Photosynthesis
+ 6H2O + 6CO2  C6H12 O6 + 6O2
Reactants
Products
Light Energy + Water + Carbon Dioxide yield Glucose + Oxygen
Early Scientific Research on
Photosynthesis
 1643 – Belgium
 Jan van Helmont
 With your group:
analyze van
Helmont’s
experiment
Conclusions from van
Helmont’s experiment
 “…164 pounds of wood, bark, and roots had arisen
from water alone.” The mass of the tree did NOT come
from the soil.
Partially correct
 Was van Helmont correct? _____________________
 The mass of a plant comes in part from water…NOT
from soil (except for a tiny fraction)
 Plants are made of carbohydrates. The term “hydrate”
= water.
Late 1700’s England
Joseph Priestley
 Joseph Priestley
discovered oxygen
in 1774
 He continued to
experiment with
gases, plants and
animals.
With your group
analyze Priestley’s
experiment!
Priestley’s Photosynthesis
Experiment
 Priestley concluded
green plants
produce “oxygen”,
which is necessary
for a fire to burn and
animals to breathe.
Late 1700’s Jan Ingenhousz’s
 Jan Ingenhousz was born in
1730 in the Netherlands. He
trained as a medical doctor.
 In 1779, Ingenhousz took a
position in the same
laboratory as Joseph
Priestley.
 Ingenhousz carried out
research on photosynthesis.
Ingenhousz’s Photosynthesis
Experiment
 Ingenhousz placed a pond
plant in a jar filled with water
 He placed the jar in bright
sunlight and observed
bubbles produced by the
plant
 He placed the jar in low light
conditions and observed no
bubbles produced by the
plant
Ingenhousz’s Photosynthesis
Experiment
 Ingenhousz knew the bubbles produced by
plants are made of oxygen gas.
 He concluded that oxygen is only produced if
the green plant is in the presence of
Light
__________.
Photosynthesis
 By the mid-1800’s, it was understood that plants
produce glucose (a type of carbohydrate) and oxygen
using light energy and carbon dioxide and water.
 Photosynthesis Reaction:
6CO2 + 6H2O +
 C6H12O6 + 6O2
Light
 When all colors within white light are reflected back to
our eyes  we see WHITE!
 When all colors within white light are absorbed by an
object  we see BLACK!
 A surface appears a particular color because it contains
a "pigment" that reflects that particular color and
absorbs all other colors.
 Pigment = light absorbing colored molecule*
Name the color
 What is the color of a sweater that absorbs blue, green
and yellow light? (Hint: Which color is NOT absorbed
but instead must be reflected?)
Which color is reflected by
this sweater?
Name the color
 What is the color of a pair of jeans that absorbs all
colors of the rainbow?
Which color is
reflected by the
jeans?
NONE!
What colors are absorbed by
Green Plants?
Green Plants
 Reflect green light
 Absorb all other colors of light
Green Plants
Photosynthesis
 If organisms make their own food they are called
autotrophs
Or
 Organisms EAT plants or animals and are called
heterotrophs
__________________________________
Photosynthesis
 Autotrophs use light energy from the sun (or chemical
energy) to produce energy rich sugars/carbohydrates.
Examples of autotrophs:
green plants
some protista
_____________________,________________,
some bacteria
____________________________
 Energy in most ecosystems on earth comes from
Photosynthesis
 CO2 enters
plants
through
stomata in
leaves and
stem.
 O2 and water
exit the
stomata*
Carbon Dioxide
Water
 H2O enters plants through roots and is carried by the
veins to leaves
Water travels
through the
plant’s xylem
(upward veins)
from the roots
to the leaves
Products of Photosynthesis
 Glucose and Oxygen
 Glucose is carried from the
leaves of the plant in phloem
(downward veins) to the
parts of the plant where
photosynthesis does not
occur (roots, flowers).
 Glucose is stored in fruits
(apples, oranges, etc.) and
roots (onions, potatoes, etc.)
 Oxygen is released from
stomata.
Photosynthesis
 Complete worksheet on Green Plants!
What else is needed for
Photosynthesis?
Chloroplast

 Photosynthesis occurs in the chloroplasts of plant cells.
