Which of the following balanced chemical equations best summarises the overall process of photosynthesis in green plants?

Introduction / Context:
This chemistry biology crossover question tests your knowledge of the overall balanced equation for photosynthesis. While the actual biochemical pathway of photosynthesis is complex and involves many intermediate steps, at the school level it is often summarised by a single balanced equation showing how carbon dioxide and water are converted into glucose and oxygen using the energy of sunlight.

Given Data / Assumptions:

• The question presents several possible overall equations involving carbon dioxide, water, glucose, and oxygen.
• You are expected to identify the equation that correctly represents photosynthesis as taught in basic science.
• Understanding of reactants and products in photosynthesis and of balanced chemical equations is assumed.

Concept / Approach:
The standard overall equation for photosynthesis in green plants can be written as:
6CO2 + 6H2O -----> C6H12O6 + 6O2 (in the presence of light and chlorophyll).
Here, carbon dioxide and water are reactants, and glucose and oxygen are products. The coefficients 6, 6, and 6 make the equation balanced, meaning the number of atoms of each element is the same on both sides. Option D, C6H12O6 + 6O2 -----> CO2 + 6H2O, is essentially the reverse equation and represents aerobic respiration, where glucose and oxygen are used to release energy, carbon dioxide, and water. Option A is unbalanced, and option B has reactants and products arranged incorrectly for photosynthesis.

Step-by-Step Solution:

Verification / Alternative check:
Biology and chemistry textbooks consistently present the simplified overall photosynthesis equation as 6CO2 + 6H2O -----> C6H12O6 + 6O2, often with light and chlorophyll written above the arrow. They explain that in this process, plants capture light energy and store it in the chemical bonds of glucose, while releasing oxygen as a by product. They also present the respiration equation as the reverse process, C6H12O6 + 6O2 -----> 6CO2 + 6H2O, where stored energy is released for use by cells. These standard presentations confirm that option C is the correct representation of photosynthesis, and option D instead represents respiration.

Why Other Options Are Wrong:

CO2 + H2O -----> C6H12O6 + 6O2 is wrong because it is not balanced and does not respect conservation of mass; the number of atoms of each element on both sides does not match.

6O2 + 6H2O -----> C6H12O6 + 6CO2 is incorrect because it misplaces oxygen as a reactant and carbon dioxide as a product, which contradicts the known roles of these gases in photosynthesis.

C6H12O6 + 6O2 -----> CO2 + 6H2O is wrong as an answer here because it represents aerobic respiration, the process by which organisms break down glucose using oxygen to release energy, not the building of glucose in photosynthesis.

Common Pitfalls:
Students often confuse photosynthesis and respiration equations because they involve the same substances but in opposite directions. Some also ignore balancing and choose an equation that looks similar but is not correct. To avoid these mistakes, remember that photosynthesis uses carbon dioxide and water to form glucose and oxygen (6CO2 + 6H2O -----> C6H12O6 + 6O2), while respiration uses glucose and oxygen to produce carbon dioxide and water, with the arrow reversed.