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Chapter 2LectureOutline

Learning OutcomesAfter studying this chapter, you should be able to answer the following questions:

• What are systems, and how do feedback loops regulate them?• Chemical bonds hold atoms and molecules together. What would

our world be like if there were no chemical bonds, or if they were so strong they never broke apart?

• Ecologists say there is no “away” to throw things, and that everything in the universe tends to slow down and fall apart. What do they mean?

• All living things—except for some unusual organisms living in extreme conditions—depend on the sun as their ultimate energy source. Explain.

• What qualities make water so unique and essential for life as we know it?

• Why are big, fierce animals rare?• How and why do elements such as carbon, nitrogen, phosphate,

and sulfur cycle through ecosystems?2-2

Most institutions demand unqualified faith; but the institution of science

makes skepticism a virtue.–Robert King Merton

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2.1 Systems Describe Interactions

• A system is a network of interdependent components and processes

• For example, an ecosystem might consist of countless animals, plants, and their physical surroundings.

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Systems can be described in termsof their characteristics

• Open systems are those that receive inputs from their surroundings and produce outputs that leave the system.

• A closed system exchanges no energy or matter with its surroundings.

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Positive & Negative Feedback

• An increase in the state variable leads to further increases in the same variable, is called a positive feedback.

• Negative feedback results in a decrease in the causative variable.

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2.2 Elements of Life

• In this section we will examine matter and the elements and compounds on which all life depends.

Figure 2.5 As difficult as it may be to imagine when you look at a solid object, all matter is composed of tiny, moving particles, separated by space and held together by energy. This model rep resents a carbon-12 atom, with a nucleus containing six protons and six neutrons; the six electrons are represented as a fuzzy cloud of potential locations, rather than as individual particles.

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Chemical bonds hold molecules together

• Atoms often join to form compounds, or substances composed of different kinds of atoms (fig. 2.6).

• A pair or group of atoms that can exist as a single unit is known as a molecule.

• When ions with opposite charges form a compound, the electrical attraction holding them together is an ionic bond.

• Sometimes atoms form bonds by sharing electrons, forming covalent bonds.

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Electrical charge is an importantchemical characteristic

• Atoms frequently gain or lose electrons, acquiring a negative or positive electrical charge. Charged atoms (or combinations of atoms) are called ions.

• Negatively charged ions (with one or more extra electrons) are anions.

• Positively charged ions are cations.• A hydrogen (H) atom, for example, can give up its

sole electron to become a hydrogen ion (H).• Chlorine (Cl) readily gains electrons, forming

chlorine ions (Cl).

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pH: Acids, Bases, and Buffers

• Substances that readily give up hydrogen ions in water are known as acids.

• Substances that readily bond with H ions are called bases or alkaline substances.

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The four major groups of organic molecules

• Figure 2.8 The four major groups of organic molecules are based on repeating subunits of these carbon-based structures. Basic structures are shown for (a) butyric acid (a building block of lipids) and a hydrocarbon,(b) a simple carbohydrate, (c) a protein, and (d) a nucleic acid.

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Cells are the fundamental units

of life• All living organisms are

composed of cells, minute compartments within which the processes of life are carried out (fig. 2.10).

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2.3 Energy

• Energy is the ability to do work such as moving matter over a distance or causing a heat transfer between two objects at different temperatures.

• Energy can take many different forms. Heat, light, electricity, and chemical energy are examples that we all experience.

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Kinetic Energy

• The energy contained in moving objects is called kinetic energy.

• A rock rolling down a hill, the wind blowing through the trees, water flowing over a dam (fig. 2.11), or electrons speeding around the nucleus of an atom are all examples of kinetic energy.

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Potential Energy

• Potential energy is stored energy that is latent but available for use. • A rock poised at the top of a hill and water stored behind a dam are

examples of potential energy. 2-15

Energy continued…

• Heat describes the energy that can be transferred between objects of different temperature.

• The first law of thermodynamics states that energy is conserved.

• The second law of thermodynamics states that, with each successive energy transfer or transformation in a system, less energy is available to do work.

• The second law recognizes that disorder, or entropy, tends to increase in all natural systems.

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2.4 Energy for Life: Green plants get energy from the sun

• Green plants are often called primary producers because they create carbohydrates and other compounds using just sunlight, air, and water.

• Nearly all organisms on the earth’s surface depend on solar radiation for life-sustaining energy, which is captured by green plants, algae, and some bacteria in a process called photosynthesis.

• Photosynthesis converts radiant energy into useful, high-quality chemical energy in the bonds that hold together organic molecules.

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The electromagnetic spectrum

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How does photosynthesis capture energy?

• In chloroplasts, chlorophyll is involved with two interconnected cycles of chemical reactions, the light-dependent & the light-independent reactions.

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Respiration & Photosynthesis

• Animals (like us) eat plants—or other animals that have eaten plants—and break down the organic molecules in our food through cellular respiration to obtain energy (fig. 2.15).

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2.5 From Species to Ecosystems

• A population consists of all the members of a species living in a given area at the same time.

• All of the populations of organisms living and interacting in a particular area make up a biological community.

• An ecological system, or ecosystem, is composed of a biological community and its physical environment.

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Food chains, food webs, and trophic levels link species

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Trophic Levels

• Herbivores are plant eaters

• Carnivores are flesh eaters

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Ecological pyramids describe trophic levels

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A numbers pyramid

• The total number of organisms and the total amount of biomass in each successive trophic level of an ecosystem also may form pyramids (fig. 2.20) similar to those describing energy content.

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2.6 Biogeochemical Cycles and Life Processes

• The elements and compounds that sustain us are cycled endlessly through living things and through the environment.

• As the great naturalist John Muir said, “When one tugs at a single thing in nature, he finds it attached to the rest of the world.”

• On a global scale, this movement is referred to as biogeochemical cycling.

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The hydrologic cycle

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The carbon cycle

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The nitrogen cycle

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The phosphorus cycle

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Practice Quiz1. What two problems did Arcata, California, solve with its constructed

wetland?2. What are systems and how do feedback loops regulate them?3. Your body contains vast numbers of carbon atoms. How is it possible that

some of these carbons may have been part of the body of a prehistoric creature?

4. List six unique properties of water. Describe, briefly, how each of these properties makes water essential to life as we know it.

5. What is DNA, and why is it important?6. The oceans store a vast amount of heat, but this huge reservoir of energy is

of little use to humans. Explain the difference between high-quality and low-quality energy.

7. In the biosphere, matter follows circular pathways, while energy flows in a linear fashion. Explain.

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Practice Quiz continued…

8. Which wavelengths do our eyes respond to, and why? (Refer to fig. 2.13.) What is the ratio of short ultraviolet wavelengths to microwave lengths?

9. Where do extremophiles live? How do they get the energy they need for survival?

10. Ecosystems require energy to function. From where does this energy come? Where does it go?

11. How do green plants capture energy, and what do they do with it?12. Define the terms species, population, and biological community.13. Why are big fierce animals rare?14. Most ecosystems can be visualized as a pyramid with manyorganisms in the lowest trophic levels and only a few individuals at the top. Give

an example of an inverted numbers pyramid.15. What is the ratio of human-caused carbon releases into the atmosphere

shown in figure 2.22

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