Photosynthesis Turning Light into Sugar

By the end I will be able to… o explain how energy is absorbed by pigments, transferred through the reduction of NADP + to NADPH, and then transferred as chemical potential energy to ATP by chemiosmosis o explain how NADPH and ATP are used to reduce Carbon in the light independent reactions for the production of glucose o identify where in the chloroplast these steps occur

ATP WHAT IS ATP? Universal Energy Molecule Energy in a form the cell can use Makes energy readily available Continuously being remade Stands for Adenosine Triphosphate AdenosineP P + P AdenosineP P P High Energy Bond Tri=3

ATP What is ATP used for? 1.Motion 2.Transport of ions and molecules 3.Building molecules 4.Switching reactions on or off How ATP works

Redox Reactions Redox reactions (reduction-oxidation reactions) happen throughout photosynthesis as electrons get transferred from one molecule to another. There are a couple of ways to remember what happens to the electron OIL RIG (Oxidation is losing, Reduction is gaining) LEO goes GER (lose electrons = oxidation; gain electrons = reduction) This is just a chain reaction of gaining electrons (e-) and passing them to the next compound

Redox Reactions

Photosynthesis The process of storing light energy (photons) as chemical energy (carbohydrates) in the cell.

The equation If you haven’t memorized it in previous classes, now is the time. The equation will provide you with an outline of the process. Work your way to memorizing the bottom format.

Photosynthesis occurs in Chloroplasts

Chloroplast Parts Thylakoid 1 disk Granum = a stack of disks Grana = plural granum (many stacks of disks) Site of the light dependent reaction (holds the chlorophyll) Stroma Gel surrounding the thylakoids Site of the light independent reaction

Parts of Chloroplast

Chlorophyll A green chemical which traps sunlight energy Located in the thylakoid of a chloroplast The pigments chlorophyll a and chlorophyll b absorb light wavelengths on the red and blue ends of the spectrum They reflect green light, that’s why plants look green.

Leaves in the fall Why do leaves change colour in the fall if chlorophyll a and b reflect green light?

Pigments Leaves contain other light absorbing pigments (chemicals) besides chlorophylls. Carotenoids (including carotene which reflects orange light, xanthophyll which reflects yellow light, and lycopene which reflects red light) Flavonoids (more yellow reflecting pigments and anthocyanin which reflects shades of red, blue, and purple) Different plants have different concentrations of these chemicals. In the fall, chlorophylls begin to break down, and the other reflected colours begin to show through without the green to overpower them.

Light Absorption Spectrum High peaks mean they absorb those colours Low peaks mean they reflect those colours

Photosynthesis There are two main parts to photosynthesis Light dependent reaction Needs light, therefore it takes place in the thylakoid membrane where the chlorophyll is Takes in water and creates oxygen as a byproduct Creates intermediary (not final) products of ATP and NADPH for the Calvin Cycle Light independent reaction Doesn’t need light so it happens outside the thylakoid in the stroma Also referred to as the dark reactions (misleading because it doesn’t only happen in the dark) Takes in CO 2 and the ATP and NADPH from the thylakoid to make glucose in a process called the Calvin Cycle.

Photosynthesis

Light Dependent Reaction All of these steps are happening at the same time, but for simplicity’s sake we will learn them separately 1.Photosystem II (PSII) -PSII is a group of chlorophyll pigments located on the thylakoid membrane. e- -It absorbs the sunlight energy, transforming it into chemical energy in the form of excited electrons ( e- ) e- -These e- are unstable and leave the chlorophyll, attaching to molecules in the ETC (electron transport chain). -The chlorophyll loses its electrons, so it is oxidized (remember LEO)

Photosynthesis 2.Photolysis (Photo = light lysis = split, therefore: using light to split) ‒In order to replace the electrons lost from the chlorophyll, a water molecule will be split apart ‒Light energy is used to split H 2 O into its parts ‒The Oxygen now leaves the thylakoid and the chloroplast and goes into the air for us to breathe ‒The H splits into its proton H + and its electron e- e- ‒The e- goes to the chlorophyll to replace the e- it lost ‒The chlorophyll has gained more electrons, therefore it has been reduced

