Problem 7 - Campbell Biology

Question

Level \(3 :\) Synthesis/Evaluation In agricultural areas, farmers pay close attention to the weather forecast. Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to mention why hydrogen bonds are responsible for this phenomenon.

Step-by-Step Solution

Answer

Spraying water on crops releases heat as water freezes, thanks to hydrogen bonds. This helps shield plants from frost.

Step 1: Understand the Properties of Water

Water has a high specific heat capacity and forms hydrogen bonds. These properties influence how water behaves in different environmental conditions.

Step 2: Hydrogen Bonds and Freezing

Hydrogen bonds between water molecules stabilize the temperature by absorbing heat when water freezes. This is because energy is released as water transitions from liquid to solid.

Step 3: Application of Spraying Water

When farmers spray water on crops, the water releases heat as it freezes, which warms the plants and the surrounding air slightly, providing a protective layer against frost.

Step 4: Conclusion

Therefore, the practice of spraying water on crops helps shield them from freezing temperatures due to the heat released from water solidifying.

Key Concepts

Hydrogen Bonds

Water is a unique molecule with many fascinating properties, largely due to the hydrogen bonds that help hold water molecules together. These bonds form when the slightly positive hydrogen atoms of one water molecule attract the slightly negative oxygen atoms of another.
This attraction is relatively weak compared to covalent or ionic bonds, but it is crucial for many of water's properties.
In agriculture, hydrogen bonds significantly affect how water behaves, especially when it transitions between different states.
For example, when water freezes to become ice, hydrogen bonds become more stable and form a crystalline structure. This process releases heat, helping to warm the surrounding environment.
Hence, farmers use hydrogen bonds to their advantage by spraying water on crops to protect them from frost damage. This trick harnesses energy released from the formation of hydrogen bonds when water freezes, warming the plants and preventing freezing damage.

Specific Heat Capacity

Another important property of water is its high specific heat capacity, which is the amount of heat energy required to raise the temperature of one gram of water by one degree Celsius.
Water's specific heat capacity is higher than most other substances, meaning it can absorb or release a lot of heat energy with minimal temperature change.
This property is particularly useful in agriculture, where stable temperatures are crucial for plant health.
For farmers, this means that water can moderate fluctuations in temperature, providing a buffer against sudden freezes.
By spraying water on crops before a predicted frost, the water absorbs heat from the atmosphere as it cools down but does not significantly drop in temperature itself.
This absorbed heat is then gradually released, helping keep the air and plants warmer than they would be otherwise.
In this way, water's specific heat capacity provides a defense mechanism against the cold, ensuring crops can survive frost conditions.

Freezing and Heat Release

When water freezes, it undergoes a phase transition from liquid to solid, releasing a specific amount of heat known as the latent heat of fusion.
For water, the latent heat of fusion is high, meaning it releases a substantial amount of energy when it freezes.
This energy release has a warming effect on the surrounding environment.
Farmers can use this property by spraying water on their crops before a frost.
As the water begins to freeze, it releases heat, slightly warming the air and plants around it.
This warming effect can be the difference between a healthy plant and a frost-damaged one.
Importantly, the released heat helps maintain the temperature around freezing, which prevents the plant tissues from dropping below freezing point.
This method effectively creates a protective barrier that shields plants from the coldest temperatures encountered during overnight freezes, helping to ensure their survival and continued growth.