Science Test #7 Flashcards
6 cards from real GED practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Science Test #7 flashcards as text
A researcher observes that a population of bacteria doubles every 20 minutes under ideal conditions. If a culture starts with 500 bacteria, how many bacteria will be present after 2 hours?
Answer: 32,000
2 hours = 120 minutes. Dividing by 20 minutes per doubling gives 6 doubling periods. Starting with 500: 500 × 2^6 = 500 × 64 = 32,000 bacteria.
Which of the following best explains why water has an unusually high boiling point compared to other molecules of similar molecular mass?
Answer: Water molecules form hydrogen bonds with each other
Water's boiling point is elevated because oxygen is highly electronegative, creating a partial negative charge that attracts the partial positive charge on hydrogen atoms of neighboring molecules — forming hydrogen bonds. These require extra energy to break, raising the boiling point well above comparable molecules like H₂S.
A scientist performs an experiment where she applies a stimulus to one end of a severed nerve fiber isolated in a solution. She detects an action potential traveling along the fiber but notices it stops before reaching the other end. Which of the following most likely explains this observation?
Answer: The fiber passed through a region where the myelin sheath was damaged
Myelin sheaths insulate nerve fibers and allow saltatory conduction (signal jumping between nodes of Ranvier). If the myelin sheath is damaged in a section, the action potential cannot be propagated through that region, causing it to stop. Since the signal did initiate and travel partway, the stimulus clearly exceeded threshold.
Carbon-14 has a half-life of approximately 5,730 years. A fossilized wood sample is found to contain 12.5% of the carbon-14 concentration found in a living tree today. Approximately how old is the sample?
Answer: 17,190 years
Starting at 100%: after 1 half-life → 50%, after 2 half-lives → 25%, after 3 half-lives → 12.5%. Three half-lives have passed: 3 × 5,730 = 17,190 years.
Two plant species occupy the same geographic area. Species A produces flowers in early spring before its leaves emerge, while Species B flowers in late summer and produces nectar only at night. Which ecological concept BEST explains why both species can coexist in the same habitat without directly competing?
Answer: Resource partitioning through temporal niche differentiation
Resource partitioning occurs when species divide up available resources to reduce direct competition. Here, the two plants partition time — one uses pollinators in early spring, the other uses nocturnal pollinators in late summer — allowing coexistence in the same habitat through temporal niche differentiation.
A sealed container holds a gas at 300 K and 2 atm of pressure. The container is heated until the pressure reaches 3 atm. Assuming the volume remains constant, what is the new temperature of the gas?
Answer: 450 K
Using Gay-Lussac's Law (P₁/T₁ = P₂/T₂ at constant volume): 2/300 = 3/T₂. Solving: T₂ = (3 × 300)/2 = 900/2 = 450 K. The temperature and pressure are directly proportional at constant volume.