Photosynthesis and Respiration

Photosynthesis: Process by which green plants synthesize organic food (glucose) from inorganic raw materials (CO₂ and H₂O) using light energy.

Site: Chloroplasts in mesophyll cells of leaves.

Significance: (1) Primary source of food for all organisms, (2) Releases oxygen for respiration, (3) Maintains atmospheric balance, (4) Stores solar energy as chemical energy.

Autotrophic Nutrition: Plants make their own food through photosynthesis. Self-sufficient.

Overall Equation: 6CO₂ + 12H₂O + Light energy → C₆H₁₂O₆ + 6O₂ + 6H₂O (in presence of chlorophyll).

Simplified Equation: 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂.

Chloroplast: Double membrane-bound organelle; site of photosynthesis. Found in mesophyll cells.

Outer Membrane: Smooth, permeable. Encloses the chloroplast.

Inner Membrane: Less permeable. Regulates entry of substances.

Stroma: Colorless fluid matrix. Contains enzymes for dark reaction, DNA, ribosomes.

Thylakoids: Flattened membrane sacs. Contain chlorophyll. Site of light reaction.

Grana: Stacks of thylakoids (10-20 thylakoids per granum). Increase surface area for light absorption.

Chlorophyll: Green pigment that absorbs light energy. Located in thylakoid membranes.

Diagram Importance: Labeled diagram of chloroplast showing outer membrane, inner membrane, stroma, grana, and thylakoids is crucial.

Carbon Dioxide (CO₂): Enters through stomata. Dissolved in cell sap. Used in dark reaction to form glucose.

Water (H₂O): Absorbed by roots. Transported via xylem. Split in light reaction (photolysis) to release O₂.

Light Energy: Absorbed by chlorophyll. Converted to chemical energy (ATP and NADPH).

Chlorophyll: Essential pigment. Absorbs red and blue light, reflects green (why plants look green).

Optimal Conditions: Light intensity 1000-1500 foot-candles, Temperature 25-35°C, CO₂ concentration 0.03-0.04%.

Location: Thylakoid membranes of grana.

Light-dependent: Requires light energy. Occurs during day.

Process: (1) Chlorophyll absorbs light energy, (2) Water molecules split (photolysis): 2H₂O → 4H⁺ + O₂, (3) Oxygen released as by-product, (4) Hydrogen used to reduce NADP to NADPH₂, (5) ATP synthesized (photophosphorylation).

Products: ATP (energy), NADPH₂ (reducing power), O₂ (released).

Photolysis: Light-induced splitting of water. Source of oxygen released during photosynthesis.

Energy Conversion: Light energy → Chemical energy (ATP and NADPH₂).

Location: Stroma of chloroplast.

Light-independent: Does not require light directly. Uses products of light reaction. Can occur day or night.

Process: (1) CO₂ fixation - CO₂ combines with 5-carbon compound (RuBP) using enzyme RuBisCO, (2) Forms unstable 6-carbon compound, (3) Splits into two 3-carbon compounds (PGA), (4) Reduction using ATP and NADPH₂ from light reaction, (5) Forms glucose (C₆H₁₂O₆).

Products: Glucose (C₆H₁₂O₆), which is converted to starch for storage.

Calvin Cycle: Named after Melvin Calvin. Series of reactions fixing CO₂ into organic compounds.

RuBisCO: Most abundant enzyme on Earth. Catalyzes CO₂ fixation.

Light Intensity: Increases rate up to saturation point. Beyond that, no effect. Low light limits photosynthesis.

Carbon Dioxide Concentration: Increases rate up to 1%. Normal atmospheric CO₂ is 0.03-0.04% (limiting factor).

Temperature: Optimum 25-35°C. Below 0°C and above 45°C, enzymes inactive. Affects dark reaction.

Water: Essential raw material. Deficiency closes stomata, reducing CO₂ entry.

Chlorophyll: More chlorophyll increases photosynthesis. Deficiency (yellowing) reduces rate.

Limiting Factor: Factor in shortest supply that limits the rate. Liebig's Law of Minimum.

Blackman's Law: Rate limited by factor present in minimum quantity. Increasing other factors won't help.

Starch Test (Iodine Test): Tests for starch production. Leaf boiled in water → alcohol (removes chlorophyll) → iodine solution. Blue-black color indicates starch.

Necessity of Light: Half leaf covered with black paper. Only exposed part shows starch (turns blue-black).

