TOPIC 5- ON THE WILD SIDE
- Created by: CiaraRedmond
- Created on: 11-11-13 09:36
ON THE WILD SIDE
5.1 Photosynthesis
Need for energy
ð Autotrophic organisms make organisms compounds from carbon dioxide
ð Heterotrophic organisms generally eat plants or other animals which have eaten plants, using the products of photosynthesis indirectly
ð 6CO2 + 6H2O à C6H12O6 + 6O2
o Oxygen is released as a waste product
ATP
ð Constantly available in an accessible form
ð Found in all living organisms in exactly the same form
o Adenosine triphosphate (ATP)
o Nucleotide with 3 phosphate groups attached
o The 3rd phosphate bond can be broken by a hydrolysis reaction
§ Catalysed by the enzyme ATPase
§ The result is adenosine diphosphate (ADP) and a free inorganic phosphate
§ Reversible reaction
ð Making ATP- electron transport chain
o Synthesised by the removal of hydrogen atoms from several of the intermediates in a metabolic pathway
o When two hydrogen atoms are removed from a compound they are picked up by a hydrogen carrier and acceptor
o The acceptor become reduced
o Electrons are passed along a series of carriers known as an electron transport chain
o The components are reduced when they receive electrons and oxidised when they pass them on
o Redox reactions release energy to drive the synthesis of an ATP molecule
Chloroplasts
ð Structure
o The membranes within a chloroplast are arranged in stacks (grana)
o A granum is made up of stacks of membrane disks (thylakoids) where the green pigment chlorophyll is found
o The grana are surrounded by a matrix called the stroma
ð Chlorophyll
o A group of 5 closely related pigments
§ Include chlorophyll a (blue green) and chlorophyll b (yellow green) and the carotenoids
o Each of the pigments absorbs and captures light from particular areas of the spectrum
o Photosystem 1 (PS1) and photosystem 2 (PS2) contain different combinations of chlorophyll pigments so absorbs light in a different area of the spectrum
Light-dependent stage
ð Only occurs in light and produces materials to use in light-independent stage
ð Occurs on the thylakoid membranes
ð Produces ATP and splits water molecules in a photochemical reaction to provide hydrogen ions to reduce CO2
ð When a photon of light hits a chlorophyll molecule, the energy is transferred to the electrons of that molecule
o The electrons are excited and raised to higher energy levels
o Excited electrons are picked up by and electron acceptor resulting in the synthesis of ATP by cyclic and non-cyclic photophosphorylation
Cyclic and non-cyclic photophosphorylation
ð Cyclic
o Involves only PS1 and drives the production of ATP
o When an electron returns to the chlorophyll molecule in PS1 it can then be excited again
ð Non-cyclic
o Involves PS1 and PS2 to…
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