Photosynthesis
Photosynthesis Overview
Objectives
Explain the role of light and pigments
in photosynthesis
Explain the role of electron carrier
molecules in photosynthesis
State the overall equation for
photosynthesis
Think About It
How would you design a system to
capture the energy of sunlight and
convert it into a useful form?
Caution: solar panels are not very
effective or cheap
Photosynthesis Defined
Is the process by which autotrophs use
the energy of sunlight to produce highenergy carbohydrates (sugars and
starches) that can be used as food
From the Greek words “photo,” which means
_____ and “synthesis,” meaning
____________
In other words, it is _____________
In the process of photosynthesis, plants
convert the energy of sunlight into
chemical energy stored in the bonds of
carbohydrates
Light & Pigments
Visible light from the sun is in a
__________ but perceived as “white”
When separated by a prism, it is red at
one end and violet at the other
When light strikes an object it can be
_______, ________, or ________
Pigments are organic compounds within
objects that absorb light
Visible Light Spectrum
Photosynthetic Pigments
There are 3 main kinds of photosynthetic
pigments in living things
1. Chlorophylls—green pigments
 Chlorophyll a is found in all plants, algae and
cyanobacteria
 Chlorophyll b is found in all plants and green
algae
 Chlorophyll c is found in diatoms and brown
algae
 Chlorophyll d is found in red algae
Photosynthetic Pigments
2. Carotenoids—red, orange, or yellow pigments
 Carotene is found in most plants and some
algae
 Carotene gives carrots their color
 Fucoxanthin is found in brown algae and
diatoms
3. Phycobilins—blue or red pigments
 Phycobilins are found only in red algae and
cyanobacteria
 Some phycobilins are fluorescent
Chlorophylls
Chlorophylls are located in the chloroplasts
Chlorophylls absorbs light very well in the
_____ and _____ regions of the spectrum
They do not absorb light in the _____ region
of the spectrum
The 2 most common types are chlorophyll a &
chlorophyll b
Chlorophyll a is the main pigment responsible
for capturing light
Chlorophyll b is an accessory pigment
Carotenoids provide the yellow, orange and
brown pigment colors seen during the fall
Think About It
So, why are plants green?
Why do leaves turn colors in the fall?
HINT: explain your answers in terms
of light absorption and reflection
Parts of the Chloroplast
1. Outer membrane
2. Inner membrane
3. Thylakoids: system of membranes
arranged in flattened sacs
4. Grana: are stacks of thylakoids
(Granum s.)
5. Stroma: is the aqueous solution
surrounding the grana
High-Energy Electrons
Are produced by chlorophyll and are
____________
They require a special electron carrier
molecule
An electron carrier is a compound that
can accept a pair high-energy electrons
and transfer them, along with most of
their energy, to another molecule
The main carrier molecule in
photosynthesis is ________
NADP+
Is also known as nicotinamide
adenine dinucleotide phosphate
Its job is to accept and hold 2
high-energy electrons, along with a
hydrogen ion (H+)
Once it has done this, NADP+ coverts
to _________
This conversion allows some of the
energy of sunlight to be trapped in
chemical form
Overview of Photosynthesis
Reactants
Products
Photosynthesis Equation
Light Energy
6 CO2
6 H2O
Carbon
Dioxide
Water
C6H12O6
6 O2
Glucose
Oxygen
Two major steps
1. Light-dependent reactions
 AKA _____________
 Use energy from sunlight to produce
energy-rich compounds such as ATP
 Take place in the ________ of the
_________ of the chloroplasts
 Water is a requirement as it is the
source of electrons and hydrogen ions
 Oxygen is released as a __________
Two major steps
2. Light-independent reactions
 AKA The Calvin Cycle, the Calvin-Benson
cycle, and the dark reactions
 ATP and NADPH molecules are used
to produce high-energy sugars from
carbon dioxide
 No light is required for this step and
its takes place in the ________ of
the chloroplasts
Photosynthesis: An Overview
Chloroplast
Light
CO2
NADP+
ADP + P
Calvin
Cycle
Light
Reactions
ATP
NADPH
O2
Sugars
1. Where does ALL energy
for life come from?
TURNING LIGHT ENERGY
INTO CHEMICAL ENERGY
2. In what cellular
structure does it
happen?
The Importance of Chlorophyll
3. Explain the importance of
chlorophyll.
What color is it and why is
that so?
What is its role in
photosynthesis?
4. Name the requirements of
photosynthesis.
5. Name the products of
photosynthesis.