Photosynthesis Flashcards
Photosynthesis converts
light energy to the chemical
energy of food
The light reactions convert
solar energy to the chemical
energy of A T P and N A D P H
The Calvin cycle uses the
the chemical energy of A T P and
N A D P H to reduce CO2
to sugar
photosynthesis nourishes
almost the entire living world
autotrophs
sustain themselves without eating anything from other organisms
autotrophs are
producers
producers
produce organic molecules from CO2 and other inorganic molecules
most plants are
photoautotrophs
photoautotrophs
use the energy from sunlight to make organic molecules
what organisms can do photosynthesis
plants
algae
protists
prokaryotes
heterotrophs
consumers
consumers
obtain organic molecules from other organisms
heterotrophs consume _____ directly and _____ indirectly
plants and animals
most heterotrophs depend on
photoautotrophs for food and O2
how are fossil fuels formed
organisms that died hundreds of millions of years ago
fossil fuels represent what
stores of solar energy from the past
chloroplasts are similar to the
photosynthetic bacteria that they evolved from
photosynthetic enzymes and other molecules are arranged
together in thylakoid membranes
why is having all photosynthetic enzymes and molecules together good
more efficient chemical reactions of photosynthesis can happen
where are the major locations of photosynthesis
leaves
where else can photosynthesis happen
anywhere that is green
chloroplasts are found in what type of cells in the leaves
mesophyll
how many chloroplasts in a mesophyll cell
30 to 40 each
what enters through the stomata
CO2
what leaves through the stomata
O2
what two gases can diffuse across membranes in and out of chloroplasts
CO2 and O2
chloroplasts are surrounded by
two envelope membranes
what do the two membranes enclose in chloroplasts
a dense interior fluid called the stroma
interior thylakoid membranes form
interconnected sacs
where is the pigment chlorophyll found
in thylakoid membranes
what makes the leaves green in plants
chlorophyll
what are the stacks of thylakoids called
grana
Chemical equation of photosynthesis
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
Net consumption of water photosynthesis equation
6CO2 + 6H2O → C6H12O6 + 6O2
the simplest possible form of the photosynthesis reaction
CO2 + H2O → [CH2O] + O2
what do the brackets mean in [CH2O]
not an actual sugar but represents the general formula for a carbohydrate
Need 6 repetitions of simplest equation to
produce a glucose molecule
The actual product of photosynthesis is a
three-carbon sugar that can be used to MAKE glucose
One of first clues to the mechanism of photosynthesis
discovery that O2 is given off by plants is derived from H2O and NOT from CO2
Chloroplast splits water into
hydrogen and oxygen
Photosynthesis in sulphur bacteria
Used hydrogen sulphide rather than water for photosynthesis
CO2 + 2H2S = [CH2O] + H2O + 2S
Oxygen-18 isotope
O2 from plants was labelled ONLY with this isotope if water was the source of the tracer
If this isotope was introduced to the plant in the form of CO2
it was not in the release of O2
electrons released by splitting water
incorporated into sugar
oxygen is released as a
by-product
what does CO2 give rise to in the equation
Carbon and oxygen in glucose
oxygen in water
what does water give rise to in the equation
hydrogen in glucose
hydrogen in water
oxygen
what is reversed in photosynthesis compared to respiration
electron flow
what is oxidized in photosynthesis
H2O
what is reduced in photosynthesis
CO2
photosynthesis is an ______ process
endergonic
two stages in photosynthesis
- light reaction
- Calvin reaction
where does light reaction happen
thylakoids
what four things does the light reaction do
- split water
- releases oxygen
- reduces NADP+ to NADPH
- generates ATP from ADP by photophosphorylation
Calvin cycle does what to carbon
fixes carbon and incorporates CO2 into organic molecules
what is used to drive the Calvin cycle
energy from ATP and NADPH in light reaction
chloroplast thylakoids transform
light energy into chemical energy of ATP and NADPH
light is a form of
electromagnetic energy or radiation
