ANSWERS
Chapter 1Introduction to Biological Concepts and Research
Why It Matters [pp. 1-2]
1. life
1.1 What is Life?[pp. 2-7]
2. hierarchy; 3. cell; 4. unicellular organism; 5. multicellular organism; 6. population; 7. community; 8.ecosystem; 9. biosphere; 10. emergent properties; 11. DNA; 12. RNA; 13. protein; 14. metabolism; 15. primary producers; 16. consumers; 17. decomposers; 18. external environment; 19. homeostasis; 20. reproduction; 21.inheritance; 22. development; 23. life cycle; 24. biological evolution; 25. biology; 26. ecology; 27.homeostasis; 28. ecosystem; 29. biosphere; 30. protozoa; 31. organized chemical system surrounded by a membrane; 32. multicellular organism; 33. population; 34. the collection of all of the populations of different organisms living in the same place; 35. ecosystem; 36. energy flows and mass cycles; 37. b; 38. a; 39. a; 40. c; 41. b; 42. b; 43. d; 44. a; 45. c; 46. g; 47. f; 48. e
1.2Biological Evolution[pp. 7-9], 1.3 Biodiversityand the Tree of Life [pp. 9-13].
49. artificial selection; 50. natural selection; 51. genes; 52. mutations; 53. adaptations; 54. species; 55. scientific name; 56. genus; 57. family; 58. order; 59. class; 60. phylum; 61. kingdom; 62. domain; 63. Archaea; 64.Bacteria; 65. Eukarya; 66. prokaryotes; 67. eukaryotes; 68. nucleus; 69. organelles; 70. Protoctista; 71. Plantae; 72. Fungi; 73.Animalia; 74. c; 75. e; 76. d; 77. a; 78. b; 79. b; 80. a; 81. c; 82. a; 83. b; 84. d; 85. f; 86. a; 87. e; 88. c; 89.b; 90. h. 91 g
1.4 Biological Research[pp. 13-19]
92. biological research; 93. scientific method; 94. basic research; 95. applied research; 96. observational data; 97.experimental data; 98. hypothesis; 99. predictions; 100. alternative hypothesis; 101. control; 102. experimental variable; 103. replicates; 104. null hypothesis; 105. model organisms; 106. biotechnology; 107. scientific theory; 108. b; 109. a; 110. c; 111. a; 112. b; 113. d; 114. a; 115. b; 116. g; 117. f; 118. c; 119. e; 120. Model organisms have rapid development, short life cycle, small adult size, and other characteristics that make them amenable to laboratory research. The fruit fly is an example of a model organism; 121. A scientific theory has been exhaustively tested and is not likely to be contradicted by future research. 122. Scientists must describe an idea in such a way that if it is wrong, they will be able to demonstrate it is wrong
Self-Test
1. b [The initial observations indicated that small size is accompanied by low IGF levels and that large size is accompanied by high IGF levels. The experiment is aimed at demonstrating a causal relationship between size and IGF level; therefore, b is correct]
2. a [a is correct because the biologist is manipulating the system; such manipulation results in experimental data]
3. a [The experiment tests the effects of saline (control) and IGF injection; therefore, the experimental variable is IGF level (none vs. 100ng/g body weight) and a is correct; all other parameters were held constant]
4. a
5. a
6. a
7. c
8. c
9. c [c is correct because species names are two-part names with a genus and a specific epithet]
10. d
11. b
12. a
Chapter 2Life, Chemistry, and Water
Why It Matters [pp. 22-23],
1. plants; 2. animals; 3. atoms; 4. chemical bonds; 5. biology; 6. chemical substances; 7. selenium; 8. low; 9. high
2.1 The Organization of Matter: Elements and Atoms[pp. 23-24]
10. elements; 11. atoms; 12. pure; 13. cannot; 14. carbon; 15. hydrogen; 16. oxygen; 17. nitrogen; 18. atom; 19.symbol; 20. atomic number; 21. atomic mass; 22. molecules; 23. compounds
2.2 Atomic Structure[pp. 24-28]
24. B; 25. C; 26. A; 27. A; 28. A; 29. B; 30. B; 31. A; 32. F; 33. C; 34. E; 35. D; 36. 2; 37. 2; 38. 2s; 39. 2p; 40. 2; 41. 3; 42. 2; 43. 2; 44. 8; 45. valence; 46. reactive; 47. 8; 48. 8; 49. 16; 50. O or oxygen; 51. 11; 52. 11; 53. 22 or 23 (most common form has 12 neutrons); 54. Na or sodium; 55. 17; 56. 17; 57. 34; 58. Cl or chlorine
