 0.01 degrees.
 Question 4
This table contains data from the National Centers for Environmental Information. It displays the average temperature in the United States at five-year intervals from 1920 to 2015.

A change of 0.2°F or more in a 5-year period is considered significant. A change of 1.0°F or more in a 5-year period is considered extreme.

### Which statement is true about the years 2010 and 2015?

 A There was an extreme increase in temperatures between 2010 and 2015 B There was a significant (but not extreme) decrease in temperature between 2010 and 2015 C There was a significant (but not extreme) increase in temperatures between 2010 and 2015 D There was an insignificant change in temperatures between 2010 and 2015.
Question 4 Explanation:
The correct answer is (A). Though some may call the change in temperatures small, relative to the changes observed in the rest of the data, the change between these two years is very high. And, we were specifically told that a change of more than 1°F in a 5-year period is considered extreme.
 Question 5
This table contains data from the National Centers for Environmental Information. It displays the average temperature in the United States at five-year intervals from 1920 to 2015.

A change of 0.2°F or more in a 5-year period is considered significant. A change of 1.0°F or more in a 5-year period is considered extreme.

### Does this data suggest that climate has changed in the last century?

 A No, because there wasn’t a significant change in temperature between 1920 and 2015. B Yes, because the change in average temperature indicates a trend of significantly increasing temperatures. C No, because the average temperature is still below room temperature. D Yes, because there was an exteme change in temperature between 2010 and 2015.
Question 5 Explanation:
The correct answer is (B). This response acknowledges that changes in temperature over time indicate changes in climate and is the most specific in its language.
 Question 6

### Questions 6–8 are based on the following information.

In the 21st century, worker bees in bee colonies have been abandoning their queens and are deserting their hives in record numbers. Known as Colony Collapse Disorder, honeybees have been mysteriously disappearing across the planet—and one area that has been seriously affected is California’s Napa Valley. This issue became more commonly known when The National Agriculture Statistics Service reported in 2008 that only 2.44 million honey-producing hives were in the United States, down from 4.5 million in 1980.

There is no consensus among scientists as to what is causing Colony Collapse Disorder, though the USDA has undertaken a plan of action to stem the collapsing colonies involving several steps: survey and data collection; analysis of samples; hypothesis-driven research; mitigation and preventive action. The first findings from the USDA were published in 2009, and suggested factors such as pesticides, parasites, and pathogens may be possible causes, all of which have affected hives in Northern California.

One researcher has hypothesized that chemical pesticides are solely responsible for Colony Collapse Disorder in Napa Valley. To test his hypothesis he is planning to run an experiment. He has obtained several healthy bee colonies and plans to expose them to pesticides while measuring the health of the colonies.

### Which additional information would be the most useful in helping him design this experiment?

 A The types of pesticides that are used in Napa Valley. B The types of parasites that are present in Napa Valley. C The types of pathogens that are present in Napa Valley. D The types of pesticides that the USDA evaluated.
Question 6 Explanation:
The correct answer is (A). In order to best support his argument that the pesticides are responsible for colony collapse, the researcher should expose the healthy bee colonies to the same pesticides used in Napa Valley. If he uses the same pesticides, as well as a control, and the colony exposed to the pesticide does collapse, then his hypothesis is well supported.
 Question 7
In the 21st century, worker bees in bee colonies have been abandoning their queens and are deserting their hives in record numbers. Known as Colony Collapse Disorder, honeybees have been mysteriously disappearing across the planet—and one area that has been seriously affected is California’s Napa Valley. This issue became more commonly known when The National Agriculture Statistics Service reported in 2008 that only 2.44 million honey-producing hives were in the United States, down from 4.5 million in 1980.

There is no consensus among scientists as to what is causing Colony Collapse Disorder, though the USDA has undertaken a plan of action to stem the collapsing colonies involving several steps: survey and data collection; analysis of samples; hypothesis-driven research; mitigation and preventive action. The first findings from the USDA were published in 2009, and suggested factors such as pesticides, parasites, and pathogens may be possible causes, all of which have affected hives in Northern California.

One researcher has hypothesized that chemical pesticides are solely responsible for Colony Collapse Disorder in Napa Valley. To test his hypothesis he is planning to run an experiment. He has obtained several healthy bee colonies and plans to expose them to pesticides while measuring the health of the colonies.

### Suppose that his experiment finds that the pesticides used in Napa Valley do cause bee colonies to collapse. Over the next few years other researchers find very similar results, and these results are widely accepted as valid. At that point, the idea that pesticides cause colony collapse would be a:

 A scientific law B scientific theory C hypothesis D conclusion
Question 7 Explanation:
The correct answer is (B). A scientific theory is an explanation of an aspect of the natural world that has been repeatedly tested, verified in accordance with the scientific method, and widely accepted as valid.
 Question 8
In the 21st century, worker bees in bee colonies have been abandoning their queens and are deserting their hives in record numbers. Known as Colony Collapse Disorder, honeybees have been mysteriously disappearing across the planet—and one area that has been seriously affected is California’s Napa Valley. This issue became more commonly known when The National Agriculture Statistics Service reported in 2008 that only 2.44 million honey-producing hives were in the United States, down from 4.5 million in 1980.

