Photosynthesis Intro
Chapter 9 & 10
What you need to know!
• How chemiosmosis generates ATP in the
light reactions
• How photosystems convert solar energy
into chemical energy
Physics of Light
• Light, like all radiation, has energy
• Radiation can be sorted into an
electromagnetic wave spectrum according
to its wavelength
• Visible light can be broken up into: red,
orange, yellow, green, blue, indigo, violet
Colored Solid Objects
• The color of solid objects is a result of
absorbing and reflecting parts of the visible
light spectrum
• Example: Green object
– Reflects green
– Absorbs: red, orange, yellow, blue, purple
– Absorbance spectrum of plants
• Reflected light is useless to plants. Plants
cannot grow under green light
– It has the same affect as total darkness
Structure of a Chloroplast
• Chloroplasts have a double membrane
(endosymbiotic theory)
• Inner membrane builds thylakoids: hollow
membrane compartments that form stacks
called grana.
Thylakoid Membrane
•
Molecules embedded in the phospholipid
bilayer of the thylakoid membrane:
1. ATPase
•
Thylakoid space is used for H+ gradient and
ATP synthase in the membrane
2. Pigments
•
Chlorophyll a, b, carotenoids, and xantophylls
are the main pigments serving photosynthesis
are embedded in the membrane
3. Electron transport chain molecules:
•
Ubiquinones, and cytochromes are embedded
in the membrane
Structure of Cholorophyll
Structure of Chlorophyll
• Magnesium Porphyrine Ring
• Chlorophyll is a molecule that contains
nitrogen (present in fertilizer, decaying
compost, and proteins) or has to bound
out of the air’s N2 (by nitrobacteria)
• Expensive molecule: is recycled in fall in
temperate climates
• Chlorophyll has a hydrocarbon tail to make
it lipophilic for membrane attachment
Structure of Cholorophyll
• Chlorophyll exists in two different versions:
chlorophyll a and b. Absorbance
spectrums for both pigments maximize
absorbance in the red and blue range
Leaf Structure and
Photosynthesis
• Photosynthesis takes place in the
mesophyll of a plant’s leaf.
• Gas exchange will take place through the
stomata, during photosynthesis, stomata
need to be open. Plants inevitably
transpire through open stomata, which
also helps to keep plants cool, but:
• Only turgid stomata cells are open; if they
become flaccid, they close, and
photosynthesis stops.
Leaf Structure and
Photosynthesis
Cuticle
Mesophyll
Vein
Stomata
Paper Chromatography
•
•
•
Technique for separating and identifying
pigments from cell extracts.
The solvent moves up chromatography
paper by capillary action
Pigments (solutes) are dissolved in the
solvent and are carried up the paper
Paper Chromatography
• Differing pigments have different
properties:
– Solubility, size/shape, polarity
• Different bands form as the solutes
separate while they migrate up the paper
Rf Values of Pigments
• Rf is a ratio of the migration of the
pigment (B) over the migration of the
solvent (F)
• Rf = B/F
• B = distance (mm) from the bottom of
the pigment origin to the bottom of
the pigment migration
• If more than one pigment molecule is
tested the highest band is B1, the
next band is B2, etc.
• F = distance from the bottom of the
pigment origin to the bottom of the
solvent front
Solvent Front
Rf Values of Pigments
B4
Band #
Distance
migrated
Rf value
Identification
of
substance
1
2
• Rf values of substances are
specific to the chromatography
B3
system used. If paper or
solvent is changed, Rf values
B2
change
• Rf values do not change with
migration length in a system
B1
• Rf values are always between
0&1
Pigment Origin