GRE Subject Test: Biology : Plant Biology
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Example Questions
Example Question #21 : Plant Biology
What are the protein channels in plants that allow high rates of water flow through the membrane via passive transport?
Carrier proteins
Plasmodesmata
Aquaporins
Xylem
Water does not need a protein channel to pass through the membrane
Aquaporins
The correct answer is aquaporins. While water can move across a membrane via simple diffusion, these transmembrane proteins increase the flow of water. Remember that water is a polar molecule, and is thus relatively impermeable to the plasma membrane despite its small size.
Example Question #1 : Plant Reproduction
What is the female reproductive structure in angiosperms?
Pollen
Stamen
Integument
Pistil
Petal
Pistil
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 : Plant Reproduction
Double fertilization in angiosperms results in a __________ zygote and a triploid __________.
haploid . . . fruit
haploid . . . endosperm
diploid . . . seed
diploid . . . endosperm
diploid . . . fruit
diploid . . . endosperm
Double fertilization is the process by which two sperm cells are introduced to the ovule. One sperm (
Example Question #3 : Plant Reproduction
Indole-3-acetic acid (IAA) is the most abundant hormone in plants. IAA falls under which classification of plant hormone?
Cytokinins
Abscisic acid
Gibberellin
Ethylene
Auxin
Auxin
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 #22 : Plant Biology
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?
Abscisic acid (ABA)
Gibberellins
Ethylene
Cytokinins
Ethylene
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 #23 : Plant Biology
Which of the following is not true of auxins, a class of plant hormones?
Indoleacetic acid (IAA) is a natural auxin
They promote fruit ripening, which triggers the production of more auxins
They are responsible for phototropism—plants' tendency to grow toward light sources
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
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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