Topic 06
Photosynthesis
I. Nutrition
A. Types of Nutrition
– 1. Autotrophic nutrition - organisms make
their own food through the process of
photosynthesis or chemosynthesis includes plants and algae
– 2. Heterotrophic nutrition – organisms
cannot make their own food – must get
food from an outside source

B. Photosynthesis
– 1. Process by which the energy of light is
converted to the chemical bond energy of
organic compounds (glucose-food)
– 2. Importance of photosynthesis - source of
oxygen and food for other organisms
– 3. Photosynthetic pigments - organelles known
as chloroplasts contain the photosynthetic
pigment chlorophyll (green) – capture energy
from light – all colors except green – green light
is reflected
Structure of
chloroplasts
More views of
chloroplasts
– 4. Chemical process - carbon dioxide and
water are the starting materials - the end
products are glucose, water, and oxygen
- red and blue light work the best for this
process
5. Equation of photosynthesis
 6CO2 + 6H2O + light energy -> C6H12O6 +
6O2

An Overview of
Photosynthesis
II. Details of Photosynthesis –
occurs in two steps – the light
and dark reactions
 A.
Light reactions (photochemical) occurs in the grana – chlorophyll a
absorbs light energy which is used to
break apart water molecules in a
process known as photolysis - some of
the light energy is used to make ATP
Antennae pigments – absorb other
wavelengths of light – transfer energy to
chlorophyll a – examples are carotene,
chlorophyll b, xanthophyll
1.

2. Chlorophyll a is used by two complex
systems called photosystem I and
photosystem II – when light particles called
photons strike chlorophyll, electrons are
excited and transferred through the
photosystems to a reaction center
B. The reactions of photosynthesis can be
called photophosphorylation and are
grouped into two types of reactions using
the two photosystems – I and II and also
the process can be cyclic and noncyclic
cyclic – conducted by PSI – contribute to
the ATP production but not to the production
of NADPH
(b) noncyclic – requires both PSI and PSII –
produces ATP, NADPH, and Oxygen
(a)
C. Noncyclic – most common – uses
photosystem I and II
1. Photosystem II – also called P680 because
of the wavelength of light absorbed - begin with
the excitement of chlorophyll in photosystem II –
excited chlorophyll then sends the electron
through a redox reaction - makes ATP – at the
end, the electrons are donated to photosystem I
which will excite the electrons and use their
energy to make NADPH
Noncyclic flow
2. Photosystem I – also called P700
because of the wavelength of light
absorbed chlorophyll is excited, the
electron passes to a system of
electron carriers - NADPH is created
Noncyclic flow
cyclic – photosystem I only - used
to make ATP – at the end of the chain
– if there is not enough ATP, the
electron is given back to chlorophyll to
be excited once again – it is a cycle
 D.
Cyclic flow
VCAC: Cellular Processes:
Photosynthesis: The Movie
E. Dark reactions - (carbon fixation) - do
not require light - occur in the stroma hydrogen atoms goes through a series of
changes that make PGAL (a three carbon
compound) - this will eventually form
glucose – series of oxidation and
reduction reactions – leo the lion goes
grrr
(Loses Electrons Oxidation)
(Gain electrons Reduction)
Phase 1 of the Dark
Reactions
Phases 1 and 2 of the
Dark Reactions
Phases 1, 2, and 3 of
the Dark Reactions
Dark Reactions
Photosynthesis
Light Reactions and
Dark Reactions