AP Biology: Photosynthesis and Plant Structures

AP Biology: Photosynthesis and Plant Structures

This AP Biology lesson focuses on the process of photosynthesis and the structures that plants have evolved to supply the necessary components. Students will review the light reactions of photosynthesis, including the need

About AP Biology: Photosynthesis and Plant Structures

PowerPoint presentation about 'AP Biology: Photosynthesis and Plant Structures'. This presentation describes the topic on This AP Biology lesson focuses on the process of photosynthesis and the structures that plants have evolved to supply the necessary components. Students will review the light reactions of photosynthesis, including the need. The key topics included in this slideshow are . Download this presentation absolutely free.

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Slide1AP Biology2007-2008 Photosynthesis: Variations on the Theme

Slide2AP BiologyRemember what  plants  need…  Photosynthesis  light reactions  light  H 2 O  Calvin cycle  CO 2 What structures have plants evolved to supply these needs?   sun   ground    air O O C

Slide3AP BiologyLeaf Structure H 2 O CO 2 O 2 H 2 O phloem (sugar) xylem (water) stomate guard cell palisades layer spongy layer cuticle epidermis O 2 CO 2 Transpiration vascular bundle Gas exchange

Slide4AP BiologyControlling water loss from leaves  Hot or dry days  stomates close to conserve water  guard cells  gain H 2 O = stomates open  lose H 2 O = stomates close  adaptation to living on land, but…       creates PROBLEMS!

Slide5AP BiologyWhen stomates close… xylem (water) phloem (sugars) H 2 O O 2 CO 2 CO 2 O 2  Closed stomates lead to…  O 2  build up    from light reactions  CO 2  is depleted    in Calvin cycle  causes problems in Calvin Cycle The best laid schemes of mice and men… and plants !  

Slide6AP BiologyInefficiency of RuBisCo: CO 2  vs O 2  RuBisCo in Calvin cycle  carbon fixation enzyme  normally bonds  C   to  RuBP  CO 2  is the optimal substrate  reduction  of RuBP  building  sugars  when O 2  concentration is high  RuBisCo bonds  O   to  RuBP  O 2  is a competitive substrate  oxidation  of RuBP  breakdown  sugars photo synthesis photo respiration

Slide7AP Biology6C unstable intermediate 1C CO 2 Calvin cycle when CO 2  is abundant 5C RuBP 3C PGA ADP ATP 3C NADP NADPH ADP ATP G3P to make glucose 3C G3P 5C RuBisCo C3 plants

Slide8AP BiologyCalvin cycle when O 2  is high 5C RuBP 3C 2C to mitochondria ––––––– lost as CO 2 without making ATP photorespiration O 2 Hey Dude, are you high on oxygen ! RuBisCo It’s so  sad to see a good enzyme, go  BAD!

Slide9AP BiologyImpact of Photorespiration  Oxidation of RuBP  short circuit of Calvin cycle  loss of carbons to CO 2  can lose 50% of carbons fixed by Calvin cycle  reduces production of photosynthesis  no ATP  (energy) produced  no C 6 H 12 O 6  (food) produced  if photorespiration could be reduced, plant would become 50% more efficient  strong selection pressure to evolve alternative carbon fixation  systems

Slide10AP BiologyReducing photorespiration  Separate carbon fixation from Calvin cycle  C4 plants  PHYSICALLY separate carbon fixation from Calvin cycle  different cells to fix carbon vs. where Calvin cycle occurs  store carbon in 4C compounds  different enzyme to capture CO 2  (fix carbon)  PEP carboxylase  different leaf structure  CAM plants  separate carbon fixation from Calvin cycle by TIME OF DAY  fix carbon during night  store carbon in 4C compounds  perform Calvin cycle during day

Slide11AP BiologyC4 plants  A better way to capture CO 2  1st step before Calvin cycle, fix carbon with enzyme PEP carboxylase  store as 4C compound  adaptation to hot, dry climates  have to close stomates a lot  different leaf anatomy  sugar cane, corn, other grasses… sugar cane corn

Slide12AP BiologyC4 leaf anatomy PEP (3C) + CO 2     oxaloacetate (4C) CO 2 CO 2  O 2 light reactions C4 anatomy C3 anatomy  PEP carboxylase enzyme  higher attraction for CO 2  than O 2  better than RuBisCo  fixes CO 2  in 4C compounds  regenerates CO 2   in inner cells for RuBisCo  keeping O 2  away from RuBisCo bundle sheath cell RuBisCo PEP carboxylase stomate

Slide13AP BiologyComparative anatomy C3 C4 Location, location,location ! PHYSICALLY separate C fixation from Calvin cycle

Slide14AP BiologyCAM ( Crassulacean Acid Metabolism ) plants  Adaptation to hot, dry climates  separate carbon fixation from Calvin cycle by TIME  close stomates during day  open stomates during night  at night : open stomates &  fix carbon in 4C “storage” compounds  in day : release CO 2  from 4C acids to Calvin cycle  increases concentration of CO 2  in cells  succulents, some cacti, pineapple It’s all in the timing !

Slide15AP BiologyCAM plants succulents cacti pine apple

Slide16AP BiologyC4 vs CAM Summary C4 plants separate 2 steps of C fixation anatomically  in 2 different cells CAM plants separate 2 steps of C fixation temporally  = 2 different times night vs. day solves CO 2  / O 2  gas exchange   vs. H 2 O loss   challenge

Slide17AP BiologyWhy the C3 problem?  Possibly evolutionary baggage  Rubisco evolved in high CO 2  atmosphere  there wasn’t strong selection against active site of Rubisco accepting both CO 2  & O 2  Today it makes a difference  21% O 2   vs.  0.03% CO 2  photorespiration can drain away 50% of carbon fixed by Calvin cycle on a hot, dry day  strong selection pressure to evolve better way to fix carbon & minimize photorespiration We’ve all got baggage !

Slide18AP BiologyC4 photosynthesis CO 2 O 2 CO 2 O 2  Outer cells  light reaction & carbon fixation  pumps CO 2  to inner cells  keeps O 2  away from inner cells  away from RuBisCo  Inner cells  Calvin cycle  glucose to veins PHYSICALLY separated C fixation from Calvin cycle