Lecture 2: Light, Pigments and Photosynthesis Flashcards
(32 cards)
what is Stoke’s shift?
the difference between the excitation and the emission wavelengths
what is quantum efficiency?
the number of photons emitted divided by the number of photons absorbed
what is luminescence?
light emitted as the result of a chemical reaction
what is light composed of and how does it behave?
composed of photons and behaves as both a particle and a wave
how does light produce colour?
through being different wavelengths (nm) or different temperatures (K)
what is irradiance?
intensity of light received by an object (microEinsteins)
what does a shorter wavelength mean?
more energetic light
what is the visible light spectrum?
400-700nm
what occurs if light wavelengths are shorter than ultraviolet?
they are too energetic and break chemical bonds which damages molecules
what occurs if light wavelengths are longer than far red?
they are not energetic enough therefore the electrons within the molecules are not stimulated to a higher energy state (so they aren’t visible)
what 5 ways may light interact with matter?
absorption, reflection, generation, fluorescence, iridescence
what is spectroscopy used for?
quantifies the absorption spectrum (by colour or turbidity - cloudiness)
what is the spectroscopy output dependent on?
distance between light source and sample AND the light path length
what is luminometry?
the requirement of a photometer/low-light imaging camera
what 2 ways is light perceived in plants?
sensory (relative to environment) and assimilatory (photosynthesis)
what photopigments are used in sensory light perception?
cryptochromes, phototropins (blues) and phytochromes (reds)
what photopigments are used in photosynthesis (assimilatory light perception)?
chlorophylls a and b
what are the features of cryptochromes?
blue light photoreceptors, flavoproteins, have 2 cofactors (pterin at 380nm and FAD at 450nm), produce anthocyanin that acts as sunscreen
what is blue light mediated cell expansion?
the energy (light) absorbed by Pterin is passed onto FAD making FADH that causes autophosphorylation and translocation to the nucleus
what are features of phototropins?
blue light photoreceptors, localised flavoproteins, 2 functional domains (LOV1 & LOV2 and FMN chromophore)
what are phototropins used for?
blue light mediated phototropism, stomatal opening, chloroplast movement, leaf flattening
what are the 2 states of phytochromes?
synthesised at Pr (inactive) that absorbs red light at 666nm, converted to Pfr (active) that absorbs red light at 720nm
what are phytochromes used for?
(de)etiolation, nastic (no tropism) movement, seed germination, photomorphogenesis (changes in plant determined by location)
what is the MAIN photosynthetic pigment?
chlorophyll a
