chapter 1 activity 2

Question 1

prokaryotes

Answer 1

Question 2

eukaryotes

Answer 2

Question 3

Scenario: Compare how E. coli (a bacterium) and Saccharomyces cerevisiae (baker’s yeast)
organize their cellular biochemistry.
Step 1: Identify key structural differences

Answer 3

Question 4

Scenario: Compare how E. coli (a bacterium) and Saccharomyces cerevisiae (baker’s yeast)
organize their cellular biochemistry.
Step 2: Analyze biochemical implications

Answer 4

Question 5

Scenario: Compare how E. coli (a bacterium) and Saccharomyces cerevisiae (baker’s yeast)
organize their cellular biochemistry

Step 3: Compare specific biochemical processes

Answer 5

Question 6

Step 4: Predict outcomes

Scenario: Compare how E. coli (a bacterium) and Saccharomyces cerevisiae (baker’s yeast)
organize their cellular biochemistry

Answer 6

Question 7

Background: Prokaryotes have DNA in a nucleoid region (not membrane-bound), while
eukaryotes have DNA enclosed in a nucleus with nuclear pores.

2. What are TWO advantages of separating transcription and translation?
   Advantage 1: _________________________________________________________________
   Advantage 2:

Answer 7

Advantage 1:
Allows mRNA processing and quality control (capping, splicing, poly-A tail) before translation.

Advantage 2:
Provides greater regulation of gene expression, so proteins are made only when and where needed.

Question 7

Background: Prokaryotes have DNA in a nucleoid region (not membrane-bound), while
eukaryotes have DNA enclosed in a nucleus with nuclear pores.

1. In prokaryotes, transcription and translation can occur simultaneously - ribosomes can
   attach to mRNA while it’s still being transcribed. Draw a simple diagram showing this:
   In eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm. Why
   can’t they occur simultaneously?

Answer 7

Explanation (why this works in prokaryotes):
Prokaryotes lack a nucleus, so ribosomes can bind to mRNA while it is still being transcribed.

In eukaryotes, DNA is enclosed in the nucleus, while ribosomes are in the cytoplasm. mRNA must first be fully transcribed and processed, then exported through nuclear pores, so transcription and translation cannot occur simultaneously.

Question 8

Background: Prokaryotes have DNA in a nucleoid region (not membrane-bound), while
eukaryotes have DNA enclosed in a nucleus with nuclear pores.

3. Eukaryotic mRNA is processed before leaving the nucleus (5’ cap, 3’ poly-A tail,
   splicing). Why is this processing important?

Answer 8

mRNA processing:

Protects mRNA from degradation (5′ cap, poly-A tail)

Ensures correct protein sequence (splicing removes introns)

Helps ribosomes recognize mRNA for efficient translation

Without processing, mRNA would be unstable or produce incorrect proteins.

Question 9

Background: Prokaryotes have DNA in a nucleoid region (not membrane-bound), while
eukaryotes have DNA enclosed in a nucleus with nuclear pores.

4. Nuclear pores control what enters and exits the nucleus. Predict what would happen if
   nuclear pores allowed everything to pass freely:

Answer 9

Loss of gene regulation

Proteins meant for the cytoplasm could enter the nucleus randomly

RNA and enzymes could move uncontrollably

Increased risk of DNA damage and improper gene expression

Overall: the nucleus would lose functional control.

Question 10

Background: Prokaryotes have DNA in a nucleoid region (not membrane-bound), while
eukaryotes have DNA enclosed in a nucleus with nuclear pores.

Despite the advantages, the nucleus has costs. What is ONE disadvantage of nuclear
compartmentalization?

Answer 10

Disadvantage:
It slows down gene expression because transcription, processing, and transport must occur before translation.

The nucleus increases regulation and accuracy of gene expression but at the cost of speed and energy efficiency.

Question 11

Background: Eukaryotic cells have specialized organelles (mitochondria, ER, Golgi, lysosomes,
peroxisomes), while prokaryotes lack these structures.

