Transcript Photosynthesis - Tasker Milward

Photosynthesis
Mrs Martin
Plants and animals are dependent upon the products of photosynthesis.
They use the products of photosynthesis to for respiration
6CO2 + 6H2O (+ light energy) - C6H12O6 + 6O2
C6H12O6 + 6O2  6CO2 + 6H2O
Photoautotrophs and heterotrophs can release the chemical potential
energy in complex organic molecules during photosynthesis. They can also
use the waste product Oxygen produced by photosynthesis for aerobic
respiration.

Autotroph


Organisms that can produce their own complex
organic compounds, using light energy or chemical
energy, from inorganic sources.
Chemoautotroph

Prokaryotes that use the energy from exergonic
reactions (chemical reactions that release heat) to
synthesise complex organic compounds


Nitrifying bacteria that oxidise ammonia to nitrate or
oxidising nitrite to nitrate.
Bacteria using sulphur rich substances bubbling from the
vents of volcanoes. These bacteria help to support food
chains living in those areas.

Photoautotroph


Use the sun as their energy source and the
inorganic molecules carbon dioxide and water.
Most of the world’s food chains have
photoautotrophs as their producers
Heterotrophs

These organisms cannot make their own food and
are reliant on digesting other organisms to obtain
their complex organic molecules into more simple
soluble molecules. These simple molecules can
then be rebuilt to produce proteins, lipids and
nucleic acids.
Structure of the chloroplast
Chloroplasts- main regions

Stroma

Fluid filled matrix contains starch grains, oil droplets,
DNA and and prokaryote-type ribosomes


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Chloroplast DNA and ribosomes can make some proteins
needed for photosynthesis
Site of light independent reactions
Enzymes needed for these reactions are found here
Surrounds Grana so products of light dependent
reactions can easily pass into the stroma
Chloroplasts- main regions

Grana

Stacks of flattened membrane compartments –
thylakoids




Can only be seen using an electron microscope
Site of light dependent reactions


Up to 100 stacks
Provides large surface area for photosynthetic pigments,
electron carriers and ATP synthase (required for light
dependent reactions)
Light is absorbed and ATP synthesised
Contain Photosynthetic pigments arranged into
photosystems
Photosystem
Photosystem, a funnel
shaped light harvesting
cluster of photosynthetic
pigments held in place by
proteins in the thylakoid
membrane.
The primary pigment
reaction centre is a
molecule of Chlorophyll a.
The accessory pigments
consist of molecules of
chlorophyll b and
carotenoids.
Structure of chlorophyll a
Essential molecule in the
process of photosynthesis.
 Gives plants their intense green
colour
 When vegetation is cooked the
central magnesium is replaced
with a hydrogen ion. This
changes the colour of the
leaves

Chlorophyll a
Active
part
of
the
chlorophyll
molecule.
Central Mg bonded to 4 N
atoms. Changes in the
electrons in this part of
the molecule enable it to
absorb light very strongly
Hydrocarbon tail is
non-polar.
It is
hydrophilic
so
sticks
into
the
thylakoid
membrane
Photosynthetic pigments

Substances that absorb some
wavelengths of light and reflect others.

The colour they appear is the colour they
are reflecting
This light is reflected
Two forms of chlorophyll a
Pigments
P680 absorbs at 680nm- found in
photosystem II
P700 absorbs at 700nm- found in
photosystem I
Both also absorb blue light at around 450nm
Chlorophyll b absorbs around 500nm &
640nm
Carotenoids absorb blue light and reflect
orange/yellow light
Knowledge check
What is a chemoautotroph? Can you name an example
What type of trophic organism are the majority of food chains
reliant upon?
3. Name the membrane that makes up the grana
4. Suggest what this membrane is composed of
5. Suggest why scientists have proposed the idea of
endosymbiosis
6. State where the light independent reactions of photosynthesis
take place
7. Explain why the majority of plants are green
8. Suggest why in the autumn leaves may turn red
9. Explain how a chlorophyll molecule is adapted for its function
10. Describe how a photosystem is able to maximise the amount
of energy it can obtain from light
1.
2.
(a) The distribution of photosystems on granal and intergranal lamellae;
(b) Formation of ATP during non-cyclic photophosphorylation
(b)
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This document may have been altered from the original
The Z-scheme
© Pearson Education Ltd 2009
This document may have been altered from the original
Light dependent reactionsnon-cyclic photophosphorylation

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Light energy strikes photosystem II and cascades
through to the primary pigment reaction centre
If enough energy strikes the primary pigment molecule
the energy levels of a pair of electrons are raised. The
electrons leave the chlorophyll molecule to an electron
transport chain
As the electrons go down the electron transport chain
they lose energy which is used to convert ADP + Pi 
ATP
New electrons are needed to replace the electrons lost
from photosystem II
Photolysis of water
enzyme
H20  2H+ + 2e- + ½ O2
Protons
Used for NADP
Electrons used as a
Replacement for PS II
Waste product

