ASSIGMENT DISCUSSION

The purpose of this Biology Discussion is to help each other understand the main concepts presented in the chapters covered this week. General Biology, the required readings are Chapters 4 -7.

*One of the entries MUST ask a question about a concept/idea presented in the required readings in the textbook from the chapters covered this week. This should be a question pertaining to material that you personally do not understand or need clarification on and should be at least 40-50 words in length. Question topics cannot be claimed, and it is one question topic per student. This will aid in diversifying the discussion. Broad categories are posted already in the discussion board. Post your question under the category to which it best applies. State your question in the subject line of the post. This will create a list of questions and that everyone will be able to see.

2 Biology Discussion

The purpose of this Biology Discussion is to help each other understand the main concepts presented in the chapters covered this week. General Biology, the required readings are Chapters 4 -7.

Each student must make at least three (3) entries during the week.

*One of the entries MUST ask a question about a concept/idea presented in the required readings in the textbook from the chapters covered this week
. This should be a question pertaining to material that you personally do not understand or need clarification on and should be at least 40-50 words in length. Question topics cannot be claimed, and it is one question topic per student. This will aid in diversifying the discussion. Broad categories are posted already in the discussion board. Post your question under the category to which it best applies. State your question in the subject line of the post. This will create a list of questions and that everyone will be able to see.

*The two remaining entries must offer an explanation in answer to a classmate’s question. Your responses must be researched, and the content of your response must be supported by reliable and credible resources. These
two response posts must be a minimum of 200 words each.

*Ground rules for the Biology Discussion: Each post must be in your own words. Do NOT copy and paste from the Internet. [Review the Plagiarism presentation in the Student Resource Center.] It is better to paraphrase content/information (putting the content/information in your own words) from a resource. Paraphrased information from resource is required to be properly cited per APA requirements*, with it-text citations immediately following the information and a full reference citation at the end of the discussion board posting. [*Refer to the Getting Started area of the class for ‘Helpful Resources & Websites on Referencing Sources per APA’ and to the Student Resources tab on the left-hand side of the classroom.]

Chapter 7

Energy for Cells

Essentials of Biology

SEVENTH EDITION

Sylvia S. Mader
Michael Windelspecht

Because learning changes everything.®

7.1 Cellular Respiration
Produces ATP molecules for energy
Requires oxygen and glucose; produces carbon dioxide and water
Reason you breathe
Essentially the reverse of photosynthesis
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Figure 7.1 Cellular Respiration

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(photo): Juice Dash/Shutterstock
3

Glucose Is Broken Down in Steps
Phases of complete glucose breakdown
Glucose broken down slowly in steps
Allows energy to be captured and used to make ATP
Coenzymes (nonprotein helpers) join with hydrogen
N A D⁺ → NADH
F A D⁺→ FADH2
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Cellular Respiration Involves Redox Reactions
Oxidation = removal of hydrogen atoms
Hydrogens removed from glucose
Gives waste product carbon dioxide
Reduction = addition of hydrogen atoms
Oxygen accepts hydrogens
Become waste product water

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Figure 7.3 The Four Phases of Complete Glucose Breakdown

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7.2 Outside the Mitochondria: Glycolysis

Glycolysis
In eukaryotes, takes place in the cytoplasm
Glucose (six carbons) broken down into two molecules of pyruvate (three carbons)
Divided into:
Energy-investment steps
Energy-harvesting steps

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Figure 7.4 Glycolysis, Energy-Investment Step
The following content is arranged like a table.

3PG 3-phosphoglycerate

BPG 1,3-bisphosphoglycerate

G3P glyceraldehyde 3-phosphate

Energy-investment steps
Two ATP transfer phosphates to glucose
Activates them for next steps

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Figure 7.4 Glycolysis, Energy-Harvesting Steps
Energy-harvesting steps
Substrate-level ATP synthesis produces four ATP
Net gain of two ATP
Two NADH made
The following content is arranged like a table.

3PG 3-phosphoglycerate

BPG 1,3-bisphosphoglycerate

G3P glyceraldehyde 3-phosphate

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Figure 7.6 Glycolysis Totals

Next step depends on oxygen availability.
With oxygen, pyruvate enters mitochondria.
Without oxygen, pyruvate undergoes reduction.

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7.3 Outside the Mitochondria: Fermentation 1
Oxygen is required for the complete breakdown of glucose in aerobic respiration.
Fermentation—anaerobic breakdown of glucose
Generates only two ATP total
Animal cells
Pyruvate reduced to lactate
Brief burst of energy for muscle cells
Recovery from oxygen deficit complete when enough oxygen is present to completely break down glucose
Lactate converted back to pyruvate or glucose
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Outside the Mitochondria: Fermentation 2
Microorganisms and fermentation
Bacteria use fermentation to produce:
Lactate or other organic acids
Alcohol and carbon dioxide
Yeast—carbon dioxide makes bread rise, ethanol made into wine and beer

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Figure 7.7 The Anaerobic Pathways, Glycolysis 1

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Figure 7.7 The Anaerobic Pathways 2

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(runner): Michael Svoboda/iStockphoto/Getty Images; (wine): C Squared Studios/Photodisc/Getty Images
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Figure 7.7 The Anaerobic Pathways 3

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(runner): Michael Svoboda/iStockphoto/Getty Images; (wine): C Squared Studios/Photodisc/Getty Images
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7.4 Inside the Mitochondria

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Keith R. Porter/Science Source
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Inside the Mitochondria, Preparatory Reaction
Preparatory reaction
Occurs in mitochondrial matrix
Produces a substrate that enters the citric acid cycle
Occurs twice per glucose molecule
Pyruvate oxidized, C O2 molecule given off
N A D⁺ →NADH
2-carbon acetyl group attached to CoA to form acetyl-CoA
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Inside the Mitochondria, Citric Acid Cycle
Citric Acid Cycle
Occurs in matrix of mitochondria
Acetyl CoA transfer acetyl group to C4 molecule—produces citric acid (six carbons)
CoA returns to preparatory reaction for reuse
Acetyl group oxidized to carbon dioxide
N A D⁺ →NADH and F A D →FADH2
Substrate-level ATP synthesis produces ATP
Two cycles for each glucose molecule
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The Preparatory Reaction

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The Citric Acid Cycle

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Figure 7.11 Inputs and Outputs of the Citric Acid Cycle

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Electron Transport Chain 1
Electron transport chain location
Located in cristae of mitochondria
Series of carriers pass electrons from one to the other
NADH and FADH2 deliver electrons
Hydrogen atoms attached consist of e⁻ and H²
Carriers accept only e⁻ not H²

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Electron Transport Chain 2
High-energy electrons enter/low-energy electrons leave
As pair of electrons passed from one carrier to the next, energy is released.
Will be captured for ATP production
Final electron acceptor is oxygen—forms water.

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Figure 7.13a The Electron Transport Chain

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ATP Synthase
ATP synthesis carried out by ATP synthase in inner mitochondrial membrane
Carriers of electron transport system pass electrons
Energy used to pump H⁺ from matrix into intermembrane space—creates H⁺ gradient
ATP synthase uses energy to make ATP.

Figure 7.13b

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Figure 7.13 The Organization of Cristae

Orange arrow indicates flow of electrons through carriers in ETC
H⁺ ions accumulate in intermembrane space and are then used to in the ATP synthase complex to form ATP.

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7.5 Metabolic Fate of Food
Energy yield from glucose metabolism
Maximum of 38 ATP made
Some cells make only 36 ATPs or less.
36–38 ATP about 40% of available energy in a glucose molecule
Rest is lost as heat.

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Alternative Metabolic Pathways, Fats and Proteins
Cells use other energy sources such as proteins and fats.
Fatty acids have longer carbon chains—yields more ATP.
Intermediates can also be used to make other products.
Extra food made into fat for storage.

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(photo): C Squared Studios/Photodisc/Getty Images
28

End of Main Content
© McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.

Because learning changes everything.®
www.mheducation.com

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Figure 7.1 Cellular Respiration – Text Alternative

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The respiration process involves intake of oxygen and glucose and the release of carbon dioxide and water which takes place in the mitochondrion. The mitochondrion has a double membrane (inner and outer membranes), matrix, cristae, and intermembrane space.

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Cellular Respiration Involves Redox Reactions – Text Alternative

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In the reaction, glucose combines with six molecules of oxygen giving six molecules of carbon dioxide, six molecules of water, and energy. Both oxidation and reduction occur during cellular respiration. The glucose molecule is oxidized to produce carbon dioxide and oxygen molecules are reduced to generate water molecules.

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Figure 7.3 The Four Phases of Complete Glucose Breakdown – Text Alternative

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The first stage of cellular respiration is glycolysis in which a glucose molecule breaks down into pyruvate. Glycolysis occurs in the cytoplasm of the cell. The net gain of ATP in glycolysis is 2ATP. The pyruvate enters into mitochondria and undergoes a preparatory reaction. C O2 is produced in the reaction. Further, the products of the preparatory phase undergo a citric acid cycle reaction during which 2ATP and C O2 are produced. The last step is the electron transport chain. During the process, the carrier molecule NADH transfers electrons from the original glucose molecule to an electron transport chain. In this way, the electrons move within the inner membrane of the mitochondria by NADH and FADH2, ultimately being pulled to oxygen found at the end of the chain. The oxygen and electrons combine with hydrogen ions to form water. This step generates 34 ATP molecules.

