THE LIVING WORLD

Unit One. The Study of Life

These Antarctic Gentoo penguins share many properties with you and all living things. Their bodies are made up of cells, just as yours is. They have families, with children that resemble their parents, just as your parents did. They grow by eating, as you do, although their diet is limited to fish and krill they catch in the cold Antarctic waters. The sky above them shields them from the sun’s harmful UV radiation, just as the sky above you shields you. Not in the summer, however. In the Antarctic summer an “ozone hole” appears, depleting the ozone above these penguins and exposing them to the danger of UV radiation. Scientists are analyzing this situation by a process of observation and experimentation, rejecting ideas that do not match their data. Proceeding in this way they are learning more and more about what is going on. The study of biology is a matter of observing carefully and asking the right questions. When a possible answer—what a scientist calls a hypothesis—was proposed, that destruction of Antarctic ozone is the result of leakage of industrial chemicals containing chlorine into the world’s atmosphere, scientists carried out experiments and further observations in an attempt to prove this hypothesis wrong. Nothing they have learned so far leads them to reject the hypothesis. It appears human activities far to the north are having a serious impact on the environment of these penguins. This chapter begins your study of biology, the science of life, of penguins and people. Its study helps us to better understand ourselves, our world, and our impact on it.

1. The Science of Biology

1.1. The Diversity of Life

In its broadest sense, biology is the study of living things—the science of life. The living world is teeming with a breathtaking variety of creatures—whales, butterflies, mushrooms, and mosquitoes—all of which can be categorized into six groups, or kingdoms, of organisms. Representatives from each kingdom can be seen in figure 1.1. All organisms that are placed into a kingdom possess similar characteristics with all other organisms in that same kingdom and are very different from organisms in the other kingdoms.

Biologists study the diversity of life in many different ways. They live with gorillas, collect fossils, and listen to whales. They isolate bacteria, grow mushrooms, and examine the structure of fruit flies. They read the messages encoded in the long molecules of heredity and count how many times a hummingbird’s wings beat each second. In the midst of all this diversity, it is easy to lose sight of the key lesson of biology, which is that all living things have much in common.

Archaea. This kingdom of prokaryotes (the simplest of cells that do not have nuclei) includes this methanogen, which manufactures methane as a result of its metabolic activity.

Bacteria. This group is the second of the two prokaryotic kingdoms. Shown here are purple sulfur bacteria, which are able to convert light energy into chemical energy.

Protista. Most of the unicellular eukaryotes (those whose cells contain a nucleus) are grouped into this kingdom, and so are the multicellular algae pictured here.

Fungi. This kingdom contains nonphotosynthetic organisms, mostly multicellular, that digest their food externally, such as these mushrooms.

Plantae. This kingdom contains photosynthetic multicellular organisms that are terrestrial, such as the flowering plant pictured here.

Animalia. Organisms in this kingdom are nonphotosynthetic multicellular organisms that digest their food internally, such as this ram.

Figure 1.1. The six kingdoms of life.

Biologists assign all living things to six major categories called kingdoms. Each kingdom is profoundly different from the others.

Key Learning Outcome 1.1. The living world is very diverse, but all things share many key properties.