There is no consensus among scientists as to what is causing Colony Collapse Disorder, though the USDA has undertaken a plan of action to stem the collapsing colonies involving several steps: survey and data collection; analysis of samples; hypothesis-driven research; mitigation and preventive action. The first findings from the USDA were published in 2009, and suggested factors such as pesticides, parasites, and pathogens may be possible causes, all of which have affected hives in Northern California.

One researcher has hypothesized that chemical pesticides are solely responsible for Colony Collapse Disorder in Napa Valley. To test his hypothesis he is planning to run an experiment. He has obtained several healthy bee colonies and plans to expose them to pesticides while measuring the health of the colonies.

### After the researcher's experiment finds that pesticides are causing bee colonies to collapse, his assistant says, “If pesticides are causing colony collapse, then it is not being caused by parasites.” The assistant's statement is best described as:

 A a scientific theory B an observation C a hypothesis D a fact
Question 8 Explanation:
The correct answer is (C). A hypothesis is a proposed explanation for a phenomenon. If pesticides cause colony collapse, it may be that parasites do not cause it. But this cannot be accepted as true unless it is tested. Parasites could also cause colony collapse.
 Question 9

### Which of the following statements about photosynthesis is correct?

 A When 6 molecules of carbon dioxide are used, 1 molecule of oxygen is produced B When 1 molecule of water is used, 1 molecule of glucose is produced C When 6 molecules of water are used, 1 molecule of glucose is produced D When 1 molecule of glucose is produced, 12 molecules of oxygen are used
Question 9 Explanation:
The correct answer is (C). The reactants are on the left side of a chemical equation and the products are on the right side. In photosynthesis, 6 molecules of carbon dioxide react with 6 molecules of water (in the presence of sunlight) to produce 1 molecule of glucose and 6 molecules of oxygen.
 Question 10

### Questions 10–15 are based on the following information.

Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

### Which of the following is not an organic molecule?

 A Ammonia B DNA C Carbohydrates D Proteins
Question 10 Explanation:
The correct answer is (A). The problem statement clearly lists ammonia as an inorganic molecule, not an organic molecule.
 Question 11
Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

### Which of the following gases was believed to been important to organic molecule formation?

 A DNA B Water C Methane D Helium
Question 11 Explanation:
The correct answer is (C). In the problem statement, it was thought that in the “safe” region, methane could have potentially been tweaked to form organic molecules. Water is the medium of the chemicals, so that is wrong. DNA is an organic molecule, and Helium was not mentioned anywhere, so those two are incorrect.
 Question 12
Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

### Based upon this theory, what temperature would be optimal for the transitions of inorganic to organic molecules?

 A T > 400°C B T < 20°C C Between 400°C and 500°C D Between 20°C and 300°C
Question 12 Explanation:
The correct answer is (D). Looking at the figure, we know that it is too hot (at 400°C) for the inorganic-to-organic chemical reaction to take place, eliminating answer choices (A) and (C). It is also known that 20°C is too cold, leaving (D) as the correct answer.
 Question 13
Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

### Which of the following would be a key assumption to the geothermal vent theory of the beginning of life?

 A Sunlight is the source of energy for the change of inorganic-organic molecules B The primitive atmosphere was too harsh for organic molecules to survive C The temperature for inorganic molecules to produce organic molecules was found to be 200 C. D The pressure of the deep ocean would kill all organic molecules.
Question 13 Explanation:
The correct answer is (B). In the geothermal vent theory, it is proposed that life began in the ocean, ruling out that the sun was important in the inorganic-to-organic chemical reaction. This eliminates answer choice (A). Choice (C) is valid, but it was never verified what actual temperature the reaction takes place, nor is it an assumption. Choice (D) would render the theory wrong, leaving (B). Choice (B) is an assumption because if the atmosphere was too hard, the geothermal vents would have to be the logical place for life to begin.
 Question 14
Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

In current Biology, there are two main categories of uni-cellular life: Prokaryotes and Eukaryotes. Prokaryotes consist of Bacteria—which receive energy from either light or other organic molecules—and Archaea—which can receive energy from hydrogen sulfide. Eukaryotes can be characterized as Protozoa, algae, or fungi—all of which receive energy from either the sun or organic molecules.

### Considering the additional information provided above, which of the following types of cellular life would most likely be found in the geothermal vent?

 A Archaea B Protozoa C Fungi D Algae
Question 14 Explanation:
The correct answer is (A). From the first problem statement, we know the geothermal vent creates hydrogen sulfide, which is something the second problem statement says Archaea would use for energy.
 Question 15
Organic Molecules such as carbohydrates, proteins, DNA, lipds, etc., are part of the critical building blocks of life on Earth. A challenge scientists have to reconcile is how Earth—which used to be solely rock and inorganic materials—could have suddenly produced organic molecules which lead to life.

In the development of a theory to describe how life first started on Earth, a popular belief is that primordial unicellular organisms used geothermal vents in the deep for energy. These geothermal vents release very hot gases from inside the earth to the very cold water deep in the ocean. From the very hot gasses to the cold ocean, the temperature of the water slowly decreased, and there is a region where organisms could have found healthy organic compounds for energy. In this region, inorganic molecules such as ammonia, methane and hydrogen sulfide could have been chemically tweaked to form organic molecules:

In current Biology, there are two main categories of uni-cellular life: Prokaryotes and Eukaryotes. Prokaryotes consist of Bacteria—which receive energy from either light or other organic molecules—and Archaea—which can receive energy from hydrogen sulfide. Eukaryotes can be characterized as Protozoa, algae, or fungi—all of which receive energy from either the sun or organic molecules.