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7.2 Outside the Mitochondria: Glycolysis – Text Alternative

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The first stage of cellular respiration is glycolysis in which a glucose molecule breaks down into pyruvate. Glycolysis occurs in the cytoplasm of the cell. The net gain of ATP in glycolysis is 2ATP. The pyruvate enters into mitochondria and undergoes a preparatory reaction. Further, the products of the preparatory phase undergo citric acid reaction during which 2ATP are produced. The last step of cellular respiration is the electron transport chain. During the process, the carrier molecule NADH transfers electrons from the original glucose molecule to an electron transport chain. In this way, the electrons move within the inner membrane of the mitochondria by NADH and FADH2. This step generates 34 ATP molecules.

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Figure 7.4 Glycolysis, Energy-Investment Step – Text Alternative

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Energy-investment step:
Six carbon glucose on the conversion of two ATP molecules into two ADP molecules forms a chain of two 3-carbon glyceraldehyde 3-phosphate (G3P) molecules linked together. Further, the chain of two glyceraldehyde 3-phosphate molecules bifurcates into two molecules of glyceraldehyde 3-phosphate.

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Figure 7.4 Glycolysis, Energy-Harvesting Steps – Text Alternative

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Right Top: Step 1: energy investment step: glucose is broken down to ADP and P which is converted to G3P and P. Step 2: energy-harvesting steps: G3P is converted to BPG, while N A D superscript positive is converted to NADH in the presence of P. BPG is converted to 3PG, while ADP is converted to ATP. 3PG is converted to water and P which is converted to pyruvate. Net gain: 2 ATP.
Left Bottom: In the reaction, the reactant shows a chain of three spheres having first and third spheres linked with two phosphate groups each. The bond of the first phosphate group is marked as substrate. The phosphate group attached to the third sphere binds to an enzyme and on the conversion of ADP into ATP gives the product as a chain of three spheres with the first sphere linked to a phosphate group. A dotted curvy arrow shows the linking of the phosphate group to the ADP molecule.

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Figure 7.6 Glycolysis Totals – Text Alternative

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The inputs of glycolysis include glucose, two molecules of N A D plus, two molecules of ATP, four molecules of ADP, and two Phosphates. The outputs include two molecules of pyruvate, two molecules of NADH, two molecules of ADP, and four molecules of ATP. The net gain is shown as two molecules of ATP.

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Outside the Mitochondria: Fermentation 2 – Text Alternative

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The inputs of fermentation include glucose, two molecules of NADH, two molecules of ATP, four molecules of ADP, and four Phosphates. The outputs include two molecules of lactate or two molecules of alcohol and two molecules of carbon dioxide, two molecules of N A D plus, two molecules of ADP, and four molecules of ATP. The process of fermentation shows a net gain of two molecules of ATP.

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Figure 7.7 The Anaerobic Pathways, Glycolysis 1 – Text Alternative

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The steps are as follows:
1. A 6-carbon glucose molecule converts into two molecules of a 3-carbon compound attached with a phosphate group at one end. Two molecules of ATP break into ADP with a net loss of two molecules of ATP.
2. Two molecules of a 3-carbon compound on the addition of two molecules of phosphate and conversion of two N A D positive into two NADH forms two molecules of another 3-carbon compound attached with phosphate groups at both ends.
3. Further, the 3-carbon compound on the conversion of four molecules of ADP into four molecules of ATP forms two molecules of pyruvate.

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Figure 7.7 The Anaerobic Pathways 2 – Text Alternative

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In fermentation, two molecules of pyruvate form either two molecules of lactate or two molecules of alcohol. The formation of lactate during fermentation is called lactic acid fermentation (exemplified by a photo of a woman in activewear bent down with her hands on her knees). The formation of alcohol during fermentation is called alcohol fermentation (exemplified by a photo of an alcohol bottle). If alcohol is formed, then the conversion of two NADH taken from glycolysis converts into two N A D positive, and two molecules of carbon dioxide are given out. The net gain of the process is 2 ATP.

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Figure 7.7 The Anaerobic Pathways 3 – Text Alternative

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The steps are as follows:
Glycolysis:
1. A 6-carbon glucose molecule converts into two molecules of a 3-carbon compound attached with a phosphate group at one end. Two molecules of ATP break into ADP with a net loss of two molecules of ATP.
2. Two molecules of a 3-carbon compound on the addition of two molecules of phosphate and conversion of two N A D positive into two NADH forms two molecules of another 3-carbon compound attached with phosphate groups at both ends.
3. Further, the 3-carbon compound on the conversion of four molecules of ADP into four molecules of ATP forms two molecules of pyruvate depicting a net gain of four molecules of ATP.
Fermentation:
1. In fermentation, two molecules of pyruvate form either two molecules of lactate or two molecules of alcohol. The formation of lactate during fermentation is called lactic acid fermentation while the formation of alcohol during fermentation is called alcohol fermentation. If alcohol is formed then the conversion of two NADH taken from glycolysis converts into two N A D positive and two molecules of carbon dioxide are given out. The net gain of the process is 2 ATP.

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7.4 Inside the Mitochondria – Text Alternative

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A micrograph of mitochondrion and a drawing of the same shows outer membrane, matrix, cristae, and inner membrane space. Cristae: location of the electron transport chain, matrix: location of the prep reaction and the citric acid cycle, mitochondrion: location of aerobic respiration, cytoplasm: location of glycolysis.

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The Preparatory Reaction – Text Alternative

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The illustration shows how the preparatory reaction results in Citric acid cycle using NADH and FADH2, producing 2 ATPs in the matrix of a mitochondrion. The first stage of cellular respiration is glycolysis. The net gain of ATP in glycolysis is 2ATP. The pyruvate enters into mitochondria and undergoes a preparatory reaction. Further, the products of the preparatory phase undergo citric acid reaction during which 2ATP are produced. The last step of cellular respiration is the electron transport chain. During the process, the carrier molecule NADH transfers electrons from the original glucose molecule to an electron transport chain. In this way, the electrons move within the inner membrane of the mitochondria by NADH and FADH2. This step generates 34 ATP molecules.
Step 1 of the preparatory reaction: Each pyruvate from glycolysis is oxidized to a 2-carbon acetyl group that is carried by CoA to the citric acid cycle.

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The Citric Acid Cycle – Text Alternative

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The steps are as follows:
2) Each 2-carbon acetyl group combines with a 4-carbon molecule to produce citric acid, a 6-carbon molecule.
3) Oxidation reactions produce NADH, and C O2 is released.
4) The loss of two C O2 results in a new 4-carbon molecule.
5) ATP is produced by substrate-level ATP synthesis.
6) Additional oxidation reactions produce another NADH and an FADH2 and regenerate the original 4-carbon molecule.

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Figure 7.11 Inputs and Outputs of the Citric Acid Cycle – Text Alternative

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Inputs: 2 acetyl-C o A, 6 N A D superscript positive, 2 F A D, 2 ADP plus 2 P. Outputs: 4 C O2, 6 NADH, 2 FADH2, 2 ATP.

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Electron Transport Chain 1 – Text Alternative

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Cytoplasm:
Glucose undergoes glycolysis and forms two molecules of pyruvate with a net gain of two ATP. The two NADH plus hydrogen ion produced during glycolysis go through an electron transport chain and forms four or six ATP molecules.
Mitochondrion:
Two pyruvate converts into two acetyl coenzyme A with the release of two molecules of carbon dioxide. The two NADH plus hydrogen ion produced during the step go through the electron transport chain and form six ATP molecules.
The citric acid cycle releases four molecules of carbon dioxide. The six molecules of NADH plus hydrogen ion produced during citric acid go through the electron transport chain and produce eighteen ATP molecules. The citric acid cycle also produces two molecules of dihydro-flavin adenine dinucleotide which form four ATP molecules through the electron transport chain.
Six molecules of oxygen convert to six molecules of water.
A subtotal of four ATP obtained from the net gain of glycolysis and citric acid cycle with a subtotal of 32 or 34 ATP obtained from the electron transport chain gives out a total yield of 36 to 38 ATP.

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Electron Transport Chain 2 – Text Alternative

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Figure 7.13a The Electron Transport Chain – Text Alternative

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The cross-section of the mitochondrion shows three labeled parts including matrix, cristae, and intermembrane space. The enlarged view of intermembrane space and matrix shows the processes as follows:
a. Electron transport chain: The electron transport chain is a series of electron transporters carriers embedded in the inner mitochondrial membrane. Mobile carriers transport electrons from NADH and FADH2 to molecular oxygen. NADH produces N A D positive and FADH2 produces F A D. Hydrogen ions are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.

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ATP Synthase – Text Alternative

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The cross-section of the mitochondrion shows three labeled parts including matrix, cristae, and intermembrane space. The enlarged view of intermembrane space and matrix shows the processes as follows:
b. ATP synthesis: The synthesis of ATP from ADP and phosphate is catalyzed by the ATP synthase complex, a mitochondrial enzyme located in the inner membrane. The synthesis of ATP is driven by the flow back of hydrogen ions across a gradient generated by the ATP synthase complex.

