托福阅读真题第185篇Distribution of Seaweeds
Distribution of Seaweeds
Paragraph 1: Seaweeds are multicellular algae that inhabit the oceans. Despite their evolutionary distance from each other, seaweeds — such as brown algae, red algae, and green algae — have in common many aspects of their biology and contributions to the ecology of the seas.
Paragraph 2: Most species of seaweed are benthic (living on the seafloor); they grow on rock, sand, mud, and coral on the sea bottom. Other species live on other organisms and as part of fouling communities (plants and animals that live on pilings, boat bottoms, and other artificial surfaces). Some seaweeds attach to very specific surfaces, whereas other seaweeds are rather nonselective. In general, seaweeds inhabit about 2 percent of the seafloor. The presence of benthic seaweeds defines the inner continental shelf, where the marine community largely depends on the food and protection that seaweeds provide. Life on the outer continental shelf and in the deep sea is quite different in the absence of seaweeds. The distinction between the inner and outer shelves is based on the compensation depth of algae. The compensation depth is the depth of water at which there is just enough light for algae to survive. At that depth all the oxygen produced by photosynthesis is consumed by the algae’s respiration, so that no further growth can occur.
1. What can be inferred from paragraph 2 about the outer continental shelf?
O The outer continental shelf contains more benthic seaweeds than the deep sea does.
O The outer continental shelf lacks enough sunlight to support the growth of algae.
O The outer continental shelf has a compensation depth that is about the same as that of the inner continental shelf.
O The outer continental shelf has a greater variety of marine life than does the inner continental shelf.
2. According to paragraph 2, all of the following are true of seaweeds EXCEPT:
O Seaweeds provide food and protection for other organisms.
O Seaweeds can grow on both living and nonliving things.
O �Some seaweeds select specific surfaces to attach to, while others are not selective.
O Two percent of seaweed species live on the ocean floor.
Paragraph 3: The environmental factors that are most influential in governing the distribution of seaweeds are light and temperature. Some other abiotic (nonliving) factors critical in governing the distribution of seaweeds are duration of tidal exposure and desiccation (drying out), wave action and surge, salinity, and availability of mineral nutrients. The areas of the world most favorable to seaweed diversity include both sides of the North Pacific Ocean, Australia, southwestern Africa, and the Mediterranean Sea.
Paragraph 4: The vertical and horizontal distributions of seaweeds are limited in part by the availability of sunlight and, therefore, vary by depth, latitude, sea conditions, and season. It was once thought that the vertical distribution of red, brown, and green algae could be explained by their accessory photosynthetic pigments (photosynthetic pigments other than chlorophyll), the presence of which gives the seaweeds their characteristic colors, a concept known as chromatic adaptation. Because green light penetrates deepest in coastal waters and the accessory pigments of red algae absorb mostly green wavelengths, red algae were thought to extend to the greatest depth. It followed that green algae, which have pigments absorbing mostly blue and red wavelengths that are diminished rapidly in seawater, should be found at the shallowest depths. Because accessory pigments of brown algae absorb intermediate wavelengths of light, brown algae would be expected to be most abundant at intermediate depths. Indeed, some recent evidence would seem to support the hypothesis of chromatic adaptation because the depth record (295 meters, or 973 feet) for seaweeds is held by a yet undescribed species of red algae from the Bahamas. However, the green alga Rhipiliopsis profunda is close behind this record at 268 meters (884 feet).
3. According to the concept of chromatic adaptation explained in paragraph 4, which of the following types of algae should be found closest to the ocean’s surface?
O Red algae
O Blue algae
O Green algae
O Brown algae
4. Why does the author mention “a yet undescribed species of red algae from the Bahamas”?
O To suggest that the concept of chromatic adaptation applies only to algae living in deep waters
O To argue that location is more important than chromatic adaptation in determining the vertical distribution of algae
O To emphasize the difficulty of testing the concept of chromatic adaptation in deep waters
O To provide information that may confirm the idea that chromatic adaptation is responsible for the vertical distribution of algae
5. What can be inferred from the author’s discussion of the green algae Rhipiliopsis profunda in paragraph 4?
O Chromatic adaptation may not be an adequate explanation for the vertical distribution of algae.
O All types of algae share the same accessory photosynthetic pigments.
