Chapter 7 Photosynthesis

PHOTOSYNTHESIS LIGHT ENERGY CONVERTED TO CHEMICAL ENERGY LIGHT CARBOHYDRATES

CHAPTER 7 PHOTOSYNTHESIS Process by which plants use the energy from light to generate sugar 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

Diversity of Photosynthesizers These are autotrophs

Photosynthesis Rxn Overview However, the above is a bit of a lie…

Bioenergetics

SOLAR RADIATION 1) described in terms of energy content and wavelength in the electromagnetic spectrum 2) Photon--- energy packet of solar radiation * energy inversely proportional to wavelength 3) Divided on the basis of : a) high energy ( UV ) dangerous b) low energy ( IR ) not dangerous 4) Photosynthesis uses only visible portion of the spectrum ( ROYGBIV)= white light * able to promote electrons to a higher energy level without harming cell

Energetics of Visible Light Red is less energetic Violet is more energetic

Energetics of Visible Light 680 nm, PS II 700 nm, PS I

Why Plants are Green?

Green is what’s not Adsorbed

Photon Energy Boosts Electron

LOCATION OF PHOTOSYNTHESIS * OCCURS IN CHLORPLASTS OF AUTOTROPHS

Occurs in the chloroplast Light reactions ( thylakoid) Calvin cycle ( stroma) Photophosphorylation– process by which ATP is made during the light reaction Photolysis –process by which water is split into hydrogen ions and oxygen atoms and electrons are released ( light reaction)

Chloroplast (a plastid) Thylakoids are membrane-bound organelles inside of a membrane-bound organelle

STRUCTURE AND FUNCTION OF CHLOROPLAST STROMA– solution where carbon dioxide is reduced; LIGHT INDEPENDENT OCCURS THYLAKOIDS– flattened sacs Within stroma that have membranes that contain pigments such as chlorophyll GRANA – stacks of thylakoids

Chloroplast Overview  Thylakoids: Membrane “discs” arranged in stacks (grana, sing. granum) which contain chlorophyll and other important molecules Site where solar energy is trapped and converted into chemical energy (light reactions)  Thylakoid membrane: Site of ATP synthesis  Stroma: Thick fluid outside thylakoid membranes, surrounded by interior membrane Site of sugar synthesis (dark reactions)

2 main processes 1) LIGHT DEPENDENT REACTIONS- 2) LIGHT INDEPENDENT REACTIONS

2 general reactions’ 1) Light – Dependent Reactions– produce energy molecules byproduct oxygen ) Light- Independent Reaction- ( Calvin Cycle) produce sugar and uses energy molecules formed in the light dependent reactions

Bioenergetics

LIGHT DEPENDENT REACTION 1) energy capturing photosystems (PS1 and PS2) are involved 2) Water is split and oxygen is released. H+ and electrons are energized when light is absorbed 3) Electrons move to the ETS and produce ATP due to H+ gradient ( chemiosmosis); ATP is used in the light independent reaction 4) Electrons are gained by NADP+ and form NADPH to be used in the Light independent reaction

Light – Dependent rxs --cyclic and noncyclic Occurs in thylakoid 1) Non-Cyclic- produces ATP and Oxygen and NADPH ) Cyclic – produces ATP only

Photosytem Note transfer of energy rather than redox reactions

Photosystems energy transfer energy transfer

Photosytem

Non Cyclic Light Dependent 1) Inputs are light and water 2) light strikes photosystem II 3) Electrons pass along until they reach primary electron acceptor 4) Photolysis occurs- water split into hydrogen ions and oxygen atoms 5) Electrons pass down ETC to photosystem I forming ATP by chemiosmosis 6) 3 products are : ATP, NADPH and O 2

Non-Cyclic Flow (repeat)

Oxidation of water regenerates photosystem II, generating O 2 in the process Note not NADH but NADPH Photophosphorylation

Overview of Light Rxn All of this stuff you are responsible for from other slides Don’t worry too much about names of specific ETS members

Cyclic Light Dependent RX 1) involves photosystem I 2) ATP is only product

Cyclic Electron Flow

Light Reaction Z Scheme

Light Independent Reaction ( CALVIN CYCLE) 1) ATP and NADPH are used to drive this reaction 2) Carbon dioxide is reduced to form PGAL; 2 PGAL is used to form glucose CALVIN CYCLE DIAGRAM HANDOUT

CALVIN CYCLE ( LIGHT- INDEPENDENT RX) 1) Uses ATP and NADPH formed in the light reactions 2) Begins with Carbon fixation – where the carbon from CO2 is converted into a useable form 3) Three main steps a) carbon fixation b) chemical reshuffling c) reforming of RuBP

1)The carbon atom from CO2 bonds with a five carbon sugar called ribulose biphosphate ( RuBP) to form an unstable six carbon sugar 2)The six carbon sugar formed in step 1 splits into two 3 carbon molecules 3)ATP and NADPH are used to convert the 3 carbon molecules above into 3 carbon molecules with higher energy called PGAL * total = 2 PGAL 4) One out of every 6 molecules created is transferred to the cytoplasm and used for synthesis of glucose and other carbohydrates 5) Other 5 molecules of PGAL are used to synthesize 3 molecules of RuBP

Calvin Cycle Reducing power Energy

Factors affecting Photosynthesis 1) Light quality –color 2) Light Intensity 3) Light Period 4) Carbon Dioxide availability 5) Water Availability

Other pathways 1) Calvin cycle only –C3 plants 2) C4 plants fix CO2 into a 4 carbon compound ex: corn, sugar cane 3) CAM– cactus, ; open stomata at night close during day ; take in CO2 at night and fix

TYPES OF PLANTS * CREATE A FOLDABLE OR CHART USING TEXT ON C3. C4 AND CAM PLANTS

Photosynthesis (overview) “Dark” Reaction Carbon fixation

Bioenergetics Proton- motive force

The End