GRE Subject Test: Biology : Plant Reproduction

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

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Example Questions

Example Question #1 : Understanding Angiosperms

What is the female reproductive structure in angiosperms?

Possible Answers:

Integument

Pistil

Petal

Pollen

Stamen

Correct answer:

Pistil

Explanation:

Angiosperms are flowering plants. They have both male and female reproductive organs.

The pistil is the female reproductive structure, and consists of three parts. The stigma is the sticky knob used to catch pollen. It is situated at the top of the style, while the ovary contains egg cells and is located below the style. 

The stamen is the male reproductive structure, and consists of two parts. The anther produces pollen, and the filament helps in holding up the anther.

Example Question #1 : Understanding Plant Reproduction

Double fertilization in angiosperms results in a __________ zygote and a triploid __________.

Possible Answers:

haploid . . . fruit

diploid . . . endosperm

diploid . . . fruit

haploid . . . endosperm

diploid . . . seed

Correct answer:

diploid . . . endosperm

Explanation:

Double fertilization is the process by which two sperm cells are introduced to the ovule. One sperm () fertilizes the egg (), creating a zygote(). The other sperm combines with the two polar nuclei (), forming the endosperm () that will nourish the embryo.

Example Question #1 : Plant Reproduction

Indole-3-acetic acid (IAA) is the most abundant hormone in plants. IAA falls under which classification of plant hormone?

Possible Answers:

Gibberellin

Ethylene

Auxin

Cytokinins

Abscisic acid

Correct answer:

Auxin

Explanation:

The correct answer is auxin. IAA is the most abundant auxin naturally found in plants, and plays key roles in plant development and growth. 

Example Question #2 : Plant Reproduction

Perishable fruit is often picked before it is ripe. This hard, unripe fruit is easier to transport as it is less likely to bruise or spoil while in transit. Once fruit reaches its destination, it can be sprayed with a plant hormone that will promote its rapid ripening. What hormone is most likely used for this function?

Possible Answers:

Abscisic acid (ABA)

Ethylene

Gibberellins

Cytokinins

Correct answer:

Ethylene

Explanation:

Ethylene gas promotes fruit ripening; in a classic example of a positive feedback loop, ripe fruit causes the production of more ethylene gas, which promotes more fruit ripening (this is the origin of the phrase "one bad apple spoils the bunch!")

Cytokinins stimulate cell division and cytokinesis, and they can delay senescence (deterioration due to age, as in the case of cells). Gibberellins promote cell growth, and also promote stem and leaf elongation. Abscisic acid (ABA) promotes seed dormancy, inhibits plant growth, and closes plant stomata during water shortages. 

Example Question #1 : Understanding Plant Hormones

Which of the following is not true of auxins, a class of plant hormones?

Possible Answers:

They are responsible for phototropism—plants' tendency to grow toward light sources

Indoleacetic acid (IAA) is a natural auxin

They enhance apical dominance, which promotes plants' upward growth, as opposed to lateral growth

They promote fruit ripening, which triggers the production of more auxins

Correct answer:

They promote fruit ripening, which triggers the production of more auxins

Explanation:

Auxins play a number of crucial roles in plant growth, behavior, and development. They were the first major class of plant hormone to be discovered and are present in all parts of a plant in varying concentrations. Some of their more notable functions include causing phototropism, enhancing apical dominance, and softening the cell wall to stimulate cell elongation and growth. Indoleacetic acid (IAA) is a naturally occurring auxin, though some synthetic auxins are used as weed killers.

Ethylene gas is a plant hormone that promotes fruit ripening in a positive feedback loop. Ripe fruit produces more ethylene gas, which promotes more fruit ripening, and so on. It is not a kind of auxin.

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