XI Chap 13 Photosynthesis Higher Plants Flashcards
What is photosynthesis?
physico-chemical process;
plants use light energy;
synthesis of organic compounds
Photosynthesis is important for what 2 reasons?
- primary source of all food on earth
2. oxygen into the atmosphere
__________ in ______ performed a series of experiments that revealed the role of air in the growth of green plants
Joseph Priestley in 1770
_______ discovered oxygen in _____
Joseph Priestley in 1774
________ used the same setup used in Priestley but modified it placing it once in dark and once in sunlight to show that ________
Jan Ingenhousz, sunlight is essential to plant process that purifies air
________ in an experiment with an aquatic plant showed that in bright sunlight, small ____ were formed around green parts of plants which did not form in dark
Jan Ingenhouse, bubbles of oxygen
It wasn’t until ____ that _______ provided evidence for production of glucose when plants grow.
1854, Julius von Sachs
What were the experiments done by TW Engelmann?
Described the action spectrum of photosynthesis.
Split light using a prism -> placed a green alga Cladophora in suspension of aerobic bacteria -> observed that bacteria accumulated in blue and red light
In what years was T W Engelmann alive?
1843 - 1909
By the middle of _______ century, key features of plant photosynthesis were known (i.e plants use light to make carbohydrates from CO2 and water).
19th
What was microbiologist Cornelius van Niel’s contribution to study of photosynthesis?
studies of purple and green bacteria,
showed that hydrogen from a suitable oxidisable compound reduces CO2 to carbohydrates
In green plants ______ is the hydrogen donor oxidized to O2
H2O
Some organisms do not release O2 during photosynthesis. T or F?
True
When H2S is the hydrogen donor for purple and green bacteria, the oxidation product is _____ or _____
sulphur or sulphate
How do we know that O2 evolved by green plants comes from H2O and not CO2?
Experiments with H2S and purple/green bacteria that produced sulphur/sulphate and not oxygen (later proved by using radioisotopic techniques)
What is the equation that represents photosynthesis accurately?
6CO2 + 12H2O —– (light) —-> C6H12O6 + 6H2O + 6O2
Photosynthesis is a single-step process represented by one equation. T or F?
False, multi-step process
________ cells in the leaves have a large number of chloroplast
Mesophyll
Why do chloroplasts align themselves to the walls of the mesophyll cells?
they get optimum quantity of incident light
There is clear division of labour in chloroplast. T or F?
True
Membrane system is responsible for trapping light energy in chloroplasts and for the synthesis of ATP and NADPH. T or F?
True
In stroma, enzymatic reactions synthesize ______ which in turn forms _____
sugar, starch
What are light and dark reactions?
Light - directly light driven
Dark - not directly light-driven but depend on products of light reactions
Light reactions are aka _________, dark reactions are aka _________
photochemical reactions,
carbon reactions / biosynthetic phase
Synthesis of ATP and NADPH - is it a light or dark reaction?
Light
Synthesis of sugar and starch - light or dark reactions?
Dark
Dark reactions occur in darkness and are not light-dependent. T or F?
False
You can separate leaf pigments of any green plant through ________ process
paper chromatography
Color in leaves are due to how many pigments? What are they and their colors on chromatogram?
4
Chlorophyll a - bright or blue green
Chlorophyll b - yellow green
Xanthophylls - yellow
Carotenoids - yellow to yellow orange
_______ are substances that have the ability to absorb light at specific wavelengths.
Pigments
_________ is the chief pigment associated with photosynthesis
Chlorophyll a
Most of photosynthesis takes place in ___ and ____ regions of the spectrum
blue and red
No photosynthesis takes place outside the blue and red regions of the spectrum. T or F?
False, some does
What are the pigments responsible for trapping light other than chlorophyll?
Thylakoid / accessory pigments: chlorophyll b, xanthophylls, cartenoids
Accessory pigments transfer the energy from light absorbed to chlorophyll a. T or F?
True
Accessory pigments enable a wider range of wavelength of incoming light to be utilized and protect chlorophyll a from ________
photo-oxidation
What is the photochemical phase?
