Biology Homework Chapter 7: Photosynthesis - the Calvin Cycle and CAM Pathways
Textbook assignment: Chapter 7: Photosynthesis: Using Light to Make Food, sections 10-14.
- 7.10 The Calvin cycle, like the Krebs cycle, uses some components over and over to produce new products with each cycle, that is, each iteration of the reaction run. In this case, we get three-carbon molecules (G3P) from carbon dioxide. The energy for the cycle comes from the ATP and NADPH of the light reactions, so this is part of a coupled-reaction process. As with the cellular respiration reaction process, each step of the Calvin cycle requires a unique enzyme. Each reaction step requires multiple molecules.
- #1 In the carbon fixation step, free carbon dioxide molecules are fixed by the enzyme rubisco to form six 3-GPA molecules.
- #2 In the reduction step, six ATP and six NADPH molecules reduce six 3-GPA molecules to six G3P molecules.
- #3 In the release step, one of the G3P molecules is released to become part of a glucose molecule. This is the only product of the Calvin cycle.
- #4 In the final step, the remaining five G3P molecules are rearranged to for three RuBP (rubisco + CO2 molecules) that re-enter the Calvin cycle.
- 7.11 Some plants can use a different process from the Calvin cycle (C3 cycle) to force carbon into starch or sugar molecule format. C4 and CAM plants make 4-carbon sugars, using different processes that do not require as much water as the C3 process. These plants have an advantage in desert areas.
- 7.12 Photosynthesis is a key step to biological systems on earth. Plants are their own consumers: about 50% of the energy harvested by photosynthesis is used by a plant's own mitochondria to create ATP that drives that plant's growth and reproduction activities. Plant carbohydrate production is necessary to support all other life forms.
- 7.13 CO2 in the atmosphere traps heat in a process called the greenhouse effect. Changing the amount of CO2 in the atmosphere may lead to global climate change, although the direction and severity of a given change are still hotly debated. Earth also seems to compensate for some changes. As deforestation occurs, the rate at which the remaining plants process increased levels of CO2 also increases, and may mitigate some of the more detrimental effects of CO2 release.
- 7.14 High energy solar radiation converts O2 in the atmosphere to O3, ozone. The intercepted energy does not reach the ground, preventing organisms from receiving harmful levels of ultraviolet radiation. Destruction of the ozone layer by CFC emissions has stopped due to worldwide voluntary cutbacks in CFC production and use. Recovery of the ozone layer (replace of ozone) is not expected for another generation.
Read the following weblecture before chat: Dark Reactions
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Use the OLABS Importance of Light in Photosynthesis lab simulation to explore how the amount of light changes the rate of photosynthesis.
- Read the theory tab.
- Read the lab procedure tab on how the simulator works.
- Watch the animation so that you understand the procedure.
- Use the simulator to run the experiment several times. Change only one factor at a time, but record how many bubbles are produced for 30-second or one-minute intervals if you
- Change the wattage on the light.
- Change the distance between the plant and the light.
- Change the color filters on the light.
Is it possible to have too much light? Is one color filter better than another? How can you explain your results?
Optional Website: There is a more detailed discussion of the Calvin Cycle reactions in J. Kimball's biology pages, and another good summary of the individual dark reactions produced by Academic Television Services.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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