Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Photosynthesis

Overview
• Light is harvested and converted into chemical energy and molecules used to make
ATP during respiration
...

• Leaf is main photosynthetic structure in eukaryotic plants
...


Structure of the Leaf: Adaptations
Raw materials: water, carbon dioxide and light
Waste products: oxygen and glucose

Trait
Benefit
Large SA
To Absorb as much light as possible
Arrangement
Minimise overlapping avoiding shadowing
of leaves so all obtain sunlight
Thin
Most light is absorbed in first few
micrometres so diffusion distance is short
Transparent Cuticle and Epidermis
Let light through to photosynthetic
mesophyll cells beneath
Long and Narrow
Upper mesophyll cells packed with
chloroplasts that collect sunlight
Numerous Stomata that Open and
All mesophyll cells are only a short diffusion
Close
pathway away and can respond to changes
in light intensity and many
Many Air Spaces
In lower mesophyll to allow rapid diffusion
in gas phase of CO2 and O2
...

• Surrounded by a double membrane
...

• Protein + Pigment = Photosystem
• There are 2 types of photosystems
...
Photosystem II (PSII) absorbs light best at 680nm
...
Only
chlorophyll a can participate directly in light reaction of photosynthesis the
accessory pigments in chlorophyll b and carotenoids can absorb wavelengths of
light that chlorophyll a cannot and pass the energy (photons) to chlorophyll a thus
broadening the spectrum that can effectively drive photosynthesis
...
Thylakoids
hold photosynthetic pigment chlorophyll
...

Stroma – fluid filled matrix where light independent stage occurs containing enzymes,
sugars, organic acids and starch grains
...


Stroma fluid surrounds the Grana
Contains both DNA and Ribosomes

Products of the light dependent stage in
the grana can readily diffuse into the
stroma
Can quickly and easily manufacture some
of the protein involved in the light
independent reaction















Oxidation and Reduction
Oxidation
Reduction
Gains Oxygen
Loses Oxygen
Loses Hydrogen
Gains Hydrogen
Loses Electrons
Gains Electrons
Energy is given out
Energy is taken in

Photoautotrophic Organisms – Green Plants and photosynthetic bacteria

Light – Dependent Reaction (Photophosphorylation Non - Cyclic and Cyclic)
Takes place in thylakoids of chloroplasts and requires light
1
...
Chlorophyll is now ionised
...
Electrons are taken up by an electron carrier and move down the electron transport
chain to PSI
...
As the excited electrons from chlorophyll leave PSII they have to been replaced so it
can continue to absorb light
...
Catalysed by enigmatic ‘oxygen-evolving
complex’


4
...
This creates a proton gradient (electrochemical) across the
membrane to drive ATP synthesis in chemiosmosis
...

Some of this energy is used to combine Pi to ADP to make ATP
...


5
...
Energy to drive
this process come from electrons released in photolysis
...
Protons move down the concentration gradient into the stroma via the ATP synthase
channel proteins embedded in the thylakoid membrane as the rest of the membrane
is impermeable to protons
...

7
...

8
...

9
...
Electrons from chlorophyll
aren’t passed onto NADP but are passed back to PSI via electron carriers
...


The Light Independent Reaction
Takes place in stroma of chloroplasts and does not require light but requires the
products of the light dependent reaction and so ceases when light is absent
...
CO2 undergoes carbon fixation where it diffuses into the leaf via the stomata,
dissolving in the water around the mesophyll cells ad diffusing through the cell
surface membrane, cytoplasm and chloroplast membranes into the stroma of the
chloroplast
...
In the stroma CO2 reacts with Ribulose Bisphosphate (5C) (RuBP)
...

3
...
Reduced NADP from the light dependant stage is used to reduce GP into Triose
Phosphate (TP) using energy supplied by ATP
...
NADP is therefore reformed and is recycled back into the light dependent reaction
...
Some TP molecules are converted into organic substances: starch, cellulose, lipids,
glucose, amino acids and nucleotides
...

