25 Inside Living Things-Low

INSIDE LIVING THINGS Written by Ron Fridell

《生物内部》作者:罗恩·弗里德尔

Introduction Suppose you had special vision that let you look deep inside living things. What would you learn? What might you discover deep inside a rose? Or an elephant? Or a human being like yourself? This book will explore these questions by looking deep inside living things.

假设你有一种特殊的视力，可以看到生物的内部深处。 你会学到什么?你会在玫瑰的深处发现什么? 还是一头大象?还是像你这样的人类? 这本书将通过深入观察生物的内部来探讨这些问题。

Cells All living things are made of cells. Cells are the smallest units of life. They make the energy that living things need in order to grow and function. Some living things have only one cell. Algae, diatoms, and protozoa are organisms that have only one cell. All of the tasks that each organism needs in order to live are carried on in its cell. Organisms with one cell are found in many places, such as ponds and soil. Some are even found inside the bodies of other living things. Other organisms have many cells. All of the cells work together so the organism can live. Most of the time, the bigger the organism the more cells it has. For example, a huge whale has trillions of cells.

所有生物都是由细胞组成的。 细胞是生命的最小单位。 它们制造生物生长和运作所需的能量。 有些生物只有一个细胞。 藻类、硅藻和原生动物都是只有一个细胞的生物。 每个生物体为了生存所需要的所有任务都在它的细胞中进行。 只有一个细胞的生物可以在很多地方发现，比如池塘和土壤。 有些甚至在其他生物的体内被发现。 其他生物有许多细胞。 所有的细胞共同工作，生物体才能生存。 大多数时候，有机体越大，它的细胞就越多。 例如，一只巨大的鲸鱼有数万亿个细胞。

There are two basic types of cells: plant cells and animal cells. Let's look at an animal cell It has an outer covering called the cell membrane. This membrane is like a filter. It allows certain things to pass into and out of the cell. Things needed by the cell are allowed to enter the cell. Waste is allowed to exit. Inside the cell membrane is a jellylike fluid called cytoplasm. Other cell parts float in the cytoplasm One important part is the nucleus. The nucleus is like the cell's brain. It runs all the cell's activities.

细胞有两种基本类型:植物细胞和动物细胞。 让我们来看一个动物细胞，它有一层叫做细胞膜的外层。 这层膜就像一个过滤器。 它允许某些物质进出细胞。 细胞需要的东西被允许进入细胞。 废物被允许排出。细胞膜内部是一种叫做细胞质的胶状液体。 细胞的其他部分漂浮在细胞质中细胞核是一个重要的部分。 细胞核就像细胞的大脑。 它负责细胞的所有活动。

In many ways, plant cells are like animal cells. Both have a cell membrane, a nucleus, and cytoplasm. But they also have some parts that are different. A plant cell has a cell wall. It surrounds the cell membrane. The cell wall supports the cell. Animal cells do not have cell walls. All cells turn food into energy the cell can use. Mitochondria are the parts of a cell that have this job. Most cells also have structures called vacuoles. These structures store food and water until the cell needs them. They also hold waste until it can be removed from the cell. PLANT CELLS: FOOD AND STORAGE Animals have to eat food in order to live. Plants can make their own food, though. Plant cells have a special material called chlorophyll. The chlorophyll traps energy from sunlight. This energy is used with other materials from air and water to make food. This method of making food is called photosynthesis. Animal cells do not have chlorophyll.

在很多方面，植物细胞和动物细胞很像。 两者都有细胞膜、细胞核和细胞质。 但它们也有一些不同之处。 植物细胞有细胞壁。 它包围着细胞膜。 细胞壁支撑着细胞。 动物细胞没有细胞壁。 所有细胞都将食物转化为细胞可利用的能量。 线粒体是细胞中负责这项工作的部分。 大多数细胞也有液泡结构。 这些结构储存食物和水，直到细胞需要它们。 它们还可以保存废物，直到可以从细胞中清除。 植物细胞:食物和贮藏动物为了生存必须吃东西。 不过，植物可以自己制造食物。 植物细胞有一种叫做叶绿素的特殊物质。 叶绿素从阳光中吸收能量。 这种能量与空气和水中的其他物质一起用来制造食物。 这种制造食物的方法叫做光合作用。 动物细胞不含叶绿素。

Different Kinds of Cells Not all cells are alike. An organism's cells are different, depending on what they do. Let's take a look at some cells found in animals. Most animals have many parts that work together. Each part is made up of different kinds of cells. Muscles have muscle cells. Blood has blood cells. Even nerves have cells. There are hundreds of types of cells All types of cells must work together to keep an animal alive and healthy. Do You Know? Scientists think there are about 75 trillion (75,000,000,000,000) cells in the human body. But the number keeps changing. Cells are always growing and being replaced. These cells are very small. It would take ten thousand (10,000) cells just to cover the head of a pin.

不同种类的细胞并非所有的细胞都是一样的。 生物体的细胞是不同的，这取决于它们的功能。 让我们来看看在动物身上发现的一些细胞。 大多数动物有许多部分共同工作。 每个部分都由不同种类的细胞组成。 肌肉有肌肉细胞。 血液中有血细胞。甚至神经也有细胞。 所有类型的细胞必须共同工作，以保持动物的生存和健康。 你知道吗?科学家认为人体内大约有75万亿个(75,000,000,000,000)细胞。 但这个数字一直在变化。 细胞总是在生长和被替换。 这些细胞非常小。 光是覆盖一根针尖就需要一万个细胞。