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
- 0 m, where the most sugar is made
- 30 m, where 3 is made and 3 is used
- 20 m, where the sugar made is twice the sugar used
Bo follows cells that sit at 40 m for a whole day. What happens to their sugar stores?
- They grow, since sugar is still being made at that depth
- They grow by 1.5 units an hour, made minus used
- They shrink, since 1.5 is made and 3 is used each hour
- They stay the same, since some light still reaches 40 m
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
- 40 m, where half of 1.5 is nearly zero
- 15 m, half of the old zero depth of 30 m
- 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?
- 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
- No depth, since warm water above and low oxygen below leave no layer
- 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?
- Cold water holds very little oxygen, so the bottom has to be low
- 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
Luz reads that wind mixes the whole lake in autumn. What happens to the oxygen at 12 m?
- It stays the same, since the bottom is a separate lake
- It rises, as mixing carries oxygen-rich surface water down
- It falls, because mixing warms the bottom water
- It stays low, because cold water cannot hold oxygen
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 After a dry spell, Noah finds the station ranges from 20 to 34 ppt. Which organism could stay all day?
- 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
- Marsh grass, since 2 to 25 covers 20
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?
- Iron, since cells need it to make their chlorophyll
- No nutrient, since the bottle with nothing added grew too
- Phosphorus, since cells need it for DNA and RNA
- Nitrogen: adding it raised chlorophyll to 4.2
In Region A, nitrogen with phosphorus gave 4.4 against 4.2 for nitrogen alone. What does Tala conclude?
- Phosphorus adds almost nothing once nitrogen is there
- Phosphorus is not needed by phytoplankton
- The bottles are too different to compare fairly
- The 0.2 gap shows that nitrogen was not the limit
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
- Nitrogen limits both regions, since it limited Region A
- Iron limits both regions, since it limited Region B