Light reactions
What does the photochemical phase include?
Light absorption,
water splitting,
oxygen release and
formation of ATP and NADPH
What are the protein complexes involved in photochemical phase?
2 discrete photochemical light harvesting complexes, one in Photosystem I (PS I) and one in Photosystem II (PS II)
PS I and II are numbered according to the order….?
in which they were discovered NOT in which they function
What are LHC made up of?
hundreds of pigment molecules bound to proteins
Each photosystem has all the pigments except ____________
one molecule of chlorophyll a
What are antenna
light harvesting system formed by all the pigments in the photosystem
What role do LHC play?
make photosystem more efficient, pigments absorb different wavelengths of light
What is a reaction centre?
single chlorophyll a molecule, different in both photosystems
Absorption peaks for reaction centres for PS I and PS II?
PS I - absorption peak at 700nm (P700)
PS II - absorption peak at 680nm (P680)
In PS II, reaction centre absorbs 680nm wavelength of ____ light causing electrons to become excited and ________
red light,
jump into an orbit farther away from the atomic nucleus
Excited electrons in PS II are picked up by __________ which passes them on to an electrons transport
electron acceptor
Electron transfer system consists of ________
cytochromes
Movement of electrons in transport system is ________ (uphill or downhill) in terms of an oxidation-reduction or redox potential scale.
Downhill
Electrons are used up as they pass through the electron transport chain. T or F?
False, they’re passed on to pigments of PS I
Electrons in PS I are excited when they receive _____ light of wavelength _____ and are transferred to ______ that has _____ (lesser/greater) redox potential than PS II
red, 700nm, another acceptor molecule, greater
From the acceptor associated with PS I, electrons are moved _______ (uphill/downhill) to a molecule of _______
downhill,
energy-rich NADP+
Addition of electrons to NADP+ _____________ (oxidises/reduces) it to _____________
reduces
NADPH + H+
What is Z scheme?
Transfer of electrons starting from PS II - uphill to the acceptor - down the electron transport chain to PS I - excitation of electrons - transfer to another acceptor - finally down hill to NADP+ reducing it to NADPH + H+
Z-shape for Z-scheme is formed when all the carriers are placed in a sequence on __________ scale
redox potential scale
How does PS II supply electrons continuously?
Splitting of water, water is split into 2H+ , O and electrons
Splitting of water creates ______ one of the net products of photosynthesis
oxygen
Electrons needed to replace those removed from PS II are provided by PS I. T or F?
False, other way around. PS II supplies electrons to PS I
Water splitting complex is associated with PS I or II?
PS II
PS II is located on the inner side of the membrane of the ________
thylakoid
What is phosphorylation?
process by which ATP is synthesized by cells
Where does phosphorylation take place?
in mitochondria and chloroplasts
What is photo-phosphorylation?
synthesis of ATP from ADP and inorganic phosphate in presence of light
When PS II and PS I work in a series, ________ occurs. When only PS I is functional, ____________ occurs.
Non-cyclic photo-phosphorylation,
Cyclic photo-phosphorylation
Possible location for cyclic photophosphorylation is _______
stroma lamellae
Grana membrane or lamellae lacks PS II as well as NADP reductase enzyme. T or F?
False, stroma lamellae,
grana lamellae has both PS I and PS II
In cyclic photophosphorylation, excited electron does not pass on to _________ but is cycled back to the PSI complex through the ___________
NADP+,
electron transport chain
Cyclic flow results in the synthesis of _____
only ATP, not NADPH + H+
Cyclic photophosphorylation occurs when only light of ________ is available for excitation
wavelength beyond 680nm
What is the chemiosmotic hypothesis?
Explanation for ATP synthesis
Unlike respiration, in photosynthesis, ATP synthesis is linked to development of a proton gradient across a membrane. T or F?
False, LIKE respiration, everything else is correct
ATP synthesis in occurs across ___ membrane in the case of photosynthesis.
thylakoid
In respiration, protons accumulate in __________ whereas in photosynthesis they accumulate ___________
intermembrane space of the mitochondria,
inside of the membrane
What are the three processes that result in creation of a photon gradient?