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Figure 7.13 The Organization of Cristae – Text Alternative

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The cross-section of the mitochondrion shows three labeled parts including matrix, cristae, and intermembrane space. The enlarged view of intermembrane space and matrix shows the processes as follows:
a. Electron transport chain: The electron transport chain is a series of electron transporters carriers embedded in the inner mitochondrial membrane. Mobile carriers transport electrons from NADH and FADH2 to molecular oxygen. Hydrogen ions are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.
b. ATP synthesis: The synthesis of ATP from ADP and phosphate is catalyzed by the ATP synthase complex, a mitochondrial enzyme located in the inner membrane. The synthesis of ATP is driven by the flow back of hydrogen ions across a gradient generated by the ATP synthase complex.

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7.5 Metabolic Fate of Food – Text Alternative

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The data given in the table are as follows:
Phase; Glycolysis, NADH; 2, FADH2; blank, ATP yield; 2
Phase; Prep reaction, NADH; 2, FADH2; blank, ATP yield; blank
Phase; Citric acid cycle, NADH; 6, FADH2; 2, ATP yield; 2
Phase; Electron transport chain, NADH; 10, FADH2; 2, ATP yield; 34
Total ATP; 38

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Alternative Metabolic Pathways, Fats and Proteins – Text Alternative

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Proteins: During respiration, proteins reversibly split into amino acids which further lose ammonia and undergo different steps including glycolysis, formation of acetyl co A and citric acid cycle. The products of the citric acid cycle undergo an electron transport chain. ATP is released during glycolysis, citric acid cycle, and electron transport chain.
Carbohydrates: Carbohydrates reversibly convert into glucose which goes through the further steps of respiration including glycolysis, formation of acetyl co A and citric acid cycle. The products of the citric acid cycle undergo an electron transport chain. Oxygen O2 is reduced to form water H2O via electron transport chain. ATP is released during glycolysis, citric acid cycle, and electron transport chain.
Fats: Fats break up into fatty acids and glycerol before being used in respiration. Fatty acids are broken into acetyl coenzyme A and then enter the citric acid cycle. Glycerol enters glycolysis and further steps of respiration. ATP is also released during the steps of fat respiration.

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Chapter 5

The Dynamic Cell

Essentials of Biology

SEVENTH EDITION

Sylvia S. Mader
Michael Windelspecht

Because learning changes everything.®

5.1 What Is Energy?
Energy is the capacity to do work.
Our biosphere gets its energy from the sun.
Two basic forms of energy
Potential energy—stored energy
Kinetic energy—energy of motion
Two forms are converted back and forth.
During conversions, some lost as heat.
2

Figure 5.1 Potential Energy Versus Kinetic Energy

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Calorie and Kilocalorie
Measuring energy
Food energy is measured in calories.
Calorie—amount of heat required to raise temperature of 1 g of water by 1°C
Kilocalorie or calorie = 1,000 calories
Value listed on food packages
4

Energy Laws
Two energy laws
First law—conservation of energy
Energy cannot be created or destroyed, but it can be changed from one form to another.
Second law
Energy cannot be changed from one form to another without a loss of usable energy.
Heat is the least usable form of energy.
5

Entropy 1
Entropy:
Every energy transformation leads to an increase in the amount of disorganization or disorder.
Entropy—relative amount of disorganization
Only way to maintain or bring about order is to add energy.
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Entropy 2
Entropy, continued
Our universe is a closed system.
All energy transformations increase the total entropy of the universe.
Energy provided by the sun allows plants to make glucose from the more disorganized water and carbon dioxide.
Some of sun’s energy is lost as heat.
7

Figure 5.2a Cells and Entropy

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(photos: both): Keith Eng, 2008
8

Figure 5.2b Cells and Entropy

Unequal distribution of hydrogen ions

Equal distribution of hydrogen ions
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5.2 ATP: Energy for Cells
Adenosine triphosphate (ATP)
Energy currency of cells
Cells use ATP to carry out nearly all activities.
One nucleotide along with three phosphate groups makes it unstable.
Easily loses a phosphate group to become adenosine diphosphate (ADP)
Continual cycle of breakdown and regeneration
10

Figure 5.3 ATP

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Figure 5.4 The ATP Cycle

ATP releases energy quickly.
Amount of energy released is usually just enough for a biological purpose.
Breakdown can be easily coupled to an energy-requiring reaction.

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Coupled Reactions
Coupled reactions:
Energy-releasing reaction can drive an energy-requiring reaction.
Usually, energy-releasing reaction is ATP breakdown.

Figure 5.5 Coupled Reaction

ATP breakdown provides the energy for muscle movement.
Myosin combines with ATP.
ATP breaks down.
Release of ADP + P causes myosin to change shape and pull on the actin filament.

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The Flow of Energy
The flow of energy:
Activities of chloroplasts and mitochondria enable energy to flow from the sun through all living things.
Photosynthesis—solar energy used to convert water and carbon dioxide into carbohydrates
Food for plants and other organisms
Cellular respiration—carbohydrates broken down and energy used to build ATP
Useful energy is lost with each transformation.
Living things dependent on constant in/out of solar energy
15

Figure 5.6 Flow of Energy

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(leaves): ooyoo/Getty Images; (woman): Karl Weatherly/Photodisc/Getty Images
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Humans and Energy
Humans are also involved in the cycling of molecules between plants and animals and in the flow of energy from the sun.
Inhale oxygen, eat plants and animals
Energy rich foods allow us to produce the ATP required to maintain our bodies and carry on activities.
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5.3 Metabolic Pathways and Enzymes

a. Active enzyme and active pathway

b. Feedback inhibition

c. Inactive enzyme and inactive pathway
Metabolic pathway—series of linked reactions
The letters

represent enzymes.
Protein molecules that function as organic catalysts speed up reactions.
Can only speed up possible reactions

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Figure 5.7 Enzymatic Action

Enzymes
Act on substrates
May facilitate breakdown or synthesis reactions
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Enzyme’s Active Site
Enzyme’s active site
Accommodates substrate
Like a lock and key—specific to one substrate
Induced fit model—undergoes slight shape change to accommodate substrate
Change in shape facilitates reaction
Active site returns to original shape after releasing product(s)
Enzymes are not used up by the reaction.
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Enzyme Inhibition
Enzyme inhibition:
Occurs when an active enzyme is prevented from combining with its substrate.
Cyanide is a poison because it binds to and inhibits cytochrome c oxidase.
Penicillin interferes with a bacterial enzyme that kills the bacteria.
Feedback inhibition
When a product is in abundance, it competes with substrate for active site
An end product of a pathway can inhibit the first enzyme in the pathway—binds to a site other than active site to cause shape change—which shuts the entire pathway down
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Figure 5.8a Feedback Inhibition—Active Enzyme and Active Pathway

a. Active enzyme and active pathway

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Figure 5.8b Feedback Inhibition

b. Feedback inhibition
When a product builds up—the body doesn’t need more
Product binds to enzyme and changes its shape
Loss of shape = loss of function

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Figure 5.8c Feedback Inhibition, concluded

c. Inactive enzyme and inactive pathway
Now the substrate can’t bind to enzyme and the reaction stops
When the product gets low, enzyme will go back to original shape.
Enzyme starts working again.
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Energy of Activation
Energy of activation:
Molecules frequently do not react with each other unless activated.
Energy of activation (

)—energy needed to cause
molecules to react with one another
Enzymes lower the amount of energy required.
Enzymes bring substrates into contact and even sometimes participate in the reaction.
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Figure 5.9 Energy of Activation (E sub a)

A LOWER hurdle is easier/faster to get over
A LOWER energy of activation makes a reaction easier/faster

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5.4 Cell Transport
Plasma membrane regulates traffic in and out of the cell.
Selectively permeable—some substances pass freely, some transported, some prohibited
Three ways to enter
Passive transport—substances move from higher to lower concentration, no additional energy is required.
Active transport—substances move from lower to higher concentration, additional energy is required.
Bulk transport—movement independent of gradients, additional energy is required.
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Passive Transport
Passive transport:
No energy required for simple diffusion
Molecules move down their concentration gradient until equilibrium is reached.
Cell does not expend additional energy—molecules already in motion.
Some molecules slip between phospholipids.
Facilitated diffusion—others use transport protein specific to molecule
Water uses aquaporins—this explains faster than expected transport rate.
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Figure 5.10 Simple Diffusion Demonstration

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Figure 5.11 Facilitated Diffusion

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Figure 5.12 Osmosis Demonstration

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Figure 5.13 Osmosis in Animal and Plant Cells—Isotonic Environment
Effect of osmosis on cells
Isotonic solution
No net gain or loss of water
Concentration of water same on both sides of the membrane
0.9% saline isotonic to red blood cells

Figure 5.13 Osmosis in Animal and Plant Cells—Hypotonic Environment
Hypotonic solution
Concentration of water outside cell greater than inside cell
Cell gains water.
Animal cells may lyse or burst
Plant cells use this to remain turgid.

Figure 5.13 Osmosis in Animal and Plant Cells—Hypertonic Environment
Hypertonic solution
Concentration of water outside cell less than inside cell
Cell loses water.
Animal cells shrink.
Plant cells undergo plasmolysis and may wilt.

Figure 5.14 Active Transport

Active transport:
Cells expend energy to move molecules against a concentration gradient.
Requires transport protein
Sodium–potassium pump is important in maintaining gradient of ions used in the nerve impulse conduction.

