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  7. A2 Unit F214 - Communication, Homeostasis and Energy

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photosynthesis summary
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coincise notes on photosynthesis, including the structure of chloroplasts, photosynthetic pigments, Thin layer chromatography, photsytems, light dependent and independent reactions, limiting factors.

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  • January 13, 2024
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  • 2023/2024
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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)

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