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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 7. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. How do gasoline-powered hedge trimmers demonstrate the principle of the first law of thermodynamics?
  2. How does an aging tool shed demonstrate the principle of the second law of thermodynamics?
  3. What is the primary energy source for all living organisms?
  4. What is a “bomb calorimeter” and what does it measure?
  5. How is the “activation energy” for a chemical reaction similar to the sides of a basket holding a litter of puppies?
  6. What are enzymes and what function do they play in biochemical reactions?
  7. How might metabolism shorten the lifespan of living organisms?
  8. How many minutes of energetic dancing would be needed to burn the number of calories consumed from a large hamburger and fries?

A Guide to the Reading

When exploring the content in Chapter 7 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Laws of Thermodynamics

Thermodynamics is a dedicated field of physics which studies the dynamics of heat (from the Greek term thermo).  Heat is a form of energy that is involved in almost all chemical reactions.  There are certain universal laws that govern how energy behaves in all chemical reactions; these are the “laws of thermodynamics”.  As discussed in the chapter, the first law of thermodynamics dictates that energy cannot be created (or destroyed), but can only be transformed from one form to another.  An excellent example of this is the gasoline used to power automobiles.  Gasoline contains energy in a liquid form that is stable at room temperature.  When burned inside an engine, the energy is released from the gasoline.  This energy takes on different forms – force (used to power the movement of the pistons, propelling the car forward) and heat.  In this example, the amount of energy contained in the gasoline exactly equals the amount of energy utilized as force and lost as heat.  In this (and all cases), energy is not destroyed or created – it is merely transformed from one form (liquid gasoline) to another (force and heat).  The second law of thermodynamics dictates that all systems (i.e., a cell, a bedroom, a yard, the biosphere) always tend to become more disordered.  An excellent example of this would be your dormitory room.  Over time, the room will always become more messy (disordered).  The only way to reverse this trend is through the expenditure of energy (cleaning your room).  Without this input of energy to restore order to the system, it will remain in a perpetual state of disorder.  The use of energy in a cell is governed by these two laws of thermodynamics without exception.  The multitude of chemical reactions that provide the cell’s metabolism must always follow these rules.

For more information on this concept, be sure to focus on:

  • In Section 7.1, The laws of thermodynamics apply to living systems
  • Figure 7.1, The Second Law of Thermodynamics

Oxidation and Reduction Reactions

The process of electron transfer plays a crucial role in the multitude of chemical reactions in which cells utilize, capture, and store energy.  The transfer of electrons between molecules will result in one molecule gaining electrons (reduction) and the other molecule losing electrons (oxidation).  It is important to note that oxidation and reduction often occur as a paired process.  Because of this close association, the textbook indicates these reactions are often called “oxidation-reduction”, or redox, reactions.  The loss of electrons is called oxidation because when carbon atoms lose electrons through this process, they are often bound to oxygen atoms as a result.  Therefore, while the carbon atom has lost electrons, it has gained oxygen atoms – hence the term ‘oxi’-dation.  Conversely, compounds that are capable of accepting electrons will also tend to lose oxygen atoms, leaving them in a reduced state; hence the term reduction.  Oxidation-reduction reactions play a huge role in the capture of energy, in the form of sugar during photosynthesis, and ATP during respiration.

For more information on this concept, be sure to focus on:

  • In Section 7.2, Capturing energy from foods requires the transfer of electrons

Enzyme Catalysis

As described in the chapter, all chemical reactions require a certain amount of activation energy in order to proceed.  The activation energy required prevents the reaction from proceeding without regulation.  For many reactions, however, the activation energy can be prohibitive.  Cells have found a way to overcome this limitation by employing a special class of proteins, called enzymes, which work to “catalyze” or speed up a chemical reaction.  Catalysis is accomplished by lowering the amount of activation energy required to drive the reaction forward.  Enzymes can accomplish this in several ways, including by binding to the substrates of the reaction, bringing them in close proximity to one other, or placing stress on chemical bonds.  The key concept to remember when discussing enzymes is that, while they play a key role in driving chemical reactions, they are not consumed during the reaction.  This means a single enzyme molecule can catalyze the same reaction multiple times, remaining unchanged throughout the process.  Another concept to keep in mind is that enzymes are highly specific – they typically drive one, and only one, chemical reaction.

For more information on this concept, be sure to focus on:

  • In Section 7.3, Enzymes speed up chemical reactions
  • In Section 7.3, The shape of an enzyme directly determines its activity
  • Figure 7.6, Enzymes as Molecular Matchmakers

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Chemical Structures found in Cells

  • Chapter 4 – Section 4.5, The Chemical Building Blocks of Living Systems

ATP: Energy for the Cell

  • Chapter 4 – in Section 4.5, Nucleotides store information and energy

Chloroplast and Energy Capture

  • Chapter 5 – in Section 5.5, Chloroplasts capture energy from sunlight
  • Chapter 8 –Section 8.2, Photosynthesis: Capturing Energy from Sunlight

Mitochondria and Energy Production

  • Chapter 5 – in Section 5.5, Mitochondria are the power stations of the eukaryotic cell
  • Chapter 8 – Section 8.3, Catabolism: Breaking Down Molecules for Energy

DNA Synthesis

  • Chapter 12 – Section 12.2, The Three-Dimensional Structure of DNA


  • Chapter 20 – Maintaining the Internal Environment

Carbon Fixation and Cycling

  • Chapter 21 – Nutrition and Digestion
  • Chapter 38 – Global Change

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