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Figure 5.15 Sodium–Potassium Pump

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Bulk Transport
Bulk transport:
Macromolecules are often too large to be moved by transport proteins.
Vesicle formation takes them in or out of cell.
Exocytosis—movement out of cell
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Figure 5.16a Bulk Transport—Exocytosis

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Figure 5.15b Bulk transport—Endocytosis

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Endocytosis
Endocytosis—movement into cell
Phagocytosis—cell surrounds, engulfs, and digests particle
Pinocytosis—vesicle forms around liquid or small particles
Receptor-mediated endocytosis—receptors for particular substances found in coated pit—selective and more efficient.
40

Figure 5.17 Receptor-Mediated Endocytosis

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(photos): Mark Bretscher
41

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43

Figure 5.1 Potential Energy Versus Kinetic Energy – Text Alternative

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Plants capture solar energy and store it as potential energy in different parts of the plant like fruits, stems, and leaves. When a man eats a fruit, the potential energy enters his body where it is transformed into kinetic energy when he moves from one location to another. At every stage of the energy flow, some energy is also lost as heat.

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Figure 5.2a Cells and Entropy – Text Alternative

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The photo on the left depicts a clean, organized room with everything in its right place. The right photo shows a dirty, disorganized room with items strew on the bed and the floor.

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Figure 5.3 ATP – Text Alternative

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The structure of ATP consists of adenine, ribose, and triphosphate bonded together.

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Figure 5.4 The ATP Cycle – Text Alternative

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The ADP combines with a P utilizing the energy from cellular respiration to give ATP. ATP releases energy for cellular activity (for example, protein synthesis, nerve conduction, muscle contraction) and breaks down into ADP and P. The structure of ADP consists of adenine, ribose, and diphosphate bonded together.

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Figure 5.5 Coupled Reaction – Text Alternative

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The reaction takes place as follows: Myosin assumes its resting shape when it combines with ATP. ATP splits into ADP and P, causing myosin to change its shape and allowing it to attach to actin. Release of ADP and causes myosin to again change shape and pull against actin, generating force and motion.

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Figure 5.6 Flow of Energy – Text Alternative

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Chloroplasts present in green plants trap solar energy and convert it into chemical energy (carbohydrate) through photosynthesis. Oxygen and heat are released during the process. Mitochondria convert chemical energy to ATP molecules, which are stored in cells. Cells use this stored energy in chemical work, transport work, and mechanical work. During cellular respiration in mitochondria, carbon dioxide and water are produced, which are utilized by chloroplast during photosynthesis.

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5.3 Metabolic Pathways and Enzymes – Text Alternative

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a. The first substrate S binds with the active site of enzyme E1 with another binding site also. Further, multiple enzymes E2, E3, and E4 also react in the metabolic pathway, and finally, end product P is formed.
b. The binding forms a product enzyme complex in which the shape of the active site is changed.

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Figure 5.8a Feedback Inhibition—Active Enzyme and Active Pathway – Text Alternative

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The first substrate S binds with the active site of enzyme E1 with another binding site also. Further, multiple enzymes E2, E3, and E4 also react in the metabolic pathway, and finally, end product P is formed.

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Figure 5.8b Feedback Inhibition – Text Alternative

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The binding forms a product enzyme complex in which the shape of the active site is changed.

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Figure 5.9 Energy of Activation (E sub a) – Text Alternative

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A curve labeled with enzyme starts from the reactants, reaches a small peak, and slopes down to the product. The energy of activation needed is less. A curve labeled without enzyme starts from the reactants, reaches a bigger peak, and slopes down to the product. The energy of activation needed is high.

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Figure 5.10 Simple Diffusion Demonstration – Text Alternative

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The diagram is discussed as follows:
a. A purple crystal of dye is placed in water at the bottom of the aquarium. Its molecular view shows separate groups of water and dye molecules.
b. After some time, the water of the aquarium starts turning purple. Due to the beginning of diffusion, the water and dye molecules are somewhat mixed in its molecular view.
c. After the passage of some more time, the water of the aquarium turns completely purple. The molecular view of the dye shows the equal distribution of water and dye molecules as a result of complete diffusion.

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Figure 5.11 Facilitated Diffusion – Text Alternative

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It shows a carrier protein embedded in the plasma membrane of a cell. The solute particles outside the cell enter the cell through the carrier protein.

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Figure 5.12 Osmosis Demonstration – Text Alternative

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The setup consists of a thistle tube with the broad end covered by a semipermeable membrane filled with 10% salt solution. It is immersed in a beaker containing 5% salt solution. After sometime, the concentration of the beaker solution becomes more than 5% and the solution in the thistle tube becomes less concentrated (less than 10%).

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Figure 5.14 Active Transport – Text Alternative

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From the left, the first diagram shows solute molecules outside of a cell moving toward the transport protein embedded in the bilayer of the plasma membrane. The adenosine triphosphate present inside the cell provides energy for the movement of the solutes. In the second diagram, the transport protein holds a solute by changing its shape accordingly. The breakdown of adenosine triphosphate molecules releases adenosine diphosphate and one phosphate group. The released phosphate group attaches to the transport protein towards the interior of the cell. The third diagram shows the release of the solute to the inside of the cell. The arrowheads show the direction of the movement of the solute. The phosphate group now dissociates from the transport protein, which again causes its shape to change.

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Figure 5.15 Sodium–Potassium Pump – Text Alternative

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The enlarged diagrams show a carrier protein with the phospholipid bilayer at the sides, along with the sodium and potassium cations. The six steps are as follows:
1. Carrier protein has a shape that allows it to take up three sodium cations.
2. Adenosine triphosphate (ATP) is split, and phosphate group attaches to carrier.
3. Change in shape results and causes carrier to release three sodium cations outside the cell.
4. Carrier has a shape that allows it to take up two Potassium cations.
5. Phosphate group is released from carrier.
6. Change in shape results and causes carrier to release two Potassium cations inside the cell.

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Figure 5.16a Bulk Transport—Exocytosis – Text Alternative

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A vesicle is formed inside the cell which fuses with the plasma membrane and ultimately discharges the vesicle content to the outside of the cell.

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Figure 5.15b Bulk transport—Endocytosis – Text Alternative

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It shows a vesicle-like pit formed inside the plasma membrane which ultimately forms a vesicle and moves inside the cell.

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Chapter 6

Energy for Life

Essentials of Biology

SEVENTH EDITION

Sylvia S. Mader
Michael Windelspecht

Because learning changes everything.®

6.1 Overview of Photosynthesis
Photosynthesis
Transforms solar energy into chemical energy of carbohydrates
Plants, algae, and cyanobacteria
Producers—feed themselves and all of the consumers (most other living organisms on Earth)
2

Figure 6.1 Photosynthetic Organisms

(kelp): Chuck Davis/The Image Bank/Getty Images; (diatoms): ©Ed Reschke; (Euglena): M I (Spike) Walker/Alamy Stock Photo; (sunflower): Hammond HSN/Design Pics; (mosses): Steven P. Lynch; (cyanobacteria): John Hardy, University of Washington – Stevens Point Department of Biology
3

Figure 6.2 Leaves and Photosynthesis
Plants as photosynthesizers
Green portions carry on photosynthesis.
Carbon dioxide enters leaves through stomata.
Roots absorb water.
C O2 and H2O diffuse into mesophyll cells and then into chloroplasts.

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(mesophyll cell): Dr. David Furness, Keele University/Science Source; (chloroplast): Omikron/Science Source
4

Chloroplast
Chloroplast:
Double membrane surrounds stroma.
Third membrane forms thylakoids.
Grana—stacks
Thylakoid space
Chlorophyll and other pigments reside within thylakoid membrane.
Pigments absorb solar energy.
Carbon dioxide will be reduced in the stroma into carbohydrates.
Glucose is the chief organic energy source for most organisms.
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The Photosynthetic Process 1
The photosynthetic process:
Begins with the end products of cellular respiration—C O2 and H2O
Hydrogen atoms removed from water are added to carbon dioxide.
Solar energy is required.
Oxygen is a by-product of the oxidation of water.
End product is CH2O or glucose C6H12O6.

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The Photosynthetic Process 2
Two sets of reactions
Light reactions
Occur in thylakoid membrane
Chlorophyll absorbs solar energy and energizes electrons.
Water is oxidized, releasing electrons, hydrogen ions, and oxygen.
ATP produced in electron transport chain
NADP⁺ → N A D P H
Calvin cycle reactions
Occur in stroma
C O2 taken up
ATP and N A D P H used to reduce C O2 to a carbohydrate.
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Figure 6.4 The Photosynthetic Process

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6.2 The Light Reactions—Harvesting Energy
Pigments absorb solar energy.
Solar energy can be described in terms of its wavelength and energy content.
Visible light contains various wavelengths.
Shorter wavelengths contain more energy.
Longer wavelengths contain less energy.
Less than half of the solar radiation reaching the Earth hits the surface.
Vision and photosynthesis are adapted to use the most prevalent wavelengths (visible light).
9

Wavelengths and Pigments
Figure 6.5 The electromagnetic spectrum.

Figure 6.6 Photosynthetic pigments and photosynthesis.

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Photosynthetic Pigments
Photosynthetic pigments:
Most photosynthesizing cells have chlorophylls and carotenoids.
Both chlorophyll a and b absorb violet, blue, and red wavelengths better than other colors.
Because green is reflected, leaves appear green.
Accessory pigments, such as carotenoids, appear yellow or orange because they reflect those colors—they absorb light in the violet-blue-green range.
Accessory pigments become noticeable in fall when chlorophyll breaks down.
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Figure 6.7 Leaf Colors 1

Chlorophylls absorb violet, blue, and red wavelengths best.
Leaves looks green because they reflect green light.
Chlorophylls cover up accessory pigments, which are more visible in autumn.

