Chap#3|Chloroplasts|Cell and subcellular organelles|Class 11 biology|New Edition Book скачать в хорошем качестве

Chap#3|Chloroplasts|Cell and subcellular organelles|Class 11 biology|New Edition Book

🌿 Chloroplasts — The Photosynthesis Powerhouses ✅ What are Chloroplasts? Chloroplasts are double-membrane bound organelles found mainly in green plant cells and algae. They are sites of photosynthesis, the process by which light energy is converted into chemical energy stored in glucose. 📌 Where Are Chloroplasts Found? ✔️ Present in green parts of plants (especially leaves) ✔️ Located in the mesophyll cells of leaves ✔️ Absent in non-photosynthetic cells (like root cells) 🧬 Discovery Chloroplasts were first observed by botanists studying plant cells under the microscope. They became central to understanding photosynthesis. 🧱 Structure of Chloroplasts Chloroplasts have several important parts: 🔹 1. Chloroplast Envelope Outer boundary made of two membranes Outer membrane: smooth & permeable Inner membrane: less permeable This double membrane controls movement of materials in and out of the chloroplast. 🔹 2. Stroma Fluid-filled space inside chloroplast Contains enzymes, DNA, ribosomes Site of the Calvin Cycle (light-independent reactions) 🔹 3. Thylakoids Flattened, disk-like sacs inside stroma Each thylakoid has chlorophyll and other pigments Light reactions occur here 🔹 4. Grana (singular: Granum) Stacks of thylakoids Increases surface area for light absorption 🔹 5. Chlorophyll & Accessory Pigments Chlorophyll pigments (mainly chlorophyll a and b) absorb sunlight. Accessory pigments broaden the range of light absorbed. 🔹 6. DNA & Ribosomes Chloroplasts contain their own circular DNA and 70S ribosomes, enabling them to make some of their own proteins. 🧠 How Do Chloroplasts Work? (Photosynthesis Summary) Photosynthesis has two main stages: ✴️ 1. Light-Dependent Reactions ✔ Occur on thylakoid membranes ✔ Require light energy ✔ Produce: • ATP (energy) • NADPH (electron carrier) • O₂ gas (released) 👉 Light excites electrons in chlorophyll → energy captured ✴️ 2. Light-Independent Reactions (Calvin Cycle) ✔ Take place in the stroma ✔ Do not need light directly ✔ Use ATP + NADPH + CO₂ ✔ Produce glucose 👉 Forms sugars that the plant uses for energy and growth 🌱 Functions of Chloroplasts ✔ Photosynthesis (main role) ✔ Energy conversion from light to chemical form ✔ Production of oxygen ✔ Support plant metabolism and growth 🧠 Why Are Chloroplasts Important? ✅ Basis of food production for almost all life on Earth ✅ Oxygen released sustains life ✅ Chloroplasts link sunlight energy to living matter 📌 Quick Facts for Class 11 Chloroplasts originated from endosymbiotic bacteria Found in mesophyll cells of leaves Contain chlorophyll & carotenoids Photosynthesis produces glucose + oxygen ✨ Summary Table Feature Description Location Mesophyll cells of leaves Membrane Type Double membrane Internal Structures Stroma, thylakoids, grana Pigments Chlorophyll a, b & accessory pigments DNA & Ribosomes Yes (circular DNA, 70S) Main Function Photosynthesis