- Photolysis of water
- Pumping of H+
- Formation of NADPH
Splitting of water molecule takes place on _____ (outer / inner) side of the thylakoid membrane. Protons accumulate within the ________ (lumen / stroma)
inner, lumen
During chemiosmosis, which has a higher concentration of H+ ions? Stroma or lumen?
Lumen
As electrons move through the photosystems, ________ are transported across the membrane
photons
Why are photons transported across the membrane due to PS electron movement?
primary electron accepter (located towards the outside of the membrane) transfers electron not to an electron carrier but an H carrier (proton from stroma)
When this molecule passes on its electron to the second electron carrier on inner side => proton released in the lumen
NADP reductase enzyme (FNR) is located on ______ (lumen / stroma) side of the membrane.
Stroma
Along with electrons that come from ___________, protons are necessary for the reduction of NADP+ to _______
acceptor of electrons of PS I,
NADPH + H+
Protons for the reduction of NADP+ are removed from _________
stroma
Accumulation of protons creates a gradient across the membrane as well as measurable ________ in pH in the lumen
decrease
Breakdown of the proton gradient leads to the synthesis of _______
ATP
Protons move across the membrane from lumen to stroma through ____________
CF0 of the ATP synthase
ATP synthase enzyme consists of ___ parts? What are they?
2 parts
CF0 - transmembrane channel embedded in thylakoid membrane
CF1 - protrudes on outer surface of thylakoid membrane on stroma side
CF0 carries out ____ diffusion of protons across membrane
facilitated
Breakdown of the gradient creates enough energy to cause a ________ change in the _____ particle of the ATP synthase which makes it synthesize ATP
conformational, CF1
Chemiosmosis requires? (4)
membrane
proton pump
proton gradient
ATP synthase
Energy is not required to pump protons to create a gradient. T or F?
False, it is required
Once protons have accumulated in the lumen, _______ has a channel that allows _______ of protons back across the membrane
ATP synthase, diffusion
What part of the chemiosmosis process releases enough energy to catalyse the formation of ATP?
diffusion of protons BACK across the membrane (from lumen to stroma)
NADPH and ATP are both used eventually in the biosynthetic reaction fixing CO2 and synthesis of sugars. T or F?
False, used immediately - not eventually
Products of light reaction are?
ATP, NADPH, O2
After light reactions, where does O2 produced go?
diffuses out of the chloroplast
What is biosynthetic phase?
synthesis of food/sugars using ATP and NADPH, not directly dependent on light (dark reaction)
_______ used ____________ in algal photosynthesis to discover the first CO2 fixation product was ____________
Melvin Calvin, radioactive 14C,
3-carbon organic acid / 3-phosphoglyceric acid (PGA)
The complete _________ is called Calvin cycle.
biosynthetic pathway
________ pathway has PGA as the first product of CO2 fixation.
__________ pathway has OAA as the first product of CO2 fixation.
C3 pathway.
C4 pathway
In C4 pathway plants, there are ____ carbon atoms in the first product. The acid is called __________
4, oxaloacetic acid (OAA)
Acceptor molecule of CO2 has _____ carbons, though scientists thought it would have ______
5, 2
The acceptor molecule of CO2 is __-carbon ____ sugar aka _______
5-carbon ketose sugar,
ribulose biphosphate RuBP
Calvin cycle works in a _____ manner i.e. RuBP is regenerated.
cyclic
Calvin pathways occurs in almost all photosynthetic plants. T or F?
False, occurs in ALL
Calvin cycle has how many stages? What are they?
Carboxylation
Reduction
Regeneration
Carboxylation?
fixation of CO2 into a stable organic intermediate
___________ is the most crucial step of the Calvin cycle
Carboxylation of RuBP
Carboxylation of RuBP is catalysed by the enzyme __________ which results in the formation of ________
RuBP carboxylase,
two molecules of 3-PGA
The more correct name for enzymeRuBP is __________ given it also has an oxygenation activity
Ribulose Biphosphate Carboxylase-Oxygenase (RuBisCO)
_________ is the second stage of the Calvin cycle where _______ is formed.
Reduction,
glucose/carbohydrate/sucrose/starch
Reduction in Calvin Cycle is a series of reactions in which carbohydrate is formed at expense of photochemically made ATP and NADPH. T or F?
