Chapter 7 : Nutrition in Plants 7.1 Photosynthesis

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.

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?

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.

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)

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)

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.

Word Equations of Photosynthesis: Carbon Dioxide + Water  Glucose + Oxygen + Water Chemical Equations of Photosynthesis: Light energy Chlorophyll 6 (CO2) + 12 H2O 6(O2) + 6(H2O) + C6H12O6

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.

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

Limiting Factor Effect 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)

Limiting Factor Effect 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.

Limiting Factor Effect 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.

Temperature is the limiting factor only when carbon dioxide concentration is high as it results in a significant increase in rate of reaction

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.

Why Photosynthesis is important? Makes chemical energy available to animals Removes carbon dioxide and provides oxygen Energy is stored in coal through photosynthesis.