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Lab 4 Photosynthesis

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  • 1. BSC 2011L Photosynthesis Today’s Lab... 1.) Turn in library worksheet. 2.) Quiz # 1 3.) Photosynthesis Lab 4.) Due next wk -- abstract (15 pts) -- graphs (10 pts) 5.) Quiz #2 next week, Ann teaches
  • 2. Michelle C 4 Kristen H. 0.5 Allison H. 1 Alex H. 0.5 Michelle H. 5 Dallas J. 2 Sheena M. 2 Michael D. 2 David E. 2.5 Dahlia K. 3.5 Brian M. 2.5 Joseph M. 1 Anna P. 3
  • 3. 3. What is the difference between a reflex and a reaction? DRAW AND LABEL A SIMPLE DIAGRAM to explain your answer. 4. Close your right eye, look at the cross with your left eye. The circle will disappear. EXPLAIN WHAT IS HAPPENING 5. In this lab we will be measuring 2 factors that affect the rate of photosynthesis they are A) temperature and light B) chlorophyll A and chlorophyll B C) wavelength and intensity D) DCPIP and NADPH E) glucose and sucrose
    • What is indicated by the arrow, and what is its function?
    • List two structures of the eye are directly involved in accommodation.
    QUIZ 1 Quiz Bank: NOTE the number of the question you wish to substitute - DO NOT answer that question!
  • 4. Cyanobacteria
  • 5. CYANOBACTERIA 2.7 billion years old
  • 6. An overview of photosynthesis
  • 7. L eaves are structured to facilitate photosynthesis
  • 8.
    • Epidermis with stomata .
    • Spongy mesophyll - gas exchange.
    • Pallisade mesophyll - chloroplasts.
      • chlorophyll is the pigment within chloroplasts
    L eaves are structured to facilitate photosynthesis
  • 9. The site of photosynthesis in a plant
  • 10. Chloroplast structure
    • A. 2 membranes ( outer and inner ).
    • B. Stroma - fluid filled interior.
    • C. Thylakoid membranous sacs.
    • D. Thylakoid sacs layered as grana.
    • E. Chlorophyll in thylakoid membranes.
    • F. Thylakoids function in converting light energy to chemical energy (= light-dependent reaction).
    • G. CO 2 conversion to sugars occurs in the stroma (= carbon-assimilation reaction) = Calvin cycle .
  • 11. The Photosynthetic Reaction
    • A. What happens:
    • 1. Plants capture light energy.
    • 2. Combine carbons from CO 2 into CHOs.
    • 3. Incidentally release O 2 .
    • B. 6 CO 2 + 12 H 2 O + light 1 C 6 H 12 O 6 + 6 O 2 + 6 H 2 O
    • C. This is a reverse of cellular respiration.
  • 12. Tracking atoms through photosynthesis Carbon dioxide Water Glucose Water Oxygen
  • 13. Interaction of light with chloroplasts
  • 14. Light DEPENDENT reactions Photosystem I & Photosystem II
  • 15.  
  • 16.  
  • 17. Light-dependent Reaction
    • A. S olar energy ---> chemical energy.
    • B. Light absorbed by chlorophyll.
    • C. Drives transfer of e - from split water to NADP + , temporarily stores e - as NADPH + H +.
    • D. O 2 is released.
    • E. Generates ATP by adding phosphate to ADP = photophosphorylation.
  • 18. Results of Light-dependent reaction
    • 1. NADPH - source of energized electrons.
    • 2. ATP - energy source for cellular activities.
    • 3. Release of O 2 .
  • 19. Light independent reaction Carbon Assimilation Reaction
    • A. Incorporates CO 2 from air into organic material = carbon fixation .
    • B. Fixed carbon is reduced to carbohydrate
    • by addition of e - .
    • REQUIRES ENERGY and electrons
    • C. NADPH offers electrons .
    • D. ATP offers energy .
    • E. Carbon Assimilation reaction results in formation of sugars .
  • 20. Light independent reaction – making the donuts! Light dependent reaction – capturing energy from the sun ?
  • 21. LIGHT REACTION DARK REACTION *note: “dark reactions” = “light independent” reaction = Calvin cycle = carbon fixation  happens in dark and light
  • 22. What are we doing in this experiment?
    • A. We use an artificial electron acceptor (DCPIP) in place of NADP+.
    • ...oxidized DCPIP is blue
    • ...reduced DCPIP is colorless
    • B. So...we can use the spectrophotometers to measure the decrease in oxidized DCPIP.
  • 23. DCPIP used in place of NADP+.
