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Lesson Overview
Photosynthesis: An Overview
Lesson Overview
8.2 Photosynthesis:
An Overview
Lesson Overview
Photosynthesis: An Overview
Light and pigments
•Energy from the sun travels
to Earth in the form of light.
•Sunlight is a mixture of
different wavelengths.
• The wavelengths we see is
known as the visible
spectrum:
• The colors of the visible
spectrum are red, orange,
yellow, green, blue, indigo,
and violet.
Lesson Overview
Photosynthesis: An Overview
• Plants gather the sun’s energy
with light-absorbing molecules
called pigments.
• Chlorophyll – absorbs all
colors in light but reflects
green (so, plants appear
green)
• Chlorophyll is the main
pigment in plants
• Carotenoids (Carotene) an accessory pigment in
plants that absorbs all light
except for red, orange, or
yellow (usually seen in
Autumn leaves)
Lesson Overview
Photosynthesis: An Overview
Pigments
We see the green
colors of plants most of
the time, because the
green color of the
chlorophyll overwhelms
the other pigments.
As temperatures drop,
chlorophyll molecules
break down, the red and
orange pigments may be
seen.
Pigments absorb the
light energy needed for
photosynthesis.
Lesson Overview
Photosynthesis: An Overview
The Chloroplast
Structure
• Grana - Stacks of
membrane sacks (singular
= Granum)
• Thylakoid – the individual
membrane sacks of grana
• Chlorophyll is located
on membrane of
thylakoid, where light
absorption occurs
• Stroma – fluid space
surrounding grana
http://www.youtube.com/watch?v=scl
K6duS9zQ
Lesson Overview
Photosynthesis: An Overview
The Process of Photosynthesis
2 Steps:
1. Light-dependent reactions – uses sunlight to produce two
energy carriers: NADPH and ATP
2. Light-independent reactions – uses carbon dioxide (CO2)
to produce glucose, using energy from NADPH and ATP
(from step 1)
Lesson Overview
Photosynthesis: An Overview
1. Light-dependent Reactions
• Requires sunlight to work
• Occurs on the membrane
of the thylakoid in the
chloroplast
• Clusters of chlorophyll,
called photosystems,
absorb sunlight and excite
electrons
• Water is required as a source
of electrons and hydrogen
ions.
• Oxygen is released as a
byproduct (waste).
Lesson Overview
Photosynthesis: An Overview
• Electrons are passed
along a chain of
molecules
• Energy from this is
used to produce
2 molecules:
• NADPH is made
from NADP+
• ATP is made
from ADP
Lesson Overview
Photosynthesis: An Overview
High-Energy Electrons (R-Track)
• NADP+ (nicotinamide adenine dinucleotide phosphate)
is a carrier molecule.
• NADP+ accepts and holds two high-energy electrons,
along with a hydrogen ion (H+). In this way, it is
converted into NADPH.
Lesson Overview
Photosynthesis: An Overview
2. Light-independent reactions-No light required
• Also called the Calvin Cycle
• Calvin Cycle- a series of reactions that produces the organic
molecule (carbohydrates).
• Occurs in the stroma (open space) of the chloroplast
• The light-independent reaction is a continuous chain of
chemical reactions in which energy is used to convert CO2
into glucose
• ATP and NADPH molecules produced in the lightdependent reactions are used to produce high-energy
sugars (carbohydrates) from carbon dioxide (in the air).
Lesson Overview
Photosynthesis: An Overview
Lesson Overview
Photosynthesis: An Overview
An Overview of Photosynthesis
(you must know this equation!)
• Reactants: carbon dioxide & water
• Products: sugar (carbohydrates) & oxygen
Photosynthesis uses the energy of sunlight to convert water and
carbon dioxide into high-energy sugars and oxygen.
Light
• In symbols: 6 CO2 + 6 H2O -------> C6H12O6 + 6 O2
Light
6 molecules Carbon dioxide +6 molecules Water ----> 1 molecule Sugar + 6 molecules Oxygen
Lesson Overview
Photosynthesis: An Overview
Summary of Photosynthesis (Do not Write)
Stage 1
 Light energy is
captured
Lesson Overview
Photosynthesis: An Overview
Summary of Photosynthesis (Do not Write)
Stage 2. Light energy is used to make ATP & NADPH
CO2 + H2O
Photosynthesis
Carbs
Proteins
Lipids + O2
Cellular (Aerobic)
Respiration
(ATP Produced)
Lesson Overview
Photosynthesis: An Overview
Summary of Photosynthesis (Do not Write)
Stage 3. ATP & NADPH are
used to power the
manufacture of energy rich
carbohydrates using CO2 from
the air
Lesson Overview
Photosynthesis: An Overview
An Overview of Photosynthesis
Lesson Overview
Photosynthesis: An Overview
Photosynthesis animation
http://www.youtube.com/
watch?v=1gLa5EWn9OI
Lesson Overview
Photosynthesis: An Overview
Factors Affecting Photosynthesis
Factors that affect photosynthesis are:
• Temperature: enzymes that affect
photosynthesis function best between 0°C
and 35°C.
• Light intensity: High light intensity increases
the rate of photosynthesis
• Availability of water: a shortage of water can
slow or even stop photosynthesis.
Lesson Overview
Photosynthesis: An Overview
Photosynthesis Under Extreme Conditions
Plants that live in dry
conditions:
• Often have waxy
coatings on their
leaves to reduce
water loss.
• C4 and CAM plants
have biochemical
adaptations that make
photosynthesis more
efficient under dry
conditions.
plants in dry conditions adaptations
Lesson Overview
Photosynthesis: An Overview
C4 Photosynthesis
•“C4 plant”-named from the
fact that the first compound
formed in this pathway
contains 4 carbon atoms.
•They can capture even
very low levels of carbon
dioxide and pass it to the
Calvin cycle (where
carbohydrates are formed).
•Require extra ATP to
function.
•C4 organisms include crop
plants like corn, sugar cane,
and sorghum.
sugar cane
sorghum
corn
Lesson Overview
Photosynthesis: An Overview
CAM Plants
• Use a process called
Crassulacean Acid
Metabolism (CAM) to make
carbs.
• At night, they take in CO2 to
produce organic acids,
“trapping” the carbon within
the leaves.
• In the daytime, when leaves
are tightly sealed to prevent
water loss, these compounds
release carbon dioxide,
enabling carbohydrate
production.
• Ex. pineapple, many desert
cacti, and “ice plants”.
pineapple
cacti
ice plants