PHOTOSYNTHESIS

1. PHOTOSYNTHESIS Chapter 7

2. A. Light Visible light makes up only a small portion of the electromagnetic spectrum. Sunlight consists of: • 4% Ultraviolet (UV) radiation • 44% Visible light • 52% Infrared (IR) radiation

3. Overview of Photosynthesis Photosynthesis- process by which plants, algae and some microorganisms harness solar energy to make biochemicals. Occur in organelles –chloroplasts Two stages –light reaction and carbon reaction The products of photosynthesis, glucose and other carbohydrates –photosynthate.

4. Characteristics of Visible Light: • is a spectrum of colors ranging from violet to red • consists of packets of energy called photons • photons travel in waves, having a measurable wavelength (λ) λ= distance a photon travels during a complete vibration [measured in nanometers (nm)]

5. A photon’s energy is inversely related to its wavelength... ...the shorter the λ, the greater the energy it possesses. Which of the following photons possess the greatest amount of energy? Green photons λ = 530nm Red photons λ = 660nm Blue photons λ = 450nm

6. What happens to light when it strikes an object? • reflected (bounces off) • transmitted (passes through) • absorbed Only absorbed wavelengths of light function in photosynthesis.

8. B. Photosynthetic Pigments Molecules that capture photon energy by absorbing certain wavelengths of light. 1. Primary pigments • Bacteriochlorophyll - green pigment found in certain bacteria. • Chlorophylls a & b - bluish green pigments found in plants, green algae & cyanobacteria.

9. Chlorophyll a is the dominant pigment in plant cells.

10. 2. Accessory Pigments • Carotenoids - red, orange, yellow pigments found in plants, algae, bacteria & archaea. • Xanthophylls – red and yellow pigments found in plants, algae & bacteria. • Fucoxanthin –brown pigment found in brown algae, diatoms, & dinoflagellates • Phycoerythrin- red pigment found in red algae. • Phycocyanin- blue pigment found in red algae & cyanobacteria. • Bacteriorhodopsin– purple pigment found in halophilic archaea Each pigment absorbs a particular range of wavelengths.

12. Light- form of energy- exists as photons. Photons possess different wavelengths that represent different energy levels. • Different wavelengths seen as different colors. Pigment molecules possess different abilities to absorb wavelengths and appear as different colors. • Chlorophyll is the major pigment molecule and appears as green. • Plants and other photosynthetic species use different pigments to absorb different wavelengths and use light more efficiently.

13. C. Chloroplasts Sites of photosynthesis in plants & algae. Concentrated in mesophyll cells of most plants.

14. Chloroplast structure: • Stroma- gelatinous matrix; contains ribosomes, DNA & various enzymes. • Thylakoid - flattened membranous sac; embedded with photosynthetic pigments.

15. Chloroplasts – type of plastid- unique organelles with multiple layers which increase surface area to improve efficiency. • Chlorophyll is imbedded within the membrane layers in complexes that maximize the absorption and transduction of energy.

16. D. Photosynthesis 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O Occurs in two stages: • Light reactions - harvest photon energy to synthesize ATP & NADPH. • Carbon reactions (Calvin cycle) - use energy from light reactions to reduce CO2 to carbohydrate.

17. Overview of Photosynthesis Molecules in thylakoid membrane capture sunlight energy and transfer energy to molecules of ATP and NADPH. Enzymes of caebon reactions use this energy to capture CO2 abd build glucose.

18. 1. Light Reactions • require light • occur in thylakoids of chloroplasts • involve photosystems I & II (light harvesting systems). Photosystems contain antenna complex that captures photon energy & passes it to a reaction center.

19. Light Reactions of Photosynthesis

20. ATP Production by Chemiosmotic Phosphorylation

21. Light reactions of photosynthesis boost electrons into higher energy levels. • Transfer them to the carriers NADPH and ATP for use in the cell. • Additional energy is used to pump hydrogen ions into lumen of thylakoids- establishing gradient called proton motive force.

22. Protons escape through a membrane-bound ATP synthase – uses the energy release to phosphorylate ATP (chemiosmotic phosphorylation) • Electrons – ultimately replaced by converting water to protons and oxygen.

23. 2. Carbon Reactions (Calvin cycle; C3 cycle) • do NOT require light (occur in both darkness & light as long as ATP & NADPH are available) • occur in stroma of chloroplasts • require ATP & NADPH (from light reactions), and CO2

24. Calvin Cycle

25. Plants that use only the Calvin cycle to fix carbon are called C3 plants. Ex. cereals, peanuts, tobacco, spinach, sugar beets, soybeans, most trees & lawn grasses.

26. Carbon fixation uses energy from ATP and NADPH to convert gaseous carbon dioxide to organic molecules such as glucose. • The enzyme system constantly recycles its components, forming Calvin cycle. • Key enzyme – rubisco attaches carbon to the carrier ribulose bisphosphate.

27. E. Photorespiration Process that counters photosynthesis. Occurs when stomata close under hot, dry conditions: • O2 levels in plant increase • CO2 levels in plant decrease Under these conditions, rubisco fixes O2 (rather than CO2). Thus, PGAL is NOT produced.

28. F. C4 and CAM Photosynthesis Adaptations that allow certain plants to conserve water and reduce photorespiration at higher temperatures. 1. C4 Photosynthesis C4 plants reduce photorespiration by physically separating the light reactions and Calvin cycle.

29. Leaf anatomy of a C4 plant C4 Photosynthesis: • Light reactions occur in chloroplasts of mesophyll cells. • Calvin cycle occurs in chloroplasts of bundle sheath cells.

30. 2. CAM Photosynthesis CAM plants reduce photorespiration by acquiring CO2 at night. Night: • mesophyll cells fix CO2 as malic acid • malic acid is stored in vacuoles. Day: • malic acid releases CO2 which enters Calvin cycle. Malic acid

32. Inefficiency of rubisco causes photorespiration. • To live in hot climates, plants adept at manipulations that reduce photorespiration. • C4 plants use a intermediate to separate the light and carbon reactions from each other within different cell types.

33. Resulting in higher carbon dioxide concentration within bundle-sheath cells – reduce photorespiration. • CAM plants fix carbon at night when temperatures are lower and water loss is less of a problem.