Leaves

1. Leaves

2. Leaf Structure • Epidermal tissue system • chloroplasts only in guard cells • Ground tissue system • mesophyll • Vascular tissue system • Leaf adaptations • sun and shade leaves • xerophytes

3. CO2 sunlight, water Dark reacti ons (Calvin cycle) Light reactions Oxygen (O2) Glucose (C6H12O6) (carbohydrates) Photosynthesis

4. Start with the Big Picture • It’s all about energy • potential vs kinetic energy • Nearly all energy used on earth comes from the sun • Nearly all energy used on earth ends up as heat • Metabolism • the way living things manage energy

5. Laws of Thermodynamics • Energy can neither be created nor destroyed but it can be converted from one form to another • In any transfer of energy there is always loss of useful energy, usually as heat

6. What makes chemical reactions happen? • Chemical bonds have potential energy • When the bonds are broken, the energy is released • Cells transfer energy from one molecule to another, often as a proton (H+) or electron (e-) • Enzymes are proteins that speed up chemical reactions • ATP has high-energy phosphate bonds • ATP bonds come from glucose • Glucose comes from...

7. Solar energy captured in chemical bonds Chemical bond energy is released to do work Metabolism summary • Photosynthesis • light reactions • dark reactions • Respiration • glycolysis • Krebs cycle • electron transport • fermentation

9. CO2 sunlight, water Dark reacti ons (Calvin cycle) Thylakoid membrane ATP, NADPH Light reactions Chlo roplast stroma oxygen Glucose (C6H12O6) (carbohydrates) Photosynthesis

10. Movie

11. Light Reactions of Photosynthesis • Chlorophyll is a pigment in the thylakoid membrane • It can absorb light energy • The absorbed energy knocks an electron out of the chlorophyll molecule • This electron is transported from one molecule to another • The energy is used to make ATP • The original electron is replaced with one from a molecule of water, releasing O2 Movie 1 Movie 2

12. A good summary...

13. Dark Reactions (Calvin cycle) • Occurs in the stroma of the chloroplast • CO2 diffuses into spongy mesophyll cells • RUBISCO is the enzyme that fixes the CO2 into a carbon compound • it’s the most abundant protein on earth • a very complicated enzyme!

14. Rubisco

16. Calvin cycle Movie

17. The atmosphere contains oxygen because of photosynthesis

18. Oxygen causes a problem for RUBISCO • RUBISCO binds O2 as well as CO2 • the substrates compete for the active site • O2 results in no new sugar • Someplants have evolved a way to avoid this wasteful reaction

21. Some C4 plants

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34. End of Show

35. Dicot leaf surface Monocot leaf surface

37. Palisade parenchyma Upper epidermis Xylem Stoma Phloem Spongy parenchyma Lower epidermis

38. Sun leaf and shade leaf sections Genetic vs environmental differences in leaves

40. Xerophytes are plants that grow in dry conditions

41. What are the adaptations to dry conditions?

42. Leaf cross section Which tissue holds the water?

43. Parallel venation (monocots) Net or pinnate venation (dicots)

44. Typical horizontal leaf Typical vertical leaf