photosynthesis Flashcards
how is ATP formed
from a condensation reaction between ADP and an inorganic phosphate using the enzyme ATP synthase
this creates a high energy bond
how is ATP used
ATP is easily hydrolysed into ADP and phosphate using ATP hydrolase
this releases energy
why is ATP useful
- releases energy is small amounts in a one step reaction
- adds phosphate to substances ( phosphorylation )
- lowers activation energy
- can be reformed / made again
what is NADP
a molecule which acts as an hydrogen acceptor becoming reduced to NADPH
this provides reducing power within its reactions as it loses this hydrogen, becoming re oxidised to NADP
what is the internal structure of a chloroplast
- double membrane
- thylakoids
- stack of thylakoids = a granum
- starch
- stroma
- inner membrane
- outer membrane
what is the equation for photosynthesis
6C02 + 6H2O – C6H12O6 + 6O2
what photosynthetic pigments are found in plants and where are they located
- chlorophyll
- carotene
located in photostems embedded in the thylakoid membrane
photostems funnel light energy to the chlorophyll a molecule
type of graph
what does an action spectrum show
shows rate of photosynthesis
what does an absorbance spectrum show
rate of absobption
why do plants require additional pigments to chlorophyll e.g. carotene anf xanthophylls
to increase the range of wavelengths of light energy they absorb, this increases rate of photosynthesis allowing more glucose to be produced
plants that are adapted to shaded conditions have more pigment which absorb different wavelengths of light to other plants
where does the light dependant reaction take place
in the grana, across the thylakoid membranes
what is the products of the light independant reaction
ATP and NADPH
what happens in the light independant reaction
- light energy is absorbed by the chlorophyll
- electrons in the chlorophyll gain energy and are rasied to a higher energy level ( photoionisation )
- chlorophyll is oxidised and the electrons trasnfer down an electron trasnfer chain in the thylakoid membrane
- the electrons lose energy at each stage of the etc and some of this energy is used to form pump protiens into thylakoid space creating a proton gradient
- protons pass back through membrane through ATP synthase down its gradient
- energy used to produce ATP from ADP +PI
- electrons and H+ used to reduce NADP
- chlorophyll electrons replaced by electrons from the photolysis of water
where does the light independant reaction take place
in the stroma
what is required for the light independant reaction to take place
the products of the light independant reaction - ATP and NADPH
what occurs in the calvin cylce ( light independant reaction )
- CO2 reacts with RuBP
- this forms 2 molecules of GP
- each GP is reduced to triose phosphate using energy from ATP nd using reduced NADP
- some of the triose phosphate is converted into useful carbohydrates ( glucose, sucrose , starch ) and triglycerides or combined with other products to make amino acids which can be used to make protiens
- some triose phosphate is used to regenerate RuBP
- ## products are recycled into the light dependant reaction
what are the factors affecting the rate of photosynthesis
abiotic factors act as a limiting factor on growth rate
- temperature
-CO2 concentration
- light intensity
- water availability
explain how DCPIP can be used to investigate dehydrogenase activity in e
DCPIP is blue but accepts the electrons normally used by NADP when they are released by the etc when the chlorophyll absorbs light and this turns the solution colourless
this can therefore be used as a measurement of dehydrogenase
in the dehydrogenase activity practical why is a tieb with foil wrapped around it needed
acts as a control to show light is required for DCPIP to change colour
in the dehydrogenase practical why is DCPIP and isolation medium but no chloroplasts needed
acts as a control to show DCPIP does not decolourise in the presence of light +chemicals in isolation medium
the change is due to chloroplasts
what is the dehydrogenase practical
in the LDR normally when light strikes the chlorophyll the electrons are excited and reduce NADP, in this experiment the electrons are accepted by the blue dye DCPIP casuing a change in colour ( colourless )
by measuring the tiem taken for DCPIP to change from blue to green ( DCPIP colourless, green from chloroplasts ), you can measure the rate of LDRs for different independant variables ( moving light source further away )
a chloroplast extract is produced from a blended spinach leaf that is centrifuged
one tube wrapped in foil = no light so colour change must be due to LDR
one tube had no chloroplasts = DCPIP will not decolourise alone
what happened in the dehydrogenase practical when ammonium hydroxide was added
DCPIP decolourised more slowly
could have inhibited movement of electrons down etc or inhibited photolysis
less electrons / hyrdogen available to reduce DCPIP so less ATP produced, less NADPH , less GP converted to triose phosphate
outline calvins lollypop experiment and explain how the results were used to describe the light independant reaction
exposed algae to c-14 labelled carbon dioxide
and then anaylised the compounds produced during photsynthesis
samples were taken at different time intervals
the compounds were analysed to identify which molecules had incorporated the radioactive carbon
they could trace how co2 is fixed and converted into organic molecules during photosynthesis - showing the calvin cycle
