TPO73阅读真题+题目+答案下载：How Effective Are Structural Plant Defenses?

TPO73阅读真题+题目+答案下载：How Effective Are Structural Plant Defenses?

Some of the least costly defenses,in terms of energy use,available to plants are structures that make penetration by predators difficult,if not impossible. These include tough leaves,spines,and epidermal hairs on leaves,which may trap,impale,or fence out insects and discourage browsing by vertebrate herbivores,as well as hard-coated seeds.These structures may have evolved early in the history of the plants,when they might have been subject to even greater predatory pressures.Because they represent little investment,plants still retain them.

Many seeds have thick,hard seed coats that provide protection from seed- eating animals.The problem with such seed defense is that the seeds need to be scarified-the hard seed needs scratching or scoring of the seed coat to weaken it-so the seedling itself can escape.If the seed is not scarified,the seedling embryo is sealed in,never to germinate.Many plants,however,have turned seed predation into a mechanism for seed dispersal,such as the transport and caching of seeds by squirrels,jays,mice,and ants.

The role of structural defenses in plants was largely presumed until experimental evidence was sought to demonstrate the effectiveness of such apparent defensive structures against grazing herbivores.Researchers investigated experimentally the effects of plant spinescence on the feeding habits of three large browsing mammalian herbivores of Africa.These were the kudu,a large African antelope attaining a female body weight of 180 kilograms; the impala,a medium-sized African antelope attaining a female body weight of 50 kg;and the Boer goat,a domestic ungulate weighing about 35 kg.。。。。。余下托福TPO73阅读真题省略！

1.The word “retain” in the passage is closest in meaning to （ ）？

A. Keep

B. Need

C. Defend

D. Develop

2.Paragraph 1 supports which of the following statements about the defense system of plants?

A. Its development requires lots of energy on the part of the plant.

B. Its design is less elaborate today than at the time of its origin.

C. It was probably of greater necessity in the early stages of plant evolution.

D. It developed relatively late in the plant's evolutionary history.

3.What can be inferred from paragraph 2 about seed-producing plants?

A. They depend on one particular animal species to disperse their seeds.

B. Some of them have turned seed predation into an action that benefits them.

C. Most are quite vulnerable to attacks by predatory animals.

D. Most have seedlings that automatically emerge out of the seed coats. 

。。。。。余下托福TPO73阅读真题题目省略！

3篇完整版托福TPO72阅读真题及答案下载，15元有偿！