light travels in
waves
wavelength
the distance between crests of waves
wavelength determines
the type of electromagnetic energy
electromagnetic spectrum
the entire range of electromagnetic energy or radiation
visible light
wavelengths that produce colours we can see
light also behaves as discrete particles
photons
shorter wavelengths
higher energy
wavelength with most energy
gamma rays and purple light
longer wavelengths
lower energy
wavelength with lowest energy
radio waves and red light
pigments
molecules that absorb visible light
different pigments
absorb different wavelengths
wavelengths that are not absorbed
are transmitted
why do leaves appear green
chlorophyll is reflected and transmits green light
is green light used IN photosynthesis
no, its reflected
absorption spectrum
plots a pigment’s light absorption versus its wavelength
absorption spectrum of chlorophyll a
violet-blue and red wavelengths are best for photosynthesis
action spectrum
profiles the effect of different wavelengths on a process
Englemann experiment
the growth of algae in red and purple light was higher in gree light
chlorophyll a
main photosynthetic pigment
accessory pigments
chlorophyll b
carotenoids
chlorophyll b
broadens spectrum used for photosynthesis
carotenoids
absorb excess light that can damage chlorophyll and the cell
CH3 is in
chlorophyll a
CHO is in
chlorophyll b
what happens when a pigment absorbs light
it becomes excited but VERY unstable
what has higher energy ground or excited state
excited state
how can energy be released in the form of protons of light or heat
excited electrons have high energy and fall back to the ground state with lower energy
a solution of isolated chlorophyll will do what when illuminated
will fluoresce and give off red light and heat
photosystem
consists of a reaction-centre complex that is surrounded by light harvesting complexes
light-harvesting complexes transfer
the energy of photons to the reaction center
what are light-harvesting complexes made from
pigments bound to proteins
primary electron acceptor
in the photosystem, it accepts excited electrons from the reaction centre chlorophylls
where is chlorophylls oxidized
in the reaction centre
what is reduced in a photosystem
primary electron acceptor
first step of light reactions
transfer of an electron from chlorophyll a to primary electron acceptor
two types of photosystems in thylakoid membranes
- photosystem 2 (PS II)
- photosystem 1 (PS I)
what photosystem functions first
PS II
what is the reaction centre of PS II called
P680
why is reaction centre of PS II called P680
chlorophyll a is best at absorbing 680 nm wavelengths
reaction centre of the PS I
P700
Why is the reaction centre of PS I called P700
absorbs the 700 nm wavelength best
Two possible routes for electron flow
cyclic and liner
linear electron flow involves
BOTH photosystems
linear electron flow produces
ATP and NADPH
step 1 in linear electron flow
a photon of light is absorbed by PS II and the energy is transferred amongst pigments until it reaches P680
step 2 in linear electron flow
excited electron is transferred from P680 to the primary electron acceptor
It has generated P680+
step 3 in linear electron flow
the electrons come from water and the electrons are transferred to P680+ which reduces it back to P680
step 4 in linear electron flow
the electron falls down an electron transport chain from primary electron acceptor of PS II to the PS I
step 5 in linear electron flow
the energy released during the fall is used to move protons across the thylakoid membrane which generates a proton gradient that drives ATP synthesis
step 6 in linear electron flow
light energy excites the P700 reaction centre in PS I like in PS II
P700 becomes P700+ as it loses an electron
missing electron from P700+ is replaced when it accepts electron passed from PS II
step 7 in linear electron flow
electron falls from PS I to ferredoxin (Fd)
step 8 in linear electron flow
electrons are transferred to NADP+ reducing it to NADPH
how is NADP+ reduced to NADPH in linear system
NADP+ reductase
what drives the ATP synthesis
generating a proton gradient by the energy released during fall of electron at PS I
