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
- 30 m, where 3 is made and 3 is 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 shrink, since 1.5 is made and 3 is used each hour
- They grow, since sugar is still being made at that depth
- They grow by 1.5 units an hour, made minus used
- 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?
- 20 m, where half of 6 equals the 3 used
- 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
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
- Only 6 m, with 14 °C and 6.1 mg per L
- No depth, since warm water above and low oxygen below leave no layer
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 rises, as mixing carries oxygen-rich surface water down
- It stays low, because cold water cannot hold oxygen
- It stays the same, since the bottom is a separate lake
- It falls, because mixing warms the bottom water
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?
- Sea star, since 30 to 35 covers 34
- Mussel, since 10 to 35 covers 20 to 34
- Marsh grass, since 2 to 25 covers 20
- Estuary clam, since 4 to 30 covers 20 and most of the rest
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
- Marsh grass, since it tolerates the lowest salt
- 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 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
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