  • 24. We will look at the effects of two variables on photosynthetic rate:
    • 1.) Light intensity
    • u Einstein /m 2
    • 2. Wavelength
    • (nm)
  • 25. “ What is an Einstein ?”
    • u Einstein /m 2 /min is a common measure of light irradiance or light “intensity”
    • 1 "Einstein" = 1 mole of photons
    • 1 mole = 6.02 x10 23 particles of a substance, such as atoms, molecules or photons
    • In this case the units are "microEinstein"
      • 1 u Einstein = 1 millionth of a mole of photons
      • 1 u Einstein = 6.02 x 10 17 photons
  • 26. The electromagnetic spectrum
  • 27. Photosynthetic wavelengths
  • 28. LET’S HYPOTHESIZE... I.) Wavelength II.) Light intensity
  • 29. Spectrophotometers
    • A. Should be set at 600 nm.
  • 30. You will prepare three cuvettes... Why?
    • * an experimental
    • * a control
    • * a blank
      • Blanks for these trials will include everything but the DCPIP.
    • For the wavelength experiments only, add 0.5 ml of thylakoids .
    • Reduce the amount of water added.
  • 31. 0.5 ml 0.5 ml 0.5 ml 1.7 ml 4.2 ml 1.7 ml wavelength wavelength wavelength What to put in cuvettes...
  • 32. Make the cuvettes
    • Each group will need 5 ml DCPIP, 8.5 ml water and 6 ml buffer.
    • Mix the blank first.
    • Then Mix DCPIP/H 2 O/buffer for the experimental and control cuvettes.
    • When ready to begin, mix the chloroplasts well
    • Turn off the lights before adding 0.2 ml of chloroplasts to each cuvette and mixing.
    • TAKE TIME ZERO READING IMMEDIATELY.
  • 33. Thylakoid suspensions are exposed for two (2) minutes, then light can be shut off while absorbencies are measured.
  • 34. Wavelength experiment
    • You will test photosynthetic rate in four different wavelengths of light (blue, green, red, and far red).
    • The distances between the light sources and filters have been calibrated so that the same light intensity exists beneath each filter.
    • DO NOT ADJUST THE LIGHTS. They are set at a constant number of microeinsteins/m 2 /sec; 1 einstein = 1 mole of photons.
    • Keep water in the glass casserole dishes .
      • If liquid in casserole dishes in low, add distilled water.
  • 35. Light intensity experiment
    • A. You will analyze the effects of light intensity on photosynthetic rate.
    • B. Distance from the light source and light intensity will be recorded on the counter underneath the light tunnel.
  • 36. 4 figures with captions required
    • 2 Raw data graphs (one for wavelength, one for intensity)
    • Absorbance vs. time
    • fit straight best-fit line
    • slope of line = reaction rate
    • subtract reaction rate of control (ie. Light pollution) from reaction rate of experimental cuvette to get reaction rate of only the wavelength/intensity tested
  • 37.
      • The Reaction Rate ve. Intensity graph -- The amount of energy falls off as the square of the distance from the source (= the inverse square law).
    • The Reaction Rate vs. wavelength graph might mimic (roughly) the absorption spectrum for chlorophylls a and b .
    2 more graphs 1. reaction rate vs wavelength 2. reaction rate vs. intensity
  • 38. A Reaction Rate versus distance graph would be an exponential curve. A Reaction Rate versus intensity should be linear. Figures
    • A. These take some time to get right.
    • B. Pay close attention to format.
    • C. There will need four for this assignment
      • 2 raw data figures (absorbance vs. time)
      • 2 reaction rate figures (reaction rate vs. parameters, I.e., wavelength and intensity)
  • 39. Example of a proper graph... * Ensure that axes are properly labeled, with units specified, even if there are no units (AU=arbitraty units) * Do not connect the points on the graph with lines; draw a best-fit line through the data set. * The independent variable (the variable you manipulate) should always be on the X-axis and the dependent variable (the read out from the instrument) should be on the Y-axis. * Include a descriptive title that explains what kind of plot it is, the technique that was used, which substance was measured, and what instrument was used to measure it. * IMPORTANT: Titles should not include (or be) "Plot of...", "Graph of...", or "...over a range of data points." - Be concise, but complete. * Do not plot too many data sets on a single graph - make multiple graphs if required. WRITE A DETAILED CAPTION FOR EACH GRAPH see -- http://abacus.bates.edu/~ganderso/biology/resources/writing/HTWtablefigs.html
  • 40.
    • * Use different colors or symbols for each variable.
    • * A best fit line for each set of data.
    • * Use this line to calculate reaction rate values.