Photosynthesis Flashcards
What is a chloroplast?
are the organelles in plant cells where photosynthesis occurs
What are each chloroplast surrounded by?
a double-membrane envelope
Each of the envelope membranes is a phospholipid bilayer
What are chloroplast filled with?
fluid known as the stroma
What is the stroma the site of?
the light-independent stage of photosynthesis
A separate system of membranes is found in the stroma.
What is it called?
- what is the membrane system the site of?
Thylakoids
the light-dependent stage of photosynthesis
What does the thylakoid membrane contain?
the pigments, enzymes and electron carriers required for the light-dependent reactions
thylakoid
membrane system consists of a series of flattened fluid-filled sacs
when thylakoids stack up what structure do they form?
grana (singular – granum)
What are grana connected by?
membranous channels called stroma lamellae, which ensure the stacks of sacs are connected but distanced from each other
What does the membrane of the grana create?
a large surface area to increase the number of light-dependent reactions that can occur
What does the membrane system (thylakoid) provide?
a large number of pigment molecules in an arrangement that ensures as much light as necessary is absorbed
What does the stroma contain?
small (70S) ribosomes, a loop of DNA and starch grains
What does the loop of DNA code for in the stroma?
The loop of DNA codes for some of the chloroplast proteins (other chloroplast proteins are coded for by the DNA in the plant cell nucleus)
the protiens coded for by the loop of DNA in the stroma of chloroplast DNA are produced where?
at the 70S ribosomes
Stroma
What are sugars formed during photosynthesis stored as?
starch inside starch grains
Photosynthesis occurs in 2 stages. What are they and where do they take place?
- the light-dependent stage, which takes place in the thylakoid membranes and the thylakoid spaces (the spaces inside the thylakoids)
- the light-independent stage, which takes place in the stroma
What happens during the light- dependent stage of photosynthesis (overview) ?
- Reduced NADP is produced when hydrogen ions combine with the carrier molecule NADP using electrons from the photolysis of water
- ATP is produced (from ADP and Pi by ATP synthase in a process called photophosphorylation (ADP + Pi → ATP)
- Photophosphorylation uses the proton (H+) gradient generated by the photolysis of water
- Energy from ATP and hydrogen from reduced NADP are passed from the light-dependent stage to the light-independent stage of photosynthesis
light-dependent stage of photosynthesis
the energy and hydrogen are used during…?
the light-independent reactions (known collectively as the Calvin cycle) to produce complex organic molecules, including (but not limited to) carbohydrates, such as:
- Starch (for storage)
- Sucrose (for translocation around the plant)
- Cellulose (for making cell walls)
What is the site of photosynthesis?
chloroplast
Define photosystem
The pigment molecules are arranged in light-harvesting clusters
grana provides a large number of pigment systems.
In a photosystem, the different pigment molecules are arranged in?
funnel-like structures the thylakoid membrane (each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre)
What are dissolved in the stroma?
CO2, sugars, enzymes and other molecules
What is the stroma ?
The stroma is the fluid that fills the chloroplasts and surrounds thylakoids
What do Chloroplasts contain several different of ?
photosynthetic pigments within the thylakoids, which absorb different wavelengths of light
What are the 2 group of pigments?
-
Chlorophylls:
Chlorophyll a and b -
Carotenoids:
Carotene and xanthophyll
Chlorophylls:
What are the pigment colours of Chlorophyll a and Chlorophyl b ?
Chlorophyll a -> yellow-green
Chlorophyll b -> blue-green
Carotenoids:
What are the pigment colours of carotene and Xanthophyll?
carotene -> orange
Xanthophyll -> yellow
What do Chlorphylls absorbe wavelengths in?
What do they reflect?
the blue-violet and red regions of the light spectrum
They reflect green light, causing plants to appear green
What wavelengths of light mainly do Carotenoids absorb ?
mainly in the blue-violet region of the spectrum
What is an absorption spectrum?
is a graph that shows the absorbance of different wavelengths of light by a particular pigment
What is an action spectrum?
is a graph that shows the rate of photosynthesis at different wavelengths of light
When is the rate of photosynthesis th highest according to spectrums?
