Photosynthesis revision For F214 January 25th 2010

Revising photosynthesis Basic knowledge Explain the similarities and differences between an autotroph and a heterotroph Describe the relationship between photosynthesis and respiration in living organisms Write the overall chemical equation for photosynthesis Name the 2 sets of reactions involved in photosynthesis and state where exactly each occurs Explain why the very large surface area provided by the grana is important in photosynthesis 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 Carbon dioxide Water CHLOROPHYLL Light Carbohydrate Oxygen Light independent reaction Light dependent reaction

The cells and tissues of a leaf

Chloroplasts under LM and EM Chloroplasts in an Elodea leaf using LM 2. Chloroplasts in a maple leaf using TEM TEM of a single chloroplast

Chloroplast

Revising photosynthesis Light dependent reactions 1) List the products of the light dependent reaction 2) Distinguish between an absorption spectrum and an action spectrum 3) State the wavelength of visible light at which least photosynthesis takes place. Why is this? 4) State the role of accessory pigments in a photosystem 5) Describe the different roles of photosystems 1 and 2 6) 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 excited electrons 2e- chlorophyll a in photosystem I P 700 electron acceptor + chain of electron carriers 2e- ADP + Pi  ATP

photolysis of water H2O  OH- + H+ NADP + H+ oxygen O2 reduced NADP e- e- Non-cyclic photophosphorylation ADP + Pi ATP photosystem II P680 photosystem I P700

Non-cyclic photophosphorylation p http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html

This is also called chemiosmosis Making ATP by photophosphorylation and chemiosmosis (needed in the light independent stage) p14 A photon of light hits a chlorophyll molecule 2 electrons get excited! They are released from chlorophyll to electron acceptors They travel along electron carriers on thylakoid membranes Energy released during electron transport is used to pump H+ into thylakoid space between membranes H+ (proton) gradient is formed H+ 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 This is also called chemiosmosis

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 photosynthesis Light independent reactions / Calvin cycle 1) Explain the term carbon dioxide acceptor 2) Describe the reaction catalysed by the enzyme rubisco 3) State the roles of ATP and reduced NADP in the Calvin cycle 4) List the possible fates of triose phosphate formed in the Calvin cycle. Which is the most likely to happen?

NADPH NADP 2 x3C 2x GP ATP ADP+Pi RUBISCO 2x Triose P 2 x3C CO2 RuBP 5C ATP ADP Hexose sugar RuP 5C 6C

Revising photosynthesis Limiting 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.

How did Engelmann explain these results?

Light intensity and the compensation point refer to bicarbonate indicator expt