### In a laboratory, scientists have been able to show that when struck with a high voltage, methane converts to organic molecules. Their new hypothesis suggests that life was created by a random lightning strike. Which of the following is accurate?

 A This new information supports the geothermal vent theory B This new information is evidence that the geothermal vent theory may not be correct C Electric shocks from the geothermal vents may have caused life to form D Methane does not exist in the deep ocean so this information does not affect the geothermal vent theory
Question 15 Explanation:
The correct answer is (B). In this proposal, lightning was the catalyst for life to begin, not energy from geothermal vents. Hence, it suggests that the geothermal vent theory may not be correct. It would not support the geothermal vent theory, making choice (A) wrong. There is no mention of electric shocks in the ocean, leaving (C) wrong. Methane is stated as existing in the deep ocean, making (D) wrong.
 Question 16

### Questions 16–18 are based on the following information.

During a solar eclipse, the view of the Sun from Earth gets obstructed by the Moon. The Sun’s rays are temporarily blocked by the moon, so the Earth gets no sunshine. Some eclipses are partial—where the Moon does not block the entire Sun. Some eclipses are total solar eclipses, where the perceived diameter of the Moon and Sun are approximately the same such that the entire Sun is blocked:

### Which of the following is correct?

 A A spaceship at point Y would not see the Sun B A spaceship at point X would only see the Moon and Earth C A spaceship at either point X or point Y sees the Sun D A spaceship at point Y only sees the Earth
Question 16 Explanation:
The correct answer is (A). During an eclipse, anything in between the Moon and Earth will not see the Sun, so a spaceship at Y wouldn’t see it either.
 Question 17
During a solar eclipse, the view of the Sun from Earth gets obstructed by the Moon. The Sun’s rays are temporarily blocked by the moon, so the Earth gets no sunshine. Some eclipses are partial—where the Moon does not block the entire Sun. Some eclipses are total solar eclipses, where the perceived diameter of the Moon and Sun are approximately the same such that the entire Sun is blocked:

### According to the above figure, what most likely happens when the Sun’s rays hit the Moon?

 A They stop transmitting and do not hit the Earth B They enter the Moon’s atmosphere and reflect back to the Sun C They reflect off the Moon and continue to the Earth D They pass through the Moon to the Earth
Question 17 Explanation:
The correct answer is (A). There are some reflected rays that barely clip the Moon, but for the most part rays will stop and do not hit the Earth. Nothing is mentioned about the Moon’s atmosphere. Rays do not reflect back to the Sun and rays passing through the Moon to the Earth does not makes sense.
 Question 18
During a solar eclipse, the view of the Sun from Earth gets obstructed by the Moon. The Sun’s rays are temporarily blocked by the moon, so the Earth gets no sunshine. Some eclipses are partial—where the Moon does not block the entire Sun. Some eclipses are total solar eclipses, where the perceived diameter of the Moon and Sun are approximately the same such that the entire Sun is blocked:

### Since the size of the Sun is much greater than that of the Earth, most of the Earth still gets struck by the Sun's rays during a total solar eclipse. The underlined part of this sentence is best described as:

 A An experiment B A hypothesis C An observation D An assumption
Question 18 Explanation:
The correct answer is (B). If the size of the Sun is much greater than the Earth, than the Moon only covers a very small amount of the Earth’s surface. Hence, the Earth should still be getting a lot of sunlight. It could be disputed because the size of the Moon is in question, but it nevertheless sets up the idea that most of the Earth gets sun.
 Question 19

### Questions 19–24 are based on the following information.

A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### If each of the four outcomes is equally likely, what is the chance of these parents having a blue-flowered offspring?

 A 50% B 25% C 75% D Not possible
Question 19 Explanation:
The correct answer is (B). One square out of four has a bb genotype, which is required to have blue flowers. This is a 25% chance.
 Question 20
A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### If a YY parent mates with a bb parent, what is the chance of this pair having a blue-flowered offspring?

 A 50% B 25% C 75% D 0%
Question 20 Explanation:
The correct answer is (D). In this crossing, none of the subsquares of the Punnett square would have a bb genotype, so it is not possible for this pair to produce a blue-flowered offspring.

 Question 21
A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### If a bb parent mates with a Yb parent, what is the chance of this pair having a blue-flowered offspring?

 A 50% B 25% C 75% D 0%
Question 21 Explanation:
The correct answer is (A). In this crossing, there would be two squares with a bb genotype, or a 50% chance.

 Question 22
A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### In codominant alleles, neither allele is dominant or recessive, and mixed genotypes lead to mixed traits. For the square above, what would be the probability of having a Green-flowered offspring if the alleles were codominant?

 A 50% B 25% C 75% D 0%
Question 22 Explanation:
The correct answer is (A). Since Blue and Yellow mix to make Green, Green-flowered offspring will occur when a Y (yellow) allele “mixes” with b (blue) allele. There are two squares with a Yb genotype, or a 50% chance.
 Question 23
A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### What does the Punnett square tell us about the ratio of dominant to recessive traits in a population?