PSII and Photolysis Start of the ETC

Photosynthesis 3.Electron Transport Chain (ETC) e- ‒The e- from the PSII are transferred through the ETC like a bucket brigade (one molecule accepts it, and then passes it onto the next molecule) e- e- ‒This is a series of redox reactions, as the molecule that accepts the e- is being reduced, but then is oxidized when it passes the e- onto the next molecule (** You don’t have to know the names of the individual molecules**) e- ‒When the e- are being transferred, some of their energy is used to take H + that are floating around in the stroma and pump them into the thylakoid lumen (H + are floating around everywhere in cells)

Photosynthesis ETC continued. ‒The pumping of H + into the thylakoid is an example of active transport (watch a tutorial on membrane transport)tutorial e- ‒This means it is using energy (from the e-) and the movement is against the concentration gradient. ‒The H + are being pumped from an area of low concentration to an area of high concentration ‒Building up a H + concentration gradient means that the inside of the thylakoid is more positively charged than the stroma ‒This is a form of potential energy (electrochemical gradient) e- ‒The e- lose their excess energy as they are transferred in the ETC until they reach Photosystem I (PSI) ‒PSI comes after PSII, but they’re numbered backwards because that’s the order they were discovered in

Photosynthesis ETC Active Transport

Photosynthesis 4.Reduction of NADP + e- -When the low energy e- reaches PSI, it gets reenergized by the sun (e- into e-) -It leaves the thylakoid at PSI and joins with H + and NADP + (floating around waiting to be reduced) in the stroma to make NADPH e- -NADPH is an electron carrier. It moves the e- and its H + from the thylakoid to the Calvin Cycle.

Photosynthesis 5.Chemiosmosis -This is the process of making ATP using the potential electrochemical energy from the H + concentration gradient. -The H + concentration has built up in the thylakoid lumen thanks to the active transport of H + inside by the ETC. -The high concentration of H + means that they want to diffuse out in order to achieve equilibrium -The H + cannot diffuse across the membrane because they are charged, so they must use a protein channel (facilitated diffusion) -The protein channel they diffuse out through is called the ATP Synthase Complex.

Photosynthesis

Chemiosmosis continued. ‒As the H + diffuse through the ATP Synthase channel, the structure turns the potential energy (from H + gradient) into kinetic energy that turns the protein channel ‒This kinetic energy is then transferred to the chemical bond between ADP and P to make the energy rich compound ATP. This website has a really good animation of the Light Dependent Reaction.website Following are some overview pictures as well.

Photosynthesis Light Independent Reaction This is takes place in the stroma of the chloroplast It is also called the Calvin Cycle It is a complicated cycle involving many steps that you don’t need to know e- In this step, the CO 2 from the air is bonded to the e- and H + from NADPH to make glucose (C 6 H 12 O 6 ) – Carbon fixation Oxidizing NADPH back into NADP + ATP donates its stored chemical energy to bond the C, H, and O together by breaking apart into ADP and P Now you have the final product of glucose And the ADP, P, and NADP + can go back to the thylakoid to be used in the Light Dependent Reactions again They continue to cycle back and forth between the main stages

Photosynthesis

Summary Light energy is absorbed by chlorophyll and turned into chemical energy by exciting electrons Water is broken apart to replace lost e- in PSII The electrons’ energy is used to create a H + concentration gradient (electrochemical potential energy now) in the ETC This gradient in turn transfers the energy into stored chemical energy in the ATP molecule when H + diffuse through the ATP synthase complex. The electrons absorb more sunlight energy and are carried from the thylakoid to the Calvin Cycle by NADPH The energy from ATP bonds the e- and H + from NADPH to the CO 2 to make C 6 H 12 O 6

Some helpful review videos: Crash Course Great Animation Teacher TutorialTeacher Tutorial (up to 8:35) Taylor Swift song 1 Taylor Swift song 2 Teacher Song

Recall o explain how energy is absorbed by pigments, transferred through the reduction of NADP + to NADPH, and then transferred as chemical potential energy to ATP by chemiosmosis o Light Dependent Reaction (Photolysis, ETC, Chemiosmosis) o explain how NADPH and ATP are used to reduce Carbon in the light- independent reactions for the production of glucose o Light Independent Reaction (Calvin Cycle) o identify where in the chloroplast these steps occur o Thylakoid and Stroma