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 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 shrink, since 1.5 is made and 3 is used each hour
- They grow, since sugar is still being made at that depth
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?
- 40 m, where half of 1.5 is nearly zero
- 30 m, because the sugar used did not change
- 20 m, where half of 6 equals the 3 used
- 15 m, half of the old zero depth of 30 m
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?
- 9 m and 12 m, which are both colder than 15 °C
- 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
- 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
- Photosynthesis at 12 m uses up the oxygen that is left
- Decomposers use up oxygen, and the cold layer is cut off from air
- 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?
- Mussel, since 10 to 35 reaches below 12 too
- Marsh grass, since 2 to 25 covers 2 to 12
- Sea star, since it handles the most salt
- Estuary clam, since 4 to 30 covers 12
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
- Sea star, since 30 to 35 covers 34
- Estuary clam, since 4 to 30 covers 20 and most of the rest
- Mussel, since 10 to 35 covers 20 to 34
Over a whole year, Pia finds the station ranges from 2 to 34 ppt. Which organism could stay all year?
- Estuary clam, since 4 to 30 is the widest range
- Mussel, since 10 to 35 reaches the top of the range
- None, since no range covers all of 2 to 34
- Marsh grass, since it tolerates the lowest salt
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?
- Phosphorus, since cells need it for DNA and RNA
- No nutrient, since the bottle with nothing added grew too
- Nitrogen: adding it raised chlorophyll to 4.2
- 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 bottles are too different to compare fairly
- The 0.2 gap shows that nitrogen was not the limit
- Phosphorus adds almost nothing once nitrogen is there
- Phosphorus is not needed by phytoplankton