Photosynthesis Lecture Notes

Introduction to Photosynthesis

• Plants, algae, and some microorganisms perform photosynthesis.
• Photosynthesis is the process by which these organisms synthesize their own food using sunlight, water, and carbon dioxide.
• They produce glucose (a form of sugar) and oxygen.

Why Photosynthesis is Essential

• Plants are autotrophs; they make their own food from light energy.
• They do not consume food as humans and animals do.
• Important for plant growth and survival.

Process of Photosynthesis

• Inputs: Carbon dioxide (CO2), water (H2O), and sunlight.
• Outputs: Glucose (C6H12O6) and oxygen (O2).

Steps in Photosynthesis

1. Carbon Dioxide Intake:

   • Plants take in CO2 through tiny holes in leaves, flowers, branches, stems, and roots.

2. Water Absorption:

   • Water is absorbed through plant roots.
   • Water availability varies by environment: desert plants vs. water-abundant environments.

3. Sunlight Utilization:

   • Sunlight provides energy needed for chemical reactions.
   • Light energy breaks down CO2 and H2O molecules, reorganizing them into glucose and oxygen.

4. Energy Conversion:

   • Glucose is broken down by mitochondria for growth and repair.
   • Oxygen is expelled through the same openings CO2 entered.
   • Oxygen is essential for the survival of other organisms.

Photosynthesis Chemical Equation

• 6CO2 + 6H2O + Light energy → C6H12O6 + 6O2

Energy Transfer in Ecosystems

• Energy from sunlight is stored in glucose molecules.
• Example: A pea plant uses energy from sunlight to grow, storing excess sugar after pod formation.
• Herbivores such as rabbits consume the plants, gaining energy initially from the sun.

Importance for Humans

• Humans and animals cannot produce their own food like autotrophs.
• They rely on photosynthesis for food, directly or indirectly (e.g., eating plants or plant-eating animals).
• Photosynthesis underpins food chains.

Additional Resources

• "Photosynthesis: Blinded by the Light" video explores common misconceptions about photosynthesis.

This content is from the "Structure and Function" unit of the Science and Technology Concepts Middle School curriculum.

Published by the Smithsonian Science Education Center on April 12, 2017.