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(White Birch Forest): Exactostock/SuperStock
12

Figure 6.7 Leaf Colors 2
Carotenoids absorb violet, blue, green.
But reflect yellow-orange
Leaf looks yellow-orange.
When chlorophylls are no longer produced, we see the other pigments.

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(Silver Birch Forest): Ron Crabtree/Digital Vision/Getty Images
13

The Light Reactions: Capturing Solar Energy
Electron pathway of the light reactions
Capture sun’s energy and stores in the form of a hydrogen ion (H⁺) gradient
Gradient used to produce ATP
N A D P H is also produced
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Figure 6.8 The Light Reactions of Photosynthesis

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The Light Reactions 1
Two photosystems used
Named for order discovered
Consist of pigment complex (contains chlorophyll and carotenoids) and an electron acceptor
Complex serves as antenna for gathering solar energy and passing it to the reaction center (chlorophyll a molecule).
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The Light Reactions 2
Photosystem II
Absorption of solar energy energizes electrons.
Electrons escape to electron acceptor molecule.
Sent through electron transport chain
Replacement electrons obtained by splitting water
Releases oxygen gas as waste product
Electron transport chain
Series of carriers pass electrons along, releasing energy
Energy stored in the form of H⁺ gradient
Will be used to make ATP
Photosystem 1
Absorption of solar energy energizes electrons.
Electrons captured by another electron acceptor molecule.
Electrons and a hydrogen passed to NADP⁺ to become N A D P H.
Replacement electrons come from electron transport chain.

The Electron Transport Chain 1
Organization of thylakoid membrane
PS II, PS1, and the electron transport system are located within the thylakoid membrane.
Promotes efficient transfer of electrons
ATP synthase complex also here
ATP production
Thylakoid space is a reservoir for H⁺
Each time water is split, 2 H⁺ remain in thylakoid space.
Energy from electrons transferred between carriers used to pump more H⁺ from the stroma into the thylakoid space
Establishes H⁺ gradient = large amount of potential energy

The Electron Transport Chain 2
H⁺ gradient is used to produce ATP
The H⁺ flow down concentration gradient
Pass through ATP synthase complex
Energy release allows for production of ATP
Captures released energy
NADP⁺ is a coenzyme that accepts electrons and a H⁺ to become N A D P H.
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Figure 6.9 The Electron Transport Chain 1

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Figure 6.9 The Electron Transport Chain 2

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6.3 The Calvin Cycle Reactions—Making Sugars
Powered by ATP and N A D P H generated by light reactions
Occurs in stroma of chloroplasts
End product is glucose C6H12O6.
Three steps
Carbon dioxide fixation
Carbon dioxide reduction
Regeneration of first substrate (RuBP)
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Fixation of Carbon Dioxide
Fixation of carbon dioxide:
C O2 from the atmosphere attached to RuBP by RuBP carboxylase (rubisco)
6-carbon molecule split into two 3-carbon molecules.
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Reduction of Carbon Dioxide
Reduction of carbon dioxide:
Uses N A D P H (for electrons) and some ATP (for energy) from light reactions
Forms G3P, which can become glucose
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Regeneration of RuBP
Regeneration of RuBP:
1 G3P can be made into glucose or other organic molecules.
5 G3P used to reform RuBP (5-carbon molecule)
Utilizes ATP from light reactions
25

Figure 6.10 The Calvin Cycle Reactions, C O2 Fixation

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Figure 6.10 The Calvin Cycle Reactions, C O2 Reduction

The Calvin cycle is divided into three portions: C O2 fixation, C O2 reduction, and regeneration of RuBP. Because five G3P are needed to re-form three RuBP, it takes three turns of the cycle to achieve a net gain of one G3P. Two G3P molecules are needed to form glucose.

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Figure 6.10 The Calvin Cycle Reactions, Regeneration of RuBP

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Figure 6.11 The Uses of G3P
Fate of G3P
Plants and algae can make any molecule they need from G3P.
Form amino acids, fatty acid, and glycerol
Form glucose for energy needs
Form sucrose for transport through plant
Form starch for storage
Form cellulose for cell walls

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6.4 Variations in Photosynthesis
Plants are adapted to the light and rainfall conditions of their environment.
C3 Photosynthesis
When light and rainfall are moderate:
Use C3 photosynthesis – C3 plant – C3 compound formed first after C O2 fixation
30

Figure 6.12 Carbon Dioxide Fixation in C3 Plants

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(photo): Nick Kurzenko/Alamy Stock Photo
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Variations in Photosynthesis, C4 Photosynthesis
When weather is hot and dry, preventing water loss is critical.
Closing stomata to limit water loss also limits C O2 intake and allows O2 buildup.
Some types of plants use C4 photosynthesis – C4 plant – where a C4 compound formed first after C O2 fixation.
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Comparing C3 and C4 Photosynthesis
C4 photosynthesis
Anatomy of C4 plant different from C3 plant
C3 plant has mesophyll cells arranged in parallel rows.
Calvin cycle and light reactions both occur here.
C4 plant has layered arrangement around leaf veins.
Chloroplasts in mesophyll cells fix C O2 only, shield bundle sheath cells from buildup of O2
Chloroplasts in bundle sheath cells carry out Calvin cycle only.
Partitioning of pathways in space
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Figure 6.13 Comparison of C3 and C4 Plant Anatomy

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Comparing C3 and C4 Plants
C3 plants carry out both reactions in the mesophyll cell.
Advantage in moderate conditions
C4 plants partition reactions
Allows stomata to stay closed (conserving water) while avoiding oxygen exposure to rubisco
Advantage in hot, dry weather
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Figure 6.14 Carbon Dioxide Fixation in C4 Plants

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(photo): Doug Wilson/USDA
36

C A M Photosynthesis
C A M photosynthesis:
Crassulacean-acid metabolism
Most succulents in a desert environment
Partitioning in time
During the night, C A M plants open stomata when it is cooler.
Use C3 molecules to fix C O2 forming C4 molecules
Store C4 molecules in vacuoles
During the day, keep stomata closed to avoid water loss
Release stored C O2 when N A D P H and ATP available from light reaction
37

Figure 6.15 Carbon Dioxide Fixation in a C A M Plant

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(photo): Dinodia/Pixtal/age fotostock
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Evolutionary Trends
Evolutionary trends:
C4 plants most likely evolved in, and are adapted to, areas of high light, high temperature, and limited rainfall.
More sensitive to cold—C3 plants do better than C4 plants below 25°C
Over 20% of total annual plant growth is conducted by these plants despite only 4% of plant species being C4 plants.
Of the 18 most problematic weed plants on the planet, 14 are C4 plants.
C A M plants compete well with C3 or C4 when the environment is extremely arid.
C A M is quite widespread.
39

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41

Figure 6.2 Leaves and Photosynthesis – Text Alternative

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The cross-section of a leaf part shows an upper cuticle, a chain of rectangular cells of the upper epidermis, layers of mesophyll cells consisting of chloroplasts, and a circular vascular bundle. The vascular bundle appears in the cut part of the leaf vein. A chain of rectangular cells of the lower epidermis is present at the lower side with a circular opening of stomata for absorbing carbon dioxide and releasing oxygen.
An enlarged view of a mesophyll cell shows several chloroplasts stacked inside a membrane.
An enlarged view of chloroplast shows the outer covering with a stack of disc-like structures labeled granum, and the fluid surrounding granum labeled stroma. Each disc-shaped component of the granum is labeled as thylakoid.
The micrograph of chloroplast shows dark green regions on roughly rectangular structures labeled granum and longitudinal and lateral blank spaces labeled stroma.

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The Photosynthetic Process 1 – Text Alternative

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a. Reaction shows that H two O plus C O two yields C H two O plus O two, or water reacts with carbon dioxide in presence of solar energy forming end products of carbohydrate and oxygen. Carbon dioxide undergoes reduction through the gain of electrons and forms carbohydrates. Water undergoes oxidation through the loss of electrons and forms oxygen.

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Figure 6.4 The Photosynthetic Process – Text Alternative

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The process takes place inside the chloroplast. The thylakoid membranes absorb the solar energy and water for the light reactions and produce oxygen. The ADP to ATP conversion and the NADP superscript positive to N A D P H conversion also take place inside the thylakoid. The Calvin’s cycle inside the chloroplast converts ATP to ADP and N A D P H to NADP superscript positive. It utilizes the C O2 and produces CH2O (carbohydrate).

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Wavelengths and Pigments – Text Alternative

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Figure 6.5: Wavelength and energy are represented with arrows, showing that as wavelength increases, energy decreases. The electromagnetic spectrum shows a continuum of 7 electromagnetic waves including gamma rays, X-rays, UV rays, infrared rays, micro-waves, and radio waves. The visible light spectrum, which lies between ultraviolet light and infrared light is expanded to show specific wavelengths marked as 380, 500, 600, and 750 nanometers each for different colors.
Figure 6.6: The horizontal axis represents wavelengths in nanometers ranging from 380 to 750. The vertical axis shows relative absorption ranging from low through high.
The line curve representing chlorophyll a has two distinct peaks, one in the range of violet to blue-violet light at around 400 nanometers and another in the range of red-orange light at around 700 nanometers. The line curve representing chlorophyll b has two peaks as well, one in the blue range at about 450 nanometers and one in the orange range at around 650 to 700 nanometers. The line curve of carotenoid has two distinct peaks in the blue-to-blue-green range, both between 400 and 500 nanometers.
Note: All data is approximate.

