Chapter 2.9
Photosynthesis
Victoria Barros
Understandings, Applications and Skills
2.9.U1 Photosynthesis is the production of carbon compounds in cells using light
energy
2.9.U2 Visible light has a range of wavelengths with violet the shortest wavelength
and red the longest
2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green
light more than other colours; visible light has wavelengths from 400-700 nanometres
2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water
2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from
carbon dioxide
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible
limiting factors on the rate of photosynthesis
2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to
photosynthesis
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for
photosynthesis
2.9.S2 Design of
experiments to
investigate the effect of
limiting factors on
photosynthesis; water
free of dissolved carbon
dioxide for
photosynthesis
experiments, can be
produced by boiling and
cooling water
2.9.S3 Separation of
photosynthetic pigments
by chromatograph;
paper chromatography
can be used to separate
photosynthetic pigments
but thin layer
chromatography gives
better results
2.9.U1 Photosynthesis is the production of carbon compounds in cells using
light energy
Photosynthesis – the synthesis of a complex organic material using CO2, H2O,
inorganic salts and light energy (natural sun light) captured by light-absorbing
pigments such as can be found in the organelle chloroplast
𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑤𝑎𝑡𝑒𝑟 → 𝑔𝑙𝑢𝑐𝑜𝑠𝑒 + 𝑜𝑥𝑦𝑔𝑒𝑛
6𝐶𝑂2 + 6𝐻2 𝑂 → 𝐶6 𝐻12 𝑂6 + 6𝑂2
Carbon Dioxide
Enters leaf
through stomates
by diffusion
+
Water
+
Light energy

Oxygen
+
Glucose
Transported to Absorbed by
chlorophyll in
leaf in xylem
chloroplast
The glucose produced in photosynthesis has three main uses:
1. Glucose is essential in cell respiration for energy release
2. Glucose is essential for cellulose production, which is essential in the cell wall
of a plant since its main component is cellulose
3. Glucose is essential for protein production including various enzymes and
chlorophyll
Glucose is stored in starch, as well as fats and oils.
Notes from Textbook 2.9
Photosynthesis – the production of carbon compounds in cells using light energy
 Through photosynthesis many living organisms obtain carbon compounds
necessary to build the structure of the cell as well as to carry out life processes
 It is an example of energy conversion from light energy to a variety of carbon
compounds including carbohydrates, proteins and lipids
 Always has a wastage of heat
Separating photosynthetic pigments by chromatography
The chloroplast in a plant
Pigment
Colour of Pigment Rf
cell is what allows photosynthesis
Carotene
orange
0.98
to occur. It contains several types
Chlorophyll a
blue-green
0.59
of chlorophyll as well as other
Chlorophyll b
yellow-green
0.42
pigments. The main pigment used
Phaeophytin
olive
green
0.81
is chlorophyll a, with additional
accessory pigments: chlorophyll b, Xanthophyll 1
yellow
0.28
caretonene, phaeophytin and
Xanthophyll 2
yellow
0.15
xanthophyll 1 and xanthophyll 2.
These pigments can be separated by simple paper chromatography. The procedure is
as follows:
1. Take a leaf or leaves of a certain kind and immerse it in boiling water for a
few seconds.
2. Grind the leaves into mush in order to dissolve the pigments, adding pure
acetone (propanone) to them.
3. Draw a line with a pencil on a chromatography paper (2-3 cm away from an
end) in order to indicate the mark of start.
4. Then with a capillary tube take drops of the solution of leaf pigments and
acetone ad carefully place on the center of line and dry with a hair dryer or a
heating lamp. Repeat for 15-20 minutes. Put aside.
5. Fill test tube with a solvent of acetone and petroleum, so it is just below the
pencil drawn on the chromatography paper.
6. Place the chromatography paper in the test tube and wait for 10-15 minutes,
which is enough time for the pigments to separate.
Rf Value
 Determines how light or heavy a pigment is (i.e. how far up the
chromatography paper a certain pigment travels)
 If the pigment is light it will travel higher on the chromatography paper
and it will have a high Rf value
 If the pigment is heavy it will travel lower on the chromatography paper
and it will have a low Rf value
 𝑹𝒇 =
𝒂
𝒃
Wavelengths of Light
 Visible light has a range of
wavelengths
 The shorter the
wavelength, the more the
frequency, the more
energy it has
 The longer the
wavelength, the less the
frequency, the less energy
it has
 The shortest wavelength segment are the gamma rays
 The longest wavelength segment are radio waves
 The wavelengths visible to the eye are those used in photosynthesis, which is
why they penetrate the earths atmosphere more abundantly
Light Absorption by Chlorophyll
 Chlorophyll absorbs red
and blue light most
effectively and reflects
green light more than
other colours
- This is why plants on
average are green,
since they contain
chloroplast with
chlorophyll, which
reflects green light
- Outer membrane is
permeable to small
ions
- Inner membrane is less permeable and has transport proteins embedded
in it
- Intermembranes space is around 10-20ηm
- Lamellae (a.k.a. thylakoids) are thin plates created from the inner
membrane folds
- Grana is the pile of stacked thylakoids in which the light-dependent
stage of photosynthesis takes place
 Absorbs light and makes ATP
- Integral lamellae are connections between the grana
-