2.3 Chemical Bonds and Chemical Reactions[pp. 28-32]
59. O or oxygen; 60. 6; 61. Na or sodium; 62. 1; 63. Cl or chlorine; 64. 7; 65. Na; 66. Cl; 67. ionic; 68. 1; 69.Na; 70. positive; 71. Cl; 72. negative; 73. charge; 74. ionic bond; 75. electrochemical; 76. Na+; 77. Cl-; 78.covalent; 79. hydrogen; 80. van der Walls forces; 81. covalent; 82. electrons; 83. equal; 84. unequal; 85.electronegativity; 86. nonpolar covalent; 87. polar covalent; 88. polar; 89. attracted; 90. repealed; 91. polar; 92.hydrophilic; 93. nonpolar; 94. hydrophobic
2.4 Hydrogen Bonds and the Properties of Water[pp. 32-36]
95. Polar water molecules have a negative end (oxygen) and positive ends (hydrogen). Hydrogen bonds form between the oxygen of one water molecule and the hydrogen of another water molecule. Thus a lattice type structure will form between adjacent water molecules; 96.Polar ends of a molecule will associate with water (hydrophilic), while the nonpolar ends will be repealed (hydrophobic). The nonpolar ends will be attracted to each other and thus a bilayer structure will form. The nonpolar ends of two lipids will be attracted to each other and the polar ends will associate with the water lattice.; 97. Heat is transported to the surface by increased blood flow to the skin. As a result of increased blood flow, sweat gland activity will increase. The heat energy in the blood is transferred to the sweat which is excreted on the surface of the skin. Evaporation of the sweat is a primary heat loss mechanisms in humans.
98A. phosphate; 98B. fatty acid; 98C. polar; 98D. hydrophobic; 98E. polar; 98F. membrane;
99. E; 100. C; 101. B; 102. A; 103. D; 104. True; 105. False, heat of vaporization; 106. False, cohesion; 107. True; 108. True
2.5 Water Ionization and Acids, Bases, and Buffers[pp. 36-38]
109. hydrogen (H+); 110. hydroxide (OH-); 111. acid; 112. base; 113. buffer; 114. accepting; 115. releasing; 116.hydrogen (H+); 117. A; 118. B; 119. B; 120. A; 121. C
Self-Test
1. d [an isotope has variable numbers of neutrons; electrons can be gained or lost; proton number is unique to each type of atom for a given element]
2. a [isotopes differ in the number of neutrons]
3. b [the positive charge of the nucleus attracts the electrons. In outer orbitals, the negative charge of the electrons contributes to the reactivity of the atom]
4. a [polar covalent bonds in a molecule cause the molecule to have a positive and a negative end, thus hydrogen bonds can form between two adjacent polar molecules]
5. d [molecules with ionic or polar covalent bonds produce ions or atoms with a positive or negative end which are more likely to dissolve in water]
6. b [hydrogen-bond lattice becomes rigid and the spaces are farther apart, the volume increases, but the density decreases]
7. c [high specific heat allows water to freeze from the top down. A large of amount of heat loss is required for water to change from a liquid to a solid. Cold air temperature next to the surface of the water will cause heat to be lost at the top first]
8. b [surface tension is the force between the air and water layer which places a tension on the water, this tension is able to support small insects such as water striders; cohesion is the will hold water in a column due to a lattice type network of hydrogen bonds between the water molecules.
9. c [due to small size of water molecules and their highly polar nature, water is a good solvent. Solutes will dissolve and associate with the “+” and “-“ ends of the water molecule.
10. a [molarity is the concentration of solute per unit solvent, the solute concentration is directly related to the molarity]
11. c [pH 9.3 is the only basic pH. If enzyme activity occurs in an acidic pH, then a basic pH would be expected to decrease activity.]
12. a [buffers either release or bind to hydrogen ions, thus the pH would not be expected to greatly change].
