QUESTION TEXT: In a vast ocean region, phosphorus levels…
QUESTION TYPE: Must be True
Runoff ➞ Phosphorus doubled ➞ plankton ➞ oxygen consumed ➞ few fish survive
ANALYSIS: This question is, in fact, pretty straightforward. It’s a “must be true” question, so you’re not trying to find a flaw in the information.
Instead, you just have to understand the information. I recommend making a diagram like I did above in the “FACTS” section. The stimulus gives you a lot of complex information. If you can reduce it to a short diagram, you can go through the answers more quickly. Everything connects left to right.
- CORRECT. If you look at the diagram in the “FACTS” above, you can see that this is true. Runoff is the first term, and it leads directly to plankton, the third term.
- We can’t say this. We know few fish survive now. But we don’t know how many fish could survive before: maybe only 37% of fish could survive before. That’s more than few, but it’s not most.
- The second sentence says that phosphorus stimulates the growth of plankton. Stimulates just means increases. There could still be some plankton for the bacteria even without runoff.
- Phosphorus levels increased, but that could happen with a constant runoff rate. Runoff flows continously, like water flowing into a bucket. A flow of water at a steady rate will fill a bucket: the rate doesn’t need to increase! Similarly a steady rate of runoff will gradually increase phosphorus levels.
Imagine you pour water into a bucket. You can pour at a constant rate, and the total water level in the bucket will double. Same with phosphorus. Runoff is constantly flowing, and the ocean region is a fixed quantity, like a bucket.
- This is waaaaay too broad. We only know about one ocean region. We can’t say if phosphorus produces this impact in every part of the ocean.
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