photosynthesis Flashcards
(40 cards)
1
Q
where do the light-dependent & light-independent reactions occur in plants?
A
- light-dependent = in thylakoids of chloroplasts
- light-independent = stroma of chloroplasts
2
Q
Explain the role of light in photoionisation.
A
- chlorophyll absorb energy from light - “excites” 2 electrons, causing them to be released from chlorophyll.
- chlorophyll ionised by light + energy from released electrons used to make ATP + reduced NADP in chemiosmosis.
3
Q
name the 2 main stages involved in ATP production in light-dependent reaction.
A
1) electron transfer chain
2) chemiosmosis
4
Q
what happens in electron transfer chain (ETC)?
A
- electrons released from chlorophyll move down series; carrier proteins embedded in thylakoid membrane undergo series of redox reactions, releasing energy.
5
Q
how is a proton concentration gradient established during chemiosmosis?
A
- some energy released from electron transport chain coupled to active transport of H+ ions (protons) from stroma into thylakoid space.
6
Q
how does chemiosmosis produce ATP in the light-dependent stage?
A
- an electrochemical gradient created - protons pass thru enzyme ATP synthase - ATP production.
- H+ ions move down their concentration gradient from thylakoid space into stroma via channel protein ATP synthase
- ATP synthase catalyses ADP + Pi —> ATP
7
Q
explain the role of light in photolysis .
A
- light energy splits molecules of water releasing H+, O2 + electrons
- 2H2O (water) —> 4H+ (protons) + 4e- (electrons)+ O2 (oxygen)
8
Q
what happens to the products of photolysis of water ?
A
- H+ ions = move out thylakoid space via ATP synthase + reduce coenzyme NADP
—> picked up by NADP + form NADPH (used in LIR.) - e- = replace electrons lost from chlorophyll + passed along chain of electron carrier proteins
- O2 = used for respiration / diffuses out of leaf as waste gas .
9
Q
how and where is reduced NADP produced in light dependent reaction?
A
- NADP + 2H+ + 2e- —> reduced NADP.
- catalysed by dehydrogenase enzymes.
- stroma of chloroplasts
10
Q
where do the H+ ions and electrons used to make reduced NADP come from?
A
- H+ ions = photolysis of water
- electrons = NADP acts as the final electron acceptor of ETC.
11
Q
explain what is meant by reduction reactions.
A
- involved addition of electrons/ hydrogen atoms to a molecule OR removal of oxygen
12
Q
explain what is meant by oxidising reactions.
A
- involves removal of electrons / hydrogen atoms OR addition of oxygen.
- oxidant agent in photosynthesis = phosphorylated nucleotide / NADP => accepts and passes on protons + electrons
13
Q
explain the role of chlorophyll A in a photosystem
A
- absorbs light energy + use to boost energy level of electrons
—> when energy makes happen comes from light = photoionisation
14
Q
define the word photosynthesis.
A
- the process by which green plants use sunlight to synthesise nutrients from carbon dioxide and water
- 6CO2 + 6H2O —> C6H12O6 + 6O2
15
Q
define the term “photosystems”
A
- groups of chlorophyll and other pigment molecules found in membranes inside chloroplasts .
16
Q
define the term, “photophosphorylation” and the process.
A
- high energy e- used to make ATP during photosynthesis.
- ATP made when e- passed along electron transfer chain, on thylakoid membranes —> energy used to pump protons across membrane.
- as they diffuse back: protons pass thru ATP synthase enzyme, use energy of gradient to combine ADP with inorganic phosphate.
17
Q
define the term, “photoionisation”
A
- ionisation produced in a medium by the action of electromagnetic radiation.
- energy transferred of electrons, which released from chlorophyll molecules
18
Q
name the 3 main stages in the calvin cycle.
A
1) carbon fixation
2) reduction
3) regeneration
19
Q
what happens during carbon fixation?
A
- reaction between CO2 + ribulose bisphosphate (RuBP) catalysed by rubisco
- forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)
20
Q
what happens during reduction (in calvin cycle) ?
A
- 2 molecules of glycerate-3-phosphate contain -COOH group
- 2 x GP reduced to 2 x triose phosphate (TP)
- requires 2 x reduced NADP + 2 x ATP
- forms 2 x NADP + 2 x ADP
21
Q
how does light dependent reaction result in production of useful organic substances ?