Answer 11

Question 12

Background: Eukaryotic cells have specialized organelles (mitochondria, ER, Golgi, lysosomes,
peroxisomes), while prokaryotes lack these structures.

2. Lysosomes maintain pH ~5 (acidic) using proton pumps. The enzymes inside work best at
   acidic pH and would damage the cell at neutral pH. Why is this compartmentalization
   essential?

Answer 12

ysosomal compartmentalization is essential because it protects the rest of the cell from the lysosome’s destructive enzymes.

Lysosomes contain acidic hydrolase enzymes that function optimally at low pH (~5). By enclosing these enzymes in a membrane-bound compartment and maintaining an acidic environment with proton pumps, the cell ensures that:

The enzymes are active only inside the lysosome

They do not digest cellular components in the cytoplasm, which is near neutral pH

Any enzymes that leak into the cytoplasm become largely inactive

Without this compartmentalization, lysosomal enzymes could damage or destroy essential cellular structures, threatening cell survival.

In short: compartmentalization allows safe, controlled breakdown while protecting the rest of the cell.

Question 13

Background: Eukaryotic cells have specialized organelles (mitochondria, ER, Golgi, lysosomes,
peroxisomes), while prokaryotes lack these structures.

3. The ER can maintain a different calcium concentration than the cytoplasm. Why is this
   useful for cell signaling?

Answer 13

Maintaining a different calcium concentration in the ER is useful because it allows the cell to use Ca²⁺ as a fast, tightly controlled signaling molecule.

The ER acts as a calcium storage reservoir, keeping Ca²⁺ levels low in the cytoplasm. When a signal is received, calcium channels in the ER membrane open and rapidly release Ca²⁺ into the cytoplasm, creating a brief calcium spike. This sudden increase activates specific proteins and pathways involved in processes such as muscle contraction, secretion, and metabolism.

After signaling, calcium is pumped back into the ER, turning the signal off. This compartmentalization allows calcium signals to be rapid, localized, and reversible, preventing constant or uncontrolled activation.

Question 14

Background: Eukaryotic cells have specialized organelles (mitochondria, ER, Golgi, lysosomes,
peroxisomes), while prokaryotes lack these structures

4. Peroxisomes contain enzymes that produce hydrogen peroxide (H₂O₂) and catalase that
   breaks it down. Why must these reactions be compartmentalized?.

Answer 14

These reactions must be compartmentalized because hydrogen peroxide (H₂O₂) is highly reactive and damaging to cellular components.

Peroxisomes isolate enzymes that produce H₂O₂ so that this toxic molecule does not accumulate in the cytoplasm, where it could damage DNA, proteins, and membranes. By keeping both H₂O₂-producing enzymes and catalase inside the peroxisome, the cell ensures that hydrogen peroxide is generated and broken down in a controlled space.

Without compartmentalization, oxidative reactions could cause widespread cellular damage. In short, peroxisomes allow useful oxidative chemistry while protecting the rest of the cell.

Question 15

Background: Eukaryotic cells have specialized organelles (mitochondria, ER, Golgi, lysosomes,
peroxisomes), while prokaryotes lack these structures.

5. Estimate: What percentage of a eukaryotic cell’s volume is occupied by organelles?
   ☐ <10% ☐ 10-30% ☐ 30-50% ☐ >50%
   What does this tell you about the “cost” of compartmentalization?

Answer 15

☑ 30–50%

n a typical eukaryotic cell, membrane-bound organelles (nucleus, ER, mitochondria, Golgi, lysosomes, etc.) occupy a large fraction of the cell’s interior, but not most of it. The cytosol still makes up a significant portion, so values below 30% are too small and above 50% is usually too high.

