How do plants harvest energy from the sun to make sugars? What atoms, molecules, macromolecules, and organelles are involved?
The correct answer and explanation is:
Plants harvest energy from the sun through a process called photosynthesis. This process occurs primarily in the chloroplasts of plant cells. During photosynthesis, plants use sunlight to convert carbon dioxide and water into glucose (a form of sugar) and oxygen. The general chemical equation for photosynthesis is:
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
Atoms, Molecules, and Organelles Involved:
- Atoms:
- Carbon (C), Hydrogen (H), and Oxygen (O) atoms are crucial. Carbon atoms are taken from carbon dioxide (CO₂), while hydrogen atoms come from water (H₂O). Oxygen is released as a byproduct when water molecules are split.
- Molecules:
- Chlorophyll: This green pigment inside chloroplasts captures sunlight. It absorbs light energy primarily in the blue and red wavelengths.
- Water (H₂O): Water is split into oxygen (O₂), protons (H+), and electrons during the light-dependent reactions.
- Carbon dioxide (CO₂): Plants absorb CO₂ from the air through small pores in the leaves called stomata.
- Glucose (C₆H₁₂O₆): The sugar produced during photosynthesis is used by the plant as an energy source or is stored as starch for later use.
- Macromolecules:
- Proteins in the photosystems (like Photosystem I and Photosystem II) facilitate the light reactions, helping electrons move through the electron transport chain.
- Nucleic acids (like DNA) encode the instructions for building and assembling all the components involved in photosynthesis.
- Organelles:
- Chloroplasts: These are the specialized organelles where photosynthesis occurs. They contain the pigment chlorophyll, which captures light energy.
- Mitochondria: While not directly involved in photosynthesis, mitochondria help the plant convert glucose into usable energy through cellular respiration.
Photosynthesis Process:
- Light-dependent reactions occur in the thylakoid membranes of the chloroplasts. Here, sunlight is absorbed by chlorophyll, exciting electrons. These electrons move through the electron transport chain, helping to convert ADP and inorganic phosphate into ATP and reduce NADP+ into NADPH. Water molecules are split to replace the lost electrons, producing oxygen as a byproduct.
- Calvin Cycle (light-independent reactions): In the stroma of the chloroplast, ATP and NADPH generated in the light-dependent reactions are used to fix carbon from CO₂ into glucose through a series of enzyme-mediated reactions.
In summary, plants convert light energy into chemical energy through photosynthesis, with chloroplasts, chlorophyll, water, carbon dioxide, and glucose being key components of this process.