35 Life Cycles-Mid

Life Cycles Written by Ned Jensen

《生命周期》作者:Ned Jensen

Introduction Another word for a living thing such as a plant or animal is an organism. Most organisms go through several stages from the very beginning of their lives to the end of their lives. In each stage, the organisms change. The stages an organism goes through are called its life cycle. You are an organism, too. You have gone through stages of change. And you will continue to change as you grow older.

生物(如植物或动物)的另一个词是有机体。 大多数生物从生命的开始到生命的结束都要经历几个阶段。 在每个阶段，生物体都会发生变化。 有机体所经历的阶段被称为生命周期。 你也是一个有机体。你已经经历了改变的阶段。 随着年龄的增长，你会继续改变。

Organisms of the same type go through the same stages of change. Humans, dogs, cows, and bears are all mammals. They all go through the same kinds of stages. Different types of animals, such as birds, frogs, and snakes, have different kinds of life cycles. They go through different stages of change. The life cycles of plants are different from the life cycles of animals. They go through stages of change, too. As you read this book, you will learn how the life cycles of these organisms are different.

同一类型的生物经历相同的变化阶段。 人、狗、牛和熊都是哺乳动物。 他们都经历了相同的阶段。 不同类型的动物，如鸟类、青蛙和蛇，有不同的生命周期。 他们经历了不同的变化阶段。 植物的生命周期不同于动物的生命周期。 他们也会经历变化的阶段。 当你阅读这本书时，你将了解到这些生物的生命周期是如何不同的。

Human Life Cycle Let's begin with a life cycle that is important to you— the human life cycle. The human life cycle begins with a tiny egg. This egg grows inside a mother organism. The egg soon becomes something called an embryo. After about two months, the human embryo begins to look like a human. It is still very small, but it has a head, arms, legs, and other body parts. For another seven months, the human organism develops inside its mother's body.

让我们从一个对你很重要的生命周期开始——人类的生命周期。 人类的生命周期始于一个小小的卵子。 这个卵生长在母体内。 卵子很快就变成了胚胎。 大约两个月后，人类胚胎开始长得像人。 它还很小，但它有头、胳膊、腿和其他身体部位。 在接下来的七个月里，人类有机体在母亲的体内发育。

After nine months inside its mother, the baby is born. This stage is called infancy, and the organism is called an infant. An infant needs its mother for everything. It cannot walk, talk, or feed itself. Word Wise Here are three prefixes that represent numbers. tri = 3 quad = 4 quint = 5 A mother may have more than one egg growing inside her at the same time. If two eggs are growing, twins will be born. Three eggs will produce triplets. Four eggs will produce quadruplets. And five eggs will produce quintuplets. Sometimes one egg splits into more than one embryo. When this happens, more than one baby is born.

在母体内待了九个月后，幼崽出生了。 这个阶段被称为婴儿期，有机体被称为婴儿。 婴儿做什么都需要母亲。 它不能走路，不能说话，也不能自己吃饭。 这里有三个代表数字的前缀。 tri = 3 quad = 4 quint = 5一位母亲可能同时有一个以上的卵子在她体内生长。 如果两个卵子在生长，双胞胎就会诞生。 三个鸡蛋会生三胞胎。 四个卵子将产生四胞胎。 五个卵子会生五胞胎。 有时一个卵子会分裂成多个胚胎。 当这种情况发生时，会有不止一个婴儿出生。

At about two years old, an infant enters a stage called childhood. Childhood lasts for about ten years. Then a child enters a stage called adolescence. In this stage, a person can start to make babies. A human is an adolescent until it is about 18 to 20 years old. Then the adolescent becomes an adult. Adulthood is the longest stage in the human life cycle. A human is an adult for the rest of his or her life. Do You Know? The oldest known human was a French woman who lived 122 years.

大约两岁时，婴儿进入一个叫做童年的阶段。 童年大约持续十年。 然后孩子进入一个叫做青春期的阶段。 在这个阶段，一个人可以开始生育。 一个人在18到20岁之前都是青少年。 然后，青少年变成了成年人。 成年期是人类生命周期中最长的阶段。 一个人的余生都是成年人。 你知道吗?已知最长寿的人类是一位法国妇女，她活了122岁。