TOPIC 5: ENERGY TRANSFERS IN AND BETWEEN ORGANISMS Flashcards
Location of light
dependent
reaction
Thylakoid membranes of
chloroplast
Location of light
independent
reaction
Stroma of chloroplast
Thylakoid
membranes
Folded membranes containing
photosynthetic proteins
(chlorophyll)
embedded with transmembrane
electron carrier proteins
involved in the LDRs
Chlorophyll
Located in proteins on thylakoid
membranes
mix of coloured proteins that
absorb light
different proportions of each
pigment lead to different
colours on leaves
Advantage of
many pigments
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 and
chemiosmosis
Photolysis
Light energy absorbed by
chlorophyll splits water into
oxygen, H+ and e
H2O -> 1/2O2 + 2e- +2H+
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 proteins 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
RuBP
Ribulose Bisphosphate
5-carbon molecule
GP
Glycerate-3-phosphate
3-carbon molecule
TP
Triose phosphate
3-carbon molecule
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 TP 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
Agricultural
practices to
maximise plant
growth
Growing plants under artificial
lighting to maximise light
intensity
heating in greenhouse to
increase temperature
burning fuel to release CO2
Benefit of
agricultural
practices for plant
growth
Faster production of glucose ->
faster respiration
more ATP to provide energy for
growth e.g. cell division +
protein synthesis
higher yields so more profit
Products of LIR
Hexose sugar
NADP - used in LDR
Stages of
aerobic
respiration
1) Glycolysis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation
Location of
glycolysis
Cytoplasm
Glycolysis
Substrate level phosphorylation
- 2 ATP molecules add 2
phosphate groups to glucose
glucose phosphate splits into
two triose phosphate (3C)
molecules
both TP molecules are oxidised
(reducing NAD) to form 2
pyruvate molecules (3C)
releases 4 ATP molecules
Coenzymes
A molecule which aids / assists
an enzyme
NAD and FAD in respiration both
gain hydrogen to form reduced
NAD (NADH) and reduced FAD
(FADH)
NADP in photosynthesis gains
hydrogen to form reduced NADP
(NADPH)
Products of
glycolysis
Net gain of 2 ATP
2 reduced NAD
2 pyruvate molecules
How many ATP
molecules does
glycolysis produce
2 ATP molecules used to
phosphorylate glycose to
glucose phosphate
4 molecules generated in
oxidation of TP to pyruvate
net gain 2 ATP molecules
Location of the
link reaction
Mitochondrial matrix
Link reaction
Reduced NAD and pyruvate
are actively transported to
matrix
pyruvate is oxidised to
acetate (forming reduced
NAD)
carbon removed and CO2
forms
acetate combines with
coenzyme A to form
acetylcoenzyme A (2C)
Products of the
link reaction per
glucose molecule
2 acetylcoenzyme A molecules
2 carbon dioxide molecules
released
2 reduced NAD molecules
Location of
the Krebs
cycle
Mitochondrial matrix
Krebs cycle
Acetylcoenzyme A combines
with 4C molecule to produce a
6C molecule - enters cycle
oxidation-reduction reactions