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Figure 6.7 Leaf Colors 1 – Text Alternative

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Green colored leaves are caused due to: Warm weather; more daylight hours, Much chlorophyll is produced, Leaf absorbs all colors of light but green. Hence we see reflected green light.

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Figure 6.7 Leaf Colors 2 – Text Alternative

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Yellow colored leaves are caused due to: Cool weather; fewer daylight hours, Little chlorophyll is produced, Leaf absorbs all colors but yellow to orange. We see reflected yellow to orange light.

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Figure 6.8 The Light Reactions of Photosynthesis – Text Alternative

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The photosynthesis process takes place inside the chloroplast. The thylakoid membranes absorb the solar energy and water for the light reactions and produce oxygen. The ADP to ATP conversion and the NADP superscript positive to N A D P H conversion also take place inside the thylakoid. The Calvin’s cycle inside the chloroplast converts ATP to ADP and N A D P H to NADP superscript positive. It utilizes the C O2 and produces CH2O (carbohydrate). The light reactions are as follows: water splits into two hydrogen molecules and half oxygen molecule while emitting an electron. It enters the pigment complex along with the solar energy. The electron from the pigment complex enters the electron acceptor, it enters the electron transport chain to PS1. ADP and P combine to form ATP. Electron from PS1 reaches electron acceptor and converts NADP positive and H positive to N A D P H. The ATP and N A D P H released enter the Calvin’s cycle.

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Figure 6.9 The Electron Transport Chain 1 – Text Alternative

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The photosynthetic reactions are as follows: In thylakoid space, the water splits into two hydrogen ions and half oxygen. The exited electron obtained from the splitting of water reaches photosystem two (PS 2) which is attached to the thylakoid membrane. Further, photosystem two traps solar energy and releases energized electron which is transferred to an electron transport chain The newly de-energized electrons from Photosystem two are taken up by Photosystem one (PS 1). Photosystem one also traps solar energy and releases an energized electron and passes it to NADP superscript positive, which then combines with H to form N A D P H. The hydrogen ion received from the splitting of water in thylakoid space and the electron transport chain transfers to the stroma through the protein complex ATP synthase. The ATP (adenosine triphosphate) formed from ADP (adenosine diphosphate) (ADP) and phosphate (P) and N A D P H are utilized by Calvin cycle reactions inside stroma.

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Figure 6.9 The Electron Transport Chain 2 – Text Alternative

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The photosynthetic reactions are as follows: In thylakoid space, the water splits into two hydrogen ions and half oxygen. The exited electron obtained from the splitting of water reaches photosystem two (PS II) which is attached to the thylakoid membrane. Further, photosystem two traps solar energy and releases energized electron which is transferred to an electron transport chain The newly de-energized electrons from Photosystem two are taken up by Photosystem one (PS I). A label reads, hydrogen is pumped from the stroma to the thylakoid space. Photosystem one also traps solar energy and releases an energized electron and passes it to NADP superscript positive, which then combines with H to form N A D P H. The hydrogen ion received from the splitting of water in thylakoid space and the electron transport chain transfers to the stroma through the protein complex ATP synthase. The other label reads, hydrogens flow back out into stroma through ATP synthase complex. The ATP (adenosine triphosphate) formed from ADP (adenosine diphosphate) (ADP) and phosphate (P) and N A D P H are utilized by Calvin cycle reactions inside stroma.

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Figure 6.10 The Calvin Cycle Reactions, C O2 Fixation – Text Alternative

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Key molecules of the Calvin Cycle are:
R u B P: ribulose-1,5-bisphosphate.
3PG: 3-phosphoglycerate.
BPG: 1,3-bisphosphoglycerate.
G3P: glyceraldehyde 3-phosphate.

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Figure 6.10 The Calvin Cycle Reactions, C O2 Reduction – Text Alternative

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At the end of the second stage, six molecules of glyceraldehyde-3-phosphate show the net gain of one glyceraldehyde-3-phosphate yielding glucose and other organic molecules.
Key molecules of the Calvin Cycle are:
R u B P: ribulose-1,5-bisphosphate.
3PG: 3-phosphoglycerate.
BPG: 1,3-bisphosphoglycerate.
G3P: glyceraldehyde 3-phosphate.

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Figure 6.10 The Calvin Cycle Reactions, Regeneration of RuBP – Text Alternative

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At left, in the chloroplast, solar energy is absorbed by the thylakoid membrane, where light reactions take place converting water into oxygen and producing N A D P H and ATP. These N A D P H and ATP are used by Calvin cycle reactions that occur inside the stroma. During the Calvin cycle, carbon dioxide gets converted into CH2O (carbohydrate). It also produces ADP with phosphate and NADP positive, which is again utilized in light reactions.
Three carbon dioxide molecules enter the Calvin cycle forming three hexose (glucose) molecules acting as intermediate. In carbon dioxide reduction, three hexose (glucose) molecules are transformed to six molecules of 3-phosphoglycerate which further gives six molecules of 1,3-bisphosphoglycerate. Here, six ATP received from light reaction converts to six ADP plus six phosphates. Further, six molecules of 1,3-bisphosphoglycerate on the conversion of six N A D P H into six NADP positive gives six molecules of glyceraldehyde-3-phosphate showing a net gain of one molecule of glyceraldehyde-3-phosphate, that yields glucose and other organic molecules. In the regeneration of ribulose-1,5-bisphosphate, three ATP received from light reactions convert into three ADP plus three phosphates, forming three molecules of ribulose-1,5-bisphosphate. Further, the carbon dioxide fixation occurs and the cycle continues.

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Figure 6.11 The Uses of G3P – Text Alternative

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G3P leads to amino acids, glycerol, fatty acids, and glucose phosphate. Glucose phosphate leads to starch, sucrose, and cellulose.

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Figure 6.12 Carbon Dioxide Fixation in C3 Plants – Text Alternative

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The Calvin cycle representation in the C3 plant, geranium shows the conversion of Carbon Dioxide into carbon three (C3) with the help of ribulose-1, 5-bisphosphate (RUBP) enzyme in the mesophyll cell, which further converts into glycerol 3-phosphate during the day.

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Figure 6.13 Comparison of C3 and C4 Plant Anatomy – Text Alternative

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The cross-section labeled C3 plant shows that the mesophyll cells are arranged in parallel layers containing vascular bundles with bundle sheath cells surrounding the vein. The bottom layer of the epidermis shows a stomatal opening between the epidermis cells.
The cross-section labeled C4 Plant shows that the mesophyll cells are arranged concentrically around the circular vascular bundles containing bundle sheath cells. The bottom layer of the epidermis shows a stomatal opening between the epidermis cells.

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Figure 6.14 Carbon Dioxide Fixation in C4 Plants – Text Alternative

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The Calvin cycle representation in C4 plant, corn shows the conversion of Carbon Dioxide into carbon four (C4) in the mesophyll cell, which converts into carbon dioxide in the bundle sheath cell, further converting into glycerol 3-phosphate during the day.

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Figure 6.15 Carbon Dioxide Fixation in a C A M Plant – Text Alternative

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The Calvin cycle representation in C A M plant pineapple shows the conversion of Carbon Dioxide into carbon four (C4) during the night, which converts into carbon dioxide, further converting into glycerol 3-phosphate during the day.

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Chapter 4

Inside the Cell

Essentials of Biology

SEVENTH EDITION

Sylvia S. Mader
Michael Windelspecht

Because learning changes everything.®

4.1 Cells Under the Microscope
Cells
Are extremely diverse
Each type in our body is specialized for a particular function.
Nearly, all require a microscope to be seen.
Light microscope
Invented in the seventeenth century
Limited by properties of light
Electron microscope
Invented in 1930s
Overcomes limitation by using beam of electrons
2

Figure 4.1 Using Microscopes to See Cells

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(using TEM): The Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University/McGraw Hill; (epithelial cell): Dr. Kath White, photographer/EM Research Services, Newcastle University/McGraw Hill; (pluripotent stem cell): Steve Gschmeissner/Alamy Stock Photo; (using light microscope): Fuse/Corbis/Getty Images; (Euglena): Richard Gross/McGraw Hill
3

Figure 4.2 Relative Sizes of Some Living Things and Their Components

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The Limit to Cell Size
Why are cells so small?
Need surface areas large enough for entry and exit of materials
Surface-area-to-volume ratio
Small cells have more surface area for exchange.
Adaptations to increase surface area
Microvilli in the small intestine increase surface area for absorption of nutrients
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Figure 4.3 Surface-Area-to-Volume Relationships

4.2 The Plasma Membrane
Marks boundary between outside and inside of a cell
Regulates passage in and out of a cell
Phospholipid bilayer with embedded proteins
Polar heads (hydrophilic) of phospholipids face into watery medium
Nonpolar tails (hydrophobic) face each other
Fluid mosaic model—the structure of the plasma membrane
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Figure 4.4 A Model of the Plasma Membrane

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Figure 4.5a Membrane Protein Diversity—Channel Protein
Membrane proteins
Channel proteins
Form tunnel for specific molecules

Figure 4.5b Membrane Protein Diversity—Transport Protein
Transport proteins
Involved in passage of molecules through the membrane, sometimes requiring input of energy

