SCIENCE

• Photosynthesis


  The process by which green plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar
• Food is essential for the survival of all organisms
• Modes of nutrition of living beings

  • Heterotrophic
  • Autotrophic
• Heterotrophic


  Organisms that depend on other organisms for their food
• Autotrophic


  Organisms that produce their own food within them
• Photosynthesis


  1. Absorb sunlight

  2. Synthesise glucose

  3. Release oxygen
• Chloroplast


  • Contains chlorophyll that absorbs sunlight
• Utilizing the energy from sunlight, the cells containing chlorophyll in green plants synthesize food using carbon dioxide and water as raw materials
• Factors that affect photosynthesis

  • Chlorophyll
  • Sunlight
  • Water
  • Carbon dioxide
• Obtaining water for photosynthesis

  1. Absorbed by root hairs

  2. Travels through xylem

  3. Distributed through leaf veins
• Obtaining carbon dioxide for photosynthesis

  1. Diffuses into leaf through stomata

  2. Reaches mesophyll cells via intercellular spaces
• Glucose


  Produced during photosynthesis and temporarily stored as starch in leaves
• Sucrose


  Glucose is converted into and transported to storing organs
• Oxygen is the byproduct of photosynthesis and is diffused into the atmosphere through stomata
• Photosynthesis


  Carbon dioxide + Water ---> Glucose + Oxygen
• Plants absorb red and blue light of sunlight during photosynthesis
• Starch produced during photosynthesis can be tested by adding iodine solution
• Testing for starch produced during photosynthesis

  1. Boil leaf in water

  2. Boil leaf in alcohol

  3. Add iodine solution
• Plant kept in dark for 48 hours


  Stored starch completely removed from leaves
• Experiment to show sunlight is required for photosynthesis

  1. Cover part of leaf with black polythene

  2. Cover part of leaf with colourless polythene

  3. Observe colour change with iodine
• Experiment to show carbon dioxide is required for photosynthesis


  1. Insert leaf into bag with KOH (absorbs CO2)

  2. Insert leaf into bag with water

  3. Observe colour change with iodine
• Experiment to show chlorophyll is required for photosynthesis


  1. Use mosaic leaf

  2. Observe colour change in green vs white regions with iodine
• Experiment to show oxygen is produced during photosynthesis


  1. Collect gas bubbles released from aquatic plant

  2. Test gas with glowing splinter
• Importance of photosynthesis


  • Converts solar energy to chemical energy
  • Produces food for all organisms
  • Releases oxygen
  • Removes carbon dioxide
  • Maintains carbon cycle
• Photosynthesis cannot be done artificially, it is essential for life on Earth
• Technical terms


  • Photosynthesis
  • Chloroplasts
  • Chlorophyll
  • Aquatic plants