unit 3 KA1b - photosynthesis Flashcards
how is light energy absorbed
by photosynthetic pigments to generate ATP and for photolysis
what are the three potential fates of light energy
- absorbed
- transmitted
- reflected
what are the different pigments that are used in photosynthesis
- chlorophyll a
- chlorophyll b
- carotene
- xanthophyll
what is the difference between the different pigments in photosynthesis
they each absorb different ranges of wavelengths of light
what do carotenoids do
they extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis
what are the two different spectras in photosynthesis
- absorption spectra
- action spectra
how is light energy converted to ATP for photosynthesis
- the absorbed light energy excites electrons in the pigment molecule
- transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase
how is the energy made from the light energy used
it is used for photolysis, in which water is split into oxygen, which is evolved, and hydrogen ions, which are transferred to the coenzyme NADP
what are the two stages of photosynthesis
- photolysis- the light dependent stage
- the calvin cycle - carbon fixation
what happens in the carbon fixation stage (the calvin cycle)
- the enzme RuBisCO fixes carbon dioxide by attaching it to RuBP.
- the 3-phosphoglycerate (3PG) produced is phosphorylated by ATP and combined with hydrogen ions from NADPH to form glyceraldehyde-3-phosphate (G3P)
- G3P is used to regenerate RuBP and for the synthesis of glucose
what are the possible fates of glucose
it may be used as a respiratory substrate, synthesised into starch or cellulose, or passed onto other biosynthetic pathways
what can the biosynthetic pathways lead to
the formation of a variety of metabolites such as DNA, protein and fat.
which colours of light are absorbed by the leaf pigments - ie which are the most important for photosynthesis
blue, violet and red
how can the leaf pigments be separated
chromatography
what is the most important pigment for photosynthesis
chlorophyll
what does an absorption spectrum show
these show the absorption of light of each wavelength by each pigment
what does an action spectrum show
these show the rate of photosynthesis at each light wavelength
what do xanthophyll and carotene do
they allow the plant to carry out photosynthesis in a wider range of light wavelengths
what are the accessory pigments, and why are they named this way?
- xanthophyll and carotene
- they pass the energy they capture onto chlorophyll a and b
where does absorption of light and photosynthesis take place
the grana - because this is where the photosynthetic pigments are contained
where does carbon fixation take place
the stroma of the chloroplast
describe the steps of capture of energy and photolysis
- light energy is absorbed by the chlorophyll, creating high energy electrons
- electrons are passed along the chain, pumping hydrogen ions into grana
- energy is used to split water
- hydrogen ions are picked up by NADP to make NADPH for carbon fixation (the calvin cycle)
- hydrogen ions are used by ATP synthase to make ATP for carbon fixation
what is the order of occurrence of molecules in the calvin cycle
- ribulose biphosphate
- 3-phosphoglycerste
- glyceraldehyde-3-phosphate
