1 / 12

Chapter 7.7

Chapter 7.7. C4 and CAM Carbon-Fixing Pathways. AP Biology Fall 2010. Gas Entry. Stomata : small pores on underside of leaves Entry and exit of gasses CO2, gas required for Calvin cycle, is not very abundant in nature. Gas Entry.

lucas-gilliam
Télécharger la présentation

Chapter 7.7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 7.7 C4 and CAM Carbon-Fixing Pathways AP Biology Fall 2010

  2. Gas Entry • Stomata: small pores on underside of leaves • Entry and exit of gasses • CO2, gas required for Calvin cycle, is not very abundant in nature

  3. Gas Entry • Under hot and dry environmental conditions stomata close to reduce loss of water vapor, also results in diminished supply of CO2 • Plants that normally live in these environments adapted different ways of initially fixing CO2 prior to it entering the Calvin cycle • Known as C4 and CAM pathways, takes place in cytoplasm of cell

  4. C4 Pathway • Designed to efficiently fix C2 at low concentrations • Plants that use this are known as C4 plants • First fix CO2 into a 4-C compound (C4) called oxalacetate • Occurs in cells called mesophyll cells

  5. C4 Pathway

  6. C4 Pathway • CO2 fixed to 3-C compound phosphoenolpyruvate to produce 4-C compound oxaloacetate • Enzyme catalyzing this reaction, PEP carboxylase, fixes CO2 very efficiently so C4 plants don’t need to have their stomata open as much

  7. C4 Pathway • Oxaloacetate converted to 4-C compound malate • Requires reducing power of NADPH • Malate then exits mesophyll cells and enters chloroplasts of specialized cells called bundle sheath cells • Malate is decarboxylated to produce CO2, a 3-C pyruvate, and NADPH

  8. C4 Pathway • Oxaloacetate converted to 4-C compound malate • CO2 combines with RuBP and goes through Calvin cycle • Pyruvate re-enters mesophyll cells, reacts with ATP, & converted back to phosphoenolpyruvate • Starting compound of C4 cycle

  9. CAM Pathway • CAM plants live in very dry conditions • Open stomata to fix CO2 only at night • Use PEP carboxylase to fix CO2, forming oxaloacetate • Oxaloacetate is converted to malate which is stored in cell vacuoles • During the day when stomata are closed, CO2 is removed from the stored malate and enters Calvin cycle

  10. CAM Pathway

  11. Examples • C3 • Basswood, beans, peas • C4 • Corn • CAM • Cactus

  12. Resources • Adapted from Gary E. Kaiser • http://student.ccbcmd.edu/biotutorials

More Related