Chap 6

• Photosynthesis balanced chemical equation

  6 CO2 + 6 H2O → C6H12O6 + 6 O2
• Photosynthesis products

  • Glucose, oxygen
• Photosynthesis raw materials

  • Carbon dioxide, water
• Deficiency in nitrate ions slows down plant growth and weakens the stem
• Carbohydrates usage and storage

  Glucose is converted to more complex carbohydrates for transport, used in respiration, turned into starch for storage, converted to cellulose for cell walls, converted to sucrose for transport in the phloem, used as nectar to attract insects for pollination
• Photosynthesis

  1. Plants synthesize carbohydrates from raw materials using energy from light

  2. Plants make carbohydrates from carbon dioxide and water using energy from sunlight
• Carbohydrates synthesis in photosynthesis

  Convert carbon dioxide and water into glucose using absorbed light energy from the Sun
• Photosynthesis


  The process by which plants synthesize carbohydrates from raw materials using energy from light
• Carbohydrates usage

  • Respiration
  • Storage
  • Cell wall construction
  • Transport in phloem
  • Nectar for pollination
• Chlorophyll


  A green pigment found in chloroplasts, transfers energy from light into energy in chemicals
• Deficiency in magnesium ions leads to lack of chlorophyll, yellowing of leaves, and reduced photosynthesis
• Mineral requirements for plants

  • Nitrate ions for making amino acids
  • Magnesium ions for making chlorophyll
• Factors important for photosynthesis

  • Chlorophyll
  • Light
  • Carbon dioxide
• Nitrate ions are used in building amino acids which become proteins
• Magnesium ions are required to make chlorophyll
• Plants need certain minerals to photosynthesize and grow
• Photosynthesis word equation

  Carbon dioxide + water → glucose + oxygen in the presence of light and chlorophyll
• Photosynthesis steps

  Light energy is needed, chlorophyll helps to trap or absorb light energy from the Sun, chlorophyll transfers energy from light into energy in chemicals
• Factors important for photosynthesis

  • Chlorophyll
  • Light
  • Carbon dioxide
• Destarching plants


  Leave plants in the dark for 48 hours to remove all starch for respiration
• Investigation: Plant's need for light in photosynthesis


  Detached plant by leaving in dark, cover leaf with foil, place under sunlight, test with iodine solution
• Light


  Important because it provides the energy to drive the reaction
• Removing chlorophyll


  Boil the leaf in water to make it permeable, then in ethanol to remove chlorophyll, rinse in water to soften
• Investigation: Need for chlorophyll in photosynthesis

  Use a variegated leaf, boil in water, then in ethanol, soften in water, test with iodine solution
• Carbon dioxide


  Important because it is converted into sugars such as glucose
• This video summarises part two of topic 6 plant nutrition in the Cambridge IGCSE syllabus
• Investigation: Plant's need for carbon dioxide in photosynthesis

  Destarch plants, place one in bell jar with sodium hydroxide, the other in bell jar with water, place both in bright light, test with iodine solution
• Investigations to prove the importance of factors for photosynthesis

  1. Get a functioning plant and deprive it of each factor individually to show the plant stops photosynthesizing when factors are absent

  2. Testing a leaf for starch is a reliable indicator of photosynthesis

  3. Glucose is not reliable to test for as it is quickly used, converted, or stored
• Chlorophyll


  Needed because it helps absorb light
• Factors that affect the rate of photosynthesis

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• Effect of changing temperature on the rate of photosynthesis

  Similar setup to previous experiments but changing temperature using a hot plate. The rate of photosynthesis initially increases with temperature until the optimum temperature is reached, after which the rate drops down to zero
• Preparing leaves for testing starch and observing the results


  Prepare the leaves as shown in steps three to five and test both plants for starch using iodine. The leaf from the plant near water will turn blue-black as it has all necessary requirements for photosynthesis. However, the leaf from the plant near the sodium hydroxide will not turn blue-black; it will remain orange-brown, the color of the iodine solution, as it could not photosynthesize due to the lack of carbon dioxide
• Plants need chlorophyll, light, and carbon dioxide for photosynthesis
• Investigating the rate of photosynthesis using aquatic plants

  Use an aquatic plant that photosynthesizes in water and count the number of oxygen bubbles it releases in a minute. The more bubbles produced per minute, the faster the rate of photosynthesis
• Effect of changing light intensity on the rate of photosynthesis

  Setup involves placing a photosynthesizing aquatic plant in a beaker of water with sodium hydrogen carbonate, using an inverted funnel and boiling tube, monitoring temperature, and adjusting lamp distance. Increasing light intensity initially increases the rate of photosynthesis until some other factor becomes limiting
• Effect of changing carbon dioxide concentration on the rate of photosynthesis

  Similar setup to light intensity experiment but changing carbon dioxide concentration by dissolving different amounts of sodium hydrogen carbonate. Increasing carbon dioxide concentration initially increases the rate of photosynthesis until some other factor becomes limiting
• During the day especially when the Sun is bright and the light intensity is high


  Plants photosynthesize at a faster rate than they are respiring, resulting in a higher intake of carbon dioxide and a higher output of oxygen
• If the light is bright enough

  The rate of carbon dioxide absorption becomes greater than the rate of carbon dioxide release
• Limiting factors of photosynthesis are temperature, light intensity, and carbon dioxide concentration
• Leaf structures adapted for photosynthesis

  • Chloroplasts containing chlorophyll absorb light energy. Waxy but thin cuticle protects from water loss without blocking sunlight. Guard cells open and close stomata to control carbon dioxide diffusion. Thin and transparent upper epidermis allows more light to reach Palisade cells. Air spaces in spongy mesophyll tissue allow easy carbon dioxide diffusion. Vascular bundle consists of xylem bringing water and minerals and phloem transporting sugar and amino acids