Photosynthesis Flashcards
What is photolysis?
Splitting of a molecule using light energy.
What is photophosphorylation?
Process of adding a phosphate to a molecule using light energy.
What is photoionisation?
Process of turning an atom/molecule into an ion using light energy.
What is an electrochemical gradient?
Conc gradient of ions.
What is a photoautotroph?
Organisms that use light energy to synthesise organic molecules during photosynthesis.
What is a heterotroph?
Organisms that obtain organic materials from plants to supply energy and nutrients it needs.
What is a producer?
Organism that synthesises biomass using energy from the environment in 1st trophic level of food chain.
What is a photoautotroph?
Organisms that use light energy to synthesise organic molecules in photosynthesis.
What is a heterotroph?
Orgasims that obtain organic material from plants for energy + nutrients.
What is the compensation point?
Point photosynthesis and respiration are at the same rate.
No net change of carbs.
What is the compensation period?
The time taken for the plant to reach the compensation point.
What is the structure and function of different parts of a chloroplast?
PS have pigments, electron carriers, ATP synthase
Thylakoid stacks = large SA - within, photosystems bound to proteins
Stroma surrounds grant = contains enzymes for LDR
Stroma has small ribosomes - assemble proteins for photosynthesis
Chloroplast has large SA + 3 compartments for conc and electrochemical gradients
What is a photosynthetic pigment?
Can absorb specific wavelengths of light and trap energy associated with the light.
What are accessory pigments?
Funnel energy associated with light wavelengths down to primary pigment reaction centre
made of chlorophyll a
in walls of funnel, made of chlorophyll b and carotenoids
What is chlorophyll a?
Most abundant, P680, P700, absorbs light around 440 nm
What is chlorophyll b?
Absorbs light around 400-500 nm, and 650 nm
What are carotenoids?
Absorb light around 400-500 nm, yellow/orange
What are xanophylls?
Absorb light 375-550 nm, yellow
What happens in the light dependent stage?
- photoionisation of chlorophyll a in PS2
- electrons excited and released from PS2 to electron chain
- energy from electrons - pump H+ stroma to thylakoid space
- electrons move to PS1 and re photo ionised
- electrons used to reduce NADP with NADP reductase
- H+ flows down electrochemical gradient
- via ATP synthase, to ATP by chemiososis
- photolysis and electrons replace lost electrons from PS2
What is the difference between cyclic and non-cyclic LDR?
Cyclic: PS1, water not needed, not make NADPH, used to make extra ATP to meet cell energy demands
Non-cyclic: PS1+2, needs photolysis of water, O2 evolved, NADPH synthesised, products used for LIR
What are the key roles of water?
Source of protons
Donates electrons to chlorophyll to replace lost
Photolysis of water = O2 source for respiration
Needed for turgidity - stomata open for gas exchange
What are the uses of triose phosphate?
2 TP to 1 hexose sugar so can make glucose
some glucose to sucrose/starch/cellulose
some TP to aa/fatty acids/glycerol
5 of 6 TP to regenerate RuBP
What happens in the LIR?
Aka Calvin cycle.
1. carbon fixation - CO2 in air enters via stomata and diffuses to palisade cells then to stroma. conc gradient across chloroplast envelope.
How is 1 hexose sugar made in the Calvin cycle?
6 turns of cycle for 6 spare carbons. 2 ATP for 1 glucose, other 10 TP fr RuBP regeneration.
Why can the LIR only run in daylight?
- pump H+ into space for LDR, increasing pH of stroma
- optimum for enzymes
- Mg2+ = cofactor for rubisco by bind to AS
- electrons from PS1 needed to lower ferredoxin - activates other enzymes in Calvin
What are the factors affecting photosynthesis?
Light intensity - of certain wavelength. Light compensation point = all CO2 from respiration used, little NADPH made so GP increases and Calvin not continue.
CO2 conc - if too low, RuBP not react in Calvin so increases.
Temperature - low temps have low KE so fewer enzyme collisions. Above 30’C, stomata close. If higher, denature. GP + TP decrease, RuBP increases then decreases as not regenerated.
How can water availability limit photosynthesis?
Too much decreases ion uptake, if limited stomata close and rate decreases. too little, cells lose water and become plasmolysed.
