ACT Success - Science - Practice #6
There are several passages in this test. Each passage is followed by several questions. After reading a passage, choose the best answer to each question. You may refer to the passages as often as necessary. You are NOT permitted to use a calculator on this test.
Group 1
Scientists conducted an experiment to observe how the presence of oil affects the growth of bacterial colonies over time. The study measured bacterial growth in three conditions: 0% oil, 5% oil, and 20% oil. Bacteria were cultured in three separate environments, each with a different concentration of oil contamination. The number of bacterial colonies was recorded over an 8-day period, starting from Day 2 and concluding on Day 8.
Graph showing the number of bacterial colonies over time in different oil concentrations.
Question 1a
Based on the trend in the graph, if the experiment were extended beyond Day 8, what would likely happen to the number of bacterial colonies in the 20% oil environment?
The number of colonies would continue to increase.
The number of colonies would decrease to zero by Day 10.
The number of colonies would stabilize at a low level.
The number of colonies would likely fluctuate around 10 colonies.
Question 1b
If another experiment was conducted with 10% oil, where would you expect the peak number of bacterial colonies to fall relative to the other three conditions?
Higher than the no-oil condition but lower than the 5% oil condition.
Between the 5% oil and 20% oil conditions.
Equal to the 20% oil condition.
Lower than the no-oil condition.
Question 1c
Which of the following hypotheses about oil concentration and bacterial growth is most consistent with the data in the graph?
Bacteria are inhibited by any amount of oil.
Higher oil concentrations initially encourage bacterial growth up to a certain level.
Bacterial growth is directly proportional to oil concentration over time.
Bacterial growth is unaffected by oil concentration.
Group 2
Researchers examined the relationship between sediment composition and changes in mountain peak height over a 60-year period (1910–1970) along a mountain range. The study measured changes in peak height and sediment composition at various points (0–14 km) along the mountain range. Sediment types included limestone, shale, and slate, each with characteristic particle sizes. Gains or losses in sediment, as well as changes in peak height, were recorded.
Graph showing changes in peak height and sediment composition over time.
Question 2a
Based on the data, which type of sediment is most likely associated with peak height loss over the period studied?
Limestone, because of its small particle size.
Shale, due to its moderate particle size.
Slate, since it shows the least variation in height.
A combination of shale and slate.
Question 2b
If another mountain range with primarily slate peaks was observed, what trend in peak height change would you expect, based on the findings of this study?
Slate peaks would likely show a consistent loss of height.
Slate peaks would likely maintain or gain height over time.
Slate peaks would experience greater variation in height changes.
Slate peaks would likely erode faster than other sediment types.
Question 2c
Suppose a new measurement showed that shale sediment had been eroded at a rate twice as fast as limestone. How would this finding likely impact the interpretation of the graph's data on peak height change?
It would suggest that limestone is more resistant to erosion than previously thought.
It would mean that slate contributes more to height gain than shale.
It would imply that shale is not as stable as initially interpreted, leading to larger height losses.
It would indicate that all sediment types contribute equally to peak height loss.
Group 3
Causes of Dinosaur Extinction The extinction of dinosaurs approximately 66 million years ago remains one of the most widely debated topics in paleontology. Several theories have been proposed to explain what led to the mass extinction event that wiped out most dinosaur species. Three scientists offer differing explanations for this event.
Scientist 1 Scientist 1 argues that the primary cause of the dinosaur extinction was a large asteroid impact. According to this theory, an asteroid struck Earth in what is now the Yucatán Peninsula, creating a massive crater and releasing an enormous amount of debris into the atmosphere. This debris blocked sunlight, resulting in a dramatic drop in temperature and a reduction in photosynthesis, which caused a collapse of food chains. Scientist 1 points to the presence of a worldwide layer of iridium-rich clay, a rare element on Earth but common in asteroids, as evidence supporting an impact event.
Scientist 2 Scientist 2 believes that extensive volcanic activity, particularly in the Deccan Traps region of what is now India, was the primary driver of dinosaur extinction. This volcanic activity would have released large amounts of sulfur dioxide and carbon dioxide into the atmosphere, causing both short-term cooling and long-term global warming. Scientist 2 argues that these extreme and rapid climate changes would have disrupted ecosystems and made it difficult for dinosaurs to survive. Geological studies show increased volcanic ash deposits in sediments from around the time of the extinction, which Scientist 2 cites as evidence of prolonged volcanic eruptions.
