Problem 2 - Campbell Biology

Question

Photoautotrophs use \begin{equation}\begin{array}{l}{\text { (A) light as an energy source and } \mathrm{CO}_{2} \text { as a carbon source. }} \\ {\text { (B) light as an energy source and methane as a carbon source. }} \\ {\text { (C) } \mathrm{N}_{2} \text { as an energy source and } \mathrm{CO}_{2} \text { as a carbon source. }} \\ {\text { (D) } \mathrm{CO}_{2} \text { as both an energy source and a carbon source. }}\end{array} \end{equation}

Step-by-Step Solution

Answer

The correct answer is (A) light as an energy source and CO₂ as a carbon source.

Step 1: Identify the Definition of Photoautotrophs

Photoautotrophs are organisms that use light as the energy source for synthesizing organic compounds.

Step 2: Determine the Energy Source for Photoautotrophs

Based on the definition, photoautotrophs use light as their energy source. So, the correct answers need to include 'light' as the energy source.

Step 3: Determine the Carbon Source for Photoautotrophs

Photoautotrophs utilize carbon dioxide (CO₂) from the atmosphere as their carbon source to produce organic molecules.

Step 4: Examine the Provided Options

(A) light as an energy source and CO₂ as a carbon source. (B) light as an energy source and methane as a carbon source. (C) N₂ as an energy source and CO₂ as a carbon source. (D) CO₂ as both an energy source and a carbon source.

Step 5: Match the Correct Answer

Based on Step 2 and Step 3, the correct option must use light as an energy source and CO₂ as a carbon source. Option (A) states this exactly: 'light as an energy source and CO₂ as a carbon source.'

Key Concepts

light energy source

Photoautotrophs are a special group of organisms that have the ability to harness sunlight to fuel their life processes. This trait primarily occurs in plants, algae, and some bacteria. These organisms contain pigments like chlorophyll that enable them to absorb light, most effectively in the blue and red wavelengths.
Once the light is absorbed, it is converted into chemical energy in the form of ATP and NADPH through a process known as photosynthesis. This conversion is essential because it provides the energy necessary for the synthesis of organic molecules.
The process is summarized by the light reactions within the thylakoid membranes of chloroplasts. Here, light energy splits water molecules, releasing oxygen, and generating high-energy molecules.

• Light energy absorption is crucial for the photosynthetic process.
• The conversion of light to chemical energy occurs in the thylakoid membranes.
• Pigments like chlorophyll play a vital role in capturing light.

carbon dioxide carbon source

In addition to light, photoautotrophs also need a source of carbon to produce organic molecules necessary for growth and development. They obtain this carbon from carbon dioxide (CO₂) present in the atmosphere.
During the Calvin cycle of photosynthesis, CO₂ is fixed and converted into glucose, a simple sugar that plants and other photoautotrophs use for energy and as a building block for more complex organic compounds such as starch and cellulose.
Understanding this process is crucial because it emphasizes the role of photoautotrophs in reducing atmospheric CO₂ levels and combating climate change.

• CO₂ is the primary carbon source for photoautotrophs.
• CO₂ fixation occurs during the Calvin cycle.
• The organic compounds formed include glucose, starch, and cellulose.

This cyclical process is vital for maintaining the balance of carbon in the environment.

organic synthesis in photoautotrophs

Photoautotrophs play a crucial role in the ecosystem by synthesizing organic molecules that serve as the foundation for almost all other living organisms. Through the process of photosynthesis, these organisms convert light energy and CO₂ into glucose and other organic compounds.
The synthesized glucose is used not only for energy but also as a building block for creating other organic molecules such as amino acids, lipids, and nucleic acids.
This is fundamentally important for sustaining life because it forms the base of food chains in both terrestrial and aquatic ecosystems.

• The organic synthesis process starts with glucose formed via photosynthesis.
• Glucose serves as a precursor for other essential organic molecules.
• Photoautotrophs support food chains by providing organic compounds that feed other organisms.

By understanding how photoautotrophs synthesize organic materials, we gain insight into their indispensable role in supporting life on Earth.