A
- 1C leaves the cycle ( i.e. some of TP converted into useful organic molecules.)
22
Q
what happens during regeneration (in calvin cycle)?
A
- After 1C leaves the cycle, the 5C compound RuP forms
- 5 molecules triose phosphate used to regenerate 3 molecules of ribose bisphosphate
- regenerated from RuP using 1x ATP + forms 1x ADP
- remaining amount ATP —> synthesise lipids/ amino acids
23
Q
state the roles of ATP + (reduced) NADP in the light-independent reaction.
A
- ATP: reduction of GP to TP + provides phosphate group to convert RuP into RuBP
- (reduced) NADP: coenzyme transports electrons needed for reduction of GP to TP
24
Q
describe the stage of organic molecule production (calvin cycle)
A
- 2 molecules triose phosphate combine to form intermediate hexose sugar fructose 1,6 bisphosphate —> forms molecules of glucose
25
state the number of carbon atoms in RuBP, GP + TP.
- RuBP : 5
- GP : 3
- TP : 3
26
describe the structure of a chloroplast
- usually disc-shaped
- double membrane (envelope)
- thylakoids : flattened discs stack to form grana
- intergranal lamellae : tubular extensions attach thylakoids in adjacent grana.
- stroma : fluid-filled matrix
27
how does the structure of chloroplast maximise the rate of light-dependent reaction?
- ATP synthase channels within granal membrane + establishment of proton gradient
- large surface area of thylakoid membrane for ETC
- photosystems position chlorophyll to enable maximum absorption of light.
- DNA + ribosomes - synthesise protein needed in light dependent reaction.
28
how does structure of chloroplast maximise the rate of the light-independent reaction ?
- own DNA + ribosomes for synthesis of enzymes (rubisco)
- concentration of enzymes + substrates in stroma is high.
29
define’ “limiting factor”
- a factor that determines maximum rate of a reaction, even if other factors change to become more favourable.
30
ESQ: Name the products of the light dependent stage of photosynthesis.
- oxygen : waste product of photolysis of water + diffuses out of chloroplast + into atmosphere
- ATP : made by photophosphorylation + contains light energy absorbed by chlorophyll
- Reduced NADP : contains proteins + e-s (hydrogen)from water molecules that split by photolysis
31
what does the term electron carrier mean?
- molecule situated in the inner membrane of a mitochondrion and the thylakoid membranes in a chloroplast; passes electrons from one molecule to the next and generates ATP.
32
what does the term electron transfer chain mean?
- chain of electron carrier molecules in the inner membrane of a mitochondrion or thylakoid membranes in a chloroplast
33
Name 4 environmental factors that can limit the rate of photosynthesis.
- light intensity (light-dependent stage)
- CO2 level (light-dependent stage)
- temperature (enzyme-controlled steps)
- mineral/magnesium levels (maintain normal functioning of chlorophyll)
34
Outline some common agricultural practices used to overcome effect of limiting factors in photosynthesis.
- artificial light, especially at night
- artificial heating.
- additional of CO2, to greenhouse atmosphere
35
Why do farmers try to overcome the effect of limiting factors ?
- to increase yield.
- additional cost must be balanced with yield to ensure maximum profit .
36
Suggest how a student could investigate the effect of a named variable on the rate of photosynthesis.
- dependent variable : rate of O2 production/ CO2 consumption
1) use a potometer
2) place balls of calcium alginate containing green algae in hydrogen carbonate indicator (colour change orange —> magenta as CO2 consumed & pH increases.)
37
State the purpose and principle of paper chromatography.
- molecules in mixture separated based on their relative attraction to the mobile phase (running solvent) vs stationary phase (chromatography paper)
38
outline a method for extracting photosynthetic pigments .
- use a pestle and mortar to grind a leaf with an extraction solvent (propanone)
39
Outline how paper chromatography used to seperate photosynthetic pigments
1) use capillary tube to spot pigment extract onto pencil “start line” 1cm above bottom paper
2) place chromatography paper in solvent
3) allow solvent to run until almost touches other end of paper . pigments move different distances .
40
what are Rf values ? how can they be calculated ?
- ratios that allow comparison of how far molecules have moved in chromatograms
- Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front.
