Photosynthesis Flashcards
(29 cards)
Identify environmental factors that limit the rate of photosynthesis
- light intensity (light-dependent stage)
- co2 levels (light-independent stage)
- temperature
- mineral/Mg levels
Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
- artificial light, esp at night
- artificial heating
- addition of co2 to greenhouse atmosphere
Where do the light-dependent and light-independent reactions occur in plants
light-dependent: in the thylakoids of chloroplasts
light-independent: stroma of chloroplasts
Explain the role of light in photoionisation
- chlorophyll molecules absorb energy from photons of light
- this ‘excites’ 2 electrons (raises them to a higher energy level), causing them to be released from the chlorophyll
Name the 2 main stages involved in ATP production in the light-dependent reaction
- electron transfer chain
- chemiosmosis
What happens in the electron transfer chain
electrons released 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 (protons) from the stroma into the thylakoid space
How does chemiosmosis produce ATP in the light-dependent stage
H+ ions move down their conc 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
What happens to the products of the photolysis of water
- H+ ions: move out of 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- to 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 stages of the Calvin cycle
1- carbon fixation
2- reduction
3- regeneration
What happens during carbon fixation?
- reaction between CO2 & ribulose bisphosphate (RuBP) catalysed by rubisco
- forms unstable 6C intermediate that breaks down into 2x glycerine 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 2x ATP
- forms 2x NADP and 2x ADP
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, the 5C compound RuP forms
- RuBP is regenerated from 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 no of carbon atoms in RuBP, GP, TP
RuBP: 5
GP: 3
TP: 3
Describe the structure of a chloroplast
- usually disc shaped
- double membrane
- thylakoids: flattened discs stack 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 of 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 e.g rubisco
- 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
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