P680+ is a very strong
oxidizing agent
what is available to help drive the Calvin cycle
high-energy electrons of NADPH
NADPH formation removes
hydrogen ion from the stroma
what is not involved in the cyclic electron flow
PS II
what direction does the electron flow in the cyclic cycle without PS II
back from Fd to PS I
what is NOT released in cyclic cycle
oxygen
what is used in cyclic electron flow
only PS I
what is produced in cyclic electron flow
ATP and NOT NADPH
why is it important that the cyclic cycle only produces ATP
satisfies the Calvin cycle’s need for more ATP than NADPH
what may have evolved first
cyclic electron flow or linear
cyclic electron flow
what does the cyclic electron flow may do
protect the cell from light-induced damage
how is chemiosmosis in chloroplast similar to mitochondria
both generate ATP by chemiosmosis
what differs in chloroplast and mitochondria during chemiosmosis
sources of energy
mitochondria transfer
chemical energy from food to ATP
chloroplasts transform
light energy into the chemical energy of ATP
where does chemiosmosis take place in mitochondria
the inner membrane
where does chemiosmosis take place in chloroplasts
the thylakoid membrane AND the stroma
where is there a higher hydrogen concentration (PH) during chemiosmosis
inter-membrane space (mitochondria)
thylakoid space (chloroplast)
where is there a lower hydrogen concentration (PH) during chemiosmosis
mitochondria matrix (mitochondria)
stroma (chloroplast)
where does the Calvin cycle take place
in the stroma
the Calvin cycle regenerates
its starting material
the Calvin cycle builds new organic molecules that leads to
the production of sugar
the Calvin cycle uses _____ and the _____ power of electrons carried by ____
ATP
reducing
NADPH
NADPH is a
reducing power that can be passed along the electron acceptor
ATP is a
versatile energy currency of cells
what part of photosynthesis makes NO sugar
light reaction
white pigment
the colour we see is the colour most reflected by the pigment
black pigment
absorbs all wavelengths
when there is high light, where are chloroplasts found in the cell
closer to the wall
when there is lower light, where are chloroplasts found in the cell
closer to the center
is photosynthesis going towards equlibrium
NO
what parts of the light reactions are endergonic
reducing NADP+ to NADPH
generates ATP from ADP
what is known as the dark reaction
Calvin cycle
what s known as the photo part of photosynthesis
the light reactions
what s known as the synthesis part of photosynthesis
Calvin cycle
where does electrons come from in linear electron flow
the splitting of water
where does electrons end in linear electron flow
the NADP+
can the PS I and PS II work interchangeably in linear electron flow
NO
where does O2 come from
linear or cyclic
linear
ration of ATP to NAPH in linear
1:1
how many carbons on there for the phase 1 and 2 of Calvin cycle
18
phase 1 of Calvin cycle
carbon fixation
phase 2 of Calvin cycle
reduction
phase 3 of Calvin cycle
regeneration of CO2 acceptor
how many CO2 enters per cycle of Calvin cycle
1
what is total input of CO2 in Calvin cycle
3
what is the short lived intermediate formed with the addition of CO2 in Calvin cycle
its 3 6-carbon sugar that is highly unstable
what does the short-lived sugar in Calvin cycle turn into
6 3-carbon sugar called 3-phosphoglycerate
how much ATP is spent to form 3-phosphoglycerate
6 ATP molecules
what does 3-phosphoglycerate split into with the ATP
6 3-carbon sugars called 1,3-Bisphosphoglycerate
what is used to break down 1,3-Bisphosphoglycerate into G3P
6 molecules of NADPH
what does 1,3-Bisphosphoglycerate turn into with the usage of NADPH
6 molecules of G3P
what is released to have a total of 5 G3P molecules
a G3P molecule in the form of a sugar
what are the 5 molecules of G3P turned into
3 molecules of ribulose biphosphate (RuBP)
what must be used to transform G3P into RuBP
3 ATP molecules
RuBP becomes what with the addition of a CO2 group
the short-lived intermediate molecule once again
in the Calvin cycle, carbon enters as _____ and leaves as _____
CO2 and G3P
