How Photosynthesis Works

Tap a term to see what it means.

What Photosynthesis Is

The process by which plants, algae, and certain bacteria convert light energy, water, and carbon dioxide into glucose (chemical energy) and oxygen.

Chlorophyll

The green pigment found in chloroplasts that absorbs light energy, primarily from the red and blue wavelengths of the light spectrum, which is also why most plants appear green to us (they reflect, rather than absorb, green light).

Light-Dependent Reactions

The first stage of photosynthesis, occurring in the chloroplast's thylakoid membranes, where light energy is captured and used to split water molecules, releasing oxygen and generating energy-carrying molecules.

The Calvin Cycle (Light-Independent Reactions)

The second stage of photosynthesis, occurring in the chloroplast's stroma, where the energy generated in the first stage is used to convert carbon dioxide into glucose, without requiring light directly.

Why Photosynthesis Matters

Photosynthesis produces the oxygen that most life on Earth depends on to breathe and forms the foundational base of nearly every food chain on the planet, since plants convert solar energy into a form nearly all other organisms can ultimately use.

The process that powers nearly all life on Earth

Photosynthesis is often described as one of the most important biochemical processes on the planet, since it is ultimately responsible for both the oxygen in Earth's atmosphere and the vast majority of the energy that flows through food chains, from the smallest insect to the largest whale.

Frequently Asked Questions

Do plants perform photosynthesis at night?

No β€” photosynthesis requires light energy to occur, so it stops at night; plants instead perform cellular respiration continuously, both day and night, to convert stored glucose into usable energy.

Why do leaves change color in autumn?

As autumn approaches and daylight decreases, many trees break down and reabsorb their chlorophyll, which reveals the yellow and orange pigments that were present in the leaf all along but were previously masked by the dominant green chlorophyll.