Photosynthesis Photosynthesis

I. How do living things get the energy they need to live? Photosynthesis: The process by which plants (autotrophs) and some other organisms use sunlight to synthesize foods from carbon dioxide and water. It involves the green pigment chlorophyll and generates oxygen as a byproduct. What does autotroph mean? __________________________________

I. How do living things get the energy they need to live? Reactants  Products CO 2 + H 2 O + light energy  C 6 H 12 O 6 + O 2 _______ _____ _________ ________ _____

II. Where does all of this happen?

II. Where does all this happen?  Inside plant cells there are organelles called chloroplasts. Inside the chloroplast there are stacks of membranes called grana.  Each granum contains several layers of thylakoid membranes.

II. Where does all this happen?  Each thylakoid membrane is packed with chlorophyll (a green pigment) and proteins that carry out photosynthesis.  The space between grana is called the stroma.

III. So how does it actually happen? There are two stages of photosynthesis: I.Light-dependent reactions (In thylakoid membrane) 1.Light strikes the first photosystem (a group of proteins), which causes some electrons to get “excited” (jump to a higher energy level). 2. Since excited electrons are unstable, they almost immediately transfer the energy to a nearby molecule.

A photosystem:

III. So how does it actually happen? 3. The excited electrons are replaced by splitting a water molecule into hydrogen ions (H + ) and oxygen (O 2 ). 4. Oxygen diffuses out of the chloroplast as waste. 5. The excited electrons travel down a chain of membrane proteins called the electron transport chain (ETC).

III. So how does it actually happen? 6. The energy given off by this process is used to pump hydrogen (H + ) ions across the membrane. 7. More excited electrons from the second photosystem are added to NADP + to make NADPH. 8. The H + concentration gradient is used to power a membrane protein called ATP synthase, which produces ATP.

Let’s watch a movie of it. Light reactions Light reactions Cool – ATP synthase Cool – ATP synthase

In summary: Light + H 2 O  ATP + NADPH + O 2

III. So how does it actually happen? II. Light-independent reactions, aka the Calvin Cycle (in stroma) 1.CO 2 is added to a 5-carbon sugar called ribulose bisphosphate (RuBP). The enzyme that catalyzes this reaction is called rubisco. 2. The 6-carbon sugar splits in half to form two molecules of 3-phosphoglycerate (3-PGA).

III. So how does it actually happen? 3. ATP and NADPH from the light reactions provide energy and electrons to convert 3-PGA into glyceraldehyde 3-phosphate (G3P). 4. After three turns of the cycle, six molecules of G3P are made.

III. So how does it actually happen? 5. Out of these six G3P molecules, five of them enter a process that makes more RuBP to continue the cycle. 6. Only one of the six G3P molecule exits the cycle. This G3P can be converted into glucose or other sugars that the plant needs.