Problem 7 - Biology: The Essentials

Question

In \(1771,\) Joseph Priestley found that if he placed a mouse in an enclosed container with a lit candle, the mouse would die. But if he also added a plant to the container, the mouse could live. Explain this observation.

Step-by-Step Solution

Answer

The plant produces oxygen through photosynthesis, which replenishes the oxygen used by the mouse and candle, allowing the mouse to live.

Step 1: Introduction to the Problem

We are asked to explain why adding a plant to an enclosed container with a mouse and a lit candle allows the mouse to live, whereas without the plant, the mouse dies.

Step 2: Understanding the Candle’s Effect

A lit candle burns oxygen and produces carbon dioxide. Once the oxygen is depleted, the candle will extinguish and there will be no more oxygen for respiration.

Step 3: Mouse’s Need for Oxygen

Mice, like all animals, require oxygen for respiration. Without adequate oxygen, the mouse will not be able to survive and will eventually die.

Step 4: Role of the Plant

Plants perform photosynthesis during which they absorb carbon dioxide and release oxygen. The plant in the container can produce oxygen, thereby replenishing the oxygen consumed by the mouse and the candle.

Step 5: Balance of Gases

With a plant in the container, a balance is maintained. The mouse and candle consume oxygen, and the plant produces oxygen. This balance allows the mouse to continue to live.

Step 6: Conclusion

The addition of a plant ensures a continuous supply of oxygen. Thus, the mouse can survive because the plant compensates for the oxygen consumption by the candle and the mouse.

Key Concepts

Oxygen Production

Understanding oxygen production is crucial to grasp why the mouse survives when a plant is added to the container. Plants produce oxygen through a process known as photosynthesis. During photosynthesis, plants take in light energy, usually from the sun, and use it to convert water (H₂O) and carbon dioxide (CO₂) into glucose (a type of sugar) and oxygen (O₂). The chemical equation for photosynthesis can be written as: \[ 6CO₂ + 6H₂O + light energy \rightarrow C₆H₁₂O₆ + 6O₂ \] This reaction occurs in the chloroplasts of plant cells, where the green pigment chlorophyll captures light energy. The oxygen produced is released into the air, which the mouse can then breathe to stay alive. Since the candle and mouse consume oxygen, the plant continuously replenishes it, creating a livable environment for the mouse.

Carbon Dioxide Absorption

Plants not only produce oxygen but also play a vital role in absorbing carbon dioxide. Carbon dioxide is a byproduct of both respiration (the mouse) and combustion (the candle). High levels of carbon dioxide can be harmful to animals. During photosynthesis, plants use carbon dioxide along with water and sunlight to produce glucose and oxygen: \[ 6CO₂ + 6H₂O + light energy \rightarrow C₆H₁₂O₆ + 6O₂ \] By absorbing carbon dioxide, plants help maintain a healthy balance of gases in the environment. In the enclosed container, the plant absorbs the carbon dioxide produced by the mouse and the candle, lowering carbon dioxide levels and so preventing harmful conditions for the mouse.

Gas Balance

The concept of gas balance is key to understanding why the mouse survives in the container with a plant. Animals like the mouse and processes like the burning candle use up oxygen and produce carbon dioxide. If left unchecked, this would create an environment with too much carbon dioxide and too little oxygen, leading to suffocation. The plant, through photosynthesis, produces oxygen and absorbs carbon dioxide. This simultaneous process creates a balanced environment:

• Oxygen levels are replenished by the plant.
• Carbon dioxide levels are kept in check.

In simple terms, the presence of the plant ensures a continuous cycle of oxygen production and carbon dioxide absorption. This cycle maintains a balance of gases that is essential for the survival of the mouse. Without the plant, the imbalance in gases would lead to the mouse's death.