How relationships between species keep an ecosystem stable

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Termites and the protozoa in their guts (data: OpenStax Biology)

   partner	effect	what happens
   termite	gains	the protozoa break down the cellulose in wood, so the termite gets energy from it
   protozoa	gains	the termite's gut gives them a protected home

2. 1.

   Ari reads the table about termites and the protozoa that live in their guts. Which relationship does it show?

   • Competition: the termite and the protozoa need the same wood
   • Commensalism: both partners gain, and neither one is harmed by the other
   • Parasitism: the protozoa gain a home from the termite
   • Mutualism: the termite and the protozoa each gain from the other

3. Growth of two model species alone and together (model data)

   species	growth alone (model units)	growth together (model units)
   M	20	26
   N	20	20

4. 2.

   Bo reads the model data on growth. Which relationship fits the table?

   • Competition: both species grow less when together
   • Mutualism: both species gain, because species N did not lose
   • Commensalism: species M gains and species N is unchanged
   • Parasitism: species M gains and species N is harmed

5. Host plants per plot with and without a model parasite (model data)

   year	without the parasite	with the parasite
   1	50	50
   2	54	49
   3	58	46
   4	62	44

6. 3.

   Jun reads the model data on host plants in plots. Which statement fits the table?

   • The parasite helps its host: the host count rises with it
   • No effect: both columns start at 50 plants in year 1
   • Not parasitism: a parasite would have removed its hosts well before year 4
   • Parasitism: with the parasite the host count falls from 50 to 44, not to 0

7. Two model parasites and their hosts (model data)

   parasite	days its host stays in the habitat	days it needs to reach a new host	new hosts reached
   X	10	30	0
   Y	60	30	3

8. 4.

   Luz reads the model data on two parasites. Which parasite reaches new hosts, and why?

   • Parasite Y: its host stays 60 days, longer than the 30 days it needs
   • Parasite X: its host stays 10 days, and a quick loss helps a parasite
   • Parasite Y: its host stays 60 days, so Y needs 60 days to move
   • Parasite X: it needs 30 days, the same as Y, so it reaches the most
9. 5.

   Milo reads the graph. The cycle repeats every 10 years. In which year will the lynx count peak the second time?

   • Year 10: 2 years before the second hare peak at year 12
   • Year 16: 4 years after the second hare peak at year 12
   • Year 12: the year of the second hare peak, read as the lynx peak
   • Year 14: the cycle is 10 years after the lynx peak at year 4
10. 6.

    Noah reads the graph. Which statement about when the two counts start to fall fits the graph?

    • The hare count falls after its year 3 peak, one year before the lynx count falls after its year 4 peak
    • The lynx count falls after its year 2 peak, one year before the hare count falls after its year 3 peak
    • The hare count falls after its year 2 peak, one year before the lynx count falls after its year 3 peak
    • Both counts fall after the same peak, in year 3, so neither one comes first
11. 7.

    Pia reads the graph. In the year the lynx count peaks, what is the hare count doing?

    • At its lowest: the hare count is down at 10 by the lynx peak
    • At its peak: both counts peak in the same year
    • Rising: the hare count peaks 2 years after the lynx peak
    • Falling: the hare peak came 2 years earlier, and hares are at 40

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

    species removed	individuals before removal	species left
    banded tetra	30	6
    stream snail	400	11
    stream moss	900	10

13. 8.

    Ren reads the model data. Which species is the keystone species of the stream?

    • Stream moss: it has the most individuals, 900, so removing it must matter most
    • No species is key: after one removal the stream keeps most of its species
    • Stream snail: removing it leaves the most species, 11, so it matters most to the stream
    • The banded tetra: the fewest species are left, though it has the fewest individuals

14. Phosphorus in two model streams (model data)

    stream	banded tetras	phosphorus level (model units)
    with tetras	30	60
    without tetras	0	15

15. 9.

    Tala reads the model data. By what percent is the phosphorus level lower without the banded tetras?

    • 75 percent: the level falls by 45 out of 60
    • 0 percent: one absent species leaves the phosphorus the same
    • 25 percent: 15 out of 60 is the share that is left
    • 45 percent: the fall of 45 units written as a percent
16. 10.

    Zee reads the graph. Which statement fits it?

    • After year 4, stream S falls from 12 to 7 species while stream R stays at 12
    • The tetras are not key, because 30 individuals is a small count
    • Stream R falls from 12 to 7 species after year 4, while stream S stays at 12
    • Stream S returns to 12 species, so removing one species does not matter