5.2.1 Photosynthesis Flashcards
Equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
What organisms undergo photosynthesis
Autotrophs (e.g. plants and algae)
Structure of chloroplasts
- double-membrane
- filled with stroma
- thylakoids: flattened fluid-filled sacs made of membrane
- grana: stack of thylakoids
- lamellae: connect grana
- 70S ribosomes
- DNA loops
- starch grains
Examples of pigments in chloroplasts
Chlorophyll a = primary pigment
Accessory pigments = chlorophyll b, xanthophylls, carotenoids
How are pigments organised in a chloroplast
Embedded within thylakoid membranes
- Accessory pigments, along with proteins, form a light harvesting system, absorbs light and transfers it to the reaction centre
- primary pigment is in the reaction centre, where reactions in photosynthesis occur
- light harvesting system and reaction centre forms a photosystem
What are the stages of photosynthesis
Light-dependent: energy from sunlight used to form ATP, NADP is reduced
Light-independent: organic molecules are built using ATP and reduced NADP
What wavelength does photosystem I absorb
700nm
What wavelength does photosystem II absorb
680nm
Describe non-cyclic photophosphorylation
- Light is absorbed at PSII which excites a pair of electrons, these are released from the reaction centre and passed down an ETC
- ATP is produced by chemiosmosis
- electrons lost are replaced by water that has undergone photolysis
- excited electrons are released from the reaction centre of PSI, which are passed to another ETC, ATP is produced
- electrons from PSII replace the lost electrons
- electrons are accepted along with a proton by NADP, forming reduced NADP
What is NADP
A coenzyme
What is photolysis
Splitting of water using energy from the sun
H2O -> 2H+ + 2e- + 1/2O2
Describe cyclic photophosphorylation
- electrons leaving PSI can be returned there instead of forming NADP
- ATP still produced
Where does the light-dependent stage occur
In the thylakoids membranes
What is included in the light-dependent stage
Non-cyclic/ cyclic photophosphorylation
Photolysis
Where does the light-independent stage take place
In the stroma
Describe the Calvin cycle
Fixation
Reduction
Regeneration
Fixation stage of the Calvin cycle
CO2 is combined with 5 carbon RuBP
- enzyme RuBisCO catalyses the reaction, unstable 6 carbon compound is formed
- unstable compound breaks down into 2 3 carbon GP molecules
Reduction stage of the Calvin cycle
Each GP molecules converted to TP using a hydrogen atom from NADP and energy from ATP
Regeneration stage of the Calvin cycle
RuBP regenerated from recycled TP
Some TP leaves the Calvin cycle and is used to form lipids, glucose, amino acids
What’s included in the light-independent stage of photosynthesis
The Calvin cycle
How can photosynthetic pigments be investigated
Chomatography
- mobile phase = solution of different pigments
- stationary phase = silica gel
How does light intensity affect rate of photosynthesis
Light needed as energy source
As light intensity increases, ATP and reduced NADP produced at higher rate
How does CO2 concentration affect rate of photosynthesis
Needed as a source of carbon, increasing concentration increases rate of fixation in Calvin cycle, and rate of TP production
How does temperature affect rate of photosynthesis
As temperature increases, enzyme activity increases until denaturation
- rate of photorespiration increases above 25ºC so rates may not increases despite no denaturation
