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
- 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
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.
- Atoms are the smallest unit of an element that exhibit the characteristics
of that element.
- Atoms are composed of three types of particles; protons (positively
charged), neutrons (no charge), and electrons (negatively charged).
- Charged atoms (those that have gained or lost electrons) are called ions.
- The atomic number of an atom refers to the number of protons it has.
- The atomic mass of an atom is the number of neutrons + the number of
protons. Atoms of the same element with different atomic masses are called
- Radioactive isotopes are unstable isotopes that emit radiation or
subatomic particles while changing into a different isotope or element. The
time required for half the atoms in a sample to decay is called the half-life.
- Atoms can join together to form molecules.
- A compound is a molecule containing different kinds of atoms.
- The forces that hold atoms together in a molecule are called chemical
- Organisms use some elements in large amounts, some in trace amounts, and
some not at all.
- Organic compounds are compounds made of chains of the element carbon.
Organic compounds form the materials that living organisms are made of.
- There are four major groups of bioorganic compounds; lipids,
carbohydrates, proteins, and nucleic acids.
- Most lipids are composed of chains of carbon atoms with two hydrogen atoms
attached. They make up an important part of cellular membranes.
- Carbohydrates are composed of chains or rings of carbon, hydrogen, and
- Proteins are composed of long chains of amino acids, compounds made of
carbon, hydrogen, and nitrogen.
- Nucleic acids are composed of combinations of a sugar molecule, a nitrogen
containing ring structure, and a phosphate bridge.
- All living organisms are composed of cells.
- Organisms may be composed of many cells (multicellular) or single cells
- Cells are composed of a membrane and organelles.
- Metabolism, all the reactions carried out by a cell, is made possible by a
special class of protein tools called enzymes.
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 is defined as the ability to do work and can take many forms
(light, heat, electricity, etc.) and is measured in calories, BTUs, or joules.
- The energy found in moving objects is called kinetic energy. Heat
measures the total kinetic energy of atoms or molecules in a substance.
Temperature is the measure of the speed of motion of atoms or molecules in a
substance. Heat and temperature are NOT the same.
- Potential energy is stored energy that is latent but available for use.
- Food and gasoline are examples of chemical energy.
- Power is defined as the rate of doing work.
- Energy can be low-quality or high quality.
The principal of the conservation of matter states that matter is
neither created nor destroyed.
The study of thermodynamics deals with how energy is transferred in
- The first law of thermodynamics states that energy is conserved; that is,
it is neither created nor destroyed. It may change forms but the total amount
does not increase nor decrease.
- The second law of thermodynamics states that, with each successive energy
transfer or transformation in a system, less energy is available to do work.
- Natural systems tend to move towards a higher state of entropy or
Most organisms depend on the sun for the energy needed to create
structures and carry out life processes.
- Solar energy is essential for life.
- Most organisms survive within a narrow temperature range. The necessary
heat is provided by the sun.
- Organisms depend on solar radiation for life-sustaining energy, which is
captured by green plants, algae, and some bacteria in a process called
photosynthesis. However, only about 1-2% of the total solar radiation hitting
the earth is utilized by living organisms.
- Chlorophyll, a green molecule found in chloroplasts within plant
cells, absorbs light energy and uses it to create high-energy chemical bonds in
substances that serve as the fuel for all subsequent cellular metabolism.
- Chlorophyll is assisted in this process by a large group of sugar, lipid,
protein, and nucleotide molecules.
- The light reactions of photosynthesis occur only while the chloroplast is
receiving light energy. They result in the splitting of water to form
molecular oxygen and small high energy molecules that serve as fuel for the
dark reactions of photosynthesis.
- The dark reactions of photosynthesis can occur after light is no longer
being received. They result in the addition of a carbon atom to a small sugar
Photosynthesis can be summed as 6H2O + 6CO2 + solar energy -> C6H12O6 + 6O2
- Cellular respiration is the process in which glucose (the sugar) is split
apart and its energy released for use by cellular metabolism.
- Animals do not have chlorophyll and gain their energy by eating other
plants or animals and breaking down their organic molecules for energy.
Ecologists study interactions at the species, population, community, and
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.
- A population consists of all the members of a species living in a given
area at the same time.
