Back to: MICROBIOLOGY 200 LEVEL
Welcome to class!
Hey superstar! I’m so glad you’re back again. You’re doing amazingly well, and I’m proud of your dedication. Today’s topic is one that’s filled with wonder—Light and Dark Reactions in photosynthesis. You’ve probably seen a plant basking in the sunlight or watched green leaves dancing in the breeze, but have you ever wondered what’s really going on inside those leaves? Let’s break it down in a simple, relatable way—just like gist between friends under a mango tree.
Light And Dark Reactions
What Are Light and Dark Reactions?
Photosynthesis—the process by which plants and some microorganisms make their own food—actually happens in two stages:
The light reactions (also called light-dependent reactions)
The dark reactions (also called light-independent reactions or the Calvin cycle)
These two work together like a Nigerian cooking duo: one lights the fire, the other stirs the pot. Let’s meet them one by one.
Light Reactions
As the name suggests, these reactions need light to happen. They take place in the thylakoid membranes of chloroplasts (tiny green structures in plant and algal cells).
What happens here?
Sunlight hits special pigments like chlorophyll.
This energy is used to split water molecules into oxygen, protons (H⁺), and electrons.
The electrons go on a journey through a chain of proteins (the electron transport chain).
Along the way, they help form ATP (energy molecule) and NADPH (another energy carrier).
Oxygen is released as a by-product. That’s the oxygen we breathe—thank you, plants!
So, light reactions are all about capturing energy from sunlight and converting it into forms the plant can use.
Dark Reactions
Now, don’t be fooled by the name—they don’t only happen in darkness. They’re called dark reactions because they don’t need light directly. Instead, they use the ATP and NADPH produced during the light reactions.
These reactions happen in the stroma of the chloroplast.
What happens here?
The plant takes in carbon dioxide (CO₂) from the air.
Using ATP and NADPH, it builds glucose (a sugar) from the CO₂.
This process is called the Calvin cycle.
The glucose made can now be used by the plant for energy or stored for later.
Think of it this way: the light reactions charge the “power bank”, and the dark reactions use that energy to cook the food.
Simple Analogy
Imagine you’re cooking jollof rice at home:
The light reactions are like turning on the gas and boiling the water—you’re getting everything ready.
The dark reactions are like adding the rice, spices, and tomatoes—you’re using the heat (energy) to cook the actual food (glucose).
Why Are Both Important?
Without the light reactions, there would be no energy to drive the second part.
Without the dark reactions, the energy from light would have nowhere to go—it would be wasted.
Together, they allow plants and microorganisms to make their own food and release oxygen into the environment.
Summary
- Light reactions need sunlight, happen in the thylakoid membranes, and produce ATP, NADPH, and oxygen.
- Dark reactions don’t need light directly, happen in the stroma, and use ATP and NADPH to make glucose from CO₂.
- Both stages are essential for complete photosynthesis.
Evaluation
- What are the two main stages of photosynthesis?
- What is the main product of the dark reactions?
- Why is oxygen released during light reactions?
- Where in the cell do the light and dark reactions take place?
You did fantastic today! Learning how plants make their food and give us oxygen is powerful knowledge. Keep shining bright—your mind is growing, and your future is unfolding beautifully. With Afrilearn by your side, nothing can stop your greatness. Let’s
keep moving forward—you’re doing brilliantly!