1. Photosynthesis

2. Energy needs of life All life needs a constant input of energy
Heterotrophs (Animals)
get their energy from “eating others”
eat food = other organisms = organic molecules
make energy through respiration
Autotrophs (Plants)
produce their own energy (from “self”)
convert energy of sunlight
build organic molecules (CHO) from CO2
make energy & synthesize sugars through photosynthesis
consumers
producers

3. How did we figure out all of these components are what a plant needs?

4. making energy & organic molecules from ingesting organic molecules
How are they connected?
Heterotrophs
making energy & organic molecules from ingesting organic molecules
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +
oxidation = exergonic
Autotrophs
making energy & organic molecules from light energy
So, in effect, photosynthesis is respiration run backwards powered by light.
Cellular Respiration
oxidize C6H12O6  CO2 & produce H2O
fall of electrons downhill to O2
exergonic
Photosynthesis
reduce CO2  C6H12O6 & produce O2
boost electrons uphill by splitting H2O
endergonic
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +
reduction = endergonic

5. Willow Soil Initial Mass 5lbs. 200 lbs. Final Mass 169 lbs. 3 oz.
Points of understanding
What did his experiment show about what contributes to the mass of a plant?
Willow
Soil
Initial Mass
5lbs.
200 lbs.
Final Mass
169 lbs. 3 oz.
199 lbs. 14 oz.
Change in mass
+ 164 lbs. 3 oz.
- 2 oz.

6. Early Experiments Van Helmont Showed roots don’t “eat” dirt
Plants are made of H20

7. Early Experiments Joseph Priestly
Candles & animals remove oxygen from the air
Plants replace oxygen

8. Early Experiments Senebier
Plants use carbon dioxide when they produce oxygen
Plants take in CO2, not just water
CO2 was a source of “nutrition”

9. + water + energy  glucose + oxygen
General formula
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +
Notice that oxygen comes solely from water, not from carbon dioxide
Shown with isotope experiments

10. Blackman’s Evidence What he found out…
Rate of photosynthesis increases as light intensity increases
Photosynthesis increases as temperature increases
Something else other than light is needed for photosynthesis, since it can also occur in the dark!
Reminder… this is information that was discovered before we knew what the names of proteins, photosystems, etc. were.
Evidence for two stages of photosynthesis was presented in 1905 by the English plant physiologist, F.F. Blackman. He measured the individual and combined effects of changes in light intensity and temperature on the rate of photosynthesis. Based on his experiments, Blackman came to the following conclusions:
there is a set of LIGHT DEPENDENT reactions which are TEMPERATURE INDEPENDENT; the rate of these reactions in the dim to moderate light range could be accelerated by increasing the light intensity, but they were not accelerated by increase in temperature
there is a second set of reactions that are TEMPERATURE DEPENDENT
Both sets of reactions are required for photosynthesis.
RATE CHANGES
When the rate of one set of reactions increases, the rate of the entire process increases until the second set of reactions begins to hold back the first (becomes RATE-LIMITING). Photosynthesis was shown to have a light-dependent stage, the "light reactions," as well as a light-independent stage, the "dark reactions." The so-called dark reactions occur in the light. They require the products of the "light" reaction. Light is NOT directly involved in the "dark" reactions.
At low light intensities, light is limiting, temperature and carbon dioxide concentration are not.
At high light intensities, the pigment molecules are saturated and the chemical reactions are limited due to changes in temperature and carbon dioxide concentration.
Light independent ("dark") reactions increase in rate as temperature increases until about degrees C (dependent upon plant in question), after which the rate begins to decrease. Blackman concluded that these (dark) reactions are controlled by enzymes since this is the way enzymes respond to temperature.
In the light dependent phase of photosynthesis, light energy is used to form ATP from ADP and to reduce electron carrier molecules.
In the light independent phase of photosynthesis, the energy products of the first stage are used to reduce carbon from carbon dioxide to a simple hexose sugar.
The conversion of carbon dioxide into organic compounds is known as CARBON FIXATION.

11. Data/Evidence Conditions Something depends on light Constant temp
Increasing light intensity
Something depends on light
Rate of photosynthesis
Increasing light intensity

12. Data/Evidence Conditions
Constant light intensity
Increasing temp
There must also be a chemical reaction WITHOUT light
Rate of photosynthesis
Increasing temp
expected if ONLY a light rxn is involved

13. Structures of Photosynthesis Refer to handout…

14. Chloroplast structure
lamellae
(thylakoid reservoir)
Lumen: thylakoid reservoir; where hydrogen ions accumulate to supply energy for the chemiosmotic synthesis of ATP
Thylakoid membranes contain 3 important groups of molecules
Photosystems: contain pigments and reaction centers
Chloroplasts’s electron transport chain
Protein complexes involved in ATP synthesis
Stroma: contain enzymes that make carbs; as well as DNA, RNA, and ribosomes
Note the large surface area provided by the thylakoid membranes  more surface area allows more photosynthesis to take place

15. Chloroplast structure
Lumen: thylakoid reservoir; where hydrogen ions accumulate to supply energy for the chemiosmotic synthesis of ATP
Thylakoid membranes contain 3 important groups of molecules
Photosystems: contain pigments and reaction centers
Chloroplasts’s electron transport chain
Protein complexes involved in ATP synthesis
Stroma: contain enzymes that make carbs; as well as DNA, RNA, and ribosomes
Note the large surface area provided by the thylakoid membranes  more surface area allows more photosynthesis to take place

16. Pigments
Appear to be colored because they absorb some wavelengths of light than others; reflect a different color to our eyes.
Electromagnetic spectrum shows all types of wavelengths
Visible light can be separated into waves  wavelength (λ) determines color

17. Absorption spectrum

18. Chlorophyll (chloro = green; phyll = leaf)
Absorb at blue and red wavelengths (λ) mostly
Transmit/reflect the middle λ around green!

20. Engelmann’s Experiment

21. Engelmann’s Experiment

22. Engelmann’s Experiment
Observed spirogyra w/ aerobic bacteria under microscope
Inserted a prism into beam of light from micrscope
Separated light into different wavelengths

23. Engelmann’s Experiment

24. Engelmann’s Experiment
Aerobic bacteria gathered in a oxygen-rich area
meant more photosynthesis action was occurring at those wavelengths
Conclusion
Chlorophyll played a role in photosynthesis
Red and blue light were most effective in photosynthesis