True
Steps involved in reduction utilize ____ molecules of ATP for phosphorylation and ____ of NADPH for reduction per CO2 molecule fixed.
2, 2
The fixation of ___ molecules of CO2 and ____ turns of the Calvin cycle are required for one molecule of glucose
6, 6
What happens in regeneration phase of Calvin cycle?
RuBP is regenerated using 1 molecule of ATP
_____ ATP molecules are required for phosphorylation to form RuBP in regeneration.
1
To produce 1 molecule of glucose, how many CO2, ATP and NADPH molecules are required?
6, 18, 12
What are the 3 products of Calvin Cycle?
Glucose, ADP, NADP
Cyclic phosphorylation helps in making up for what difference?
Cyclic Phosphorylation creates ATP not NADPH => to make up for the different number of ATP and NADPH used in dark reaction (18 ATP vs 12 NADPH)
Plants adopted to tropical regions have the _____ pathways.
C4
C4 pathway plants use C3 pathway / Calvin cycle as the main biosynthetic pathway. T or F?
True
How are C4 plants special? (5)
special type of leaf anatomy can tolerate higher temperatures respond to high light intensities lack photorespiration greater biomass productivity
The large cells around the vascular bundles in C4 plants are called ________. These leaves are said to have ______ anatomy.
bundle sheath cells, Kranz anatomy
‘Kranz’ anatomy is named after the biologist who discovered the C4 pathway and special leaf anatomy of C4 plants. T or F?
False, Kranz = wreath => arrangement of bundle sheath cells around vascular bundles
Features of Kranz anatomy?
- wreath structure bundle sheath cells have: - large number of chloroplasts - thick walls impervious to gaseous exchange - no intercellular spaces
What is the Hatch and Slack pathway?
C4 pathway
Calvin cycle is cyclic process but Hatch and Slack is a linear pathway. T or F?
False, both cyclical
Primary CO2 acceptor in H&S pathway is ___________ and is present in ______ cells
3-carbon molecule phosphoenol pyruvate (PEP);
mesophyll cells
Enzyme responsible for CO2 fixation in H&S pathway?
PEP carboxylase / PEPcase
Mesophyll cells in both C4 and C3 plants have RuBisCO enzymes as both are capable of Calvin cycle. T or F?
False. C4 plants do not.
Bundle sheath cells of C4 plants have RuBisCO enzymes, just like C3 plants. T or F?
True
Bundle sheath cells of C4 plants have PEPcase to catalyze the 3-carbon molecule phosphoenol pyruvate (PEP). T or F?
False, that’s mesophyll cells. Bundle sheath cells have RuBisCo for C3, not PEP case.
OAA is formed in _____ cells of C4 plants.
Mesophyll
C4 acid forms other 4-carbon compounds like ______ or _______ in the H&S pathway.
malic acid, aspartic acid.
C4 acid forms 4-carbon compounds transported from _______ to _______ cells.
mesophyll to bundle sheath
In ________ cells, C4 acids are broken down to release ________ and ________. This process is called?
bundle sheath cells, CO2, 3-carbon molecule;
Decarboxylation
3-carbon molecule is transported from bundle sheath back to mesophyll cell to _______
be converted to PEP again, completing the cycle (regeneration)
In C4 plants, CO2 in bundle sheath cells enters the ______ pathway
Calvin / C3
Calvin pathway occurs in mesophyll cells of C3 and even C4 plants. T or F?
False,
C3 - mesophyll
C4 - bundle sheath
What is an important process that occurs in C3 plants only?
Photorespiration
What is the reaction for the first CO2 fixation step in Calvin cycle?
