1 Nutrition in flowering plants

• Photosynthesis


  The absorption of light energy from chlorophyll in green plants to make glucose from carbon dioxide and water, and oxygen is released as a by-product

  
• Chlorophyll


  A green pigment found in the chloroplasts of plant cells that absorbs light energy and converts it to chemical energy in the process of photosynthesis

  
• Photosynthesis


  1. Absorption of light energy

  2. Conversion to chemical energy

  3. Formation of glucose

  4. Oxygen released as by-product

  
• Photosynthesis makes chemical energy available to animals and other organisms

  
• Glucose made from photosynthesis can be converted to other forms of nutrients to be stored in plants (producers)
• When the plant is consumed, the chemical energy released from the breaking down of the nutrients is made available to the growth and metabolism of the consumers
• Photosynthesis removes carbon dioxide from the atmosphere and releases oxygen

  
• Energy stored in fossil fuels are from photosynthesis

  
• Uses of glucose from photosynthesis

  • Respiration
  • Conversion to starch and stored in leaves
  • Conversion to sucrose and transported to other parts of the plant
  • Conversion to fats
  • Conversion to amino acids and proteins
• If there are no nitrates in the soil, glucose cannot be converted to amino acids and proteins
• Limiting factor


  A factor that directly affects the rate of chemical reaction
• Limiting factors in photosynthesis

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
  • pH
  • Water availability

  
• As light intensity increases

  Rate of photosynthesis increases

  
• At point X


  Light intensity is a limiting factor
• From point Y onwards

  Light intensity is no longer a limiting factor
• From point Y onwards

  Carbon dioxide concentration becomes the new limiting factor
• Leaf structure


  • Large, broad, flattened surface
  • Xylem and phloem vessels
  • Petiole holds the leaf blade away from the stem
• Internal leaf structure


  • Cuticle (upper and lower)
  • Upper epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Lower epidermis
  • Vascular bundle (xylem and phloem)
• Cuticle


  Waxy, waterproof layer to prevent excessive evaporation of water from leaf cells; Transparent to allow light penetration
• Upper and lower epidermis

  Single layer of closely packed cells without chloroplasts; Presence of guard cells in lower epidermis to control stomata size for gaseous exchange
• Palisade mesophyll


  Long, cylindrical cells closely packed and vertically aligned with highest concentration of chloroplasts
• Spongy mesophyll


  Irregularly-shaped cells loosely packed with large air spaces; Lower concentration of chloroplasts compared to palisade mesophyll; Thin film of water on cells to dissolve gases and speed up diffusion
• Guard cells


  • Regulate the size of stomata by changing turgor pressure; Flaccid - stomata closes; Turgid - stomata opens
• How guard cells regulate stomata

  1. During day (high light): Photosynthesis produces glucose, used for active transport of potassium ions into guard cells, decreasing water potential and causing water entry by osmosis, making guard cells turgid and stomata open

  2. During night (low light): Potassium ions diffuse out of guard cells, increasing water potential and causing water exit by osmosis, making guard cells flaccid and stomata close
• How plants obtain CO2

  During photosynthesis, CO2 concentration decreases in air spaces, creating a diffusion gradient from atmosphere; CO2 diffuses into air spaces through stomata, dissolves in water film, and diffuses into mesophyll cells towards chloroplasts

  
• During respiration at night, plants release CO2
• Photosynthesis produces oxygen, respiration consumes oxygen

  
• Experiments to show photosynthesis

  1. Terrestrial plant: Measure growth, test for presence of starch in leaves

  2. Aquatic plant: Measure growth, observe release of oxygen gas

  
• Testing for starch in a leaf


  1. Step 1: Destarch the leaf by putting it in darkness for 48 hours

  2. Step 2: Remove chlorophyll from the leaf

  3. Step 3: Perform iodine test for presence of starch
• Variegated leaf


  Shows difference in photosynthesis between green and white/yellow parts
• Experiment to test effect of CO2

  1. Destarch leaf first

  2. Use CO2 absorbing chemicals like potassium hydroxide, sodium hydroxide, calcium hydroxide, or sodalime

  3. Significance of control

  4. Use polythene bag to enclose leaf
• Experiment to provide CO2 source

  1. Use diluted sodium hydrogencarbonate solution or baking soda to release CO2

  2. Observe release of oxygen gas to confirm photosynthesis