Topic 5 (Photosynthesis) Flashcards
What are the 2 stages of photosynthesis? + where
Light-dependent stage (occurs in thylakoid membranes)
Light-independent (occurs in stroma)
What are grana joined together by?
Lamallae
What is chloroplasts made up of?
Grana (stack of thylakoids)
Starch grains
Stroma
Double membrane
Why do plants have different colours?
Photosynthetic pigments
Absorb certain wavelengths of light
What we see is what’s being reflected
What are the types of photosynthetic pigments?
Chlorophylls (a and b) (blue/green/yellow)
Carotenoids (xanthophyll and carotenes) (yellow/orange)
What is the structure of chlorophyll?
Magnesium in the middle
Hydrophilic porphyria ring group (lies flat on surface of thylakoids)(head)
Hydrophobic hydrocarbon chain (attaches to lipid membrane)(tail)
How is energy being absorbed by chlorophyll?
- excites pair of electrons with the Mg
- pass along electron transport chain
Why is the hydrophilic head lied flat on the thylakoids?
To maximise light absorption
How can you tell if a plant is magnesium deficient?
Yellow leaves - can’t make enough chlorophyll
Aka chlorosis
What are accessory pigments?
Carotenoids
They absorb wavelengths that aren’t well absorbed by chlorophylls and pass energy to chlorophyll a
Reflect yellow and orange light, absorb blue light
Why are there more colours in autumn months?
- cold nights: low temp destroy chlorophyll, enhancing red ccolour
- dry weather, sugars more concentrated in leaves , hence redder
- bright sunny days: more anthrocynin
= more colours like red and orange
What’s a photosystem?
Funnel shaped structures
Embedded in thylakoids membranes
Proteins holding them in place
What are the 2 types of photosystem?
PS1 AND PS2
wavelength of light they absorb out of visible spectrum of light
(Has a primary pigment reaction centre, at either P680 or P700)
What are PSI AND PSII
Photosystem I - absorbs light at 700 nm (found on inter-granal lamallae)
Photosystem II - at 680nm (found on grana)
What are the layers in plants? From top to bottom
Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis
Why is accessory pigment necessary?
Accessory pigments allow energy from light at a wider range of wavelengths to be used in the light-dependent reactions.
Why is the absorption spectrum the shape it is?
- chlorophyll a and b absorb strongly at blue and red ends
- chlorophyll a peaks at 430nm
- b peaks at 470
Why are there a variety of pigments in chlorophyll to take up different wavelengths of light?
To maximise light absorbed
as greater range of wavelengths can be absorbed
How do you explain the peaks of wavelength absorbed at 680 and 700?
P680 - photosystem 2
P700 - photosystem 1
Explain why seaweeds have different absorption spectra and action spectra. (3 marks)
Because…
- Each pigment absorbs diff wavelengths
- Diff amounts of wavelengths
- action spectra shows rate of p/s absorbing diff wavelengths of light
(- reduce competition)
Explain why seaweeds occupy different positions of a submerged rock and have different colours. (3 marks)
- positioned differently to reduce competition
- shallow water seaweeds: cannot absorb green light, so reflects green and looks green. Can absorb red and blue
- height of diff wavelengths
- so on
Compare light dependent and independent reactions
light dependent / independent
thylakoid / stroma
light needed / not needed
Makes ATP and Red NADP / uses ATP and red NADP
describe the light dependent stage of photosynthesis
- enables photolysis: water split into H+, e- and O
- light energy is converted into chemical energy in the form of ATP and reduced NADP
….
where does light dependent stage of photosynthesis take place
across thylakoid membrane
what is NADP
- a coenzyme
- transfers hydrogen between molecules
- When NADP gains hydrogen it becomes reduced NADP / NADPH
what are 2 types of photophosphorylation
cyclic
non cyclic
What is chemiosmosis
Flow of H+ ions down the electrochemical gradient through ATP synthase
where does the light independent cycle take place
Stroma of chloroplasts
What does rubisco do
Combine RuBP and Carbon dioxide
Aka fixation of carbon
What are 3 steps of Calvin cycle
- Carbon fixation
- Reduction
- Regeneration
What is the role of RuBP?
- 5C compound
- CO2 acceptor
- found in stroma
What is the role of Rubisco?
- enzymes that catalyses the reaction between RuBP and CO2
What is GP made from ?
- 3C products of RuBP and CO2
How is GALP formed? What is it used in?
- formed from reduction + photophosphorylation of GP
- ATP + reduced NADP from light independent reaction used
what is photolysis
splitting water into H+, e- and O
What is NADP and what does it do?
NADP is a coenzyme
- transfers hydrogen from one molecule to another
- becomes reduced NADP
Describe the (non-cyclic) light dependent stage of photosynthesis
- light hits PSI and PSII
- e-s excited
- accepted by e- proton chain
- takes place in thylakoid membrane
- flow of H+ thru ATP synthase via chemiosmosis
- rotates ATP synthase
- ADP + Pi → ATP
- movement of e-s from water to PSII
- replacement of e-s from photolysis
- NADP + H+ + e-s - → Reduced NADP
Describe the cyclic light dependent stage of photosynthesis
Light hits PSI
e-s are excited and leave PS
and returns to e- transport chain, e-s rejoin PSI
Compare the non cyclic and cyclic photophosphorolation
Non cyclic / cyclic
doesnt / e-s come back to same molecule
first e- donor is water / PSI
involves PSI and II / PSI only
last e- acceptor is NADP / PSI
Net products ATP, NADPH, O2 / ATP only
reduction of NADP / no
What are NAD and FAD?
Coenzymes
Coenzymes are not…
ENZYMES!!