The rate of photosynthesis is highest at the blue-violet and red regions of the light spectrum, as these are the wavelengths of light that plants can absorb (ie. the wavelengths of light that chlorophylls and carotenoids can absorb)
There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum:
Explain
- Both graphs have two main peaks – at the blue-violet region and the red region of the light spectrum
- Both graphs have a trough in the green-yellow region of the light spectrum
What is Chromatography?
is an experimental technique that is used to separate mixtures:
- The mixture is dissolved in a fluid/solvent (called the mobile phase) and the dissolved mixture then passes through a static material (called the stationary phase)
- Different components within the mixture travel through the material at different speeds
- This causes the different components to separate
- A retardation factor (Rf) can be calculated for each component of the mixture
Rf value =
Rf value = distance travelled by component ÷ distance travelled by solvent
What are the two of the most common techniques for separating these photosynthetic pigments ?
- Paper chromatography – the mixture of pigments is passed through paper (cellulose)
- Thin-layer chromatography – the mixture of pigments is passed through a thin layer of adsorbent (eg. silica gel), through which the mixture travels faster and separates more distinctly
What can chromatography be used to separate and identify?
chloroplast pigments that have been extracted from a leaf as each pigment will have a unique Rf value
What does an Rf value demonstrate?
how far a dissolved pigment travels through the stationary phase
A smaller Rf value indicates the pigment is less soluble and larger in size
What is the Rf value for Carotene?
0.95
What is the Rf value for Xanthophyll?
0.71
What is the Rf value for Chlorophyll A?
0.65
What is the Rf value for Chlorophyll B?
0.45
Although specific Rf values depend on the solvent that is being used, in general:
- Carotenoids have the highest Rf values (usually close to 1)
- Chlorophyll B has a much lower Rf value
- Chlorophyll A has an Rf value somewhere between those of carotenoids and chlorophyll B
- Small Rf values indicate the pigment is less soluble and larger in size
During the light-dependent stage of photosynthesis (detailed):
- Light energy is used to breakdown water (photolysis) to produce hydrogen ions, electrons and oxygen in the thylakoid lumen
- A proton gradient is formed due to the photolysis of water resulting in a high concentration of hydrogen ions in the thylakoid lumen
- Electrons travel through an electron transport chain of proteins within the membrane
- Reduced NADP (NADPH) is produced when hydrogen ions in the stroma and electrons from the electron transport chain combine with the carrier molecule NADP
- ATP is produced during a process known as photophosphorylation (ADP + Pi → ATP) using the proton gradient between the thylakoid lumen and stroma to drive the enzyme ATP synthase
The photophosphorylation of ADP to ATP can be?
cyclic or non-cyclic, depending on the pattern of electron flow in photosystem I or photosystem II or both
How many photosystems involved in cyclic photophospohrylation?
only photosystem I
How many photosystems involved in non-cyclic photophosphorylation?
both photosystem I and photosystem II are involved
What are pohotsystems collections of ?
photosynthetic pigments that absorb light energy and transfer the energy onto electrons, each photosystem contains a primary pigment
What is Photosystem I primary pigmant?
- wavelength of light absorbed?
Photosystem I has a primary pigment that absorbs light at a wavelength of 700nm and is therefore called P700
Photosystem I is in the middle of the electron transport chain
The energy carried by the ATP is then used during the light-independent reactions of photosynthesis
What is Photosystem II primary pigment?
- wavelength of light absorbed?
Photosystem II has a primary pigment that absorbs light at a wavelength of 680nm and is therefore called P680
marscheme ans
Describe how non-cyclic photophosphorylation produces ATP and reduced NADP?