What this tells you about the “cost” of compartmentalization

This shows that compartmentalization is expensive for the cell:

Requires large amounts of membrane (lipids + proteins)

Takes up physical space that could otherwise be cytoplasm

Requires energy to maintain gradients (pH, ions, molecules)

Despite these costs, cells keep organelles because the benefits—efficiency, regulation, protection, and specialization—outweigh the space and energy costs.

Bottom line: compartmentalization is costly, but it dramatically improves cellular control and function.

Question 16

Background: Prokaryotes are typically 1-10 μm, while eukaryotes are 10-100 μm. Cell size is
limited by the surface area-to-volume ratio.

1. As a cell gets larger, what happens to its surface area-to-volume ratio?
   ☐ Increases ☐ Decreases ☐ Stays the same

Answer 16

Decreases

Why:
Volume increases faster than surface area as size increases.

Question 17

Background: Prokaryotes are typically 1-10 μm, while eukaryotes are 10-100 μm. Cell size is
limited by the surface area-to-volume ratio.

5. Why do filamentous or branched bacteria have an advantage?

Answer 17

Long or branched shapes increase surface area without greatly increasing volume, helping maintain a high SA/V ratio and allowing efficient nutrient and gas exchange.

As cells get bigger, SA/V ratio decreases, so cells evolve shapes and internal membranes to compensate.

Question 18

Background: Prokaryotes are typically 1-10 μm, while eukaryotes are 10-100 μm. Cell size is
limited by the surface area-to-volume ratio.

2. Why is a high surface area-to-volume ratio important for cells?

Answer 18

A high SA/V ratio allows faster exchange of nutrients, gases, and wastes across the cell membrane. Cells rely on diffusion, so having more surface area relative to volume makes transport more efficient.

Question 19

Background: Prokaryotes are typically 1-10 μm, while eukaryotes are 10-100 μm. Cell size is
limited by the surface area-to-volume ratio.

3. Calculate surface area-to-volume ratio for these spherical cells:
   Small prokaryote (diameter = 2 μm):
    Surface area = 4πr² = _____________
    Volume = (4/3)πr³ = _____________
    SA/V ratio = _____________
   Large eukaryote (diameter = 20 μm):
    Surface area = _____________
    Volume = _____________
    SA/V ratio = _____________
   Which has a higher SA/V ratio? ☐ Prokaryote ☐ Eukaryote

Answer 19

3. Calculate SA/V ratio for spherical cells
   Small prokaryote (diameter = 2 μm)

Radius
𝑟
=
1
 
𝜇
𝑚
r=1μm

Surface area

4
𝜋
𝑟
2
=
4
𝜋
(
1
)
2
=
4
𝜋
≈
12.6
 
𝜇
𝑚
2
4πr
2
=4π(1)
2
=4π≈12.6μm
2

Volume

4
3
𝜋
𝑟
3
=
4
3
𝜋
(
1
)
3
=
4
3
𝜋
≈
4.2
 
𝜇
𝑚
3
3
4
​

πr
3
=
3
4
​

π(1)
3
=
3
4
​

π≈4.2μm
3

SA/V ratio

12.6
4.2
≈
3
4.2
12.6
​

≈3

Large eukaryote (diameter = 20 μm)

Radius
𝑟
=
10
 
𝜇
𝑚
r=10μm

Surface area

4
𝜋
(
10
)
2
=
400
𝜋
≈
1256
 
𝜇
𝑚
2
4π(10)
2
=400π≈1256μm
2

Volume

4
3
𝜋
(
10
)
3
=
4000
3
𝜋
≈
4189
 
𝜇
𝑚
3
3
4
​

π(10)
3
=
3
4000
​

π≈4189μm
3

SA/V ratio

1256
4189
≈
0.3
4189
1256
​

≈0.3

Which has a higher SA/V ratio?

☑ Prokaryote

Question 20

Background: Prokaryotes are typically 1-10 μm, while eukaryotes are 10-100 μm. Cell size is
limited by the surface area-to-volume ratio.