Figure 4.5c Membrane Protein Diversity—Cell Recognition Protein
Cell recognition proteins
Enable our body to distinguish between our own cells and cells of other organisms

Figure 4.5d Membrane Protein Diversity—Receptor Protein
Receptor proteins
Allow signal molecules to bind, causing a cellular response

Figure 4.5e Membrane Protein Diversity—Enzymatic Proteins
Enzymatic proteins
Directly participate in metabolic reactions

Figure 4.5f Membrane Protein Diversity—Junction Proteins
Junction proteins
Form junctions between cells
Cell-to-cell adhesion and communication

4.3 The Two Main Types of Cells
Cell theory
All organisms are composed of cells.
All cells come only from preexisting cells.
All cells have:
A plasma membrane to regulate movement of material
Cytoplasm where chemical reactions occur
Genetic material for growth and reproduction
Two main types of cells
Based on organization of genetic material
Prokaryotic cells—lack membrane-bounded nucleus
Eukaryotic cells—have nucleus housing DNA
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Prokaryotic Cells
Prokaryotic cells
Organisms from the domains Bacteria and Archaea
Generally smaller and simpler in structure than eukaryotic cells
Allows them to reproduce very quickly and effectively
Extremely successful group of organisms
Bacteria
Well known because some cause disease
Others have roles in the environment
Some are used to manufacture chemicals, food, drugs, and so on.
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Bacterial Structure
Bacterial structure:
Cytoplasm surrounded by plasma membrane and cell wall
Sometimes a capsule—protective layer
Plasma membrane is the same as eukaryotes
Cell wall maintains the shape of a cell
DNA—single circular, coiled chromosome located in nucleoid (region—not membrane enclosed)
Ribosomes—site of protein synthesis
Appendages
Flagella—propulsion
Fimbriae—attachment to surfaces
Conjugation pili—DNA transfer
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Figure 4.6 A Prokaryotic Cell

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(photo): Sercomi/Science Source
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4.4 A Tour of the Eukaryotic Cell
Protists, fungi, plants, and animals
Have a membrane-bounded nucleus housing DNA
Much larger than prokaryotic cells
Compartmentalized and contain organelles
Four categories of organelles:
Nucleus and ribosomes
Endomembrane system
Energy-related
Cytoskeleton
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Figure 4.7 Structure of a Typical Animal Cell

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(a): EM Research Services/Newcastle University
20

Figure 4.8a Structure of a Typical Plant Cell

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(a): Biophoto Associates/Science Source
21

Figure 4.8b Structure of a Typical Plant Cell

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Nucleus and Ribosomes
Nucleus and ribosomes:
Nucleus
Stores genetic information
Chromatin—diffuse DNA, protein, some RNA
Prior to cell division, DNA compacts into chromosomes
DNA organized into genes, which specify a polypeptide
Relayed to ribosome using messenger RNA (mRNA)
Nucleolus—region where ribosomal RNA (rRNA) is made
Nuclear envelope—double membrane
Nuclear pores permit passage in and out
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Figure 4.9 Structure of the Nucleus

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(photo): Biophoto Associates/Science Source
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Ribosomes
Ribosomes
Carry out protein synthesis in the cytoplasm
Found in both prokaryotes and eukaryotes
Composed of two subunits
Mix of proteins and rRNA
Receive mRNA as instructions sequence of amino acids in a polypeptide
In eukaryotes:
Some ribosomes free in cytoplasm
Many attached to endoplasmic reticulum
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Figure 4.10 The Nucleus, Ribosomes, and Endoplasmic Reticulum (ER)

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Endomembrane System 1
Endomembrane system:
Consists of nuclear envelope, membranes of endoplasmic reticulum, Golgi apparatus, and numerous vesicles
Helps compartmentalize cell
Restricts certain reactions to specific regions
Transport vesicles carry molecules from one part of the system to another.
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Endoplasmic Reticulum
Endoplasmic reticulum:
Complicated system of membranous channels and saccules
Physically continuous with outer membrane of nuclear envelope
Rough ER
Studded with ribosomes
Modifies proteins in lumen
Forms transport vesicles going to Golgi apparatus
Smooth ER
Continuous with rough ER
No ribosomes
Synthesizes lipids like phospholipids and steroids
Function depends on cell
Produces testosterone, detoxifies drugs
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Figure 4.11 Endoplasmic Reticulum (ER)

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(photo): Martin M. Rotker/Science Source
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Figure 4.12 Endomembrane System

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Endomembrane System 2
Golgi apparatus
Stack of flattened saccules
Transfer station
Receives vesicles from ER
Modifies molecules within the vesicles
Sorts and repackages for new destination
Some are lysosomes.
Lysosomes
Vesicles that digest molecules or portions of the cell
Digestive enzymes
Tay-Sachs disease
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Vacuoles
Vacuoles:
Membranous sacs
Larger than vesicles
Rid a cell of excess water
Digestion
Storage
Plant pigments
Animal adipocytes
32

Figure 4.13 Vacuoles

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(a): micro_photo/iStock/Getty Images; (b): Biophoto Associates/Science Source
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Energy-Related Organelles
Energy-related organelles:
Mitochondria
Found in both plants and animals
Usually only visible under an electron microscope
Bounded by double membrane
Break down carbohydrates to produce adenosine triphosphate (ATP)
Cellular respiration—needs oxygen, produces carbon dioxide.
Inner membrane folds called cristae
Increase surface area
Inner membrane encloses matrix
Mixture of enzymes assisting in carbohydrate breakdown
Reactions permit ATP synthesis.
Matrix also contains its own DNA and ribosomes.
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Chloroplasts
Chloroplasts:
Use solar energy to synthesize carbohydrates through the process of photosynthesis
Plants and algae
Three-membrane system
Double membrane enclosing stroma
Thylakoids formed from third membrane.
Thylakoid membrane contains pigments that capture solar energy
Chloroplasts have their own DNA and ribosomes.
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Figure 4.14a Chloroplast Structure

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Figure 4.14b Electron Micrograph of a Chloroplast

(b): Omikron/Science Source
37

Figure 4.15 Mitochondrion Structure

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(b): Keith R. Porter/Science Source
38

The Cytoskeleton and Motor Proteins 1
The cytoskeleton and motor proteins:
Cytoskeleton—network of interconnected protein filaments and tubules
Extends from the nucleus to the plasma membrane
Only in eukaryotes
Maintains cell shape
Motor proteins—allow cell and organelles to move
Myosin, kinesin, and dynein
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The Cytoskeleton and Motor Proteins 2
Motor proteins:
Instrumental in allowing cellular movements
Myosin
Interacts with actin
Cells move in amoeboid fashion
Muscle contraction
Kinesin and dynein
Move along microtubules
Transport vesicles from Golgi apparatus to final destination
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Figure 4.16a Motor Proteins

Figure 4.16b Motor Proteins

The Cytoskeleton and Motor Proteins—Microtubules and Intermediate Filaments
Microtubules
Small, hollow cylinders
Assembly controlled by centrosome
Help maintain cell shape and act as track for organelles and other materials to move
Intermediate filaments
Intermediate in size
Ropelike assembly
Run from nuclear envelope to plasma membrane
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Figure 4.17 Microtubules

Figure 4.18 Actin Filaments

Actin filaments:
Two chains of monomers twisted in a helix
Forms a dense web to support the cell
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The Cytoskeleton and Motor Proteins—Centrioles
Centrioles:
Made of nine sets of microtubule triplets
Two centrioles lie at right angles
In animal cells; not present in plant cells
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Figure 4.19 Centrioles

(photo): Don W. Fawcett/Science Source
47

Cilia and Flagella
Cilia and flagella:
Eukaryotes
For movement of the cell or fluids past the cell
Similar construction in both
9+2 pattern of microtubules
Cilia shorter and more numerous than flagella
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Figure 4.20 Cilia and Flagella

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(a): (cilia): Cultura Creative Ltd/Alamy Stock Photo; (flagella of sperm): David M. Phillips/Science Source; (b): (flagellum cross section): Steve Gschmeissner/Science Source
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4.5 Outside the Eukaryotic Cell
Plant cell walls
Primary cell walls
Cellulose fibrils and noncellulose substances
Wall stretches when cell is growing
Secondary cell walls (some plant cells)
Forms inside primary cell wall
Woody plants
Lignin adds strength
Plasmodesmata
Plant cells connected by numerous channels that pass through cell walls
For exchange of water and small solutes between cells
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Figure 4.21 Animal Cell Extracellular Matrix

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Exterior Cell Surfaces in Animals
Exterior cell surfaces in animals:
No cell wall
Extracellular matrix (ECM)
Meshwork of fibrous proteins and polysaccharides
Collagen and elastin—well-known proteins
Matrix varies—flexible in cartilage, hard in bone
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Cell Wall
Cell wall provides support to cell in many nonanimal cells
plant
fungi
protists
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Extracellular Matrix
The extracellular matrix, found in animal cells, is a meshwork of fibrous proteins and polypeptides in close association with the cell that produced them.
Collagen—resists stretching
Elastin—provides resilience
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Figure 4.22 Junctions Between Cells of the Intestinal Wall

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Adhesion Junctions
Junctions between cells
Adhesion junctions
Internal cytoplasmic plaques joined by intercellular filaments
Sturdy but flexible sheet of cells

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Tight Junctions
Junctions between cells
Tight junctions
Impermeable barrier
Adjacent plasma membraned joined

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Gap Junctions
Junctions between cells
Gap junctions
Allow communication between two cells
Adjacent plasma membrane channels joined

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60

Figure 4.1 Using Microscopes to See Cells – Text Alternative

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The first photo shows a scientist using an electron microscope. The second photo shows a transmission electron micrograph (TEM) of a cell showing its numerous organelles. The third photo shows a scanning electron micrograph (SEM) of a stem cell at 4,000 times magnification. The stem cell has two types of projections, small and circular, and numerous finger-like projections. The fourth photo shows a scientist using a light microscope. The fifth photo shows a light microscopic view of a Euglena at 470 times magnification. Euglena is an elongated cell with a red eyespot and many organelles.