 A There will be more individuals with recessive traits than dominant traits. B There will be more individuals with dominant traits than recessive traits. C There will be an equal number of individuals with dominant and recessive traits. D The ratio of dominant to recessive traits cannot be predicted.
Question 23 Explanation:
The correct answer is (B). Three out of four possibilities for this Punnett square will express the dominant phenotype. It is clear that if a recessive phenotype requires two recessive alleles, and a dominant phenotype can be produced with one, then there will generally be more dominant phenotypes.
 Question 24
A Punnett square is a way to predict the genotype (gene allele combination) for specific traits for the offspring of specific parents. Each parent’s genotype is placed on one side of the square, and the resulting combinations are found in the boxes inside. Because some traits are dominant (only require one allele to be expressed in the phenotype, or appearance) and others are recessive (require two alleles to be expressed), the Punnett square can also be used to predict the chance of having an offspring with a certain trait. For this square, Y is the dominant allele for yellow flowers, and b is the recessive allele for blue flowers.

### Why would a Punnett square not be a good tool for predicting more complicated traits in humans, like height and facial features?

 A Complex traits require more than one gene, so they can’t be laid out in a Punnett square that can only do one gene at a time. B The Punnett square only works for plants. C Not all possible genotypes are equally probable in humans. D There are no dominant or recessive alleles in humans.
Question 24 Explanation:
The correct answer is (A). This question involves some conjecture, but the most reasonable conjecture to make here is that complex traits must involve more complex genes. The other responses involve more assumptions, and are thus incorrect here.
 Question 25

### Multiple studies have supported the following two hypotheses:

I. Increasing the temperature of Solvent A allows all dissolvable solutes to dissolve faster.

II. Substance A is dissolvable in Solvent A, while Substance B is not.

### Given these two hypotheses, which of the following is most likely to be true?

 A Substance A will dissolve faster in Solvent A at higher temperatures B Substance B will dissolve slower in Solvent A at higher temperatures C Substance B will dissolve slower than Substance A in Solvent A, regardless of the temperature of the solution D Substance A and Solvent A will not form a solution at any temperature
Question 25 Explanation:
The correct answer is (A). Substance A will dissolve faster in Solvent A at higher temperatures. This statement is true based on the transitive relation of the two hypotheses. As stated in hypothesis II, Substance B will not dissolve in Solvent A, regardless of the temperature. Substance A will dissolve in Solvent A, therefore the only possible choice is that Substance A will dissolve faster in Solvent A at higher temperatures, which is supported by hypothesis I.
 Question 26

### Questions 26–29 are based on the following information.

In the early 1800’s, English naturalist RS Edleston discovered a peppered moth (Biston betularia) that was almost totally black. This was highly unusual at the time, because the peppered moth was thought to always be a combination of black and white.

By 1900, the populations of peppered moths in English cities were up to 98% black, with only 2% peppered or white. This was the height of the industrial revolution, when English cities were burning large amounts of coal, which blackened tree bark with smoke and soot. In the second half of the 20th century, coal use was dramatically reduced, and the proportion of black moths continues to decrease to this day.

### Which of the following is a reasonable hypothesis for why the moth population might have shifted in favor of black moths?

 A The moths were coated in the same soot the trees were. B The soot was contaminating the moths’ food source C The black moths had an evolutionary advantage because they could camouflage against the trees. D The soot was poisonous to the lighter moths.
Question 26 Explanation:
The correct answer is (C). Based on the information provided, it is impossible to tell if the moths were ingesting the soot, and the changes in color are clearly changes in the color of the moths themselves, not an external covering of soot.
 Question 27
In the early 1800’s, English naturalist RS Edleston discovered a peppered moth (Biston betularia) that was almost totally black. This was highly unusual at the time, because the peppered moth was thought to always be a combination of black and white.

By 1900, the populations of peppered moths in English cities were up to 98% black, with only 2% peppered or white. This was the height of the industrial revolution, when English cities were burning large amounts of coal, which blackened tree bark with smoke and soot. In the second half of the 20th century, coal use was dramatically reduced, and the proportion of black moths continues to decrease to this day.

### Which of the following would be a feasible experiment to test a hypothesis about the changes in the moth color?

 A Capturing many black moths and bringing them back to the lab to see if they will breed and produce white moths. B Placing discreet markers on a selection of captured moths in the wild, releasing them, then recapturing them to see how well black moths verses white moths survive in the wild. C Capturing moths and feeding them different foods to see if they change color. D Capturing many lighter moths and exposing them to soot in the lab to see if they change color.
Question 27 Explanation:
The correct answer is (B). In this case, the best experiment will involve observing the moths in the wild, not the lab, because it is the environment that has caused the moths to change. So a strategy of marking and rereleasing is best (and is the actual experiment performed in history).
 Question 28
In the early 1800’s, English naturalist RS Edleston discovered a peppered moth (Biston betularia) that was almost totally black. This was highly unusual at the time, because the peppered moth was thought to always be a combination of black and white.

By 1900, the populations of peppered moths in English cities were up to 98% black, with only 2% peppered or white. This was the height of the industrial revolution, when English cities were burning large amounts of coal, which blackened tree bark with smoke and soot. In the second half of the 20th century, coal use was dramatically reduced, and the proportion of black moths continues to decrease to this day.

### Would you expect to find a greater proportion of black moths in forests outside the city of Beijing, or in rural Nepal?