- All the populations of organisms living and interacting in a particular
area make up a biological community.
- An ecosystem is composed of a biological community and its physical
- 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
- 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.
- By arranging the organisms in a food web by trophic levels, an
ecological pyramid can be formed with producers at the wide base and fewer and fewer
individuals in the higher levels. This follows the second law of
thermodynamics that less and less energy is available in succeeding trophic
- The total number of organisms and total biomass in each successive trophic
level in an ecosystem may also form pyramids.
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.
- Carbon serves two purposes for organisms; 1) it is a structural component
of organic molecules, and 2) the energy-holding chemical bonds it forms
represent energy "storage".
- The carbon cycle begins with the intake of carbon dioxide by
photosynthetic organisms. Carbon and oxygen are incorporated into sugar
molecules. These molecules are taken up by other organisms, and carbon dioxide
is released following respiration, closing the cycle.
- Not all carbon is cycled. Some forms (coal and oil) may be sequestered
for millions of years without being released.
- Tying up carbon in the bodies and byproducts of organisms favorably
affects the biosphere. It helps balance carbon dioxide generation and
utilization and so regulates the greenhouse effect.
- Oceans and heavily vegetated areas are important carbon sinks.
- Organisms cannot exist without amino acids, peptides, and proteins which
are all molecules containing nitrogen.
- Although nitrogen is the most abundant gas in the atmosphere,
plants cannot use N2 gas.
Nitrogen-fixing bacteria convert nitrogen gas (N2) to nitrites (NO2-). Another
group converts nitrites to nitrates (NO3-) which can be absorbed and used by
plants. Plants convert nitrates into ammonuim (NH4+) which is used to build
- Some plants (legumes) have nitrogen fixing bacteria living in their roots
and so are especially useful to agriculture.
- Nitrogen reenters the environment in several ways including the death of
organisms and animal wastes. Denitrifying bacteria break these down back into
nitrogen gas which reenters the atmosphere.
- Synthetic fertilizers may cause an excess of nitrogen in the environment
leading to acidification of lakes and rivers, blooms of toxic algae, loss of
soil nutrients, and rising atmospheric concentrations of the greenhouse gas
- Minerals are available to organisms after they have been released from
rocks. Phosphorus and sulfur are two examples of this.
- Phosphorus is important because it is an essential component of many high
energy compounds such as ATP.
- The phosphorus cycle begins when phosphorus compounds are leached from
rocks and minerals.
- Inorganic phosphorus is taken in by producer organisms, incorporated into
organic molecules, and passed on to consumer organisms.
- High concentrations of phosphorus in aquatic systems may lead to algal
blooms, suffocating other life in lakes and streams.
- 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
- Release of dimethylsulfide (DMS) by oceanic phytoplankton could be a
feedback mechanism that keeps temperature within a suitable range for
- Certain conditions, including the availability of required chemical
elements, solar energy, mild surface temperatures, liquid water, and a suitable
atmosphere are all essential for the presence of life on earth.
- Ecosystem dynamics are governed by physical laws, including the law of
conservation of matter and the first and second laws of thermodynamics.
- An ecosystem is composed of a biological community and all the biotic and
abiotic factors that make up the environment in a defined area.
- Matter and energy are processed through the trophic levels of an ecosystem
via food chains and food webs.
- The biosphere is a source of large quantities of essential elements whose
cycling is essential to life.
- Define atom and element. Are these terms interchangeable?
- 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
- In the biosphere, matter follows a circular pathway while energy follows
a linear pathway. Explain.
- 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.
- 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
- 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?
- Photosynthesis and cellular respiration are complementary processes.
Explain how they exemplify the laws of conservation of matter and
- What do we mean by carbon-fixation or nitrogen-fixation? Why is it
important to humans that carbon and nitrogen be "fixed"?
- 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.
- 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?
- 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?
- 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?
- 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?
- 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
- The ecosystem concept revolutionized ecology by introducing holistic
systems thinking as opposed to individualistic life history studies. Why was
this a conceptual breakthrough?
- 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
- 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
- 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?
- 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
- The DMS feedback control of global climate is offered by some people as
evidence for the Gaia hypothesis. Why might they take this position?