Question

Exercise 9 described the formation of glucose in plants, which take in \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) and give off \(\mathrm{O}_{2}\). Is this process exothermic or endothermic? If exothermic, where does the energy go? If endothermic, where does the energy come from?

Short answer

Photosynthesis is endothermic; energy comes from sunlight.

Step-by-step solution

Define the Process

The formation of glucose in plants, known as photosynthesis, involves the intake of carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)), while releasing oxygen (\(\mathrm{O}_{2}\)). The reaction can be simplified to \[6\mathrm{CO}_{2} + 6\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6} + 6\mathrm{O}_{2}\].

Understand Exothermic vs Endothermic

Exothermic processes release energy, often in the form of heat, whereas endothermic processes absorb energy from their surroundings.

Determine the Nature of Photosynthesis

Photosynthesis is an endothermic process because plants absorb energy from sunlight to convert carbon dioxide and water into glucose and oxygen.

Identify the Energy Source for Photosynthesis

In photosynthesis, the energy absorbed comes from sunlight, which is captured by chlorophyll in the plant's leaves. This energy is used to drive the chemical reactions that form glucose.

Key concepts

Endothermic Process

In nature, there are processes that either absorb or release energy. Photosynthesis is one such process found in plants. It belongs to the category known as endothermic processes. This means that photosynthesis requires the intake of energy to proceed.

An endothermic process is characterized by the consumption of energy from the surroundings, resulting in products that contain higher energy levels than the reactants. The opposite would be an exothermic process, where energy gets released into the surroundings. For photosynthesis, the energy source is crucial, which is captured from sunlight.

Energy in Plants

Plants are unique organisms capable of utilizing sunlight to produce their energy. This energy is stored in the form of glucose, a simple sugar made during photosynthesis.

Several essential activities in plants rely on this stored energy, including growth, reproduction, and repair. Composed of carbon, hydrogen, and oxygen, glucose serves as an energy reserve that can be used when sunlight is not available, such as during nighttime.

• Growth: Energy fuels cell division and growth.
• Reproduction: Produces fruits and seeds.
• Repair: Helps heal damaged tissues.

Photosynthesis Reaction

Photosynthesis is a chemical reaction that occurs within the chloroplasts of plant cells. Here, light energy from the sun is converted into chemical energy within glucose molecules. The overall chemical equation for photosynthesis is:
\[6\mathrm{CO}_{2} + 6\mathrm{H}_{2}\mathrm{O} + ext{light energy} \rightarrow \mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6} + 6\mathrm{O}_{2}\]

Key components involved in the photosynthesis reaction include:

• Carbon Dioxide (\(\mathrm{CO}_2\)): Absorbed from the air through small openings in leaves known as stomata.
• Water (\(\mathrm{H}_2\mathrm{O}\)): Taken up by the roots from the soil.
• Glucose (\(\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6\)): The sugar produced, used for energy and as a building block for growth.
• Oxygen (\(\mathrm{O}_2\)): Released as a by-product into the atmosphere.

Sunlight Energy Absorption

Sunlight plays a critical role in photosynthesis as the primary energy source. Plants possess a green pigment called chlorophyll, located in the chloroplasts, that is instrumental in capturing sunlight.

The chlorophyll absorbs sunlight and converts it into chemical energy, which is then used to drive the photosynthesis reaction. Without sunlight absorption, the conversion of carbon dioxide and water into glucose wouldn't occur, essentially halting the photosynthesis process.

• Chlorophyll's Role: Vital in the absorption of sunlight energy.
• Chloroplasts Location: Site where absorption and photosynthesis take place.
• Dependence on Sunlight: Photosynthesis occurs during daylight when sunlight is available.

In essence, without the sunlight energy absorption, plants wouldn't manufacture their food, impacting not just them, but the entire ecosystem.