Necessity of CO₂: Plant kept in KOH solution (absorbs CO₂). No starch formed. Control plant shows starch.

Necessity of Chlorophyll: Variegated leaf (green and white parts). Only green parts show starch.

Oxygen Evolution: Hydrilla experiment in inverted funnel. Bubbles of oxygen collected in test tube. Glowing splinter test confirms O₂.

Moll's Half-Leaf Experiment: One half in CO₂-free air, other in normal air. Only normal air side produces starch.

Large Surface Area: Maximum light absorption. Flat and broad shape.

Thin Structure: Short distance for gas diffusion. Light penetrates easily.

Chlorophyll: Abundant in mesophyll cells. Absorbs light energy.

Stomata: Allow CO₂ entry and O₂ exit. More on lower surface.

Vein Network: Xylem supplies water. Phloem transports glucose.

Transparent Epidermis: Allows light to reach mesophyll.

Palisade Mesophyll: Columnar cells with many chloroplasts. Main photosynthetic tissue.

Spongy Mesophyll: Loosely arranged with air spaces. Facilitates gas exchange.

Food Production: Primary source of organic food for all living organisms. Base of food chain.

Oxygen Release: Maintains atmospheric oxygen (21%). Essential for aerobic respiration.

Carbon Dioxide Utilization: Reduces atmospheric CO₂. Helps control global warming.

Energy Storage: Converts solar energy to chemical energy (glucose). Stored as starch.

Fuel Formation: Ancient plants formed fossil fuels (coal, petroleum) through photosynthesis.

Ecological Balance: Maintains balance between O₂ and CO₂ in atmosphere.

Economic Importance: Agriculture, forestry, and food industry depend on photosynthesis.

Respiration: Process of breakdown of organic food (glucose) to release energy. Occurs in all living cells.

Types: (1) Aerobic respiration (with oxygen) - complete breakdown, (2) Anaerobic respiration (without oxygen) - incomplete breakdown.

Site: Mitochondria in eukaryotic cells. Cytoplasm in prokaryotic cells.

Significance: (1) Releases energy for cellular activities, (2) ATP production, (3) Maintains life processes.

Overall Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP).

Connection to Photosynthesis: Photosynthesis produces glucose and O₂, respiration uses glucose and O₂ to produce CO₂ and H₂O.

Definition: Complete oxidation of glucose in presence of oxygen to release maximum energy.

Location: Mitochondria (Powerhouse of cell).

Stages: (1) Glycolysis (cytoplasm), (2) Krebs cycle (mitochondrial matrix), (3) Electron transport chain (cristae).

Glycolysis: Breakdown of glucose (6C) to pyruvic acid (3C). Produces 2 ATP, 2 NADH. Anaerobic process.

Krebs Cycle: Pyruvic acid → Acetyl CoA → CO₂ + H₂O. Produces CO₂, NADH, FADH₂, 2 ATP.

Electron Transport Chain: NADH and FADH₂ oxidized, electrons passed through carriers. Produces 34 ATP.

Total ATP: 36-38 ATP per glucose molecule (2 from glycolysis + 2 from Krebs + 32-34 from ETC).

Products: CO₂, H₂O, Energy (ATP).

Definition: Incomplete breakdown of glucose in absence of oxygen. Releases less energy.

In Animals: Lactic acid fermentation. Glucose → Lactic acid + 2 ATP.

In Plants and Yeast: Alcoholic fermentation. Glucose → Ethanol + CO₂ + 2 ATP.

Lactic Acid Fermentation: Occurs in muscle cells during heavy exercise. Causes muscle fatigue.

Alcoholic Fermentation: Used in baking (CO₂ makes bread rise) and brewing (ethanol production).

ATP Production: Only 2 ATP per glucose (very less compared to aerobic respiration).

Importance: Provides energy when oxygen is insufficient.

Photosynthesis: (1) Occurs in green plants, (2) Uses CO₂ and H₂O, (3) Produces glucose and O₂, (4) Requires light, (5) Anabolic process, (6) Chloroplasts.

Respiration: (1) Occurs in all living cells, (2) Uses glucose and O₂, (3) Produces CO₂ and H₂O, (4) Occurs day and night, (5) Catabolic process, (6) Mitochondria.

Relationship: Photosynthesis and respiration are complementary processes. Photosynthesis stores energy, respiration releases energy.

Balance: Photosynthesis: 6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂, Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy.

Importance: Maintains atmospheric balance of O₂ and CO₂.