- photosystem | (PI) and photosystem II (PII) involved;
- light harvesting clusters;
- light absorbed by accessory pigments;
- primary pigment is chlorophyll a;
- energy passed to, primary pigment / chlorophyll a ;
- electrons, excited / raised to higher energy level;
7.(electrons) taken up by electron acceptor; - (electrons) pass down electron carrier chain (to produce ATP) ;
- PlI has (water splitting) enzyme;
- water split into protons, electrons and oxygen;
- H2O → 2H+ + 2e- + ½O2
- photolysis;
- electrons from PII pass to PI / electrons from water pass to PII;
- to replace those lost; give either in relation to PI or PIl
- protons and electrons combine with NADP (to produce reduced NAD) ;
can award these marking points from a diagram
Marscheme ans
Outline the steps of the Calvin Cycle
- RuBP combines with carbon dioxide ;
- rubisco;
- forms unstable 6C compound;
- produces two molecules of, GP
- GP converted to TP;
- by reduced NADP and ATP;
- TP used to regenerate RuBP;
- using ATP;
- TP can form, hexose / fatty acids / acetyl CoA
Describe the photoactivation of chlorophyll and its role in cyclic photophosphorylation
1.(photosynthetic pigments) arranged in light harvesting clusters;
2. primary pigments / chlorophyll a ;
3. at reaction centre;
4. P700 / PI, absorbs light at 700m ;
5. accessory pigments / chlorophyll b / carotenoids ;
6. surround, primary pigment / reaction centre / chlorophyll a ;
7. absorb light;
8. pass energy to, primary pigment / reaction centre / chlorophyll a ;
9. (light absorbed results in) electron excited / AW;
10. emitted from, chlorophyll / primary pigment / reaction centre;
11. passes to electron, acceptor / carrier;
12. (electron) passes along, chain of electron carriers / ETC;
13. ATP (synthesis) ;
14. electron returns to, P700 / PI;
Explain briefly how reduced NADP is formed in the light-dependent stage and how it is used in the light-independent stage
- photolysis of water;
- releases H+ ;
- by, P680 / PII;
- e- released from, P700 / PI;
- e- (from PI) and H+ combine with NADP;
- used in Calvin cycle;
- reduces, GP;
- to TP;
- ATP used (during reduction of GP) ;
- NADP, regenerated / oxidised ;
Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis?
1 closely packed to absorb maximum light;
2 vertical/at right angles to surface of leaf to reduce number of cross walls;
3 large vacuole pushes chloroplasts to edge of cell ;
4 chloroplasts at edge short diffusion path for carbon dioxide;
5 chloroplasts at edge to absorb maximum light;
6 large number of chloroplasts to absorb maximum light;
7 cylindrical cells or air spaces to circulate gases/provide a reservoir of CO2;
8 large surface area for diffusion of gases
9 moist cell surfaces for diffusion of gases;
10 cell walls thin for maximum light penetration/diffusion of gases;
11 chloroplasts can move towards light;
12 chloroplasts can move away from high light intensity to avoid damage;
Outline the light-independent stage of photosynthesis
13 Calvin cycle/stroma;
14 carbon dioxide fixed by RuBP;
15 rubisco ;
16 2 molecules of GP formed ;
17 (GP) forms TP;
18 use of ATP:
19 use of, reduced NADP/NADPH;
20 from light dependent stage;
21 some TP forms, hexose/sucrose/starch/cellulose/glycerol;
22 some TP converted to acetyl CoA;
23 some TP used to regenerate RuBP;
24 using ATP;
allow either mp 18 or mp 24
marks can be awarded on a diagram
Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosyphorylation
1 arranged in light harvesting, clusters/system;
2 primary pigments/chlorophyll a;
3 at reaction centre:
4 P700/P1, absorbs at 700(nm) ;
5 P680/P11, absorbs at 680(nm);
6 accessory pigments/chlorophyll b/carotenoids, surround, primary pigment/reaction centre/ chlorophyll a ;
7 pass energy to, primary pigment/reaction centre/chlorophyll a;
8 P700 / PI, involved in cyclic photophosphorylation ;
9 (light absorbed results in) electron excited/AW;
10 emitted from, chlorophyll/photosystem;
11 flows along, chain of electron carriers/ETC;
12 ATP synthesis;
13 electron returns to, P700/P1;
[8 max]
Explain why increasing the concentration of CO2 may increase the rate of production of carbohydrates at high light intensities
1 light not limiting;
2 much, ATP / reduced NADP, available;
