Chapter 1 Biology

Life on Earth takes on a staggering variety of forms, often with appearances and behaviors that may be strange to humans. As we will see in this chapter, one of the ways that biologists classify life is by species. So how many species are there on the planet? The truth is, we really don’t know. Recent estimates suggest that there may be around 8.7 million species on the planet, but many scientists believe that number is probably much higher, especially when the bacteria are factored in. So far, less than 2 million species have been identified, and most of those are insects.

As we will learn in this chapter, although life is diverse, it also shares a number of important characteristics.

As you read through this chapter, think about the following questions:

1. What are the general characteristics that separate living organisms from nonliving things?

2. How do species fit into the biological levels of organization?

3. What are some of the challenges facing science today?

1.1 What is Biology?

 

  Biology is the study of life in all of its diverse forms. Alongside physicsand chemistry, biology is one of the largest and most important branches ofscience. At the highest level, biology is broken down based on the type of organism being studied: zoology, the study of animals; botany, of plants; and microbiology, of microorganisms. Each field has contributed to mankindor the Earth’s well-being in numerous ways. Most prominently:botany, to agriculture; zoology, to livestock and protection of ecologies; and microbiology, to the study of disease and ecosystemsin general.

    The foundations of modern biology include four components: cell theory; that life is made of fundamental unitscalled cells; evolution, that life is not deliberately designedby rather evolves incrementally through random mutations and natural selection; genetheory, that tiny molecular sequences of DNA dictate the entire structure ofan organism and are passed from parents to offspring; and homeostasis, that each organism’s body includes acomplex suite of processes designed to preserve its biochemistry from the entropic effects of the external environment.

    The basic picture in biology has stayed roughly the same since DNA was first imagedusing x-ray crystallography in the 1950s, although there areconstant refinements to the details, and life is so complex that it could becenturies or even millennia before we begin to understand it in its entirety.But it should be made clear that we are moving towards complete understanding:life, while complex, consists of a finite amount of complexity that onlyappreciably increases on relatively long timescales of hundreds of thousands ormillions of years. Evolution, while creative, operates slowly.

biology [bai'ɔlədʒi] n. 生物学

organism ['ɔ:gənizəm] n. 生物体

zoology [zəu'ɔlədʒi] n. 动物学

botany ['bɔtəni] n. 植物学

microbiology [maikrəubai'ɔlədʒi] n. 微生物学

microorganism [maikrəu'ɔ:gənizəm] n. 微生物

well-being ['wel'bi:iŋ]n. 健康，福利

agriculture ['ægrikʌltʃə]n. 农业

livestock ['laivstɔk]n. 家畜，牲畜

ecology [i:‘kɔlədʒi] n. 生态学

disease [di'zi:z] n. 疾病

ecosystem ['ekəusistəm]n. 生态系统

classification [klæsifi'keiʃən] n. 分类，类别

biochemistry ['baiəu'kemistri] n. 生物化学

molecular biology 分子生物学

molecular level 分子水平

cellular biology 细胞生物学

physiology [fizi'ɔlədʒi]n. 生理学

tissue ['tisju:]n.（生物的）组织

organ ['ɔ:gən]n.（生物的）器官

interaction [intə'rækʃən]n. 相互关系，相互作用

ethology [i:'θɔlədʒi] n. 动物行为学

genetics [dʒi'netiks] n. 遗传学

overlap ['əuvə'læp] n. 重叠，重复

code [kəud] n. 密码，法则

cell theory n. 细胞理论

evolution [i:və'lu:ʃən] n. 进化

random mutation 随即突变

natural selection 自然选择

gene theory 基因理论

molecular sequence 分子序列

parent ['pɛərənt] n. 亲本，母本

offspring ['ɔ:fspriŋ]n. 后代，子孙

homeostasis [həumiə'steisis] n. 自动平衡，体内平衡

entropic effect 熵效应

1.4 Additional Reading

Biologists study not only lifes diversity but also the characteristics that are shared by all living organisms. These characteristics include levels of organization, the ability to acquire materials and energy, the ability to maintain an internal environment, the ability to respond to stimuli, the ability to reproduce and develop, and the ability to adapt and evolve to changing conditions. By studying these characteristics, we gain insight into the complex nature of life, which helps us distinguish living organisms from nonliving things. 

The complex organization of life begins with atoms, the basic units of matter. Atoms combine to form small molecules, which join to form larger molecules within a cell, the smallest, most basic unit of life. Although a cell is alive, it is made from nonliving molecules. The majority of the organisms on the planet, such as the bacteria and most protists, are single-celled. Plants, fungi, and animals are multicellular organisms and are therefore composed of many types of cells, which often combine to form tissues. Tissues make up organs, as when various tissues combine to form a heart or a leaf. Organs work together in organ systems; for example, the heart and blood vessels form the cardiovascular system. Various organ systems work together within complex organisms. 

The organization of life extends beyond the individual organism. 

A species is a group of similar organisms that are capable of interbreeding. All of the members of a species within a particular area belong to a population. When populations interact, such as the humans, zebras, and trees, they form a community. At the ecosystem level, communities interact with the physical environment (soil, atmosphere, etc.). Collectively, the ecosystems on the planet are called the biosphere, the zone of air, land, and water at the surface of the Earth where living organisms are found. 

Life Requires Materials and Energy 

Life from single cells to complex organisms cannot maintain organization or carry on necessary activities without an outside source of materials and energy. Food provides nutrient molecules, which are used as building blocks or energy sources. Energy is the capacity to do work, and it takes work to maintain the organization of the cell and the organism. When cells use nutrient molecules to make their parts and products, they carry out a sequence of chemical reactions. The term metabolism encompasses all the chemical reactions that occur in a cell.