Photosynthesis Detailed Summary

detailed summary of the current a2 spec for photosynthesis in pdf.

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  • Created on: 21-04-16 14:11
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amelia kirk
Photosynthesis summary
Key Terms Light energy from the sun chemical energy, believed to
Autotrophs: organisms that use light
have first evolved in some prokaryotes 2500 million years
energy or chemical energy and inorganic
molecules to synthesise complex organic
ago, nearly all life on Earth depends on photosynthesis,
molecules chemical potential energy is available to consumers and
Heterotrophs: organisms that ingest decomposers, releases oxygen so all aerobes depend on it.
and digest complex organic molecules, releasing
the chemical potential energy stored in them Chemoautotrophs: first life forms, prokaryotes, synthesised
Photosynthetic pigments: complex organic molecules using energy from exergonic
molecules that absorb light energy, each pigment chemical reactions, nitrifying bacteria obtain energy from
absorbs a range of wavelengths in the visible oxidising ammonia to nitrite or nitrite to nitrate, some
region and has its own distinct peak of absorption, chemoautotrophs support very specific food chains.
other wavelengths are reflected
Photophosphorylation: the
making of ATP from ADP and Pi in the presence of
The majority of food chains on Earth have producers that are
light photoautotrophs. Photoautotrophs and heterotrophs release
Electron carriers: molecules that chemical potential energy in complex organic molecules -
transfer electrons respiration.
Electron acceptors: chemicals that 6CO2 + 6H2O (+light energy) C6H12O6 + 6O2
accept electrons from another compound, they Radioactive isotopes - using water containing radioactive
are reduced while acting as oxidising agents isotopes of oxygen, the oxygen released in photosynthesis
Light-independent stage: carbon was radioactive, but not when the carbon dioxide had the
dioxide is fixed and used to build complex organic isotopes, so the oxygen is released from water.
Limiting factor: the factor that is Photosynthesis takes place in organelles - chloroplasts.
present at the lowest or least favourable value
Photosynthesis happens in two main stages, consisting of
Photosynthometer: used to measure
the rate of photosynthesis by collecting and
smaller steps.
measuring the volume of oxygen produced in a
certain time
Chloroplasts are 2-10µm long, surrounded by an
envelope. Inter membrane space, 10-20nm wide.
Outer membrane permeable to small ions, inner
membrane has transport proteins - folded into
lamellae stacked to form grana, between grana are
intergranal lamellae. Stroma - fluid-filled matrix,
reactions of light-independent stage. Grana - stacks
of flattened membrane compartments (thylakoids), Photosynthetic pigments absorb certain
sites of light absorption and ATPsynthesis during light- wavelengths of light and reflect others. In
dependent stage. thylakoid membranes, arranged in funnel-shaped
structures called photosystems. Chlorophylls -
Inner membrane controls substance movement, grana mixture of pigments, long phytol chain and a
provide large surface area, photosynthetic pigments porphyrin group. Two forms of chlorophyl - P680
arranged into photosystems, fluid-filled stroma (photosystem II, 680nm) and P700 (photosystem I,
contains necessary enzymes, grana surrounded by 700nm), centre of photosystems and known as
stroma so products of light-dependent reaction can primary pigment reaction centre, chlorophyll a
readily pass into the stroma. Chloroplasts can make absorbs blue light, chlorophyll b absorbs light
some proteins needed. wavelengths 500nm - 640nm.

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Accessory pigments - carotenoids reflect yellow and orange light and absorb blue light, do not contain
porphyrin group, not directly involved in light-dependent reaction, carotene and xanthophyll are main
carotenoid pigments
The Light-Dependent Stage
Takes place in the thylakoid membranes. PSI mainly on intergranal
lamellae, PSII on granal lamellae. Trap light to be converted into
chemical energy.…read more

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Limiting Factors
Light and supplies of carbon dioxide and water are present in the environment and may influence the rate
at which photosynthesis proceeds. The factors affecting the rate of photosynthesis are all operating
simultaneously, the factor present in the least favourable amount limits the process - limiting factor.…read more

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Limiting Factors and the
Calvin Cycle
Light intensity - increase alters rate of light-
dependent reaction, more light excites electrons
which take part in photophosphorylation so more ATP
and reduced NADP produced which are both used in
light-independent stage as sources of hydrogen and
energy to reduce GP to TP, ATP used to
phosphorylate 5/6 molecules of TP to regenerate
RuBP, decrease in light intensity means GP cannot
be changed to TP so GP accumulates and TP levels
fall, which lowers amount of RuBP reducing…read more


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