4. How do eukaryotic cells compensate for lower SA/V ratio?

Answer 20

Eukaryotic cells increase internal surface area using membranes such as:

Endoplasmic reticulum

Mitochondrial cristae

Golgi membranes

These structures allow efficient reactions and transport inside the cell, even though the external SA/V ratio is low.

Question 21

Scenario: Antibiotics like penicillin target bacterial cell walls, while antibiotics like tetracycline
target bacterial ribosomes. These drugs kill bacteria but don’t harm human cells.

1. Why doesn’t penicillin harm human cells?

Answer 21

Penicillin targets peptidoglycan, a key component of bacterial cell walls. Human cells do not have cell walls—only plasma membranes—so penicillin has no target in human cells and does not affect them.

Question 22

Scenario: Antibiotics like penicillin target bacterial cell walls, while antibiotics like tetracycline
target bacterial ribosomes. These drugs kill bacteria but don’t harm human cells.

2. Tetracycline targets 70S ribosomes. Predict: Could tetracycline affect mitochondria?
   ☐ Yes ☐ No
   Explain:

Answer 22

Yes

Explanation:
Mitochondria evolved from bacteria (endosymbiotic theory) and contain 70S ribosomes, which are similar to bacterial ribosomes. Because of this similarity, tetracycline can sometimes interfere with mitochondrial protein synthesis, especially at higher doses or with prolonged use.

Question 23

Scenario: Antibiotics like penicillin target bacterial cell walls, while antibiotics like tetracycline
target bacterial ribosomes. These drugs kill bacteria but don’t harm human cells.

3. Some antibiotics that target bacterial ribosomes can cause side effects related to
   mitochondrial function. Give an example of a possible side effect:

Answer 23

Fatigue or muscle weakness (due to reduced ATP production)

Other acceptable examples:

Neurological symptoms (e.g., dizziness)

Gastrointestinal distress

Lactic acidosis (in severe cases)

These occur because mitochondria are responsible for cellular energy production.

Question 24

Scenario: Antibiotics like penicillin target bacterial cell walls, while antibiotics like tetracycline target bacterial ribosomes. These drugs kill bacteria but don't harm human cells 4. Why is it important that antibiotics target structures unique to prokaryotes?.

Answer 24

It allows antibiotics to kill bacteria selectively without harming human cells. Targeting prokaryote-specific structures (like peptidoglycan cell walls or 70S ribosomes) maximizes effectiveness while minimizing toxicity to the host. ⭐ One-sentence takeaway (great to memorize): Antibiotics work best when they target structures bacteria have that human cells do not, allowing selective toxicity.

Question 25

Scenario: Prokaryotes show incredible metabolic diversity - some photosynthesize, some use sulfur instead of oxygen, some produce methane, some survive on rocks. 1. Why are prokaryotes more metabolically diverse than eukaryotes?

Answer 25

Prokaryotes are more metabolically diverse because they have simpler cell organization, rapid evolution, and flexible metabolic pathways, allowing them to use many different energy sources and electron acceptors.

Question 26

Scenario: Prokaryotes show incredible metabolic diversity - some photosynthesize, some use sulfur instead of oxygen, some produce methane, some survive on rocks. \ 2. Extremophiles are prokaryotes that live in extreme environments (hot springs, salt lakes, deep ocean). What cellular features allow this?

Answer 26

Extremophilic prokaryotes have: Specialized enzymes that function at extreme temperatures or pH Unique membrane lipids that remain stable in harsh conditions Protective proteins and DNA-stabilizing mechanisms

Question 27

Scenario: Prokaryotes show incredible metabolic diversity - some photosynthesize, some use sulfur instead of oxygen, some produce methane, some survive on rocks. 3. Why is nitrogen fixation valuable?

Answer 27

Nitrogen fixation converts inert N₂ gas into ammonia (NH₃), a form that can be used to make amino acids and nucleotides. This ability is valuable because most organisms, including eukaryotes, cannot use atmospheric nitrogen directly.

