章节大纲

  • 常规

    全部折叠 展开全部

  • 生命的特征

    What you will learn
    ::你会学到什么

    • What are the characteristics of living things
      ::生活事物的特征是什么?

    Various stylized bacteria in a blue color scheme, illustrating characteristics of life.
    A cartoon frog illustrating the concept of life characteristics in a lesson.

    What do a bacterium and a frog have in common?
    ::细菌和青蛙有什么共同点?

    Do they share characteristics with us? All living organisms , including the smallest and a frog , share certain characteristics of life. Without these characteristics, there is no life.
    ::它们是否与我们具有相同的特征?所有生物体,包括最小的生物体和青蛙,都具有生命的某些特征。没有这些特征,就没有生命。

    Characteristics of Life
    ::生命的特征

    Look at the duck decoy in the Figure . It looks very similar to a real duck. Of course, real ducks are living things. What about the decoy duck? It looks like a duck, but it is actually made of wood. The decoy duck doesn’t have all the characteristics of a living thing. What characteristics set the real ducks apart from the decoy duck? What are the characteristics of living things?
    ::看看图中的鸭子诱饵。它看起来与真正的鸭子非常相似。当然,真正的鸭子是活的。真的鸭子是活的。关于诱饵鸭呢?它看起来像鸭子吗?它看起来像鸭子,但实际上是木制的。诱饵鸭并不具有活的事物的所有特性。什么特性将真正的鸭子与诱饵鸭分开?活鸭子的特性是什么?

    A duck decoy resembling a real duck, placed near plants on a wooden surface.
    This duck decoy looks like it’s alive. It even fools real ducks. Why isn’t it a living thing?

    Not all scientists agree exactly about what makes up life. Many characteristics describe most living things. However, with most of the characteristics listed below, we can think of one or more examples that would seem to break the rule, with something non-living being classified as living or something living being classified as non-living. There is not just one distinguishing feature that separates a living thing from a non-living thing. A cat moves but so does a car. A tree grows bigger, but so does a cloud. A has structure, but so does a crystal. Biologists define life by listing characteristics that living things share. Something that has all of the characteristics of life is considered to be alive.
    ::并非所有科学家都同意生命的构成。 许多特征描述着大多数生物。 然而,根据下面列出的大多数特征,我们可以想象出一个或几个似乎打破了规则的例子,一些非生物被归类为生活,或者某些生活被归类为非生活。有生命的东西被归类为生活。一个有生命的东西与非生活的东西区别开来,猫动起来,汽车也动起来。一棵树变大了,但云也变大了。一个有结构,但水晶也变了。生物学家通过列出生物共有的特征来定义生命。有生命所有特征的东西被认为是活的。

    There are many characteristics that living organisms share. All living organisms:
    ::生物体有许多共同特征。

    • Respond to their environment.
      ::回应他们的环境。
    • Grow and develop.
      ::成长和发展。
    • Produce offspring.
      ::生儿育女
    • Maintain .
      ::维持.
    • Have complex chemistry.
      ::具有复杂的化学成分。
    • Consist of cells.
      ::细胞的合体。

    Response to the Environment
    ::对环境的反应

    All living things detect changes in their environment and respond to them. What happens if you step on a rock? Nothing; the rock doesn’t respond because it isn’t alive. But what if you think you are stepping on a rock and actually step on a turtle shell? The turtle is likely to respond by moving—it may even snap at you!
    ::所有生物都检测到环境的变化并作出反应。如果你踩到岩石,会发生什么情况?没有;岩石没有反应是因为它不是活的。 但如果你觉得自己踩在岩石上,实际上踩在龟壳上,又会怎样? 乌龟可能会通过移动作出反应,甚至会崩溃!

    Bacteria moving towards sugar crystals, illustrating attraction to nutrients.
    Most bacteria are attracted to sugar crystals.
    A frog jumps away from a large red shoe, illustrating reactive behavior.
    If you step close to a frog it will likely jump away quickly.

    Growth and Development
    ::增长与发展

    All living things grow and develop. For example, a plant seed may look like a lifeless pebble, but under the right conditions, it will grow and develop into a plant. Bacteria grow by increasing in cell size and volume. also grow and develop. How will the tadpoles change as they grow and develop into adult frogs?
    ::所有生物的生长和发育。例如,植物种子可能看起来像没有生命的卵石,但是在适当的条件下,它会生长并发展成植物。细菌会通过细胞大小和体积的增加而生长,也会生长和发展。当它们成长和成长成成年青蛙时,它会如何变化呢?

    The Transformation From Tadpole In Water To Adult Frog On Land.
    Tadpoles go through many changes to become adult frogs.
    DID YOU KNOW?
    If iodine is absent in , a tadpole cannot grow and develop into a frog. 
     

    Reproduction
    ::复制复制

    All living things are capable of . Reproduction is the process by which living things give rise to offspring. Reproducing may be as simple as a single cell dividing to form two daughter cells . Generally, however, it is much more complicated. Nonetheless, whether a living thing is a frog or a microscopic bacterium, it is capable of reproduction.
    ::所有生物都有能力 。 繁殖是生命产生后代的过程。 繁殖可能像单细胞一样简单, 形成两个女儿细胞。 但是,一般来说, 更复杂得多。 然而, 活物是青蛙还是微生物, 它能够繁殖。

    There are two types of reproduction, asexual and . Sexual reproduction is a type of reproduction that involves two parents and produces genetically different offspring. is a type of reproduction that involves a single parent and results in offspring that are all genetically identical to the parent. For example, bacteria reproduce by asexual reproduction creating an exact copy of themselves.
    ::性生殖是两种生殖方式,一种是非性生殖方式,一种是生殖方式,涉及双亲,产生遗传上不同的后代。 性生殖是一种生殖方式,涉及单亲家庭,产生与父母在遗传上完全相同的后代。 例如,通过性生殖方式复制细菌,可以产生准确的自我复制。

    Binary fission in bacteria, showing cell division into two identical cells.
    Binary fission is a type of asexual reproduction in bacteria.

