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?
- Neither: plants can't grow on rock
- Secondary succession
- A climax community
- Primary succession
A fire clears a forest, but the soil stays, with seeds in it. Which kind of succession follows, Esme?
- Secondary succession
- Bare-rock succession
- Primary succession
- Neither: the forest can't grow back
New lava has cooled into bare rock. Which living things usually settle there first, Jun?
- Shrubs
- Tall trees
- Lichens and mosses
- Plants can't grow on rock
On new lava, which plant type usually shows up last, Kira?
- Lichens and mosses
- Grasses
- Ferns in the cracks
- Trees
On new lava in Hawaii, park scientists looked for the first mosses and ferns. Where did those plants grow first, Luz?
- In deep soil on the lava
- On top of tall trees
- In shady cracks in the lava
- On the hottest open rock
At 80 years after the lava flow, which plant type covers the most ground, Milo?
- Shrubs
- Grasses
- Trees
- Lichens and mosses
How much of the ground do trees cover 160 years after the lava flow, Noah?
Use the picture in question 6.
- 10%
- 60%
- 30%
- 50%
Between 80 and 200 years after the lava flow, what happens to the grasses line, Pia?
Use the picture in question 6.
- It falls from 40% to 10%
- It rises from 10% to 40%
- It stays at 40%
- It rises from 0% to 60%
On a lava island, why do grasses spread after the pioneers instead of before them, Tala?
- The lava gets hotter
- By then there is some soil
- Grasses grow first, before lichens
- Grasses need bare rock
Bits of moss and lichen break down on the rock each year. What do they add to the new soil, Zee?
- Salt water
- Plant matter with nutrients
- Bare rock
- More lava