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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 6. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. How can lichens be used to tell us about impending and potential environmental problems?
  2. What properties of a phospholipid bilayer make it “selectively permeable”?
  3. What percentage of the energy expended by a person at rest is used to fuel active transport across the plasma membrane?
  4. What structures present in the cell act as “transport luggage”?
  5. How many gallons of water are contained in a typical person’s body?
  6. What mechanisms facilitate cellular “eating” and “drinking” activities?
  7. What property of steroid hormones allows them to pass easily through the plasma membrane of target cells?

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.


As discussed in the chapter, the process of diffusion drives molecules to spread from areas of relatively high concentration to areas of lower concentration.  In a similar fashion, when two solutions of different concentrations are separated by a selectively permeable membrane (which restricts the passage of the dissolved molecules) water molecules will exhibit directional movement.  The movement of water molecules across a selectively permeable membrane is referred to as osmosis.  The direction in which water moves across the membrane is a function of the relative concentrations of the two solutions.  As an example, consider Solution A with a relatively higher concentration of dissolved molecules than Solution B.  In this example, Solution A would be considered “hypertonic” relative to Solution B, since it has a higher concentration of dissolved molecules.  In contrast, Solution B, with a lower concentration of dissolved molecules, would be considered “hypotonic”.  The key to understanding these two terms is realizing that hypertonic and hypotonic can only be used when comparing one solution to another; a single solution cannot be hypertonic or hypotonic since there would be no companion solution to compare it to.  In terms of osmosis, water molecules will always move across a membrane from the hypotonic solution toward the hypertonic solution.  This can actually be thought of in terms of diffusion – since the hypertonic solution, which has a higher concentration of dissolved molecules taking up space, would actually have less room for water molecules.  As a result, hypertonic solutions would have relatively fewer water molecules than hypotonic solutions while hypotonic solutions would have relatively more water molecules.  If you now think of osmosis as the diffusion of water, it is easy to see why water would always move from the hypotonic solution (relatively higher concentration of water) toward the hypertonic (relatively lower concentration of water) solution.  In addition, solutions that have the same concentration can be described as being “isotonic”.

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

  • Section 6.2, Water Requires a Cellular Balancing Act
  • Figure 6.4, Water Moves Into and Out of Cells by Osmosis

Cellular Signaling

Multicellular organisms require a reliable, efficient mechanism for facilitating communication between the cells of the body.  This is most typically accomplished by the release of a signaling molecule (proteins, hormones, gasses) from one cell, which is then received by a target cell, which then responds in a highly specific fashion.  The types of signaling molecules and their effects on their respective target cells vary greatly.  One thing to understand about signaling molecules and their target cells is the fact that in order for a target cell to receive and respond to a chemical signal, it must possess a specific receptor protein for that particular signal.  These receptor proteins are typically found on the surface of the target cell and work to transmit a signal into the cell when a signaling molecule binds to it.  Other classes of receptor proteins may actually be located in the cytoplasm of the cell.  In this case, the signaling molecule must be permeable across the plasma membrane in order to stimulate the target cell to respond in the desired manner.  Another key concept to understand about signaling molecules is that their longevity depends upon how far the molecule must travel to reach its intended target cell.

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

  • Section 6.6, Signaling Molecules in Cell Communication
  • Figure 6.8, Receptors for Signaling Molecules

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:

Kingdoms of Life

  • Chapter 3 –Section 3.1,The Major Groups in Context


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

The Plasma Membrane

  • Chapter 5 – Section 5.2, The Plasma Membrane: Separating Cells from the Environment

The Cytoskeleton

  • Chapter 5 – Section 5.5, The Cytoskeleton: Providing Shape and Movement

Genes and Proteins

  • Chapter 13 – Section 13.2, How Genes Control the Production of Proteins


  • Chapter 24 – Hormones

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