RuBP + CO2 —-RuBisCo—-> 2 x 3PGA
_________ is the most abundant enzyme in the world
RuBisCo
Active site of RuBisCo can bind to both CO2 and O2. T or F?
True
RuBisCO has much greater affinity for _____ when ratio of ____ is nearly equal
CO2, CO2:O2
RuBisCO binding is competitive. What does this mean?
Relative concentration of O2 and CO2 that determines which will bind to enzyme.
What happens in photorespiration? i.e. when O2 binds to RuBisCO
RuBP binds with O2 to form 1 molecule of phosphoglycerate and phosphoglycolate (2 Carbon)
No synthesis of sugars, ATP or NADPH.
Releases CO2 and utilizes ATP.
Biological function of photorespiration is to produce sucrose and starch in plants. T or F?
False, function unknown
Why do C4 plants not photorespire?
Mechanism that increases concentration of CO2 i.e. CO2 released in bundle sheath cells when C4 acid is broken down => intracellular concentration of CO2 is increased
In C4 plants, increased concentration of CO2 ensures that RuBisCo functions as a ____________ minimizing the _______ activity
carboxylase, oxygenase
Initial carboxylation reaction occurs in mesophyll for both C3 and C4 plants. T or F?
True
Rate of photosynthesis is important in determining ________
crop yield
Internal factors affecting photosynthesis? (6)
Number, size, age and orientation of leaves, mesophyll cells and chloroplasts, internal CO2 concentration amount of chlorophyll
External factors affecting photosynthesis? (4)
Availability of sunlight,
temperature,
CO2 concentration,
water
At any point, photosynthesis rate will be determined by ___ factor
sub-optimal / limiting factor
_________ stated the Law of Limiting Factors in _____ year
Blackman, 1905
Law of Limiting Factors are applicable to any biochemical process, not just photosynthesis. T or F?
True
What are the 3 aspects of light factor that can affect photosynthesis?
Quality, intensity and duration of exposure
At higher light intensities, the rate of photosynthesis will always increase, demonstrating their linear relationship. T or F?
False, true in lower light intensities. In higher, other limiting factors.
Light saturation occurs at ____ percent of the full sunlight.
10 per cent
Why is light rarely a limiting factor in nature?
Just 10% of sunlight can be saturation for plants, they don’t need too much.
Increase in light beyond a point causes the breakdown of chlorophyll and decrease in photosynthesis. T or F?
True
___________ is a major limiting factor for photosynthesis. Why?
CO2.
Concentration is very low in atmosphere
CO2 concentration in atmosphere is between ___ and ___ percent
0.03 to 0.04%
Increase in concentration up to ____% can cause increase in CO2 fixation rates, beyond that level it comes damaging over longer periods
0.05%
C3 and C4 plants respond similarly to CO2 concentrations. T or F?
False
Describe how C3 and C4 plants respond to high CO2 conditions in low light and high light conditions.
Low light - neither group responds
High light - both show increase in rate of photosynthesis, however, C4 plants show saturation at 360 μl/L whereas C3 at 450 μl/L
Current availability of CO2 levels is limiting only to C3 plants. T or F?
True
An example of how humans use the knowledge that C3 plants respond to higher CO2 concentration?
Greenhouse crops (tomatoes, bell pepper) grown in CO2 enriched atmosphere => higher yield
Dark reactions are temperature controlled. Why?
Enzymatic
Dark reactions are temperature sensitive but less so than light reactions. T or F?
False, reverse
C4 plants respond to higher rate of photosynthesis in _______ temperatures (higher / lower)
Higher
Temperature optimum for photosynthesis of different plants also depends on _______
habitat
Water has a direct effect on photosynthesis. T or F?
False, indirect
Examples of effect of water on photosynthesis
water stress => stomata close => less CO2 available
water stress => leaves wilt => reduce surface area of leaves => reduce metabolism
Within chloroplasts, membranes are the sites for light reaction while the chemosynthetic pathway occurs in stroma. T or F?
True
RuBisCO also catalyses a wasteful carboxylation reaction in C3 plants: photorespiration. T or F?
False, wasteful oxygenation reaction.
