ACT Science Practice Test 1

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Directions: The passage below is followed by several questions. After reading the passage, choose the best answer to each ACT Science practice question. You may refer to the passage as often as necessary. Calculators may NOT be used on this test.

Passage I

Eutrophication is a phenomenon where excessive amounts of nutrients are added to a marine ecosystem. These nutrients cause plant life like algae to multiply rapidly, leading to very high population densities. In freshwater ecosystems, the algae can become so dense that it can turn ponds, lakes or even smaller rivers green. The algae grows to an unreasonable level at a very fast rate. The algae are known as phytoplankton and are microscopic, single-celled organisms.

A body of water that is experiencing eutrophication and a resulting bloom can be quickly devastated. Eutrophication affects all living organisms in the area including fish, birds and mammals. The top layer of phytoplankton causes such a build-up on the surface that they accumulate sediment. When this occurs the sunlight is blocked and it will choke off the plant life below the surface. The phytoplankton will also cause less surface area for the water to interface with air. As a result, there will be less oxygen available in the water. As oxygen continues to deplete, the depletion can have a negative effect on life as there will be less oxygen to support the organisms below the surface that depend on the oxygen from plants that diffuses into the water.

Scientist 1
The root cause of eutrophication is not known. However, the frequency and increasing incidents of eutrophication point to human farming activity as the potential cause. The growth of the phytoplankton is caused by runoff that contains multiple sources of nitrates that are also found in fertilizer. The nitrates allow for the phytoplankton to grow rapidly. The solution to the problem is to either move the drainage so the runoff from the human farming activity cannot reach the water source or move the farms.

Scientist 2
Sometimes eutrophication can happen naturally without any real cause. Sometimes when there are periods of heavy rain, the increase in rain water leads to an imbalance in the pH of the water. This in turn creates favorable conditions for the phytoplankton to grow and proliferate. This is a natural cycle that also ensures that too many fish and other animals do not build up in a freshwater source. This type of bloom is nature’s way of eliminating overpopulation with an abiotic factor. Although many organisms will die as a result, it will help to thin the numbers of organisms and ensure a healthier freshwater source.

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Question 1
According to Scientist 1, which of the following is the cause of the eutrophication?

A change in the pH of the water.
The increasing changes in phytoplankton.
Agricultural run-off from human activity.
The build-up of phosphates in the body of water.
Question 1 Explanation: 
The correct answer is (C). Scientist 1 believes that human farming and agriculture are responsible for the eutrophication of the water. He believes nitrates that are being added as run-off are the main cause of the growth of the algae.
Question 2
What is the main point of disagreement between Scientist 1 and Scientist 2?

The source of the nitrogen.
The root cause of the eutrophication.
The effects of the lack of oxygen.
The effect of the plant life in the aquatic ecosystem.
Question 2 Explanation: 
The correct answer is (B). The two scientists have differing opinions on what the main cause of the eutrophication is. Scientist 1 believes it is human based with nitrates as the cause. Scientist 2 believes it is a natural phenomenon with a change in pH as the cause.
Question 3
Both scientists would likely agree that eutrophication is

algae that will occasionally grow in aquatic ecosystems due to human activities.
a bloom of phytoplankton that grows in response to high levels of phosphates.
a large build-up of algae that grows at a rapid rate in a body of water.
an explosion of algae due to natural factors and the need to reduce overpopulation.
Question 3 Explanation: 
The correct answer is (C). Both would agree on what eutrophication is. They would both say that it is an explosive growth of algae known as phytoplankton. They both indicate this in their passages.
Question 4
According to Scientist 2, eutrophication is necessary for

the control of overpopulation in an aquatic ecosystem.
the natural control of the pH of water in an aquatic ecosystem.
the normal process that takes place in a pond in response to farmland runoff.
the rejuvenation of aquatic life, which thrives during such an event.
Question 4 Explanation: 
The correct answer is (A). Scientist 2 believes that this event is meant to prevent overpopulation in an aquatic environment. He believes that the die-off is necessary to manage overpopulation. Thus, only those organisms that survive can replenish the environment. This ensures that only the strong survive and reproduce.
Question 5
Scientist 1 probably mentions farming and agriculture in order to:

point to a human activity that would cause eutrophication.
show that humans changing natural land is bad for the environment.
bolster his case for humans causing a change in the pH of the water that leads to eutrophication.
bolster his case that human activity such as farming increases nitrates, leading to eutrophication.
Question 5 Explanation: 
The correct answer is (D). Scientist 1 believes that the main cause of the eutrophication is nitrates from farming fertilizer. So he mentions this to bolster his case for his suspected cause of the algal bloom.
Question 6
The end result of a severe eutrophication event will always be:

A regrowth of new life because of the nitrates in the water.
The death of the phytoplankton when it over-accumulates.
A massive die off of both plant and animal life in the aquatic environment.
The growth of more plant life in the water as they grow well with plankton.
Question 6 Explanation: 
The correct answer is (C). Eutrophication is a devastating condition. The overgrowth of algae will build up to the point where the sun is blocked. The oxygen interface with the water is also compromised. Between the lack of sun for plants and the lack of oxygen, the aquatic ecosystem will eventually die off.
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