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- 精华
- 1
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- 733
- 经验
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- 53 点
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- 405 ￥
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- 184
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5.食物链（附内容很一致的文章）---原文！！！！！----
Biomagnification means that the level of atoxin in animals' tissues rises as one moves up the food chain. For instance,as larvae eat algae, fish eat the larvae, and bigger fish eat smaller fish, the toxin present in the algae becomes increasingly concentrated; top predators like swordfish and polar bears end up with the highest doses in their tissues.This can happen with stable, fatsoluble chemicals that aren't easily excretedin urine or feces. Biomagnification was first studied in the late 1960s in aquatic food webs, explains Frank Gobas, professor at Simon Fraser University and leader of the study. To screen chemicals, scientists began using a property known as Kow, which indicates how readily a chemical dissolves in water compared with fat and thus predicts how easily it will move from a fish's blood lipids into water through its gills（鱼鳞）. Low-Kow, or more water soluble, chemicals don't build up in the fish food chain and were assumed to be safe.
Environmental chemists realized, however, that this assumption might not hold in food chains involving mammals and birds because their lungs are in contact with air, not water. This means that many chemicals that are relatively soluble in water and therefore don't accumulate in fish might remain in the tissues ofl and animals if they aren't volatile enough to easily move from the lungs into the air (predicted by a property called Koa). Supporting this idea, some organic chemicals that don't biomagnify in fish appeared to be doing so in other wildlife and humans.
To explore this hypothesis, Gobas and graduate student Barry Kelly and colleagues collected plant and animal tissue samples— from lichens to beluga whales killed in Inuit hunts—in the Arctic, where, because of weather patterns and cold temperatures, organic pollutant levels are high. They tested the samples not only for known POPs but also for several chemicals with a low Kow but high Koa, which suggested they might biomagnify in air-breathing animals. The measured levels of contaminants for various animals in aquatic and land food webs were similar to those predicted from a bioaccumulation model incorporating Koa and Kow, suggesting the model was correct. Chemicals with low Kow and high Koa stood out as potentially risky.
逻辑简图：
第一段：科学家发现动物身体的毒素会随着食物链而传导。Since幼虫吃藻类，鱼吃幼虫，大鱼吃小鱼----最后大鱼或北极熊这种终极动物则身体里毒素会变高。但是由于水生动物身体里有一种物质可以溶于脂肪，帮助他们将体内毒素排出，所以他们LOW kow，也就是说他们是安全的
第二段：但是，科学家发现哺乳动物和鸟类则不然。发现他们由于身体里的那种物质不是溶于水的，而是不容易排出的在空气中，所以他们更加危险----对于中毒这个事件。而物质不容易挥发在空气中则被称为High Koa。也就是说，水生鱼类和其他陆地动物不一样。
第三段:G和其学生做实验，研究鲸鱼体内的化学物质以及某些陆生动物的体内化学物质。最后发现无论是动物还是植物，体内若有Low kow，high koa，则很危险。
题目：
1.问algae的作用 |
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