Question 28

Scenario: Prokaryotes show incredible metabolic diversity - some photosynthesize, some use sulfur instead of oxygen, some produce methane, some survive on rocks. 4. Biotechnology uses prokaryotes to produce insulin, antibiotics, and other products. What advantages do prokaryotes offer for industrial production? Advantage 1: _________________________________________________________________ Advantage 2: _________________________________________________________________ Advantage 3: _____________________________________

Answer 28

Advantage 1: They grow rapidly and reproduce quickly. Advantage 2: They are easy and inexpensive to culture. Advantage 3: They are genetically easy to manipulate (plasmids, simple genomes).

Question 29

Scenario: Imagine a mutant eukaryotic cell that loses its nuclear envelope but retains all other organelles. 1. Predict THREE immediate consequences:

Answer 29

Consequence 1: Loss of separation between transcription and translation, causing poorly regulated gene expression. Consequence 2: Unprocessed or partially processed mRNA could be translated, leading to faulty or nonfunctional proteins. Consequence 3: Nuclear proteins and cytoplasmic proteins would mix freely, disrupting DNA regulation and increasing risk of DNA damage.

Question 30

Scenario: Imagine a mutant eukaryotic cell that loses its nuclear envelope but retains all other organelles. 2. Could this cell survive? ☐ Yes, normally ☐ Yes, but poorly ☑ No

Answer 30

☑ No Explain: The nuclear envelope is essential for gene regulation and mRNA processing. Without it, gene expression becomes disorganized and error-prone, making long-term survival unlikely.

Question 32

Scenario: Imagine a mutant eukaryotic cell that loses its nuclear envelope but retains all other organelles. 3. During mitosis, the nuclear envelope breaks down temporarily. How do cells prevent problems during this time?

Answer 32

Cells temporarily shut down transcription, tightly regulate protein activity, and rapidly reassemble the nuclear envelope after mitosis to restore compartmentalization before normal gene expression resumes.

Question 33

Scenario: Imagine a mutant eukaryotic cell that loses its nuclear envelope but retains all other organelles. 4. Some viruses disrupt nuclear transport. Why is this harmful to cells?

Answer 33

Disrupting nuclear transport prevents proper movement of proteins and RNA between the nucleus and cytoplasm, leading to failed gene regulation, impaired protein synthesis, and loss of cellular control, which can ultimately cause cell death.

Question 34

Part 2: Endosymbiotic Theory Evidence Background: The Endosymbiotic Theory The endosymbiotic theory proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Over time, they became permanent residents (endosymbionts). Key Predictions: If mitochondria and chloroplasts were once independent prokaryotes, they should: 1. Have their own DNA (circular, like bacteria) 2. Have their own ribosomes (70S, like bacteria) 3. Be surrounded by two membranes (inner = original prokaryote, outer = from engulfment) 4. Replicate independently by binary fission 5. Have similar size to bacteria Evidence Analysis For each piece of evidence, evaluate how strongly it supports endosymbiotic theory: Evidence 1: Mitochondrial DNA Observation: Mitochondria contain circular DNA molecules, separate from nuclear DNA. 1. Does this support endosymbiotic theory? ☐ Yes ☐ No ☐ Neutral 2. Strength of evidence: ☐ Weak ☐ Moderate ☐ Strong 3. Explain your reasoning: 4. Could there be an alternative explanation for mitochondrial DNA?

Answer 34

1. Does this support endosymbiotic theory? ☑ Yes 2. Strength of evidence: ☑ Strong 3. Explain your reasoning: This strongly supports endosymbiotic theory because circular DNA is a hallmark of prokaryotes (bacteria), and mitochondria having their own separate genome matches the prediction that they were once independent bacteria that kept some of their DNA after being engulfed. 4. Could there be an alternative explanation for mitochondrial DNA? A possible alternative is that mitochondria evolved inside eukaryotes and retained a separate genome for local control of energy-related genes. However, this is less convincing because the DNA is circular and bacteria-like, and it fits multiple predictions of endosymbiosis better than a purely internal origin.

