Chapter 10: Photosynthesis Flashcards
What is the equation of photosynthesis?
6CO2+6H20+light–>C6H1206(glucose)+602
How does CO2 enter?
through stomata
How is water added?
from soil
Where does O2 come from?
H20
What are the two pathways of photosynthesis?
- Light reactions
2. Calvin-Benson cycle (Dark reactions)
Light reactions
convert light energy into chemical energy in the form of ATP and NADPH+H+
Calvin-Benson cycle (Dark reactions)
CO2 and ATP plus NADPH+H+ produced in light reactions are used in the Calvin-Benson cycle to produce sugars
What are some properties of light?
Light is a form of electromagnetic radiation: it exists as photons which exhibit wave-like properties
; the energy content of a photon is inversely proportional to the wavelength of the light
What’s the order of the electromagnetic spectrum?
Cosmic/gamma rays–>X-rays–>UV–>visible(ROYGBIV)–>IR–>microwaves
Absorption spectrum
each molecule has this; for a particular atom can only absorb photons corresponding to the atom’s available electron energy levels
What are Chlorophylls a and b?
Predominant pigments in green plants chlorine ring containing Mg2+, and a hydrocarbon tail chlorophylls absorb blue and red wavelengths
What are accessory pigments?
absorb photons in the region between blue and red cartenoids
What is the reaction for chlorophyll excitation?
Chl+ + A –> Chl+ + A-
What happens in the chlorophyll excitation?
excited electron shuttled along series of electron-carrier molecules in photosynthetic membrane–>at proton-pumping channel, proton translocation occurs, resulting in ATP synthesis by chemiosmosis
What is photosystem I?
reaction center containing a chlorophyll a (P700) wavelength absorption
What is photosystem II?
reaction center containing a cholorphyll a (P680) wavelength absorption; requires more energetic photons than I
What does that graph on slide 18 show?
That two photosystems are required for noncyclic electron transport.
What is noncyclic electron transport?
Uses photosystems I and II to produce NADPH + H+ together with ATP. Electrons from H20 replenish chlorophyll molecules which gave up electrons. O2 is a byproduct of the breakdown of H20
What is the general pathway of noncyclic electron transport?
Photosystem II (1/2O2 & 2H+ formed)–>Electron Transport (ATP is generated)–>Photosystem I–>Fd–>NADP+ reductase (NADPH formed)
What does cyclic electron transport form?
ATP but not NADPH
What does electron transport do?
electrons are returned to electron-deficient chlorophylls - no O2 is produced; produces additional ATP for reactions in the Calvin-Benson cycle
What is the pathway of cyclic electron transport?
Electron goes to P700 photosystem I, excites –>Fd–>Electron Transport–>electron
How do chloroplasts form ATP by chemiosmosis? (Slide 25)
electrons move through a series of redox reactions, releasing energy–>allows protons to be pumped across the thylakoid membrane from the stroma–>a pH gradient is established (proton-motive force)–>ATP synthase couples diffusion of protons back to the stroma with ATP synthesis
What is the arrangement of atoms in Photosystem II?
4 manganese, 5 oxygen, 1 calcium atom are linked in cluster on which water is split
What is the Calvin-Benson cycle?
Light-independent reactions (“dark reactions”)
What happens during the Calvin-Benson cycle?
CO2 reacts with ribulose biphosphate (RuBP) forming 2 molecules of 3-phosphoglyceric acid - catalyzed by RuBP carboxylase (rubisco)
What does the Calvin-Benson cycle require?
ATP and NADPH+H+ (products of noncyclic electron transport)
Where does the Calvin-Benson cycle take place?
The stroma
What does the production of 1 molecule of glucose require?
operation of the cycle 6 times on successive CO2 molecules
What is Ribulose 1,5 biphosphate?
the CO2 acceptor
What are the Calvin-Benson cycle inputs?
CARBON FIXATION: 6CO2; REDUCTION AND SUGAR PRODUCTION: 12 ATP, 12 NADPH+12H+; REGENERATION OF RuBP: 6 ATP
What are the outputs of Calvin-Benson cycle?
REDUCTION AND SUGAR PRODUCTION: 12ADP, 12Pi, 12NADP+, Sugars; REGENERATION OF RuBP: 6ADP
How many steps is the reduction of 3-phosphoglycerate to glyceraldehyde 3-phosphate (G3P)
2
What is G3P
3-carbon sugar phosphate (glyceraldehyde 3-phosphate)
What happens to G3P?
mostly recycled back to ribulose biphosphate (requires 12 steps of 15 reactions in Calvin cycle) and some exits the chloroplast to the cytoplasm –>hexoses (glucose and fructose)
What is photorespiration?
rubisco catalyzes reaction with O2 as well as with CO2
What does photorespiration reaction require?
light and uses oxygen
What does photorespiration do?
reduces efficiency of photosynthesis
What happens during photorespiration?
RuBP+O2 forms glycol ate (2C) which enters peroxisomes, is oxidized, and the product enters mitochondria and is broken down releasing CO2. Oxygenase function of rubisco is favored at higher temperatures and low CO2 levels
What does rubisco do?
can add either O2 or CO2 to ribulose biphosphate
