Question

How do primary producers such as plants and algae fix radiant energy into organic molecules?

• A. A) Respiration
• B. B) Fermentation
• C. C) Photosynthesis
• D. D) Decomposition

Answer 1

Answer:

C. C) Photosynthesis

Photosynthesis: The Foundation of Life

• Photosynthesis is the biochemical process by which primary producers, such as plants, algae, and some bacteria (e.g., cyanobacteria), convert light energy into chemical energy.
• This chemical energy is stored in organic molecules, primarily glucose, which serve as the basic food source for nearly all life forms on Earth.

Key Components and Process:

• Energy Conversion: Radiant energy (sunlight) is absorbed and transformed into chemical energy, primarily in the form of ATP (Adenosine Triphosphate) and NADPH (Nicotinamide Adenine Dinucleotide Phosphate hydrogen).
• Light Absorption: The primary pigment responsible for absorbing light energy is chlorophyll, found within specialized organelles called chloroplasts in eukaryotic cells (plants and algae).
• Inputs: The raw materials required for photosynthesis are carbon dioxide (CO2), which enters through stomata in leaves, and water (H2O), absorbed by roots.
• Outputs: The main products are glucose (C6H12O6), a sugar used for energy and building plant structures, and oxygen (O2), which is released as a byproduct into the atmosphere and is vital for aerobic respiration in most organisms.

Stages of Photosynthesis:

1. Light-Dependent Reactions:
   • Occur in the thylakoid membranes of chloroplasts.
   • Light energy is captured by chlorophyll and used to split water molecules (photolysis), releasing oxygen, electrons, and protons.
   • This energy is then used to synthesize ATP and NADPH.
2. Light-Independent Reactions (Calvin Cycle or Dark Reactions):
   • Occur in the stroma of chloroplasts.
   • ATP and NADPH, produced during the light-dependent reactions, are used to fix atmospheric CO2 into organic molecules, specifically glucose.
   • This process does not directly require light but depends on the products of the light reactions.

Ecological Significance and Competitive Exam Facts:

• Primary Producers: Organisms capable of photosynthesis are known as autotrophs (self-feeders) and form the base of almost all food chains, making them indispensable for ecosystem stability.
• Energy Flow: Photosynthesis is the initial step in the flow of energy through most ecosystems, transferring energy from the sun to biological systems.
• Carbon Cycle: It plays a crucial role in the global carbon cycle by removing CO2 from the atmosphere and converting it into organic compounds, thus helping to regulate Earth's climate.
• Oxygenation of Earth: The evolution of photosynthesis significantly increased atmospheric oxygen levels, paving the way for the evolution of aerobic life forms.
• Maximum Photosynthesis: Generally occurs in the red and blue regions of the visible light spectrum, as chlorophyll absorbs these wavelengths most effectively. Green light is largely reflected, which is why plants appear green.
• Limiting Factors: The rate of photosynthesis can be limited by factors such as light intensity, CO2 concentration, temperature, and water availability.