How an ecosystem rebuilds after a change
Grade 7 Science Worksheet - Building Confidence
Circle the best answer.
A volcano builds a brand-new island of bare lava rock with no soil. Which kind of succession starts there, Ari?
- Primary succession
- Neither: plants can't grow on rock
- A climax community
- Secondary succession
A farm field is left alone. Its soil is still there, and weeds sprout each spring. Which kind of succession is this, Bo?
- A climax community
- Primary succession
- Secondary succession
- Neither: the field has no plants
A fire clears a forest, but the soil stays, with seeds in it. Which kind of succession follows, Esme?
- Neither: the forest can't grow back
- Secondary succession
- Primary succession
- Bare-rock succession
New lava has cooled into bare rock. Which living things usually settle there first, Jun?
- Plants can't grow on rock
- Shrubs
- Lichens and mosses
- Tall trees
At 80 years after the lava flow, which plant type covers the most ground, Milo?
- Lichens and mosses
- Trees
- Grasses
- Shrubs
How much of the ground do trees cover 160 years after the lava flow, Noah?
Use the picture in question 5.
- 50%
- 10%
- 30%
- 60%
Between 80 and 200 years after the lava flow, what happens to the grasses line, Pia?
Use the picture in question 5.
- It stays at 40%
- It rises from 10% to 40%
- It rises from 0% to 60%
- It falls from 40% to 10%
Lichens and mosses grow on bare lava for many years. How does that help the plants that come later, Ren?
- They make the rock harder
- They don't help; trees come first
- They turn into trees
- They help build soil from the rock
On a lava island, why do grasses spread after the pioneers instead of before them, Tala?
- Grasses need bare rock
- Grasses grow first, before lichens
- The lava gets hotter
- By then there is some soil
Bits of moss and lichen break down on the rock each year. What do they add to the new soil, Zee?
- Plant matter with nutrients
- Salt water
- Bare rock
- More lava