Where life lives in oceans, lakes and rivers

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Light in clear ocean water (model rule)

   depth (m)	share of surface light left (%)
   0	100
   30	50
   60	25

   Rule: light halves every 30 m.

2. 1.

   Ari reads the rule for clear ocean water. What share of surface light is left at 90 m?

   • 0 percent, since three steps of 50 percent remove the light
   • 25 percent, the share read at 60 m
   • 12.5 percent, after three halvings
   • 6.25 percent, after four halvings
3. 2.

   Bo knows the photic zone ends where 1 percent of surface light is left. About how deep is that in clear water?

   • About 200 m, between 180 m and 210 m
   • About 100 m, where about 10 percent is left
   • About 60 m, where two steps of 50 percent take the light away
   • About 300 m, after ten halvings
4. 3.

   Esme checks a coral at 120 m in clear water. Its algae need at least 5 percent of surface light. Do they get enough?

   • Yes: 120 m is four halvings, which leaves 6.25 percent
   • Yes: photosynthesis works at any depth in the ocean
   • No: four halvings leave 4 percent
   • No: four steps of 50 percent remove the light

5. Most oxygen that fresh water can hold (real data, from USGS DOTABLES)

   temperature (°C)	oxygen (mg per L)
   0	14.6
   10	11.3
   20	9.1
   25	8.3
   30	7.6

6. 4.

   Jun reads the oxygen table. A pond warms from 10 °C to 30 °C. How does the most oxygen it can hold change?

   • It rises by 3.7 mg per L
   • It falls by 2.2 mg per L
   • It falls by 3.7 mg per L
   • It falls by 7.6 mg per L
7. 5.

   Kira reads that a trout needs at least 8.5 mg per L of oxygen. What is the warmest temperature in the table that can still supply that?

   • 30 °C, since warmer water holds more oxygen
   • 25 °C, since 8.3 is close to 8.5
   • 20 °C, which holds 9.1 mg per L
   • 10 °C, because colder water holds more oxygen
8. 6.

   At dawn, Luz measures 4.5 mg per L in a 20 °C pond. About what share of the most oxygen it could hold is that?

   • About 200 percent, since 9.1 is about twice 4.5
   • About 20 percent, from the 20 in 20 °C
   • About half, since 4.5 is close to half of 9.1
   • About 5 percent, reading 4.5 mg as 4.5 percent

9. Salt in some waters (model data)

   place	salt (ppt)
   cell fluid of a river fish	9
   river water	0.5
   ocean water	35
   estuary water at mid-tide	9. ppt means parts of salt per thousand parts of water

10. 7.

    Milo puts a river fish cell in river water. Water crosses the cell membrane by osmosis. Which way does the net movement go?

    • Neither way, because the cell is built to stop water
    • Both ways equally, so the cell stays the same size
    • Into the cell, toward the saltier cell fluid
    • Out of the cell, toward the fresher river water
11. 8.

    Noah moves the same cell into ocean water. Which way does the net movement of water go?

    • Both ways equally, so the cell stays the same size
    • Neither way, because both sides hold salt
    • Into the cell, toward the fresher cell fluid
    • Out of the cell, toward the saltier ocean water

12. Vent bacteria in four sealed bottles (model data)

    bottle	light	hydrogen sulfide	sugar made (units)
    A	no	yes	14
    B	yes	yes	15
    C	no	no	0
    D	yes	no	0

13. 9.

    Tala wants to see whether light helps when hydrogen sulfide is present. Which two bottles should be compared?

    • A and C, since only the hydrogen sulfide differs
    • C and D, since only the light differs, but neither has hydrogen sulfide
    • A and B, since only the light differs
    • B and C, since both conditions differ
14. 10.

    Zee reads the bottle results. What is the best conclusion about where these bacteria could live?

    • In sunlit water alone, since bottle B made the most sugar
    • Where both light and hydrogen sulfide are present
    • Anywhere with water, since no bottle was ever dry
    • Anywhere hydrogen sulfide is supplied, even in total darkness