Question 34

Part 2: Endosymbiotic Theory Evidence Background: The Endosymbiotic Theory The endosymbiotic theory proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Over time, they became permanent residents (endosymbionts). Key Predictions: If mitochondria and chloroplasts were once independent prokaryotes, they should: 1. Have their own DNA (circular, like bacteria) 2. Have their own ribosomes (70S, like bacteria) 3. Be surrounded by two membranes (inner = original prokaryote, outer = from engulfment) 4. Replicate independently by binary fission 5. Have similar size to bacteria Evidence Analysis For each piece of evidence, evaluate how strongly it supports endosymbiotic theory: Evidence 2: Double Membrane Observation: Mitochondria and chloroplasts have two membranes. The inner membrane has different proteins than the outer membrane and resembles bacterial membranes. 1. How does the double membrane support endosymbiotic theory? 2. Draw a diagram showing how engulfment would create a double membrane:3. The inner membrane has proteins for electron transport (like bacterial membranes). The outer membrane has porins (like the outer membrane of Gram-negative bacteria). What does this similarity suggest?

Answer 34

1. How does the double membrane support endosymbiotic theory? The double membrane supports endosymbiotic theory because it matches what would happen if a free-living prokaryote were engulfed by a larger cell. The inner membrane corresponds to the original bacterial membrane, while the outer membrane comes from the host cell’s engulfing vesicle. 3. What does the membrane protein similarity suggest? The similarity suggests that mitochondria and chloroplasts evolved from bacteria, not from the host cell itself. Electron transport proteins in the inner membrane resemble bacterial energy membranes Porins in the outer membrane resemble Gram-negative bacterial outer membranes This strongly supports the idea that these organelles were once independent prokaryotes that became permanent endosymbionts. One-sentence takeaway (great for exams): The double membrane and bacterial-like membrane proteins of mitochondria and chloroplasts provide strong evidence that they originated from engulfed prokaryotic cells.

Question 36

Part 2: Endosymbiotic Theory Evidence Background: The Endosymbiotic Theory The endosymbiotic theory proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Over time, they became permanent residents (endosymbionts). Key Predictions: If mitochondria and chloroplasts were once independent prokaryotes, they should: 1. Have their own DNA (circular, like bacteria) 2. Have their own ribosomes (70S, like bacteria) 3. Be surrounded by two membranes (inner = original prokaryote, outer = from engulfment) 4. Replicate independently by binary fission 5. Have similar size to bacteria Evidence Analysis For each piece of evidence, evaluate how strongly it supports endosymbiotic theory: Evidence 3: Ribosomes Observation: Mitochondrial and chloroplast ribosomes are 70S (like bacterial ribosomes), not 80S (like eukaryotic cytoplasmic ribosomes). 1. Why is this significant? 2. Antibiotics that target bacterial ribosomes (like streptomycin) also affect mitochondrial ribosomes. What does this tell you? 3. Is this evidence: ☐ Strong ☐ Moderate ☐ Weak Explain:

Answer 36

1. Why is this significant? This is significant because ribosome structure is highly conserved and fundamental to cell biology. The presence of 70S ribosomes in mitochondria and chloroplasts closely matches prokaryotic ribosomes, supporting the idea that these organelles originated from bacteria rather than from the host eukaryotic cell. 2. Antibiotics that target bacterial ribosomes also affect mitochondrial ribosomes. What does this tell you? This tells us that mitochondrial ribosomes are functionally similar to bacterial ribosomes. Because antibiotics like streptomycin specifically bind bacterial 70S ribosomes, their effect on mitochondria indicates a shared evolutionary origin. 3. Is this evidence: ☐ Strong ☐ Moderate ☑ Strong Explain: This is strong evidence because it matches a clear prediction of the endosymbiotic theory and involves a complex cellular structure that is unlikely to independently evolve to be so similar by chance. One-sentence takeaway: The bacterial-like ribosomes of mitochondria and chloroplasts strongly support their origin as engulfed prokaryotes.

