Chapter 1 Summary

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Core Concepts Summary

1.1 The scientific method is a deliberate way of asking and answering questions about the natural world.

Observations are used to generate a hypothesis, a tentative explanation that makes predictions that can be tested. page 4

On the basis of a hypothesis, scientists design experiments and make additional observations that test the hypothesis. page 5

A controlled experiment typically involves several groups in which all the conditions are the same and one group where a variable is deliberately introduced in order to determine if that variable has an effect. page 5

If a hypothesis is supported through continued observation and experiments over long periods of time, it is elevated to a theory, a sound and broad explanation of some aspect of the world. page 6

1.2 Life works according to fundamental principles of chemistry and physics.

The living and nonliving worlds follow the same chemical rules and obey the same physical laws. page 8

Experiments by Redi in the 1600s and Pasteur in the 1800s demonstrated that organisms come from other organisms and are not spontaneously generated. page 10

Life originated on Earth about 4 billion years ago, arising from nonliving matter. page 11

1.3 The fundamental unit of life is the cell.

The cell is the simplest biological entity that can exist independently. page 12

Information in a cell is stored in the form of the nucleic acid DNA. page 12

The central dogma describes the usual flow of information in a cell, from DNA to RNA to protein. page 13

The plasma membrane is the boundary that separates the cell from its environment. page 14

Cells with a nucleus are eukaryotes; cells without a nucleus are prokaryotes. page 14

Metabolism is the set of chemical reactions in cells that build and break down macromolecules and harness energy. page 14

A virus is an infectious agent composed of a genome and protein coat that uses a host cell to replicate. page 15

1.4 Evolution explains the features that organisms share and those that set them apart.

When there is variation within a population of organisms, and when that variation can be inherited, the variants best able to grow and reproduce in a particular environment will contribute disproportionately to the next generation, leading to a change in the population over time, or evolution. page 15

Variation can be genetic or environmental. The ultimate source of genetic variation is mutation. page 16

Organisms show a nested pattern of similarity, with humans more similar to primates than other organisms, primates more similar to mammals, mammals more similar to vertebrates, and so on. page 16

Evolution can be demonstrated by laboratory experiments. page 18

1.5 Organisms interact with one another and with their physical environment, shaping ecological systems that sustain life.

Ecology is the study of how organisms interact with one another and with their physical environment in nature. page 19

These interactions are driven in part by the anatomy, physiology, and behavior of organisms, that is, the basic features of organisms shaped by evolution. page 19

1.6 In the 21st century, humans have become major agents in ecology and evolution.

Humans have existed for only the most recent 1/200 of 1% of life’s 4-billion-year history. page 20

In spite of our recent arrival, our growing numbers are leaving a large ecological and evolutionary footprint. page 21

Solving biological problems requires an integrated understanding of life, with contributions from all the fields of biology, including molecular biology, cell biology, genetics, organismal biology, and ecology, as well as from chemistry, physics, and engineering. page 22

Self-Assessment

  1. Name and summarize the steps in the scientific method.

    Self-Assessment 1 Answer

    The steps of the scientific method consist of Observation, Hypothesis, Prediction, Experiment, and Theory. The first step is observation. An observation is a phenomenon that you see occurring in the world around you. It allows you to ask a pointed question about a particular aspect of nature. The second step is formulating a hypothesis to suggest tentative answer to that question. The third step in the scientific method is to make a prediction. A prediction allows the hypothesis to be tested experimentally and can often be answered by yes or no. To test the prediction, and ultimately, the hypothesis, you need to run experiments or make new observations. This fourth step of the scientific method is an important one because a hypothesis can be rejected or supported at this point. If the original hypothesis is rejected based on your experiments or new observations, a new hypothesis can be formulated that would then be tested. A test result or observation that supports the initial hypothesis makes the hypothesis less tentative and more certain. When a hypothesis is supported again and again over time, through experiments and observations, it will usually be regarded as an acceptable explanation for what we initially observed. At this point, the hypothesis becomes a theory. For example, the theory of evolution has been tested for more than a century and shown to be a supported explanation of many biological observations.

  2. Differentiate among a guess, a hypothesis, and a theory.

    Self-Assessment 2 Answer

    A guess is just that. It does not make predictions as to why an observation or event is happening, nor can it be tested to prove that it is right or wrong. A hypothesis is an explanation of that observation or event that predicts the results of experiments or new observations that will be tested. A theory is a broad explanation that accounts for a number of related hypotheses that have been repeatedly supported through vigorous testing, often over a long period of time.

  3. Describe the difference between a test group and a control group, and explain why they are important.

    Self-Assessment 3 Answer

    In a controlled experiment, there are several groups to be tested, keeping the conditions as similar as possible from one group to the next. In each of the test groups, the researcher introduces a single variable that he or she hypothesizes might have an effect. In the control group, no variable is introduced and the expectation is that no effect will occur. The test and control groups are both important because, together, they allow the researcher to determine if the variable has an effect.