 A Nepal, because there is more fresh air in rural locations. B Beijing, because cities provide more surfaces for moths to lay eggs. C Nepal, because there are more moths in rural countries. D Beijing, because Beijing produces more pollution.
Question 28 Explanation:
The correct answer is (D). The city of Beijing will have much more pollution than rural (countryside) Nepal. We know that greater pollution leads to a greater proportion of black moths.
 Question 29
In the early 1800’s, English naturalist RS Edleston discovered a peppered moth (Biston betularia) that was almost totally black. This was highly unusual at the time, because the peppered moth was thought to always be a combination of black and white.

By 1900, the populations of peppered moths in English cities were up to 98% black, with only 2% peppered or white. This was the height of the industrial revolution, when English cities were burning large amounts of coal, which blackened tree bark with smoke and soot. In the second half of the 20th century, coal use was dramatically reduced, and the proportion of black moths continues to decrease to this day.

### In polluted areas, would we expect to see a similar change in color in the dog population?

 A No, because dogs reproduce more slowly than moths. B Yes, because both dogs and moths have lighter and darker variations. C No, because these traits offer no evolutionary advantage. D Both (A) and (C)
Question 29 Explanation:
The correct answer is (D). Because dogs reproduce more slowly than moths, any evolutionary benefit of a darker color would take much, much longer to appear in the population of dogs. And, it is unlikely that any evolutionary benefit to being darker or lighter in a forest environment exists in dogs (unlike the moths, who camouflage themselves against the trees).
 Question 30

### Questions 30–34 are based on the following information.

A titration is a type of chemistry experiment used to determine the unknown concentration of an acid. Acids have a lower pH (<7) and bases have a higher pH (>7), so these chemicals neutralize each other. Because of this, a base of known concentration can be dripped in small, measured amounts into a known volume of the unknown acid, with a chemical indicator added to change the color when the solution is basic or acidic. When the solution switches from acidic to neutral, the color changes, indicating the titration is over. Calculations can then be performed to determine the concentration of the acid using the volumes of the base and acid and the concentration of the base.

### If the number of drops of base required to titrate the acid was very large, what does this mean about the acid?

 A The acid has a low concentration. B The acid has a high concentration. C The acid could have a very high concentration, depending on the concentration of the base used. D The concentration is equal to that of the base used.
Question 30 Explanation:
The correct answer is (C). This is the most specific and accurate response. How the number of drops influences the calculated concentration of acid in a titration depends on the concentration of base used. Many drops of a lower concentration base will produce the same result as a few drops of a higher concentration.
 Question 31
A titration is a type of chemistry experiment used to determine the unknown concentration of an acid. Acids have a lower pH (<7) and bases have a higher pH (>7), so these chemicals neutralize each other. Because of this, a base of known concentration can be dripped in small, measured amounts into a known volume of the unknown acid, with a chemical indicator added to change the color when the solution is basic or acidic. When the solution switches from acidic to neutral, the color changes, indicating the titration is over. Calculations can then be performed to determine the concentration of the acid using the volumes of the base and acid and the concentration of the base.

### What happens to the pH of the solution in the flask as drops are added?

 A It gets lower, because acid is being added to base. B It gets higher, because base is being added to acid. C It gets higher, because acid is being added to base. D It gets lower, because base is being added to acid.
Question 31 Explanation:
The correct answer is (B). The information in the exhibit clearly states that higher pH values are associated with bases and lower ones with acids. It also states that the titration experiment involves dripping base into acid.
 Question 32
A titration is a type of chemistry experiment used to determine the unknown concentration of an acid. Acids have a lower pH (<7) and bases have a higher pH (>7), so these chemicals neutralize each other. Because of this, a base of known concentration can be dripped in small, measured amounts into a known volume of the unknown acid, with a chemical indicator added to change the color when the solution is basic or acidic. When the solution switches from acidic to neutral, the color changes, indicating the titration is over. Calculations can then be performed to determine the concentration of the acid using the volumes of the base and acid and the concentration of the base.

### Would titration still work if the concentration of base is not known?

 A Yes, because the solution is still basic, so the color of the indicator in the acid solution will change. B No, because the indicator in the acid solution will no longer change color. C No, because a base of unknown concentration may introduce impurities into the sample. D No. The indicator will still change color eventually, but the calculations at the end cannot be done with an unknown base concentration.
Question 32 Explanation:
The correct answer is (D). This is the most accurate response based on the information given. The color change of the indicator is caused by the addition of base, regardless of its concentration. There is no mention of impurities anywhere, and the goals of the titration are clearly stated to be calculating the concentration of the unknown acid, which can only happen when three out of four variables are known (i.e. concentration of base, volume of base, and volume of acid).
 Question 33
A titration is a type of chemistry experiment used to determine the unknown concentration of an acid. Acids have a lower pH (<7) and bases have a higher pH (>7), so these chemicals neutralize each other. Because of this, a base of known concentration can be dripped in small, measured amounts into a known volume of the unknown acid, with a chemical indicator added to change the color when the solution is basic or acidic. When the solution switches from acidic to neutral, the color changes, indicating the titration is over. Calculations can then be performed to determine the concentration of the acid using the volumes of the base and acid and the concentration of the base.