Question 37

Part 2: Endosymbiotic Theory Evidence Background: The Endosymbiotic Theory The endosymbiotic theory proposes that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. Over time, they became permanent residents (endosymbionts). Key Predictions: If mitochondria and chloroplasts were once independent prokaryotes, they should: 1. Have their own DNA (circular, like bacteria) 2. Have their own ribosomes (70S, like bacteria) 3. Be surrounded by two membranes (inner = original prokaryote, outer = from engulfment) 4. Replicate independently by binary fission 5. Have similar size to bacteria Evidence Analysis For each piece of evidence, evaluate how strongly it supports endosymbiotic theory: Evidence 4: Independent Replication Observation: Mitochondria and chloroplasts replicate by binary fission (splitting in two), independent of cell division. 1. How does this support endosymbiotic theory? 2. Predict: What would happen if mitochondria couldn't replicate independently?

Answer 37

1. How does this support endosymbiotic theory? Binary fission is a defining feature of prokaryotic reproduction. The fact that mitochondria and chloroplasts divide this way—rather than being made by the cell from scratch—supports the idea that they descended from free-living bacteria that retained their original replication mechanism after becoming endosymbionts. 2. Predict: What would happen if mitochondria couldn’t replicate independently? If mitochondria could not replicate on their own: Daughter cells might receive too few or no mitochondria during cell division ATP production would drop dramatically Cells would have severe energy deficits and likely die Bottom line: independent replication is essential for maintaining mitochondrial number and cellular energy balance. One-sentence takeaway: Mitochondrial binary fission mirrors bacterial division and is strong evidence that mitochondria originated as independent prokaryotes.

Question 38

Observation: Mitochondrial DNA sequences are most similar to α-proteobacteria. Chloroplast DNA sequences are most similar to cyanobacteria. 1. Is this: ☐ Strong evidence ☐ Moderate evidence ☐ Weak evidence 2. Why is DNA sequence comparison powerful evidence? 3. This evidence suggests: ☐ Mitochondria and chloroplasts evolved from the same prokaryote ☐ Mitochondria and chloroplasts evolved from different prokaryotes ☐ Mitochondria and chloroplasts evolved independently (not from prokaryotes)

Answer 38

1. Is this evidence strong, moderate, or weak? ☑ Strong evidence 2. Why is DNA sequence comparison powerful evidence? DNA sequences provide a direct record of evolutionary history. High sequence similarity indicates shared ancestry, and comparing whole genomes or conserved genes allows scientists to trace lineage relationships with high confidence. This is stronger than structural similarity alone because it’s based on heritable genetic information. 3. This evidence suggests: ☐ Mitochondria and chloroplasts evolved from the same prokaryote ☑ Mitochondria and chloroplasts evolved from different prokaryotes ☐ Mitochondria and chloroplasts evolved independently (not from prokaryotes) Explanation: Mitochondria clustering with α-proteobacteria and chloroplasts clustering with cyanobacteria indicates two separate endosymbiotic events involving different bacterial ancestors. One-line takeaway: Genetic similarity pinpoints mitochondria and chloroplasts as descendants of different bacterial lineages, strongly supporting endosymbiotic theory.

Question 39

Synthesis: Evaluating the Theory 1. Overall, how strong is the evidence for endosymbiotic theory? ☐ Very strong (almost certainly correct) ☐ Strong (probably correct) ☐ Moderate (plausible but uncertain) ☐ Weak (unlikely) 2. What is the STRONGEST piece of evidence? Why? 3. Are there any observations that DON'T fit endosymbiotic theory? 4. Modern mitochondria can't survive outside cells. How does this fit with endosymbiotic theory?

