Photosynthesis
Photosynthesis
1. Definition
PHOTO = produced by light
SYNTHESIS = manufacturing.
PHOTOSYNTHESIS is the process whereby
plants, algae and some bacteria, use the energy of
the sun to synthesize organic compounds
(sugars) from inorganic compounds (CO2 and
water). Basically, the light is transformed into
chemical energy.
2. General Equation of
Photosynthesis.
Carbon Dioxide + Water+ Light
CO2 + H2O+Light
H2O
Glucose + O2
C6H12O6 + O2 +
pigments, enzymes
3. Where?
LEAVES:
„
Function: Photosynthesis
(food production for the
whole plant).
„
Blade: Flat expanded area
„
Petiole: stalk that connects
leaf blade to stem, and
transports materials
Typical Dicot
Leaf
4. Steps
1.Light dependent reaction
A. Absorption of light.
B. Transformation of light.
2.Light independent reaction
Fixation of carbon dioxide
and the production of glucose
1.
Light dependent reaction.
A. Absorption of Light.
ƒ
Light moves in waves, in energy units called
PHOTONS.
ƒ
Energy of a PHOTON inversely proportional to
its wavelength (the shorter the wavelengyh the
more energy it carries).
ƒ
Visible light (between UV and IR) occurs in a
spectrum of colors.
The electromagnetic spectrum
„ Absorption spectrum of
chlorophyll a: BLUE
& RED
„ Action spectrum of photosynthesis closely
matches absorption spectrum of
chlorophyll a, but not perfectly (due to
accessory pigments)
Accessory pigments like chlorophyll b and
carotenoids (beta-carotene, lycopene) absorb light
at different wavelengths, (extending the light
absorption range) and transfer the absorved
energy to chlorophyll a.
„The
combination of accessory pigments,
chlorophyll a and structural proteins make a
structure called the photosystem.
„There
are 2 photosystems in higher plants:
P680 and P700
Chlorophyll a is the primary
photosynthetic pigment that drives
photosynthesis.
Accessory pigments absorb at
different wavelengths,
extending the range of light
useful for photosynthesis.
The transformation of light.
1. Occurs in the thylakoid membrane of
chloroplasts. Here, the light is absorbed by all
the pigments and transferred to chlorophyll a.
Chlorophyll a transform the light energy into
chemical energy.
2. Use light energy (photons) to generate two
chemical energy compounds: ATP & NADPH
(carrier of H).
3. Water is split into oxygen gas O2 and H+
Light Independent Reactions
„
1. Light independent (can occur in light or
dark; some enzymes require activation by
light).
„
2. Occur in the stroma of chloroplasts
„
3. Use the chemical energy produced in
the Light Reactions (ATP; NADPH) to fix
CO2 to carbohydrate (sugar).
4. The enzyme RUBISCO is the main enzyme
that catalyzes the fixation reaction.
RUBISCO: Is the most abundant protein on
earth!
5. Fixation is the transformation of inorganic
carbon into the organic carbon of glucose.
WHY IS PHOTOSYNTHESIS
SO IMPORTANT?
PHOTOSYNTHESIS is one of the most
important biological process on earth!
„ Provides the oxygen we breathe
„ Consumes much of the CO2
„ Food
„ Energy
„ Fibers and materials