Stroma is a fluid filled matrix inside the inner membrane in which the
light-independent stage of photosynthesis occurs
 The stroma contains starch grains, oil droplets, own chromosomal
DNA and ribosomes
The first stage of photosynthesis is the absorption of sunlight
- Involves chemical substances called pigments
- A white or transparent substance does not absorb visible light
- Pigments that do appear coloured to us therefore absorb light
- Pigments that absorb all of the colours appear black, because they emit
no light
- The pigments that aren’t absorbed, reflect that colour of wavelength,
which then is visible to the eye and thus the object possesses that colour
Oxygen Production in Photosynthesis
 Oxygen is produced in photosynthesis through photolysis
- Photolysis – the decomposition or separation of molecules by the action
of light
- In the case of photosynthesis the molecule being split up is water, in
order to release electrons needed in other stages
- 𝐻2 𝑂 → 4𝑒 − + 4𝐻 + + 𝑂2
- The oxygen produced in photolysis of water is therefore a waste product
and it diffuses away
Effects of Photosynthesis on Earth
 Changes to the Earth’s atmosphere, oceans and rock deposition occur due to
photosynthesis
 The first organisms to perform photosynthesis were prokaryotes, then joined by
algae and plants that have gets photosynthesis as the way they produce energy
 One of the consequences of photosynthesis is the rise on oxygen concentration
of the atmosphere
- Began 2,400 million years ago and is known as the Great Oxidation Event
- At the same time the Earth experienced its first glaciation, presumably
due to the reduction of the green house effect (more oxygen means less
carbon dioxide)
- Increase of oxygen caused oxidation of dissolved iron in the ocean
water, causing it to precipitate onto the sea bed
 A distinctive rock formation resulted called the banded iron
formation, with layers of iron oxide alternating with other
minerals
 For this reason currently there is an abundance of steel (thanks to
the photosynthesis of bacteria)
- Around 750 million years ago, as multicellular organisms began
developing the rate of increase of oxygen rose from 2% to 20%
Production of Carbohydrates
 Energy is needed to produce carbohydrates and other carbon compounds from
carbon dioxide
- Plants do this through photosynthesis from CO2 and H2O
-
Simplified equation:
𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 + 𝑤𝑎𝑡𝑒𝑟 = 𝑐𝑎𝑟𝑏𝑜ℎ𝑦𝑑𝑟𝑎𝑡𝑒 (𝑢𝑠𝑢𝑎𝑙𝑙𝑦 𝑔𝑙𝑢𝑐𝑜𝑠𝑒) + 𝑜𝑥𝑦𝑔𝑒𝑛
To carry out the process, energy is needed, making photosynthesis an
endothermic process
 That energy is obtained by absorbing light, thus the reason for
photosynthesis
⇒ Light energy is converted into chemical energy in the
carbohydrates
Limiting Factors
 Temperature, light intensity and carbon dioxide concentration are possible
limiting factors of the rate of photosynthesis
- These factors can limit rate if they are below the optimal level
- Usually only one factor at a time limits the rate, which is the factor
further away from the optimum
- If change the limiting factor closer to optimum, reaction rate will
increase
- If a non-limiting factor is changed then it will make no difference
2.9.U5 Energy is needed to produce carbohydrates and other carbon
compounds from carbon dioxide

