1. Photosynthesis

2. Energy transfer
Photosynthesis transfers light energy into chemical potential energy
This energy can then be released for work in respiration
Almost all energy transferred to ATP is derived from light energy

3. Energy transfer in autotrophs
Photoautotrophs: green, photosynthetic plants and protists. Use light energy to obtain energy
Chemoautotrophs: bacteria that use chemicals to obtain energy (ex: nitrifying bacteria)

4. 6𝐶 𝑂 2 +6 𝐻 2 𝑂 𝑙𝑖𝑔ℎ𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝐶 6 𝐻 12 𝑂 6 +6 𝑂 2
Photosynthesis
Photosynthesis is the fixation of carbon dioxide and its subsequent reduction to carbohydrates, using hydrogen from water
Overall equation:
𝑛𝐶 𝑂 2 +𝑛 𝐻 2 𝑂 𝑙𝑖𝑔ℎ𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝐶 𝐻 2 𝑂 𝑛+𝑛 𝑂 2
Since hexose sugars are commonly formed, the following equation is often used:
6𝐶 𝑂 2 +6 𝐻 2 𝑂 𝑙𝑖𝑔ℎ𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝐶 6 𝐻 12 𝑂 6 +6 𝑂 2

5. PHOTOSYNTHESIS Two sets of rxns involved: Light-dependent rxns
Light-independent rxns
Pigment: any substance whose presence in the tissues or cells of animals or plants colors them.

6. photosynthesis Photosynthesis takes placed in thylakoid membranes
In prokaryotes, thylakoids are embedded in cell surface membrane
In eukaryotes, thylakoids are stacked in chloroplasts

8. Light dependent reactions
Light energy is necessary
Only take place in presence of suitable pigments that absorb certain wavelengths of light
Light energy splits (photolysis) water into hydrogen and oxygen (oxygen is waste byproduct)
Light energy also needed to provide chemical energy in the form of ATP for the reduction of carbon dioxide during light independent reactions

9. Light dependent reactions
Photosynthetic pigments involved fall into two categories: primary pigments and accessory pigments
Pigments are arranged in light-harvesting clusters called photosystems

10. photosystems
In a photosystem, several hundred accessory pigment molecules surround a primary pigment molecule
Energy of light absorbed by A-pigs is transferred to P-pig
Primary pigments are 2 forms of chlorophyll
Primary pigments said to act as reaction centers

11. Do now 9/18
What is the chemical formula for photosynthesis?

12. Light dependent reactions
Include photolysis of water and ATP synthesis
ATP synthesized during photophosphorylation
Photophosphorylation can be cyclic or non-cyclic
H+ ions from water combine with carrier NADP to form NADPH (reduced NADP)
ATP and NADPH are passed from light dependent to light independent reactions

13. Cyclic photophosphorylation
Involves only photosystem I
Light is absorbed by photosystem I and is passed to the primary pigment (chlorophyll)
An e- in chlorophyll molecule is excited to a higher energy level and is emitted

14. Cyclic photophosphorylation
Instead of falling back into the photosystem and losing thermal energy, the e- is captured by an electron acceptor and is passed back to chlorophyll via a series of electron carriers (called cytochromes)
This releases enough energy to synthesize ATP from ADP and Pi by chemiosmosis
ATP then passes to light independent rxns

15. Cyclic photophosphorylation

16. Cyclic photophosphorylation

17. Non-cyclic photophosphorylation
Involves both photosystem I and photosystem II in a “Z-scheme” of electron flow
Light is absorbed by both photosystems and excited electrons are emitted from p-pigs of both rxn centers

18. Non-cyclic photophosphorylation
Electrons from photosystem II are absorbed by electron acceptors and pass along chains of electron carriers
Primary pigment of photosystem I absorbs electrons from photosystem II
Electrons are replaced from photolysis of water
ATP is synthesized as electrons generate potential energy gradient for chemiosmosis

20. Non-cyclic photophosphorylation
Photolysis of water: Photosystem II includes water-splitting enzyme that catalyzes the breakdown of water:
𝐻 2 𝑂 →2 𝐻 + +2 𝑒 − 𝑂 2
Oxygen is a waste product
Hydrogen ions combine with NADP to create high-energy carrier NADPH