GRE閱讀真題200篇LEVEL2: Traditionally, pollination...

2015/11/04 瀏覽次數:504 收藏

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  60. Traditionally, pollination by wind has

  Traditionally, pollination by wind has been viewed as a reproductive process marked by random events in which the vagaries of the wind are compensated for by the generation of vast quantities of pollen, so that the ultimate production of new seeds is assured at the expense of producing much more pollen than is actually used. Because the potential hazards pollen grains are subject to as they are transported over long distances are enormous, wind-pollinated plants have, in the view above, compensated for the ensuing loss of pollen through happenstance by virtue of producing an amount of pollen that is one to three orders of magnitude greater than the amount produced by species pollinated by insects.

  However, a number of features that are characteristic of wind-pollinated plants reduce pollen waste. For example, many wind-pollinated species fail to release pollen when wind speeds are low or when humid conditions prevail. Recent studies suggest another way in which species compensate for the inefficiency of wind pollination. These studies suggest that species frequently take advantage of the physics of pollen motion by generating specific aerodynamic environments within the immediate vicinity of their female reproductive organs. It is the morphology of these organs that dictates the pattern of airflow disturbances through which pollen must travel. The speed and direction of the airflow disturbances can combine with the physical properties of a species’ pollen to produce a species-specific pattern of pollen collision on the surfaces of female reproductive organs. Provided that these surfaces are strategically located, the consequences of this combination can significantly increase the pollen-capture efficiency of a female reproductive organ.

  A critical question that remains to be answered is whether the morphological attributes of the female reproductive organs of wind-pollinated species are evolutionary adaptations to wind pollination or are merely fortuitous. A complete resolution of the question is as yet impossible since adaptation must be evaluated for each species within its own unique functional context. However, it must be said that, while evidence of such evolutionary adaptations does exist in some species, one must be careful about attributing morphology to adaptation. For example, the spiral arrangement of scale-bract complexes on ovule-bearing pine cones, where the female reproductive organs of conifers are located, is important to the production of airflow patterns that spiral over the cone’s surfaces, thereby passing airborne pollen from one scale to the next. However, these patterns cannot be viewed as an adaptation to wind pollination because the spiral arrangement occurs in a number of non-wind-pollinated plant lineages and is regarded as a characteristic of vascular plants, of which conifers are only one kind, as a whole. Therefore, the spiral arrangement is not likely to be the result of a direct adaptation to wind pollination.

  21. The author of the passage is primarily concerned with discussing

  (A) the current debate on whether the morphological attributes of wind-pollinated plants are evolutionary adaptations

  (B) the kinds of airflow patterns that permit wind-pollinated plants to capture pollen most efficiently

  (C) the ways in which the reproductive processes of wind-pollinated plants are controlled by random events

  (D) a recently proposed explanation of a way in which wind-pollinated plants reduce pollen waste

  (E) a specific morphological attribute that permits one species of wind-pollinated plant to capture pollen

  22. The author suggests that explanations of wind pollination that emphasize the production of vast quantities of pollen to compensate for the randomness of the pollination process are

  (A) debatable and misleading

  (B) ingenious and convincing

  (C) accurate but incomplete

  (D) intriguing but controversial

  (E) plausible but unverifiable

  23. According to the passage, the “aerodynamic environments” mentioned in line 23, when they are produced, are primarily determined by the

  (A) presence of insects near the plant

  (B) physical properties of the plant’s pollen

  (C) shape of the plant’s female reproductive organs

  (D) amount of pollen generated by the plant

  (E) number of seeds produced by the plant

  24. According to the passage, true statements about the release of pollen by wind-pollinated plants include which of the following?

  I. The release can be affected by certain environmental factors.

  II. The amount of pollen released increases on a rainy day.

  III. Pollen is sometimes not released by plants when there is little wind.

  (A) II only

  (B) III only

  (C) I and II only

  (D) I and III only

  (E) I, II, and III

  25. The passage suggests that the recent studies cited in lines 19-21 have not done which of the following?

  (A) Made any distinctions between different species of wind-pollinated plants.

  (B) Considered the physical properties of the pollen that is produced by wind-pollinated plants.

  (C) Indicated the general range within which plant-generated airflow disturbances are apt to occur.

  (D) Included investigations of the physics of pollen motion and its relationship to the efficient capture of pollen by the female reproductive organs of wind-pollinated plants.

  (E) Demonstrated that the morphological attributes of the female reproductive organs of wind-pollinated plants are usually evolutionary adaptations to wind pollination.

  26. It can be inferred from the passage that the claim that the spiral arrangement of scale-bract complexes on an ovule-bearing pine cone is an adaptation to wind pollination would be more convincing if which of the following were true?

  (A) Such an arrangement occurred only in wind-pollinated plants.

  (B) Such an arrangement occurred in vascular plants as a whole.

  (C) Such an arrangement could be shown to be beneficial to pollen release.

  (D) The number of bracts could be shown to have increased over time.

  (E) The airflow patterns over the cone’s surfaces could be shown to be produced by such arrangements.

  27. Which of the following, if known, is likely to have been the kind of evidence used to support the view described in the first paragraph?

  (A) Wind speeds need not be very low for wind-pollinated plants to fail to release pollen.

  (B) The female reproductive organs of plants often have a sticky surface that allows them to trap airborne pollen systematically.

  (C) Grasses, as well as conifers, generate specific aerodynamic environments within the immediate vicinity of their reproductive organs.

  (D) Rain showers often wash airborne pollen out of the air before it ever reaches an appropriate plant.

  (E) The density and size of an airborne pollen grain are of equal importance in determining whether that grain will be captured by a plant.