Question 21 Answer and Explanation _ACT December 2019 Form C03 Science Section

Passage IV

Four students observed that in a population of land plants, Population A, a plant could have a green stem or a purple stem. Each student proposed an explanation for this observation.

Student 1

All plants in Population A produce the green pigment chlorophyll. If a plant receives 8 hr or more of sunlight each day, it also produces a purple pigment, causing its stem to be purple. If a plant receives less than 8 hr of sunlight each day, it does not produce this purple pigment, so its stem is green. All plants in Population A are genetically identical, so they all have the ability to produce both pigments.

Student 2

All plants in Population A produce the green pigment chlorophyll. If a plant receives too little phosphorus (a nutrient), it also produces a purple pigment, causing its stem to be purple. If a plant receives enough phosphorus, it does not produce this purple pigment, so its stem is green. All plants in Population A are genetically identical, so they all have the ability to produce both pigments. The amount of sunlight received by a plant does not affect stem color.

Student 3

All plants in Population A produce the green pigment chlorophyll. The production of purple pigment is determined by Gene Q, which has 2 alleles (Q and q) and 3 possible genotypes (QQ, Qq, and qq). A plant with either the Gene Q genotype QQ or the Gene Q genotype Qq produces the purple pigment, causing its stem to be purple. A plant with the Gene Q genotype qq does not produce this purple pigment, so its stem is green. The amount of sunlight or nutrients received by a plant does not affect stem color.

Student 4

All plants in Population A produce the green pigment chlorophyll. The production of purple pigment is determined by Gene Q, which has 2 alleles (Q and q) and 3 possible genotypes (QQ, Qq, and qq). A plant with the Gene Q genotype qq produces the purple pigment, causing its stem to be purple. A plant with either the Gene Q genotype QQ or the Gene Q genotype Qq does not produce this purple pigment, so its stem is green. The amount of sunlight or nutrients received by a plant does not affect stem color.

21. Suppose it were found that the presence of the purple pigment in some plant tissues protects those tissues from being damaged by sunlight. Would this finding better support the explanation of Student 1 or the explanation of Student 2 ?

A. Student 1, because Student 1 indicated that the plants receiving the most sunlight will have purple stems.

B. Student 1, because Student 1 indicated that the plants receiving the most sunlight will have green stems.

C. Student 2, because Student 2 indicated that the plants receiving the most sunlight will have purple stems.

D. Student 2, because Student 2 indicated that the plants receiving the most sunlight will have green stems.

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

First of all, student 2 said that the color has nothing to do with sunlight, and CD was excluded, while student 1 said that only plants with a lot of light will have purple pigment, so it is further consistent that purple pigment is used to prevent sunlight from harming plants