Question

Who demostrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidizable compound reduces \(\mathrm{CO}_{2}\) to carbohydrates? (a) Engelmann (b) Von Sachs (c) C. B. Van Niel (d) Jan Ingenhousz

Short answer

The scientist who demonstrated that photosynthesis is primarily a light-dependent process is (d) Jan Ingenhousz.

Step-by-step solution

Recalling the history of photosynthesis

In this step, the goal is to remember the correct scientist who demonstrated that photosynthesis is primarily a light-dependent process, where hydrogen from a compound able to be oxidized reduces carbon dioxide to form carbohydrates. After revisiting the history of photosynthesis studies, one can remember that it was Jan Ingenhousz who discovered this fact.

Key concepts

Light-dependent reactions

Photosynthesis is a fundamental process by which plants, algae, and some bacteria convert light energy into chemical energy. Light-dependent reactions are crucial to this process. These occur in the thylakoid membranes of chloroplasts, where sunlight is absorbed.
The absorbed light energy excites electrons, which move through an electron transport chain.
This process generates ATP and NADPH, which are energy carriers needed for the next stage of photosynthesis.

• In light-dependent reactions:
  • Water ( H_2O ) molecules are split into oxygen and protons (photolysis).
  • Oxygen is released as a byproduct.
  • The energy from excited electrons converts ADP to ATP.
  • NADP+ is reduced to NADPH.

The ATP and NADPH produced provide the necessary energy and electrons for the Calvin cycle, where CO2 is fixed and reduced to form glucose.

Jan Ingenhousz

Jan Ingenhousz was a Dutch physician and scientist, pivotal in the study of photosynthesis. In the 1770s, he expanded on the work of Joseph Priestley. He demonstrated that sunlight is essential for the photosynthesis process.
By experimenting with plants in transparent containers in light and darkness, Ingenhousz showed that gas exchange in plants only happens in the presence of light.
This was a significant step in understanding that photosynthesis is a light-dependent process.

• Ingenhousz's contributions:
  • Highlighted the importance of light in photosynthesis.
  • Identified that green parts of plants release oxygen during photosynthesis.
  • Set the foundation for later discoveries in plant biology.

His work established a crucial linkage between light and life, showing that plants convert carbon dioxide and water into organic compounds using sunlight.

CO2 reduction

Carbon dioxide reduction is a critical phase in photosynthesis, closely tied to the Calvin cycle or light-independent reactions. During this phase, the carbon from CO2 is assimilated into organic molecules like glucose.
Light-dependent reactions provide the necessary ATP and NADPH as energy and reducing power to convert CO2 into carbohydrates. This happens through a series of reactions known as the Calvin cycle.

• Key steps in CO2 reduction include:
  • Carbon fixation: CO2 is attached to a five-carbon sugar, ribulose bisphosphate (RuBP), by the enzyme Rubisco.
  • Reduction phase: The resultant compound is reduced, using electrons from NADPH, converting it into glyceraldehyde-3-phosphate (G3P).
  • Regeneration phase: Part of G3P is used to regenerate RuBP, enabling the cycle to continue.

This reduction of CO2 into carbohydrates is essential for generating the energy-rich compounds that support plant growth and development.