B6 | Plant Nutrition

• Photosynthesis

  • Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
  • At the same time oxygen is made and released as a waste product
  • The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
  • So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
• Photosynthesis Word Equation

  A) carbon dioxide

  B) water

  C) light

  D) chlorophyll

  E) glucose

  F) oxygen

  
• Photosynthesis equation process

  A) xylem

  B) leaves

  C) stomata

  D) respiration

  E) energy

  F) stomata

  G) respiration

  
• • Chlorophyll is a green pigment that is found in chloroplasts within plant cells
  • It reflects green light, giving plants their characteristic green colour
  • Chlorophyll absorbs light energy; its role is to transfer energy from light into energy in chemicals, for the synthesis of carbohydrates, such as glucose
  • Photosynthesis will not occur in the absence of chlorophyll
• How are the products of photosynthesis used?

  • The carbohydrates produced by plants during photosynthesis can be used in the following ways:
  • Converted into starch molecules which act as an effective energy store
  • Converted into cellulose to build cell walls
  • Glucose can be used in respiration to provide energy
  • Converted to sucrose for transport in the phloem
  • As nectar to attract insects for pollination

  
• • Photosynthesis in plants produces carbohydrates, proteins, lipids, and nucleic acids.
  • Plants need to produce these substances themselves as they do not eat.
  • Carbohydrates contain carbon, hydrogen, and oxygen, while proteins also contain nitrogen.
  • Different chemicals in plants contain various elements, such as magnesium and nitrogen in chlorophyll.
  • Without a source of these elements, plants cannot properly photosynthesize or grow.
  • Plants obtain mineral ions from the soil through active absorption by root hair cells.
  • "Mineral" refers to any naturally occurring inorganic substance.
• Mineral deficiencies in plants

  A) magnesium

  B) nitrate

  C) amino acids

  D) growth

  E) chlorophyll

  F) light

  
• Mineral Deficiencies Table

  A) chlorophyll

  B) amino acids

  C) yellowing

  D) stunted growth

  E) yellowing

  
• • Leaves can be tested for starch using the following procedure:
  • Boil the leaf to kill cells & break down cell membranes.
  • Put the leaf in hot ethanol in a boiling tube for 5-10 mins to remove chlorophyll to see iodine color changes.
  • Soften the leaf by dipping it in boiling water.
  • Place the leaf on a white tile and apply iodine solution.
  • In a green leaf, the leaf turns black indicating chlorophyll.
  • Use a variegated leaf to determine if chlorophyll is essential for photosynthesis. Green chlorophyll-containing areas turn black, while non-chlorophyll, white areas remain orange, indicating no starch.
• • Although plants make glucose in photosynthesis, leaves cannot be tested for its presence as the glucose is quickly used, converted into other substances and transported or stored as starch.
  • Starch is stored in chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.
• Variegated leaf


  A leaf that is partially green (parts with chlorophyll) and partially white (parts without chlorophyll)
• Testing for Need of Light

  1. The plant needs to be destarched by placing it in a dark area for 24h
  2. This makes the plant use all starch present, so it doesn't make our results wrong
  3. A leaf should be partially covered with aluminium foil and placed in sunlight for a day
  4. The leaf can then be tested for starch using iodine
  5. The area covered with aluminium foil will stay orange-brown as it didn't photosynthesise (lack of sunlight) and the part exposed to sunlight will turn blue-black.
  6. This proves that light is necessary for photosynthesis to produce starch
• Testing for Need for Carbon Dioxide

  1. Destarch two plants by placing in the dark for 24h
  2. Place one in a bell jar with a beaker of sodium hydroxide (which absorbs carbon dioxide)
  3. Place the other one in a bell jar with a beaker of water (which won't absorb carbon dioxide)
  4. Place both plants in bright light
  5. Test both plants for starch with iodine
  6. The leaf from the plant near sodium hydroxide will remain orange-brown as it couldn't photosynthesise
  7. The leaf from the plant near water should turn blue-black as it could photosynthesise
• Testing the Rate of Photosynthesis

  • As photosynthesis occurs, oxygen gas is released
  • As pondweed is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed.
  • The number of bubbles produced per minute can be counted to record the rate
  • A more accurate version of this experiment is to collect the oxygen released in a test tube inverted over the top of the pondweed over a longer time and then measure the volume of oxygen collected
• Investigating the effect of changing light intensity

  • This can be done by moving a lamp different distances away from the beaker with the pondweed.
  • The glass tank between the lamp and the beaker is there to stop heat from going to the beaker. The glass tank acts as a heat filter.

  
• Investigating the effect of changing temperature

  • This can be done by changing the temperature of the water in the beaker

  
• Investigating the effect of changing carbon dioxide concentration

  • This can be done by dissolving different amounts of sodium hydrogen carbonate in the water in the beaker 

  
• Photosynthesis and respiration in plants

  A) chloroplasts

  B) palisade mesophyll

  C) spongy mesophyll

  D) guard cells

  E) oxygen

  
• • Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration
• • Plants photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis
• • At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide
• Balanced Photosynthesis Chemical Equation

  A) 6CO2

  B) 6H2O

  C) C6H12O6

  D) 6O2

  E) light

  F) chlorophyll