Chapter 3 -- Matter, Energy, and Life
After studying this chapter, you should be able to:
  • describe matter, atoms, and molecules and give simple examples of the role of four major kinds of organic compounds in living cells.

  • define energy and explain the difference between kinetic and potential energy.

  • understand the principles of conservation of matter and energy and appreciate how the laws of thermodynamics affect living systems.

  • know how photosynthesis captures energy for life and how cellular respiration releases that energy to do useful work.

  • define species, populations, communities, and ecosystems and understand the ecological significance of these levels of organization.

  • discuss food chains, food webs, and trophic levels in biological communities and explain why there are pyramids of energy, biomass, and numbers of individuals in the trophic levels of an ecosystem.

  • recognize the unique properties of water and explain why the hydrologic cycle is important to us.

  • compare the ways that carbon, nitrogen, sulfur, and phosphorus cycle within ecosystems.

From Atoms to Cells

Atoms, Molecules, and Compounds

Matter is anything that takes up space and has mass. Matter can come in three physical forms; solid, liquid, or gas. It also exists in three chemical forms; elements, molecules, and compounds.

Organic Compounds

Cells: The Fundamental Units of Life

Energy and Matter

Energy and matter are essential constituents of living organisms. Matter is the material of which they are made, and energy provides a force to hold structures together, tear them apart, and move them.

Energy Types and Qualities

Conservation of Matter

The principal of the conservation of matter states that matter is neither created nor destroyed.

Thermodynamics and Energy Transfers

The study of thermodynamics deals with how energy is transferred in natural processes.

Energy for Life

Most organisms depend on the sun for the energy needed to create structures and carry out life processes.

Solar Energy: Warmth and Light

How Does Photosynthesis Capture Energy?

From Species to Ecosystems

Ecologists study interactions at the species, population, community, and ecosystem level.

The word species refers to all organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring.

Populations, Communities, and Ecosystems

Food Chains, Food Webs, and Trophic Levels

  • Photosynthesis is the base of the energy economy of most ecosystems.
  • Productivity is the amount of biomass produced in a given area during a given period of time.
    • Photosynthesis is described as primary productivity because it is the basis for almost all other growth in an ecosystem.
    • Manufacture of biomass by organisms that eat plants is termed secondary productivity.
  • A food chain is a linked feeding series of organisms.
  • Individual food chains may be interconnected to form food webs.
  • Producers (organisms that transform solar energy into chemical energy) and consumers (organisms that consume the chemical energy harnessed by producers) occupy different trophic levels.
    • Organisms can be identified by their trophic level at which they feed and by what kinds of foods they eat (herbivores, carnivores, and omnivores).
    • Scavengers, detritivores, and decomposers also occupy important places in the trophic levels.

Ecological Pyramids

Material Cycles and Life Processes

Maintenance of conditions suitable for life on earth requires constant cycling and recycling of essential nutrients and substances.

You should become familiar with the cycles for carbon, nitrogen, phosphorus, and sulfur. Each cycle is under the direction of natural and human-influenced factors. Point the mouse to each of the cycle names in the figure above to see some important components of the cycles.

The Carbon Cycle

The Nitrogen Cycle

The Phosphorus Cycle

The Sulfur Cycle

  • Sulfur compounds are a minor but essential portion of protein molecules.
  • Inorganic sulfur stored in rocks is released into the air and water by weathering, volcanic eruptions, and seafloor vent emissions.
  • The sulfur cycle is complicated by the large number of oxidation states sulfur can assume. Which of the states it is found in depends on oxygen concentrations, pH, and light levels.
  • Human activities resulting in the release of large quantities of sulfur contribute to problems such as acid rain, the greenhouse effect, and human health problems.
  • Release of dimethylsulfide (DMS) by oceanic phytoplankton could be a feedback mechanism that keeps temperature within a suitable range for life.


Questions for Review

  1. Define atom and element. Are these terms interchangeable?
  2. Your body contains vast numbers of carbon atoms. How is it possible that some of these carbon atoms may have been part of the body of a prehistoric creature?
  3. In the biosphere, matter follows a circular pathway while energy follows a linear pathway. Explain.
  4. The oceans store a vast amount of heat, but (except for climate moderation) this huge reservoir of energy is of little use to humans. Explain the difference between high-quality and low-quality energy.
  5. Ecosystems require energy to function. Where does this energy come from? Where does it go? How does the flow of energy conform to the laws of thermodynamics?
  6. Heat is released during metabolism. How is this heat useful to a cell and to a multicellular organism? How might it be detrimental, especially in a large, complex organism?
  7. Photosynthesis and cellular respiration are complementary processes. Explain how they exemplify the laws of conservation of matter and thermodynamics.
  8. What do we mean by carbon-fixation or nitrogen-fixation? Why is it important to humans that carbon and nitrogen be "fixed"?
  9. The population density of large carnivores is always very small compared to the population density of herbivores occupying the same ecosystem. Explain this in relation to the concept of an ecological pyramid.
  10. A species is a specific kind of organism. What general characteristics do individuals of a particular species share? Why is it important for ecologists to differentiate among the various species in a biological community?

Questions for Critical Thinking

  1. When we say that there is no "away" where we can throw things we don't want anymore, are we stating a premise or a conclusion? If you believe this is a premise, supply the appropriate conclusion. If you believe it is a conclusion, supply the appropriate premises. Does the argument change if this statement is a premise or a conclusion?
  2. Suppose one of your classmates disagrees with the statement above, saying, "Of course there is an `away.' It's anywhere out of my ecosystem." How would you answer?
  3. A few years ago laundry detergents commonly contained phosphates for added cleaning power. Can you imagine any disadvantages to adding soluble phosphate to household products?
  4. The first law of thermodynamics is sometimes summarized as "you can't get something for nothing." The second law is summarized as "you can't even break even." Explain what these phrases mean. Is it dangerous to oversimplify these important concepts?
  5. The ecosystem concept revolutionized ecology by introducing holistic systems thinking as opposed to individualistic life history studies. Why was this a conceptual breakthrough?
  6. Why is it important to recognize that ecosystems often are open and that boundaries may be fuzzy? Do these qualifications diminish the importance of the ecosystem study?
  7. The holistic or systems approach to biology has sometimes been criticized as "black box" engineering. It allows us to make broad generalizations about what goes into or comes out of a system without knowing the precise details of how the system works. What do you think are the benefits and limitations of this approach?
  8. Compare and contrast the views of F.E. Clements and H.A. Gleason concerning the concept of biological communities as superorganisms. How could these eminent biogeographers study the same communities and reach opposite interpretations? What evidence would be necessary to settle this question? Is lack of evidence the problem?
  9. The properties of water are so unique and so essential for life as we know it that some people believe it proves that our planet was intentionally designed for our existence. What would an environmental scientist say about this belief?
  10. The DMS feedback control of global climate is offered by some people as evidence for the Gaia hypothesis. Why might they take this position?