Topic 5 - on the wild side, biology A2, edexcel snab unit 4

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  • Created on: 03-01-13 18:31
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ON THE WILD SIDE
PHOTOSYNTHESIS
Producers (autotrophs) make their own food by photosynthesis
6CO2 + 6H20 602 + CH12O6
(in the presence of light and chlorophyll)
Photolysis is used, the process of splitting water using light energy
Photosynthesis stores energy as glucose
CHLOROPLASTS
Photosynthesis occurs in the chloroplasts (small, flattened organelles).
Thylakoid membranes: A system of interconnected, flattened fluid filled sacs.
Proteins including photosynthetic pigments and electron carriers are in the
membrane and are involved in the light-dependent reaction
Granum: A stack of thylakoids
Thylakoid space: Fluid within the thylakoid sacs contain enzymes for photosynthesis
Stroma: Fluid surrounding the thylakoid membranes. Contains enzymes needed for
the light-independent reactions
Starch grain: Stores the products of photosynthesis
LIGHT DEPENDENT REACTIONS
In the thylakoid membrane
ADP + Phosphate ATP
Produce reduced NADP, ATP and waste oxygen
1) Light energy provided by sun
2) Light absorbed by chlorophyll pigment in chloroplasts
3) Light energy excites electrons in the chlorophyll so they get boosted up to a higher
energy level
4) Electrons are accepted and pass along protein carriers in an electron transport chain
5) Energy released from oxidation and reduction of carriers enables ATP to form ADP
and a phosphate (photophosphorylation).
6) Electrons and hydrogen ions from the water move along carriers and are accepted by
the coenzyme NADP. NADP becomes reduced NADP (NADPH) through photolysis.

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As well as two hydrogen ions being taken from the water, two electrons are taken to
replace those from the chlorophyll. The electron transport chain splits water
(photolysis) using energy from sunlight.
8) The oxygen from the water is released through the leaf (waste product).…read more

Page 3

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Chlorophyll a excited and promotes electron to higher energy level
e- picked up by electron carrier
Enough energy released to photophosphorylate
Electrons aren't passed on to NADP, but are passed back into photosystem I via
electron carriers ­ electrons repeatedly flow through PSI (recycled).…read more

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Photolysis: Splitting of a molecule using light
Hydrolysis: Splitting of a molecule using water (ATP hydrolysed to ADP)
Redox reactions: Involve oxidation (losing electrons) and reduction (gaining
electrons)
Chloroplasts are adapted for photosynthesis because thylakoids have a large surface area so
more light can be absorbed. Stroma contains the enzymes needed for light independent
reactions and the chloroplast envelops keeps reactants close to reaction sites.…read more

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Parasitism ­ diseased animals will be weakened and not reproduce
successfully. They cannot hunt well and are more likely to be caught. Parasites
can wipe out whole populations and spread fast when there is a high
population (close proximity).
Competition for resources
Grazing
Anthropogenic factors arise from human activity and can be both abiotic and biotic.…read more

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NPP (Net Primary Productivity) is the rate that organic molecules are made into new
biomass.…read more

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Other factors of climate change are:
Degree of reflection from ice and snow
Extent of cloud cover
Changes in sun's radiation
Extrapolation = extending a line on a graph ­ we assume there is enough data to establish
the trend accurately and present trends continue. Extrapolation is often the basis for
predictions.…read more

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Biofuels ­ fuels directly from biomass which are burnt to release energy,
producing carbon dioxide. Because the amount of carbon dioxide released
when burnt is the same removed by photosynthesis, plants are carbon
neutral so have no net increase. Plants can be grown all the time so are a
renewable energy source. Examples are wood, straw and vegetable oil. They
can reduce the use of limited fossil fuels, reducing carbon emissions.…read more

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Hybrid inviability: Hybrids produced but don't live long enough to reproduce
Hybrid sterilisation: Hybrid survives long enough to breed but is infertile
VALIDATING SCIENCE
In order to test theories, data needs to be collected to prove or disprove it. Scientists
within the scientific community accept evolution as there is evidence to make it reliable and
valid.
Scientists validate data in 3 ways:
1) Scientific journals ­ scientists publish articles describing their work ­ share ideas,
theories, experiments, evidence and conclusions.…read more

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iruka

I'm so Grateful Thank you

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