2. Photosynthesis: Using Light to Make Food

3.  Energy classification  Autotrophs—self nourishing Obtain carbon from CO 2 Obtain energy from light (photosynthesis) or chemical reactions (chemosynthesis)  Heterotrophs—use others for energy source Obtain carbon from autotrophs Obtain energy from autotrophs Even if ingest other heterotrophs, at some point the original carbon & energy came from an autotroph  Carbon & Energy  Enter life through photosynthesis (autotrophs)  Released through glycolysis & cellular respiration (heterotrophs)

4.  Chlorophyll  Plants  Algae  Some bacteria  Transfer sun’s energy into chemical bonds  Converts energy of photons to energy stored in ATP  Oxygen production is a byproduct

5.  Three stages  Light-capturing  Light-dependent Convert light energy into chemical energy  Light-independent Form organic compounds (glucose)  CO 2 + H 2 O => C 6 H 12 O 6 (glucose) + O 2  Remember that this is the opposite direction but the same basic reaction as cellular respiration.

6.  Wavelength  Spectrum

7.  Photons  Packets of particle-like light  Fixed energy (each photon a specific energy wavelength)  Think of them as bundles of energy, like an electrified rubber ball  Energy level  Low energy = long wavelength Microwaves, radio waves  High energy = short wavelength Gamma rays, x-rays  Only a small part of spectrum (400-750 nm) is used for vision & photosynthesis

8.  The light that you see is REFLECTED, not absorbed.  Therefore, a green plant is reflecting the green part of the spectrum (and photons of that energy), not absorbing them; it absorbs all parts of the spectrum except green.

9.  Molecules that absorb photons of only a particular wavelength  Chlorophyll a  Absorbs red, blue, violet light  Reflects green, yellow light  Major pigment in almost all photoautotrophs  Chlorophyll b  Absorbs red-orange, some blue  Reflects green, some blue

10.  Carotenoids  Absorb blue-violet, blue-green light  Reflect red, orange, yellow light  Give color to many flowers, fruits, vegetables  Color leaves in Autumn

11.  Anthocyanins  Absorb green, yellow, some orange light  Reflect red, purple light  Cherries, many flowers  Color leaves in Autumn  Phycobilins  Absorb green, yellow, orange light  Reflect red, blue-green light  Some algae & bacteria

12.  Pigment absorbs light of specific wavelentgh  Corresponds to energy of photon  Electron absorbs energy from photon  Energy boosts electron to higher level  Electron then returns to original level  When it returns, emits some energy (heat or photon)

13.  Stage 1 (Light-Dependent)  Light energy converted to bond energy of ATP  Water molecules split, helping to form NADPH  Oxygen atoms escape  Stage 2 (Light-Independent)  ATP energy used to synthesize glucose & other carbohydrates

19.  Occurs in thylakoids  Electrons transfer light energy in electron transport chain in photosystems

20.  Photosystems—Clusters of chlorophyll, pigments, proteins  Light-gathering “antennae”  Photosystem I (P680)—absorbs red light at 680nm  Photosystem II (P700)—absorbs far-red light at 700nm

21.  Electrons transfer from photosystems  Electron transfers pump H + into inner thylakoid compartment  Repeats, building up concentration and electric gradients  Chemiosmosis!

22.  H + can only pass through channels inside ATP Synthase  Ion flow through channel makes protein turn, forcing Phosphate onto ADP  Phosphorylation!

23.  Electrons continue until bonding NADP+ to form NADPH  NADPH used in next part of cycle  Process is very similar to cellular respiration!!!!  Oxidative phosphorylation

28.  ATP provides energy for bond formation  NADPH provides hydrogen & electrons  CO 2 provides carbon & oxygen

29.  CO 2 in air diffuses into stroma  CO 2 attaches to rubisco (RuBP)  Enters Calvin cycle (also called Calvin- Benson)  RuBP splits to form PGA  PGA gets phosphate from ATP, then H + and electrons from NADPH  Forms PGAL  Two PGAL combine to form glucose plus phosphate group

30.  Some PGAL recycles to form more RuBP  Takes 6 “turns” of cycle to form one glucose molecule  6 CO 2 must be fixed and 12 PGAL must form to produce one glucose molecule and keep the cycle running

31. *(G3P = PGAL)

34.  Microscopic openings in leaves  Close when hot & dry  Keeps water inside  Prevents CO 2 & O 2 exchange

35.  Basswood, beans, peas, evergreens  3-Carbon PGA is first stable intermediate in Calvincycle  Stomata close, O 2 builds up  Increased O 2 levels compete w/ CO 2 in cycle  Rubisco attaches oxygen, NOT carbon to RuBP  This yields 1 PGA rather than 2  Lowers sugar production & growth of plant  12 “turns” rather than 6 to make sugars  Better adapted to cold & wet

36.  Corn, sugar cane, tropical plants  Adapted to hot, dry climates  Close stomata to conserve water  This limits CO2 entry and allows O2 to accumulate  This allows CO 2 to remain high for Calvin cycle  Carbon stored in special cells, can be donated to Calvin cycle later  Requires 1 more ATP than C3, but less water lost & more sugar produced

38.  Desert plants (cactus)  Crassulcean Acid Metabolism (CAM)  Opens stomata at night, uses C4 cycle  Cells store malate & organic acids  During day when stomata close, malate releases CO 2 for Calvin cycle