Download - 3.8 8.2 Photosynthesis PPT
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Topics 3.8 + 8.2
Photosynthesis
IB Biology
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Leaves • Green tissue in the interior
of the leaf (mesophyll) = contains chloroplasts
• CO2 enters the leaf and O2 exits through the stoma
• Stomata = bottom of leaf
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Chloroplasts
• similar to mitochondria• outer and inner membrane• membranous sacs: THYLAKOIDS• thylakoids = concentrated in
stacks called GRANA• thylakoids: contain chlorophyll
(capture light)• filled with fluid: STROMA (where
sugars are made from CO2 )
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Overview
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Electromagnetic Spectrum
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The 2 stages of Photosynthesis
• Light Dependent Reactions:– convert light energy to chemical
energy (ATP + NADPH) and produce oxygen gas as a waste product
• Light Independent Reactions (Calvin Cycle):
– make sugar using carbon dioxide and the energy-containing products of the light-reactions (ATP + NADPH)
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Light Dependent Reaction
• Light can be..– Absorbed– Reflected– Transmitted
• Occurs in thylakoids
• Chlorophyll A and B = main photosynthetic pigments (also carotenes, anthocyanins)
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Light Dependent Reaction• Light energy is used to split water. • H + is released = used by ATP Synthase to produce ATP• NADP + is reduced to NADPH+ • ATP and NADPH = used in light independent reactions• O2 = waste product
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Photosystems• Photosystem: place in
thylakoid where light is harvested
• Photon is absorbed by a pigment molecule = electrons gain energy
• Excited electron is passed to a neighboring molecule - the primary acceptor
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Photosystems I & II work together
• Both photosystems absorb light
• Electron Transport Chain = electrons go down an energy hill = lose energy at each step - this energy is stored in ATP or NADPH
• Electrons released from PSI is replaced by electrons coming from PSII
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Chemiosmosis/Photophosphorylation
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Role of Water
• The light energy is used to split water molecules (photolysis)
• H2O → H+ + O + e- The electrons allow
reduction of NADP+ / replace those leaving photosystem II
H + flow allows ATP production
The O2 is released and leaves the plant through the stoma
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Mechanical Analogy for Making ATP
• As electrons skip down the ETC, ATP are generated.
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Animations
http://www.youtube.com/watch?v=hj_WKgnL6MI
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Light Independent Reaction (Calvin Cycle)
• Glucose phosphate is produced = stored as starch• CO2 , ATP and NADPH are used
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Simple Calvin Cycle animations:
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Summary
Light dependent
reaction
Light independent
reaction
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plateau
At low CO2 concentration, rate is positively correlated with concentration
CO2 is a substrate in an enyme-catalysed light-dependent reaction.
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At low light intensity, rate of photosynthesis is proportional to light intensity.
plateau
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Increased temp. gives increased energy and increased rate of photosynthesis
Optimum temperature
Above the optimum temp., enzymes are denatured and rate drops steeply.
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Light intensity
Rate
of
phot
osyn
thes
is
What are the conditions of each of these trials?