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托福听力生物学背景知识：痕量金属

2017-09-22 17:25:55来源：网络

　　为了帮助考生更好的熟悉托福听力考试，在考试中能有更好的发挥，新东方在线托福网为大家带来托福听力生物学背景知识：痕量金属一文，希望对大家托福备考有所帮助。更多精彩尽请关注新东方在线托福网!

　　Introduction：

　　Trace Metal

　　痕量金属,是指只含量极少的金属。一般是指水中、气体中的微量金属。

　　Background information：

　　Trace metals are metals in extremely smallquantities that are present in animal and plant cells and tissue. They are anecessary part of nutrition and physiology. Ingestion of, or exposure to,excess quantities is often toxic. However, insufficient plasma or tissue levelsof certain trace metals can cause pathology as well; as is the case with iron.

　　Trace metals are depleted through theexpenditure of energy by various metabolic processes living organisms. They arereplenished in animals through diet as well as environmental exposure, and inplants through the uptake of nutrients from the soil in which the plant grows.

　　Human vitamin pills and plant fertilizersboth contain trace metals as additional sources for trace metals. The harderyou work to expend energy, the more trace metals you will lose. These metals needto be replaced so that your body can properly function. Things such as vitaminsand sports drinks can help with this along with fresh fruits and vegetables.

　　Some metals are naturally found in the bodyand are necessary for proper human health. Iron can help to prevent anemia, andzinc is a cofactor in over 100 enzyme reactions. Although trace metals are goodfor humans, in high doses they may be toxic to the body.

本文关键字: 托福听力背景知识 托福听力知识

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