chapter 7 : nutrition in plants 7.1 photosynthesis
TRANSCRIPT
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Chapter 7 : Nutrition in Plants
7.1 Photosynthesis
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Photosynthesis
• A process in which light energy is absorbed by chlorophyll and converted to chemical energy
• Chemical energy is used for synthesis of carbohydrates from water and carbon dioxide.
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How Does Plant Obtain their Food?
• Plants need carbon dioxide, water and sunlight to produce food.
• How can we prove that the raw materials (Sunlight and carbon dioxide) are important?
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How can we find out if Carbon Dioxide is necessary?
• Destarch to remove all starch before the experiment.
• Potassium Hydroxide and Soda lime (or any hydroxide) is used to remove all carbon dioxide in the air.
• Control set-up would have positive starch test as carbon dioxide are used by leaves to produce carbohydrates.
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What gas is produced during Photosynthesis?
• Dilute sodium hydrogencarbonate provides carbon dioxide in water
• Gas evolved to oxygen• When a glowing splint is inserted into the
test tube, glowing splint is rekindled (Catches fire)
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Essential Conditions of Photosynthesis
• For starch to produce, plant would need light source, carbon dioxide and chlorophyll.
• Light source:– Can be light stage (light-dependent)– Dark stage (light-independent)
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Essential Conditions of Photosynthesis
• Light-dependent stage– Chlorophyll is converted to chemical energy by light
energy.– Sunlight breaks down water into hydrogen and
oxygen (Photolysis of water)
• Light-independent stage– Hydrogen produced during light stage will convert
carbon dioxide to glucose.– Enzymes are involve in dark stage.
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Word Equations of Photosynthesis: Carbon Dioxide + Water Glucose + Oxygen + Water
Chemical Equations of Photosynthesis:
6 (CO2) + 12 H2O 6(O2) + 6(H2O) + C6H12O6
Light energy
Chlorophyll
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Spectrum of Light affecting rate of Photosynthesis• Red and Blue : Colour causing highest rate of
photosynthesis– Highest point of graph shows a maximum amount of light
absorbed– Blue and red light are absorbed– These points are also where photosynthesis occurs at its
maximum level.
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Limiting Factor
• Any factor that directly affects a process if its quantity is changed is called a limiting factor.
• Rate of photosynthesis is affected by:– Light intensity– Concentration of Carbon Dioxide– Temperature
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Limiting FactorEffect of Light Intensity
• Rate of Photosynthesis increases as light intensity is increasing from O to A (Light is a limiting factor)
• Rate of Photosynthesis remains constant as light intensity continues from A to B. (Light is not a limiting factor)
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Limiting FactorEffect of Carbon Dioxide
• Temperature remained constant at 20 ℃ but concentration of carbon dioxide is being changed.
• A significant increase in rate of photosynthesis when concentration of carbon dioxide is being increased.
• Since Carbon Dioxide affects rate of photosynthesis significantly, it’s an important limiting factor.
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Limiting FactorEffect of Temperature
• Concentration of Carbon Dioxide remains constant at 0.03%
• But temperature is changed from 20 to 30.
• Very small increase in rate of photosynthesis
• Temperature does not bring about a large different in rate of photosynthesis
• Temperature is not an important limiting factor.
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Temperature is the limiting factor only when carbon dioxide concentration is high as it results in a significant increase in rate of reaction
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What happens to glucose that’s formed during Photosynthesis?
• Used immediately by plant cells
• Converted to sucrose or starch in leaves
• Used to form amino acids and proteins
• Used to form fats.
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Why Photosynthesis is important?
• Makes chemical energy available to animals
• Removes carbon dioxide and provides oxygen
• Energy is stored in coal through photosynthesis.