Chloroplast Structure & Pigment Chemistry
हरितलवक रचना आणि रंगद्रव्यांची प्रकाश रासायनिक अभिक्रिया (Class 7 Science, Chapter 4)
Green plants synthesize their food through the physiological process called Photosynthesis (प्रकाशसंश्लेषण). The chief organelle responsible for this transformation of solar radiant flux into biochemical ATP is the Chloroplast (हरितलवक).
Figure 4.2: Schematic diagram of double-membraned chloroplast with grana thylakoids & stroma matrix.
1. Internal Morphology: Granum & Stroma
Each chloroplast is enveloped by a double lipoprotein membrane. Within the organelle lies two distinct structural regions:
- Granum (ग्रेनम - अनेकवचन Grana): Stacks of coin-like flattened membranous sacs called thylakoids. The thylakoid membranes contain Chlorophyll-a & Chlorophyll-b, which absorb blue and red wavebands while reflecting green light. Photolysis of water occurs strictly on the granum surface.
- Stroma (स्ट्रोमा): The homogeneous, transparent protein-rich aqueous ground substance surrounding the grana stacks. It contains metabolic enzymes required for the light-independent dark reaction (Calvin cycle) to synthesize carbohydrates.
Question for 2 Marks: "What is the primary difference between Light and Dark reactions?"
Answer: Light reaction takes place in the Granum in the presence of sunlight; Dark reaction takes place in the Stroma and does not require direct light.
2. Dual Language Summary (द्विभाषिक संकल्पना सारांश)
हरितद्रव्य (Chlorophyll) सूर्यप्रकाशातील ऊर्जेचे शोषण करते. पाण्यातील हायड्रोजन व ऑक्सिजन वेगळे होतात (पाण्याचे प्रकाशअपघटन). कार्बन डायऑक्साइडच्या मदतीने ग्लुकोज तयार होते.
Chlorophyll absorbs solar radiation. Water molecules undergo photolysis to liberate oxygen. Carbon dioxide is reduced in the stroma to form glucose sugars.
Where do the light reactions of photosynthesis occur inside the chloroplast?