photosynthesis Flashcards
what are the 2 stages of photosynthesis?
light dependent reaction and light independent reaction.
where does each stage occur?
LDR- occurs on thylakoid membrane/grana
LIR- occurs on stroma
what happens during the LDR?
light energy and water are used to produce ATP and reduced NADP, which is needed for the LIR.
what are the 4 stages of the LDR?
1) photoionisation of chlorophyll
2) production of ATP and reduced NADP.
3) chemiosmosis
4) photolysis
photolysis
photo means light
lysis means splitting
the light absorbed by chlorophyll is used to break down water into hydrogen ions, electrons and oxygen.
the hydrogen ions are picked up and added to NADP to form NADPH- which is used in the LIR
oxygen is used in respiration or diffuses out of the leaf via the stomata.
photoionisation of chlorophyll
light energy is absorbed by chlorophyll
energy causes electrons to become excited and they increase an energy level to leave the chlorophyll
so chlorophyll has been ionised/lost electrons by the light
some energy from the released electrons is used to produce ATP and NADP during chemiosmosis.
chemiosmosis
the electrons that gained energy and left the chlorophyll move across a series of proteins embedded in the thylakoid membrane.
as they move along, they release energy. some energy is used to pump hydrogen ions across chloroplast membranes.
hydrogen ions pass through ATP synthase enzyme, which leads to the production of ATP.
hydrogen ions join with the co enzyme NADP to form reduced NADP.
as the hydrogen ions are moving from a high to low concentration, this is called chemiosmosis.
structure of chloroplasts
double membrane/inner and outer membrane- controls what substances leave/enter the organelle.
stroma- fluid filled centre which contains enzymes used in LIR.
grana- stacks of thylakoid membranes
thylakoid membranes- folded membranes
contains chlorophyll and electron carrier proteins- used in LDR.
light independent reaction
occurs in the stroma
contains RuBIsco enzyme which catalyses the reaction.
stage is temperature sensitive as it involves enzymes.
cycle is called the calvin cycle.
what happens in the LIR?
CO2 and RuBP- rubisco enzyme- produces 2 molecules of GP (3 carbon compounds)
2x GP
reduced to
2x TP
by hydrolysis of ATP to release energy and hydrogen ion from reduced NADP.
1 carbon atom is removed from each cycle
cycle occurs 6 times so hexose sugar forms
glucose is the product but can form disaccharides e.g. sucrose or polysaccharides e.g. starch and cellulose.
remaining 5 carbon atoms used to reform RuBP using ATP.
what is a limiting factor?
any factor that reduces the rate of photosynthesis.
what are the limiting factors for the rate of photosynthesis?
light intensity
carbon dioxide concentration
temperature
common agricultural practises to reduce the effect of limiting factors on the rate of photosynthesis
to maximise the rate of photosynthesis and hence plant growth, common agricutlural practises incorporate techniques to reduce the effect of limiting factors
growing plants under artifical light- increased light intensity
burning fuels e.g. parrafin oil to increase carbon dioxide concentration.
heating a greenhouse- increased temperature.
photosynthesis practical
investigating different pigments from different leaves through chrompatography
pigments of chlorophyll
chlorophyll is made of 5 similar pigments.
most abundant- chlorophyll a
plants have different concentrations of each pigment to maximise light absorption as each pigment absorbs a different wavelength of light.
