Multiple Choice
According to the theory of evolution by natural selection, from what type of organism are all living things believed to have descended, and approximately how long ago did this ancestor exist?
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21. Evolution
Introduction to Evolution and Natural Selection
Multiple Choice
Which change in Earth's atmosphere was most crucial for the evolution of complex multicellular organisms?
A
A decrease in atmospheric nitrogen levels
B
A rise in atmospheric carbon dioxide levels
C
The complete removal of methane from the atmosphere
D
An increase in atmospheric oxygen levels
Verified step by step guidance1
Understand the role of oxygen in cellular respiration: Oxygen is crucial for aerobic respiration, a process that allows cells to produce large amounts of ATP (energy). This energy is necessary to support the functions of complex multicellular organisms.
Recognize the historical context: Early Earth's atmosphere had very low levels of oxygen. The increase in atmospheric oxygen occurred during the Great Oxygenation Event, primarily due to photosynthetic organisms like cyanobacteria.
Connect oxygen levels to multicellularity: Higher oxygen levels allowed for more efficient energy production, enabling the development of larger and more complex organisms with specialized cells and tissues.
Eliminate incorrect options: Decreasing nitrogen levels, increasing carbon dioxide levels, or removing methane do not directly support the energy demands or structural complexity required for multicellular life.
Conclude that the increase in atmospheric oxygen levels was the most crucial change, as it directly facilitated the evolution of complex multicellular organisms by providing the energy needed for their development and maintenance.
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