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Listen to part of a lecture in a biology class.
聽一段生物課。
OK, just before the end of the last class, we started talking about trace metals, metals found in living organisms in very small quantities that serve an important biological and important nutritive function in those organisms.
好了，就在上節課結束前， 我們開始講微量金屬，即在生物體中含量非常低的金屬元素，對生物體而言具有很重要的生物和營養功能。
And one trace mental that serves a nutritive function is zinc.
一種具有營養功能的微量金屬是鋅。
Zinc assists in a number of processes in humans, but we are going to focus on just one, one that applies to a number of organisms, not just humans.
鋅在人體內協助很多生物進程的進行，但今天我們主要關注于一種進程，不僅僅適用于人類，也適用于很多其它生物體。
See, zinc plays a major role in carbon cycling, the conversion of various kinds of molecules with carbon, like carbon dioxide into other kinds of molecules with carbon that organisms can use.
鋅在碳循環中起重要作用，即不同的含碳分子之間的轉換，像是二氧化碳轉變成其它種類的含碳分子，可供生物體利用。
So, take respiration, our bodies---our cells produce carbon dioxide when they break down sugars.
拿呼吸作用舉例，我們的身體——我們的細胞在分解糖分時會產生二氧化碳。
We need to get CO2 out of our bodies, so the CO2 is converted into carbonic acid, which the blood is able to carry to the lungs.
我們要把二氧化碳排出體外，所以二氧化碳被轉成了碳酸，這樣血液就能將其運輸至肺部。
Once the carbonic acid reaches the lungs, it's converted back into carbon dioxide, so that we can breathe it out.
一旦碳酸到達肺部，就會重新轉變成二氧化碳，然后我們就能通過呼吸排出。
Now, this whole conversion process relies on a particular enzyme.
整個轉變過程依靠一種特定的酶。
Um, who remembers what an enzyme is? Bob?
誰記得這種酶是什么？鮑勃？
Um, it's a protein, a specific kind of protein, one that speeds up chemical reactions.
這是一種蛋白質，一種特定的蛋白質，能加快化學反應。
Exactly, different enzyme assists in different chemical reactions.
正確，不同的酶能輔助不同的化學反應。
Now, the one that speeds up the conversion of carbon dioxide has zinc in it.
那種能加快二氧化碳轉化的酶含有鋅。
So this zinc enzyme is critical for getting CO2 out of our bodies through the lungs.
所以，要把二氧化碳由肺部排出我們體外，這種含鋅酶至關重要。
And it's also extremely important for plants.
同時它對植物也非常重要。
Bob, can you tell us why?
鮑勃，你能告訴我們這是為什么嗎？
For making food, for photosynthesis?
為了制造養分，為了光合作用？
Exactly! For photosynthesis.
完全正確！就是為了光合作用。
Plants also convert carbon dioxide into different forms of carbon-containing molecules and the conversion process used relies on the very same enzyme that works in humans.
植物也會將二氧化碳轉化為其它含碳分子，其涉及的轉化過程中也依靠于這種酶，和在人體中起作用的酶一樣。
So, zinc is also important for plants.
所以，鋅對植物來說也很重要。
OK, but zinc is scarce in certain environments, and it is particularly scarce in waters near the surface of rivers and lakes and shallower parts of oceans, which might make us wonder how plants could live there at all.
好了，但鋅在一些環境中很稀少，特別是在接近水面的河水和湖水里，還有較淺的海水里，這不禁讓我們感到疑惑，在那兒的植物是怎么活下來的。
In fact, there are a lot of marine plants that survive, that grow and reproduce in surface waters.
事實上，有很多海洋植物生存下來了，在表層水里茁壯成長，不斷繁殖。
In particular, there are a lot of diatoms.
那里特別多硅藻。
