Nutrition in flowering plants

• Raw materials of photosynthesis:

  • Carbon dioxide and water
• Conditions of photosynthesis:

  • Light and chlorophyll
• Products of photosynthesis:

  • Oxygen and glucose
• Chemical equation for photosynthesis:

  • 6H20 + 6CO2 ---> 6O2 + C6H12O6
• Chloroplasts:

  • Contains chlorophyll
  • Chlorophyll absorbs light energy and converts it into chemical energy in leaves
• Carbon dioxide:

  • Raw material of photosynthesis
  • Enters plant by diffusion through tiny pores of stomata
• Water:

  • Raw material of photosynthesis
  • Absorbed by root hair cell by osmosis
  • Water is transported to the leaves by xylem vessels
• Glucose:

  • Main product of photosynthesis
  • Contains chemical energy converted from the absorbed light energy
  • Converted to sucrose in leaves
• Oxygen:

  • Waste product of photosynthesis
  • Diffuses out of leaves through stomata
• Summary (first part):

  • Photosynthesis is the process whereby light energy is absorbed by chlorophyll
  • Light energy is converted into chemical energy which is stored in glucose
  • The leaf uses the raw materials of water and carbon dioxide
  • The products, glucose and oxygen, are produced during the process
• External structure of leaf

  Petiole

  • Function: To hold the lamina away from stem to absorb light and carbon dioxide

  Vein

  • Function: To transport water and mineral salts to the leaf
  • Transports food away from leaf

  Lamina

  • Function: To provide large surface area to volume ratio to absorb light and carbon dioxide
• Cuticle:

  • Waxy and waterproof
  • Function: To prevent excessive water loss
• Upper epidermis:

  • Function: To protect the inner layers of cells
• Palisade mesophyll:

  • Contains the most number of chloroplasts
  • Located at the upper part of the leaf
  • Function: To absorb maximum sunlight for photosynthesis
• Spongy mesophyll:

  • Contains chloroplasts
  • Works with intercellular air space for diffusion of gases
• Xylem:

  • Function: To transport water and mineral salts from roots to leaves by transpiration pull
  • Provides mechanical support
• Phloem:

  • Function: To transport food to other parts of the plant
• Intercellular air space:

  • Function: To allow diffusion of gases, carbon dioxide diffuses into the leaf, oxygen and water vapor diffuse out of the leaf
• Lower epidermis:

  • Function: To protect the inner layers of cells
• Guard cell:

  • Function: To control the opening and closing of stomata
  • Contains chloroplasts and can carry out photosynthesis
• Stoma:

  • Function: During photosynthesis, oxygen diffuses out of the leaf, carbon dioxide into the leaf
  • More stomata are found at the lower epidermis to reduce water vapor loss on the cooler, shady underside of the leaf
• Guard cells

  High light intensity

  1. Amount of glucose produced increases
  2. Water potential in guard cells decreases
  3. Water from epidermal cells move into guard cells by osmosis
  4. Guard cells become turgid
  5. Stoma opens
  6. More carbon dioxide diffuses into stoma
  7. Rate of photosynthesis increases
• Fate of glucose during photosynthesis:
• Used for aerobic respiration to release energy
• Used to form cellulose cell wall
• Converted to starch during daylight to maximise amount of glucose produced
• Converted back to glucose during darkness for aerobic respiration to release energy
• Converted to fats for storage and for synthesis of new protoplasm
• Reacts with nitrates absorbed from soil (fertilizers) and converted to amino acids
• Transported by phloem to form protein in cells and to make protoplasm in leaf
• Excess glucose is converted to sucrose (glucose too reactive, convert to sucrose)
• Transported by phloem to storage organs (e.g. seed, underground stem) and stored as starch
• Or converted to other forms (e.g. fats in seeds)
• Experiments for photosynthesis

  Experiment 1

  • Purpose: To demonstrate the presence of stomata in leaves

  Procedure:

  • Pick up a fresh leaf with a pair of forceps
  • Hold the leaf below the surface of a beaker of hot water

  Results

  • More gas bubbles appear from the lower epidermis than from the upper epidermis

  Conclusion

  • Gas diffuses out from the stomata which are mainly found in the lower epidermis