How relationships between species keep an ecosystem stable

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   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

2. 1.

   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
   • Parasitism: species M gains and species N is harmed
   • Commensalism: species M gains and species N is unchanged

3. Two Paramecium species grown alone and together (model data)

   species	count alone	count together
   Paramecium aurelia	160	140
   Paramecium caudatum	150	0

4. 2.

   Esme reads the model data on two Paramecium species in a test tube. Which relationship fits the table?

   • Competition: both use one limited resource, and one drops to 0
   • Commensalism: both species gain from sharing the same test tube
   • Mutualism: both species do better together than they do alone
   • Parasitism: Paramecium aurelia gains from Paramecium caudatum

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
   • Parasitism: with the parasite the host count falls from 50 to 44, not to 0
   • Not parasitism: a parasite would have removed its hosts well before year 4

7. Shoots on a host plant with different numbers of model parasites on it (model data)

   parasites on the host plant	shoots on the host plant
   0	20
   2	17
   4	14
   6	11

8. 4.

   Kira reads the model data on host plants. Which statement fits the table?

   • Each 2 extra parasites go with 3 fewer shoots, and the host keeps shoots
   • Each 2 extra parasites go with 3 more shoots, so the parasites help the host
   • One parasite removes the host, so shoots would be 0 at 2 parasites
   • Each 2 extra parasites go with 6 fewer shoots on the host

9. 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

10. 5.

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

    • Parasite X: it needs 30 days, the same as Y, so it reaches the most
    • 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 Y: its host stays 60 days, longer than the 30 days it needs
11. 6.

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

    • 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
    • Year 10: 2 years before the second hare peak at year 12
12. 7.

    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 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
    • The lynx count falls after its year 2 peak, one year before the hare count falls after its year 3 peak
13. 8.

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

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

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?

    • 25 percent: 15 out of 60 is the share that is left
    • 45 percent: the fall of 45 units written as a percent
    • 0 percent: one absent species leaves the phosphorus the same
    • 75 percent: the level falls by 45 out of 60
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 S returns to 12 species, so removing one species does not matter
    • Stream R falls from 12 to 7 species after year 4, while stream S stays at 12