3.2 Photosynthesis 5 Flashcards
What is a cholorplast?
An organelle found in plants and algae, site of photosynthesis
Describe structure of chloroplast
Double membrane
Grana - stacks of thylakoids that contain photosystems, electron transport chains, ATP Synthase
Grana connected by Intergranal lamellae
Stroma - fluid filled matrix containing enzymes
Where are chloroplasts located in an angiosperm leaf?
Mainly found in mesophyll layers
How are chloroplasts adapted for photosynthesis?
- Thylakoids have large surface area for light dependent reactions
- Photosynthetic pigments arranged into photosystems to maximise light absorption
- Stroma directly surrounds grana - products of photosynthesis diffuse directly into stroma
- Contain their own DNA and ribosomes
- Inner chloroplast membrane less permeable than outer allows control over the movement of substances
How are angiosperm leaves adapted for photosynthesis?
- Large surface area to maximise light absorption
- Upper epidermis transparent to allow light to strike mesophyll layers
- Palisade layers densely packed to contain many chloroplasts
- Vein network - transports water and minerals to leaf and takes away sugars
- Air spaces reduce diffusion distance for CO2
- Thin to reduce diffusion distance for CO2
- Stomata - allows CO2 to diffuse into the leaf
What is a transducer? Why are chloroplasts described as transducers?
Something that converts one form of energy into another
Chloroplasts convert light energy into the chemical energy of ATP
What is a photosynthetic pigment?
A molecule present in chloroplast that absorb certain wavelengths of light
Examples of photosynthetic pigments
Chlorophyll a
Chlorophyll b
Xanthophyll
Beta Carotene
Purpose of chromatography?
To separate different products from a mixture
Equation used to calc the retention value (Rf)
Retention value (Rf)= distance travelled by component/ distance travelled by solvent
What is photosynthesis?
Complex metabolic pathway that synthesises organic molecules in the presence of light: 6CO2+6H2O -> C6H12O6 + 6O2
Two stages of Photosynthesis:
Light dependent stage
Light independent stage
What is a Photosystem?
- Two types: Photosystem I and Photosystem II
- Protein complex consisting of an antenna complex and a reaction centre
- Involved in the absorption of light and transfer of electrons in photosynthesis
Difference between Photosystems I & II
They absorb different wavelengths of light
Describe the process of light harvesting:
Antenna complex absorbs light energy of varying wavelengths and transfers to the reaction centre
Energy absorbed by two chlorophyll a molecules which emit excited electrons.
Absorption Spectra?
Graph showing wavelengths of light absorbed by a pigment
Action Spectra?
Graph of the rate of photosyntesis against each wavelength of light absorbed by a pigment
The sources of electrons for the electron transport chain
cyclic and non-cyclic photophosphorylation
Define cyclic photophosphorylation
The formation of ATP invovling Photosystem I only
Outline cyclic photophosphorylation
Involves only Photosystem I
Excited electrons enter the electron transport chain to produce ATP and return to Photosystem I
No reduction of NADP and no water required to replace lost electrons
What is the purpose of cyclic photophosphorylation
Produces additional ATP to provide surplus energy demands of the cell
Define non-cyclic photophosphorylation
The formation of ATP and reduced NADP involving both Photosystems I and II
Outline non-cyclic photophosphorylation
Involves Photosystems I and II
Excited electrons enter the electron transport chain to produce ATP
NADP acts as a final electron acceptor and is reduced
Water is photolysed to compensate for electrons lost from Photosystem II
What is the purpose of non-cyclic photophosphorylation?
Produces ATP and reduced NADP for the Calvin cycle
How does chemiosmosis produce ATP in the light dependent stage?
Protons flow down their concentration gradient from the thylakoid space into the stroma via ATP synthase
ATP synthase phosphorylates ADP to form ATP as protons flow through it
Describe photolysis
The splitting of a water molecule in the presence of light that occurs during the light dependent stage of photosynthesis producing protons electrons and oxygen
H2O -> 2H+ + 2e- + 1/2O2
What happens to the products of photolysis?
H+ - used in proton pumping and to reduce NADP
e- - replaces electrons lost from chlorophyll a in PSII
O2 - by-product used in respiration or diffuses out of leaf as waste gas.
Explain how the electron transport chain results in the production of reduced NADP.
NADP acts as a final electron acceptor, is subsequently reduced
Describe the light-independent stage of photosynthesis
Second stage of photosynthesis
Does not require light energy and takes place in the stroma
Uses carbon dioxide and the products of the light-dependent stage to build organic molecules
What is the light-independent stage also known as?
The Calvin Cycle
The three main stages of the Calvin Cycle:
- Carbon fixation
- Reduction
- Regeneration
What happens during the carbon fixation of the Calvin Cycle?
- Reaction between CO2 and ribulose biphosphate (RuBP) catalysed by the enzyme RuBisCo
- Forms unstable 6C intermediate that breaks down into two molecules of glycerate 3-phosphate (GP)
What happens during the reduction of the Calvin Cycle?
2x GP are reduced to 2x triose phosphate (TP)
Requires 2x reduced NADP and 2x ATP formed during the light-dependent reaction
Forms 2x NADP and 2x ADP that enter the light dependent reaction
What happens during the regeneration of the Calvin Cycle?
After 1C leaves the cycle the 5C compound RuP forms
RuBP is regenerated fron RuP using 1x ATP
Forms 1x ADP
How are nutrients produced as a result of photosynthesis?
Formation of amino acids from GP (required nitrates and sulfates)
TP molecules used to produce sugars e.g. glucose, fructose, sucrose
What is a limiting factor?
A variable that limits the rate of a particular reaction
Name the factors that limit the rate of photosynthesis. What stage do they limit?
Light intensity - light-dependent stage
Light wavelength - absorption of chlorophyll
CO2 levels - light-independent stage
Temperature - enzyme-controlled reactions
pH - enxyme-controlled reactions
Describe the role of nitrogen in plant metabolism.
Synthesis of amino acids, nucleotides and chlorophyll.
What does nitrogen deficiency in plants cause?
Stunted growth
Chlorosis (yellowing of the leaves)
Describe the role of magnesium in plant metabolism.
Synthesis of chlrophyll
What does magnesiumdeficiency in plants cause?
Chlorosis (yellowing of the leaves)
