2020年8月22日托福阅读真题+题目+答案：Energy Distribution in Plants

2020年8月22日托福阅读真题+题目+答案：Energy Distribution in Plants

Annuals are plants that go through their entire life cycle within a single year. Annuals begin their life cycles in the spring when seeds that survived the winter germinate (begin to grow). In regions with distinct dry and wet seasons, germination occurs with the onset of the rainy season. Because it has only one growing season, an annual has to distribute its photosynthates (energy-rich molecules) first to leaves. Leaves, in turn, become involved in photosynthesis which replenishes the supply of photosynthates and increases overall plant biomass. At the time of flowering, the plant decreases the amount of energy distributed to leaves and diverts most of its photosynthate to reproduction. For example, in the sunflower, the biomass of leaves declines from approximately 60 percent of the total plant weight during the period of growth to 10 to 20 percent by the time the seeds are ripe. When in bloom, the sunflower distributes 90 percent of its photosynthate to the flower head and the remainder to the leaves, stem, and roots.

1.Why does the author provide the information that "When in bloom the sunflower distributes 90 percent of its photosynthate to the flower head and the remainder to the leaves, stem, and roots"?

A.To argue against the idea that annuals distribute photosynthates primarily to leaves rather than to other tissues.

B.To explain why plants such as the sunflower only live through one growing season.

C.To emphasize how much difference life stage makes in how annuals distribute their energy.

D.To support the idea that leaves, stems, and roots do not require much energy after they have developed.

2.According to paragraph 1. all of the following are true of annual plants EXCEPT:

A.They begin to grow in the spring or at the start of the rainy season.

B.They initially distribute energy primarily to leaves.

C.Leaves are involved in the production of energy.

D.Leaf biomass increases significantly at the time of reproduction.

Perennial plants maintain a vegetative structure over several years.▋ Once established, they distribute their energy in a very different manner from annuals.▋ Before perennials expend any energy on reproduction, they divert photosynthate to the roots. ▋This distribution to roots is in excess of that required for the development of roots for the uptake of nutrients and water from the soil.▋ In some species, such as the skunk cabbage, the roots develop into large storage organs. Energy stored in the roots makes up a reserve upon which the plants draw when they begin growth the following growing season. When they are ready to flower, perennials divert energy from storage to the production of flowers and fruit. As the flowers fade and the fruits ripen. the plant once more sends photosynthate to the roots to build up the reserves it will need for the following spring.

Trees and woody shrubs live a long time, which greatly influences the manner in which they distribute energy. Early in life, leaves make up more than one-half of their biomass; however, as trees age, they accumulate more woody growth. Trunks and stems become thicker and heavier, and the ratio of leaves to woody tissue changes. Eventually leaves account for only 1 to 5 percent of the total mass of the tree. The production system (the leaf mass) that supplies the energy is considerably less than the rest of biomass it supports. Thus, as the woody plant grows, much of the energy goes into support and maintenance, which increases as the plant ages.

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