Photosynthesis: How Plants Make Food

Learning Objectives

Write the overall chemical equation for photosynthesis.

Identify the reactants and products of photosynthesis.

Explain the role of chlorophyll and chloroplasts in the process.

Describe why photosynthesis is essential for almost all life on Earth.

The Green Machine

Have you ever wondered how a giant oak tree grows from a tiny acorn? Where does all that mass come from? It doesn't come from the soil—it comes mostly from the air! Plants are masters of a process called photosynthesis, where they use sunlight to turn air and water into their own food.

Photosynthesis is the process that converts light energy into chemical energy in the form of sugar.

The Recipe for Photosynthesis

Like any good recipe, photosynthesis has ingredients (reactants) and finished dishes (products). We can write it as a chemical equation:

6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

Let's break that down:

Reactants (Ingredients):

6CO₂: Six molecules of Carbon Dioxide. This is the gas that animals (including us) breathe out. Plants take it in from the atmosphere through tiny pores in their leaves called stomata.

6H₂O: Six molecules of Water. Plants absorb water from the soil through their roots.

Light Energy: The energy source that powers the entire reaction. This comes from the sun.

Products (Finished Dishes):

C₆H₁₂O₆: One molecule of Glucose. This is a type of sugar. It is the 'food' that the plant uses for energy to grow and function.

6O₂: Six molecules of Oxygen. This is released as a waste product into the atmosphere. It's the oxygen that we and most other animals need to breathe!

The Photosynthesis Factory: Chloroplasts and Chlorophyll

This amazing chemical reaction doesn't just happen anywhere in the plant. It takes place in a special organelle inside plant cells called the chloroplast.

Inside the chloroplast is a green pigment called chlorophyll. Chlorophyll is what gives plants their green color. Its job is to absorb the light energy from the sun. Think of chlorophyll as the solar panel of the plant cell. It captures the sun's energy so it can be used to power the conversion of carbon dioxide and water into glucose.

Why is Photosynthesis So Important?

1.It creates food: Photosynthesis is the foundation of almost every food chain on Earth. The producers—plants, algae, and some bacteria—create the energy-rich glucose that all other organisms (consumers) rely on for their survival. Without photosynthesis, there would be no food for herbivores, and therefore no food for carnivores.

2.It produces oxygen: The oxygen in our atmosphere that we need for cellular respiration (the process of getting energy from our food) is almost entirely a byproduct of photosynthesis. Billions of years ago, there was very little oxygen in Earth's atmosphere until the first photosynthetic organisms evolved.

In short, photosynthesis feeds us and provides the air we breathe. It is the most important chemical process for life on our planet.

Key Terms

**Photosynthesis: The process by which green plants and some other organisms use sunlight to synthesize foods (glucose) from carbon dioxide and water.
**Chloroplast: The organelle in plant cells where photosynthesis takes place.
**Chlorophyll: The green pigment inside chloroplasts that absorbs light energy from the sun.
**Reactant: A substance that takes part in and undergoes change during a chemical reaction. In photosynthesis, the reactants are carbon dioxide and water.
**Product: A substance that is formed as the result of a chemical reaction. In photosynthesis, the products are glucose and oxygen.
**Glucose (C₆H₁₂O₆): A simple sugar that is an important energy source in living organisms and is a product of photosynthesis.