Unit Checkpoint
Unit Review
This checkpoint covers all key concepts from the Ecology unit:
- Population dynamics and growth patterns
- Biodiversity and ecosystem interactions
- Lab analysis and data interpretation
- Scientific writing with claims and evidence
Comprehensive Quiz
Test your mastery of ecology concepts. Click to reveal each answer.
Question 1: Define the levels of ecological organization from smallest to largest.
Answer: Organism - Population - Community - Ecosystem - Biome - Biosphere
Explanation: Each level builds on the previous. A population is a group of one species; a community is multiple species; an ecosystem adds the abiotic environment.
Question 2: Explain how density-dependent and density-independent limiting factors differ.
Answer: Density-dependent: effects increase as population grows (competition, disease, predation). Density-independent: affect populations regardless of size (weather, natural disasters, pollution).
Explanation: Disease spreads faster in crowded populations (density-dependent). A hurricane kills the same percentage regardless of population size (density-independent).
Question 3: A population of 1000 has reached carrying capacity. What happens next?
Answer: The population will fluctuate around K. It may overshoot slightly, then decline due to resource depletion, then recover. Growth rate approaches zero at K.
Explanation: At K, births approximately equal deaths. The population stabilizes but continues to fluctuate due to environmental variation.
Question 4: Describe the relationship between producers, primary consumers, and decomposers in an ecosystem.
Answer: Producers (plants, algae) convert solar energy to chemical energy. Primary consumers (herbivores) eat producers. Decomposers break down dead organisms and waste, returning nutrients to the soil for producers.
Explanation: Energy flows in one direction (sun to producers to consumers). Nutrients cycle continuously through all trophic levels.
Question 5: Why is biodiversity important for ecosystem stability?
Answer: Higher biodiversity provides: ecosystem services, genetic resources, food web resilience, and recovery capacity. Diverse ecosystems better resist and recover from disturbances.
Explanation: If one species declines, others can fill its role. Monocultures are vulnerable because they lack backup species.
Question 6: Using mark-recapture data: 40 marked, 50 recaptured, 8 marked in recapture. What's the estimated population?
Answer: N = (40 x 50) / 8 = 250 individuals
Explanation: Lincoln-Peterson equation assumes: marks don't affect survival, marked and unmarked have equal capture probability, closed population (no births, deaths, migration between samples).
Question 7: Compare primary and secondary succession. Give an example of each.
Answer: Primary: starts on bare substrate with no soil (volcanic rock, retreating glacier). Secondary: starts where soil remains after disturbance (after fire, logging). Primary takes longer because soil must form first.
Explanation: Both lead toward climax community but secondary succession is faster because seeds and nutrients already exist in the soil.
Question 8: Explain the carbon cycle and how human activities have altered it.
Answer: Carbon cycles through atmosphere (CO2), organisms (organic compounds), and lithosphere (fossil fuels, limestone). Humans have increased atmospheric CO2 by burning fossil fuels and deforestation, faster than natural cycles can absorb it.
Explanation: For millions of years, carbon was sequestered in fossil fuels. Burning releases it rapidly, overwhelming ocean and plant absorption.
Question 9: Write a claim-evidence-reasoning statement about this data: "Streams near farms have 10x more nitrogen than forested streams."
Sample CER: Claim: Agricultural runoff increases nitrogen levels in waterways. Evidence: Streams near farms contain 10 times more nitrogen than streams in forested areas. Reasoning: Farms apply nitrogen fertilizers which wash into streams during rain. Forests have natural nitrogen cycling that doesn't produce excess runoff.
Question 10: What is a trophic cascade? Provide an example.
Answer: A trophic cascade occurs when changes at one trophic level ripple through the food web. Example: Removing wolves (top predator) increased deer (herbivore), which overgrazed plants, which caused erosion and habitat loss for other species.
Explanation: Yellowstone's wolf reintroduction is a classic example - wolves changed deer behavior, allowing vegetation recovery, which stabilized stream banks and increased beaver populations.
Next Steps
- Review any topics where you scored below 80%
- Continue to the next Science unit when ready
- Practice applying ecological concepts to real-world issues