托福聽力的背景知識很重要，出國留學網(wǎng)托福欄目小編整理了相關(guān)的資料，希望可以幫助考生度過考試的難關(guān)，下面是小編搜集的托福聽力生物學背景知識的相關(guān)資訊，歡迎參考!
托福聽力生物學背景知識：痕量金屬
Introduction：
Trace Metal
痕量金屬,是指只含量極少的金屬。一般是指水中、氣體中的微量金屬。
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.
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