Announcements

1. Announcements • Test 4 will be on Friday May 23 over photosynthesis, cellular respiration, and biogeochemical cycles • These information is not in your textbook, so notes will be provided, it is critical you attend class to get the notes • Posters Due Wednesday, May 28 • Final Exam Schedule

2. Photosynthesis SC.912.L.18.7 Identify the reactants, products, and basic functions of photosynthesis.

3. Photosynthesis meaning “light” “Building” • Biological process by which energy from the sun (radiant energy) is transformed into chemical energy of sugar molecules 6 CO2 + 12 H2O + radiant energy C6H12O6 + 6 H2O + 6 O2

4. Photosynthesis Equation • Photosynthesis: “Synthesis from light” • The broad outline: • Plants take in CO2, produce carbohydrates, and release water and O2 • Light is required

5. Photosynthesis Overview • Energy for all life on Earth ultimately comes from photosynthesis. • Oxygenic photosynthesis is carried out by: • cyanobacteria, 7 groups of algae, all land plants

6. Photosynthesis is divided into two main parts • light-dependent reactions • capture energy from sunlight • make ATP and reduce NADP+ to NADPH • Occurs in thylakoid membrane • carbon fixation reactions • use ATP and NADPH to synthesize organic molecules from CO2 • Occurs in stroma

7. Photosynthesis structure • Photosynthesis takes place in chloroplasts. • Chloroplasts are found in the leaves of plants • thylakoid membrane – internal membrane arranged in flattened sacs that containchlorophyll and other pigments • grana– stacks of thylakoid membranes • stroma – semiliquid substance surrounding thylakoid membranes

8. Photosynthesis Two pathways: Light reactions: Convert light energy to chemical energy as ATP and NADPH Light-independent reactions: Use ATP and NADPH (from the light reactions) plus CO2 to produce carbohydrates; sometimes called Calvin Cycle

9. Photosynthesis

10. How sunlight is captured • photon: a particle of light • acts as a discrete bundle of energy • energy content of a photon is inversely proportional to the wavelength of the light • photoelectric effect: removal of an electron from a molecule by light • occurs when photons transfer energy to electrons

11. Electromagnetic spectrum

12. Pigments • Pigments: molecules that absorb visible light • Each pigment has a characteristic absorption spectrum, the range and efficiency of photons it is capable of absorbing. • Chlorophyll a – primary pigment in plants and cyanobacteria; absorbs violet-blue and red light • Chlorophyll b – secondary pigment absorbing light wavelengths that chlorophyll a does not absorb • Carotenoids- secondary pigment absorbs different light wavelengths, orange-red pigment; contains the antioxidant beta-carotene • Xanthophylls- secondary pigment; yellowish pigment

13. Absorption spectrum of 3 pigments

14. Stomata=pores in the leaf of plants • Gas Exchange • CO2 in and O2 out • Water evaporates

15. 3 Different types of photosynthesis • C3 Plants- use the normal Calvin cycle to fix CO2 to glucose; called C3 b/c CO2 is first incorporated into 3 carbon compound; stomata are open during day; most plants fall into this group • C4 Plants- use a different enzyme and have a special anatomy; called C4 b/c CO2 is incorporated into 4 carbon compound; stomata are open during day; examples include corn, Bermuda grass • CAM plants- CAM stands for Crassulacean Acid Metabolism; stomata are closed during the day; CO2 is converted to an acid at night; examples include pineapple plant, cacti, agaves

16. CAM photosynthesis

17. Climatic adaptation • Each method of photosynthesis has advantages and disadvantages • Depends on the climate C4 plants most adapted to: • high light intensities • high temperatures • Limited rainfall C3 plants better adapted to • Cold (below 25C) • High moisture CAM plants better adapted to extreme aridity • CAM occurs in 23 families of flowering plants