Where life lives in oceans, lakes and rivers

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Algae need at least 1 percent of surface light. Ari compares the two waters. How does the depth of the photic zone in clear ocean water compare with the bay's?

   • About 10 times as deep, roughly 200 m against 20 m
   • About 100 times as deep, since 1 percent is 1 in 100
   • 27 m deeper, the gap between 30 m and 3 m
   • The same depth, since light halves in both
2. 2.

   Trout need water at 15 °C or colder with at least 5 mg per L. A hot summer warms every layer by 3 °C and cuts oxygen by 1 mg per L at each depth. Esme rechecks the lake. How much trout habitat is left?

   • The same band as before, since the two changes cancel out
   • 9 m, since 12 °C is cool enough
   • 6 m, since its oxygen is still 5.1 mg per L
   • None: 6 m is 17 °C and 9 m has only 1.0 mg per L
3. 3.

   Nitrate is a nutrient; µM is how much of it is dissolved in the water. Jun reads a tropical ocean profile. Which explanation best fits the chlorophyll peak at 75 m?

   • Light is bright enough at 75 m, so that is where cells peak, as light feeds growth
   • Nitrate is plentiful at 75 m, so that is where cells peak, as nitrate feeds growth
   • Deep water holds more oxygen, so cells peak at 75 m
   • At 75 m there is enough of both: above, nitrate runs low; below, light fades
4. 4.

   These bacteria grow best at about 20 to 45 °C. Kira reads a vent profile. Which explanation best fits the bacteria peak at 5 m rather than at the vent mouth?

   • More sunlight reaches the water at 5 m, so the bacteria grow better there
   • Hydrogen sulfide is highest at 0 m, so the count at 0 m must be a mistake
   • At 5 m the water is cool enough and still rich in hydrogen sulfide
   • Bacteria prefer the coldest water, so the peak at 5 m is a counting error
5. 5.

   Streams brought the same load all year. A writer blames pollution for the low oxygen at 12 m in August. Luz looks for data that favor summer layering. Which feature is strongest?

   • The August value of 0.8 is very low for any fish in the lake
   • Oxygen fell from 8.0 in April to 0.8 in August, as the lake layered and warmed
   • Oxygen jumped from 0.9 to 7.5 once the layers mixed, with inputs unchanged
   • Oxygen stayed low in October, close to the August value of 0.8

6. Read this first

   Use this

   Notebook, 4 lines. Line 1: Light halves every 30 m in clear water. Line 2: In a bay it halves every 3 m. Line 3: At 18 m the bay has six halvings, which leaves about 1.6 percent of surface light. Line 4: So algae at 18 m in the bay do about as well as algae at 18 m in clear water.

7. 6.

   Milo reads a classmate's notebook about two waters. Which line has the flaw?

   • Line 1: clear water loses light as it goes down, so a 30 m halving is too far
   • Line 2: a bay cannot lose light faster than clear water does at that depth
   • Line 4: at 18 m clear water keeps about two thirds of the light, the bay 1.6 percent
   • Line 3: six halvings remove 300 percent of the light, so the bay has no light left

8. Use this

   Notebook, 4 lines. Line 1: A station had 40 snails in a low-tide sample and 3 in a high-tide sample. Line 2: The water was 8 ppt and 14 °C at low tide, and 26 ppt and 21 °C at high tide. Line 3: So salinity was the only thing that changed between the samples. Line 4: So snails may do better at low salinity, and a test that holds temperature steady would settle it.

9. 7.

   Noah reads a classmate's notebook about snails in an estuary. Which line has the flaw?

   • Line 2: water cannot be measured in ppt and °C at once
   • Line 4: no test could ever separate salinity from temperature
   • Line 1: 40 and 3 are very different sizes, so the samples cannot be compared at all
   • Line 3: temperature also changed, so salinity was not the only difference

10. A pond at dawn after a hot night (model data)

    measure	value
    water temperature (°C)	30
    oxygen measured (mg per L)	2.1
    most oxygen fresh water holds at 30 °C (mg per L)	7.6
    fish need at least (mg per L)	4

11. 8.

    A classmate says pollution caused the fish loss, since clean water would hold plenty of oxygen. Ren checks the card. Which reply is best?

    • Agree: warm water holds more oxygen than cool water, so 2.1 is far too low
    • Not shown: water at 30 °C holds at most 7.6, and night respiration can lower it
    • Disagree: warm water holds no oxygen, so fish cannot live at 30 °C
    • Agree: 2.1 is far below 7.6, so pollution alone could explain a gap that large

12. Three places (model data)

    place	kinds of species	young fish per 100 m²
    open ocean	400	12
    estuary	60	85
    river	120	20

13. 9.

    A classmate says estuaries are poor habitats because their salinity keeps changing. Tala checks the table. Which reply is best?

    • Not supported: the estuary has the most kinds of species
    • Supported: it has just 60 kinds of species, the fewest of the three
    • Not supported: the estuary has fewer kinds of species but far more young fish, 85 per 100 m²
    • Supported: just the species that tolerate shifting salt live there, so they do poorly

14. Spring in a cold ocean (model data)

    month	daylight (hours)	surface water (°C)	nitrate (µM)	chlorophyll (µg per L)
    February	10	4	12	0.5
    March	12	4	12	0.8
    April	14	6	10	6.0
    May	15	9	3	3.5
    June	16	13	0.5	1.0

15. 10.

    A classmate says the spring bloom starts because the water warms. Zee checks the table. Which reply is best?

    • Not supported: only daylight matters, since nitrate and temperature changed very little
    • Supported: chlorophyll peaks in April, right after the water warms from 4 to 6 °C, so warmth is the cause
    • Not supported: temperature cannot affect phytoplankton at all
    • Not supported: chlorophyll jumped in April at only 6 °C; June was warmest, nitrate nearly gone