Chapter 3Biological Molecules: The Carbon Compounds of Life
Why It Matters [pp. 42-43],
1. carbon; 2. carbon dioxide, CO2; 3. carbon; 4. organisms; 5. photosynthesis; 6. history or past; 7. climate;
3.1Formation and Modification of Biological Molecules[pp. 43-47],
8. organic; 9. carbon; 10. inorganic; 11. four electrons; 12. covalent polar; 13. carbon; 14. hydrogen; 15.hydrocarbons; 16. carbon; 17. hydrogen; 18. oxygen; 19. nitrogen; 20. carbohydrates; 21. lipids; 22. proteins; 23. nucleic acids; 24. alcohols, water; 25. amino; 26. carboxyl; 27. organic acids; 28. phosphate; 29.ketones; 30. dehydration synthesis; 31. hydroxyl; 32. hydrogen; 33. oxygen; 34. synthesis; 35. water; 36.dehydration; 37. hydrolysis; 38. water; 39. hydroxyl; 40. hydrogen; 41. hydrolysis
3.2 Carbohydrates[pp.47-50],
42. poly; 43. mono; 44. carbon; 45. hydrogen; 46. oxygen; 47. 1 (carbon): 2 (hydrogen): 1 (oxygen); 48.Polymerization; 49. dehydration synthesis; 50. polysaccharides or polymers; 51. four; 52. asymmetric; 53. isomers; 54. formula; 55. different; 56. Molecules with the same chemical formula (same ratio of atoms) but different molecular structures. Optical isomers are mirror images, while structural isomers have different arrangement of the atoms. 57. Both glycogen and cellulose are polymers of glucose. Glycogen is branched with alpha-linkages, while cellulose is unbranched with beta-linkages. Most animals lack the enzyme necessary to break beta-linkages, thus digestion of cellulose is not possible.
3.3 Lipids[pp. 50-54],
58. neutral; 59. phospholipids; 60. steroids; 61. glycerol; 62. three; 63. fatty acid; 64. triglycerides; 65. carboxyl; 66. dehydration synthesis; 67. carboxyl; 68. hydroxyl; 69. saturated; 70. hydrogen; 71. unsaturated; 72. double; 73.monounsaturated; 74. polyunsaturated. 75. Double bonds cause fatty acids to have bends, thus the chain has less organization and is more likely to be fluid and melt at lower temperatures. Lack of double bonds cause fatty acid chains to be solid (due to more uniformity and organization) with higher melting temperatures; 76. One of the fatty acid chains is replaced with a polar phosphate group. 77A. phosphate; 77B. fatty acids, monounsaturated, polyunsaturated; 77C & E. hydrophilic or polar; 77D. hydrophobic or nonpolar; 77F. membrane; 78. Phospholipids will orient so that the hydrophobic portions (fatty acid chains) away from the polar or hydrophilic solution. The phosphate group will associate with the polar or hydrophilic solution. 79. The membrane would like it were inside-out—the phosphate ends (polar) would orient to be away from the nonpolar solution. The fatty acid chains would be faced or associate with the nonpolar solution; 80. Cholesterol is the structural unit of steroids. Steroids play important roles in membrane structure as well as hormones.
3.4 Proteins[pp. 54-63],
81. proteins; 82. amino acids; 83. amino; 84. carboxyl; 85. R; 86. N-terminal; 87. amino; 88. C-terminal; 89.carboxyl; 90. peptide; 91. dehydration synthesis; 92. polypeptide; 93. B; 94. D; 95. C; 96. C; 97. A; 98. D; 99. Hydrogen bonds: 100. Hydrogen bonds are broken and the protein looses its three-dimensional structure and often function. Extreme temperatures as well as acid or basic conditions; 101. F; 102. C; 103. B; 104. A; 105. D; 106. E
3.5 Nucleotides and Nucleic Acids[pp. 63-66]
107. nucleic acids; 108. deoxyribonucleic acid; 109. DNA; 110. ribonucleic acid; 111. RNA; 112. nucleotide; 113.nucleotide; 114. nitrogenous base; 115. 5 carbon; 116. phosphate; 117. two; 118. pyrimidines; 119. purines; 120. sugar; 121. phosphate; 122. phosphodiester bond; 123. two; 124. single; 125. complementary; 126. C; 127. E; 128. B,E; 129. A,C,D; 130. C; 131. A; 132. F; 133. G; 135A. 2; 135B.deoxyribose; 135C. adenine; 135D. thymine; 135E. guanine; 135F. cytosine; 135G. 1; 135H. ribose; 135I.adenine; 135J. uracil; 135K. guanine; 135L. cytosine;
Summary
136. carbohydrate; 137. lipid—triglyceride; 138. lipid—phospholipid; 139. lipid—steroid; 140. protein; 141.nucleic acid;
Self-Test
1. a [Cell membranes have a polar portion and nonpolar portion; phospholipids with a phosphate group are the primary lipid type in membranes.]