### Why would it be important to drip slowly during a titration, particularly near the end?

 A Because dripping too fast could lead to a violent chemical reaction. B Because base can always be added but cannot be removed once added. C Because the solution may very quickly change color. D Both (B) and (C)
Question 33 Explanation:
The correct answer is (D). Both considerations given in this response are important for titration. This is why they are performed with calibrated burets, and the last drops are dripped very slowly.
 Question 34
A titration is a type of chemistry experiment used to determine the unknown concentration of an acid. Acids have a lower pH (<7) and bases have a higher pH (>7), so these chemicals neutralize each other. Because of this, a base of known concentration can be dripped in small, measured amounts into a known volume of the unknown acid, with a chemical indicator added to change the color when the solution is basic or acidic. When the solution switches from acidic to neutral, the color changes, indicating the titration is over. Calculations can then be performed to determine the concentration of the acid using the volumes of the base and acid and the concentration of the base.

### What is the significance of the colored indicator in a titration experiment?

 A The indicator reacts with the acid. B The indicator reacts with the base. C Without the indicator, there is no way to tell when the titration is finished. D Without the indicator, the acid cannot react with the base.
Question 34 Explanation:
The correct answer is (C). The name “indicator” suggests that its only purpose is to indicate whether the solution is acidic or basic. Nowhere in the given information is it stated that the indicator is directly involved in the chemical reaction itself.
 Question 35

### Questions 35–36 are based on the following information.

A study was done to measure the effectiveness of an antibiotic on different bacteria. The antibiotic Vancomycin was tested on 3 types of bacteria: Enterococcus, Staphylococcus, and Streptococcus. Bacterial growth was measured at 3 different durations of time exposure to the antibiotic: 1 hour, 24 hours, and 7 days. The rate of bacterial growth was measured by bacterial colony size at each time interval. The data for each duration was calculated and compiled into the graph shown below. As a control, each bacteria species was also grown with no exposure to the antibiotic. This control culture was measured after 7 days.

### Based on these results, Vancomycin is most effective against:

 A Enterococcus B Staphylococcus C Streptococcus D It is equally effective against Staphylococcus and Streptococcus.
Question 35 Explanation:
The correct answer is (C). An effective antibiotic prevents the growth of bacteria. So, to determine which bacteria Vancomycin is most effective against, locate the bacteria with the smallest colony size across each exposure time. According to the chart, Streptococcus has the smallest colony size at all three durations.
 Question 36
A study was done to measure the effectiveness of an antibiotic on different bacteria. The antibiotic Vancomycin was tested on 3 types of bacteria: Enterococcus, Staphylococcus, and Streptococcus. Bacterial growth was measured at 3 different durations of time exposure to the antibiotic: 1 hour, 24 hours, and 7 days. The rate of bacterial growth was measured by bacterial colony size at each time interval. The data for each duration was calculated and compiled into the graph shown below. As a control, each bacteria species was also grown with no exposure to the antibiotic. This control culture was measured after 7 days.

### What are the independent and dependent variables in this experiment?

 A The independent variable is the duration of exposure to Vancomycin; the dependent variable is bacterial colony size. B The independent variable is the bacterial colony size; the dependent variable is the duration of exposure to Vancomycin. C The independent variable is the bacterial colony size; the dependent variable is the type of bacteria. D The independent variable is the duration of exposure to Vancomycin; the dependent variable is the type of bacteria.
Question 36 Explanation:
The correct answer is (A). An independent variable is a variable that is changed or controlled in a scientific experiment in order to test the effects on the dependent variable. In this case the researchers could control the duration of exposure and the type of bacteria. The dependent variable responds to the independent variable. It is called dependent because it "depends" on the independent variable.

In this case the bacteria colony size depends on the duration of exposure and the type of bacteria. In this study there are two independent variables and there is one dependent variable. The independent variables are the duration of exposure to Vancomycin and the type of bacteria used. The dependent variable is the bacterial colony size.
 Question 37

### Questions 37–42 are based on the following information.

Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, they must reflect that wavelength of light, while absorbing every other wavelength of light.

### What can be inferred from the above paragraph?

 A White objects reflect all wavelengths of light B Black objects reflect all wavelengths of light C White objects absorb all wavelengths of light D Glass absorbs all wavelengths of light
Question 37 Explanation:
The correct answer is (A). The problem statement says that for an object to appear as they are, it reflects that wavelength of light. Example: green objects reflect green, but absorb red, yellow, blue, purple. Glass is known to be see-through, so no light is reflected, and answer choice (D) is wrong. Black absorbs all light, so (B) is wrong, leaving (A) or (C). If Black absorbs all light, it can be inferred that white does the opposite, it reflects all light.
 Question 38
Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, they must reflect that wavelength of light, while absorbing every other wavelength of light.

### Consider the following two statements: I. John has a type of color blindness that makes it hard to tell the difference between yellow and green II. Yellow and green are similar wavelengths of light Which of the following describes the relationship between statements I and II?

 A Both statements are observations B Both statements are explanations C Statement I is an observation; statement II is a possible explanation for I D Statement II is an observation, statement I is a possible explanation for II
Question 38 Explanation:
The correct answer is (C). From the spectrum, we know that yellow and green have very similar wavelengths. John has trouble telling the difference between the two. Hence, statement I about John is an observation, and that statement II is a possible explanation for why yellow and green are hard for John to tell apart.
 Question 39
Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, they must reflect that wavelength of light, while absorbing every other wavelength of light.

