Lesson 3 of 12

🌿 Photosynthesis & Respiration

🎯 Grades 6–8⏱ ~30 min💚 Intermediate

What You'll Learn

Write and interpret the equations for photosynthesis and cellular respiration
Explain how these two processes are opposites
Understand how energy flows through living systems

Photosynthesis

Photosynthesis occurs in chloroplasts and converts light energy into chemical energy stored as glucose:

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Carbon dioxide comes in through the stomata. Water is absorbed by roots. Sunlight is captured by chlorophyll (the green pigment). Glucose is stored or used for energy. Oxygen is released as a byproduct.

Cellular Respiration

Cellular respiration is the reverse — it breaks down glucose to release energy (ATP) that the cell can use:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (energy)

This happens in the mitochondria and is essentially combustion in slow motion. All living cells — plant and animal — do cellular respiration.

💡

The Carbon Cycle Connection

Photosynthesis removes CO₂ from the air; respiration and combustion add it back. Burning fossil fuels releases ancient stored carbon much faster than photosynthesis can absorb it, which is why atmospheric CO₂ is rising.

🌿 Virtual Lab: Photosynthesis Rate Simulator

Adjust light intensity and CO₂ level. Watch how fast the plant produces oxygen!

☀ Light intensity 60%

🏭 CO₂ level 50%

Quick Check

Where does photosynthesis take place inside a cell?

AMitochondria

BChloroplasts

CNucleus

Cellular respiration and photosynthesis are best described as:

AOpposite processes that form a cycle of energy and matter

BThe same process with different names

CProcesses that only occur in plants