net synthesis of 1 G3P how many times must the Calvin cycle turn
three times to fix three CO2
what catalyzes the carbon fixation step of Calvin cycle
Rubisco
most common enzyme in plants
Rubisco
what is the molecule that accepts CO2 in the Calvin cycle
RuBP
what is a problem for plants
dehdyration
when do plants close their stomata
on hot days
what does closing the stomata conserve for plants
H2O but it also limits photosynthesis
why does closing the stomata reduce photosynthesis
reduces access to CO2 and causes a build up of O2
Photorespiration
take up oxygen in the light and give out some carbon dioxide
C3 plants
initial fixation of CO2 is by Rubisco and makes a 2-carbon compound
during photosynthesis of C3 plants
Rubisco uses O2 instead of CO2 which produces a two-carbon sugar
what does photorespiration use instead of making
ATP
does photorespiration make a sugar
NO
when did Rubisco first evolve
when the atmosphere had less O2 and more CO2
why does Rubisco not exclude O2 in photorespiration
evolved in time that it didn’t have to
benefit of photorespiration
can limit damaging products of light reactions
disadvantage of photorespiration
can drain almost 50% of the carbon fixed by Calvin cycle
C4 plants
the Calvin cycle forms a four-carbon sugar as a first product
types of cells in C4 plants
bundle-sheath cells and mesophyll cells
bundle-sheath cells
arranged in tightly packed sheaths around the veins of the leaf
mesophyll cells
more loosely packed between the leaf structure and bundle-sheath cells
how do C4 plants minimize the cost of photorespiration
first using CO2 into a 4-carbon compound and THEN increasing CO2 near Rubsico
why would C4 plants increase CO2 near Rubisco
to increase its carbon-fixing efficiency
3 stages of the C4 sugar production
- the 4-carbon compound is produced by Pep Carboxylase
- the 4-carbon compounds are exported to the bundle-sheath cells
- CO2 is released from the 4-carbon compound in bundle-sheath cells and enters the Calvin cycle
what is the 4-carbon compound called in stage 1 of C4 plant sugar production
Oxaloacetate
what has a higher affinity for CO2 than Rubisco in C4 plants
PEPC (pep carboxylase)
Does PEPC have a higher affinity for CO2 than Rubisco in C4 plants even with O2 present
YES
how does the CO2 released by the 4-carbon compound in C4 plants enter the Calvin cycle
through fixation by Rubisco
CAM plants
Open stomata during the night and close them during the day
how do some plants use to fix carbon that is a variation of C4 metabolism
Crassulacean acid metabolism (CAM)
what happens in CAM plants with stomata open at night
CO2 is incorporated into 4-carbon organic acids
what happens in CAM plants with stomata closed during the day
CO2 is released from the organic acids and used in the Calvin cycle
when is the CO2 released from the organic acids and used in the Calvin cycle
when the CAM stomata’s are closed during the day
the C4 photosynthesis process takes place in
two separated cells (physically)
what takes place in the mesophyll cell of C4 plants
organic acid creation
what takes place in the bundle-sheath cell in C4 plants
Calvin cycle
what does the photosynthesis process look like in CAM plants
its the SAME cell, not separated, but split into night and day usage
what is done at night in CAM plants
organic acid formation
what is done in the day in CAM plants
Calvin cycle
where is excess sugar stored as starch
roots, tubers, seeds and fruits
where does the pigment go in the cyclic electron flow after reaching the primary acceptor
to Fd through the Cytochrome complex to Pc
what are the enzymes of the first electron transport chain in linear electron flow
Pq - cytochrome complex - Pc
what are the enzymes of the second electron transport chain in linear electron flow?
Fd to NADP+ reductase to the products of NADPH
how many linear and cyclic cycles are needed to form a molecule of glucose
12 linear cycles for 12 NADPH and 12 ATP
6 cyclic cycles for 6 ATP
how many molecules of ATP and NADPH for one molecule of glucose
18 ATP and 12 NADPH
NADPH is an _____ agent because it _____
oxidizing and gives
the Calvin cycle is _______
cyclic
Rubisco has a higher affinity for
oxygen
