AP Biology AP Biology John D. O’Bryant School of Mathematics and Science November 8, 2012

AP Biology Agenda  Do Now (Table of Contents)  HW discussion  Photosynthesis: Modeling  Quiz

Table of Contents (Notes/Classwork) DateTopicPage number 11/1/12Cellular Respiration summary; Photosynthesis: Overview 11/2/12Photosynthesis: Overview, Light Reactions; Pigment lab 11/5/12Photosynthesis: Calvin Cycle, Light Reactions 11/6/12Photosynthesis: Modeling 11/7/12Photosynthesis: Calvin Cycle, Modeling 11/8/12Photosynthesis: Modeling 11/9/12Photosynthesis: Modeling

AP Biology HW

AP Biology Modeling Photosynthesis Task: In pairs, build a dynamic model of C3 photosynthesis using cutout pieces of paper to represent the molecules, ions, and membrane transporters or pumps. You should be able to manipulate or move carbon dioxide and water and its breakdown products through the various steps of the process.

AP Biology Quiz  1. The end products of the light-dependent reactions of photosynthesis are  A)ADP, H2O, NADPH2  B)ADP, PGAL, RuBP (RuDP)  C)ATP, CO2, H2O  D)ATP, NADPH2, O2  E)CO2, H+, PGAL

AP Biology Quiz  2. Which of the following enzymes is responsible for CO2 fixation in C3 plants?  A) Succinate dehydrogenase  B) RuBP (RuDP) carboxylase  C) Hexokinase  D) Amylase  E) DNA polymerase

AP Biology Quiz  3. All of the following statements about a chloroplast and a mitochondrion are true EXCEPT:  A) Both use proton gradients for energy production.  B) Both capture light energy.  C) Both contain DNA.  D) Both are bound by two unit membranes.  E) Both synthesize ATP.

AP Biology Quiz  4. If plants are grown for several days in an atmosphere containing 14CO2 in place of 12CO2, one would expect to find  A)very little radioactivity in the growing leaves  B)large amounts of radioactive water releasedfrom the stomates  C)a large increase in 14C in the starch stored in theroots  D)a large decrease in the rate of carbon fixation inthe guard cells  E)an increase in the activity of RuBP carboxylasein the photosynthetic cells

AP Biology Quiz  5. The O2 released during photosynthesis comes from  A) CO2  B) H2O  C) NADPH  D) RuBP (RuDP)  E) C6H12O6

AP Biology Quiz  6. Which of the following is an important difference between light- dependent and light-independent reactions of photosynthesis?  A) The light-dependent reactions occur only during the day; the light- independent reactions occur only during the night.  B) The light-dependent reactions occur in the cytoplasm; the light- independent reactions occur in chloroplasts.  C) The light-dependent reactions utilize CO2 andH2O; the light- independent reactions produceCO2 and H2O.  D) The light-dependent reactions depend on the presence of both photosystems I and II; the light-independent reactions require only photosystem I.  E) The light-dependent reactions produce ATP and NADPH; the light- independent reactions use stored energy in ATP and NADPH.

AP Biology Quiz  7. Carbohydrate-synthesizing reactions of photosynthesis directly require  A) light  B) products of the light reactions  C) darkness  D) O2 and H2O  E) chlorophyll and CO2

AP Biology Quiz  8. All of the following could reduce the yield of photosynthetic products EXCEPT  A) lower concentrations of carbon dioxide in the atmosphere  B) increased photorespiration  C) reduced carbon dioxide concentrations inthe air spaces of the leaf  D) increased frequency of stomata openings  E) fewer Calvin cycle enzymes

AP Biology Quiz  9. All of the following are common to C3 and C4 photosynthesis EXCEPT  A) Photolysis  B) Initial step of CO2 fixation  C) Cyclic photophosphorylation  D) Noncyclic photophosphorylation  E) Chemiosmotic phosphorylation

AP Biology

AP Biology Photosynthesis: Variations on the Theme

AP Biology Remember what plants need…  Photosynthesis  light reactions  light H2OH2O  Calvin cycle  CO 2 What structures have plants evolved to supply these needs?  sun  ground  air O O C

AP Biology Leaf Structure H2OH2O CO 2 O2O2 H2OH2O phloem (sugar) xylem (water) stomate guard cell palisades layer spongy layer cuticle epidermis O2O2 CO 2 Transpiration vascular bundle Gas exchange

AP Biology Controlling 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!

AP Biology When stomates close… xylem (water) phloem (sugars) H2OH2O O2O2 CO 2 O2O2  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!  

AP Biology Inefficiency 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 photosynthesis photorespiration

AP Biology 6C 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

AP Biology Calvin cycle when O 2 is high 5C RuBP 3C 2C to mitochondria ––––––– lost as CO 2 without making ATP photorespiration O2O2 Hey Dude, are you high on oxygen! RuBisCo It’s so sad to see a good enzyme, go BAD!

AP Biology Impact 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

AP Biology Reducing 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

AP Biology C4 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

AP Biology C4 leaf anatomy PEP (3C) + CO 2  oxaloacetate (4C) 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

AP Biology Comparative anatomy C3C4 Location, location,location! PHYSICALLY separate C fixation from Calvin cycle

AP Biology CAM ( 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!

AP Biology CAM plants succulents cacti pineapple

AP Biology C4 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

AP Biology Why 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!

AP Biology It’s not so easy as it looks… Any Questions??

AP Biology Ghosts of Lectures Past (storage)

AP Biology A second look inside a leaf…  Gas exchange & water flow  CO 2 in   O 2 out   H 2 O out  photosynthesis gas exchange water loss xylem (water) O2O2 CO 2 for Calvin cycle waste from light reactions for light reactions phloem (sugars) H2OH2O O2O2 CO 2

AP Biology C4 photosynthesis CO 2 O2O2 O2O2  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

AP Biology Supporting a biosphere  On global scale, photosynthesis is the most important process for the continuation of life on Earth  each year photosynthesis…  captures 121 billion tons of CO 2  synthesizes 160 billion tons of carbohydrate  heterotrophs are dependent on plants as food source for fuel & raw materials

AP Biology The poetic perspective…  All the solid material of every plant was built by sunlight out of thin air  All the solid material of every animal was built from plant material Then all the plants, cats, dogs, elephants & people … are really particles of air woven together by strands of sunlight! sun air

AP Biology If plants can do it… You can learn it! Ask Questions!!

AP Biology Plant pigment lab