IB MYP Integrated Science- Biology - Photosynthesis-Study Notes - New Syllabus

Photosynthesis

🌟 Introduction

Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to make their own food.
They convert light energy → chemical energy (glucose).
It is the foundation of all food chains.

🌱 What Is Photosynthesis

• Happens mainly in leaves.
• Occurs inside chloroplasts (contain chlorophyll).
• Uses carbon dioxide + water + sunlight to produce glucose + oxygen.

Basic equation

CO₂ + H₂O → C₆H₁₂O₆ + O₂
(Sunlight + chlorophyll required)

🍃 Structure of a Leaf (for photosynthesis)

Leaves are adapted to absorb maximum light.

• Broad surface → more light.
• Thin → short diffusion distance.
• Stomata → allow CO₂ entry and O₂ exit.
• Veins → carry water (xylem) and food (phloem).
• Chloroplasts packed in upper layers for light absorption.

🧬 Chloroplast Structure

Chloroplasts contain:

• Thylakoids (flattened membranes)
• Grana (stacks of thylakoids)
• Stroma (fluid filled)
• Chlorophyll pigment embedded in thylakoid membranes

Light reactions occur in grana.
Dark reactions occur in stroma.

🔆 Two Stages of Photosynthesis

A) Light Dependent Reactions (in Thylakoids)

• Require light.
• Main events:
  • Light energy absorbed by chlorophyll
  • Water splits (photolysis) → releases O₂
  • ATP and NADPH are produced
  • These molecules drive the next stage.

Outputs

• Oxygen (waste)
• ATP
• NADPH

B) Light Independent Reactions / Calvin Cycle (in Stroma)

• Do not require light directly.
• Use ATP + NADPH to convert CO₂ → glucose.

Steps:

• CO₂ enters the cycle
• Carbon fixation
• Glucose formation
• Some molecules recycled to restart cycle

💧 Raw Materials for Photosynthesis

• Carbon dioxide
  Enters through stomata. Comes from the air.
• Water
  Absorbed by roots. Transported through xylem.
• Light
  Sunlight is the natural source. Artificial light also works.
• Chlorophyll
  Captures light energy. Gives green color to leaves.

🌡️ Factors Affecting Photosynthesis

1. Light intensity
   Higher light → faster rate until saturation.
2. Carbon dioxide concentration
   More CO₂ → faster rate. Limited in air (0.04 percent).
3. Temperature
   Controlled by enzymes. Very high heat denatures enzymes.
4. Water
   Less water slows photosynthesis and closes stomata.

Importance of Photosynthesis

• Produces oxygen for respiration
• Provides glucose for energy
• Base of food chains
• Removes CO₂ from atmosphere
• Maintains global oxygen carbon balance

Products of Photosynthesis and Their Uses

• Glucose
  Used for respiration, stored as starch, forms cellulose, makes proteins and lipids.
• Oxygen
  Released into air, supports aerobic respiration.

📌 Summary Table

📦 Quick Recap
Photosynthesis makes glucose + oxygen using light.
Happens in chloroplasts.
Two stages:
Light reactions → make oxygen + energy molecules
Calvin cycle → makes glucose
Rate depends on light, CO₂, temperature, water.
Essential for life: provides food and oxygen.