Monday
COPY BAT:
Explain what is meant by oxidation and
reduction.
Explain how ATP is made during the lightdependent reaction.
Starter
Write down what you can remember about
oxidation and reduction reactions.
Oxidation - this is when a substance
combines with oxygen
•
The substance to
which oxygen has
been added is said to
be oxidised
•
When one substance
gains oxygen from
another, the one
losing the oxygen is
said to be reduced.
•
This process is known
as reduction.
Another way of looking at it ....
•
When a substance is
oxidised it loses
electrons
•
When a substance is
reduced it gains
electrons
•
This is in fact the
more usual way
to define oxidation
Oxidation and Reduction always take
place together.
•
Oxidation
results in energy
being given out.
•
Reduction
results in energy
being taken in
Write down the 3 ways that oxidation
and reduction can be described - copy
and complete table.
electrons
Oxidation
Reduction
hydrogen
oxygen
Gain of
oxygen
electrons
hydrogen
oxygen
Oxidation
Loss of
electrons
Loss of
hydrogen
Gain of
oxygen
Reduction
Gain of
electrons
Gain of
hydrogen
Loss of
oxygen
For GCSE Chemistry you may have learnt
OILRIG - Oxidation Is Loss (of electrons) Reduction Is Gain
The Making of ATP
•
When a chlorophyll
molecule absorbs light
energy it boosts a
pair of electrons in
the chlorophyll molecule
and raises them to a
higher energy level
•
These electrons are said
to be in an ‘excited’
state
The electrons become so excited that
they leave the chlorophyll molecule all
together.
•
They are taken up by a
molecule called an
electron carrier.
•
The chlorophyll
molecule has lost
electrons so we say it
has been __________.
•
The electron carrier has
gained electrons so it
has been __________.
The electrons are now passed along a
number of electron carriers in a series of
oxidation-reduction reactions.
•
These electron
carriers form a
transfer chain located
in the thylakoid
membranes.
•
Each electron carrier
is at a slightly
lower energy level
than the previous one
and so the electrons
lose energy at each
stage.
What is lost energy used for?
•
It is used to make
ATP
•
It is used to
combine an
inorganic
phosphate
molecule Pi with
a molecule of
ADP.
COPY BAT:
Explain the role of photolysis in the lightdependent reaction.
Describe how chloroplasts are adapted
to carry out the light-dependent reaction
Starter
Explain what is meant by ‘photolysis’.
The loss of electrons when light
strikes a chlorophyll molecule leaves it
short of electrons.
•
What would happen
if these were not
replaced?
If the chlorophyll molecule is to continue
absorbing light energy, these electrons
must be replaced.
•
The replacement
electrons are
provided from the
water molecules
that are split using
light energy.
•
This photolysis of
water also produces
hydrogen ions what is another name
for a hydrogen ion?
2H2O > 4H + + 4e- + O2
water
protons
•
The hydrogen ions or
protons are taken up
by an electron carrier
called NADP
•
As the NADP has had
hydrogen added to it we
say it has become
____________
electrons oxygen
The reduced NADP then enters the
light INDEPENDENT reactions
along with electrons from the
chlorophyll molecules.
•
The reduced NADP
(NADPH) is important
because it is a further
potential source of
chemical energy to the
plant.
•
What do you think
happens to the oxygen byproduct from the
photolysis of water?
It is either used in respiration or
diffuses out of the leaf as a waste
product of photosynthesis.
Label diagram ‘ Photosynthesis:
light-dependent stage’
Now answer the following questions
fully:
•
1. Where precisely within a plant cell are the electron
carriers involved in the light-dependent reaction found?
•
•
2. Describe what happens in the photolysis of water.
3. In each of the following, state whether the process
involves oxidation or reduction of the molecule
named:
.....................................................................
a) An unsaturated fat molecule gains a hydrogen atom.
b) Oxygen is lost from a carbon dioxide molecule
c) Light causes an electron to leave a chlorophyll
molecule.
Where does the light-dependent
reaction take place?
•
In the
thylakoids
of
chloroplasts.
How are chloroplasts adapted to their
function?
•
1. The thylakoid
membranes provide
a large surface area
for the attachment
of chlorophyll,
electron carriers
and enzymes that
carry out the lightdependent
reaction.
•
2. A network of proteins in the grana hold the chlorophyll
in a very precise manner that allows maximum absorption
of light.
•
3. The granal
membranes have
enzymes attached
to them, which
help manufacture
ATP.
4. Chloroplasts contain both DNA and
ribosomes - why is this useful?
•
So that they can
quickly and easily
manufacture
some of the
proteins needed
for the lightdependent
reaction
What is lost energy used for?
•
It is used to make
ATP
•
It is used to
combine an
inorganic
phosphate
molecule Pi with
a molecule of
ADP.
Other useful Sources
http://preuniversity.grkraj.org/html/7_PHOTOSYNTHESIS.htm
http://www.ftexploring.com/photosyn/chloroplast.html
http://youtu.be/C1_uez5WX1o - photosynthesis song
http://youtu.be/mYbMPwmwx88 - photosynthesis
http://www.biologymad.com/master.html?http://www.biologymad.com/A2Biology.htm photosynthesis and respiration
http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_1/
photosynthesis_1.html - Photosynthesis questions.
References
Glenn Toole, Susan Toole (2008). A2 Biology. Cheltenham: Nelson