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Figure 4.2 Relative Sizes of Some Living Things and Their Components – Text Alternative

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The scale shows the following: atoms: 0.1 nm, amino acids: 1 nm, proteins: 10 nm, viruses: 100 nm, chloroplast: 1 μm, most bacteria: 10 μm, plant and animal cells: 100 μm, human egg: more than 100 μm. Frog egg: 1 mm, ant: 1 cm, mouse: 0.1 m, man: 1 m, blue whale: 10 m. Organisms below 100 μm are categorized under electron microscope, organisms between 100 nm and 1 mm are under light microscope, organisms between 100 μm and 1 km are categorized under unaided eye.

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Figure 4.4 A Model of the Plasma Membrane – Text Alternative

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A magnified image of the plasma membrane of a cell shows a thick phospholipid bilayer. It consists of a polar head which is hydrophilic and nonpolar tails which are hydrophobic. Protein molecule, cholesterol, and glycol proteins are embedded in the bilayer. A carbohydrate chain is attached to the glycol protein. Cytoskeleton membranes emerge from the bottom. The upper surface is labeled external membrane surface and the lower surface is labeled internal membrane surface.

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Figure 4.6 A Prokaryotic Cell – Text Alternative

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The cylindrical cross-sectional diagram of a prokaryotic cell shows the labels and their descriptions as follows:
Capsule: Gel-like coating outside the cell wall.
Nucleoid: Location of the bacterial chromosome.
Ribosome: Site of protein synthesis.
Plasma membrane: Sheet that surrounds the cytoplasm and regulates entrance and exit of molecules.
Cell wall: Structure that provides support and shapes the cell.
Cytoplasm: Semifluid solution surrounded by the plasma membrane; contains nucleoid and ribosomes.
Flagellum: Rotating filament that propels the cell.
The micrograph of Escherichia coli shares the same top six labels of the diagram of the prokaryotic cell, other than the flagellum.

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Figure 4.7 Structure of a Typical Animal Cell – Text Alternative

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a. The micrograph shows five different cellular components including mitochondrion, nucleus, chromatin, peroxisome, and endoplasmic reticulum.
b. The cross-section of an animal cell shows 19 parts, labeled clockwise from bottom left as follows, Golgi apparatus, plasma membrane, cytoplasm, lysosome, smooth ER (Endoplasmic Reticulum), ribosome (attached to rough ER), mitochondrion, rough ER (Endoplasmic Reticulum), centrioles (in centrosome), vesicle, vesicle formation, nuclear envelope, nuclear pore, nucleolus, chromatin, filaments, microtubules, polyribosome (in cytoplasm), and ribosome (in cytoplasm). The nuclear envelope, nuclear pore, chromatin, and nucleolus are parts of the nucleus while filaments and microtubules are parts of the cytoskeleton.

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Figure 4.8a Structure of a Typical Plant Cell – Text Alternative

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It has the following parts labeled: chloroplast, cell wall, plasma membrane, nucleus, ribosomes, mitochondrion, peroxisome, and central vacuole.

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Figure 4.8b Structure of a Typical Plant Cell – Text Alternative

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It has the following parts labeled: cell wall, plasma membrane, cytoplasm, cell wall of adjacent cell, plasmodesmata, cytoskeleton: microtubule filaments, endomembrane system: rough ER, smooth ER, lysosome, Golgi apparatus, vesicle, energy organelles: chloroplast, mitochondrion, nucleus: ribosome (attached to rough ER), nuclear pore, chromatin, nucleolus, nuclear envelope, centrosome, central vacuole, ribosome in cytoplasm.

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Figure 4.9 Structure of the Nucleus – Text Alternative

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The cross-sectional diagram of an animal cell points to the enlarged view of the nucleus. The enlarged view of the nucleus shows eight labeled parts as follows: nuclear envelope consisting of outer membrane and inner membrane, nucleolus, chromatin, nucleoplasm, ER (Endoplasmic Reticulum) lumen, ribosome, endoplasmic reticulum, and nuclear pores.
The micrograph at 30,000 times magnification shows nuclear envelope containing numerous nuclear pores.

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Figure 4.10 The Nucleus, Ribosomes, and Endoplasmic Reticulum (ER) – Text Alternative

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The steps are as follows:
1) mRNA is produced in the nucleus but moves through a nuclear pore into the cytoplasm.
2) In the cytoplasm, the mRNA and ribosomal subunits join, and polypeptide synthesis begins.
3) If a ribosome attaches to a receptor on the ER, the polypeptide enters the lumen of the ER.
4) At termination, the polypeptide becomes a protein. The ribosomal subunits disengage, and the mRNA is released.
The labels include DNA, mRNA, and nuclear pore in the nucleus; cytoplasm; large unit; small subunit; polypeptide; ribosome; receptor; lumen of the ER; and ER membrane.

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Figure 4.11 Endoplasmic Reticulum (ER) – Text Alternative

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The cross-sectional diagram of the animal cell points to the enlarged view of the endoplasmic reticulum, which is attached to the nuclear envelope. Rough ER with ribosomes on its surface and smooth ER without ribosomes are also labeled. The micrograph shows the smooth ER and rough ER.

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Figure 4.12 Endomembrane System – Text Alternative

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Rough ER: synthesizes proteins and packages them in vesicles, transport vesicles contain products coming from ER. Golgi apparatus modifies lipids and proteins; sorts them and packages them in vesicles. Secretory vesicles fuse with the plasma membrane as secretion occurs. Smooth ER: synthesizes lipids and performs other functions. Transport vesicles contain products coming from ER. Lysosomes digest molecules or old cell parts. Incoming vesicles bring substances into the cell.

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Figure 4.13 Vacuoles – Text Alternative

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The micrograph of a plant cell labeled B, shows a roughly oval-shaped mitochondrion, nucleus, peroxisome adhered to the circumference, spots of ribosomes across the surface, an irregularly circular and large central vacuole, plasma membrane, external circumference of cell wall, and chloroplast.

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Figure 4.14a Chloroplast Structure – Text Alternative

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The cross-sectional diagram of a plant cell points to the enlarged diagram of the chloroplast labeled a. The enlarged diagram shows an oval-shaped structure covered with a double membrane: an outer membrane and an inner membrane. There are two distinct regions found inside the chloroplast called the granum and stroma. The space inside the inner membrane is filled with the homogenous matrix labeled stroma. A granum is made up of tight stacks of disc-shaped structures labeled thylakoids. The cut section of the thylakoid shows thylakoid space and thylakoid membrane.

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Figure 4.15 Mitochondrion Structure – Text Alternative

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The capsule shaped mitochondrion has the following parts labeled: outer membrane, inner membrane, matrix, and cristae.

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Figure 4.20 Cilia and Flagella – Text Alternative

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The micrographs and the diagram are as follows:
a. The micrograph shows hair-like cilia in the bronchial wall of lungs. Another micrograph of the sperm cell shows flagella of sperm attached to the oval heads.
b. The diagram shows a three-dimensional view of the structure of the flagella with five labels as follows: thin, tail-like flagellum, central microtubules, microtubule pairs, motor proteins, and plasma membrane of a cell. The TEM micrograph at 20,000 times magnification shows the cross-section of a flagellum with three joint labels, central microtubules, microtubule pairs, and motor proteins.

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Figure 4.21 Animal Cell Extracellular Matrix – Text Alternative

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It consists of an elastic fiber, collagen, polysaccharide, receptor protein, plasma membrane, cytoskeleton filament, and cytoplasm.

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Figure 4.22 Junctions Between Cells of the Intestinal Wall – Text Alternative

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A, Adhesion junction: The diagram shows the adhesion junction which forms a bridge between the plasma membranes of two adjacent cells. The parts labeled are intercellular space, filaments of cytoskeleton, plasma membranes, and intercellular filaments.
B, Tight junction: The diagram shows the tight junction which forms a protein that seals the plasma membranes of two adjacent cells. The parts labeled are intercellular space, tight junction proteins, and plasma membranes.
C, Gap junction: The diagram shows the gap junction which forms gap channels that link the plasma membranes of two adjacent cells. The parts labeled are plasma membranes, membrane channel, and intercellular space.

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Adhesion Junctions – Text Alternative

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Adhesion junction forms a bridge between the plasma membranes of two adjacent cells. The parts labeled are plasma membranes, filaments of cytoskeleton, intercellular filaments, and intercellular space.

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Tight Junctions – Text Alternative

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Tight junction forms proteins that seal the plasma membranes of two adjacent cells. The parts labeled are plasma membranes, tight junction proteins, and intercellular space.

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Gap Junctions – Text Alternative

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Gap junction forms gap channels that link the plasma membranes of two adjacent cells. The parts labeled are plasma membranes, membrane channel, and intercellular space.

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