Photosynthesis

• Photosynthesis - which plants convert light energy into chemical energy, which can be used later for plants’ own processes.
• Autotrophs

  • produce their own food (glucose) 
  • Process called Photosynthesis
  • Mainly occurs in leaves
• Van Helmont - partially discovered the process of photosynthesis
• Priestly - carried out an experiment that showed that plants produce oxygen
• Ingenhouz - discovered that light is necessary for photosynthesis 
• Van Helmont’ s Experiment 

  • Planted a seed into a pre-measured amount of soil and watered it for 5 years 
  • He weighed the plant and the soil
  • He discovered that the weight of the soil is the same
  • He concluded that plant mass came from water
• Priestly ’ s Experiment 

  • He put a mint plant in a closed container with a burning candle.
  • The candle flame used up the oxygen and went out. 
  • After 27 days, Priestley was able to re-light the candle 
  • This showed that plants produce a gas that allows fuels to burn. 
  • This gas is oxygen.
• Ingenhousz's Experiment


  Ingenhousz met with and built upon the work of the English Joseph Priestly
• Ingenhousz's findings


  1. In 1779 Ingenhousz found out that in the presence of light, plants give of light, plants give off bubbles from their green areas

  2. In the shade these bubbles stop

  3. He determined this gas to be oxygen
• Ingenhousz's further discoveries


  1. Plants produce carbon dioxide in the dark

  2. Plants undergo cellular respiration like animals

  3. More oxygen is given off in the light than carbon dioxide in the dark

  4. Some of the mass of plants comes from the soil
• Why is photosynthesis important?

  • Energy
  • Sustaining Life
  • Cellular Respiration
• Energy - The energy within oil and coal was originally captured from the sun by plants and algae growing millions of years ago and then transformed into fossil fuels by geological forces. 
• Energy - oxygen is vital to nearly all life in processes that release stored energy. 
• sustaining life - Oxygen is given off as a by-product of the process
• sustaining life - Much of the sugar produced by plants is converted to wood, fibers (such as cotton and linen), and other structural materials
• sustaining life - The first products of photosynthesis may also be converted to disaccharides, such as sucrose; polysaccharides, such as starch; and other storage forms of carbohydrates.
• sustaining life - The digestive activities of living organisms break down the carbohydrates to smaller molecules.
• sustaining life - Sugars produced by photosynthesis are also involved in the synthesis of amino acids for proteins and a host of other cell constituents
• Cellular Respiration - a series of chemical reactions that break down glucose to produce ATP, which may be used as energy to power many reactions throughout the body
• Cellular Respiration

  
• The Process of Photosynthesis

  • Chloroplasts
  • Chlorophyll
  • Cardon Dioxide
  • Water
  • Light
• Chloroplasts - are specialized organelles found in plant cells that are responsible for photosynthesis.
• Chloroplast - These structures are found in the mesophyll cells of leaves and in other green tissues of plants
• Chloroplasts - contain chlorophyll pigments that are capable of absorbing light energy and converting it into chemical energy in the form of ATP.
• Chlorophyll - is a green pigment that plays a crucial role in the process of photosynthesis.
• Chlorophyll - is responsible for the green color of plants, as it reflects green light and absorbs other colors of light such as blue and red.
• The carbon dioxide - in the air surrounding the leaves of plants reaches the chloroplasts in the mesophyll cells by diffusing through the stomata into the leaf interior
• The carbon dioxide - goes into solution in a thin film of water on the outside walls of cells.
• Carbon Dioxide -

  • It then diffuses through the cell walls, across cell membranes, and into the cytoplasm, where it finally reaches the chloroplasts
• Water - Less than 1% of all the water absorbed by plants is used in photosynthesis
• The water - used is the source of electrons involved in photosynthesis
• If water - is in short supply, it may indirectly become a limiting factor in photosynthesis; under such circumstances, the stomata usually close and sharply reduce the carbon dioxide supply
• Light - Leaves commonly absorb about 80% of the visible light that reaches them.
• Light - in the green range is reflected.
• Light - Plants vary considerably in the light intensities they need for photosynthesis to occur at optimal rates.
• Light

  • Photorespiration
  • Photooxidation
• The Light-Dependent Reactions - The reactions are initiated when units of light energy (photons) strike chlorophyll molecules embedded in the thylakoid membranes of chloroplasts.
• Robin Hill - found that a solution of fragmented and whole chloroplasts could briefly produce oxygen if an electron acceptor were present to receive electrons from water (Hill Reaction)
• During the Light-Dependent Reactions

  • water molecules are split apart, releasing electrons and hydrogen ions, and oxygen gas is released;
  • the electrons from the split water molecules are passed along an electron transport system;
  • energy-storing ATP molecules are produced;
  • some hydrogen from the split water molecules is involved in the reduction of NADP (nicotinamide adenine dinucleotide phosphate) to form NADPH (reduced nicotinamide adenine dinucleotide phosphate), which carries hydrogen and is used in the second phase of photosynthesis, the light-independent reactions.
• The Light-Independent Reactions - Also known as the Calvin Cycle or Dark reactions