Photosynthesis Photosynthesis (Anything with **** by (Anything with **** by

it, write on your note it, write on your note handout)handout)

Photosynthesis - Method of converting sun’s energy into chemical energy usable by cells

Autotrophs: self feeders, organisms capable of making their own food– Photoautotrophs: use sun’s energy e.g. plants

photosynthesis-makes organic compounds (glucose) from light

– Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

**** Photosynthesis does not give plants energy. It provides them with the food (glucose) that mitochondria can then use to create energy (ATP).

Photosynthesis

Photosynthesis takes place in specialized structures inside plant cells called chloroplasts. Chloroplasts are located in the leaves of plants (so that’s where photosynthesis occurs).

Light absorbing pigments in chloroplast

– **** Chlorophyll IS NOT the only light absorbing pigment in plants. It is just the most abundant (which is why chloroplasts (and thus plants) are green).

– **** Different pigments are responsible for absorbing different wavelengths of light. Remember ROYGBIV.

– **** Pigments include chlorophyll a, chlorophyll b, carotenoid, among others.

– ****If chlorophyll are green, what colors of light do they absorb?– Paper Chromatography

Draw this picture of a chloroplast on your note

handout

Overall Reaction **** Cellular Respiration Equation is exact opposite of photosynthesis equation (minus the sunlight)

6CO2 + 6 H2O + light energy → C6H12O6 + 6O2

Carbohydrate made is glucose Water is split as a source of electrons from hydrogen atoms releasing O2 as a

byproduct Electrons increase potential energy when moved from water to sugar therefore

energy is required Why does it take 6 carbon dioxide and 6 waters to make 1 glucose (and

release 6 oxygen)?? ****To remember this equation, think “what does a plant need and what

does it make”– **** It “needs” CO2to turn into glucose, water for electrons, and

sunlight. Energy from sunlight breaks water. H+ are taken from water and given to CO2.

– **** It makes glucose for food and oxygen as a byproduct (waste). Adding H+ to CO2 generates glucose and taking H+ from water generates oxygen.

Light-dependent Reactions – occurs in Thylakoid membrane

Overview: Light energy is absorbed by chlorophyll molecules. This light energy excites electrons and boosts them to higher energy levels. They are trapped by electron acceptor molecules that are poised at the start of a neighboring transport system. The electrons “fall” to a lower energy state, releasing energy that is harnessed to make ATP

Energy Shuttling

Recall ATP: cellular energy-nucleotide based molecule with 3 phosphate groups bonded to it, when removing the third phosphate group, lots of energy liberated= superb molecule for shuttling energy around within cells.

Other energy shuttles-coenzymes (nucleotide based molecules): move electrons and protons around within the cellNADP+, NADPH NAD+, NADH FAD, FADH2

**** The purpose of NADPH in photosynthesis is to “carry electrons” from

broken from water to the next step of photosynthesis (Calvin Cycle).

Light-dependent Reactions – occurs where?

Photosystem: light capturing unit, contains chlorophyll, the light capturing pigment

Electron transport system: sequence of electron carrier molecules that shuttle electrons, energy released to make ATP

Electrons in chlorophyll must be replaced so that cycle may continue-these electrons come from water molecules, Oxygen is liberated from the light reactions

Light reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

Light Reactions Overview:***H20 + Light energy O2 + ATP + NADPH**** Note that this is where we use water and light as well as make oxygen. What other parts of the photosynthesis equation are not used / made here (so they have to be in next step)?

****ELECTRON TRANSPORT CHAIN pumps H+ ions into the thylakoid space and CHEMIOSMOSIS uses this to

make ATP using ATP Synthetase

Calvin Cycle (light independent or “dark” reactions) – occurs in stroma

ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.

(Underline this on handout) Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)

**** Basically, Calvin Cycle uses products from light reactions to make glucose.

**** Even though this is called the “dark reactions” they still occur mostly during the day. Why?

Calvin Cycle Overview:**** 6 CO2 + ATP + NADPH C6H12O6 (glucose) + ADP (P) + NADP+

**** Note that ATP and NADPH are not in overall equation because they are constantly recycled (ATP ADP + P and NADPH NADP+)