Chapter 11: Photosynthesis in Higher Plants

🌱 Why Photosynthesis Matters

All animals (including humans!) depend on plants for food. Green plants are autotrophs – meaning they make their own food through photosynthesis 🌞. This process uses light energy to create organic compounds and releases oxygen. Without photosynthesis, we wouldn’t have food or oxygen to breathe!

🔍 11.1 What Do We Know?

Photosynthesis needs three things to work:

  1. 🌿 Chlorophyll (green pigment in leaves)
  2. 💡 Light
  3. 🌬️ Carbon dioxide (CO2)

Simple experiments prove this:

  • Experiment 1: A variegated leaf (green and white parts) exposed to light → starch forms only in green areas.
  • Experiment 2: Half a leaf covered with black paper → only uncovered parts make starch.
  • Experiment 3: Half a leaf in a tube with KOH (absorbs CO2), half in air → only the air-exposed half makes starch. This proves CO2 is essential!

🧪 11.2 Early Experiments

Joseph Priestley (1770)

Priestley discovered:

  • A candle 🕯️ in a closed jar burns out → “damaged air.”
  • A mouse 🐁 in a closed jar suffocates → same “damaged air.”
  • But with a mint plant 🌱 in the jar → candle keeps burning and mouse stays alive! 🎉

Conclusion: Plants restore air that animals and candles “spoil.”

Jan Ingenhousz (1779)

Ingenhousz added sunlight to the mix:

  • With sunlight ☀️ → Aquatic plants release oxygen bubbles from green parts.
  • In the dark 🌑 → No bubbles.

Conclusion: Only green parts of plants release oxygen, and sunlight is essential.

💡 NEET Must-Know Concepts

These ideas pop up often in exams:

  1. 3 essentials for photosynthesis: Chlorophyll, light, CO2.
  2. Priestley’s experiment: Plants restore “spoiled” air (O2 production).
  3. Ingenhousz’s discovery: Sunlight + green plant parts → Oxygen release.
  4. Starch tests: Prove photosynthesis occurs ONLY in green areas exposed to light.