Where life lives in oceans, lakes and rivers
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
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?
- 27 m deeper, the gap between 30 m and 3 m
- About 10 times as deep, roughly 200 m against 20 m
- About 100 times as deep, since 1 percent is 1 in 100
- The same depth, since light halves in both
Read this first
Net sugar made by layer of a 40 m column (model data)
layer thickness (m) net sugar per meter of layer (units) 0 to 10 m 10 8 10 to 20 m 10 5 20 to 30 m 10 2 30 to 40 m 10 −1 Bo adds up the net sugar made in the whole column. What is the total?
- 140 units
- 150 units, treating the bottom layer as zero
- 80 units, the top layer alone where light is strongest
- 14 units, adding the four rates without the thickness
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
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
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?
- Hydrogen sulfide is highest at 0 m, so the count at 0 m must be a mistake
- Bacteria prefer the coldest water, so the peak at 5 m is a counting error
- At 5 m the water is cool enough and still rich in hydrogen sulfide
- More sunlight reaches the water at 5 m, so the bacteria grow better there
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 stayed low in October, close to the August value of 0.8
- 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
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.
Milo reads a classmate's notebook about two waters. Which line has the flaw?
- Line 3: six halvings remove 300 percent of the light, so the bay has no light left
- 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
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 A classmate says pollution caused the fish loss, since clean water would hold plenty of oxygen. Ren checks the card. Which reply is best?
- Disagree: warm water holds no oxygen, so fish cannot live at 30 °C
- Agree: warm water holds more oxygen than cool water, so 2.1 is far too low
- Agree: 2.1 is far below 7.6, so pollution alone could explain a gap that large
- Not shown: water at 30 °C holds at most 7.6, and night respiration can lower it
Three places (model data)
place kinds of species young fish per 100 m² open ocean 400 12 estuary 60 85 river 120 20 A classmate says estuaries are poor habitats because their salinity keeps changing. Tala checks the table. Which reply is best?
- Supported: it has just 60 kinds of species, the fewest of the three
- Supported: just the species that tolerate shifting salt live there, so they do poorly
- Not supported: the estuary has the most kinds of species
- Not supported: the estuary has fewer kinds of species but far more young fish, 85 per 100 m²
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 A classmate says the spring bloom starts because the water warms. Zee checks the table. Which reply is best?
- Not supported: temperature cannot affect phytoplankton at all
- Supported: chlorophyll peaks in April, right after the water warms from 4 to 6 °C, so warmth is the cause
- Not supported: chlorophyll jumped in April at only 6 °C; June was warmest, nitrate nearly gone
- Not supported: only daylight matters, since nitrate and temperature changed very little