photosynthesis (energy transfers in and between organisms) Flashcards
where in the chloroplasts do each of the stages of photosynthesis take place
light dependent reaction - thylakoids
light independent reaction - stroma
explain the role of light in photoionisation
chlorophyll molecules absorb light energy which excites 2 electrons (raises them to a higher energy level), causing them to be released from chlorophyll
name the 2 main stages of the light dependent reaction
electron transfer chain
chemiosmosis
what happens in the electron transfer chain?
electrons removed from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions which releases energy
how is a proton concentration gradient established during chemiosmosis?
some energy released from the etc is coupled to the active transport of H+ ions from the stroma into the thylakoid space
how does chemisosmosis produce atp in the light dependent stage
H+ ions move down their concentration gradient from the thylakoid space into the stroma via the channel protein, ATP
synthase
Explain the role of light in photolysis
Light energy splits molecules of water
2H2O > 4H+ + 4e- + O2
What happens to the products of the photolysis of water
H+ ions: move out of the thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
e-: replace electrons lost from chlorophyll
O2: used for respiration or diffuses out of leaf as waste gas
How and where is reduced NADP produced in the light-dependent reaction?
NADP + 2H+ + 2e- > reduced NADP.
Catalysed by dehydrogenase enzymes
Stroma of chloroplasts
Where do the H+ ions and electrons used to reduce NADP come from?
H+ ions: photolysis of water
electrons: NADP acts as the final electron acceptor of the electron transfer chain
Name the 3 main stages in the Calvin Cycle
Carbon fixation
Reduction
Regeneration
What happens during carbon fixation?
Reaction between CO2 and ribulose bisphosphate (RuBP) catalysed by the enzyme rubisco
forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)
What happens during reduction in the calvin cycle
2x GP are reduced to 2x triose phosphate (TP)
requires 2x reduced NADP and 2xATP
forms 2xNADP and 2x ATP
How does the light independent reaction result in the production of useful organic substances
1C leaves the cycle (Some of the TP is converted into useful organic molecules)
What happens during regeneration in the calvin cycle
After 1C leaves the cycle, 5C compound RuP forms
RuBP is regenerated form RuP using 1x ATP
forms 1x ADP
state the roles of ATP and (reduced) NADP in the light independent reaction
ATP: reduction of GP to TP and provides phosphate group to convert RuP into RuBP
(reduced) NADP: coenzyme transports electrons needed for reduction of GP to TP
State the number of carbon atoms in RuBP, GP and TP
RuBP : 5
GP: 3
TP: 3
Describe the structure of a chloroplast
usually disc shaped
double membrane (envelope)
thylakoids: flattened dics to form grana
intergranal lamellae: tubular extensions attach thylakoids in adjacent grana
stroma: fluid-filled matrix
How does the structure of the chloroplast maximise the rate of the light-dependent reaction?
ATP synthase channels within granal membrane
large surface area pf thylakoid membrane for ETC
photosystems position chlorophyll to enable maximum absorption of light
How does the structure of the chloroplast maximise the rate of the light-independent reaction
own DNA and ribosomes for synthesis of enzymes
concentration of enzymes and substrates in stroma is high
define limiting factor
factor that determines maximum rate of a reaction, even if other factors change to become more favourable
name 4 environmental factors that can limit the rate of photosynthesis
light intensity (LDR)
CO2 levels (light-independent reaction)
temperature ( enzyme-controlled steps)
mineral/magnesium levels (maintain normal functioning of chlorophyll
outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
artificial light
artificial heating
addition of CO2 to greenhouse atmosphere
Why do farmers try to overcome the effect of limiting factors
to increase yield
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 hydrogencarbonate indicator (colour change orange to magenta as CO2 is consumed and pH increases)
state the purpose and principle of paper chromatography
molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper)
Outline a method for extracting photosynthetic pigments
use a pestle and mortar to grind a leaf with an extraction solvent (propanone)
outline how paper chromatography can be used to seperate photosynthetic pigments
- use a capillary tube to spot pigment extract onto pencil ‘start line’ 1cm above the bottom of the paper
- place chromatography paper in the solvent (origin should be above the solvent level)
- allow solvent to run until it almost touches the other end of the paper. pigments move different distances
What are Rf values and 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
