The Rate at Which Pollen Settles is Dictated Principally by the Size and Density of the Grain.

Reading Passage Question

The rate at which pollen settles is dictated principally by the size and density of the grain. The slower the settlement rate, the greater the dispersal range. Numerous species reduce the density of their pollen grains through air cavities in their walls. The grains of many species quickly dehydrate after release.

There is a limit, however, to the lower range of pollen size. The smaller a particle becomes, the more difficult its capture, because as airflow carrying particles sweeps past surfaces, inertia represents a principal component of the mechanism for capture. Usually considered a―primitive‖ feature in textbooks, wind-pollination has, in fact, reappeared independently in many plant groups relatively recently in geological time.

General textbooks still often give the impression that the anemophilous syndrome is rather uninteresting, often defining it mainly as a combination of negatives: a lack of nectar, scent, petals, etc. Wind pollination has traditionally been viewed as a reproductive process dominated by random events—the vagaries of the wind and weather. This view seems justified by the potential hazards a pollen grain is subject to when transported over long distances.

Pollen loss through happenstance is compensated for in wind-pollinated plants to a large degree by pollen-to-ovule ratios that greatly exceed those of insect-pollinated species. And unlike the sticky pollen grains of plants pollinated by insects, the pollen grains of wind-pollinated plants are smooth and dry, to avoid clumping and precipitating, and the stigma of the female is huge, sticky, and feathery, the better to catch any floating pollen grains. Similarly, wind-pollinated plants typically evolved to grow in stands, such as pine forests, corn fields and grasslands. Indeed the wind vector is only useful in large, near-monoculture populations.

However, recent research has shown that several remarkably sophisticated mechanisms for dispersal and capture are characteristic of wind-pollinated plants. Pollen release is often tied to the recognition of unambiguous environmental clues. The devices that operate to prevent self-pollination are also sometimes extremely intricate. Many species take advantage of the physics of pollen motion by generating aerodynamic environments within the immediate vicinity of their reproductive organs. Two biological features appear to be critical in this process: the density and size of the pollen grain and the morphology of the ovulate organ.

The shape of the female organ creates patterns of airflow disturbances through which pollen grains travel. The obstructing organ causes airflow to separate around windward surfaces and creates turbulence along leeward surfaces as ambient wind speeds increase. Because the geometry of female organs is often species-specific, airflow disturbance patterns that are also species-specific can be generated. The speed and direction of this pattern combines with the physical properties of a species‘ pollen to produce a highly synergistic pattern of pollen collision on windward surfaces and sedimentation on leeward surfaces of reproductive organs. The aerodynamic consequences of this synergism can significantly increase the pollen-capture efficiency of an ovulate organ.

“The rate at which pollen settles is dictated principally by the size and density of the grain.” - this is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 4 comprehension questions. The GMAT Reading Comprehension questions are designed for testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. In general, according to the author of the passage, pollen grains that would have the greatest dispersal range would have which of the following characteristics?

1. Small size
2. Dryness
3. Low-density

1. I only
2. I and II only
3. I and III only
4. I, II and III
5. II and III only

2. Which of the following is the tone of the passage, in the most part?

1. Critical
2. Descriptive
3. Laudatory
4. Humorous
5. Condescending

3. Based on the information set forth in the passage, all the following mechanisms serve to reduce pollen loss in wind-pollinated plants EXCEPT:

1. retention of pollen within the male organ when weather conditions are not conducive to dispersal.
2. growth of plants in large populations with few species.
3. creation of species-specific air-flow disturbance patterns by the morphology of the ovulate organ.
4. development of intricate mechanisms to prevent self-pollination.
5. high pollen-to-ovule ratios

4. Based on passage information, it is reasonable to conclude that wind pollinated plants are LEAST likely to be found:

1. in tropical rain forests of South America.
2. in the taiga and other northern European coniferous forests.
3. in the valleys of California.
4. along river banks in temperate climates
5. on the windy slopes of the Himalayas

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