Important words and concepts from Chapter 10,
Campbell & Reece, 2002 (1/29/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to
access text’s website Vocabulary
words
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(1) Chapter title: Photosynthesis
(a)
Photosynthesis is how most ecosystems make the
food that serves as their energy (and reducing-electrons and
fixed-carbon) foundation
(b)
[photosynthesis (Google Search)] [photosynthesis] [index]
(a)
Organisms that obtain their carbon and energy
(especially the former) without eating other organisms are called autotrophs
(b)
Some autotrophs (though not all) obtain their energy from photons
(i.e., light)
(c)
In most ecosystems,
in fact, the organisms at the base of all food chains are photoautotrophs (i.e., autotrophs that obtain
energy from photons)
(d)
The most common of the terrestrial autotrophs are the green plants
(e)
See Figure 10.1:
Photoautotrophs
(f)
[autotroph or autotrophs
(Google Search)] [index]
(a)
Heterotrophs are organisms that obtain their carbon (in particular) and their energy by
eating other organisms
(b)
[heterotroph or heterotrophs
(Google Search)] [index]
(4) Chloroplast
structure, review
(a)
See Figure 10.2, Focusing in
on the location of photosynthesis in a plant
(b)
Recall that a chloroplast may be
differentiated into the following structures (going from outside to in):
(i)
Outer membrane
(ii)
Intermembrane space
(iii)
Inner membrane
(iv)
Stroma
(v)
Thylakoid
(vi)
Thylakoid space (or compartment or lumen)
(c)
Recall additionally that the thylakoids are derived from the inner
membrane (think of them as sealed off cristae-equivalents)
(d)
[chloroplast (Google Search)] [chloroplast links (MicroDude)] [index]
(5) Photosynthesis,
overall reaction
(a)
The overall reaction of photosynthesis may be described in shorthand
as:
(i)
CO2 + H2O + energy à CH2O + O2
(b)
See Figure 10.3, Tracking
atoms through photosynthesis (and, no, I don’t expect you to know this figure,
though do note that the actual reaction is perhaps more complex than expected
with water appearing on both sides of the equation)
(c)
Note that here energy is “light energy,” i.e., photons
(d)
Note also that CH2O represents a one carbon unit of carbohydrate
(recalling that carbohydrate molecules have more than one carbon)
(e)
In terms of glucose, the above equation may be written
as:
(i)
6CO2 + 6H2O + energy
à C6H12O6
+ 6O2
(f)
Note how this equation is essentially the reverse of the equation for
the oxidation of glucose:
(i)
C6H12O6 + 6O2 à 6CO2 + 6H2O
+ energy
(g)
[photosynthesis (Google Search)] [photosynthesis links
(MicroDude)] [index]
(a)
The CO2 given off by cellular respiration is ultimately taken up as
a substrate of photosynthesis
(b)
The O2 given off by photosynthesis is ultimately taken up as
a substrate (final electron acceptor) of cellular respiration
(c)
All of the atmospheric molecular oxygen, in fact, came/comes from
photosynthesis
(d)
See Figure 9.1: Energy flow
and chemical recycling in ecosystems
(e)
[carbon cycle, oxygen cycle (Google Search)] [carbon cycle links
(MicroDude)]
[index]
(7) Two reactions of photosynthesis
(a)
Photosynthesis is not a single reaction pathway but two, one
dependent on the other
(b)
See Figure 10.4, An overview
of photosynthesis: cooperation of the light reactions and the Calvin cycle
(c)
The light reactions represents the “photo”
part of photosynthesis
(i)
This is where the energy of
photons is captured
(ii)
The light reaction supplies the energy and reducing electrons to drive forward the Calvin cycle
(d)
The Calvin
Cycle
represents the “synthesis” part of photosynthesis
(i)
This is where the “fixing” of CO2
(leading to the making of carbohydrate)
occurs
(ii)
The Calvin cycle serves to store the energy and reduced electrons generated by the light reaction, i.e., store
energy and reduced electrons as carbohydrate
(e)
Both reactions are anabolic, involving the phosphorlyation of ATP
(not, in this case, as a product of catabolism), reduction of NADP+ (both products of the light
reactions) or carbohydrate formation (the product of the dark reactions)
(f)
[photosynthesis two reactions
(Google Search)] [stages of photosynthesis
(Online Biology Book)]
[photosynthesis links (MicroDude)]
[index]
(8)
Light
reaction of photosynthesis
(a)
The light reactions of photosynthesis involve the following
(i)
Capture of a photon of light by a chlorophyll photosystem
(ii)
Conversion of photon energy to energy stored by electrons (chemical energy)
(iii)
Capture of this chemical energy by the reaction center
chlorophyll of a photosystem
(iv)
Oxidation of the reaction center chlorophyll by the
primary electron acceptor
(vi)
Oxidation of water
(vii)
Cyclic electron flow
(b)
Overall these reactions produce molecular oxygen
(O2; a waste product given off by one of the light reactions of
