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Chapter 7

Chapter 7. Plants and photosynthesis . Major Plant organs . Leaves – photosynthesis, gas exchange, water movement Stem – transport, made of xylem (water) and phloem (sugar) Roots - absorb water and minerals, anchor plant Flowers - reproduction Fruit/seeds – dispersion /reproduction.

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Chapter 7

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  1. Chapter 7 Plants and photosynthesis

  2. Major Plant organs • Leaves – photosynthesis, gas exchange, water movement • Stem – transport, made of xylem (water) and phloem (sugar) • Roots- absorb water and minerals, anchor plant • Flowers- reproduction • Fruit/seeds – dispersion /reproduction

  3. Leaf Structures • Cuticle- prevents water loss • Epidermis • Spongy and palisade parenchyma-photosynthetic • Vascular bundles- move water and sugar • Stomata/guard cells- allow for water and gas exchange

  4. Stem structures • Xylem – moves water from roots to leaves via transpiration. Active transport of minerals, osmosis, cohesion and adhesion are all involved. Water evaporates constantly from stomata • Phloem moves from source (makes or stores sugar) to sink (uses or stores sugar) as sap by Translocation

  5. Photosynthesis Overview • Two phases • Light dependent reactions in thylakoid membranes of chloroplasts • Light independent reactions or Calvin Cycle in stroma of chloroplasts

  6. Photosynthesis

  7. Light dependent reactions • Convert light energy to energy stored in ATP and NADPH using chlorophyll • Reactants- Water • Products- ATP, NADPH, and Oxygen from the splitting of water (photolysis) • Photophosphorylation, chemiosmosis

  8. Chlorophyll • Needed to absorb visible light • Acts as a catalyst • When it absorbs light electrons are excited

  9. Visible Spectrum

  10. chromatography

  11. Calvin Cycle • Uses ATP and NADPH from light reactions to energize CO2 molecules and link them together to form a glucose • Process- carbon fixation • Reactants- CO2, ATP, NADPH • Product – Glucose

  12. Light reactions details • Light reactions occur in the thylakoid membrane • Chlorophyll molecules are arranged into clusters called photosystems • Chlorophyll a and b antenna pigments surround a chlorophyll a reaction center • Antenna pigments absorb the sun’s energy and pass it to the reaction center

  13. Photosystems • Two kinds arranged in sequence along the thylakoid membrane • Photosystem II: P680 • Photosystem I:P700 • Each is associated with an electron transport chain

  14. Sequence of steps in the light reactions • Antenna pigments absorb the sun’s energy and pass it off to the reaction center of the photosystems • An electron from the reaction center becomes excited and moves to a higher energy level • The excited electron is captured by the first protein in the electron transport chain

  15. Sequence continued • The electron then “falls” down the etc and loses energy. As the electron falls down the electron transport chain H+ ions are pumped by active transport- chemiosmosis • ETChains make two products • H+ ion gradients that drive ATP production • NADPH

  16. Sequence continued • H+ ions rush through ATP synthase to make ATP • Water is split in photolysis to replace electrons lost from photosystems • This creates oxygen as a waste

  17. Calvin cycle • Occurs in stroma • Enzyme called rubiscocombines CO2 with molecules of RuBP • Energy from NADPH and ATP is used to energize the molecules . Make NADP+ and ADP • I molecule called G3P is produced and RuBPis regenerated • 2 G3Ps make 1 glucose • NADP+ and ADP are recycled back to the light reactions

  18. photorespiration Calvin cycle adaptations • C3 plants- Use normal un-modified Calvin Cycle • Dry weather causes stomates to close and plants cannot take up CO2. when CO2 levels are low rubisco will try to fix O2 instead of CO2- photorespiration- useless • C4 and CAM plants are adapted to hot dry climates

  19. C4 and CAM plants • C4- keep stomata closed to reduce water loss, converts CO2 into a 4 carbon product and shuttles it deep into the leaf- corn and sugar cane • CAM- pineapple, cacti, succulents – takes in CO2 at night when it is cool, stores CO2 as an acid. Stomates are closed all day

  20. Greenhouse effect • CO2 in our atmosphere traps radiant heat from the sun. excess CO2 is removed by plants. Without it surface temp would be -18 C • Excess CO2 and other greenhouse gases trap too much heat. • In 1850 CO2- 0.03% of atmosphere • Today CO2 – 30% of atmosphere • Development, use of fossil fuels, cutting down trees all increase CO2 in atmosphere

  21. Global climate change • Melting of polar ice • Weather changes that may effect agriculture, spread of tropical disease like malaria • Widespread drought

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