托福阅读事实信息题是阅读考试中比较常见的一种题型，tpo则是托福阅读备考最权威的材料，所以托福小编综合二者，为大家集中整理了tpo阅读中考察的事实信息题及其对应的解析，供大家参考使用。本文带来的是TPO17-3的事实信息题，一起来看看吧。
TPO17-3 Symbiotic Relationships
paragraph 2
Parasitism is a kind of predator-prey relationship in which one organism, the parasite, derives its food at the expense of its symbiotic associate, the host. Parasites are usually smaller than their hosts. An example of a parasite is a tapeworm that lives inside the intestines of a larger animal and absorbs nutrients from its host. Natural selection favors the parasites that are best able to find and feed on hosts. At the same time, defensive abilities of hosts are also selected for. As an example, plants make chemicals toxic to fungal and bacterial parasites, along with ones toxic to predatory animals (sometimes they are the same chemicals). In vertebrates, the immune system provides a multiple defense against internal parasites.
3. According to paragraph 2 which of the following is true of the action of natural selection on hosts and parasites?
Hosts benefit more from natural selection than parasites do.
Both aggression in predators and defensive capacities in hosts are favored for species survival
The ability to make toxic chemicals enables a parasite to find and isolate its host
Larger size equips a parasite to prey on smaller host organisms.
解析：以natural selection做关键词定位至第四句，说自然选择会选择那些最容易寻找寄主的寄生者，同时也会选择寄主的防御能力，也就是说不管是寄生者还是寄主都被最大程度保留下来，所以答案是B。A的比较，C的toxic material和isolate，还有D的大小均没有相关信息
【2】寄生现象是一种捕食式的关系，其中，寄生物通过削弱其寄主而获得自身所需食物。寄生物的形体往往小于寄主。绦虫是寄生的例子之一，它生存在较大型动物的肠道中，并吸收寄主体内的营养。自然选择青睐那些寻找寄主并且寄生能力强的寄生虫，同时，防御能力强的寄主也被选择出来。比如说，有些植物会产生对真菌和细菌寄生物有毒的化学物质，也会产生那些对捕食动物有毒的化学物质(有时这些化学物质是一样的)。而对于脊椎动物来说，其身体的免疫系统可以对体内的寄生物进行多层防御。
paragraph 5
The third type of symbiosis, mutualism, benefits both partners in the relationship Legume plants and their nitrogen-fixing bacteria, and the interactions between flowering plants and their pollinators, are examples of mutualistic association. In the first case, the plants provide the bacteria with carbohydrates and other organic compounds, and the bacteria have enzymes that act as catalysts that eventually add nitrogen to the soil, enriching it. In the second case, pollinators (insects, birds) obtain food from the flowering plant, and the plant has its pollen distributed and seeds dispersed much more efficiently than they would be if they were carried by the wind only. Another example of mutualism would be the bull's horn acacia tree, which grows in Central and South America. The tree provides a place to live for ants of the genus Pseudomyrmex. The ants live in large, hollow thorns and eat sugar secreted by the tree. The ants also eat yellow structures at the tip of leaflets: these are protein rich and seem to have no function for the tree except to attract ants. The ants benefit the host tree by attacking virtually anything that touches it. They sting other insects and large herbivores (animals that eat only plants) and even clip surrounding vegetation that grows near the tree. When the ants are removed, the trees usually die, probably because herbivores damage them so much that they are unable to compete with surrounding vegetation for light and growing space.
8. According to paragraph 5, the relationship between legumes and bacteria benefits the soil by
adding enriching carbohydrates
speeding the decay of organic matter
destroying enzymes that pollute it
contributing nitrogen to it
解析：以legume，bacteria和soil做关键词定位至第二句，说植物给细菌提供有机物，而细菌中的酶可以作为催化剂向土壤中添加氮，所以答案是D，其他都没说
【5】第三种关系，互利共生，是指共生双方能够互利互惠。其中典型的例子有豆科植物和固氮细菌，以及开花植物和授粉生物。在第一个例子中，植物可以为细菌提供碳水化合物以及其他一些化合物，而这些细菌则能产生一种起催化作用的酶，它最终增加土壤中的氮元素来丰富土壤。在第二个例子中，授粉生物(昆虫、鸟类等)从开花植物中获取食物，而植物则可以通过它们来传递花粉和种子，这比仅仅依靠风来传递要高效得多。还有一个互利共生的例子是生长在美国中南部的牛角金合欢树。这种树为一种伪蚁属的蚂蚁提供了栖居地。这些蚂蚁住在大的中空的荆棘丛中，汲取金合欢树分泌出来的糖分。它们还吃树叶末端的黄色组织：这个部分富含蛋白质，但是除了吸引蚂蚁，似乎对树本身没有任何功能。而这些蚂蚁们则可以帮助它们的寄主攻击外界几乎所有的威胁。它们会叮咬昆虫和食草动物(只以植物为食的动物)，甚至可以削减生长在树周围的其他植物。一旦蚂蚁被清除掉，这种树就难以存活，很可能是因为它们被食草动物损害而无力与周围的其他植物争夺阳光和生长空间。
以上就是托福阅读TPO17-3中的事实信息题及其解析，大家可以在备考的时候参考复习，希望能够帮助大家的考前准备。最后前程百利祝大家都能取得理想的托福考试成绩。
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