Wjec Biology // By4 // 4.3 // Photosynthesis

Front 1

Summary
1. Where does photosynthesis take place and where are they found?
2. What absorbs sunlight energy?
3. What are the two stages of photosynthesis?

Back 1

1. Photosynthesis takes place in the chloroplasts which are found in the mesophyll and guard cells of leaves.
2. The pigment chlorophyll.
3. The light-dependent and light-independent.

Front 2

Photosynthetic Pigments
1. Two main pigments
2. What part of the spectrum do these two pigments absorb light
3. What are carotenes and xantophylls?

Back 2

1. Chlorophylls and Carotenoids
2. Chlorophylls absorb light from the red and blue-violet region. Carotenoids absorb from the blue-violet region.
3. They are accessory pigments

Front 3

Absorption and Action Spectra
1. What does the action spectrum show?
2. What would super-imposing a light absorbance and rate of photosynthesis graph show?
3. What does the absorption spectra show?

Back 3

1. Rate of photosynthesis at different wavelengths of light.
2. There is a close correlation between absorption and action spectrum.
3. How much light a pigment absorbs at each wavelength.

Front 4

Light Harvesting
1. Where are chlorophylls and accessory pigments found?
2. What are a group of these pigment molecules called?
3. Describe the process of light reaching the reaction centre
4. What are the two reaction centres and what is it called?

Back 4

1. They are found in the thylakoid membranes of the chloroplast.
2. Each cluster of several hundred molecules make up an antenna complex.
3. The pigments funnel photons of light from one another, until they reach chlorophyll A.
4. Cholorophyll A is a primary pigment.
Photosystem I (PSI) is arranged around chlorophyll a, with an absorption peak of 700nm.
Photosystem II (PSII) is arranged around chlorophyll a, with an absorption peak of 680nm.

Front 5

Light Dependent Stage of Photosynthesis
1. What does the LD stage involve?
2. What are the two ways ATP can be synthesised?

Back 5

1. It involves; Photolysis, splitting up of water molecules by light to produce hydrogen ions and electrons.
Synthesis of ATP from ADP+Pi, known as Photophosphorylation.
Combination of H ions with NADP to produce reduced NADP.
2. Non-Cyclic Photophosphorylation and Cyclic Photophosphorylation.

Front 6

Describe the process of Non-Cyclic phosphorylation

Back 6

Photons of light are absorbed by PSII, passed to chlorophyll a.
This displaces two high energy electrons, raising them to another higher energy level where they are picked up via electron acceptors.
These electron acceptors pass electrons along a chain of carriers, through a proton pump and to PSI.
Energy lost by electrons converts ADP to ATP
Photons of light are absorbed into PSI and passed too Chlorophyll A.
This causes two electrons to be emitted raising them to a higher energy where they are pictured up by another electron acceptor.
PSII is unstable, as it has lost electrons. They are replaced by electrons from photolysis of water.
The second electron acceptor passes some of these electrons to hydrogen ions outside the thylakoid membrane, allowing them to reduce NADP.
Electrons not recycled back.

Front 7

1. Describe the process of Cyclic
2. What is the process of ATP production called?

Back 7

1. Cyclic only involves PSI
Photos of light are absorbed by PSI and passed to chlorophyll A.
They are emitted and raised to a higher energy level which are then picked up by second electron acceptor.
Those electrons not taken up by the production of red. NADP are passed along carriers, and then returns to PSI.
Sufficient energy is created from electron passing along chain of carriers, generating ATP.
No reduced NADP produced during this process.
2. Chemiosmosis

Front 8

Light Independent Stage
1. Where does the LID take place?
2. What does the LID do?
3. Describe the process of the LID

Back 8

1. It takes place in the stroma of the chloroplast.
2. Uses ATP and reduced NADP to reduce Carbon Dioxide to synthesise hexose sugar.
3. A 5C molecule, RuBP combines with Carbon Dioxide, forming an unstable 6C compound. This is catalysed by Rubisco.
The 6C compound immediately splits into two 3C compounds called Glycerate-3-Phosphate
GP is then phosphorylated by ATP and reduced by NADP to triose phosphate.
Some of this TP is built up into Glucose Phosphate and then starch by condensation.
Most of the TP however enters a series of reactions driven by ATP regenerating RuBP.
The NADP is reformed and goes back to the LD to be reduced again.
Known as the calvin cycle.