Photosynthesis in Higher Plants PDF

# Photosynthesis in Higher Plants ## Plant Physiology *Study of life processes.* * **Photosynthesis:** It is a redox reaction in which CO₂ is reduced to carbohydrate and H₂O is oxidized to O₂ in presence of sunlight and chlorophyll. * **Reduction** - gain of H<...

# Photosynthesis in Higher Plants ## Plant Physiology *Study of life processes.* * **Photosynthesis:** It is a redox reaction in which CO₂ is reduced to carbohydrate and H₂O is oxidized to O₂ in presence of sunlight and chlorophyll. * **Reduction** - gain of H⁺ * **Oxidation** - loss of e^- (H⁺ donor) CO₂(g) + H₂O(l) -> C₆H₁₂O₆ + O₂(g) *Sunlight + Chlorophyll* * **By-product** - Removal of H - Loss of e^- (H-donor). * **OR** * CO₂ is both physical & chemical change * It is a physico-chemical change in which inorganic compound (CO₂, H₂O) is converted in organic compound (C₆H₁₂O₆) in presence of sunlight & chlorophyll. * **Demonstration to show occurrence of photosynthesis:** ### I. To show that light is necessary for photosynthesis: * **Plant should be destarched by keeping in the dark for 24 hrs** **Instructions:** 1. **Prepare materials** - Pluck a leaf on which we put black paper to block light. Add boiling alcohol to kill the leaf so no further reaction takes place. Place the leaf in light for 2-4 hrs. 2. **Conduct the iodine test** * **Positive test** - If starch is present, the iodine will turn blue. * **Negative Test** - If starch is absent, the iodine will remain its original color. ### II. To show Chlorophyll is necessary for photosynthesis: * **Take "Variegated" leaf plant** **Instructions:** 1. **Prepare materials** - Desfarch the plant (keep in the dark for 24 hrs). 2. **Conduct the iodine test** * **Positive Test** - The green parts of the leave (containing chlorophyll) will show the presence of starch. * **Negative test** - The yellow parts of the leaf (without chlorophyll) will not show the presence of starch. ### III. To show CO₂ is necessary for photosynthesis: * **Moll’s Half Leaf Experiment:** **Instructions:** 1. **Prepare materials** - Destasch the plant. 2. **Conduct the experiment** * **Set up** - Do not allow CO₂ to enter the plant. Absorb CO₂ with KOH soaked cotton. * **Observation** - The only part of the plant exposed to CO₂ will show the presence of starch. ## Early Experiments in Photosynthesis ### I. Bell Jar Experiment (1770s) - Joseph Priestly **Instructions:** 1. **Set up Bell jar 1** - Place a mouse in a Bell jar with a lit candle. * **Observation 1** - The mouse and candle will die because CO₂ is produced, and the oxygen is used up. 2. **Set up Bell jar 2** - Place a plant in a bell jar with a lit candle and a mouse. * **Observation 2** - The mouse and candle live because the plant produces oxygen through photosynthesis. ## Conclusion and Further Experiments * Both respiration & photosynthesis occur in a plant. * But rate of photosynthesis is higher than respiration. * Burning of a candle and the respiration of mice fouls the air quality. * The fouled air can be restored by placing plants. * In the year 1774, Priestly discovered O₂. ### **I. Jan Ingenhousz** * Performed the same Bell Jar Experiment as Priestly, but in day and night. * **Conclusion** * Restoring of air quality by plants occurred during the day only. * **2nd experiment:** * In aquatic plant, Hydrilla, he observed bubbles during the day. * In his experiments, he realized the bubbles were O₂. ### II. Julius von Sachs (1854) * **Experiment** - Through his experiments, he proved that starch is produced and stored in green colored bodies (chloroplasts – leucoplasts).