How an ecosystem rebuilds after a change

Grade 7 Science Worksheet

Circle the best answer.

1. 1.

   Ari orders the stages of primary succession on a new lava island. Which order is right?

   • Bare rock, grasses, lichens and mosses, trees, shrubs
   • Bare rock, lichens and mosses, grasses, shrubs, trees
   • Bare rock, trees, shrubs, grasses, lichens and mosses
   • Bare rock, shrubs, lichens and mosses, grasses, trees
2. 2.

   In an old field left alone, grasses now cover the ground. Which plant type usually spreads next, Esme?

   • No new plants arrive
   • Tall trees right away
   • Lichens and mosses
   • Shrubs
3. 3.

   Why does secondary succession usually move faster than primary succession, Jun?

   • It starts with soil already in place
   • It needs no sunlight
   • It starts with no plants or seeds
   • It starts on bare rock
4. 4.

   Which starting place leads to primary succession, Kira?

   • A new lava flow with no soil
   • A lawn that was just mowed
   • A forest cleared by fire, soil left
   • A field left alone, with its soil
6. 5.

   From 60 to 120 years after the fire, what happens to the shrubs line, Milo?

   • It rises from 20% to 70%
   • It falls from 50% to 20%
   • It rises from 30% to 50%
   • It stays at 50%
7. 6.

   At 150 years after the fire, which plant type covers the most ground, Noah?

   Use the picture in question 5.

   • Grasses
   • Trees
   • Each covers the same
   • Shrubs
8. 7.

   In which year do trees first cover more ground than shrubs, Pia?

   Use the picture in question 5.

   • Year 150
   • Year 90
   • Year 30
   • Year 60
9. 8.

   After 30 years, the grasses line falls while shrubs and trees rise. Which explanation fits, Ren?

   • Taller plants shade the grasses and replace them
   • The soil turns back into rock
   • Trees grew first and took the room
   • Grasses stop needing sunlight
10. 9.

    On a lava island, lichens and mosses cover 40% of the ground at 40 years but 10% at 200 years. Which explanation fits, Tala?

    • Later plants grew in the new soil and replaced them
    • Trees came first and crowded them out
    • The soil was there before the pioneers
    • The pioneers turned into trees
11. 10.

    Zee sees the grasses line fall on a succession graph and says the data must be wrong. Is the falling line a mistake?

    • Yes: grasses come last, so they rise late
    • Yes: a line should keep rising
    • No: taller plants are replacing the grasses
    • No: grasses are spreading faster