GRE Subject Test: Biology : Understanding Alternation of Generations

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Alternation Of Generations

Which of the following refers to the principle of alternation of generations in plants?

Possible Answers:

The differences between a tree and a seed

Gamete-producing sporophytes

The need for external pollinators

A life cycle which includes a unicellular haploid stage

A life cycle that includes a multicellular haploid stage

Correct answer:

A life cycle that includes a multicellular haploid stage

Explanation:

Plants have a multicellular haploid stage called the gametophyte. Gametophytes () produce gametes () through mitosis, which combine to produce a zygote (). The zygote grows into a multicellular, diploid sporophyte (), which produces spores () through meiosis. Those spores give rise to multicellular gametophytes.

Example Question #1 : Classes Of Plant

Fill in the blanks.

The __________ generation is dominant in the bryophyte life cycles, and the __________ generation is dominant in seedless vascular plants.

Possible Answers:

gametophyte . . . sporophyte

gametophyte . . . gametophyte

sporophyte . . . sporophyte

sporophyte . . . gametophyte

Correct answer:

gametophyte . . . sporophyte

Explanation:

Bryophytes are nonvascular plants, such as mosses. Gametophytes are species that have haploid cells during their mature lives, while sporophytes are predominantly diploid during their adult phases.

Bryophytes have the gametophyte generation as dominant, with the sporophytes relying on the parental gametophyte. Starting with the evolution of seedless vascular plants, the gametophytes become reduced and are no longer the dominant life cycle. By the formation of angiosperms (seed plants), the gametophytes have become dependent on the parental sporophyte. 

Example Question #1 : Understanding Alternation Of Generations

Which of the following structures would be found in a tracheophyte, but not in a bryophyte?

Possible Answers:

Plasmids

Chloroplasts

Xylem

Cell walls

Correct answer:

Xylem

Explanation:

All plants can be classified as either bryophytes or tracheophytes. Plants that contain transport vessels (xylem and phloem) are tracheophytes, while those without transport vessels are bryophytes. All plants contain cell walls and chloroplasts, but only a tracheophyte would contain xylem. Plasmids are structures that are almost exclusively found in bacteria or protozoans.

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