They just bind to them / help
What is the structure of ATP
It is a phosphorylated nucleotide
- adenosine (adenine + ribose sugar)
- three phosphate groups (T= triphosphate)
What are 2 ways of ATP production
- Substrate level phosphorylation
- Oxidative phosphorylation
What is substrate level phosphorylation?
Simply
ADP + Pi -> ATP
What are some limiting factors for photosynthesis?
- temp
- light intensity
- CO2 conc
- number of chloroplasts
Increasing the light intensity will increase the production of which 3 products in the light dependent stage?
ATP, reduced NADP, O2
Why will the light independent cycle be affected by the level of production from light dependent cycle?
More energy from ATP and NADP to reduce GP into GALP, driving cycle forward
Why does GP increase in dim light?
Less ATP and Red NAPD from LDC to change into GALP
Why does increasing CO2 conc lead to more proteins, polysaccharides and lipids being made?
More carbon is fixed by rubisco
So more GP = more GALP = more products
Why may an increase in CO2 conc lead to the plant wilting?
Stomata’s open to increase gas exchange,
To increase rate of transpiration
Why does temp have little effect on the light dependent cycle but huge effect on Calvin cycle?
Calvin is more dependent on enzyme e.g. Rubisco
Above 25C photorespiration occurs, how does this reduce the rate of photosynthesis?
When O2 enters Rubisco’s active site, blocking it from fixing carbon
Also wastes ATP and red NADP
Increased temp also increases water loss during transpiration. Why does this also then affect photosynthesis?
When plants lose too much water, stomata closes, = reduces CO2 intake
= cannot photosynthesise
what is an absorption spectrum?
graph to show the % of wavelengths of light absorbed by each pigment
what is an action spectrum?
graph of overall rate of p/s at each wavelength of light
what are 2 main groups of photosynthetic pigments?
chlorophyll (a and b)
carotenoids (carotene and xanthophylls)
where are photosynthetic pigments found
thylakoid membrane of chloroplasts
what are roles of chlorophyll a and b?
a- primary photosynthetic pigment
b- accessory pigment
why do plants have such a variety of photosynthetic pigments?
to widen range of wavelengths they absorb to maximise light absorption hence max rate of p/s
what does light do in photosynthesis?
excites e-s , causing release from chlorophyll
then they go in the e- transport chain
how is ATP produced? (in terms of chemiosmosis)
H+ ions move down the conc gradient from thylakoid into stroma, spinning the ATP synthase
ADP+Pi -> ATP
What does NADP act as in non-cyclic photophosphorylation?
final e- acceptor
what are the purposes of cyclic and non-cyclic photophosphorylation?
cyclic: produce ATP
non: produce ATP and Red NADP
what are e-s used for in photophosphorylation when they are produced from photolysis?
replaces e-s lost from chlorophyll
what is needed to convert GP into GALP?
2 Red NADP -> 2x NADP +
2 ATP -> 2 (ADP+Pi)
Explain why a wider/more stomata increases their yield. (3 marks)
- more carbon dioxide intake to be fixed
- faster rate of photosynthesis so more GALP produced in Calvin cycle and more biomass produced
- increased rate of transpiration also
- so more Mg for chlorophyll
Why does the thylakoid have higher pH than stroma, and what is the significance?
Energy from an e- transport chain is used to actively transport protons from the stroma to the thylakoid lumen
So that more H+ can be used to produce more ATP via chemiosmosis through the ATP synthase as it travels from a higher to lower H+ concentration.
Compare and contrast the structure of a chloroplast and mitochondrion. (3 marks)
Both have - double membrane, ribosomes, circular DNA
while
Chloroplasts as stroma and mitochondria have matrix as fluid medium
Inner membrane is flat / folds and form Cristae
Have starch grains / do not
Describe the role of photolysis in non-cyclic photophosphorylation. (2 marks)
Photolysis splits water molecules into H+, e- and O.
E-s released are used to replace e-s lost from PS2/photosystems
What is the opposite of phosphorylation?
ATP + Pi-> ATP = phosphorylation
ATP + Pi <- ATP = ??
Dephosphorylation
Or
Hydrolysis
Explain why light energy is converted into energy stored in ATP. (2 marks)
- it becomes an energy currency usable for plant later in the Calvin cycle
- used to fix carbons into GP into GALP
- light energy cannot be directly used by plant
Explain the role of light energy in the light dependent cycle. (3 marks)
- light excites e-s from chlorophyll
- so e-s can be used in chemiosmosis
- photolysis to replace lost e-s by chlorophyll
- to produce ATP and Red NADP for Calvin
What products in light dependent are used for light independent?
Reduced NADP
What inorganic ions are needed to synthesise protein?
Nitrates
What inorganic ions are needed to synthesise RNA?
Nitrates and phosphates
What inorganic molecule from which element in a simple sugar it originated from?
CnH2nOn
C from CO2
H from H2O
O from CO2
State the difference between action spectrum and absorption spectrum.
Absorption spectrum shows wavelength absorbed by pigment
Action spectrum shows overall rate of photosynthesis
State how an action spectrum and an absorption spectrum show that chlorophyll is used in photosynthesis.
Both graphs have similar peak points, their overlapping peak points reflect their causation relationship
What light is most absorbed by chlorophyll?
Red light
Describe how carbon fixation takes place in chloroplasts. (3 marks)
- carbon taken in via stroma
- binds to RuBP
- use Rubisco
- form 6C compound
Why is red light used in investigations to measure photosynthesis? (2 marks)
- red light is absorbed
- because of chlorophyll
Cells in leaf contain organelles that store molecules of starch. Name one. (1 mark)
chloroplast
State how an action spectrum show that chlorophyll is used in photosynthesis. (1 mark)
spectra overlap
peaks and troughs follow similar pattern