Chloroplasts are made of
 thylakoids – sac-like membranes containing molecules
of chlorophyll, a pigment, which absorbs red and blue
light.
 stroma – space outside of the thylakoids
• Some plants contain pigments
that reflect yellow and red.
• In the fall, the chlorophyll pigment
breaks down, and the other colors
are revealed!
If plants contain chlorophyll
why do they turn color in the
fall?
Processes of Photosynthesis
 Two Stage process:
 Light DEPENDENT reaction and
 Light INDEPENDENT reaction or CALVIN CYCLE
LIGHT DEPENDENT
REACTION
 Occurs only in light!
 Takes place in the thylakoid 
this is where chlorophyll is
found
Light Dependent Reaction
 H2O enters the thylakoid
 Chemical bonds holding H2O together are broken apart
and H+ and oxygen molecules are released
Water 
+
H
+ O2
 H+ ions are used in making glucose.
 O2 is released through stomata. This is the oxygen we
breathe.
Light Dependent Reaction
(cont)
 Light energy enters the thylakoid
 This energy is converted into chemical energy and is
stored in two chemical compounds:
 ATP (Adenosine Triphosphate) converted by light energy from

ADP (low energy)
NADPH converted by light energy from NADP+ (low energy)
 Note: The light energy hasn’t been created or destroyed by
the plant, but it has changed forms.
 TO DO: Complete a-m Light Dependent Reaction section
of Photosynthesis Worksheet!
Fact Check – Light
Dependent Reaction (p. 4)
1. In which part of the chloroplast does the light dependent
reaction occur?
thylakoid
2. Which two high energy molecules are produced using the
light energy from the sun?
ATP and NADPH
3. What is the “waste product” of the light dependent
reaction? oxygen
4. How does this waste product exit plant cells?
stomata
5. Which part of the water molecule is used to make a
molecule of glucose?
Hydrogen ions
6. What is the role of sunlight in the process of
photosynthesis?
Produces ATP
Light Independent Reaction or
Calvin Cycle
1. Occurs in stroma – the space surrounding the
thylakoid membranes
2. Takes place in light OR dark
Light Independent Reaction or
Calvin Cycle
3. CO2 enters chloroplasts through stomata.
4. Energy stored during the light dependent reaction
(ATP and NADPH) is used to convert
CO2+ H+ (from water)  C6H12O6
Light Independent Reaction or
Calvin Cycle
Chemical Energy in ATP + NADPH
H+ + CO2  Glucose
Low energy bonds in CO2
High energy bonds in glucose
ATP (high energy molecule)  ADP (low energy molecule)
NAPDH (high energy molecule)  NADP+ (low energy molecule
TO DO: Complete n-v Light Dependent Reaction section of
Photosynthesis Worksheet!
Fact Check – Light
Independent Reaction
1.
In which part of the chloroplast does the light independent
reaction occur? stroma
2.
What is another name for the Light Independent Reaction?
Calvin Cycle
Why is it called the Light Independent Reaction?
3.
Occurs with or without sunlight
4.
Which molecule is added to H+ (from the light dependent
reaction) to make glucose? CO2
5.
How does the molecule referred to in #4 enter the chloroplast?
stomata
Which molecule is used to provide the chemical energy for the
high energy bonds holding glucose molecules together? ATP
6.
Energy Molecules
 ADP charged up by light energy to
produce ATP
 NADP+ charged up by light energy to
produce NADPH
Factors affecting
Photosynthesis
1. Light - Absence of light  no photosynthesis
Factors affecting
Photosynthesis
2 Increase in light intensity increases rate of reaction (up
to a point—this point is dependent on the particular
species of plant)
3 Water - Absence of water slows or stops the process
Factors affecting
Photosynthesis
4. Temperature – Photosynthesis does NOT occur if it is
below the freezing point (0°C or 32°F) or above
35°C/95°F.
Would you expect a shortage of CO2 to be a problem for
plant growth on earth? Why or why not?
Environmental Factors
Affecting Photosynthesis
 Complete worksheet “Energy in a Cell”: Critical
Thinking and Problem Solving