### Which of these factors is most likely to affect how well an object reflects light?

 A How large an object is B The roughness of an object C How opaque an object is D The temperature of an object
Question 39 Explanation:
The correct answer is (C). Prior knowledge of what opaque means may be helpful. Otherwise, process of elimination will help here. It doesn't matter how large, say, a green object is—it always reflects green (A is wrong). From a macroscopic scale, roughness will not make a difference either—think a rough white paper plate vs. a smooth white ceramic plate (B is wrong). Finally, temperature does not seem to make much sense (D is wrong).
 Question 40
Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, they must reflect that wavelength of light, while absorbing every other wavelength of light.

A famous equation Einstein founded relates the energy $(E)$ of a light-wave to its wavelength $(\lambda)$, the photoelectric effect:

$E = \dfrac{hc}{\lambda}$

Where $h$ is a constant, $c$ is the speed of light, and $\lambda$ is the wavelength of light.

### Considering the additional information provided above, which of the following is correct?

 A Purple light has more energy than blue, but less than green B Yellow light has more energy then red, but less than blue C Red is the highest energy light D Green is the highest energy light
Question 40 Explanation:
The correct answer is (B). We are given the inverse relationship between energy and wavelength. Hence, shorter wavelengths give more energy. Purple has the shortest wavelength, so it cannot have less energy than green or red. Yellow is shorter than red, but longer than blue, leaving (B) to be correct.
 Question 41
Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, they must reflect that wavelength of light, while absorbing every other wavelength of light.

A famous equation Einstein founded relates the energy $(E)$ of a light-wave to its wavelength $(\lambda)$, the photoelectric effect:

$E = \dfrac{hc}{\lambda}$

Where $h$ is a constant, $c$ is the speed of light, and $\lambda$ is the wavelength of light.

### It found that the speed of light is smaller in glass than it is in air. What can be inferred from this statement?

 A Purple light has more energy in air B Green light has more energy than purple light in glass C Purple light has more energy in glass D Purple light has the same energy in both glass and air
Question 41 Explanation:
The correct answer is (A). We are given the direct relationship between energy and speed of light. Hence, a higher speed of light has higher energy.

Answer choices (C) and (D) can be eliminated on the premise that light in air is higher power. Answer choice (B) can be eliminated since in the same medium (e.g. glass) the shorter wavelengths will have greater energy—purple light will have more energy than green light.
 Question 42
Light is an electromagnetic wave that propagates in any medium, whether it be air or space or glass or any kind of crystal. A key characteristic of light is its wavelength. The wavelength can have a wide range of values. A range of focus is the visible spectrum, the spectrum at which humans can perceive light:

For certain objects to appear the color that they are, it must reflect that wavelength of light, while absorbing every other wavelength of light.

A famous equation Einstein founded relates the energy of a light-wave to its wavelength, the photoelectric effect:

$E = \dfrac{hc}{\lambda}$

Where $h$ is a constant, $c$ is the speed of light, and $\lambda$ is the wavelength of light.

### It is proposed to use ultraviolet $(\lambda<400 \text{ nm})$ or infared $(\lambda>700 \text{ nm})$ to scan people safely at security checkpoints in airports. What should be used and why?

 A Infared light because it is higher energy B Visible light because it is lower energy C Infared light because it is lower energy D Ultraviolet because it is higher energy
Question 42 Explanation:
The correct answer is (C). We know that lower wavelengths are higher energy, but we wish to scan people safely, so a higher wavelength should be used (infared, less energy).
 Question 43

### Use the following information to answer questions 43–46:

A sample of Robin and Snow Owl populations in Wisconsin for a given year is shown below:

### Which of the following is correct?

 A The carrying capacity of Robins are 4,000 birds B The carrying capacity of Robins is 3,800 birds C The carrying capacity of Robins is 1,400 birds D The carrying capacity of Snow Owls is 900 birds
Question 43 Explanation:
The correct answer is (B). The carrying capacity is how large a population can sustain itself. If it grows too large, the population will decrease. If the population is too small, it will increase. Robins leave during the winter. The population peaks in June, but settles at a population of around 3,800.
 Question 44
A sample of Robin and Snow Owl populations in Wisconsin for a given year is shown below:

### What conclusion can we draw from the graph?

 A Robins prefer to be in Wisconsin during winter B Snow Owls will hunt Robins if their food source is low C Snow owls are better adapted for the cold D Robins have offspring in September
Question 44 Explanation:
The correct answer is (C). Because the Snow Owl population barely changes during the winter months, and the Robin population decreases by nearly 90%, we know that Snow Owls can much better survive in the cold.
 Question 45
A sample of Robin and Snow Owl populations in Wisconsin for a given year is shown below:

### The peak Robin population for three different years is shown in the table above. When the average for these three years is calculated, the raw result is 4.663333 thousand. What should be recorded as the average population?

 A 4.663333 thousand B 4.66 thousand C 4.6633 thousand D 4.0 thousand
Question 45 Explanation:
The correct answer is (B). The population data provided for the three years has a precision of three significant figures, so the recorded average should also have a precision of three significant figures.
 Question 46

### Questions 46–47 are based on the following information.

Humans are not able to sense direct temperatures, but rather the heat flux onto your skin. Heat flux is defined by the following equation:

$q=\left|k\left(T_{\text{object}} − T_{\text{hand}}\right)\right|$

Where $q$ is the heat flux, the temperatures are the temperature of the object you are touching $(T_{\text{object}})$ and your hand $(T_{\text{hand}})$, and $k$ is a material property of the object you are touching. When skin is contacted with a very high heat flux, it can burn.

