5.6 Photosynthesis Flashcards
What is the compensation point?
When photosynthesis and respiration proceed at the same rate so there is no net gain or loss of carbohydrate
What is the compensation period?
The time taken to reach the compensation point
Does a sun plant or a shade plant have a higher compensation point?
The sun plant is higher
Because the shade plant begins to photosynthesise at a much lower light intensity than the sun plant
Define granum
- Inner part of chloroplasts made of stacks of thylakoid membranes
- where the light dependent stage takes place
Define photosynthetic pigment
- Pigment that absorbs specific wavelengths of light and traps the energy associated with light
- chlorophylls a and b, carotene and xanthophyll
Define photosystem
- System of photosynthetic pigments found in thylakoids of chloroplasts
- each photosystem contains about 300 molecules of chlorophyll that trap photons and pass their energy to a primary pigment reaction centre, a molecule of chlorophyll a, during the light dependent stage of photosynthesis
Define stroma
fluid-filled matrix of chloroplasts, where the light independent stage of photosynthesis takes place
Define thylakoid
Flattened membrane-bound sac found inside chloroplasts; contains photosynthetic pigments/photosystems and is the site of the light-dependent stage of photosynthesis
What is the reaction centre
Its at the bottom of all of the photosynthetic pigments and it contains a type of chlorophyll
Describe chlorophyll a
- there are two forms
- both appear blue green
- both absorb red light
- different absorption peaks
- both have porphyrin group
Describe P680
- PSII
- peak absorption of light at 680nm
Describe P700
- PSI
- peak absorption at 700nm
Describe chlorophyll b
400-500nm and 640nm
appears yellow/green
Describe carotenoids
- accessory pigment
- blue light
- 400-500nm
- appear orange
Describe xanthophylls
- accessory pigment
- blue and green light
- wavelength 375-550nm
- appear yellow
Difference between primary and accessory pigments
- primary pigments act as reaction centres
- accessory pigments surround the reaction centre and transfer energy to primary pigments
What is photophosphorylation?
Generation of ATP from ADP and Pi in the presence of light
What do electron carriers consist of?
Fe3+ which are reduced to Fe2+ and reoxidised to Fe3+ as e- moves on
Products of non-cyclic photophosphorylation of light dependent stage
ATP and reduced NADP
Products of cyclic photophosphorylation
ONLY ATP
Which cells use cyclic photophosphorylation?
Guard cells
- only have PSI
- ATP moves K+ into guard cell and water follows and swells
Where does reduction of NADP occur?
Stroma
Where does the light-independent stage occur?
Stroma
Why does the Calvin cycle only occur during the day?
- ATP and NADPH are used from the light dependent stage
- H+ ions that are pumped out of the stroma increase the pH to 8 which is the optimum for RuBisCo
- Extra ATP in the stroma which activates RuBisCo
- Mg2+ increase in daylight and are cofactors of RuBisCo
- Ferredoxin (reduced by e- in the light) activates enzymes in the Calvin cycle
