Introduction to Life

Introduction to Life

DOI: 10.4018/978-1-5225-8066-9.ch001
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This chapter introduces what life is and what characterises it, discusses its diversity, then introduces the theory of evolution. It ends with a section discussing how scientists investigate research problems called the “Process of Science.” Living organisms share very defined characteristics—the sum of which make the “wholeness” we call life. Carl Linnaeus proposed a binomial system of classification where each organism's scientific name has two distinct parts: the genus and the species. Charles Darwin formulated the theory of natural selection which explains how evolution works. Humans share a lot in common with other living organisms, but there are features that make us distinctly human not shared with any other living organisms. The practice of science uses a carefully formulated series of steps in investigating problems. Science cannot explain everything especially philosophical questions that involve issues of right and wrong.
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Chapter Outline

  • 1.1 Defining Life

  • 1.2 Life’s Defining Characteristics

  • 1.3 Life’s Diversity on Earth

  • 1.4 Charles Darwin and Theory of Natural Selection

  • 1.5 The Human Condition

  • 1.6 How Science Works

  • 1.7 Could Science explain Everything?

  • Chapter Summary


Learning Outcomes

  • Understand how life is defined

  • Classify life in its various diverse forms

  • Explain the theory of natural selection and diversity of life on Earth

  • Summarize the features that make us human

  • Demonstrate how the process of science works

  • Understand that science cannot explain everything


1.2 Life’S Defining Characteristics

This section discusses the characteristics that collectively define what biologists consider living.


All living organisms are organized in units as simple as cells (like bacteria) to complex multi-cellular organisms with trillions of cells (like humans). Biologists do not consider anything below a cell living as in the case of viruses. Cells function as units with very well-defined order and an enclosing boundary (cell membrane), genetic material, and an aqueous solution made up of sugars, ions, salts, amino acids, and water. Some of the earliest known forms of life are single cells—which have remained that way as life evolved over millions of years to more complex life forms we see today.

In multi-cellular organisms, cells organize together to form tissues (as in skin tissue), which in turn form organs (as in heart); organs work together in organ-systems; and systems make a whole functioning individual organism (as in a wolf). (Figure 1)

Figure 1.

Levels of biological organization (simplest levels to the biosphere)

Source: Image used under license from

Key Terms in this Chapter

Interdependency: Organisms that rely on resources in their environment to survive.

Utilization of Energy: The ability of organisms to consume and transform energy into work.

Complex Organization: Levels of organization classified from the simplest living organisms to the most complex organisms.

Life: A combination of characteristics of an organism that consist of homeostasis, organization, metabolism, growth, response to stimuli, adaptation, and reproduction.

Hypothesis: An assumption or a possible explanation that can later be scientifically tested.

Kingdoms: The second highest taxonomy under Domain, that classifies and separates the following into smaller groups called phyla: Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

Growth: The developmental process by which an organism matures or increases in size.

Scientific Process: The hypothetical-deductive stepwise procedure used in science to make inquiries, formulate hypothesis, design experiments, collect and analyze data, and make conclusions.

Natural Selection: The process that favors the survival and reproductive success of organisms that are best adjusted to the environment.

Prokaryotes: Single-celled organisms that lack membrane-bound organelles.

Reproduction: The ability of organisms to produce offspring.

Development: The process of growing and become more mature or advanced.

Eukaryotes: Multicellular or unicellular organisms with membrane bound organelles.

Domains: A taxonomy that classifies three different cellular life forms; Archaea, Bacteria and Eukarya.

Response to Stimuli: The ability of a living organism to detect a stimulus and respond accordingly.

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