### When cooking, a pan needs to heat up to 200°C. You have the choice of using either a Stainless-Steel pan ($k$ = 16.2 W/mK) or a Cast Iron Pan ($k$ = 55 W/mK). Based upon the values of $k$ and the definition of heat flux, which of the following is consistent?

 A The Stainless-steel pan will feel hotter B The Cast Iron pan will feel hotter C Both pans feel the same because they are both heated to a temperature of 200°C D It depends on what temperature your hand is
Question 46 Explanation:
The correct answer is (B). From the problem statement, we know cast iron has a higher $k$ value. From the heat flux equation, we know that heat flux is proportional to $k$. Hence, the greater the $k$ of the material, the greater the heat flux, and the “hotter” something will feel. Because they will have the same difference in temperature between hand $(T_{\text{hand}})$ and pan $(T_{\text{object}})$, answer choices (C) and (D) are incorrect.
 Question 47
Humans are not able to sense direct temperatures, but rather the heat flux onto your skin. Heat flux is defined by the following equation:

$q=\left|k\left(T_{\text{object}} − T_{\text{hand}}\right)\right|$

Where $q$ is the heat flux, the temperatures are the temperature of the object you are touching $(T_{\text{object}})$ and your hand $(T_{\text{hand}})$, and $k$ is a material property of the object you are touching. When skin is contacted with a very high heat flux, it can burn.

### Liquid Nitrogen is often used in cryogenic scenarios because of its very cold temperature (−346°F). Despite liquid Nitrogen having a very low temperature, researchers must protect themselves against burns from it. Which of the following might suggest why?

 A The $k$ value of liquid Nitrogen is very high B The $k$ value of liquid Nitrogen is very low C The difference in temperature between liquid Nitrogen and human skin is large D Nitrogen is poisonous and reacts with the skin
Question 47 Explanation:
The correct answer is (C). Again, the greater the heat flux, the hotter something will feel. Liquid Nitrogen has a very low temperature, so the difference in the temperature term $(T_{\text{object}} − T_{\text{hand}})$ will be extremely high, so the heat flux will be extremely high, resulting in the sensation of burning.
 Question 48

### Questions 48–50 are based on the following information.

Students are researching families with one brown-haired parent and one red-haired parent to understand how recessive hair-color genes interact with dominant genes. They studied the offspring of a heterozygous brown-haired man (Bb) and a homozygous recessive red-haired woman (bb). Of their four children, three have brown hair and one has red hair. The students prepared the Punnett square that is shown below.

### If the couple has another child, what is the probability that this child will have brown hair?

 A 0% B 25% C 50% D 75%
Question 48 Explanation:
The correct answer is (C). Heterozygous indicates two different genes for a hereditary characteristic. In this case, the man is heterozygous because he has one gene for brown hair (B) and one gene for red hair (b). The brown hair gene is dominant, so it is capitalized, and because it is dominant he has brown hair.

Homozygous indicates two identical genes for a hereditary characteristic. In this case, the woman has two genes for red hair (bb). The genes are in lower case since they are recessive. She only has genes for red hair, so she has red hair.

You can solve this type of problem by filling out a Punnett Square as shown below:

Children with the genes BB will have brown hair, but none of the children have this combination of genes.

Children with the genes Bb will also have brown hair (because B is dominant), and 2 out of every 4 children, or 50%, will have brown hair.

Children with the genes bb will have red hair, and 2 out of every 4 children will have red hair.
 Question 49
Students are researching families with one brown-haired parent and one red-haired parent to understand how recessive hair-color genes interact with dominant genes. They studied the offspring of a heterozygous brown-haired man (Bb) and a homozygous recessive red-haired woman (bb). Of their four children, three have brown hair and one has red hair. The students prepared the Punnett square that is shown below.

### The students then reviewed what would happen if the father had two copies of the allele for brown-hair (BB). In this scenario, the father would be described as:

 A Homozygous-dominant B Homozygous-recessive C Heterozygous D Hemizygous
Question 49 Explanation:
The correct answer is (A). A person is homozygous-dominant, if they carry two copies of the same dominant allele.
 Question 50
Students are researching families with one brown-haired parent and one red-haired parent to understand how recessive hair-color genes interact with dominant genes. They studied the offspring of a heterozygous brown-haired man (Bb) and a homozygous recessive red-haired woman (bb). Of their four children, three have brown hair and one has red hair. The students prepared the Punnett square that is shown below.

### If both parents were heterozygous, what would be the probability of their next child having red hair?

 A 0% B 25% C 50% D 75%
Question 50 Explanation:
The correct answer is (B). You should draw a new Punnett square to solve the probabilities. Since each parent is heterozygous, you know that each parent has one of each allele (Bb):

As shown above, 25% of the children will be homozygous-dominate (BB). They will have brown hair.

Two of the four squares indicate heterozygous (Bb). So another 50% of the children will also have brown hair, since the brown allele is dominant.

That leaves 25% (1 out of 4) as homozygous recessive (bb). They will have red hair.
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