Ecosystems — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. After a volcanic eruption covers an island in bare rock, which organisms are most likely to appear first?
A) Large trees that can grow quickly in volcanic soil.
B) Lichens and mosses that can grow on bare rock and begin forming soil.
C) Deer and rabbits that move in from nearby islands to graze.
D) Predators like wolves that establish territory on the empty land.
The correct answer is B) Lichens and mosses that can grow on bare rock and begin forming soil.. After a volcanic eruption covers an island in bare rock, which organisms are most likely to appear first — the answer is Lichens and mosses that can grow on bare rock and begin forming soil..
2. A forest is destroyed by a wildfire, but the soil and seeds remain intact. What type of succession will occur?
A) Primary succession, because all life was destroyed by the fire.
B) No succession, because forests cannot recover after fire damage.
C) Secondary succession, because soil and seeds are still present to support regrowth.
D) Primary succession, because fire always resets an ecosystem to bare rock.
The correct answer is C) Secondary succession, because soil and seeds are still present to support regrowth.. A forest is destroyed by a wildfire, but the soil and seeds remain intact. What type of succession will occur — the answer is Secondary succession, because soil and seeds are still present to support regrowth..
3. Ecosystem A has 50 plant species and Ecosystem B has only 5 plant species. A new plant disease arrives that kills one species. Which ecosystem is more resilient and why?
A) Ecosystem B, because with fewer species the disease spreads more slowly.
B) Both are equally resilient because one lost species has the same effect in either system.
C) Ecosystem A, because losing one out of 50 species has a smaller impact on the food web.
D) Ecosystem B, because the remaining four species will quickly fill the gap.
The correct answer is C) Ecosystem A, because losing one out of 50 species has a smaller impact on the food web.. Ecosystem A has 50 plant species and Ecosystem B has only 5 plant species. A new plant disease arrives that kills one species. Which ecosystem is more resilient and why — the answer is Ecosystem A, because losing one out of 50 species has a smaller impact on the food web..
4. Pioneer species like lichens help start primary succession. Why are they so important to the organisms that come later?
A) They provide shade so larger plants do not overheat in the sun.
B) They break down rock and create the first thin layer of soil that other plants need.
C) They attract large herbivores that spread seeds across the bare rock.
D) They produce large amounts of fruit that feed the animals arriving later.
The correct answer is B) They break down rock and create the first thin layer of soil that other plants need.. Pioneer species like lichens help start primary succession. Why are they so important to the organisms that come later — the answer is They break down rock and create the first thin layer of soil that other plants need..
Part B: Fill in the Blank
Write the correct answer on each line.
1. The gradual process by which an ecosystem changes and develops over time is called succession.
Ecological succession describes how an ecosystem gradually transforms over decades or centuries, as new species replace earlier ones until a stable community forms.
2. Primary succession begins on bare rock or land where no soil exists yet.
Primary succession starts from scratch on bare surfaces like cooled lava or exposed rock, where pioneer species must first create soil before other plants can grow.
3. The first organisms to colonize a new or disturbed area are called pioneer species.
Pioneer species like lichens and mosses are hardy enough to survive on bare rock and gradually break it down into thin soil, paving the way for larger plants.
4. An ecosystem's ability to recover after a disturbance is called its resilience.
Resilience measures how quickly and fully an ecosystem can bounce back after disturbances like fires, floods, or droughts, with biodiverse ecosystems recovering faster.
5. A mature, stable ecosystem that changes very little over time is called a climax community.
A climax community represents the final stage of succession, where the ecosystem has reached a stable balance of species that remains relatively unchanged unless disturbed.