2. a [dehydration synthesis reactions produce water]
3. d [Microbes in the GI tract contain enzymes to breakdown cellulose. In addition, the GI tract of these animals is considerably longer than humans.]
4. d [phospholipids and steroids have polar side groups and are hydrophilic; triglycerides are nonpolar and hydrophobic]
5. c [unsaturated means the carbons are not saturated with hydrogen, thus double bonds are present; monounsaturated refers to one double bond, two or more double bonds refers to polyunsaturated]
6. c [cholesterol is a lipid]
7. b [peptide bonds form between the amino and carboxyl groups of adjacent amino acids]
8. d [the primary level of protein structure is the amino acid sequence. If the sequence is wrong, both the secondary and tertiary level could be greatly altered]
9. b [a zipper is a specific type of motif, chaperones are separate proteins that are thought to assist in protein folding, domains are large structural divisions within a protein]
10. a [since there are 20 amino acids, the building blocks of proteins, the possible combination of the primary sequence is extremely large; carbohydrates are essentially carbon, hydrogen, and oxygen; lipids are similar to carbohydrates and nucleic acids; while the expression of the code is astronomical, there are 5 different nucleotides]
11. a [the two strands of DNA are held together by hydrogen bonds; each strand is complementary to the other]
12. d [hydrogen bonds form between the complementary bases].
Chapter 4Energy, Enzymes, and Biological Reactions
Why It Matters[pp. 70-71]
1. metabolism; 2. enzymes; 3. energy; 4. chemical
4.1 Energy, Life, and the Laws of Thermodynamics[pp. 71-73]
5. Energy; 6. energy; 7. radiation energy; 8. Kinetic; 9. Potential; 10. potential; 11. kinetic; 12. catabolic; 13.exergonic; 14. anabolic; 15. endergonic; 16. Thermodynamics; 17. system; 18. surroundings; 19. system; 20.open system; 21. created; 22. destroyed; 23. constant; 24. sun; 25. photosynthesis; 26. potential; 27. potential; 28.kinetic; 29. heat; 30. entropy; 31. violates; 32. total; 33. heat; 34. spontaneous; 35. Free; 36. positive; 37. negative; 38. exergonic; 39.negative; 40. positive;41. C; 42. J; 43. K; 44. D; 45. A; 46. E; 47. G; 48. F; 49. H; 50. B; 51. I
52. Catabolism:Breakdown reactions
Fat glycerol + fatty acids / 53. Anabolism:
Building reactions
Amino acids join protein
54. Kinetic energy:
Energy released by breaking down glucose to support cellular functions / 55. Potential energy:
Energy stored in glucose molecules
56. Endergonic reactions:
Photosynthesis reaction
CO2 + H2O + Light energy glucose + O2 / 57. Exergonic reaction:
Cellular respiration
glucose + O2 CO2 + H2O + Light energy
58. Positive ∆G:
Hydrolysis of sucrose to form two monosaccharides / 59. Negative ∆G
Combining of two monosaccharides to form sucrose
4.2 Free Energy and Spontaneous Reactions[pp. 73-75]
4.3 Adenosine Triphosphate (ATP): The Energy currency of the Cell [pp. 75-77]
60. Anabolic; 61. endergonic; 62. positive; 63. exergonic; 64. negative; 65. coupled; 66. coupling; 67. ribose; 68.adenine; 69. phosphate; 70. free; 71. phosphate; 72. potential; 73. phosphorylation; 74. endergonic; 75.exergonic; 76. potential; 77. ATP; 78. phosphate; 79. equilibrium; 80. reversible; 81. equilibrium; 82.products 83. C; 84. A; 85. B; 86. E; 87. D; 88. Coupled reactions are reactions that are connected; one reaction may require energy (endergonic) while the other reaction releases energy (exergonic).89. ATP is made of ribose sugar to which adenine and 3 phosphates are attached. It helps in transfer of energy from exergonic to endergonic reactions; 90. If the amount of ATP decreased, metabolism would significantly decrease – chemical reactions are highly dependent on ATP to provide the necessary energy for completion of the reaction. Chemical reactions which are endogenic would be most affected.
