Where life lives in oceans, lakes and rivers
Grade 9 Science Worksheet
Circle the best answer.
Read this first
Phytoplankton at five depths (model data)
depth (m) sugar made (units per hour) sugar used (units per hour) 0 12 3 10 9 3 20 6 3 30 3 3 40 1.5 3 Ari defines net production as sugar made minus sugar used. At which depth is net production zero?
- 40 m, the deepest depth where sugar is still made
- 30 m, where 3 is made and 3 is used
- 20 m, where the sugar made is twice the sugar used
- 0 m, where the most sugar is made
Bo follows cells that sit at 40 m for a whole day. What happens to their sugar stores?
- They stay the same, since some light still reaches 40 m
- They grow by 1.5 units an hour, made minus used
- They grow, since sugar is still being made at that depth
- They shrink, since 1.5 is made and 3 is used each hour
Esme imagines a cloudy week that halves the sugar made at every depth. Sugar used is unchanged. At which depth is net production now zero?
- 15 m, half of the old zero depth of 30 m
- 30 m, because the sugar used did not change
- 40 m, where half of 1.5 is nearly zero
- 20 m, where half of 6 equals the 3 used
A lake in late summer (model data)
depth (m) temperature (°C) oxygen (mg per L) 0 24 8.2 3 23 8.0 6 14 6.1 9 9 2.0 12 7 0.5 Decomposers use oxygen as they break down remains that sink. In summer the warm top layer and the cold bottom layer do not mix.
Jun reads that a trout needs water at 15 °C or colder with at least 5 mg per L of oxygen. Which depths meet both needs?
- Only 6 m, with 14 °C and 6.1 mg per L
- 0 m and 3 m, which both have over 5 mg per L
- No depth, since warm water above and low oxygen below leave no layer
- 9 m and 12 m, which are both colder than 15 °C
How much salt each organism tolerates (model data)
organism salt it tolerates (ppt) marsh grass 2 to 25 estuary clam 4 to 30 mussel 10 to 35 sea star 30 to 35. ppt means parts of salt per thousand parts of water Milo reads that after a flood a station ranges from 2 to 12 ppt through the tide. Which organism could stay all day?
- Marsh grass, since 2 to 25 covers 2 to 12
- Mussel, since 10 to 35 reaches below 12 too
- Estuary clam, since 4 to 30 covers 12
- Sea star, since it handles the most salt
After a dry spell, Noah finds the station ranges from 20 to 34 ppt. Which organism could stay all day?
- Marsh grass, since 2 to 25 covers 20
- Estuary clam, since 4 to 30 covers 20 and most of the rest
- Mussel, since 10 to 35 covers 20 to 34
- Sea star, since 30 to 35 covers 34
Over a whole year, Pia finds the station ranges from 2 to 34 ppt. Which organism could stay all year?
- Marsh grass, since it tolerates the lowest salt
- Estuary clam, since 4 to 30 is the widest range
- None, since no range covers all of 2 to 34
- Mussel, since 10 to 35 reaches the top of the range
Chlorophyll after five days (µg per L) (model data)
bottle Region A Region B no nutrient added 1.0 1.0 nitrogen added 4.2 1.1 phosphorus added 1.1 1.0 iron added 1.0 3.9 nitrogen and phosphorus added 4.4 1.1 Ren reads the bottle results for Region A. Which nutrient most limited growth there?
- Nitrogen: adding it raised chlorophyll to 4.2
- Iron, since cells need it to make their chlorophyll
- Phosphorus, since cells need it for DNA and RNA
- No nutrient, since the bottle with nothing added grew too
In Region A, nitrogen with phosphorus gave 4.4 against 4.2 for nitrogen alone. What does Tala conclude?
- Phosphorus is not needed by phytoplankton
- The 0.2 gap shows that nitrogen was not the limit
- Phosphorus adds almost nothing once nitrogen is there
- The bottles are too different to compare fairly
Zee compares the two regions. Which statement fits both columns?
- Nitrogen limits both regions, since it limited Region A
- Neither region is limited, since both regions grew
- It can differ by place: nitrogen in A, iron in B
- Iron limits both regions, since it limited Region B