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  4. State the first and second laws of thermodynamics and describe how they apply to living organisms.

    Self-Assessment 4 Answer

    See Figs. 1.6 and 1.7. The first law of thermodynamics states that energy can neither be created nor destroyed; it can only be transformed from one form into another. Living organisms transform energy from the environment into chemical energy that cells can utilize. To convert this energy, the cell expends energy and gives off heat as a by-product. The total amount of energy before and after this energy transformation is the same. The second law of thermodynamics states that the degree of disorder in the universe tends to increase. The amount of disorder in a system is called the entropy of the system. Living organisms are highly organized and thus need a lot of energy to remain this way. This observation does not violate the second law, however, because the cell gives off energy as heat, which causes small molecules in the environment to move more. This increase in movement increases the disorder or entropy of the entire system, thus satisfying the second law of thermodynamics.

  5. Describe what it means to say that a cell is life’s functional unit.

    Self-Assessment 5 Answer

    A cell is the simplest entity that can exist as an independent unit of life. While many organisms familiar to us are multicellular (made up of many cells; e.g., humans), life can take on a single-celled form as well. All cells have a discrete boundary that separates their interior from the external environment, and they also all have the ability to harness materials and energy from that environment.

  6. Describe the experimental evidence that demonstrates that living organisms come from other living organisms.

    Self-Assessment 6 Answer

    See Figs. 1.8 and 1.9. Experiments done by Francesco Redi and Louis Pasteur tested the hypothesis that organisms arise from other organisms. Through eloquently designed experiments, the scientists were able to show that flies and bacteria arose from other flies and bacteria, respectively. By following the scientific method, these scientists were able to disprove the hypothesis that organisms arise spontaneously.

  7. Explain how evolution accounts for both the unity and the diversity of life.

    Self-Assessment 7 Answer

    An example of how evolution is responsible for both the unity and diversity of life can be found in our own evolution. Using genetic information, scientists can relate one species to another, often elucidating information concerning the evolutionary timeline and the divergence of these species from a common ancestor. An example of this unity is found in Fig. 1.17 “The tree of life.” Evolution can also account for the diversity of life. Take a look around you. All the people you see are Homo sapiens (or humans) yet no two, without exception, look exactly the same. These differences arise from the genetic differences that exist from one person’s genome to another. Over time, these differences are established in particular groups (e.g., each member of a family having dark curly hair) and can be used to differentiate between organisms of the same species. Diversity can also be seen in the variety of species around you, all related somehow but yet all different.

  8. Name and describe several features that determine the shape of ecological systems.

    Self-Assessment 8 Answer

    Ecological systems include both the nonliving environment and the organisms that make them up. The features of these organisms, including their structure (anatomy), function (physiology), and behavior, therefore help to shape ecological systems. Often it is not only the features of one species, but the features of many that lead to a diverse ecological system.

  9. Name three ways that humans have affected life on Earth.

    Self-Assessment 9 Answer

    Humans have expanded the populations of certain organisms, many of which are related to the food supply (e.g., corn, yeast, lactose-fermenting bacteria, grapes, apples). Conversely, humans have also reduced populations of other organisms, sometimes to extinction, through hunting and habitat destruction (e.g., dodo birds, white rhinoceros, Bali tiger). Our ever-expanding population and technological abilities have significantly impacted the amounts and types of gases that enter the Earth’s atmosphere. The identification and harnessing of the powerful antibiotics have both benefited (treating once deadly infections) and harmed (evolution of antibiotic-resistant bacterial strains) the human race.

  10. Summarize the six themes that are discussed in this chapter.

    Self-Assessment 10 Answer

    (1) The scientific method is a deliberate way of asking and answering questions about the natural world. Much of what we know and believe today is due to the process of the scientific method. This method is used to inquire about and determine what is happening in the world around us.

    (2) Life works according to fundamental principles of chemistry and physics. Energy is what drives life. The basic rules of energy conservation are observed by every living organism.

    (3) The fundamental unit of life is the cell. All living organisms are made up of at least one cell, thus making the cell the simplest biological entity that can exist independently.

    (4) Both the features that organisms share and those that set them apart are explained by evolution. Evolution is the process by which certain traits are selected for via pressures in the environment. These traits can at once relate the organism to one species and distance it from another. The tree of life is a good representation of how evolution is both unifying and diversifying.

    (5) Organisms interact with one another and with their physical environment, shaping ecological systems that sustain life. An ecological system is typically made up of more than one species. There is a web of behavioral and physical interactions that help support each species in an ecological system.

    (6) In the twenty-first century, humans have become major agents in ecology and evolution. The actions of humans can be felt in almost every facet of life, positively or negatively. Whether it is curing a disease affecting cattle or driving a species into extinction, humans play, and have played, an important role in the development of life as we know it today.