Chapter 10 RQ
1.
2.
3.
4.
5.
What organelles are the site for
photosynthesis?
What are the pores in a leaf called
through which gases exchange?
From which reactant molecule does the
oxygen we breathe come from?
What is “photophosphorylation”?
What component of light is actually
ABSORBED by chlorophyll?
1. Distinguish between autotrophic and
heterotrophic nutrition.
Heterotrophic
Nutritional mode of
acquiring organic
molecules from
compounds
produced by other
organisms
Autotrophic
Nutritional mode of
synthesizing
organic molecules
from inorganic raw
materials 
2. Distinguish between photosynthetic
autotrophs and chemosynthetic autotrophs.
Photoautotrophs
Autotrophic
organisms that use
light as their
energy source
Ex: plants, algae,
some prokaryotes
Chemoautotrophs
Autotrophic organisms
that use oxidation of
inorganic substances,
such as sulfur or
ammonia, as their
energy source
Ex: unique to some
bacteria (generally
archaebacteria) 
3. Describe the location and structure of the
chloroplast.
1.
2.
3.
Chloroplasts are found within the mesophyll (the
green tissue) of a leaf
Lens-shaped organelles measuring 2-4 µm by 47µm and is divided into 3 compartments by
membranes
Intermembrane space – separates the double
membranes that encase the chloroplast
Thylakoid – chlorophyll is here  helps to
initially convert light energy to chemical
energy - composed of grana, which are stacks
of thylakoids
Stroma – the viscous fluid outside the thylakoids
where carbon dioxide is made to sugar 
4. Write a summary equation for
photosynthesis. Explain how this equation
relates to the equation for cellular
respiration.
Photosynthesis
6 CO2 + 6H2O + light energy  C6H12O6 + 6O2
Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + energy 
5. Explain van Niel’s hypothesis and describe
how it contributed to our current
understanding of photosynthesis.
Van Niel hypothesized that plants
split water as a source of hydrogen
and release oxygen as a by-product
For the experiment, 18O was used as a
tracer
CO2 + 2H2O*  CH2O + H2O + O2*
OR
CO2* + 2H2O  CH2O* + H2O* + O2 
6. Explain the role of redox reactions in
photosynthesis.
Photosynthesis is an endergonic redox
process  energy is required to reduce
carbon dioxide
 Light is the energy source that boosts
potential energy of electrons as they are
moved from water to sugar
 When water is split, electrons are
transferred from the water to carbon
dioxide, reducing it to sugar 
7. Briefly describe the purpose of the light
reactions and the Calvin Cycle.
Light Reactions
- to convert light
energy to chemical
energy (ATP)
Dark Reactions
- also known as the
Calvin Cycle
- To convert carbon
dioxide to sugar,
using chemical
energy 
8. Describe the wavelike and particlelike
behaviors of light.
Wavelike
Wavelength distance
between the crests of
electromagnetic waves
Rhythmic waves
Visible light is the
part that drives
photosynthesis
Particlelike
Behaves as if it
consists of
discrete particles
or quanta called
‘photons’
The sun radiates
the full spectrum

9. Describe the relationship between and
action spectrum and an absorption spectrum.
 Each pigment has a
characteristic
absorption spectrum;
or wavelengths is
absorbs
 The graph of
wavelength versus rate
of photsynthesis is the
action spectrum and
profiles the
effectiveness of
different wavelengths

10. Explain why the absorption spectrum for
chlorophyll differs from the action spectrum
for photosynthesis.
Chlorophyll ‘a’ is not the only pigment in
chloroplasts that absorbs light
- the absorption spectrum for chlorophyll
‘a’ underestimates the effectiveness of
some wavelengths
Even though only special chlorophyll ‘a’
molecules can participate directly in light
reactions, other pigments called ‘accessory
pigments’ can absorb light and transfer the
energy to chlorophyll ‘a’ 
11. List the wavelengths of light that are
most effective for photosynthesis.
In Photosystem I
the wavelength
absorbed is 700nm
(red color)
In Photosystem II
the wavelength
absorbed is 680nm

12. Explain what happens when chlorophyll or
accessory pigments absorb photons
(photoexcitation).
1.
2.
Colors of absorbed
wavelengths disappear
from the spectrum of
transmitted and
reflected light
The absorbed photon
boosts one of the
pigment molecules’
electrons in its lowest
energy state to an
orbital of higher
potential energy (ground
state  excited state)

