ACT science practice test 27

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


An organism's genetic information is stored within the nuclei of its cells as a set of chromosomes. The number of chromosomes in a cell varies from species to species. In some species, the number of chromosomes can vary between individuals. Table 2.1 lists the chromosome count for a variety of species.

TABLE 2.1 Species Chromosome Count

Source: http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count.

Ploidy is the number of sets of chromosomes present in the cell of an organism. The monoploid number (x) is the number of chromosomes an organism has in one set.

In most species, a gamete (sex cell) contains one complete set of an organism's chromosomes. The number of chromosomes in a gamete is referred to as the haploid number (n). The fusing of two gametes into a zygote during sexual reproduction produces somatic cells (body cells) containing two complete sets of chromosomes. The total number of chromosomes in a somatic cell is referred to as the diploid number (2n). In most species, the monoploid number (x) and the haploid number (n) are the same.

Some species have more than two sets of chromosomes present in their cells, a condition referred to as polyploidy. The somatic cells of triploid organisms have three sets of chromosomes, for example, and tetraploids have four. In polyploidy organisms, the term haploid is still used to describe the number of chromosomes in a gamete, and diploid is used to describe the number of chromosomes in a somatic cell. However, the monoploid number and the haploid number are not the same in a polyploidy organism.

1. Based on the information in Table 2.1, which species does not exhibit variation in chromosome numbers between individuals?

A. European honeybee
B. Swamp wallaby
C. Slime mold
D. Jack jumper ant

2. The first part of an organism's scientific name identifies the genus to which it belongs. Which statement about the members of a genus is best supported by the information in Table 2.1?

A. An organism's genus determines the number of chromosomes it has.
B. Organisms in the same genus tend to have similar chromosome counts.
C. No two organisms in the same genus can have the same number of chromosomes.
D. Chromosome count can vary greatly between organisms in the same genus.

3. Based on the information in Table 2.1, the relationship between diploid chromosome count and organism complexity can best be described as exhibiting:

A. a direct correlation.
B. no correlation.
C. an inverse correlation.
D. a linear correlation.

4. To which kingdom does the organism exhibiting the greatest diploid number of chromosomes in Table 2.1 belong?

A. Animalia
B. Plantae
C. Eubacteria
D. Protista

5. Which species has more chromosomes than a human but fewer chromosomes than a dog?

A. Bombyx mori
B. Canis latrans
C. Ophioglossum reticulatum
D. Mus musculus

6. Cells from which pair of organisms have the same number of chromosomes in their nuclei?

A. Horse and donkey
B. Zebra fish and pineapple
C. Earthworm and European honeybee
D. Oats and potato

7. A team of scientists have discovered three previously unknown insect species in the Amazon rain forest. Which statement about the genetic information of these species is best supported by the data in Table 2.1?

A. The largest species is most likely to have the highest number of diploid chromosomes.
B. There is no way to determine the diploid chromosome count of each species.
C. The three species are highly likely to have the same number of diploid chromosomes.
D. It is not easy to predict the diploid chromosome count of each species.

8. Based on the information in the passage, which species produces gametes that each contain 32 chromosomes?

A. Apis mellifera
B. Saccharomyces cerivisiae
C. Equus ferus caballus
D. Drosophila melanogaster

9. According to the information in Table 2.1, how many more total chromosomes does a female European honeybee have than a male?

A. 1
B. 2
C. 16
D. 32

10. Based on the information in the passage, the total number of chromosomes in a somatic cell is represented by which of the following terms?

A. n
B. x
C. 2x
D. 2n

11. Which statement about polyploidy is supported by the information in the passage?

A. The number of chromosomes varies among the somatic cells of a polyploid organism.
B. The gametes and somatic cells of a polyploid organism contain the same number of chromosomes.
C. The gametes of a polyploid organism contain more than one complete set of chromosomes.
D. The somatic cells of a polyploid organism contain too many chromosomes to be considered diploid.

12. Which of the following organisms has four complete sets of chromosomes in its somatic cells?

A. Alfalfa
B. Slime mold
C. Oats
D. Earthworm

13. Table 2.1 identifies the oat species Avena sativa as a hexaploid, containing six sets of chromosomes. The numerical representation 2n = 6x = 42 describes the total number of chromosomes in a somatic cell of this hexaploid species. How many chromosomes does Avena sativa have in one set?

A. 6
B. 7
C. 21
D. 42

14. Which of the following correctly identifies the relationship between the diploid number (2n), haploid number (n), and monoploid number (x) of Solanum tuberosum?

A. 2n is twice n, but 4 times x.
B. 2n is twice the sum of n and x.
C. 2n is the sum of n and x.
D. 2n is twice x, but 4 times n.