UST Middle School Science Challenge
Week 4 — Ecology & Ecosystems
Grades 6–8 • Focus: Food webs, energy flow, populations and environmental change
Weekly Format
Food webs, energy flow, populations and environmental change
Part A — 15 Multiple Choice
Part B — 15 Fill in the Blank
Part C — 15 Scientific Reasoning / Open Response
Part D — 5 Challenge Problems
Answers and How to Solve are separated at the end.
Part A — Multiple Choice
Questions 1–5
1. The original source of energy for most food webs is the? A) Sun B) an unrelated process C) none of these D) a different scientific idea
2. An organism that makes its own food is a? A) producer B) an unrelated process C) none of these D) a different scientific idea
3. A predator-prey relationship affects? A) population sizes B) an unrelated process C) none of these D) a different scientific idea
4. Decomposers help ecosystems by? A) recycling nutrients B) an unrelated process C) none of these D) a different scientific idea
5. Less energy is available at higher trophic levels because? A) energy is lost as heat B) an unrelated process C) none of these D) a different scientific idea
Part A — Multiple Choice
Questions 6–10
6. The original source of energy for most food webs is the? A) Sun B) an unrelated process C) none of these D) a different scientific idea
7. An organism that makes its own food is a? A) producer B) an unrelated process C) none of these D) a different scientific idea
8. A predator-prey relationship affects? A) population sizes B) an unrelated process C) none of these D) a different scientific idea
9. Decomposers help ecosystems by? A) recycling nutrients B) an unrelated process C) none of these D) a different scientific idea
10. Less energy is available at higher trophic levels because? A) energy is lost as heat B) an unrelated process C) none of these D) a different scientific idea
Part A — Multiple Choice
Questions 11–15
11. The original source of energy for most food webs is the? A) Sun B) an unrelated process C) none of these D) a different scientific idea
12. An organism that makes its own food is a? A) producer B) an unrelated process C) none of these D) a different scientific idea
13. A predator-prey relationship affects? A) population sizes B) an unrelated process C) none of these D) a different scientific idea
14. Decomposers help ecosystems by? A) recycling nutrients B) an unrelated process C) none of these D) a different scientific idea
15. Less energy is available at higher trophic levels because? A) energy is lost as heat B) an unrelated process C) none of these D) a different scientific idea
Part B — Fill in the Blank
Questions 16–20
16. Complete the statement: A predator-prey relationship affects ______.
17. Complete the statement: Decomposers help ecosystems by ______.
18. Complete the statement: Less energy is available at higher trophic levels because ______.
19. Complete the statement: The original source of energy for most food webs is the ______.
20. Complete the statement: An organism that makes its own food is a ______.
Part B — Fill in the Blank
Questions 21–25
21. Complete the statement: A predator-prey relationship affects ______.
22. Complete the statement: Decomposers help ecosystems by ______.
23. Complete the statement: Less energy is available at higher trophic levels because ______.
24. Complete the statement: The original source of energy for most food webs is the ______.
25. Complete the statement: An organism that makes its own food is a ______.
Part B — Fill in the Blank
Questions 26–30
26. Complete the statement: A predator-prey relationship affects ______.
27. Complete the statement: Decomposers help ecosystems by ______.
28. Complete the statement: Less energy is available at higher trophic levels because ______.
29. Complete the statement: The original source of energy for most food webs is the ______.
30. Complete the statement: An organism that makes its own food is a ______.
Part C — Scientific Reasoning
Questions 31–35
31. A student compares two conditions and records results over five trials. Explain how the idea “producer” is relevant. Use 2–3 complete sentences.
32. A class observes a model and explains how its parts work together. Explain how the idea “population sizes” is relevant. Use 2–3 complete sentences.
33. Students examine a data table and notice a consistent pattern. Explain how the idea “recycling nutrients” is relevant. Use 2–3 complete sentences.
34. A team changes one factor and measures the response. Explain how the idea “energy is lost as heat” is relevant. Use 2–3 complete sentences.
35. A scientist compares evidence from two possible explanations. Explain how the idea “Sun” is relevant. Use 2–3 complete sentences.
Part C — Scientific Reasoning
Questions 36–40
36. A student compares two conditions and records results over five trials. Explain how the idea “producer” is relevant. Use 2–3 complete sentences.
37. A class observes a model and explains how its parts work together. Explain how the idea “population sizes” is relevant. Use 2–3 complete sentences.
38. Students examine a data table and notice a consistent pattern. Explain how the idea “recycling nutrients” is relevant. Use 2–3 complete sentences.
39. A team changes one factor and measures the response. Explain how the idea “energy is lost as heat” is relevant. Use 2–3 complete sentences.
40. A scientist compares evidence from two possible explanations. Explain how the idea “Sun” is relevant. Use 2–3 complete sentences.
Part C — Scientific Reasoning
Questions 41–45
41. A student compares two conditions and records results over five trials. Explain how the idea “producer” is relevant. Use 2–3 complete sentences.
42. A class observes a model and explains how its parts work together. Explain how the idea “population sizes” is relevant. Use 2–3 complete sentences.
43. Students examine a data table and notice a consistent pattern. Explain how the idea “recycling nutrients” is relevant. Use 2–3 complete sentences.
44. A team changes one factor and measures the response. Explain how the idea “energy is lost as heat” is relevant. Use 2–3 complete sentences.