Answer 39

1. Overall, how strong is the evidence for endosymbiotic theory? ☑ Very strong (almost certainly correct) 2. What is the STRONGEST piece of evidence? Why? The strongest evidence is DNA sequence similarity showing mitochondrial DNA most closely matches α-proteobacteria and chloroplast DNA matches cyanobacteria. DNA comparisons directly track evolutionary ancestry, making this evidence precise and hard to explain by coincidence. 3. Are there any observations that DON’T fit endosymbiotic theory? Modern mitochondria and chloroplasts cannot live independently and have reduced genomes. At first glance this seems inconsistent with a free-living origin, but it’s explained by gene loss and transfer to the nucleus over time, which the theory predicts. 4. Modern mitochondria can’t survive outside cells. How does this fit with the theory? This fits well: after billions of years as endosymbionts, mitochondria became highly specialized and dependent on the host cell. Losing independence is expected as genes were transferred to the nucleus and functions became shared. Bottom line: Multiple independent lines of evidence—DNA, ribosomes, membranes, replication, and biochemistry—converge, making endosymbiotic theory one of the best-supported ideas in biology.

Question 40

Answer 40

Big-picture takeaway (great for conclusions): Prokaryotes prioritize speed and metabolic flexibility, while eukaryotes trade speed for control, efficiency, and complexity through compartmentalization.

Question 41

1. Is one cell type "better" than the other? Explain.

Answer 41

No. Prokaryotic and eukaryotic cells are adapted for different purposes. Prokaryotes excel at speed and survival in diverse environments, while eukaryotes excel at complex, regulated functions.

Question 42

2. What is the MAIN advantage of compartmentalization?

Answer 42

Compartmentalization allows specialized environments for different processes, increasing efficiency, regulation, and protection within the cell.

Question 43

3. What is the MAIN advantage of prokaryotic simplicity?

Answer 43

Simplicity allows fast growth and rapid response to environmental changes with minimal energy cost.

Question 44

4. How does cell organization relate to the biochemical principles from Activity 1A?

Answer 44

Cell organization reflects biochemical principles such as polarity, enzyme specificity, and structure–function relationships, allowing reactions to occur efficiently in appropriate environments.

Question 45

5. Why do you think eukaryotes evolved compartmentalization despite the costs?

Answer 45

The benefits of greater control, efficiency, and complexity outweighed the energy and space costs, enabling the evolution of multicellularity and specialized tissues.

Question 46

What are the main characteristics of **prokaryotic cells**?

Answer 46

* Simple * Fast-reproducing * Metabolically diverse ## Footnote Prokaryotic cells lack a nucleus and membrane-bound organelles.

Question 47

Why do **eukaryotic cells** use **compartmentalization**?

Answer 47

To allow biochemical specialization within different organelles ## Footnote Compartmentalization enhances cellular efficiency.

Question 48

What is a key benefit of **compartmentalization** in cells?

Answer 48

It allows incompatible processes to occur simultaneously in different compartments ## Footnote This is crucial for maintaining cellular functions.

Question 49

What does **endosymbiotic theory** explain?

Answer 49

The origin of mitochondria and chloroplasts from prokaryotic ancestors ## Footnote This theory suggests that these organelles were once free-living bacteria.

Question 50

Is one cellular organization (prokaryotic or eukaryotic) inherently better?

Answer 50

No, each is optimized for different lifestyles and functions ## Footnote Prokaryotes are suited for rapid growth, while eukaryotes are more complex.

Question 51

What limits how large a **cell** can become?

Answer 51

The surface area-to-volume ratio ## Footnote As a cell grows, its volume increases faster than its surface area.

Question 52

How do **eukaryotic cells** increase effective surface area?

Answer 52

By using internal membranes such as the ER and mitochondrial cristae ## Footnote This adaptation allows for more efficient metabolic processes.

Question 53

How has **evolution** influenced cell types?

Answer 53

Evolution has shaped both prokaryotic and eukaryotic cells for billions of years to fit their environments ## Footnote This process has led to diverse adaptations in cellular structures and functions.