Post on 22-Dec-2015
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Revising photosynthesisBasic knowledge
1) Explain the similarities and differences between an autotroph and a heterotroph
2) Describe the relationship between photosynthesis and respiration in living organisms
3) Write the overall chemical equation for photosynthesis4) Name the 2 sets of reactions involved in
photosynthesis and state where exactly each occurs5) Explain why the very large surface area provided by
the grana is important in photosynthesis6) Draw a diagram of a chloroplast and label it to show
how it is adapted for photosynthesis
Autotrophs
• Autotrophs are organisms that can synthesise complex organic molecules such as
carbohydrates, lipids, proteins, DNA, RNA, vitamins
from inorganic molecules, using an energy source.
Heterotrophs
• Heterotrophs digest complex organic molecules into simpler, soluble ones. They then synthesise molecules they need from these.
Examples of heterotrophs are
Animals Fungi Some bacteria
Photosynthesis: 2 stage process
• Takes place in chloroplasts
CHLOROPHYLLLight
Water
Oxygen
Carbon dioxide
Carbohydrate
The cells and tissues of a leaf
Chloroplasts under LM and EM
1. Chloroplasts in an Elodea leaf using LM
2. Chloroplasts in a maple leaf using TEM
3. TEM of a single chloroplast
Revising photosynthesis Light dependent reactions
1) List the products of the light dependent reaction2) Distinguish between an absorption spectrum
and an action spectrum3) State the wavelength of visible light at which
least photosynthesis takes place. Why is this?4) State the role of accessory pigments in a
photosystem5) Describe the different roles of photosystems 1
and 26) Describe the similarities and differences
between cyclic and non-cyclic photophosphorylation
Photosynthesis biochemistry p17 workbook p63 textbook
The light dependent stage on the thylakoid membranes of the chloroplast
Using light energy to make ATP (= photophosphorylation)
Also produces reduced NADP (= coenzyme NADPH)
There are 2 parts – cyclic and non-cyclic photophosphorylation
Light harvesting clusters or photosystems p12-13 workbook, p61 textbook
Quite complex animation!• http://www.learnerstv.com/animation/animation.php?ani=179&cat=biology• http://www.uic.edu/classes/bios/bios100/lectures/ps01.htm(useful info!)
cyclic photophosphorylation
chlorophyll a in photosystem I
P 700
excited electrons 2e-
electron acceptor + chain of electron carriers
ADP + Pi ATP
2e-
photosystem II P680 photosystem I P700
e- e-
ADP + Pi ATP
NADP + H+
reducedNADP
photolysis of water
H2O OH- + H+
oxygen O2
NonNon-cyclic photophosphorylation
Non-cyclic photophosphorylation p
http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html
Making ATP by photophosphorylation and chemiosmosis (needed in the light independent stage)
p14
A photon of light hits a chlorophyll molecule2 electrons get excited!They are released from chlorophyll to electron acceptorsThey travel along electron carriers on thylakoid membranesEnergy released during electron transport is used to pump
H+ into thylakoid space between membranesH+ (proton) gradient is formedH+ move down gradient through ATP synthase enzymes
making ATP So ATP is made using light energy = photophosphorylation
http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atpsynthase_an.html
The role of water in the light dependent stage
• Light energy makes it split = photolysis• Produces hydrogen ions (protons) +
electrons + oxygen atoms
• Hydrogen ions ATP synthase • Hydrogen ions reduce NADP• Electrons electron acceptors and
carriers• Oxygen waste product (but needed in
respiration)
Revising photosynthesisLight independent reactions / Calvin cycle
1) Explain the term carbon dioxide acceptor2) Describe the reaction catalysed by the
enzyme rubisco3) State the roles of ATP and reduced
NADP in the Calvin cycle4) List the possible fates of triose phosphate
formed in the Calvin cycle. Which is the most likely to happen?
CO2 RuBP
RuP
ATP
ADP
2x GP ATP ADP+
Pi
NADPH NADP
2x Triose P
Hexose sugar
2 x3C
5C
5C
2 x3C
6C
RUBISCO
Revising photosynthesisLimiting factors
• Explain what is meant by a limiting factor• List 3 factors that could limit the rate of photosynthesis
at a high concentration of carbon dioxide• Explain why the rate of photosynthesis increases as
the light increases from low to high.• Explain why increasing the light intensity does not
produce a continuous increase in the rate of photosynthesis
• Exaplin why at low light intensities temperature changes have little effect on the rate of photosynthesis
• Describe how to investigate experimentally the factors that affect the rate of photosynthesis. Include how you will make the data valid and reliable.