ACT Science OG Test 2 - Passage III

Questions 14-20 are based on the following passage.

When 2 types of bacteria found in the soil of a wet­land (land having a high water table) break down organic matter, gases are generated. Aerobic bacteria, which require O₂, generate CO₂. Anaerobic bacteria, which require little or no O₂ , generate CH₄.

Study

At the beginning of a particular summer, 3 soil sec­tions, each l .5 m long, 1 m wide, and 0.6 m deep, were removed intact from the surface of each of 2 wetlands-a bog and a/en-after all Jive plants had been removed from the sections. Each section was placed in a separate 100 L tank having sides and a lid made entirely of glass. An instrument to measure gas emissions was mounted on the underside of the lid, above the soil. All the tanks were placed at an outdoor site near the wetlands.


Different amounts of water were added to the 3 tanks containjng bog soil sections to produce a water table (WT) I cm above the surface ( + 1 cm) of the first soil section, a WT 10 cm below the surface (-10 cm) of the second soil section, and a WT 20 cm below the surface (-20 cm) of the third soil section. This procedure was repeated for the 3 tanks containing fen soil sections. All the lids were then closed.


Over the next 3 months, gas emissions from each soil section were measured, in moles of carbon per square meter (mol C/m²). Throughout this period, the temperature inside the tanks was kept the same as the outdoor tempera­ture. Figure I shows the total emission of CO₂ and the total emission of CH₄ from each bog soil section due to bacterial activity; Figure 2 does the same for each fen soil section.

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Question 14 The researchers who conducted the study most likely chose to conduct it during the summer rather than during the winter because organic matter in soil is broken down