Chapter 13 Photosynthesis Essay QS Flashcards
Describe the structure of a chloroplast. (9)
- biconvex disc
- 3 - 10 micrometres, 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
Describe the arrangement & location of chloroplast pigments & discuss their effect on absorption spectra. (8)
- chlorophyll a is primary pigment
- carotenoids/chlorophyll b, is accessory pigment
- arranged in, light harvesting clusters/photosystems
- on, grana/thylakoids
- ref. PI & PII; A P700 & 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 & b absorb light in red & 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
Describe how you would separate chloroplast pigments using chromatography. (6)
- grind leaf with solvent
- example of solvent; e.g. propanone
- leaf extract contains mixture of pigments
- ref. concentrate extract
- further detail; e.g. pencil 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
Describe the role of light in photosynthesis. (8)
- light energy converted to chemical energy
- ref. to wavelength of light absorbed
- by chlorophyll/ref. to photosystem/PS traps light energy
- electrons excited
- harnessed in ETC
- synthesis of ATP
- synthesis of NADPH2/NADPH/NADPH + H+/reduced NADP
- (ATP & NADPH2) drive dark reaction/Calvin cycle
- PHOTOLYSIS of water/DISSOCIATION of water
- electron from hydroxyl ion
- forming oxygen
- non-cyclic (photophosphorylation) produces ATP AND NADPH2/NADPH/NADPH + H+/reduced NADP
- cyclic (photophosphorylation) only produces ATP
Explain the importance of light dependent reaction in photosynthesis. (7)
- traps/converts light energy
- chlorophyll
- electrons excited
- harnessed in electron transfer chain
- synthesis of ATP from ADP & Pi
- photolysis/dissociation, of water
- forming oxygen
- electron from hydroxyl ion
- H+ to reduce NADP to NADPH/reduced NADP
- ATP & NADPH2 drive light independent reaction/Calvin Cycle
Describe how, in photosynthesis, light energy is converted into chemical energy, in the form of ATP. (8)
- light energy absorbed by, chlorophyll/photosystems/pigments
- electron, excited/raised to higher energy level
- (electron) emitted by, chlorophyll/photosystems/pigments
- passes to electron, acceptor/carrier
- passes along, chain of electron carriers/ETC/electron transfer chain
- energy released used to pump protons/ATP production here
- into thylakoid space
- thylakoid membrane impermeable to protons
- proton gradient forms
- protons move down gradient
- through/using, ATP synthase/ATP synthetase
- enzyme rotates
- ATP produced ADP & Pi
Outline the main features of the light-dependent stage of photosynthesis. (8)
- photoactivation of chlorophyll/photosystems
- excitation of electrons
- detail of membranes/pigments
- electrons passed through chain of electron carriers
- ADP + Pi –> ATP
- ref. cyclic photophosphorylation (to make more ATP)
- production of reduced NADP
- ref. non-cyclic photophosphorylation (to reduce NADP)
- photolysis of water
- to produce protons/H+ ions for reducing NADP
- to produce electrons to replace those lost from chlorophyll/photosystems
Describe the photoactivation of chlorophyll & its role in cyclic photophosphorylation. (8)
- (photosynthetic pigments) arranged in light harvesting clusters
- primary pigments/chlorophyll a
- at reaction centre
- P700/PI, absorbs light at 700 nm
- accessory pigments/chlorophyll b/carotenoids
- surround, primary pigment/reaction centre/chlorophyll a
- absorb light
- pass energy to, primary pigment/reaction centre/chlorophyll a
- (light absorbed results in) electron excite
- emitted from, chlorophyll/primary pigment/reaction centre
- passes to electron, acceptor/carrier
- (electron) passes along, chain of electron carriers/ETC
- ATP synthesis
- electron returns to, P700/PI
Outline the process of photolysis of water & describe what happens to the products of photolysis. (10)
- PII absorbs light
- enzyme (in PII) involved
- to break down water
- 2H2O –> 4H+ + 4e- + O2
- oxygen is produced
- used by cells for (aerobic) respiration
- or released (out of plant) through stomata
- protons used to reduce NADP
- with electrons from PI
- reduced NADP used in, light independent stage/Calvin cycle
- to convert GP to TP
- electrons also used in ETC
- to release energy for photophosphorylation
- to produce ATP
- electrons (from PII) go to PI
- ref. re-stabilise PI
Describe how non-cyclic photophosphorylation produces ATP & reduced NADP. (9)
- photosystem I (PI) & 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 a higher energy level
- (electrons) taken up by electron acceptor
- (electrons) pass down electron carrier chain (to produce ATP)
- PII has (water-splitting) enzyme
- water split into protons, electrons & oxygen
- photolysis
- electrons from PII to PI/electrons from water pass to PII
- to replace those lost; give either in relation to PI or PII
- protons & electrons combine with NADP (to produce NADPH)
Outline the main features of Calvin cycle. (9)
- RuBP, 5C (compound)
- combines with carbon dioxide
- rubisco/RuBP carboxylase
- to form an UNSTABLE 6C compound that IMMEDIATELY SPLITS to form
- 2GP/glycerate 3-phosphate/PGA/phosphoglyceric acid
- using H from NADPH
- using ATP
- to form TP/triose phosphate/PGal/phosphoglyceraldehyde/GALP
- TP/PGalb/GALP used to form glucose/carbohydrates/lipids/amino acids
- TP/PGal/GALP used in regeneration of RuBP
- requires ATP
- as source of phosphate
- light independent
Explain the role of NADP in photosynthesis. (6)
- coenzyme
- reduced
- carries protons
- and (high energy) electrons
- from photosystem/light stage
- on thylakoid membrane
- to stroma/Calvin cycle
- ref. regeneration of NADP
Explain briefly how reduced NADP is formed in the light-dependent stage & how it is used in the light-independent stage. (7)
- photolysis of water
- releases H+ (R hydrogen atoms)
- by, P680/PII
- electrons released from, P700/PI
- electrons (from PI) & H+ combine with NADP
- used in Calvin cycle
- reduces, GP/PGA
- to TP
- ATP used (during reduction of GP)
- NADP, regenerated/oxidised
Discuss the effects of variations in carbon dioxide concentrations & light intensity on the rate of photosynthesis. (6)
Carbon dioxide
- 0.03%
- most likely limits/major limiting/implied low in atmosphere
- increase in carbon dioxide concentration & increase in rate
- during day when light & warm
- ref. to variations in conc. e.g., within canopy/at soil surface
Light intensity
- ref. to wavelengths of light
- light saturated below full sun
- idea of limiting & saturation, with other key factor limiting
- light & stomatal aperture
- & temperature of leaf
- day length & season/morning & evening
- high light & damage to pigments
- ref. to light exciting electrons in chlorophyll
