How an ecosystem rebuilds after a change
Grade 7 Science Worksheet - Building Confidence
Circle the best answer.
A farm field is left alone. Its soil is still there, and weeds sprout each spring. Which kind of succession is this, Bo?
- Secondary succession
- Neither: the field has no plants
- Primary succession
- A climax community
A fire clears a forest, but the soil stays, with seeds in it. Which kind of succession follows, Esme?
- Secondary succession
- Bare-rock succession
- Neither: the forest can't grow back
- Primary succession
New lava has cooled into bare rock. Which living things usually settle there first, Jun?
- Plants can't grow on rock
- Tall trees
- Shrubs
- Lichens and mosses
On new lava, which plant type usually shows up last, Kira?
- Ferns in the cracks
- Lichens and mosses
- Grasses
- Trees
On new lava in Hawaii, park scientists looked for the first mosses and ferns. Where did those plants grow first, Luz?
- On top of tall trees
- In deep soil on the lava
- 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?
- Grasses
- Shrubs
- Lichens and mosses
- Trees
How much of the ground do trees cover 160 years after the lava flow, Noah?
Use the picture in question 6.
- 60%
- 30%
- 50%
- 10%
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 0% to 60%
- It stays at 40%
- It rises from 10% to 40%
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 turn into trees
- They help build soil from the rock
- They don't help; trees come first
Bits of moss and lichen break down on the rock each year. What do they add to the new soil, Zee?
- More lava
- Bare rock
- Salt water
- Plant matter with nutrients