PHOTOSYNTHESIS
BIOLOGY
___
Notes
Photosynthesis vs Respiration
In photosynthesis, light energy is trapped to synthesise glucose (anabolic)
In respiration, chemical energy is released from the breakdown of glucose (catabolic) which is
used to drive energy-requiring processes
Sunlight energy→ATP→Glucose→ATP→Energy-requiring processes
Raw materials = products of opposite reaction
CO2 released by respiration is used by plants for photosynthesis
O2 released by plants from photosynthesis is used in respiration
STRUCTURE OF CHLOROPLASTS
● Network of membranes to increase surface area to maximise light absorption
● Form flattened sacs (THYLAKOIDS) which are stacked to form GRANA, joined through
membraneous channels -LAMELLAE.
● Fluid enclosing grana is the STROMA
● Have their own DNA containing genes that code for the proteins/enzymes required in
photosynthesis
● STARCH GRAINS as a temporary storage of carbohydrates
Photosynthetic pigments
● Different pigments help optimise absorption of light energy: wider range of wavelengths
of light is absorbed
● Chlorophyll reflects green, absorbs red (680-700nm) and blue (450nm)
, ○ Chlorophyll a blue-green = reaction centre
○ Chlorophyll b yellow-green
○ Carotene orange
○ Xanthophyll yellow (rest of these are accessory pigments)
ABSORPTION spectrum
Different pigments absorb different wavelengths of light
ACTION spectrum
Rate of photosynthesis varies when exposed to different wavelengths of light
THIN-LAYER CHROMATOGRAPHY
To separate photosynthetic pigments
1) Extract pigments and apply them to TLC plate as a concentrated spot at 1 end
2) Hang it in chromatography jar with solvent at bottom
3) Different pigments have different solubilities in the solvent (mobile phase) and different
interactions with TLC plate (stationary phase)
4) So move at different rates = separate through the silica gel
5) Rf value for each spot is calculated and compared to known Rf values of pigments
PHOTOSYSTEM
Pigment bound to its associated protein
Light-harvesting system + reaction centre
accessory pigments in funnel-like structure (antennae complex/light-harvesting system)
transfer absorbed light energy to the reaction centre
1 (P700): chlorophyll a with peak absorption at 700nm in lamellae
2 (P680): chlorophyll a with peak absorption at 680nm in thylakoid membrane
LIGHT DEPENDENT STAGE in thylakoids (non-cyclic photophosphorylation)
PSII absorbs light: electrons excited to a higher energy level and released = captured by electron
carrier then passed along electron transport chain (series of electron carriers with progressively
lower energy levels)
BIOLOGY
___
Notes
Photosynthesis vs Respiration
In photosynthesis, light energy is trapped to synthesise glucose (anabolic)
In respiration, chemical energy is released from the breakdown of glucose (catabolic) which is
used to drive energy-requiring processes
Sunlight energy→ATP→Glucose→ATP→Energy-requiring processes
Raw materials = products of opposite reaction
CO2 released by respiration is used by plants for photosynthesis
O2 released by plants from photosynthesis is used in respiration
STRUCTURE OF CHLOROPLASTS
● Network of membranes to increase surface area to maximise light absorption
● Form flattened sacs (THYLAKOIDS) which are stacked to form GRANA, joined through
membraneous channels -LAMELLAE.
● Fluid enclosing grana is the STROMA
● Have their own DNA containing genes that code for the proteins/enzymes required in
photosynthesis
● STARCH GRAINS as a temporary storage of carbohydrates
Photosynthetic pigments
● Different pigments help optimise absorption of light energy: wider range of wavelengths
of light is absorbed
● Chlorophyll reflects green, absorbs red (680-700nm) and blue (450nm)
, ○ Chlorophyll a blue-green = reaction centre
○ Chlorophyll b yellow-green
○ Carotene orange
○ Xanthophyll yellow (rest of these are accessory pigments)
ABSORPTION spectrum
Different pigments absorb different wavelengths of light
ACTION spectrum
Rate of photosynthesis varies when exposed to different wavelengths of light
THIN-LAYER CHROMATOGRAPHY
To separate photosynthetic pigments
1) Extract pigments and apply them to TLC plate as a concentrated spot at 1 end
2) Hang it in chromatography jar with solvent at bottom
3) Different pigments have different solubilities in the solvent (mobile phase) and different
interactions with TLC plate (stationary phase)
4) So move at different rates = separate through the silica gel
5) Rf value for each spot is calculated and compared to known Rf values of pigments
PHOTOSYSTEM
Pigment bound to its associated protein
Light-harvesting system + reaction centre
accessory pigments in funnel-like structure (antennae complex/light-harvesting system)
transfer absorbed light energy to the reaction centre
1 (P700): chlorophyll a with peak absorption at 700nm in lamellae
2 (P680): chlorophyll a with peak absorption at 680nm in thylakoid membrane
LIGHT DEPENDENT STAGE in thylakoids (non-cyclic photophosphorylation)
PSII absorbs light: electrons excited to a higher energy level and released = captured by electron
carrier then passed along electron transport chain (series of electron carriers with progressively
lower energy levels)