Endothermic – the descriptive word used to describe reactions and process
that consume energy
 Why does photosynthesis need energy to produce the end products?
When the light-dependent reactions occur, they initially absorb light energy
and end up transforming it into chemical energy in the form of ATP and NADPH.
During this conversion, in particular during photolysis, as water is being split up,
the waste product ends up being oxygen. This oxygen accounts for one of the end
products of photosynthesis. The ATP and NADPH produced are essential in the
light-independent reactions (i.e. the Calvin Cycle) that occur in photosynthesis.
Firstly these energy-powered molecules are used in the reduction phase of the
Calvin Cycle when the 3-PGA (3 phosphoglycerate) is converted into G3P by
providing enough energy for the reaction to occur, yielding the molecule aiding in
the production of glucose, the direct product of photosynthesis. Secondly the G3P
not used for glucose production
is then with the help of ATP is
recycled and turned into the
initial reactant in the Calvin
cycle RuBP by regenerating the
molecule ribulose-5-phosphate
into ribulose-1,5-bisphosphate.
Thus ATP in this case gives not
only energy but also a
phosphate group needed to
recreate the original RuBP,
thus keeping the Calvin Cycle
repeating. The ADP and NADP+
generated in the process are
sent back into the lightdependent reactions, thus
aiding the process of photosynthesis.
Energy Used in Photosynthesis
The energy source in all types of photosynthesis is usually light energy, yet the
most common form of light energy comes from the sun, though sun light.
2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water
One use of the energy consumed in photosynthesis is the splitting of water
molecules. This essential step releases electrons, which are needed in other parts
of this process.
𝑯𝟐 𝑶 → 𝟒𝒆− + 𝟒𝑯+ + 𝑶𝟐

This process is called photolysis (in this case of water)
- Photolysis is needed in photosynthesis since in the reaction before in
which the excited electrons are produced, the electron move to the ETC
process and they need a balance thus the need to replace them. In
photolysis the light energy splits water molecules into protons (i.e. H +),
electrons as well as oxygen. However in this reaction oxygen isn’t
needed thus it exists the system using photosynthesis through gas
exchange.
2.9.S3 Separation of photosynthetic pigments by chromatograph
In class we took spinach leaves and carried out the procedure required for
chromatography. First we boiled water and dipped the spinach leaves in it. Then the
leaves were grounded up with a mortal and pestal, along with a few drops of pure
acetone. After we drew a line with a pencil on a chromatography paper, around 3cm
from one of the short edges, to indicate the starting point. Using a capillary tube, I
took in the liquid made by grinding of the spinach and put a drop in the center of the
pencil line. This action was repeated over the period of 10 minutes, and every time a
dot was added, it became more concentrated and was dried. Afterwards a test tube
was filled with a solution of acetone and petroleum, filling around 2cm of the test
tube from the bottom. The chromatography paper was placed in the test tube and
allowed to absorb the solution for around 10-20min. Finally the paper was taken out
and analysed.
What we found was that the solution, as it travelled up the paper separated
the different pigments in the leaves, thus showing that different pigments absorb
different colours, since every pigment has a different colour. The lighter pigments
travelled further up the paper while the heavier pigments did not.
2.9.U2 Visible light has a range of wavelengths with violet being the
shortest wavelength and red being the longest
2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects
green light more than other colours
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action
spectrum for photosynthesis
Light from the Sun is composed of a range of wavelengths (i.e. a range of colours).
Th
Wavelength
10-400
450-500
500-570
625-700
800e
(ηm)
1,000,000 ran
Name
Ultraviolet Visible light
Visible light
Visible light
Infra-red
ge
(indigo: 445- (green: 490- (orange: 570of
475ηm, blue: 520ηm and
620ηm and
wa
475-490ηm, yellow: 520red: 590vel
and green:
570ηm)
700ηm)
eng
490-510ηm)
ths
Does
No
Yes
No
Yes
No
of
Photosynthesis
visi
occur?
ble
It is visible?
No
Yes
Yes
Yes
lig
Energy
Very high --------------------------------------------------Low
ht
Frequency
Very high --------------------------------------------------Low
occ
upies, is from 400-700ηm.




Ultraviolet light: A light that has a wavelength from 10-400ηm that has a very
high frequency and energy, yet isn’t visible to the human eye
- These light are too short to see, yet we know they are there since these
are the lights that tan human skin and burn it, at times leading to skin
diseases such as skin cancer
Infrared light: A light that has a wavelength from 800-1,000,000ηm that has a
very low frequency and low energy, that isn’t visible to the human eye
- These lights are too long to see, but we know they are there since they
can be felt in the form of heat from things such as a campfire or a stove
The main photosynthetic pigment that is active during photosynthesis is called
Chlorophyll A
- Chlorophyll A, along with other photosynthetic pigments, is found in the
chloroplasts, in the thylakoid membrane.
 In leaves, the chloroplast is most active in photosynthesis in the
mesophyll tissue of the leaf
Action spectrum: A graph which indicates which wavelength of light can be
used by a plant to allow photosynthesis


Absorption spectrum: A graph that indicates the amount of light and to what
extent absorbed plotted against the frequencies, colours, wavelengths, etc.
GRAPH: Absorption and Action Spectra for Chlorophyll
100
% Use of Absorbed
Light
100
100
100
100
100
100
400
500
600
Wavelength of Light (ηm)
700
800
2.9.U5 Temperature, light intensity and carbon dioxide concentration are
possible limiting factors on the rate of photosynthesis
Light Intensity
% Absorption of Light
100