tailieunhanh - IELTS Academic Reading Sample 84 - The effects of light on plant and animal species

Để đạt thành tích cao trong kì thi sắp tới, các bạn học sinh có thể sử dụng tài liệu IELTS Academic Reading Sample 84 - The effects of light on plant and animal species sau đây làm tư liệu tham khảo giúp rèn luyện và nâng cao kĩ năng giải đề thi, nâng cao kiến thức cho bản thân để tự tin hơn khi bước vào kì thi chính thức. Mời các bạn cùng tham khảo đề thi. | 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 plane 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 behaviour. 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. Plane 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 plane is also clear. Short-day plane that flower in spring in the temperate zone are adapted to maximising seedling