Ecosystems — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
In the water cycle, evaporation happens when water freezes into ice on the ground.
Corrected: In the water cycle, evaporation happens when liquid water turns into water vapor and rises into the air.
Evaporation is the process of liquid water turning into invisible water vapor gas and rising into the atmosphere, which is the opposite of freezing.
2. Fix the sentence:
Plants release carbon dioxide during photosynthesis and absorb oxygen from the air.
Corrected: Plants absorb carbon dioxide during photosynthesis and release oxygen into the air.
The original sentence had the gases reversed. Plants take in carbon dioxide and release oxygen during photosynthesis, which is why forests are so important for clean air.
3. Fix the sentence:
Energy is recycled through an ecosystem just like water and carbon are recycled.
Corrected: Matter like water and carbon is recycled through an ecosystem, but energy flows in one direction and is not recycled.
Matter (water, carbon, nitrogen) cycles repeatedly through ecosystems, but energy flows in only one direction and is gradually lost as heat at each level of the food chain.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. The water cycle describes how water moves between the land, oceans, and atmosphere.
The water cycle continuously moves water through evaporation, condensation, and precipitation, recycling it between land, oceans, and the atmosphere.
2. When water vapor cools and forms clouds, the process is called condensation.
Condensation occurs when warm water vapor rises, cools in the upper atmosphere, and turns back into tiny water droplets that cluster together to form clouds.
3. Animals breathe out carbon dioxide, which plants use for photosynthesis.
Animals produce carbon dioxide as a waste product of respiration, and plants absorb this gas during photosynthesis to make glucose for energy.
4. Decomposers break down dead organisms and return nutrients to the soil for plants to use again.
Decomposers recycle nutrients like nitrogen and phosphorus from dead organisms back into the soil, where plant roots absorb them to fuel new growth.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Why is the water cycle important for all living things in an ecosystem?
Sample answer: The water cycle is important because it continuously moves fresh water to different parts of the ecosystem. All living things need water to survive, and the cycle ensures that water is cleaned and redistributed through evaporation, condensation, and precipitation.
A good answer includes: The water cycle is important because it continuously moves fresh water to different parts of the ecosystem. All living things need water to survive, and the cycle ensures that water is cleaned and redistributed through evaporation, condensation, and precipitation.
2. How do decomposers help keep nutrient cycles going in an ecosystem?
Sample answer: Decomposers break down dead plants and animals into simple nutrients that return to the soil. Plants then absorb these nutrients to grow, which keeps the cycle of matter moving through the ecosystem.
A good answer includes: Decomposers break down dead plants and animals into simple nutrients that return to the soil. Plants then absorb these nutrients to grow, which keeps the cycle of matter moving through the ecosystem.