4.4 Role of Enzymes in Biological Reactions [pp. 77-79]
4.5 Conditions and Factors Affecting Enzyme Activity [pp. 79-83]
4.6 RNA-based Biological Catalysts: Ribozymes [pp. 83-84]
91. increase; 92. activation;93. catalysts; 94. proteins; 95. active; 96. specificity; 97. -ase; 98. cofactors; 99. coenzymes; 100. product; 101. transition; 102. pH; 103. temperature; 104. collision; 105. 3-dimensional; 106. denature; 107. 3-dimensional; 108. collision; 109. saturation; 110. inhibitors; 111.active; 112. competitive inhibitors; 113. active; 114. 3-dimensional; 115. active; 116.noncompetitive inhibitors; 117. inhibitors; 118. inhibitors;119. active; 120. allosteric; 121. feedback inhibition; 122.phosphorylation; 123. dephosphorylation; 124. protein kinases; 125. protein phosphotases; 126.RNA; 127. proteins; 128. proteins; 129. N; 130. D; 131. I.; 132. E; 133. J; 134. L; 135. A; 136. M; 137. B; 138. G; 139. H; 140. C; 141.K; 142. F
143A. Enzymes use their active site to increase the chances of bringing the reactants closer together.143B. Enzymes use their active site to orient the reactants correctly to increase the chance of forming the transition state.
143C. Enzymes provide the reactants the appropriate ionic environment for forming the transition state.
Inhibitor Explanation
144A. Competitive Inhibitor / Where the inhibitor compete with the reactants for the active site144B. Noncompetitive Inhibitor / Where the inhibitor binds to sites other than the active site of the enzyme, causing a change in 3D structure of the enzyme
144C. Allosteric Regulation / Where an activator or an inhibitor binds to an enzyme, changing its 3D structure, and thereby activating or inhibiting its activity
144D. Feedback Inhibition / Where the ends product of a chain reaction acts as the inhibitor of the first enzyme
145. False—Each enzyme has its optimal range. 146. False—Competitive inhibitor binds to the active site while noncompetitive inhibitor works by binding to site other than the active site.147. True
Self-Test
1. b [Enzymes are proteins that act as chemical catalysts]
2. c [Heat is a form of kinetic energy]
3. a [Glucose has potential energy]
4. d [Entropy is defined as the state of disorder in the system]
5. c [Endergonic reactions have a negative ∆G]
6. c [Active site is where the reactant/s fit]
7. a [Competitive inhibitors inhibit by fitting into the active site—preventing the reactants from entering the active site]
8. c [Cofactors are inorganic chemicals—such as minerals—that help enzymes]; . a [coenzymes are organic—often vitamins—that help enzymes]
9.d [Enzymes are protein molecules whereas ribozymes are RNA molecules]
10. c [Enzymes speed up chemical reactions]
11. d [temperature, substrate levels, inhibitors and enzyme helpers can all have significant effects on enzyme activity]
12. b [Coupled reactions have an overall negative ∆G]
Chapter 5The Cell: An Overview
Why It Matters [pp. 88-89]
1. cell theory; 2. microscope
5.1 Basic Features of Cell Structure and Function[pp. 89-93], 5.2Prokaryotic Cells[pp. 93-94], 5.3 Eukaryotic Cells[pp. 94-107]
3. small; 4. square; 5. cube; 6. membrane; 7. enter or exit; 8. cytoplasm; 9. cytosol; 10. organelles; 11. plasma membrane; 12. prokaryotes; 13; nucleoid; 14. eukaryotes; 15. nucleus; 16. cell wall; 17. capsule; 18. bacterial chromosome; 19. ribosome; 20. prokaryotic flagellum; 21. cell wall; 22.nuclear envelope; 23. nuclear pores; 24. nucleoplasm; 25. chromatin; 26. eukaryotic chromosome; 27.nucleolus; 28. endomembrane system; 29endoplasmic reticulum; 30. Golgi complex; 31. lysosomes; 32.vesicles; 33.cisternae; 34. ER lumen; 35. rough ER; 36. smooth ER; 37. secretory vesicles; 38. exocytosis; 39.endocytosis; 40 phagocytosis; 41. mitochondria; 42. outer mitochondria membrane; 43. inner mitochondria membrane; 44. cristae; 45. mitochondrial matrix; 46. microbodies; 