Problem 1 - Biology: How Life Works

Question

Write the overall photosynthetic reaction and identify which molecules ore oxidized and which molecule are reduced.

Step-by-Step Solution

Answer

CO₂ is reduced to glucose; H₂O is oxidized to O₂.

Step 1: Write the General Equation of Photosynthesis

The chemical equation for photosynthesis can be written as: \[ 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 \] This equation represents the conversion of carbon dioxide and water into glucose and oxygen using light energy.

Step 2: Identify Oxidation and Reduction in the Photosynthesis Equation

In the photosynthesis equation, carbon dioxide (\(\text{CO}_2\)) is reduced to glucose (\(\text{C}_6\text{H}_{12}\text{O}_6\)), as the carbon gains electrons through a series of reactions. On the other hand, water (\(\text{H}_2\text{O}\)) molecules are oxidized to oxygen (\(\text{O}_2\)), losing electrons in the process. This occurs in the light-dependent reactions.

Key Concepts

Oxidation-Reduction

Photosynthesis involves a crucial chemical process known as oxidation-reduction, which is often abbreviated as redox. It's essential for converting energy from sunlight into chemical energy in plants. These reactions involve the transfer of electrons between molecules, helping to form new substances. When a molecule gains electrons, it undergoes reduction, while a molecule that loses electrons is oxidized.

• During photosynthesis, carbon dioxide ( \(\text{CO}_2\)) is reduced to form glucose ( \(\text{C}_6\text{H}_{12}\text{O}_6\)), meaning it gains electrons and energy.
• Conversely, water ( \(\text{H}_2\text{O}\)) is oxidized, losing electrons and releasing oxygen ( \(\text{O}_2\)).

Understanding these redox reactions is crucial for grasping how energy is transferred and transformed in nature.

Chemical Equation

The chemical equation for photosynthesis is a concise way to represent the entire process. This equation summarizes the conversion of carbon dioxide, water, and light energy into glucose and oxygen. It's written as:\[ 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\,\text{O}_2 \] This balanced chemical equation shows the reactants, products, and the stoichiometry, or the ratio of molecules involved.

• Reactants: Carbon dioxide, water, and light energy.
• Products: Glucose and oxygen.

Writing and understanding the chemical equation for photosynthesis helps in visualizing how plants convert light energy into usable chemical energy.

Light-dependent Reactions

Photosynthesis is divided into two main stages, and the first stage is light-dependent reactions. These reactions need light to happen and occur in the thylakoid membranes of chloroplasts. Light-dependent reactions capture energy from sunlight and use it to produce ATP and NADPH, which are energy carriers.

• Light energy splits water molecules ( \(\text{H}_2\text{O}\)), releasing oxygen ( \(\text{O}_2\)), protons, and electrons in a process known as photolysis.
• Electrons are transferred to chlorophyll and move through an electron transport chain, helping to create ATP and NADPH.

These energy-rich compounds are then used in the second stage of photosynthesis, the Calvin cycle, to manufacture glucose. Understanding light-dependent reactions is vital as they initiate the transformation of solar energy into chemical energy.