Photosynthesis

1. Unit 3: Cell Processes Notes set #2 Biology Melino Photosynthesis Part II

2. What is the glucose made by photosynthesis used for in a plant? Converted to fructose for the fruit Used in respiration to release energy Converted into fats and oils for the seeds glucose Joined together to make cellulose for cell walls Joined together to make starch for storage Combined with nitrates from the soil to make proteins for the new growth

3. Plants are composed of three major parts: • The root system • Anchors the plant in place • Stores excess sugar • Absorbs water & nutrients • The shoot system • Supports the plant body • Provides passageway for nutrients • Leaves • Where photosynthesis occurs

4. The process of photosynthesis involves the use of light energy to convert carbon dioxide and water into sugar, oxygen, and other organic compounds. This process is often summarized by the following reaction: 6 H2O + 6 CO2 + light energy --> C6H12O6 + 6 O2 • This process is an extremely complex one, occurring in two stages

5. Photosynthesis occurs in two main steps • The light-dependent reactions (Calvin cycle) of photosynthesis transform light energy into chemical energy • The chemical energy is stored in the energy carrier ATP (Adenosine Triphosphate) • The light-independent reactions of photosynthesis produce food • ATP from the light reactions supplies the energy needed to combine carbon dioxide and water to make glucose

11. The light-independent reactions can’t happen without the light reactions.

12. What is the energy for? • Building complex molecules • Cell division and growth • Movement of organelles • Movement of whole cell • Maintaining cell organization • Active transport • Transmission of nerve impulses

13. The Sun – the ultimate energy source • The sun is the perfect energy source. It contains all the energy you could ever need… if only you could catch it…. • Green bacteria figured out how to do that over 2.5 billion years ago! • Green bacteria, algae and plants use chlorophyll to absorb light energy from the sun.

14. During the light reactions of photosynthesis, chloroplasts absorb light energy from the Sun and transform it into the chemical energy stored in ATP. • When the light energy is absorbed, it splits water molecules. • The electrons from the water molecules help with the energy transformation from light energy to chemical energy in ATP. • Plants release the oxygen from the water molecules as waste, producing the oxygen we breathe

15. Plants use the energy in ATP to combine CO2 & H2O molecules to create glucose during the light-independent reactions. • To make glucose, plants first take CO2 out of the air through a process called carbon fixation • Taking CO2 and attaching it to a molecule inside the cell • Plants then use the energy from the ATP and the electrons to convert the CO2 to sugar

16. When plants make more glucose than they need, they store their excess matter and energy by combining molecules into starch. • The starch molecules can be used later or turned into other compounds such as proteins, nucleic acids, fats

17. How does the potato use starch? • One of the most important carbohydrates in our diet is the potato. Simple sugars bond to form complex carbohydrates that are stored in the fattened tubers we bake, scallop, hash and mash. This cool-season vegetable is one of the most widely grown staples in the world. Although we enjoy and need it, the potato stores starch for its own use.

19. Carbon fixation • The process by which plants turn inorganic carbon into organic compounds • Organisms that grow by fixing carbon are called autotrophs • C3 plants • C4 plants • CAM plants

20. C3 Photosynthesis : C3 plants • Called C3 because the CO2 is first incorporated into a 3-carbon compound. • Stomata are open during the day. • Photosynthesis takes place throughout the leaf. • Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy).. • Most plants are C3

21. C4 Photosynthesis : C4 plants. • Called C4 because the CO2 is first incorporated into a 4-carbon compound. • ~ 3 % of plants • Maize (CORN), sugar cane, millet, and sorghum. • Stomata are open during the day. • Uses Carboxylase for the enzyme involved in the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2 directly for photosynthesis.

22. C4 Plants • Adaptive Value: • Photosynthesize faster than C3 plants • C4 plants have a competitive advantage over plants possessing the more common C3 carbon fixation pathway under conditions of drought, high temperatures, and nitrogen or CO2 limitation

24. CAM Photosynthesis : CAM plants. CAM stands for Crassulacean Acid Metabolism • Called CAM after the plant family in which it was first found and because the CO2 is stored in the form of an acid before use in photosynthesis. • Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released for photosynthesis

25. Adaptive Value: • Better Water Use Efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.). • May CAM-idle. When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis. This is a little like a perpetual energy machine, but there are costs associated with running the machinery for respiration and photosynthesis so the plant cannot CAM-idle forever. But CAM-idling does allow the plant to survive dry spells, and it allows the plant to recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells). CAM plants include many succulents such as cactus, agaves & orchids

26. Video on C4 & CAM plants • http://www.youtube.com/watch?v=Dq38MpYOb8w

27. Summary • The cell’s two energy transforming organelles, mitochondria and chloroplasts, feed on the waste products of each other. • CO2 given off by mitochondria is what chloroplasts need to make the building block of sugars and other carbohydrates. • The oxygen released by chloroplasts is what mitochondria need to drive the electrons -- that pump in the hydrogen ions -- making it possible for ATP synthesize to add that terminal phosphate to ADP, creating ATP, the universal energy carrier.

28. Cellular respiration Products: Glucose Oxygen Reactant: Carbon Dioxide Water Energy Photosynthesis Products: Carbon Dioxide Water Reactant: Glucose Oxygen Water Comparing Cellular Respiration and Photosynthesis

29. Crash Course in Photosynthesis • http://www.youtube.com/watch?v=sQK3Yr4Sc_k&list=SP3EED4C1D684D3ADF&index=8

30. Review • http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie.htm • http://www.wiley.com/legacy/college/boyer/0470003790/animations/photosynthesis/photosynthesis.htm

31. Illuminating photosynthesis: http://www.pbs.org/wgbh/nova/nature/photosynthesis.html