Chapter 7 : Nutrition in Plants 7.1 Photosynthesis.

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:

6 (CO2) + 12 H2O 6(O2) + 6(H2O) + C6H12O6

Light energy

Chlorophyll

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 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)

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.

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.

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.