Back to: Botany 100 Level
Hello, my brilliant Afrilearn scholar! Have you ever wondered how plants make their own food? Imagine waking up in the morning, feeling hungry, and heading to the kitchen to cook a delicious meal. But instead of using rice, beans, or yam, what if you could make food just by standing in the sun? Sounds like magic, right? Well, that’s exactly what plants do through a process called photosynthesis!
Today, we will learn about photosynthesis, focusing on its two major stages: light-dependent reactions and light-independent reactions. These reactions work together to help plants convert sunlight into food. Let’s get started!
Photosynthesis: Light-Dependent And Light-Independent Reactions
What Is Photosynthesis?
Photosynthesis is the process by which plants use sunlight, carbon dioxide (CO₂), and water (H₂O) to produce glucose (food) and oxygen (O₂). This process happens in the chloroplasts, using a green pigment called chlorophyll to capture sunlight.
The equation for photosynthesis is:
6CO2+6H2O+Light→C6H12O6+6O26CO₂ + 6H₂O + Light \rightarrow C₆H₁₂O₆ + 6O₂
This means plants take in carbon dioxide and water, use sunlight to make glucose (a type of sugar), and release oxygen.
Photosynthesis occurs in two main stages:
Light-Dependent Reactions (happen in the thylakoid membranes).
Light-Independent Reactions (also called the Calvin Cycle, happen in the stroma).
1. Light-Dependent Reactions (Happens in the Thylakoids)
Imagine solar panels converting sunlight into electricity. In the same way, light-dependent reactions capture sunlight and turn it into energy that the plant can use.
What Happens?
Sunlight is absorbed by chlorophyll in the thylakoid membranes.
This energy is used to split water molecules (H₂O) into oxygen (O₂), protons (H⁺), and electrons (e⁻).
The oxygen is released into the air (this is the oxygen we breathe!).
The electrons and protons help produce energy-rich molecules:
ATP (Adenosine Triphosphate) – The energy “battery” of the cell.
NADPH (Nicotinamide Adenine Dinucleotide Phosphate) – A molecule that carries high-energy electrons.
These energy-rich molecules are now ready for the next stage—the light-independent reactions!
2. Light-Independent Reactions (The Calvin Cycle, Happens in the Stroma)
Now that the plant has captured energy, it needs to use that energy to make food. This happens in the Calvin Cycle, which does not require sunlight (that’s why it’s called “light-independent”).
What Happens?
Carbon dioxide (CO₂) from the air enters the chloroplast.
Using ATP and NADPH (from the light-dependent reactions), the plant converts CO₂ into glucose (C₆H₁₂O₆), a simple sugar.
The glucose is then used for energy or stored as starch for later use.
Even though this process does not directly need sunlight, it depends on the products of the light-dependent reactions to work.
Why Is Photosynthesis Important?
Photosynthesis is the foundation of life on Earth! Without it, there would be:
No food for plants, animals, or humans. Plants are the primary producers in food chains.
No oxygen to breathe. The oxygen released during photosynthesis keeps us alive.
No energy for growth and development. Plants use glucose to grow, and we get energy by eating plants or plant-eating animals.
Even the fuel we use (like coal and petrol) comes from ancient plants that carried out photosynthesis millions of years ago!
Summary
Photosynthesis is the process where plants use sunlight, water, and carbon dioxide to make glucose and oxygen.
It happens in two stages:
Light-Dependent Reactions (Thylakoids) – Sunlight is used to split water, produce oxygen, and generate ATP & NADPH.
Light-Independent Reactions (Calvin Cycle, Stroma) – ATP & NADPH help convert carbon dioxide into glucose.
Photosynthesis is essential for life, providing food, oxygen, and energy for all living things.
Evaluation Activities
- What are the two main stages of photosynthesis?
- Where do light-dependent reactions take place?
- What is the role of chlorophyll in photosynthesis?
- What happens to water molecules during the light-dependent reactions?
- Why is the Calvin Cycle called “light-independent”?
You are doing an amazing job! Photosynthesis is one of the most important processes in nature, and now you understand how it works! Keep up your great learning, and see you in the next lesson!
School Owner? Grow your school with Africa's most trusted school management + content platformGet more class notes, videos, homework help, exam practice on Android [DOWNLOAD]
Get more class notes, videos, homework help, exam practice on iPhone [DOWNLOAD]