Biology Now, 2e

Answers ■ A7

A3: Oxygen is sharing two electrons with carbon. Carbon is

sharing two electrons with oxygen and one electron with each of

the hydrogens.

Figure 03.C

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C O

H

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CHAPTER 4

END-OF-CHAPTER ANSWERS

1. c


2. d


3. receptor-mediated endocytosis: 2, phagocytosis: 1, pinocyto-

sis: 4, exocytosis: 3

4. chloroplast: 7, Golgi apparatus: 4, lysosome: 5, mitochon-

drion: 6, nucleus: 1, rough endoplasmic reticulum: 2, smooth

endoplasmic reticulum: 3

5. 
   

   (^) Eukaryotes
   Component Prokaryotes Animals Plants
   Plasma membrane X X X
   Cellulose cell wall X
   Nucleus X X
   Endoplasmic reticulum X X
   Golgi apparatus X X
   Ribosomes X X
   Cytoskeleton X X
   Mitochondria X X
   Chloroplasts X

   
   


6. 
   

   a

   
   


7. 
   

   The dashed curve represents simple diffusion because as

   
   

the concentration of solute increases, the rate of transport

increases in a directly proportional way. The solid curve

represents facilitated diffusion because it reaches the trans-

port protein saturation line but cannot exceed it, since facil-

itated diffusion relies on these proteins to send the solutes

across the membrane. If the transport proteins are fully in

use, adding a higher concentration of solute will not increase

the rate of transport.

8. b


9. right side, more, fewer


10. c


11. (a) isotonic, (b) neither gain nor lose, (c) equal to, (d) hyper-
    tonic, (e) lose, (f ) higher than, (g) hypotonic, (h) gain, (i) lower
    than

ANSWERS TO FIGURE QUESTIONS

Figure 4.2

Q1: What was the purpose of inserting the gene that codes for blue

pigment into the synthetic DNA?

A1: The blue color identified the cells that contained the DNA

from M. mycoides.

Q2: What part of the transformed bacterium is synthetic?

A2: Only the DNA is synthetic; all of the structural components of

the cells are from the M. capricolum cells into which the synthetic

DNA was inserted.

Q3: Did this experiment create life?

A3: Although some articles in the popular press refer to the

synthetic bacterium as a new life-form, it is better described as

“repackaged life.” The DNA is synthetic, but all the intracellular

components that enable the DNA to function were already present

in the cell.

Figure 4.3

Q1: Why is it important that the phosphate head of a phospholipid

is hydrophilic?

A1: The fact that the phosphate head is attracted to water

(hydrophilic) and also to other phosphate heads means that a

bilayer will form.

Q2: What essential component of a cell do liposomes lack, and why

is that omission important?

A2: Liposomes lack genetic material (DNA), so the characteristics

of a liposome are not transmitted to its descendants.

Q3: Could the tendency of phospholipid bilayers to spontaneously

form spheres have played a role in the origin of life? (Hint:

Refer to “The Characteristics of Living Organisms” on page 6 of

Chapter 1.)

A3: Yes. Once phospholipids formed (how that happened is still an

open question), they would have formed liposomes spontaneously,

trapping substances in their interiors.

Figure 4.4

Q1: In what ways is the plasma membrane a barrier, and in what

ways is it a gatekeeper?

A1: It is a barrier in that it keeps out many molecules. It is a

gatekeeper in that it selectively allows in other molecules.