3 CO2 is the limiting factor;
4 because low concentration COz (in atmosphere) ;
5 more CO2 combines with RuBP;
6 ref. rubisco;
7 Calvin cycle / light independent stage;
8 GP to TP;
9 more hexose produced;
10 ref. fate of hexose ;
Describe the structure of a chloroplast
- biconvex disc ;
- 3-10 um diameter;
- double, membrane / envelope;
- internal membrane system
- flattened or fluid-filled sacs / thylakoids;
- arranged in stacks / grana;
- hold pigments / named pigment;
- ref. clusters of pigments / AW ;
- (membrane of grana) hold ATP synthase;
- intergranal lamellae;
- stroma / ground substance;
- lipids / starch grains ;
- contains enzymes of Calvin cycle;
- stroma contains ribosomes / DNA etc;
- AVP; e.g. variation in shape between species
accept on labelled diagram
State precisely where the Calvin cycle occurs in plant cells
stroma of chloroplast
Describe how CO2 is fixed in the calvin cycle
Combines with (5C compound) RuBP
to form unstable 6C compound / forms 2 molecules of (3C) GP
ref. enzyme / rubisco
Explain how the products of photophosphorylation are used in the Calvin cycle
reduced NADP and ATP
(ATP is) source of energy;
(reduced NADP is for) reduction of GP to triose phosphate ;
ref use of ATP in regeneration of RuBP
ref to source of phosphate / phosphorylation
Explain what initially happens to the concentration of RuBP and GP if the supply of CO2 is reduced
RuBP - accumulates/goes up;
due to reduced combination ith CO2
GP - goes down / not much being formed;
due to converstion to TP (triose phosphate)
outline the main features of the calvin cycle
RuBP 5C:
combines with carbon dioxide;
rubisco;
to form an unstable 6C compound ;
which forms 2 X GP (PGA) ;
ATP;
energy source
and reduced NADP;
forms TP (GALP);
TP used to form glucose / carbohydrates 1 lipids / amino acids :
TP used in regeneration of RuBP
requires ATP;
as source of phosphate ;
light independent;
Explain the role of NADP in photosynthesis
coenzyme;
reduced;
carries protons;
and (high energy) electrons;
from photosystem 1 light stage;
on thylakoid membrane grana
to stroma / Calvin cycle
ref. regeneration of NADP;
Non-Cyclic Photophosphorylation
Photosystem II
Light is absorbed by photosystem II (located in the thylakoid membrane) and passed to the photosystem II primary pigment (P680)
An electron in the primary pigment molecule (ie. the chlorophyll molecule) is excited to a higher energy level and is emitted from the chlorophyll molecule in a process known as photoactivation
This excited electron is passed down a chain of electron carriers known as an electron transport chain, before being passed on to photosystem I
During this process to ATP is synthesised from ADP and an inorganic phosphate group (Pi) by the process of chemiosmosis
The ATP then passes to the light-independent reactions
Photosystem II contains a water-splitting enzyme called the oxygen-evolving complex which catalyses the breakdown (photolysis) of water by light:
H2O → 2H+ + 2e- + ½O2
As the excited electrons leave the primary pigment of photosystem II and are passed on to photosystem I, they are replaced by electrons from the photolysis of water
Photosystem I
At the same time as photoactivation of electrons in photosystem II, electrons in photosystem I also undergo photoactivation
The excited electrons from photosystem I also pass along an electron transport chain
These electrons combine with hydrogen ions (produced by the photolysis of water) and the carrier molecule NADP to give reduced NADP:
2H+ + 2e- + NADP → reduced NADP
The reduced NADP (NADPH) then passes to the light-independent reactions to be used in the synthesis of carbohydrate
Describe the role of the thylakoid membrane in photosynthesis
contains photosystems PS1 and PS2
- maintain carriers in position
- site of photophosphorylation
- site of ETC
- large SA
- produce ATP
Describe how CO2 is fixed in the stroma
Rubisco
CO2 combines with RuBP
powered by ATP and reduced by NADP
describe how CO2 reaches the inside of a palisade mesophyll cells from the external atmosphere
enters via stoma
by diffusion - down conc grad
passes through air spaces
dissolves in film of H2O through cell surface membrane
The optimum pH for the activity of rubisco is pH 8.