O Chromatic adaptation is responsible for the distribution of red algae but not for the distribution of green algae.
O Both red and green algae absorb red wavelengths.
Paragraph 5: The concept of chromatic adaptation was proposed in 1883, and the hypothesis was accepted for about 100 years, until it was realized that such zonation did not necessarily occur and that the distribution of seaweeds depended more on herbivory (the consumption of plant material), competition, varying concentration of the specialized pigments, and the ability of seaweeds to alter their forms of growth.
6. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
O For about 100 years, chromatic adaptation was thought to have a greater impact on seaweed distribution than various other factors such as herbivory and competition.
O The hypothesis of chromatic adaptation was accepted for about 100 years until it was concluded that other factors could explain the distribution of seaweeds.
O About 100 years after the concept of chromatic adaptation was developed, it was realized that seaweed zonation occurred even in the absence of chromatic adaptation.
O Until the hypothesis of chromatic adaptation became widely accepted 100 years after it was proposed, various other factors were thought to determine the distribution of seaweeds.
Paragraph 6: Temperature affects the distribution of seaweeds. The greatest diversity of algal species is in tropical waters. Farther north or south of the equator, the number of species decreases, and the species themselves are different. Many marine algae in colder latitudes are perennials, meaning that they live longer than two years. During the colder seasons only part of the alga remains alive, sometimes only a few cells, but most often a mass of stemlike structures. When the temperature warms up in the spring, this body part initiates new growth. Temperature is not usually a limiting factor for algae that live in tropical and subtropical seas, although temperatures in intertidal areas (those areas between high and low tides) may become too warm and contribute to seasonal mass mortality of many seaweeds and the animals they shelter. At high latitudes, freezing and scouring by ice may eliminate seaweeds from the intertidal and shallow subtidal zones.
7. What is the author’s purpose in discussing “temperatures in intertidal areas”?
O To emphasize the idea that warm temperatures can be just as dangerous to algae as cold temperatures
O To identify a limiting factor for algae common to both tropical seas and waters at higher latitudes
O To compare the causes of seaweed mortality in tropical seas and in seas at higher latitudes
O To note an exception to the idea that temperature does not limit the growth of algae in tropical and subtropical waters
8. According to paragraph 6, all of the following are true of perennials EXCEPT:
O Perennials live for more than two years.
O Only part of a perennial remains alive during the winter.
O A large number of the marine algae found in cold latitudes are perennials.
O Species in the tropics are more sensitive to temperature than are species in colder latitudes.
Paragraph 2: Most species of seaweed are benthic (living on the seafloor); they grow on rock, sand, mud, and coral on the sea bottom. Other species live on other organisms and as part of fouling communities (plants and animals that live on pilings, boat bottoms, and other artificial surfaces). ■Some seaweeds attach to very specific surfaces, whereas other seaweeds are rather nonselective. In general, seaweeds inhabit about 2 percent of the seafloor. ■The presence of benthic seaweeds defines the inner continental shelf, where the marine community largely depends on the food and protection that seaweeds provide. ■Life on the outer continental shelf and in the deep sea is quite different in the absence of seaweeds. ■The distinction between the inner and outer shelves is based on the compensation depth of algae. The compensation depth is the depth of water at which there is just enough light for algae to survive. At that depth all the oxygen produced by photosynthesis is consumed by the algae’s respiration, so that no further growth can occur.
9. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
They are most prevalent on the part of the sea bottom known as the continental shelf.
Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.
10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage, click on View Text.
Seaweeds are multicellular algae living in the oceans.
Answer Choices
O Seaweeds are limited to areas with enough light for them to survive, with most living on the seafloor and more species inhabiting warm waters than colder waters.
O Some recent evidence shows that the color of any species of seaweed is determined by the amount of chlorophyll contained in its accessory pigments.
O The greatest diversity of seaweed is found in warm waters, and seaweed cannot survive when the temperature is either too hot or too cold.
O Seaweeds are distributed most evenly over areas of ocean that experience changing tides, strong waves, a dry climate, and high concentrations of salt and minerals.
O The chromatic-adaptation hypothesis was long thought to explain the vertical distribution of seaweed, but current belief is that distribution is better explained by other factors.
O Temperature extremes in tropical and subtropical areas as well as at high latitudes cause seaweeds to abandon the intertidal areas for the subtidal zones of the seafloor.
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