3.2 photosynthesis Flashcards
How are angiosperm leaves adapted for photosynthesis?
Large surface area for maximum light absorption
Thin for maximum light penetration
Transparent upper epidermal cells
Palisade cells packed with chloroplasts, which orientate themselves towards the light
How are chloroplasts adapted for photosynthesis?
Chloroplasts have a large surface area to maximise absorption of light
Within the palisade mesophyll cells chloroplasts can move intracellularly in response to light intensity – they can orientate themselves so that they absorb more light
More chloroplasts in palisade mesophyll layer than spongy mesophyll because palisade mesophyll are at top of the leaf, therefore exposed to more light than spongy mesophyll layer
What do the photosynthesis action spectra show?
The rate of photosynthesis at different wavelengths of light
Name the photosynthetic pigments present in the antenna complex of the photosystems.
Xanthophylls
Beta carotene
Chlorophylls a and b
Why are chloroplasts said to be transducers?
They convert energy from one form to another - light energy to chemical energy of ATP
What do absorption spectra of photosynthetic pigments show?
Shows how much light a particular pigment absorbs at different wavelengths
What is the role of a photosystem?
To harvest light energy
Photons of light are absorbed and the energy is channelled via photosynthetic pigments down to the reaction centre
Each chlorophyll molecule loses one excited electron
What is the relationship between the absorption and the action spectra
The shapes of the graphs more or less coincide that
- most light is absorbed in the blue (short) and red (long) wavelengths
- little light is absorbed in green wavelengths (green light is mostly reflected)
- the highest rates of photosynthesis are in blue and red wavelengths
- the lowest rate of photosynthesis is in green wavelengths.
What are the components of a photosystem?
The antenna complex comprising a range of photosynthetic pigments
The reaction centre containing 2 chlorophyll a molecules
Describe non-cyclic photophosphorylation
Light is absorbed by both PSII and PSI
Excited electrons emitted by the chlorophyll a molecules in PSII are passed via the ETC to PSI
The electrons are replaced through the photolysis of water
Excited electrons from chlorophyll a molecules in PSI are passed to NADP
ATP and NADPH are produced
Describe how ATP is produced in a chloroplast
Electron transfer via carriers in the ETC (within the thylakoid membrane) releases energy
This powers the pumping of protons from the stroma into the thylakoid space (using 1 proton pump)
Protons build up, lowering the pH
Protons flow down their gradient through ATP synthetase, releasing energy to form ATP
Describe cyclic photophosphorylation
Light is absorbed by PSI
Excited electrons emitted by the chlorophyll a molecules are taken up by an electron acceptor and passed back to the ETC via a proton pump
The electrons travel back to PSI
ATP is produced
What is photolysis?
The splitting of water using light energy
Electrons produced replace those lost by the chlorophyll a molecules in PSII
Oxygen is produced as a by-product (2 protons and 2 electrons combine with NADP to form NADPH)
Which products of the light dependent stage are used by the light independent stage
ATP and NADPH
Where does the light independent stage of photosynthesis take place?
The stroma
Where does the light dependent stage of photosynthesis take place?
The thylakoids
How is the TP used that drops out of the Calvin cycle?
To manufacture glucose (actually fructose bisphosphate), lipids and amino acids
Other products include starch and cellulose
How many turns of the Calvin cycle are required to produce one molecule of glucose?
6
(3 turns will result in the availability of 1 TP for the production of glucose; 5 TP will be recycled)
What is the name of the enzyme which catalyses the fixation of carbon dioxide by ribulose bisphosphate?
Rubisco
What does carbon fixation mean?
The incorporation of inorganic carbon into an organic compound
What is produced first in the Calvin Cycle, following the fixation of carbon dioxide?
2 molecules of Glycerate-3-phosphate (G3P)
How are NADPH and ATP used in the Calvin Cycle?
Both NADPH and ATP are used to reduce Glycerate-3-phosphate (G3P) to Triose phosphate (TP)
ATP also used to reform ribulose bisphosphate from ribulose phosphate
What is the compensation point?
The point at which the rate of respiration equals the rate of photosynthesis
What is a limiting factor in photosynthesis?
The factor that limits the rate of photosynthesis as it is in the shortest supply