Explain why the illumination of chloroplasts leads to optimum pH conditions for rubisco
excited electrons leave photosystem
pass along ETC
protons present from photolysis
protons pumped into IMS (intermembrane space)
rubisco is in stroma
protons leaving stroma raises PH
Describe the role of accessory pigments in photophosphorylation
absorb light energy
passes energy onto chlorophyl a
Write a balanced equation that summarises photolysis
H2O —> 2H+ +2e- + 1/2 O2
state precisely the location of photosynthetic pigments within a chloroplast
thylakoid membrane
Describe the roles of the following substances in the light-independent stage of photosynthesis:
RuBP
CO2 fixation
production of GP
rubisco
Describe the roles of the following substances in the light-independent stage of photosynthesis:
reduced NADP
reduction of GP
GP to TP
Describe the roles of the following substances in the light-independent stage of photosynthesis:
ATP
supplies energy to convert GP to TP to regenerate of RuBP
Describe how the structure of a chloroplast is related to its functions
- ground substance/ stroma;
- for, light independent stage / Calvin cycle;
- contains enzymes / named enzyme e.g. rubisco;
- also, sugars / lipids / starch / ribosomes / DNA;
- internal membrane system;
- for, light dependent stage;
- fluid-filled sacs / thylakoids;
8.grana are stacks of thylakoids;
9.(grana) hold (photosynthetic) pigments ; - (grana) have large surface area for (maximum) light absorption;
- (pigments are arranged in), light harvesting clusters / photosystems ;
- primary pigment / reaction centre / chlorophyll a, surrounded by accessory pigments;
- (accessory pigments) pass energy to, primary pigment / reaction centre / chlorophyll a ;
- different photosystems absorb light at different wavelengths;
- membranes hold, ATP synthase / electron carriers ;
- for, photophosphorylation / chemiosmosis ;
Describe how you would separate chloroplast pigments using chromatography
- grind leaf with solvent ;
- example of solvent; e.g. propanone
- leaf extract contains mixture of pigments;
- ref. concentrate extract;
- further detail; e.g. pencil line drawn / extract placed on chromatography paper / repetitive spotting / drying between spots
- paper placed (vertically) in jar of (different) solvent ;
- solvent rises up paper;
- each pigment travels at different speed;
- pigments separated as they ascend;
- distance moved by each pigment is unique;
- Rf value ;
- two dimensional chromatography;
- better separation of pigments ;
outline the differences between cyclic and non-cyclic photophosphorylation
cyclic:
- electrons emitted returns to PSI
non-cyclic:
- electrons emitted from PSII absorbed by PSI
- reduced NADP produced
- photolysis occurs
- only involves PSII
- O2 prodiced
Explain why rate of photosynthesis levels out at 30 degrees (this is an example temp according to Q)
some other factors become limiting
CO2/light intensisty
How do these adaptions help photosynthesis:
- thin cell wall
- cylindrical shape
- large vacuole
- chloroplasts can be moved within the cell
- thin cell wall: short diffusion distance
- cylindrical shape : air spaces
- large vacuole: chloroplasts near outside of cell for better light absorption
- chloroplasts can be moved within the cell: absorbs maximum light
Name 2 products of the light-dependent stage of photosynthesis that are used in the light-independent stage
ATP
reduced NADP
Describe how ATP and reduced NADP are used in the light-independent stage of photosynthesis
ATP provides energy
reduced NADP is reducing agent for converting GP to TP
ATP used to regenerate RuBP
explain what is meant by limiting factor
process affected more than one factor
rate is limited by the factor nearest its minimum value
CO2 conc in the atmosphere may be a limiting factor in photosynthesis
Descibe how CO2 reaches the photosynthetic cells in a leaf
enters leaf through stomata by diffusion
substomatal air space
many air spaces in spongy mesophyll
spaces between palisade cells
dissolves in moisture on cells
enters through cell walls
Explain how the photolysis of water occurs
water is split into H+ and OH-
electron removed from OH-
to replace electron from photosytem
OH breaks down into O2 and water
H+ used to form reduced NADP
describe the photoactivation of chlorophyll
chlorophyll absorbs mainly red and blue light
light absorbed by antenna complex
energy transferred
reaction centers
light energy excites e- to higher energy level
e- lost from chlorophyll
describe the photoactivation of chlorophyll
chlorophyll absorbs mainly red and blue light
light absorbed by antenna complex
energy transferred
reaction centers
light energy excites e- to higher energy level
e- lost from chlorophyll
Outline how ATP is formed in the chloroplast
flow of e- down ETC
pumping H+ across membrane
proton grad across the thylakoid membrane
flow of protons down grad
via ATPase
fromation of ATP from ADP and Pi
cyclic e- return to original photosystem
non-cyclic, e- from PSII to PSI
suggest an advantage of having photsystems, the ETC and ATP synthase as part of thylakoid membrane
- increased efficiency
- short diffusion distance
describe the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra
- chlorophyll a is primary pigment;
2.carotenoids / chlorophyll b, is accessory pigment; - arranged in, light harvesting clusters / photosystems; A antenna complex
- on, grana / thylakoids ;
- ref. PI and PII; A P700 and P680
- primary pigment / chlorophyll a, in reaction centre;
- accessory pigments / carotenoids / chlorophyll b, surround primary pigment;
- light energy absorbed by, accessory pigments / carotenoids / chlorophyll b;
- (energy) passed on to, primary pigment / chlorophyll a / reaction centre;
- chlorophyll a and b absorb light in red and blue/violet region;
- carotenoids absorb light in blue/violet region;
- ref. absorption spectrum peaks;
- diagram of absorption spectrum;
- different combinations of pigments (in different plants) give different spectra;
