As chemical pollutants break down and sink into the earth, rivers become cleaner.

化学污染物并沉入地下，河流变得更加清洁。

No. They take hundreds of years to decompose – or break down by natural chemical processes.

不是的。是因为它们要需要几百年的时间。降是指通过自然化学反应的过程。

This process of using oxygen to break down sugars into chemical energy is called cellular respiration.

线粒体利用氧气把糖成化学能的过程叫做细胞呼吸。

And some chemical breakdown continues in the large intestine, thanks to our little bacterial farm there.

多亏了我们那里的小细菌农场，一化学在大肠中继续。

They can change their diets so there are fewer of the precursor chemicals that get broken down into trimethylamine.

他们可以通过改变饮食来减少先驱化学品的摄入，而这种先驱化学品会成为三甲胺。

And outside of being bitter, it's considered unreactive, so it's basically non-toxic and isn't destroyed by water or most other chemicals.

它被认为是惰性物质，因此基本上无毒，也不会溶于水或被大部其他化学物质所。

Plastics can take hundreds of years to degrade, or break down chemically.

塑料可能需要数百年才能降或化学。

While breaking down chemicals for energy is nice and all, early life did miss out on the greatest available source of energy: The Sun.

虽然化学物质的能源是一件很好的事，早期生命确实错过了最大的可用能源：太阳。

With most cases, the macrophage then fuses the phagosome with a lysosome which has hydrolytic enzymes that can pretty much break down any biochemical molecules.

大部情况下，巨噬细胞会将吞噬小体和溶酶体融合到一起；溶酶体中含有水酶可以很大程度上生物化学子。

Now we don't usually think of it this way, but that is where digestion starts — the mechanical and chemical breakdown of food through chewing and enzyme-action.

我们通常不这么想，但消化是从这里开始的——通过咀嚼和酶作用对食物进行机械和化学。

Then, a little chemistry knocked the acid off, creating what was clearly an alkene, so they named it benzene, because it was an alkene that was from the benzoin resin.

然后，用一点化学方法将酸， 产生明显是烯烃的物质， 因此他们将其命名为苯，因为它是一种来自安息香树脂的烯烃。

Moving through the digestive tract - down the esophagus, into the stomach, ending up in the small intestine food is chemically broken down into smaller molecules, and nutrients are absorbed into the body.

穿过消化道-沿食道进入胃部，最后进入小肠的食物被化学成较小的子，营养物质被吸收到体内。

That's why molecular substances like ice and water can be physically broken or separated into portions, while only a chemical reaction can break apart the molecules themselves, like how water can be split into hydrogen and oxygen using electricity.

这就是为什么像冰和水这样的子物质可以物理破碎或成几部，而只有化学反应才能子本身，就像水如何用电成氢和氧一样。