Lipids
Using glycerol which is synthesised from TP and fatty acids
which are synthesised from GP
Amino Acids
Made from GP


















Factors Affecting Photosynthesis
At any given moment the rate of a physiological process is limited by the factor that
is at its least favourable value
...
As light intensity increases, volume of oxygen
produces and CO2 absorbed will increase until the compensation point (when
oxygen absorbed and CO2 produced is exactly balance and not net exchange of gases
in the plant occurs)
...
Now some other factor is the limiting factor
...

Carbon Dioxide – 0
...
CO2 concentration effects
enzyme activity and in particular the enzyme that catalyses the combination of RuBP
with CO2
...
4% gives a higher rate of photosynthesis but any
higher and the stomata will start to close
...
At high temperatures the
stomata close to avoid water loss causing photosynthesis to slow down due to less
CO2 entering, so between 10C and 45C an increase in temperature causes an
increase in rate of photosynthesis
...
g
...

• Water bath is used to maintain a constant temperature throughout the
experiment
...

• Oxygen released during photosynthesis collects in the funnel end of the capillary
tube about the plant
...
Set up apparatus taking care not to introduce any air bubbles and that it is air
tight
...
Give a source of light whose intensity can be adjusted and arrange it close to the
apparatus which is kept in otherwise a dark room
...
Switch on the light source and leave the plant for 30 mins to allow air spaces in
the leaves to fill with oxygen
...
Read the value in mm3 on the syringe and then depress the syringe and repeat
experiment at the same light intensity to calculate a mean
...
The apparatus must be left in the dark for 2 hours before the experiment is
repeated with the light source set at a different light intensity
...

1
...

2
...

3
...

4
...
















Required Practical 7: Use of Chromatography to Investigate the Pigments Isolated from
Leaves in different Plants
Use thin layer chromatography (TLC) to determine what pigments are present
• Plants contain different photosynthetic pigments in their leaves as they absorb
different wavelengths of light so having more than one type of pigment increases the
range of wavelengths of light that can be absorbed
...
g
...

• Comparing pigments in shade tolerant and shade intolerant plants
...

• As the solvent spreads up the plate the different pigments move with it but at
different rates so they separate
...
g glass
with a thin layer of gel on top e
...
silica gel in TLC)

1
...

2
...

Two distinct layers should form the top layer being the pigment mixed with the
petroleum ether
...
Transfer some liquid form the top layer into a second test tube with some
anhydrous sodium sulfate
...
Draw a horizontal pencil line near the bottom of the TLC plate and build up a single
concentrated spot of liquid on the line by applying several drops and ensuring each
drop is dry before the next is added
...

5
...
Put a lid on the container and leave
...
When the solvent has nearly reach the top remove he plat and mark the solvent
front with a pencil and leave to dry
7
...

8
...
























Shade Tolerant plants can adapt to light conditions in their environment by processing
a different proportion of photosynthetic pigments allowing the plant to make the best
use of the light available
...
They sometimes produce
dark red and purple pigments called anthocyanins which are thought to protect their
chloroplasts from brief exposure to higher light levels
...
This is catalysed by dehydrogenase enzyme
...
DCPIP goes from blue to colourless when
reduced
...

• Measure rate of dehydrogenase activity by measuring rate at which DCPIP loses it
blue colour
...
One containing only DCPIP and chilled isolation solution
and the other with DCPIP and chloroplast extract but wrapped in tin foil so light
cannot reach the contents
...




1
...
Use a pestle and mortar to grind up the leaves with chilled isolation solution
(sucrose, potassium chloride and phosphate buffer at pH7) and filter the liquid into
a beaker through a funnel lined with muslin cloth
...
Transfer liquid to centrifuge tubes and centrifuge at a high speed for 10 mins to get
the chloroplasts to the bottom of each tube in a pellet
...
Remove the liquid from the top of the tubes leaving the pellets at the bottom
...
Re-suspend the pellets in fresh chilled isolation solution and store in ice for the rest
of the experiment
...
Set up colorimeter with red filter and zero it using a cuvette (cuboid shaped vessel)
containing the chloroplast extract and distilled water
...
Set up test tube rack at a set distance from a bench lamp and switch lamp on
...
Put a test tube in the rack and add a set volume of chloroplast extract to the tube and
a set volume of DCPIP
...

9
...
Then place
the cuvette in the colorimeter and record ab

---