【易伯华课堂】雅思阅读句子填空题讲解--The effects of light on plant and animal species

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The effects of light on plant and animal species

Light is important to organisms for two different reasons. Firstly it is used

as a cue for the timing of daily and seasonal rhythms in both planes and

animals, and secondly it is used to assist growth in plants.

Breeding in most organisms occurs during a part of the year only, and so a

reliable cue is needed to trigger breeding behavior. Day length is an excellent

cue, because it provides a perfectly predictable pattern of change within the

year. In the temperate zone in spring, temperatures fluctuate greatly from day

to day, but day length increases steadily by a predictable amount. The seasonal

impact of day length on physiological responses is called photoperiodism, and

the amount of experimental evidence for this phenomenon is considerable. For

example, some species of birds’ breeding can be induced even in midwinter simply

by increasing day length artificially (Wolfson 1964). Other examples of

photoperiodism occur in plants. A short-day plant flowers when the day is less

than a certain critical length. A long-day plant flowers after a certain

critical day length is exceeded. In both cases the critical day length differs

from species to species. Plants which flower after a period of vegetative

growth, regardless of photoperiod, are known as day-neutral plants.

Breeding seasons in animals such as birds have evolved to occupy the part of

the year in which offspring have the greatest chances of survival. Before the

breeding season begins, food reserves must be built up to support the energy

cost of reproduction, and to provide for young birds both when they are in the

nest and after fledging. Thus many temperate-zone birds use the increasing day

lengths in spring as a cue to begin the nesting cycle, because this is a point

when adequate food resources will be assured.

The adaptive significance of photoperiodism in plants is also clear.

Short-day plants that flower in spring in the temperate zone are adapted to

maximising seedling growth during the growing season. Long-day plants are

adapted for situations that require fertilization by insects, or a long period

of seed ripening. Short-day plants that flower in the autumn in the temperate

zone are able to build up food reserves over the growing season and over winter

as seeds. Day-neutral plants have an evolutionary advantage when the connection

between the favourable period for reproduction and day length is much less

certain. For example, desert annuals germinate, flower and seed whenever

suitable rainfall occurs, regardless of the day length.

The breeding season of some plants can be delayed to extraordinary lengths.

Bamboos are perennial grasses that remain in a vegetative state for many years

and then suddenly flower, fruit and die (Evans 1976). Every bamboo of the

species Chusquea obietifolia on the island of Jamaica flowered, set seed and

died during 1884. The next generation of bamboo flowered and died between 1916

and 1918, which suggests a vegetative cycle of about 31 years. The climatic

trigger for this flowering cycle is not yet known, but the adaptive significance

is dear. The simultaneous production of masses of bamboo seeds (in some cases

lying 12 to 15centimetres deep on the ground) is more than all the seed-eating

animals can cope with at the time, so chat some seeds escape being eaten and

grow up to form the next generation (Evans 1976).

The second reason light is important to organisms is that it is essential for

photosynthesjs. This is the process by which plants use energy from the sun to

convert carbon from soil or water into organic material for growth. The rate of

photosynthesis in a plant can be measured by calculating the rate of its uptake

of carbon. There is a wide range of photosynthetic responses of plants to

variations in light intensity. Some plants reach maximal photosynthesis at

one-quarter full sunlight, and others, like sugarcane, never reach a maximum,

but continue to increase photosynthesis rate as light intensity rises.

Plants in general can be divided into two groups: shade-tolerant species and

shade-intolerant species. This classification is commonly used in forestry and

horticulture. Shade-tolerant plants have lower photosynthetic rates and hence

have lower growth rates than those of shade-intolerant species. Plant species

become adapted to living in a certain kind of habitat, and in the process evolve

a series of characteristics that prevent them from occupying other habitats.

Grime (1966) suggests that light may be one of the major components direrting

these adaptations. For example, eastern hemlock seedlings are shade-tolerant.

They can survive in the forest understorey under very low light levels because

they have a low photosynthetic rate.

Questions 34-40

Complete the sentences.

Choose NO MORE THAN THREE WORDS from the passage for each answer.

Write your answers in boxes 34-40 on your answer sheet.

34Day length is a useful cue for breeding in areas where

..................... are unpredictable.

35Plants which do not respond to light levels arc referred to as

......................... .

36Birds in temperate climates associate longer days with nesting and the

availability of .........................

37Plants that flower when days are long often depend

on.........................to help them

38Desert annuals respond to..............as a signal for reproduction.

39There is no limit to the photosynthetic rate in plants such as

.............................. .

40 Tolerance to shade is one criterion for the horticulture …………………………… of

plants in forestry and horticulture.

答案与解析：

长难句练习：

1.Breeding seasons in animals such as birds have evolved to occupy the part

of the year in which offspring have the greatest chances of survival.

参考译文：例如鸟类等动物的繁殖期占据了一年中他们后代生存几率最大的时间。

知识点：句子主干Breeding seasons主语， have evolved to occupy 谓语，the part of the

year宾语，in animals定语，in which引导限定性定语从句在句中做时间状语因为in which=when。Breeding

seasons繁殖期，繁殖季节;evolve逐步进化;offspring后代

2. Long-day plants are adapted for situations that require fertilization by

insects, or a long period of seed ripening.

参考译文：长日照植物会选择适宜昆虫受精或种子成熟周期较长的时期。

知识点：Long-day plants长日照植物，are adapted for适宜，fertilization by insects昆虫受精，seed

ripening种子成熟 句子主干Long-day plants主语 ，are adapted for谓语被动态

，situations宾语，that限定性引导定语从句修饰 situations。

3.The simultaneous production of masses of bamboo seeds (in some cases lying

12 to 15 centimeters deep on the ground) is more than all the seedeating animals

can cope with at the time, so that some seeds escape being eaten and grow up to

form the next generation.

参考译文：大量的竹子同时孕育的种子产量(在一些例子中，种子在地下12-15厘米深)，超过了这一时期以种子为食的动物所能吃掉的数量，所以，一些种子就能存活下来，长成下一代。

知识点：主句主语是production，more than表语后加了一个对比关系的句子 all the seedeating animals can

cope with at the time; so that引导结果状语从句。