    Keeping Things Constant
    ::使情况保持稳定

    All living things are able to maintain a more-or-less constant internal environment. They keep things relatively stable on the inside regardless of the conditions around them. The process of maintaining a stable internal environment is called homeostasis . Human beings, for example, maintain a stable internal body temperature. If you go outside when the air temperature is below freezing, your body doesn’t freeze. Instead, by shivering and other means, it maintains a stable internal temperature. Some of tree frogs adjust their skin color as temperature changes in their environment.
    ::所有生物都能够维持一个或多或少的不变内部环境。 它们使内部环境相对稳定,不管周围环境如何。 维持一个稳定的内部环境的过程被称为家庭保持状态。 例如,人类保持一个稳定的内部体温。 如果你在空气温度低于冰冻水平时外出,身体不会冻僵。 相反,通过颤抖和其他手段,它保持一个稳定的内部温度。 一些树蛙在环境温度变化时调整其皮肤颜色。

     

    Complex Chemistry
    ::复杂化学

    All living things—even the simplest life forms—have complex chemistry. Living things consist of large, complex molecules, and they also undergo many complicated chemical changes to stay alive. Thousands (or more) of these chemical reactions occur in each cell at any given moment. Metabolism is the accumulated total of all the occurring in a cell or organism.  All living things need a continuous input source of energy to sustain life processes. Complex chemistry is needed to carry out all the functions of life.
    ::所有生物——即使是最简单的生命形式——都有复杂的化学成分。生命物质由大型、复杂的分子组成,它们还要经历许多复杂的化学变化才能生存下去。这些化学反应中成千上万(或更多)在任何特定时刻发生在每个细胞中。代谢是细胞或生物体中发生的所有事件的累积总量。所有生物都需要不断投入的能量来维持生命过程。复杂的化学成分是完成生命的所有功能所必需的。

    Frog catching a mosquito, illustrating metabolism and energy transformation in living organisms.
    Living organisms consume food to transform it into energy to stay alive.

    Cells
    ::单元格单元格

    All forms of life are built of at least one cell. A cell is the basic unit of the structure and function of living things. Living things may appear very different from one another on the outside, but their cells are very similar. Compare illustrations of the frog cells on the left and bacteria cells on the right in Figure . How are they similar?
    ::各种生命形式都是由至少一个细胞组成的。 细胞是生命结构和功能的基本单位。 生活的东西在外表上可能显得非常不同, 但是它们的细胞非常相似。 比较图中左边的青蛙细胞和右边的细菌细胞。 它们如何相似 ?

    If you zoom in very close on a leaf of a plant, or on the skin on your hand, or a drop of , you will find cells. Most cells are so small that they are usually visible only through a . Some organisms, like bacteria, plankton that live in the ocean, or paramecium, are unicellular, made of just one cell. Other organisms have millions, billions, or trillions of cells.
    ::如果你非常接近植物的叶子,或手上的皮肤,或一滴细胞,你会发现细胞。大多数细胞太小,通常只能通过一个可以看见。有些生物,如细菌、海洋中的浮游生物或,是由一个细胞组成的,没有蛋白质。其他生物有数以百万计、数十亿计或数万亿个细胞。

    Comparison of frog cells on the left and bacteria cells on the right.
    Frog Cells (left) and Bacteria Cells (right).
    DID YOU KNOW?
    A is a non-living thing. A virus is essentially or surrounded by a coat of . It is not made of cells, cannot reproduce on its own, and cannot maintain a stable internal environment. 
     

     

     

     

    Summary
    ::摘要

    • All living things detect changes in their environment and respond to them.
      ::所有生物都检测到环境的变化并作出反应。
    • All living things grow and develop.
      ::所有生物的生长和发育。
    • All living things are capable of reproduction, the process by which living things give rise to offspring.
      ::所有生物都能够繁殖, 生命产生后代的过程。
    • All living things are able to maintain a constant internal environment through homeostasis.
      ::所有生物都能够通过自成一体维持一个稳定的内部环境。
    • All living things have complex chemistry.
      ::所有生物都有复杂的化学成分
    • All forms of life are built of cells. A cell is the basic unit of the structure and function of living things.
      ::所有形式的生命都是由细胞构成的,细胞是生命结构和功能的基本单位。

    Review
    ::回顾

    1. List the characteristics of life.
      ::列出生活的特点。
    2. Define homeostasis.
      ::定义常态。
    3. What is a cell?
      ::什么是细胞?
    4. Making the next generation is known as ____________.
      ::下一代被称为... 。
    5. Assume that you found an object that looks like a dead twig. You wonder if it might be a stick insect. How could you determine if it is a living thing?
      ::假设你发现了一个看起来像死树枝的物体。你不知道它是不是一只树枝昆虫。你怎么知道它是不是活的?