45. A scientist compares evidence from two possible explanations. Explain how the idea “Sun” is relevant. Use 2–3 complete sentences.
Part D — Challenge
Questions 46–50
46. Challenge: Design or describe a short investigation that could demonstrate the concept “Sun.” Identify what you would observe or measure.
47. Challenge: Design or describe a short investigation that could demonstrate the concept “producer.” Identify what you would observe or measure.
48. Challenge: Design or describe a short investigation that could demonstrate the concept “population sizes.” Identify what you would observe or measure.
49. Challenge: Design or describe a short investigation that could demonstrate the concept “recycling nutrients.” Identify what you would observe or measure.
50. Challenge: Design or describe a short investigation that could demonstrate the concept “energy is lost as heat.” Identify what you would observe or measure.
Answer Key — Questions 1–5
Answer + How to Solve
1. Answer: A
How to solve: Producers capture solar energy.
2. Answer: A
How to solve: Plants and some microbes are producers.
3. Answer: A
How to solve: Changes in one population can affect the other.
4. Answer: A
How to solve: They break down dead matter and return nutrients.
5. Answer: A
How to solve: Energy transfer between levels is inefficient.
Answer Key — Questions 6–10
Answer + How to Solve
6. Answer: A
How to solve: Producers capture solar energy.
7. Answer: A
How to solve: Plants and some microbes are producers.
8. Answer: A
How to solve: Changes in one population can affect the other.
9. Answer: A
How to solve: They break down dead matter and return nutrients.
10. Answer: A
How to solve: Energy transfer between levels is inefficient.
Answer Key — Questions 11–15
Answer + How to Solve
11. Answer: A
How to solve: Producers capture solar energy.
12. Answer: A
How to solve: Plants and some microbes are producers.
13. Answer: A
How to solve: Changes in one population can affect the other.
14. Answer: A
How to solve: They break down dead matter and return nutrients.
15. Answer: A
How to solve: Energy transfer between levels is inefficient.
Answer Key — Questions 16–20
Answer + How to Solve
16. Answer: population sizes
How to solve: Changes in one population can affect the other.
17. Answer: recycling nutrients
How to solve: They break down dead matter and return nutrients.
18. Answer: energy is lost as heat
How to solve: Energy transfer between levels is inefficient.
19. Answer: Sun
How to solve: Producers capture solar energy.
20. Answer: producer
How to solve: Plants and some microbes are producers.
Answer Key — Questions 21–25
Answer + How to Solve
21. Answer: population sizes
How to solve: Changes in one population can affect the other.
22. Answer: recycling nutrients
How to solve: They break down dead matter and return nutrients.
23. Answer: energy is lost as heat
How to solve: Energy transfer between levels is inefficient.
24. Answer: Sun
How to solve: Producers capture solar energy.
25. Answer: producer
How to solve: Plants and some microbes are producers.
Answer Key — Questions 26–30
Answer + How to Solve
26. Answer: population sizes
How to solve: Changes in one population can affect the other.
27. Answer: recycling nutrients
How to solve: They break down dead matter and return nutrients.
28. Answer: energy is lost as heat
How to solve: Energy transfer between levels is inefficient.
29. Answer: Sun
How to solve: Producers capture solar energy.
30. Answer: producer
How to solve: Plants and some microbes are producers.
Answer Key — Questions 31–35
Answer + How to Solve
31. Answer: Response should correctly apply: producer.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Plants and some microbes are producers.
32. Answer: Response should correctly apply: population sizes.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Changes in one population can affect the other.
33. Answer: Response should correctly apply: recycling nutrients.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. They break down dead matter and return nutrients.
34. Answer: Response should correctly apply: energy is lost as heat.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Energy transfer between levels is inefficient.
35. Answer: Response should correctly apply: Sun.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Producers capture solar energy.
Answer Key — Questions 36–40
Answer + How to Solve
36. Answer: Response should correctly apply: producer.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Plants and some microbes are producers.
37. Answer: Response should correctly apply: population sizes.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Changes in one population can affect the other.
38. Answer: Response should correctly apply: recycling nutrients.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. They break down dead matter and return nutrients.
39. Answer: Response should correctly apply: energy is lost as heat.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Energy transfer between levels is inefficient.
40. Answer: Response should correctly apply: Sun.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Producers capture solar energy.
Answer Key — Questions 41–45
Answer + How to Solve
41. Answer: Response should correctly apply: producer.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Plants and some microbes are producers.
42. Answer: Response should correctly apply: population sizes.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Changes in one population can affect the other.
43. Answer: Response should correctly apply: recycling nutrients.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. They break down dead matter and return nutrients.
44. Answer: Response should correctly apply: energy is lost as heat.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Energy transfer between levels is inefficient.
45. Answer: Response should correctly apply: Sun.
How to solve: Define the concept, connect it to the scenario, and cite the observation or measurement that supports the connection. Producers capture solar energy.
Answer Key — Questions 46–50
Answer + How to Solve
46. Answer: Answers vary; investigation must correctly demonstrate Sun.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
47. Answer: Answers vary; investigation must correctly demonstrate producer.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
48. Answer: Answers vary; investigation must correctly demonstrate population sizes.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
49. Answer: Answers vary; investigation must correctly demonstrate recycling nutrients.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.
50. Answer: Answers vary; investigation must correctly demonstrate energy is lost as heat.
How to solve: State a testable setup, identify the variable/measurement, predict an observable result, and explain why that result demonstrates the concept.