27 Inside Living Things-High

Inside Living Things Written by Ron Fridell

《生物内部》作者:Ron Fridell

Introduction Suppose you had microscopic X-ray vision, and you took a deep look inside living things. What would you learn? What would you discover deep inside a rose, for example? Or an elephant? Or a human being like yourself? This book will explore these questions by looking deep inside living things.

假设你有显微镜下的x光视力，你可以深入观察生物内部。 你会学到什么?例如，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 Living things share one basic characteristic: They are all made of cells. Cells are the smallest units of life. They produce the energy that makes living things grow and function. Some living things have only a single cell. Called unicellular organisms, they include tiny algae, diatoms, and protozoa. Each of these single-celled organisms carries on all the activities it needs for survival within its single cell. These organisms live in a wide range of places, including ponds, rivers, soil, and even inside the bodies of other living things. Other organisms large and small, from fleas and mosses to whales and giant redwoods, are multicellular organisms. They are made of trillions of cells that work together. The bigger the organism, the more cells it usually has.

生物有一个共同的基本特征:它们都是由细胞组成的。 细胞是生命的最小单位。 它们产生能量，使生物生长和运作。 有些生物只有一个细胞。 它们被称为单细胞生物，包括微小的藻类、硅藻和原生动物。 这些单细胞生物中的每一个都在其单细胞内进行生存所需的所有活动。 这些生物生活在广泛的地方，包括池塘、河流、土壤，甚至在其他生物的体内。 其他大大小小的生物，从跳蚤、苔藓到鲸鱼和巨大的红杉，都是多细胞生物。 它们是由数万亿个共同工作的细胞组成的。 生物体越大，通常拥有的细胞就越多。

There are two basic types of cells: plant cells and animal cells. Let's look at a typical animal cell. The outer covering of an animal cell is called the cell membrane. The cell membrane is a sac with pores, or small openings. This membrane is like a filter. It allows some things to pass in and out of the cell. The cell membrane allows nutrients to enter the cell and waste 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 directs the cell's activities, much as your brain controls your activities.

细胞有两种基本类型:植物细胞和动物细胞。 让我们来看看一个典型的动物细胞。 动物细胞的外层被称为细胞膜。 细胞膜是一个有小孔或小开口的囊。 这层膜就像一个过滤器。 它允许一些物质进出细胞。 细胞膜允许营养物质进入细胞，废物排出。 细胞膜内部是一种叫做细胞质的胶状液体。 其他细胞部分漂浮在细胞质中。 其中一个重要的部分是细胞核。 细胞核指导细胞的活动，就像大脑控制你的活动一样。

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 typical plant cell has a cell wall, which surrounds the cell membrane and gives the cell support. Animal cells do not have cell walls. The support that a cell wall gives the plant cell is important because plants do not have a skeleton for support. All cells turn food into energy. Cells have hundreds or even thousands of mitochondria, which change energy into forms that the cells can use to do their jobs. Most cells also have several sac-like structures called vacuoles, which 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 to survive, but plants can make their own food. Plants store a special substance called chlorophyll in tiny structures called chloroplasts. Animal cells do not have chlorophyll or chloroplasts. A plant uses chlorophyll to make food from water and a gas in the air. The plant absorbs sunlight and uses the Sun's energy to make food from the water and air. This process is called photosynthesis.

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。 典型的植物细胞有一个细胞壁，它包围着细胞膜，为细胞提供支撑。 动物细胞没有细胞壁。 细胞壁对植物细胞的支持很重要，因为植物没有骨架来支撑。 所有细胞都把食物转化为能量。 细胞有数百甚至数千个线粒体，它们将能量转化为细胞可以利用的形式。 大多数细胞也有一些囊状结构，称为液泡，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:食物和储藏动物为了生存必须吃东西，但植物可以自己制造食物。 植物将一种叫做叶绿素的特殊物质储存在叫做叶绿体的微小结构中。 动物细胞没有叶绿素或叶绿体。 植物利用叶绿素从水和空气中的气体中制造食物。 植物吸收阳光，利用太阳的能量从水和空气中制造食物。 这个过程叫做光合作用。

Different Kinds of Cells Not all cells are alike. An organism's cells differ, depending on their function. To better understand how cells can differ, let's take a look at some kinds of cells found in mammals. Highly complex living things like mammals and reptiles have many parts that work together. Each part is made up of different kinds of cells. These animals have muscle cells, brain cells, nerve cells, blood cells, skin cells, and hundreds of other types of cells. All these cells must work together to keep the body growing and functioning. Do You Know? How many cells are in your body? There is no way to know the exact number. How could we count every single one? The number varies, depending on the size of the person, and the number is constantly changing. Every second you are losing cells, but your body is also manufacturing new ones. The best that scientists can do is estimate, and most say that the average human body contains about 75 trillion (75,000,000,000,000) cells. To get a better idea of how tiny a cell is, think about this. 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。 生物体的细胞因功能不同而不同。 为了更好地理解细胞是如何不同的，让我们来看看在哺乳动物中发现的一些类型的细胞。 高度复杂的生物，如哺乳动物和爬行动物，有许多部分共同工作。 每个部分都由不同种类的细胞组成。 这些动物有肌肉细胞、脑细胞、神经细胞、血细胞、皮肤细胞和数百种其他类型的细胞。 所有这些细胞必须共同工作，以保持身体的生长和功能。 你知道吗?你体内有多少细胞? 没有办法知道确切的数字。 我们怎么能数出每一个呢? 这个数字根据人的大小而变化，而且这个数字是不断变化的。 每一秒你都在失去细胞，但你的身体也在制造新的细胞。 科学家们所能做的最好的估计，大多数人说，平均人体含有大约75万亿个(75000,000,000,000)细胞。 为了更好地了解细胞有多小，想想这个。 光是覆盖一根针尖就需要一万个细胞。