Unit 1 Learning Outcomes
Section B- Photosynthesis
Content
Notes
PART 1
A. The role of light and photosynthesis Light hitting a leaf is either transmitted
pigments.
(passed through the leaf), reflected
(bounces off of the leaf surface) or
LO 1. State three possible fates of light absorbed.
striking a leaf, explaining that each term Most of the light that is absorbed is
means.
converted to and lost as heat. Only some
of the light that is absorbed can be
used for photosynthesis.
White light is made up of lights of
LO 2. Explain that light is a mixture of different wavelengths. Each wavelength
different colours which form a spectrum.
is a different colour and has a different
energy level. The range of colours is
called the Spectrum.
LO 3. Name the 4 major pigments found in Light is absorbed by special chemicals
chlorophyll.
called Photosynthetic Pigments. These
pigments are found in the chloroplasts.
LO 4. Name the mineral element which is an The main photosynthetic pigment is
essential part of a chlorophyll molecule.
called Chlorophyll.
Extra
B. Role of chlorophyll and other
photosynthetic pigments
There are two forms of chlorophyll:
Chlorophyll a and Chlorophyll b. There
are another two pigments called
accessory pigments. These are known as
Carotene and Xanthophyll.
LO 5. State the parts of the spectrum which Each pigment absorbs some wavelengths
are used in photosynthesis.
of light more than others. This is called
the Absorption Spectrum.
The main wavelengths of light absorbed
LO 6. Explain why leaves are green.
are red and blue. Green is absorbed the
least, giving leaves their green colour.
LO 7. Explain what is meant by an absorption The Action Spectrum for a plant shows
spectrum and an action spectrum.
how much photosynthesis occurs in each
light colour in the spectrum. The action
spectrum is similar to the absorption
spectrum for all the photosynthetic
pigments combined.
Once the red and blue light is absorbed
it is converted into chemical energy.
This chemical energy is used to
regenerate ATP and to split water.
The accessory pigments absorb other
wavelengths of light and pass the energy
onto chlorophyll.
C. Separation of photosynthetic pigments by
means of chromatography.
LO 8. Describe a method for extracting and
separating pigments from a plant’s leaves,
including the names of appropriate solvents.
LO 9. Identify the 4 major pigments of
chlorophyll from their positions in a
chromatograph.
Chromatography is used to separate out
the photosynthetic pigments.
1. leaf is ground with acetone to
dissolve the pigments.
2. filtering separates the cell debris
from pigment solution.
3. concentrated spot of pigment
built up near the bottom of the
chromatography paper.
4. the
pigments
separate
as
chromatography solvent (acetone
and petroleum ether) rises up the
paper.
5. The pigment that dissolves best
in the solvent rises highest.
Rf value for each pigment can be
calculated by dividing the distance
moved by the pigment by the distance
moved by the solvent front.
PART 2
D. The light dependent stage and carbon
fixation.
The detailed structure of chloroplasts should
be related to the stages of photosynthesis.
Chloroplasts are disk shaped organelles
LO 10. Describe and draw a chloroplast enclosed in a double membrane. The
organelle showing details of the membrane and grana are stacks of discs containing the
photosynthetic pigments where the light
internal structures.
dependent stage takes place.
E. The location and significance of the light
The lamellae are a network of
dependent stage.
membranes joining the grana together,
they keep the grana in position to make
LO 11. State that photosynthesis consists of 2 sure they get maximum light absorption.
The stroma is the enzyme rich fluid
reactions and give their names.
which fills the rest of the chloroplast
LO 12. State in which part of the chloroplast and is the site of the Calvin cycle.
The chloroplast may also contain starch
each reaction of photosynthesis occurs.
grains. Starch grains are the storage
products of photosynthesis.
The light dependent stage occurs inside
the grana of the chloroplast. Energy
from light absorbed by chlorophyll and
converted into chemical energy.
F. The production of ATP and hydrogen (for This chemical energy is used to split
the use in carbon fixation).
water into hydrogen and oxygen. This is
called Photolysis. The energy is also
LO 13. Describe the light stage of used in the synthesis of ATP from ADP
photosynthesis (where it takes place, raw and Pi.
materials, products, name the hydrogen The hydrogen released during photolysis
carrier, the energy change, equation)
combines with the hydrogen carrier
NADP
(nicotinamide
adenine
dinucleotide phosphate) which becomes
NADPH2 and is used in the Calvin cycle.
The oxygen produced is released as a
by-product.
The ATP produced is used to supply
energy for carbon fixation in the Calvin
cycle.
G. The location and significance of carbon
fixation (Calvin cycle)
LO 14. Describe the second stage of
photosynthesis (where it takes place, raw
materials, products, the 3 intermediates in
the cycle, the number of carbon atoms in each
intermediate, draw the cycle)
Carbon fixation takes place in the Calvin
cycle in the stroma of the chloroplast.
The Calvin cycle is a sequence of enzyme
controlled reactions that produce
glucose by the reduction of carbon
dioxide.
The requirements for the Calvin cycle:
ATP from light dependent stage,
hydrogen from the photolysis of water
and
carbon
dioxide
from
the
atmosphere.
H. The production of glucose as a result of an
enzyme-controlled sequence of reactions
requiring ATP, hydrogen (from photolysis) and
carbon dioxide.
Carbon dioxide combines with the 5
carbon RuBP (ribose bisphosphate) to
form an unstable 6 carbon compound.
This then breaks down to form 2
molecules of 3 carbon GP (Glycerate-3LO 15. Explain what happens to glucose formed phosphate).
in photosynthesis.
Some of the GP is converted into 6
carbon glucose, the rest is used to
regenerate RuBP to continue the cycle.
LO
16.
Complete
photosynthesis.
the
equation
for
LO 17. Describe what is meant by a limiting
factor and state the limiting factors for
photosynthesis.
The conversion of GP requires both
hydrogen and ATP. Glucose may be
converted to starch for storage.