Photosynthesis Flashcards
(26 cards)
Location of light
dependent
reaction
Thylakoid membrane of chloroplast
Location of light
independent
reaction
Stroma of chloroplast
Chloroplast
structure
- outer and inner membrane , with inner membrane between them
- stroma (aqueous fluid)
- lamella (long thin structure)
- thylakoid
- granum - stack of thylakoid
- lumen inside thylakoid
Thylakoid
membranes
flattened membrane sacs inside
chloroplasts
contain chlorophyll and other pigments
for absorbing light
site of the light-dependent reactions
electron transfer chain proteins and
ATP synthase are embedded in the membrane
Chlorophyll
Located in proteins on thylakoid
membranes
photosynthetic pigment
(protein) that absorbs light
different proportions of each
pigment lead to different
colours on leaves
Explain the advantage
of having many
different pigments in
chloroplasts?
Each pigment absorbs a
different wavelength of visible
light
many pigments maximises
spectrum of visible light
absorbed
maximum light energy taken in
so more photoionisation and
higher rate of photosynthesis
Light-dependent
reaction (LDR)
First stage of photosynthesis
occurs in thylakoid membranes
uses light energy and water to
create ATP and reduced NADP
for LIR
involves photoionisation of
chlorophyll, photolysis of water
and chemiosmosis
Photolysis of
water
Light energy absorbed by
chlorophyll splits water into
oxygen, H+ and e-
Products of
photolysis
H+
Picked up by NADP to form
reduced NADP for LIR
e-
passed along chain of
electron carrier proteins
oxygen
used in respiration or
diffuses out leaf via stomata
Photoionisation
of chlorophyll
Light energy absorbed by
chlorophyll excites electrons so
they move to a higher energy
level and leave chlorophyll
some of the energy released is
used to make ATP and reduced
NADP
Chemiosmosis
Electrons that gained energy
move along a series of electron
carriers in thylakoid membrane
release energy as they go along
which pumps protons across
thylakoid membrane
electrochemical gradient made
protons pass back across via
ATP synthase enzyme producing
ATP down their conc. gradient
What happens to
protons after
chemiosmosis?
Combine with co-enzyme NADP
to become reduced NADP
reduced NADP used in LIR
Products of
LDR
ATP (used in LIR)
reduced NADP (used in LIR)
oxygen (used in respiration /
diffuses out stomata)
Light
independent
reaction (LIR)
Calvin cycle
uses CO2, reduced NADP and
ATP to form hexose sugar
occurs in stroma which
contains the enzyme Rubisco
temperature-sensitive
Calvin cycle
Carbon fixation
- reaction between CO2 and ribulose biphosphate catalysed by Rubisco
- forms unstable 6C intermediate that breaks down into 2x glycerate 3 phosphate (GP)
Reduction
- 2x GP is reduced to 2x triose phosphate
- requires 2x reduced to NADP and 2x ATP
- forms 2NADP and 2 ADP
RuBP
Ribulose Bisphosphate
5-carbon molecule
GP
Glycerate-3-phosphate
3 Carbon molecule
Triose
Phosphate
3-carbon molecule
GP is reduced to form triose
phosphate in the Calvin cycle
(in photosynthesis)
Triose phosphate is oxidised to
form pyruvate in glycolysis (in
respiration).
Producing
hexose sugar
in LIR
Takes 6 cycles
glucose can join to form
disaccharides (sucrose) or
polysaccharides (cellulose)
can be converted to glycerol to
combine with fatty acids to
make lipids
Limiting factor
A factor which, if increased, the
rate of the overall reaction also
increases
Limiting
factors of
photosynthesis
Light intensity
CO2 concentration
temperature
How light
intensity limits
photosynthesis
If reduced, levels of ATP and reduced
NADP would fall
LDR limited - less photolysis and
photoionisation
GP cannot be reduced to triose
phosphate in LIR
How temperature
limits
photosynthesis
LIR inhibited - enzyme
controlled (Rubisco)
up to optimum, more collisions
and E-S complexes
above optimum, H-bonds in
tertiary structure break, active
site changes shape - denatured
How CO2
concentration limits
photosynthesis
If reduced, LIR inhibited
less CO2 to combine with RuBP
to form GP
less GP reduced to TP
less TP converted to hexose and
RuBP regenerated
