1. Capturing the Energy In Light
Photosynthesis
Capturing the Energy In Light

2. Photosynthesis
The process by which autotrophs capture energy from sunlight and store it within organic compounds (carbohydrates such as glucose and starch).
6CO2 + 6H2O C6H12O6 + 6O2
sunlight
Carbon Dioxide Water
Glucose Oxygen

3. What is an autotroph?
Eukaryotic organisms that can produce their own food using sunlight energy.
Examples: plants, algae, euglena…

4. Heterotrophs
Heterotrophs have to consume other organisms to meet their energy needs.
What happens if a heterotroph attempts to absorb sunlight energy.

5. Investigating Photosynthesis
Many Scientists Have Contributed To Understanding Photosynthesis
Early Research Focused On The Overall Process
Later Researchers Investigated The Detailed Chemical Pathways

6. Early Questions on Plants
Several Centuries Ago, The Question Was: Does the increase in mass of a plant come from the air? The soil? The Water?

7. Van Helmont’s Experiment 1643
Planted a seed into A pre-measured amount of soil and watered for 5 years
Weighed Plant & Soil. Plant Was 75 kg, Soil The Same.
Concluded Mass Came From Water

8. Priestley’s Experiment 1771
Burned Candle In Bell Jar Until It Went Out.
Placed Sprig Of Mint In Bell Jar For A Few Days.
Candle Could Be Relit And Burn.
Concluded Plants Released Substance (O2) Necessary For burning.

9. Ingenhousz’s Experiment 1779
Repeated Priestly experiment with & without sunlight

10. Results of Ingenhousz’s Experiment
Showed That Priestley’s Results Only Occurred In The Presence Of Sunlight.
Light Was Necessary For Plants To Produce The “Burning Gas” or oxygen

11. Julius Robert Mayer 1845
Proposed That Plants can Convert Light Energy Into Chemical Energy

12. Samuel Ruben & Martin Kamen 1941
Used Isotopes To Determine That The Oxygen Liberated In Photosynthesis Comes From Water
RUBIN
KAMEN

13. Melvin Calvin 1948
First to trace the path that carbon (CO2) takes in forming Glucose
Does NOT require sunlight
Called the Calvin Cycle or Light Independent Reaction
Also known as the Dark Reaction

14. Energy for Life Processes
Photosynthesis is a biochemical pathway
Involves a complex series of chemical reactions in which the product of one reaction is consumed in the next reaction.
Autotrophs use the biochemical pathways of photosynthesis to manufacture organic compounds from CO2 and water.
In the process molecular oxygen O2 is released.

15. Energy for Life Processes
Energy stored in organic compounds is released in a process called cellular respiration.
Both autotrophs and heterotrophs perform cellular respiration.
In cellular respiration organic compounds are combined with O2 to produce ATP.
CO2 and water are the waste products of cellular respiration.

16. Photosynthetic Reactions

17. Light Reactions
The initial reactions in photosynthesis are collectively known as the light dependent reactions.
Begin with the absorption of light in chloroplasts.
Chloroplasts are organelles present in plant cells and algae (some algae may have only one while a cell in a plant may have as many as 50).

18. Structure of the Chloroplast
Double membrane organelle
Outer membrane smooth
Inside the inner membrane are another system of membranes arranged as flattened stacks of connected sacs called thylakoids
Thylakoid stack is called the granun (grana-plural)
Gel-like material around grana called stroma

20. Light and Pigments
Energy From The Sun Enters Earth’s Biosphere As Photons
Photon = Light Energy Unit
Light Contains A Mixture Of Wavelengths
Different Wavelengths Have Different Colors

21. Light and Pigments Light from the sun appears white
When passed through a prism the white light’s component colors become visible, this is the visible spectrum
Component colors may be transmitted, reflected or absorbed.
Pigments are compounds that absorb light. Different colored pigments absorb different wavelengths of light.

22. Chloroplast Pigments
A variety of pigments are located in the membrane of thylakoids.
Chlorophyll
The most important are chlorophylls
Chlorophyll a and chlorophyll b are the most common.
Neither abosorb much green light.
Chlorophyll a is directly involved in the light reaction.
Chlorophyll b assists in capturing light energy and is called an accessory pigment.

23. Carotenoids – Accessory pigments found in the thylakoid membranes
yellow, brown, and orange in color
Absorb colors that chlorophyll cannot absorb.
Usually hidden by the overabundance of chlorophyll.
Apparent in fruits and in fall leaves when plants lose chlorophyll.

24. Light Independent (dark) reactions.
Use energy carrying compounds produced from the light dependent reactions and CO2 to make carbohydrates (including glucose).