Scientist 3 Scientist 3 contends that the extinction of dinosaurs was a gradual process caused by a combination of climate change and competition from newly evolving species of mammals. As Earth’s climate slowly cooled over millions of years, dinosaurs, which were adapted to warmer conditions, began to decline. Meanwhile, mammals adapted and thrived in the changing environment, gradually outcompeting dinosaurs for resources. Fossil records show a decline in dinosaur diversity over time, which Scientist 3 interprets as evidence of a slow extinction rather than a sudden catastrophic event.
Question 3a
Which of the following pieces of evidence would most strongly support Scientist 2’s explanation over those of Scientist 1 and Scientist 3?
A discovery of dinosaur fossils in regions unaffected by volcanic ash, suggesting they lived in isolated pockets after the extinction event.
Sediment analysis indicating high levels of iridium worldwide, which is associated with asteroid impacts.
Geological layers containing sulfur dioxide and carbon dioxide deposits from volcanic sources, dated to the time of the extinction.
Evidence showing that mammal populations increased significantly just before the dinosaur extinction.
Question 3b
Which observation would most directly challenge Scientist 3’s theory of gradual extinction due to competition with mammals?
Fossil evidence showing that large numbers of dinosaur species died out within a very short period.
The discovery of volcanic ash layers in rocks from the extinction period, suggesting a volcanic eruption.
Analysis showing that iridium levels spiked in the fossil record exactly at the time dinosaurs disappeared.
Studies finding that mammals and dinosaurs occupied separate ecological niches with minimal resource overlap.
Question 4a
A scientist measures the pH of three different lakes in a forested area over time. The pH levels fluctuate seasonally, with a tendency to be lowest in spring and highest in autumn. Which of the following is the most likely explanation for this seasonal variation in pH? Which of the following is the most likely explanation for this seasonal variation in pH?
Increased photosynthesis in autumn decreases carbon dioxide levels, raising the pH of the lakes.
Increased rainfall in spring dilutes the water, lowering the pH of the lakes.
Bacterial decomposition in autumn raises carbon dioxide levels, lowering the pH of the lakes.
Melting snow in spring releases acidic compounds into the lakes, lowering the pH.
Question 4b
An ecologist observes that when lake water temperature rises above 25°C, algae populations increase significantly, resulting in reduced oxygen levels in the water. However, when temperatures fall below 15°C, algae growth slows, and oxygen levels increase. Which of the following hypotheses is most consistent with these observations?
Higher temperatures decrease oxygen levels directly.
Algae thrive at high temperatures and deplete oxygen as they grow.
Algae release oxygen as they grow, leading to increased oxygen levels.
Oxygen levels in the lake are unaffected by temperature changes.
Question 4c
A biologist studies two plant species, A and B, in different soil moisture conditions. Species A thrives in soil with 40-60% moisture, while Species B grows best in soil with 20-30% moisture. When soil moisture exceeds 70%, neither species grows well. If both species were transplanted to an area where soil moisture fluctuates between 10% and 80%, which of the following would likely be observed?
Both species would thrive when moisture is at 80%.
Only Species B would survive when moisture drops to 10%.
Both species would have optimal growth at 70% soil moisture.
Species A would grow best at 60% soil moisture, while Species B would grow best at 30%.
Question 4d
A team of researchers tests the effect of light intensity on the rate of photosynthesis in Plant X. They find that as light intensity increases from 0 to 500 lumens, the rate of photosynthesis increases rapidly. Beyond 500 lumens, however, the rate plateaus and then declines after 800 lumens due to light saturation and potential damage to plant cells. If light intensity were increased to 1,000 lumens, what would be the most likely effect on the rate of photosynthesis in Plant X?
The rate of photosynthesis would increase continuously.
The rate of photosynthesis would remain stable but high.
The rate of photosynthesis would decline due to light stress.
The rate of photosynthesis would drop to zero.
Question 4e
In an experiment testing the effects of salinity on fish populations, a biologist finds that Species C survives best in low-salinity water, while Species D can tolerate a wider range of salinity. When salinity rises above 5%, both species experience decreased reproductive rates. Which of the following environments would most likely lead to a stable population of both species?
An environment where salinity fluctuates between 6% and 8%.
An environment where salinity is consistently around 2%.
An environment where salinity remains above 10%.
An environment where salinity fluctuates between 5% and 10%.
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