47. peroxisomes; 48. cytoskeleton; 49.microtubules; 50. intermediate filaments; 51. microfilaments; 52centromer; 53. centrioles; 54. flagella; 55.cilia; 56. basal body; 57. cytoplasm; 58. cytoskeleton; 59. glyoxisome; 60. peroxisome; 61. lysosome; 62.microfilament; 63. microtubule; 64. cytosol; 65. prokaryotes; 66. eukaryotes; 67. a; 68. b; 69. c; 70. c; 71. a;72. a; 73. c; 74. b; 75. b; 76. a; 77. a; 78. l; 79. h; 80. i; 81. d; 82. c; 83. b; 84. e; 85. j; 86. k; 87. f; 88. g; 89. secretory vesicles fuse with the plasma membrane and release their contents to the outside of the cell, whereas endocytotic vesicles form when material from the outside is surrounded by a small section of plasma membrane which pinches off and enters to cytoplasm of the cell; 90. The nuclear envelope is a double membrane that surrounds the nucleus, whereas nuclear pores are perforation in the envelope and the nucleoplasm is the contents of the nuleus; 91. Cells with a large surface to volume ratio are small, these cells have a large surface area to the volume of the cell to support the cell. Cells with a small surface to volume ratio are typically very big and the surface area is too small to support the volume of the cell. The surface increases by the square and the volume by the cube, thus is it advantageous to be small. 92. bacterial flagellum; 93. cell wall; 94. capsule; 95. rough ER; 96. smooth ER; 97. cisternae; 98. ER lumen; 99. Golgi complex; 100. mitochondria; 101. outer membrane; 102. inner membrane; 103. cristae; 104. matrix; 105. centriole; 106.nuclear envelope
5.4Specialized Structures of Plant Cells[pp. 107-110], 5.5 The Animal Cell Surface[pp. 110-112].
107. chloroplasts; 108. outer boundary membrane; 109. inner boundary membrane; 110. stroma; 111. thylakoids; 112.grana; 113. plastids; 114. amyloplats; 115. chromoplasts; 116. central vacuole; 117. tonoplast; 118. primary cell wall; 119. secondary cell wall; 120. middle lamella; 121. plasmodesmata; 122. extracellular matrix; 123. cell adhesion molecules; 124. cell junctions; 125. anchoring junctions; 126. desmosomes; 127. adherens junctions; 128.tight junctions; 129. gap junctions; 130. chlorophyll; 131. chromoplast; 132. amyloplast; 133. a; 134. b. 135.c; 136. c; 137. b; 138. f; 139. a; 140. e; 141. d; 142. both are channels that connect the cytoplasms of adjacent cells; plasmodesmata are membrane-lined channels that perforate cell wall material between plant cells, whereas gap junctions are protein-lined channels through the plasma membrane that align between two animal cells; 143.chloroplast; 144. outer membrane; 145. inner membrane; 146. stroma; 147. thylakoid; 148. grana; 149. central vacuole; 150. tonoplast
Self-Test
1. a, d
2. c, d [d is correct because surface area increases with the square of a dimension, whereas volume increases with the cube of a dimension; therefore, as the dimension increases, volume increases more rapidly than surface area; c is correct because the ability of a cell to take up nutrients and to eliminates wastes depends on diffusion, which is limited by surface area]
3. a, b
4. a, b, c, d
5. a, b, c, d
6. a, c, d
7. a, b, c, e
8. a, b, c [a is correct because the cytoskeleton is constantly be built up and broken down in various regions of the cell; b is correct because protein are what make up microfilaments, intermediate filaments, and microtubules; c is correct because microtubles are one of the three types of cytoskeletal elements]
9. a, c, d [a, c, and e are correct because plastids are found in plants (which are eukayotes), fungi (which is a eukaryote), and protoctistins, including algae (which also are eukaryotes), but not in animals (which also are eukaryotes), which means that some but not all eukaryotes contain plastids; e is incorrect because no prokaryotes have membrane-bound organelles, including plastids]