13. List the components of a photosystem and
explain their function.
Antenna complex: lots of chlorophyll ‘a’,
‘b’, and carotenoid molecules absorb
photons and pass energy
- different pigments absorb wider
photons
2. Reaction center chlorophyll: one of the
chlorophyll ‘a’ molecules transfers the
excited electrons that starts the light
reactions
3. Primary electron acceptor: traps the
excited electron (which is the first step
of the light reactions) 
1.
14. Trace noncyclic electron flow through
photosystems II and I.
1.
2.
3.
Light excites electrons from P700, which are
ultimately stored in NADPH, which will become
the electron donor in the Calvin Cycle
Excited electron is transferred from P700 to
the primary electron acceptor in photosystem I
They are then passed to ferredoxin (Fd), an iron
protein
- NADP+ reductase catalyzes the redox reaction
that transfers Fd
The oxidized P700 chlorophyll becomes an
oxidizing agent as the ‘hole’ is filled and
photosystem II supplies the electrons 
15. Compare cyclic and noncyclic electron
flow and explain the relationship between
these components of the light reactions.
Electrons from P680 flow to P700 during noncyclic
electron flow, restoring missing electrons in P700
Cyclic  because excited electrons that leave
chlorophyll ‘a’ return to that reaction center
- involves only photosystem I
- produces additional ATPs, without producing
NADPH or O2
[NADPH] might influence whether electron flow
will go through cyclic or noncyclic pathways 
16. Summarize the light reactions with an
equation and describe where they occur.
Light reactions occur
in the chloroplast’s
thylakoid membranes
Light energy 
chemical energy
(in NADPH & ATP)
Noncyclic  produces
ATP, NADPH, & O2 as
a byproduct
Cyclic  produces ATP

17. Describe important differences in
chemiosmosis between oxidative
phosphorylation in mitochondria and
photophosphorylation in chloroplasts.
1.
2.
Electron transport chain
- mitochondria transfer chemical energy from food  ATP
- high energy electrons pass down and are extracted by
the oxidation of food molecules
- chloroplasts transform light energy to chemical energy;
use light to drive electrons to the top of the chain
Spatial organization
- mitochondria’s inner membrane pumps protons from the
matrix out to the intermembrane space where there is
lots of protons
- chloroplasts pump protons from stroma to thylakoid 
18. Summarize the carbon-fixing reactions of
the Calvin Cycle and describe changes that
occur in the carbon skeleton of the
intermediates.
1.
2.
3.
Molecule of sugar  G3P (glyceraldehyde-3-phosphate)
Each molecule of CO2 is attached to a five carbon
sugar (ribulose biphosphate – RuBP)
Coupling of ATP hydrolysis with the reduction of 3phosphoglycerate to glyceraldehyde phosphate
Rearrangement of the 5 G3P molecules into 3 RuBP
molecules
- requires 3 ATP molecules
- regeneration of RuBP 
19. Describe the role of ATP and NADPH in
the Calvin cycle.
Converts CO2 to sugar
ATP is the energy source to do this
NADPH is the reducing agent that
adds high-energy electrons to form
sugar 
20. Describe what happens to rubisco when
the oxygen concentration is much higher that
carbon dioxide.
 Rubisco accepts O2
and transfers it to
RuBP
“photorespiration”
o Occurs because the active
site of rubisco can accept
O2 as well as CO2
o Produces no ATP molecules
o Decreases photosynthetic
output by reducing organic
molecules used in the Calvin
Cycle 
21. Describe the major consequences of
photorespiration.
Photorespiration is a metabolic pathway
that consumes O2, evolves CO2, produces
no ATP and decreases photosynthetic
output
 Fostered on hot dry bright days (close
stomata)
 In the desert, some species have evolved
alternate modes of carbon fixation that
minimize photorespiration (C4 and CAM) 
22. Describe two important photosynthetic
adaptations that minimize photorespiration.
CAM and C4 Plants
are similar….
 CO2 is first incorporated
into organic intermediates
before it enters the Calvin
Cycle
Differ….
 The initial steps of carbon
fixation in C4 plants are
structurally separate from
the Calvin Cycle; CAM the
2 steps occur at different
times 
C4 plants…
Incorporate CO2 into 4carbon compounds
Used by 1000’s of species
(corn, sugarcane, grasses)
Enhances carbon fixation
under conditions for
photorespiration
Leaf anatomy segregates
the Calvin Cycle from the
1st incorporation of CO2
into organic compounds
Calvin Cycle of these plants
is preceded by the
incorporation of CO2 into
organic compounds in the
mesophyll 
CAM plants…
1.
2.
Generally are succulent plants in very dry
regions
Open stomata primarily at night and close them
during the day (opposite of most plants)
Conserves water during the day, but prevents
CO2 from entering the leaves
When the stomata are open at night CO2 is taken up and
incorporated into a variety of organic acids (called
crassulacean acid metabolism)
Acids are stored until morning
- during the daytime the light reactions supply ATP and
NADPH for the Calvin Cycle; here is where the CO2 is
released from the organic acids from nighttime  sugar 
23. Describe the fate of photosynthetic
products.
O2 & H2O & sugars
Supply the entire plant with
chemical energy and carbon
skeletons to synthesize organic
molecules
The End 
The only reason people get lost
in thought is because it's
unfamiliar territory.