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

---