How relationships between species keep an ecosystem stable

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Effects on the two partners in a lichen (data: OpenStax Biology)

   partner	effect
   fungus	gains
   photosynthetic alga	gains

2. 1.

   Ari reads the table about a fungus and an alga living together in a lichen. Which relationship does it show?

   • Commensalism: both partners gain from living together
   • Parasitism: the alga is harmed by the fungus
   • Mutualism: both partners gain from living together
   • Competition: the fungus and the alga both lose

3. Effects on a model parasite and its host plant (model data)

   partner	effect
   parasite	gains
   host plant	harmed

4. 2.

   Esme reads the table about a model parasite that lives on a host plant. Which relationship does it show?

   • Commensalism: the parasite gains and the host is unchanged
   • Parasitism: the parasite gains and the host is harmed
   • Mutualism: the parasite gains and the host gains too
   • Competition: the parasite and the host both lose
5. 3.

   Kira reads the graph. How many years after the hare peak does the lynx peak come?

   • 1 year before: lynx peak at year 3, hares at year 4
   • 3 years after: the gap is the year of the hare peak
   • 0 years: both counts peak at year 4 together
   • 1 year after: hares peak at year 3, lynx at year 4
6. 4.

   Luz reads the graph. How many years pass from one hare peak to the next hare peak?

   • 14 years: the whole time shown on the graph
   • 5 years: halfway between two hare peaks
   • 10 years: from year 4 to year 14
   • 2 years: the gap from the hare peak to the lynx peak

7. Two species in a model stream (model data)

   species	individuals	share of the phosphorus supplied (percent)
   banded tetra	30	95
   stream snail	500	5

8. 5.

   Milo reads the model data about a stream. Which species is the keystone species?

   • Neither species: the stream does not depend on one species
   • Both species: each one lives in the stream
   • The stream snail: it has the most individuals
   • The banded tetra: few individuals, but most of the phosphorus

9. Two cases of living things sharing a place (model data)

   case	what happens
   A	two plant species in one plot use the same limited supply of water, and both grow less
   B	a bird builds a nest in a tree, and the tree stays the same

10. 6.

    Noah reads the two cases. Which case shows competition?

    • Both cases: living things share a place in each
    • Case A: both species use the same limited water
    • Neither case: competition needs animals that touch
    • Case B: the bird uses the tree for a nest

11. Effects on a model parasite and a model host (model data)

    partner	effect
    model parasite Q	gains
    model host R	harmed

12. 7.

    Pia reads the table about a model parasite and its model host. Which partner is the host?

    • Q: the host is the partner that gains
    • R: the host is the partner that is harmed
    • Neither: a host is a third kind of species
    • Both: each partner is a host to the other

13. Phosphorus in two model streams (model data)

    stream	banded tetra	phosphorus level (model units)
    P	present	40
    Q	absent	10

14. 8.

    Ren reads the model data. What does the table show about phosphorus?

    • Phosphorus is lower in stream Q, where the banded tetra is absent
    • Phosphorus is the same in both, so one species does not matter
    • Phosphorus is lower in stream P, where the banded tetra is present
    • Phosphorus is higher in stream Q, where the banded tetra is absent

15. Removing one species from a model community of 12 species (model data)

    species removed	individuals of that species	species left
    A	500	11
    B	40	5

16. 9.

    Tala reads the model data. Which removal changed the community more?

    • Species A: 11 species were left, the larger number
    • Species B: 7 species were lost, though it had fewer individuals
    • Species A: it had the most individuals, 500
    • Neither: both removals changed the community the same way

17. Species in a model stream community by year (model data)

    year	species
    1	12
    2	12
    3	9
    4	8

18. 10.

    Zee reads the model data. The banded tetra is absent from the start of year 3. How many fewer species are in year 4 than in year 2?

    • 1 fewer: 9 species in year 3 and 8 in year 4
    • 3 fewer: 12 species in year 2 and 9 in year 3
    • 0 fewer: losing one species leaves the community as it was
    • 4 fewer: 12 species in year 2 and 8 in year 4