Photosynthesis Flashcards
How are photosynthesis and respiration related ?
- CO² & H²O are the raw materials for photosynthesis and the products of respiration
- O² & glucose are the raw ,materials for respiration and the products of photosynthesis
Describe the structure of chloroplast
- Usually disc shaped
- Double membrane (envelope)
- Thylakoids : flattened discs stacked to form grana
- Intergranal lamellae : tubular extensions attach thylakoids in adjacent grana
- Stromatolites : fluid-filled matrix with high enzyme & substrate concentration & own loop of DNA
Refer to GoodNotes
Where do the light-dependent & light-independent reactions occur in plants ?
- Light-dependent: in the thylakoids of chloroplast
- Light-Independent: Stroma of chloroplast
What is the role of photosynthetic pigments ? Name the 2 main groups
Embedded within thylakoid membrane. Absorb different wavelengths of light to maximise rate of photosynthesis
- Primary pigment : chlorophyll (made of chlorophyll A & chlorophyll B) found in photosystems
- Accessory pigments : carotenoids (carotene & xanthophylls) found in light harvesting systems
Name the processes in light-dependent reactions
- Photoionisation
- electron transfer chain
- Chemiosmosis
Non-cyclic only: - Reduction of NADP
- Photolysis of water
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
What happens in the electron transfer chain (ETC) ?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reactions, which releases energy
How does chemiosmosis produce ATP in the light-dependent stage ?
- Some energy released from the ETC is coupled to active transport of H+ ions from Stroma into thylakoid space
- H+ ions move down concentration gradient from thylakoid pace into Stroma via transmembrane channel protein ATP synthase
- ATP synthase catalyses ADP + Pi —> ATP
Describe non-cyclic photophosphorylation
- Uses Photosystems I & II. Excited electrons Enter ETC to produce ATP. NADP acts as final electron acceptor & is reduced. Water is undergoes photolysis to release electrons replacing those lost from PS II
- Purpose is to produce ATP & reduced NADP for Calvin cycle to produce biological compounds
Describe cyclic photophosphorylation
- Uses only Photosystem I . Excited electrons enter ETC to produce ATP then return directly to photosystem (so no reduction of NADP & no water needed to replace lost electrons)
- Purpose is to produce additional ATP to meet surplus energy demands of cell
What happens in photolysis of water ?
Light energy splits molecules of water
2H²O —> 4H+ + 4e- + O²
What happens to the products of the photolysis of water ?
- H+ ions : move out thylakoids space via ATP synthase & 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+ (from photolysis of water) + 2e- (from acting as final electron acceptor in ETC) —> reduced NADP
- Catalysed by dehydrogenase enzymes
- Stroma of chloroplasts
Name the 3 main stages in the light-independent reaction
- Carbon Fixation
- Reduction
- Regeneration
What happens during carbon fixation ?
- Reaction between CO² & ribulose bisphosphate (RuBP) catalysed by ribulose bisphosphate carboxylate (RuBisCo)
- Forms useable 6C intermediate that breaks down into 2 x glycerate 3-phosphate
What happens during reduction in the light-independent reaction
- 2 x glycerate 3-phosphate (GP) are reduced to 2 x triose phosphate (TP)
- Requires 2 x reduced NADP & 2 x ATP
- Forms 2 x NADP & 2 x ADP
Outline the roles of Triose Phospahte from the light-independent reaction
- Raw material : 1C leaves the cycle to produce monosaccharides, amino acids & other biological molecules
- Involves in regeneration of RuBP: After 1C leaves cycle, the %C compound RuP forms. RuP is converted into RuBP using 1x ATP. Forms 1x ADP
Outline the sequence of events in the light-independent reaction
Refer to GoodNotes
State the number of Carbon atoms in RuBP, GP & GALP
- RuBP : 5
- GP : 3
- GALP : 3
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 (light-dependent stage)
- CO² levels (light-independent stage)
- Temperature (enzyme-controlled steps)
- Mineral/magnesium levels (maintain normal functioning of chlorophyll)
How does light intensity affect the rate of photosynthesis?
Low light intensity = slower light-dependent reaction = less ATP & NADPH produced to convert GP to TP in light-independent reaction
- GP level rises
- TP levels falls = RuBP levels falls
Define the implications of water stress
- Abscisic acid binds to complementary receptors on guard cell membrane, causing ca²+ ion channels on tonoplast to open. ca²+ ions diffuse from the vacuole into cytosol
- Positive feedback triggers other ion channels to open. Other ions e.g. K+ diffuse out of guard cell
- Water potential of guard cell becomes more positive. Water diffuses out via osmosis
- Guard cells become flaccid so stomata close
State the purpose and principle of thin layered chromatography (TLC)
Molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (TLC plate, usually coated in a silicate)
Outline a method for extracting photosynthetic pigments
Use a pestle and mortar to grind a leaf with an extraction solvent e.g. propanone
Outline how TLC can be used to separate photosynthetic pigments
- Use a capillary tube to spot pigment extract onto pencil ‘start line’ (origin) 1 cm above bottom of plate .
- Place chromatography paper in solvent (origin should be above solvent level)
- Allow solvent to run until it almost touches the other end of the paper. Pigments move difference distances
