PEP Edition | Grade 7 Biology: Priestley's Revelation

In 1773, the British scientistPriestley (Joseph Priestley) conducted an experiment that changed the history of biology. At the time, people generally believed the atmosphere was a static, unchanging backdrop, but Priestley astutely detected a hidden "reciprocal contract" between plants and the air.

The Elegant Logic of the Experiment

Environmental Limitations: A burning candle and a mouse's respiration quickly deplete a certain "gas" (oxygen) inside the sealed chamber, causing the flame to die out and life to end.
Compensation by Plants: Green plants absorb carbon dioxide and release oxygen, offsetting the negative effects of respiration.
The Essence of Renewal: Plants don't just "purify" the air — they transform matter. This discovery first established the irreplaceable role of plants in the biosphere's gas cycle.

Just as modern spacecraft use microalgae to buildBioregenerative Life Support Systems, Priestley's experiment revealed a fundamental truth: life does not exist in isolation — it finds balance through the rhythmic exchange of the atmosphere.

QUESTION 1

In Priestley's experiment, why did a mouse placed alone in the jar quickly die, while one placed with a plant survived? What does this reveal about the role of plants in the atmosphere?

The plant absorbed the oxygen produced by the mouse

The plant absorbed carbon dioxide through photosynthesis and produced oxygen, renewing the air

The plant provided shade for the mouse

QUESTION 2

In Priestley's experiment, if we completely block sunlight and repeat the same comparison, would the results change? What is the prerequisite for plants to "renew the air"? What does this teach us about the biosphere?

No change; prerequisite is water; insight is that the water cycle is important

Results would change — the plant would also die; prerequisite is light; insight is that photosynthesis drives the gas cycle

No change; prerequisite is soil; insight is that land conservation is important

QUESTION 3

In Priestley's experiment, the candle went out because the jar was lacking which gas?

Carbon dioxide

Oxygen

Nitrogen

QUESTION 4

The conclusions of Priestley's experiment caused a sensation at the time. Which traditional belief about the atmosphere did it primarily overturn?

The atmosphere is composed of multiple gases

The composition of the atmosphere is static and unchanging

The atmosphere can be compressed

QUESTION 5

If the plant in the experiment were a wilted artificial flower, what would happen to the mouse?

It would still survive, because the artificial flower also takes up space

It would die quickly, because the artificial flower cannot photosynthesize