Light energy also hits photosystem I. If
enough light hits the photosystem II electrons
are lost from the primary pigment centre.
 The electrons are replaced by the electrons
from photosystem II
 The electrons again leave to the electron
transport chain
 The electrons lose energy as they go down the
chain. This energy is used to make reduced
NADP (rNADP)
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons
NADP + 2H+ + 2e-
 Reduced NADP
Energy source
Protons from
photolysis
of water
From
Photosystem II
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons
REMEMBER!!!
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons
Cyclic Phosphorylation

Only photosystem I is used
 Excited electrons are passed to an electron
receptor and back to the chlorophyll molecule
from which they were lost


No photolysis of water
Small amounts of ATP are produced which maybe
used in photosynthesis or by guard cells to bring in
K ions lowering water potential and causing water
to enter by osmosis. This causes the guard cells to
swell and open, allowing exchange of gas.
Light dependent photosynthesis
The Z-scheme
© Pearson Education Ltd 2009
This document may have been altered from the original
(a) The distribution of photosystems on granal and intergranal lamellae;
(b) Formation of ATP during non-cyclic photophosphorylation
(b)
© Pearson Education Ltd 2009
This document may have been altered from the original
Week 10
•
Outline how the products of the light-dependent stage are used in the lightindependent stage (Calvin cycle) to produce triose phosphate (TP), referring
also to ribulose bisphosphate (RuBP), ribulose bisphosphate carboxylase
(rubisco) and glycerate 3-phosphate (GP).
•
Explain the role of carbon dioxide in the light-independent stage.
•
State that TP (and GP) can be used to make carbohydrates, lipids and
amino acids.
•
State that most TP is recycled to RuBP.
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Light independent photosynthesis
The reactions are not truly independent of light as the ATP and
rNADP could not be produced without light.
The light independent reactions occur within the stroma.
Carbon Dioxide is needed to produce all large organic molecules.
These molecules are used as structures or act as energy stores
or sources for all the carbon based life forms on this planet
Calvin Cycle
Inorganic form
Of Carbon
3CO2
Rubisco
2x Glycerate 3 phosphate GP
(2x 3C, not sugar)
5C acceptor
Ribulose bisphosphate
(RuBP) 5C Sugar
Now has carboxy group
This reaction is catalysed by Ribulose Bisphosphate Carboxylase
Oxygenase Rubisco. Described as the most important enzyme on
earth.
Read Stretch and challenge on page 65!
Calvin Cycle
ATP
ADP + Pi
GP
Reduced and phosphorylated
NADP
2x triose phosphate (3C)
Ose= sugar
rNADP
5 of every 6 molecules of TP are recycled by phosphorylation (using ATP
from light dependent reaction, to 3 molecules of RuBP (5C)
Calvin cycle
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This document may have been altered from the original
Limiting Factors

Lesson Objective
To discuss the factors that limit
photosynthesis
 Design an experiment to test one factor that
affects photosynthesis

Limiting Factors
 Law
 At
of limiting Factors states
any given moment, the rate of
metabolic process is limited by the
factor that is present at its least
favourable (lowest) value
Limiting factors
At any given moment,
the rate of metabolic
process is limited by the
factor that is present at
its
least
favourable
(lowest) value
Light Intensity
When light is the limiting factor the rate of photosynthesis is directly
proportional to the light intensity.
What does this mean?
Light causes the stomata to open so that Carbon dioxide can enter the
leaves
Light is trapped by chlorophyll where it excites electrons
It splits water molecules to produce protons
Electrons and protons are involved are involved in photophosphorylation
producing ATP for the fixation of carbon dioxide
Questions
1.
2.
3.
Which stage of photosynthesis will
affected by temperature? And why?
Why does light intensity affect the rate
of photosynthesis?
Why would burning an oil-fired stove in
a greenhouse increase the growth of
plants in a greenhouse?
Questions
1.


Which stage of photosynthesis will affected
by temperature? And why?
The light independent Calvin cycle.
As many of the reactions are catalysed by
enzymes, the rate rises between 0-25oC. At
the rate plateaus and fall as enzymes work
less efficiently and as oxygen competes
more successfully than carbon dioxide for
the active site of rubisco
Questions
1.
Which stage of photosynthesis will affected by temperature?
And why?
2.
Why does light intensity affect the rate of
photosynthesis?

Light is required for the light dependent phase, as
photons hit the photosystem electrons are excited
which then leave the photosystem via electron
carriers and passed along a series of protein
electron carriers which eventually produce ATP
and rNADP. A reduced light intensity will reduce
these levels. G3P will accumulate as it is not
reduced to triose phosphate (calvin cycle).
Ribulose bisphosphate levels will fall as it is not
being regenerated
Questions
1.
2.
3.
Which stage of photosynthesis will affected by temperature? And why?
Why does light intensity affect the rate of photosynthesis?
Why would burning an oil-fired stove in
a greenhouse increase the growth of
plants in a greenhouse


Burning hydrocarbons (oil, coal, natural
gas) will produce Carbon Dioxide
Burning fuel will also increase the
temperature of the greenhouse
Use your knowledge to explain the graph
Use your knowledge to explain the graph