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
- 20 m, where the sugar made is twice the sugar used
- 0 m, where the most sugar is made
- 30 m, where 3 is made and 3 is used
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?
- 30 m, because the sugar used did not change
- 15 m, half of the old zero depth of 30 m
- 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?
- No depth, since warm water above and low oxygen below leave no layer
- 0 m and 3 m, which both have over 5 mg per L
- 9 m and 12 m, which are both colder than 15 °C
- Only 6 m, with 14 °C and 6.1 mg per L
Kira asks why oxygen is only 0.5 mg per L at 12 m. Which reason fits the table and how lake layers work?
- The warm top layer pulls the oxygen up from the bottom
- Decomposers use up oxygen, and the cold layer is cut off from air
- Photosynthesis at 12 m uses up the oxygen that is left
- Cold water holds very little oxygen, so the bottom has to be low
Luz reads that wind mixes the whole lake in autumn. What happens to the oxygen at 12 m?
- It rises, as mixing carries oxygen-rich surface water down
- It stays low, because cold water cannot hold oxygen
- It falls, because mixing warms the bottom water
- It stays the same, since the bottom is a separate lake
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?
- Estuary clam, since 4 to 30 covers 12
- Sea star, since it handles the most salt
- Marsh grass, since 2 to 25 covers 2 to 12
- Mussel, since 10 to 35 reaches below 12 too
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
- Mussel, since 10 to 35 covers 20 to 34
- Sea star, since 30 to 35 covers 34
- Estuary clam, since 4 to 30 covers 20 and most of the rest
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
- No nutrient, since the bottle with nothing added grew too
- Phosphorus, since cells need it for DNA and RNA
- Iron, since cells need it to make their chlorophyll
In Region A, nitrogen with phosphorus gave 4.4 against 4.2 for nitrogen alone. What does Tala conclude?
- The 0.2 gap shows that nitrogen was not the limit
- The bottles are too different to compare fairly
- Phosphorus adds almost nothing once nitrogen is there
- Phosphorus is not needed by phytoplankton
Zee compares the two regions. Which statement fits both columns?
- It can differ by place: nitrogen in A, iron in B
- Neither region is limited, since both regions grew
- Iron limits both regions, since it limited Region B
- Nitrogen limits both regions, since it limited Region A