photosynthesis u1 AoS 1

• Photosynthesis


  Biochemical process by autotrophs to fix carbon into glucose
• Autotroph


  Organism that can produce its own food through photosynthesis
• Heterotroph


  Organism that cannot produce its own food and must consume other organisms
• Photosynthesis is considered a biochemical pathway
• Photosynthesis


  1. Light dependent reaction

  2. Light independent reaction (Calvin cycle)
• Light dependent reaction


  • Occurs in the grana of chloroplasts
  • Converts solar energy into chemical energy (ATP)
  • Splits water into hydrogen, electrons and oxygen
• Light independent reaction (Calvin cycle)


  • Occurs in the stroma of chloroplasts
  • Fixes carbon dioxide into glucose using ATP and NADPH from light dependent reaction
• Inputs of photosynthesis


  • 12 H2O
  • 6 CO2
  • Light energy
• Outputs of photosynthesis


  • C6H12O6 (glucose)
  • 6 O2
  • 6 H2O
• Photosynthesis is an anabolic biochemical reaction overall
• Life on Earth could not exist without photosynthesis as it produces the oxygen we breathe and the glucose we consume
• Photosynthesis and cellular respiration are connected, with the products of one being the reactants of the other
• Limiting factors on photosynthesis

  • Carbon dioxide levels
  • Water availability
  • Light availability
  • Temperature
• Photosynthesis can be measured by monitoring the uptake of CO2, production of O2, production of carbohydrates, or increase in dry mass
• Oxygen production from photosynthesis can be measured by counting bubbles evolved from pondweed or using the Audus apparatus
• Factors that affect the rate of photosynthesis

  • Carbon dioxide levels
  • Water availability
  • Light availability
  • Temperature
• Phosphorous and nitrogen are often limiting factors in the spring and summer. Cold temperatures limit growth in the winter.
• This is an anabolic reaction overall as although it requires some initial energy, the end product is a more complex molecule being created from combining smaller molecules.
• Heterotrophs


  Unable to create glucose through photosynthesis and rely either directly or indirectly on autotrophs for glucose
• Glucose is required for cellular respiration in order to generate enough ATP for metabolic reactions to sustain life.
• A by-product of photosynthesis is oxygen which also led to a major change in earth's atmosphere and the species that evolved. So photosynthesis autotrophs actually changed our evolutionary pathway!
• Photosynthesis


  An anabolic biochemical pathway that autotrophs (plants; cyanobacteria, some protists) use to convert inorganic materials (H2O/CO2) into organic molecules (Glucose) using an external energy source (sunlight)
• Chloroplasts


  • Evolved from cyanobacteria forming an endosymbiotic relationship with a larger host cell
  • Evidence of their bacterial origins includes: size of 1 - 5μm in diameter, an outer (host) and inner(bacteria) membrane, ribosomes consisting of bacterial-like ribosomal RNA, circular DNA that contains only exons and no intron sections
• A mature leaf cell contains 20 – 100 chloroplasts
• Chloroplast structure


  • Inner and Outer membrane
  • Stroma: a gel like matrix
  • Grana: stacks of thylakoid membrane discs (darker 'lines')
• This chemical equation only tells you that carbon dioxide and water are inputs and glucose, oxygen and water are outputs. Photosynthesis occurs in a series of biochemical reactions that involve many other compounds including enzymes & co enzymes.
• Cytoplasmic streaming


  Why would this occur?
• Oxygen is produced by photosynthesis and consumed in aerobic cellular respiration.
• Photosynthesis


  An anabolic/endergonic biochemical pathway
• Factors affecting rates of photosynthesis

  • CO2, H2O, light intensity, temperature (↑ temp = ↑ photosynthesis), concentration of chlorophyll/enzymes
• Chloroplasts contain high numbers of ribosomes (enzyme and chlorophyll production)
• Endosymbiotic theory suggests chloroplasts (like mitochondria) evolved from ancient prokaryotic cells. Evidence for this includes own circular DNA (like prokaryotes), double membrane, contain ribosomes of similar structure to prokaryotes and can split in two to copy themselves through binary fission.
• Photosynthesis requires an initial energy input but the end product is a more complex molecule being created from combining smaller molecules.
• Factors affecting the rate of photosynthesis

  • Light intensity (availability)
  • Light wavelength
  • Water availability
  • Temperature
  • Carbon Dioxide concentration
• Light saturation point


  The point where increasing light intensity no longer increases the rate of photosynthesis as the chlorophyll pigments are fully saturated with light
• Light compensation point


  The amount of light intensity where the rate of photosynthesis exactly matches the rate of respiration (i.e. where production of CO2 is equal to the use of CO2)
• Changes in temperature and pH, concentration of substrates/enzymes, competitive & non competitive inhibitors will impact on enzyme functioning in relation to photosynthesis (and cellular respiration)
• Line graphs show the relationship between the independent variable (IV) and the dependent variable (DV). The IV is plotted on the x-axis and the DV is plotted on the y-axis.
• Plateau


  When a line graph reaches a point where increasing the IV no longer increases the DV
• Interpolate


  To estimate a value within the range of known data points on a graph