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PHOTOSYNTHESIS

Chapter 3. PHOTOSYNTHESIS. Plants, algae, some protists , some bacteria capture about 5% of Sun’s energy. Absorb CO2, water, and radiant energy  chemical potential energy (glucose). Introduction. Plants, algae, some protists , and cyanpbacteria .

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PHOTOSYNTHESIS

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  1. Chapter 3 PHOTOSYNTHESIS

  2. Plants, algae, some protists, some bacteria capture about 5% of Sun’s energy. Absorb CO2, water, and radiant energy  chemical potential energy (glucose) Introduction

  3. Plants, algae, some protists, and cyanpbacteria. • Contain green-coloured pigment called _____________________: absorbs light energy and begins the process of photosynthesis. • Chlorophyll a (blue-green) (contains –CH3) at position –R • Primary light-absorbing pigment • Chlorophyll b (yellow-green) (contains –COH at –R) Photosynthetic organisms

  4. Contains a porphyrin ring attached to a long HC tail. • Porphyrin: contains a magnesium atom at center surrounded by a HC ring with – and = bonds. • Delocalized electrons in single-double bonds absorb light energy. • Different functional groups affect type of light energy molecules can absorb. Chlorophyll

  5. “blue-green algae”: largest group of photosynthesizing prokaryotes. • Evolved between 2.5 and 3.4 billion y.a. • Probably the first organisms to use sunlight in the production of organic compounds. • Produced oxygen: paved way for heterotrophic life on Earth. • Unicellular, but may grow in visible colonies Prokaryotic autotrophs: cyanobacteria

  6. Live in oceans, freshwater lakes and rivers, rocks, and soil... And polar bear fur. • Rocks? Cyanobacteria + fungi  lichens • Cyanobacterial blooms: rapid-growing colonies in water rich in nitrates and phosphates (fertilizer, detergent runoff from homes, farms, industry) • May be toxic to fish, birds, humans, and other mammals. • Produce toxin called microcystin.

  7. Endosymbiosis: ancestor of cyanobacteria engulfed by ancestor of today’s eukaryotic cells. • Mutually beneficial relationship. • Cyanobacteria protected from harsh environment • Eukaryotic host obtained food molecules from bacterium • Cyanobacteria lack membrane-bound organelles: have infoldings of cell membrane used as sites of photosynthesis and respiration. Eukaryotic autotrophs: algae, photosynthetic protists, and plants

  8. Algae, some protists, plant cells: • Contain chlorophyll within chloroplasts. • Leaves, stems, unripened fruit: green! • Chloroplasts: possible ancestors of _______________.

  9. Thin and broad, or thin and narrow • Structure and arrangement on stems and branches maximizes SA exposed to sunlight • Limits distance that gases need to travel to reach chloroplasts. Leaves: photosynthetic organs of plants

  10. Cuticle: waxy water-resistant coating • Protection against excessive absorbtion of light and evaporation of water. • Epidermis: transparent • Mesophyll: abundant with chlorplasts • Guard cells: create microscopic openings called stomata • Regulate the exchange of CO2 and O2 with atmosphere • Allow water to escape by transpiration • Vascular bundles: ‘veins’ • Transport water and minerals from roots and leaves and carry carbs from leaves to roots. Structure of leaves

  11. Stomata: responsible for more than 85% of water lost by plant. • Two ways transpiration assists in photosynthesis: • Creates ‘transpiration pull’ that helps move water, minerals, and other substances from roots  leaves. • Prevents leaves from heating to temperatures that could inhibit or denature enzymes. • Stomata open and close depending on environmental conditions. • Closed:________________________________ • Open:_________________________________ Transpiration and photosynthesis

  12. Guard cells control the size of a stoma by changing their shape in response to changes in environmental conditions. Open: guard cells turgid (swollen) Closed: guard cells flaccid (limp) Size of guard cell is controlled by osmosis, with water moving in or out based on [K+] across the plasma membrane. Opening and closing of stomata

  13. Passive K+ movement is coupled to H+ active transport through proton pumps, which requires ATP K+ comes from surrounded epidermal cells. Closing and opening of stomata

  14. Generally, open during day, closed at night. Day: blue light activates blue-light receptors in guard cell membranes. Proton pumps H+ out, K+ moves in, causing swelling. Mesophyll cells begin photosynthesizing and use up CO2 accumulated during night. Reduction of [CO2] also causes stomatal opening. Closing and opening of stomata

  15. OVERALL: Opening: Caused by movement of K+(aq) into guard cells and decrease [CO2] in the morning. Closing: Caused by reduction in sucrose concentraition in the evening Closing and opening of stomata

  16. Photosynthetic factories of plants and algae. • Have own DNA and can replicate by fission. • Two-membranes • Stroma: protein-rich semiliquid material in the ‘middle’ • Thylakoids: membrane-bound sacs that form columns. • About 30-50 per... • Grana: column of thylakoids. • About 60 in each chloroplast • Lamallae: connection between thylakoids. • Thylakoid Lumen: inside of the thylakoid fluid-filled . chloroplasts

  17. Pg. 145 #1,2,3,4,5,6,7 Seatwork/homework

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