Educational worksheet on ecosystem cycles covering the water cycle and nutrient cycles like carbon and nitrogen.

Here is the complete solution to your "Ecosystem Cycles" worksheet, with explanations for each answer.

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Part 1: Identify the parts of the water cycle

Match the letter (A–F) to the correct description.

1. Liquid water heats and changes to water vapor, a gas in the atmosphere.
→ C. evaporation
*Explanation:* Evaporation is the process where liquid water (from oceans, lakes, rivers, soil) turns into water vapor due to heat from the sun.

2. Water returns to Earth in the form of rain, snow, sleet, or hail.
→ E. precipitation
*Explanation:* Precipitation includes all forms of water falling from the sky — rain, snow, sleet, hail — after condensation forms clouds.

3. Water vapor in the air rises, cools, and changes back to liquid form, collecting on dust particles to form clouds.
→ D. condensation
*Explanation:* Condensation occurs when water vapor cools and turns back into liquid droplets, forming clouds.

4. Water flows over the land back to water sources such as rivers, lakes, streams, and oceans.
→ F. runoff
*Explanation:* Runoff is surface water that flows over land into rivers, lakes, and oceans after precipitation.

5. Water collects in underground streams that flow into larger bodies of water.
→ A. groundwater
*Explanation:* Groundwater is water that seeps into the soil and collects underground, eventually feeding into rivers, lakes, or oceans.

6. Water vapor is released from the leaves of plants into the atmosphere.
→ B. transpiration
*Explanation:* Transpiration is the release of water vapor by plants through their leaves — it’s like plant “sweating.”

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Part 2: Circle the correct word to make a true statement

7. (Nitrogen / Carbon) has to be “fixed” by bacteria before producers can use it.
→ Nitrogen
*Explanation:* Nitrogen gas (N₂) in the air must be converted (“fixed”) into usable forms (like ammonia) by nitrogen-fixing bacteria before plants can absorb it.

8. Plants release (oxygen / carbon dioxide), which is taken in by animals in the ecosystem.
→ oxygen
*Explanation:* During photosynthesis, plants take in CO₂ and release O₂, which animals breathe in.

9. Carbon dioxide in the atmosphere is taken in by (plants / animals).
→ plants
*Explanation:* Plants use CO₂ during photosynthesis to make food; animals release CO₂ during respiration.

10. (Producers / Decomposers) break down the dead organisms in an ecosystem and return (water / carbon) to the soil.
→ Decomposers / carbon
*Explanation:* Decomposers (like fungi and bacteria) break down dead matter, releasing nutrients — especially carbon — back into the soil for reuse.

11. When humans burn fossil fuels, they (add / remove) carbon dioxide (to / from) the atmosphere.
→ add / to
*Explanation:* Burning fossil fuels releases stored carbon as CO₂ into the atmosphere, contributing to climate change.

12. Water vapor in the air (cools / warms) to condense and form clouds.
→ cools
*Explanation:* For condensation to occur, water vapor must lose heat energy — so it cools.

13. During the nitrogen cycle, organisms use nitrogen compounds available in the (soil / air).
→ soil
*Explanation:* Although nitrogen gas is in the air, most organisms can only use nitrogen compounds (like nitrates, ammonium) found dissolved in soil or water.

14. Liquid water returns to gas form in the atmosphere through the process of (evaporation / precipitation).
→ evaporation
*Explanation:* Evaporation turns liquid water into water vapor (gas), returning it to the atmosphere.

15. Matter, such as water, carbon, and nitrogen, can all be (lost / recycled) in an ecosystem.
→ recycled
*Explanation:* Unlike energy, matter is not lost — it cycles continuously through ecosystems via biogeochemical cycles.

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Part 3: Short Answer Questions

16. Explain why decomposers are an important part of the carbon and nitrogen cycles.
→ *Decomposers break down dead organisms and waste materials, releasing carbon and nitrogen back into the environment in forms that living organisms can reuse. Without decomposers, nutrients would remain locked in dead matter, and ecosystems would run out of essential elements needed for life. They close the loop in nutrient cycles, ensuring sustainability.*

17. Why are diagrams that show how matter moves through organisms and the environment called cycles?
→ *They are called cycles because matter (like water, carbon, and nitrogen) does not get used up or disappear — instead, it continuously moves and transforms between different forms and locations (e.g., atmosphere, soil, organisms). The movement is circular or looping, hence the term “cycle.”*

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✔ Final Answer Key Summary:

Matching (1–6):
1. C
2. E
3. D
4. F
5. A
6. B

Circle Correct Word (7–15):
7. Nitrogen
8. oxygen
9. plants
10. Decomposers / carbon
11. add / to
12. cools
13. soil
14. evaporation
15. recycled

Short Answers (16–17): See explanations above.

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