CH7

• Photosynthetic organisms (algae, plants, and cyanobacteria) transform solar energy into the chemical energy of carbohydrates
• Autotrophs- produce their own food
• Photosynthesis: process that captures solar energy & transforms it into chemical energy, energy ends up stored in a carbohydrate
• Where does photosynthesis happen?

  In the green part of the plant
• What do leaves contain?

  Mesophyll tissue
• Which cell carries photosynthesis

  Cells with chloroplast
• The raw materials of photosynthesis

  Carbon dioxide and water
• How does water move up the roots?

  Vascular tissue
• How does CO2 enter the leaves?

  Through a small opening called stomata and diffuse into chloroplast in mesophyll tissue
• What does the thylakoid membrane of chloroplast contain?

  Chlorophyll and other pigments that absorb solar energy
• What happen to the electrons in the photosynthesis?

  gets energized
• What happens in the stroma?

  CO2 combines with H2O to form C6H12O6 (sugar)
• Autotrophs and heterotrophs relationship

  Photosynthesizers take energy from the sun and provide gases and food energy for heterotrophs (consumers)- generate chemical energy and produce carbon dioxide and water, both use organic molecules as a source of chemical energy for cellular work
• The process of photosynthesis

  It’s an example or redox reaction
• Redox reaction

  Movement of electrons from molecule to another
• Oxidation

  Loss of H atom
• Reduction

  Gain of H atom
• The 2 stages of photosynthesis

  Light reaction and Calvin cycle reaction
• Pigment and photosythesis

  Chemicals that absorb specific light wavelengths, unabsorbed wavelengths arereflected/transmitted, most of the radiation reaching earth is in the visible-light range (ex - photosynthesis), higher-energy wavelengths are blocked out by the ozone layer, lower-energy wavelengths are blocked by water vapor & CO2
• Who blocks higher and lower energy wavelength

  Higher-energy wavelengths are blocked out by the ozone layer and lower-energy wavelengths are blocked by water vapor & CO2
• Absorption spectrum

  A graph showing absorption of the differcolors of a rainbow, pigments found in chlorophyll absorb differ light portions, chlorophyll a and b are green because they absorbviolet, blue & red light, carotenoids absorb violet-blue-green light & reflect yellow and orange light
• Spectrophotometer

  Instrument that measures the amount of light of a specified wavelength which passes through a purified sample
• The 2 pathway of light reaction

  Noncyclic pathway & Cyclic pathway, light reactions capture light energy with photosystems, consist of pigment complex (molecules of Chlorophyll a, Chlorophyll b and carotenoids) & e acceptor molecules, located in thylakoid membrane, the pigment complex serves as an antenna for gathering solar energy
• what does noncyclic and cyclic produce

  Both produce ATP, no cyclic pathway also produces NADPH
• The 2 light gathering units of light reaction

  PS I and PS II
• ATP production

  Thylakoid space acts as a reservoir for H ions, Each time water is oxidized 2 H remain in the thylakoid space, e transfers down the e-transport chain producing energy, This energy is used to pump H+ across the thylakoid membrane, Protons move from stroma into the thylakoid membrane energizes ATP synthase, The flow of H back across the thylakoid membrane energizes ATP synthase, ATP synthase enzymatically produces ATP from ADP + P, This method of producing ATP is called chemiosmosis- energy tied to an H+ gradient

   
• 3 stages of Calvin cycle reaction

  1-Carbon dioxide fixation

  2-Carbone dioxide reduction

  3-RuBP regeneration
• Carbon Dioxide Fixation

  CO2 enters chloroplast stroma via leaves stroma, CO2 is attached to RuBP-a 5‐carbon molecule, Result in a 6-carbon molecule which splits into two 3-carbon molecules (3PG), Reaction is accelerated by RuBP carboxylase (Rubisco), CO2 now is “fixed” because it’s part of a carbohydrates
• Reduction of Carbon Dioxide

  Each 3PG molecules becomes G3P (glyceraldehyde-3-phosphate) in two steps, ATP phosphorylates each 3PG molecule and creates 1,3‐bisphosphoglycerate (BPG), BPG gets reduced by NADPH to G3P, NADPH & some ATP from light reactions are used here, G3P is reduced & able to store energy and form larger molecules like glucose
• Regeneration of RuBP

  RuBP used in CO2 fixation must be replaced, Every 3 turns of the Calvin cycle 1 G3P exits, Five G3P molecules remake 3 RuBP molecules, 5 X 3 (carbons in G3P) = 3 X 5 (carbons in RuBP)
• Importance of the Calvin cycle:

  G3P can be converted to many other molecules
• Hydrocarbon skeleton of G3P can form- Fatty acids & glycerol to make plant oils, Glucose phosphate, Fructose(which with glucose = sucrose), Starch & cellulose, Amino acids
• Photosynthetic Rate in C4 vs C3  Plants:

  In hot climates productivity of C4 is about 2‐3 times of C3 plants, C4 plants avoid photorespiration as PEPCase unlike RuBP carboxylase it doesn’t combine with O2, even when stomata are closed, CO2 is delivered to the Calvin cycle in the bundle sheath cells, In cool environments C4 plants can’t compete with C3 plants
• CAM Photosynthesis:

  Crassulacean‐acid metabolism called after flowering succulent plant family where it was first found, CAM plants separate carbon fixation by time not physically like C4 plants, CAM plants use PEPCase to fix some CO2 forming C4 molecules stored in large vacuoles in mesophyll cells
• C4 plants most adapted to high light intensities & temperatures, limited rainfall

  C3 plants better adapted to cold (below 25°C), high moisture

  CAM plants are better adapted to extreme aridity
• PS I

  Has pigment complex & e-acceptors, close to the enzyme that reduces NADP to NADPH
• PS II

  Consists of a pigment complex & e-acceptors, gets e from the splitting of water, oxygen is released as a gas
• Electron transport chain

  Consists of cytochrome complexes & plastoqinone, carries e between PS II and PS I, pumps H from the stroma into the thylakoid space
• ATP synthesis complex

  Has a channel for H flow, H flow through the channel, ATP synthase joins ADP & Pi
• Role of NADP/NADPH

  CO2 reduction requires energy & H atoms, Solar energy generates ATP to reduce CO2 to sugar, e needed to reduce CO2 will be carried by NADP- the active redox coenzyme of photosynthesis, When NADP is reduced it accepts 2 e & H when NADPH is oxidized it gives up its e, van niel showed that O2 released by photosynthesis comes from water and not CO2, Researchers later confirmed that using the isotope oxygen (18O), When water splits O2 is released & the hydrogen atoms are taken up by NADPH, NADPH later reduces CO2 to carbohydrate