photosynthesis), ATP, and NADPH
(c)
[photosynthesis light reactions,
photosynthesis light reaction
(Google Search)] [light reactions links
(MicroDude)]
[index]
(a)
In photosynthesis, reducing electrons are carried
by a phosphorylated derivative of NAD+ called NADP+
(b)
Analogous to the reduction of NAD+,
the reduction of NADP+ occurs thusly:
(i)
NADP+ + 2e- + 2H+ à NADPH + H+
(c)
NAD+ and NADP+ otherwise act equivalently, the
former in cellular respiration, the latter in
photosynthesis
(d)
[NADP reduction (Google Search)] [conversion of NADP+
to NADPH (Davidson College)] [NADPH oxidase page
(David Lambeth)] [NADPH oxidase (KUMC Sophomore Pathology)]
[index]
(a)
The wavelength of light is, among other things, a measure of the energy
associated with a photon
(b)
Wavelength is also equivalent to the perceived color of a photon
(c)
See Figure 10.5, The electromagnetic
spectrum
(d)
The chloroplasts of green plants do not absorb green light
(photons); this is why plants are green
(e)
See Figure 10.6, Why leaves
are green; interactions of light with matter in a chloroplast
(f)
[wavelength of light,
wavelength of light
photosynthesis (Google Search)] [the nature of light (Online Biology Book)]
[the physics of photosynthesis
(MIT Biology Hypertextbook)]
[index]
(a)
The molecule that does the actual absorption of photons in chloroplasts is chlorophyll
(b)
Chlorophyll is a complex, non-protein, organic-molecule that is
embedded, more or less, in the thylakoid membrane
(c)
See Figure 10.9, Location
and structure of chlorophyll molecules in plants
(d)
The major function of a chlorophyll molecule is to absorb a photon,
using the energy of that photon to boost a specific
chlorophyll electron to a higher energy
shell
(e)
Chlorophylls are arrayed into photosystems
(f)
[chlorophyl (Google Search)] [chlorophyll and accessory
pigments (Online Biology Book)]
[index]
(a)
Photosystems are two-dimensional arrays of chlorophyll molecules
(b)
These arrays are found embedded together in the membranes of the thylakoids of chloroplasts
(c)
These arrays serve as photon-gathering antennae
(d)
Green plants employ two slightly different photosystems termed
photosystem I and photosystem II, the former of which (photosystem I) is
involved in both non-cyclic and cyclic electron flow
(e)
See Figure 10.11, How a
photosystem harvests light
(f)
[photosynthesis photosystem or
photosystems (Google Search)] [index]
(a)
When a photon is captured by one chlorophyll of a photosystem, the energy of that photon is passed from chlorophyll to
chlorophyll until the energy reaches the photosystem reaction center
(b)
See Figure 10.11, How a
photosystem harvests light
(c)
Note that it is energy, not electrons (or photons) that are passed from
chlorophyll to chlorophyll molecule with a photosystem
(d)
[reaction center photosynthesis
(Google Search)] [index]
(14) Primary
electron acceptor
(a)
The reaction center of a photosystem is a chlorophyll
molecule that is associated with the primary electron acceptor
(b)
The primary electron acceptor accepts the now high-energy electron from the reaction center
chlorophyll and passes that electron on to an electron transport chain
(c)
See Figure 10.11, How a
photosystem harvests light
(d)
[primary electron acceptor,
primary electron acceptor
photosynthesis (Google Search)] [index]
(a)
Chlorophyll minus its electron
(i.e., having passed it on to the primary electron acceptor) is a very strong oxidizer
(b)
To proceed with another round of photon absorption, the reaction
center chlorophyll must obtain a replacement electron
(c)
This replacement electron, in green plants, is obtained, in certain
circumstances, from water:
(i)
Chlorophyll2+
+ H2O
à chlorophyll0 + 2H+
+ ½O2
(d)
Note that the O2 generated by photosynthesis
comes from water, not from CO2!
(recall that similarly the O2 used in cellular respiration serves to generate water
rather than CO2)
(e)
The H+ are generated in the thylakoid space, thus contributing to a
chemiosmotic proton gradient
(f)
[oxidation of water,
oxidation of water
photosynthesis (Google Search)] [index]
(a)
See Figure 10.12, How
noncyclic flow during the light reactions generates ATP and NADPH
(b)
Non-cyclic electron flow through the various photosystems (I and
II) is employed to produce ATP as well as reduce NADP+
(c)
Note that the production of both of these molecules is driven by light
energy that has been converted to chemical energy rather than derived from the
catabolism of food molecules (such as glucose)
(d)
Note if the figure (more or less in order):
(i)
Photon capture by photosystem II
(ii)
Oxidation of photosystem II
(iii)
Primary electron acceptor
(iv)
Oxidation of water
(v)
Electron transport
(vi)
Photophosphorylation
(vii)
Reduction of photosystem I
(viii)
Photon capture by photosystem I
(ix)
Oxidation of photosystem I