PHOTOSYNTHESIS
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Transcript of PHOTOSYNTHESIS
PHOTOSYNTHESISChapter 3
INTRODUCTION Plants, algae, some protists, some
bacteria capture about 5% of Sun’s energy.
Absorb CO2, water, and radiant energy chemical potential energy (glucose)
PHOTOSYNTHETIC ORGANISMS 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)
CHLOROPHYLL 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.
PROKARYOTIC AUTOTROPHS: CYANOBACTERIA
“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
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.
EUKARYOTIC AUTOTROPHS: ALGAE, PHOTOSYNTHETIC PROTISTS, AND PLANTS
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.
Algae, some protists, plant cells: Contain chlorophyll within chloroplasts.
Leaves, stems, unripened fruit: green! Chloroplasts: possible ancestors of
_______________.
LEAVES: PHOTOSYNTHETIC ORGANS OF PLANTS
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.
STRUCTURE OF LEAVES
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.
TRANSPIRATION AND PHOTOSYNTHESIS 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:_________________________________
OPENING AND CLOSING OF STOMATA 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.
CLOSING AND OPENING OF STOMATA 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 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 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
CHLOROPLASTS 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 .
SEATWORK/HOMEWORK Pg. 145 #1,2,3,4,5,6,7