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Chapter 10
Photosynthesis
Overall, big picture is that photosynthesis has two parts, the whole chapter is about the details of these two
parts:
Part 1 is the Energy producing reactions= Noncyclic Photophosphorylation= Photosystems I and IIthese produce large amounts of ATP and NADPH
Part 2 is the Glucose producing reactions= Calvin cycle- use CO2 and ATP and NADPH to make glucose
A. Bits and Pieces/ Intro/Background
1. Journey to the center of the leaf- you should know all the parts and cells and what they do
a. cuticle, mesophyll/ palisade cells,
vascular tissue/ veins
chloroplasts (know all parts)
xylem-transport water to chloroplast
phloem- transport glucose around plant
stomata for gas exchange-CO2 in and O2 out
2. Overall chemical reaction of photosynthesis- or the reduction of CO2 into glucose
6CO2 + 12H20 + light energy------ C6H12O6 + 6H2O + 6 O2
3. Remember: have I repeated this enough yet?????? Photosynthesis has two parts
a. Noncylic photophosphorylation- converting light energy into electrical energy then chemical
energy of ATP and NADPH bonds. Photons to e- and H+ potentials to adding P to ADP ATP and some
H+ to NADP-- NADPH
and there are two parts to noncylic photophosphorylation
Photosystem II and Photosystem I
b. Calvin cycle- is the second part to make the sugar/glucose
B. Converting light energy to chemical energy- the details of noncylic photophosphorylation
1. Let’s talk about light energy and where it comes from- the sun in the form of the electromagnetic
spectrum
a. visible light is a narrow band of the total wavelengths that come from the sun
b. broken into colors which really represent different wavelengths and thus different amounts
of energy from the sun
c. plants, algae and photosynthetic bacteria really only use a small portion of visible light
2. Chlorophyll is the compound/molecule that is the major photon (energy) collector for
photosynthesis
a. most common forms are chlorophyll a and chlorophyll b Figure 10.___
b. it is located in the thylakoid membrane
c. forms reaction centers called Photosystems
1. Photosystem is a group of lots of chlorophyll molecules that absorb energy from the
photons of light energy and transfer the energy to a special pair of chlorophyll
molecules in the center of the photosystem.
a. converting photons/light energy to electrical energy- the special pair of
chlorophyll in the center of the photosystem lose a pair of e- because these electrons
get so excited by the transfer of the energy from all the other chlorophylls that the
electrons jump to a farther away energy shell/valance than where they belong.
b. when they jump to the farther away energy shell then they can be
stolen/captured by the first protein on an electron transport chain(ETC) similar to the
mitochondrial ETC.
2. Study Figure 10.17 on page 197 until it makes sense( or until you can’t take it
anymore): follow the path of the e- from Photosystem II through the ETC to
Photosystem I to NADPH and also follow the H+ through the thylakoid membrane to fuel
ATP synthase to make ATP.
3. electrons from Photosystem II replace electrons from Photosystem I which also get
excited by photons from the sun which end up at NADPH, replacement/recharging
electrons come from splitting H2O which also provide the H+ for ATP synthase.
C. Calvin Cycle- reduction of CO2 to form glucose
1. This is an anabolic set of reactions so energy needs to be added, notice that the arrows in Fig. 10.18
are showing the oxidized forms of ATP and NADPH at the arrow heads.
2. 3 CO2 are put in the cycle at time to form one G3P( glyceraldehyde-3-phosphate) which has 3
carbons and so is like half of a glucose.
Summary of Calvin cycle
CO2
ATP used
NADPH used
G3P
1 Turn
3
9
6
1
2 Turns
6
18
12
2= one glucose
3. What is the glucose used for? cellulose, starch, glycerol for lipids, and can be moved to the
mitochondria for break down to make more ATP and intermediates that are used for amino acids, nucleic
acids, fatty acids, steroids which are all necessary for the rest of the plant to function.
D. Skip Section 10-4 which means it will not be on the exam.