Photosynthesis study guide PDF

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Study Guide / Summary – Photosynthesis Lecture 1: An introduction to photosynthesis 1. Discuss reasons why photosynthesis is such an important process on earth. 2. Explain, in simple terms, how photosynthesis works, including: a. The two parts of photosynthesis and what they do. b. What molecules are involved and how they split and combine. Lecture 2: Energy and light reactions 1. Explain why plants look green 2. Explain the functions of Photosystem II (PS II) and Photosystem I (PS I) 3. Describe how and where ATP and NADPH are produced 4. Describe how and where O2 is produced by plants Lecture 3: Carbon and the Calvin cycle 1. Describe the flow of carbon through the three phases of the Calvin cycle 2. Explain why three turns of the Calvin cycle are needed to produce one G3P molecule (the product of the Calvin cycle) 3. Calculate how many ATP and NADPH molecules are needed to produce a glucose molecule 4. Explain why the light reactions and the Calvin-cycle are interdependent Lecture 4: Alternative pathways of carbon fixation 1. Explain the negative consequences of hot and dry conditions for plants 2. Explain why photorespiration occurs 3. Describe how C4 plants avoid photorespiration 4. Describe how CAM plants avoid water loss

Possible answers: Lecture 1 1) Photosynthesis is the most important process on Earth as it converts light energy from the sun to chemical energy on Earth. Without this, we would have a dull and mostly lifeless planet. Photosynthesis makes energy rich compounds that fuel life and provide the basis for our food webs. In doing so, it creates the O2 used for cellular respiration required by almost all organisms on Earth. Without photosynthesis, the world would be a completely different place. So photosynthesis, quite simply put, is responsible for life as we know it. 2) Photosynthesis captures light energy from the sun and turns it into chemical energy used to make organic molecules (sugars, starch etc.). a. Photosynthesis has two parts, the light reactions and the Calvin Cycle. The light reactions harness the energy of the sun to make energy rich chemical compounds. The Calvin cycle takes those energy rich compounds and uses them to turn CO2 in to sugar. b. 6 CO2 + 12 H2O + light energy -> C6H12O6 + 6 H2O + 6 O2

Lecture 2: 1) Plants look green because they contain the pigment chlorophyll. Chlorophyll absorbs violet-blue and red light, and uses this energy to drive photosynthesis. Chlorophyll does not absorb green light, instead these wavelengths are reflected or transmitted. This reflected or transmitted green light gives plants their colour. 2) Photosystem II: Starts the linear electron transfer chain. PS II donates electrons from two P680 molecules, that are replaced by electrons from splitting water. Splitting the water produces O2. Creates a proton gradient in the thylakoid space that is used to produce ATP in the stroma to be used by the Calvin Cycle. Photosystem I: Uses light to increase the energy of electrons in the two P700 molecules. These electrons are sent along the chain ultimately to form NADP+ to form NADPH, which is used in the Calvin Cycle. The electrons lost from P700 are replaced by those received from PSII along the electron transport chain.

3) ATP is produced by ATP-synthase in the thylakoid membrane. It is powered by the proton gradient between the thylakoid space (high H+ concentration) and the stroma (low H+ concentration). This gradient is produced by 1) the splitting of water by PS II and the transport of electrons from PSII to PSI. NADPH is produced by NADP+ reductase in the thylakoid membrane. NADP+ reductase accepts two electrons at the end of the linear electron transport chain. These electrons together with a H+ from the stroma are combined to form NADPH. 4) O2 is produced as a by-product of splitting water to provide electrons for linear electron transport and ultimately for the formation of NADPH. This occurs in the thylakoid space of the chloroplast, where water is split by PS II and donates its electrons to P680. The O2 then diffuses out of the plant through the stomata. Lecture 3 1. The figure below shows the number of carbons at all points in the Calvin cycle. Label the figure below with the compounds at each point and add where ATP and NADPH are consumed. Highlight where each phase (Carbon fixation, Reduction, Regeneration) occurs. 2. Rubisco can bind with O2 as well as CO2. If the ratio of O2 to CO2 in the leaf is high (ie. lots of O2, not very much CO2), rubisco will bind to O2 more frequently resulting in more photorespiration. 3.

1) 4. Try to draw the figure above starting with only 1 RuBP and 1 CO2 entering the cycle. Keep track of all the carbon as you go along. When you get to the end of the Reduction phase, you only have two G3P molecules. This is not enough to both

export a G3P and regenerate RuBP. If you run the cycle three times (ie. 3 RuBPs and 3 G3Ps), you can complete the cycle by exporting 1 G3P and regenerating 5 G3P’s into 3 RuBPs. 5. You can check your answer in the text book (pg 245) 6. Both of these cycles require products from each other in order to operate as shown below. The light reactions give the Calvin cycle ATP and NADPH. The Calvin cycle gives the light reactions NADP+ and ADP + Pi.

Lecture 4: 1. Plants have to balance water loss and CO2 uptake. Under hot and dry conditions, plants have to close their stomata to prevent dehydration. This reduces the flow of CO2 into the leaf and allows O2 to build up. This favours a process called photorespiration that drains energy and carbon from the Calvin cycle. 2. C4 plants effectively “pump” CO2 into the bundle sheath cells where the Calvin cycle can take place. They do this using the enzyme PEP-carboxylase to fix CO2 into a four-carbon compound. This four-carbon compound is transferred to the bundle sheath cells where it is converted into CO2 and a 3C compound that is cycled back out to the mesophyll cells. Doing this increases the CO2 concentration in the bundle sheath and allows the Calvin cycle to occur without photorespiration, despite the presence of O2 in these tissues. 3. CAM plants avoid water loss by opening their stomata at night when conditions are cooler and moister. At night, CO2 diffuses through the open stomata and is fixed into organic acids that are stored in the vacuole until morning. In the daylight, these organic acids can be converted to CO2 and used in the Calvin cycle using energy produce from the light reactions....