DK life cycles everything from start to finish生命周期从开始到结束循环

What is a life cycle
什么是生命周期

Life is always changing, but it follows patterns too. Living things—including ourselves—grow, produce young, and die. There are repeating processes for nonliving things too, from mountains, rocks, and rivers to planets, comets, and stars. We call all these patterns life cycles.
生活总是在变化，但它也遵循着规律。包括我们自己在内的生物生长、繁殖和死亡。非生物也有重复的过程，从山脉、岩石、河流到行星、彗星和恒星。我们称所有这些模式为生命周期。

Life cycles are interlinked. Plants take nutrients and water from the soil and energy from sunlight. Animals eat plants or other animals in order to grow.
生命周期是相互关联的。植物从土壤中获取养分和水分，从阳光中获取能量。动物为了生长而吃植物或其他动物。
Many plants rely on animals such as insects to spread their pollen so they can make seeds and reproduce. When plants and animals die, their remains rot and become part of the soil that will nourish new plants.
许多植物依靠昆虫等动物传播花粉，以便它们能够制造种子并繁殖。当植物和动物死亡时，它们的残骸会腐烂，成为土壤的一部分，从而滋养新的植物。

The life cycles we see around us appear endless. Birth and growth are balanced by breakdown and decay. Yet these cycles can be fragile.
我们周围的生命周期似乎无穷无尽。衰败和衰败平衡了出生和成长。然而，这些周期可能是脆弱的。
Change—whether natural or caused by humans—can disrupt them. Vulnerable species may dwindle to extinction when their cycles get broken, while—over millions of years— new species emerge by evolution
无论是自然的还是由人类引起的变化都会破坏它们。当它们的周期被打破时，脆弱的物种可能会减少到灭绝，而经过数百万年的进化，新的物种会出现

Earth and space
地球与空间
Our Earth is constantly changing. Rocks wear away and get recycled into new rocks, while water circulates between sea, sky, and land. In space, comets and stars form from gas and dust, burn out, then return to gas and dust.
我们的地球在不断变化。岩石磨损并被回收成新的岩石，而水在海洋、天空和陆地之间循环。在太空中，彗星和恒星由气体和尘埃形成，燃烧殆尽，然后返回气体和尘埃。

Earth’s life cycles are tiny fractions of the age of the universe: 13.8 billion years
地球的生命周期只是宇宙年龄的一小部分：138亿年

Sexual life cycles
有性生命体周期
Sexual reproduction involves two parents—male and female—and each supplies a sex cell. The female egg cell fuses (joins) with the male sperm cell, in a process called fertilization. The fertilized egg develops into a new animal or plant.
有性生殖包括两个父母，一个是男性，一个是女性，每个人都提供一个性细胞。雌性卵细胞与雄性精子细胞融合（结合），这一过程称为受精。受精卵发育成新的动物或植物。

Asexual life cycles Some plants and animals reproduce asexually, from a single parent. The young develop from unfertilized eggs or form from a small part of the parent. The young are exact replicas (copies) of their parent.
无性生命周期一些植物和动物从单亲无性繁殖。幼仔由未受精的卵发育而来，或由父代的一小部分形成。年轻人完全是他们父母的复制品。

Space
太空
Space is unimaginably huge and full of exciting things, such as planets, moons, galaxies, and black holes. It is also constantly changing— stars form from beautiful clouds of dust and gas, evolve through their life cycle to slowly die away, or go out with an enormous bang. Everything that has or will ever be formed was created in space—including the building blocks of you!
太空是难以想象的巨大，充满了令人兴奋的东西，如行星、卫星、星系和黑洞。它也在不断变化——恒星是由美丽的尘埃和气体云形成的，在其生命周期中进化到慢慢消亡，或者伴随着巨大的爆炸而消失。所有已经形成或将要形成的东西都是在太空中创造的，包括你的积木！

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