Unit Checkpoint
Unit Summary
This checkpoint assesses your understanding of the entire Cell Biology unit. Review these key concepts before attempting the quiz:
- Cell Organelles: Structure and function of major organelles including nucleus, mitochondria, ribosomes, ER, Golgi apparatus, lysosomes, and cell membrane
- Cellular Respiration: Glycolysis, Krebs cycle, electron transport chain, and ATP production
- Lab Skills: Identifying variables, analyzing data, interpreting graphs
- Scientific Writing: Claim-Evidence-Reasoning framework
Unit Assessment
Complete this 10-question checkpoint to assess your mastery of Cell Biology concepts. Click on each question to reveal the answer.
1. Compare and contrast the structure and function of the rough and smooth endoplasmic reticulum.
Answer:
Rough ER: Has ribosomes attached to its surface, giving it a "rough" appearance. Functions in protein synthesis and modification, particularly for proteins that will be exported from the cell.
Smooth ER: Lacks ribosomes, giving it a "smooth" appearance. Functions in lipid synthesis, detoxification, and calcium storage.
Similarity: Both are membrane-bound organelles that form a continuous network with the nuclear envelope.
2. Write the overall equation for cellular respiration and explain what each component represents.
Answer: C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP
- C6H12O6 = Glucose (reactant/fuel)
- 6O2 = Oxygen (reactant/required for aerobic respiration)
- 6CO2 = Carbon dioxide (waste product)
- 6H2O = Water (product)
- ATP = Adenosine triphosphate (energy currency of the cell)
3. A scientist observes that a drug stops ATP production in cells. Which organelle is most likely affected by this drug?
Answer: Mitochondria. The drug is likely interfering with the mitochondria, which are the primary site of ATP production through cellular respiration. The drug may be blocking the electron transport chain or another step in the respiration process.
4. Explain why cells that divide rapidly (like cancer cells) are often targeted by drugs that interfere with DNA replication.
Answer: Rapidly dividing cells must replicate their DNA more frequently than normal cells. Drugs that interfere with DNA replication will affect these cells more severely because they depend on constant DNA replication to divide. This is why chemotherapy drugs often target DNA replication - they disproportionately affect rapidly dividing cancer cells compared to normal cells.
5. What would happen to a cell if its lysosomes were damaged and could no longer function?
Answer: The cell would be unable to break down and recycle cellular waste, worn-out organelles, or foreign materials. This would lead to accumulation of waste products, potentially causing cell death. Additionally, the cell would lose its ability to fight off pathogens through digestion. Some lysosomal storage diseases in humans result from defective lysosomes.
6. Using CER format, explain why plants can survive in light but not in complete darkness for extended periods.
Answer:
Claim: Plants cannot survive in complete darkness for extended periods because they cannot produce glucose through photosynthesis.
Evidence: Photosynthesis requires light energy to convert CO2 and H2O into glucose. Plants kept in darkness for weeks show yellowing, wilting, and eventually die.
Reasoning: While plants can perform cellular respiration to produce ATP, they need glucose as the fuel for this process. Without light, chloroplasts cannot perform photosynthesis to produce glucose. The plant will use up its stored glucose and starch reserves, and once depleted, cellular respiration stops, causing the plant to die.
7. A cell biologist measures oxygen consumption in cells under different conditions. Predict what would happen to O2 consumption if glucose were removed from the cell's environment.
Answer: Oxygen consumption would decrease significantly. Oxygen is used in the electron transport chain as the final electron acceptor during cellular respiration. Without glucose, there is no fuel for glycolysis, which means no pyruvate enters the mitochondria, no NADH/FADH2 is produced, and the electron transport chain cannot function. Therefore, O2 would not be consumed.
8. How does the structure of the mitochondria support its function in cellular respiration?
Answer: The mitochondria has a double membrane structure that is crucial for its function:
- Outer membrane: Permeable to small molecules, contains the mitochondria
- Inner membrane: Highly folded into cristae, increasing surface area for the electron transport chain proteins. The folds also create a small intermembrane space for the proton gradient needed for ATP synthesis.
- Matrix: Inner compartment where the Krebs cycle occurs, containing enzymes and mitochondrial DNA
9. Design an experiment to test whether temperature affects the rate of cellular respiration in yeast. Include your hypothesis, variables, and control.
Answer:
Hypothesis: As temperature increases (up to a point), the rate of cellular respiration in yeast will increase, measured by CO2 production.
Independent Variable: Temperature
Dependent Variable: Rate of CO2 production (mL/minute)
Controlled Variables: Amount of yeast, concentration of glucose solution, volume of solution, time of measurement
Control Group: Yeast at room temperature (25C)
Procedure: Set up identical test tubes with yeast and glucose at different temperatures (10C, 20C, 30C, 40C, 50C). Measure CO2 production using a gas collection apparatus over a set time period.
10. Explain the endosymbiotic theory and provide two pieces of evidence that support it.
Answer: The endosymbiotic theory proposes that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by ancestral eukaryotic cells and developed a symbiotic relationship.
Evidence supporting this theory:
- Own DNA: Both mitochondria and chloroplasts contain their own circular DNA, similar to bacterial DNA, which is different from the linear DNA in the nucleus.
- Double membranes: These organelles have double membranes, consistent with the idea that the inner membrane was the original prokaryote's membrane and the outer membrane came from the host cell during engulfment.
- Own ribosomes: They have their own ribosomes (70S), which are similar in size to bacterial ribosomes and different from eukaryotic cytoplasmic ribosomes (80S).
- Binary fission: They replicate independently through binary fission, similar to bacteria.
Next Steps
- Review any questions you found challenging
- Return to earlier lessons if needed for additional practice
- Move on to the next unit: Genetics
- Celebrate completing the Cell Biology unit!