Photosynthesis
THE BIG PICTURE
Scientists discovered that in the
presence of light, plants transform CO2 and water
into carbohydrates and release oxygen.
Carbon
WATER
_____________
+
____________
dioxide
6 CO2 + ____________
6 H2O
_____________
Sugars
Oxygen
_______________ + ____________
C6H12O+ 6____________
6 O2
→ _______________
PHOTOSYNTHESIS: Reactants & Products
LIGHT ENERGY
6CO2 + 6H2O
SUGAR + 6O2
In addition to water and carbon dioxide,
chlorophyll
__________________
and
light energy
__________________
are needed for photosynthesis
to happen.
Because light is a form
ENERGY any
of ___________,
molecule that absorbs
light also
ABSORBS
___________the
energy
from the light.
Pigments
• Chlorophyll A is the most important
photosynthetic pigment.
• The pigments are embedded in the membranes
of the chloroplast in groups called
photosystems.
SO WHAT WAVELENGTHS ARE
BEST FOR PHOTOSYNTHESIS?
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
THE ONES
CHLOROPHYLL
ABSORBS
THE BEST
red
________
and
_______________
Blue-violet
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
NEITHER
KIND OF
CHLOROPHYL
L IS VERY
GOOD AT
ABSORBING
_________
GREEN
LIGHT!
That’s why leaves LOOK
GREEN…..
Chlorophyll doesn’t absorb….
it ___________
REFLECTS GREEN light!
PHOTOSYNTHESIS OVERVIEW
Photosynthesis: The Chemical Process
• Occurs in two main phases.
– Light reactions
– Dark reactions (aka – the Calvin Cycle)
• Light reactions are the “photo” part of
photosynthesis. Light is absorbed by pigments.
• Dark reactions are the “synthesis” part of
photosynthesis. Trapped energy from the sun is
converted to the chemical energy of sugars.
PHOTOSYNTHESIS
Light
&
Water
Light-Dependent
Reaction
Oxygen
ATP
NADPH
Carbon
Dioxide
Light-Independent
Reactions
CALVIN CYCLE
(CH2O)n
Factors that Affect Photosynthesis
AMOUNT
OF WATER
____________________
Water is one of the raw materials needed, so
slow or stop
A shortage of water can ________________
photosynthesis
Desert plants and conifers
that live in dry conditions
have a waxy coating on
their leaves to prevent
water loss.
Factors that Affect Photosynthesis
TEMPERATURE
Photosynthesis enzymes function best
between 0° C - 35° C
At temperatures above or below this
range, photosynthesis will slow or
stop
Conifers in winter may carry out
photosynthesis only occasionally
Factors that Affect Photosynthesis
LIGHT INTENSITY
____________________
More light increases rate of photosynthesis
up to a certain level until plant reaches its
maximum rate of photosynthesis
THE BIG PICTURE
These experiments led to work by later
scientists who finally discovered that in the
presence of light, plants transform CO2 and water
into carbohydrates and release oxygen.
Carbon
WATER
_____________
+
____________
dioxide
6 CO2 + ____________
6 H2O
_____________
Sugars
Oxygen
_______________ + ____________
C6H12O+ 6____________
6 O2
→ _______________
THE BIG PICTURE
Why Should You Care?
•Photosynthesis is the process by which plants and few other
organisms use to transform light energy into chemical energy.
•Plants use chlorophyll to collect the energy from the sun rays
to create the food they need, the food we eat, the oxygen we,
all living creatures need to breath, and fossil fuels, like coal,
oil and gas that the industrialized world needs.
•Without this process, life on earth would end, and the only
organisms left would be the chemosynthesis bacteria.
•Photosynthesis is basic in the maintenance of life on earth.