AP Biology Saturday Session 3 Evolution as a Process Session 3 – Change over Time

Clue: clear-cutting & enhanced Question 1 C Clue: clear-cutting & enhanced

Succession (Mount St. Helens, WA) Use as an example of Secondary succession. This forest disappear due to the Volcanic explosion. It took several years but life is coming back, as seen in the foreground.

Stages of Succession Pioneer stage, with fireweed dominant Dryas stage 60 50 40 Soil nitrogen (g/m2) Don’t get into the minute details on the slide. What is important is that students see that hebaceous plants are replaced by taller, shading brush, and brush is replaced by taller, shading trees. 30 20 10 Pioneer Dryas Alder Spruce Successional stage Spruce stage Nitrogen fixation by Dryas and alder increases the soil nitrogen content.

Possible source of secondary succession (Forest fire destroys the forest)

Primary Succession (Remember Hawaii?) Quickly cover primary succession using the following slides.

Primary Succession (Pioneer species) Please convey to students that pioneer species have the abilty to break down rock and convert it the a fine layer of soil.

Primary Succession Soil promotes grass and herb growth. Also a possible food source for small birds. They grasses also make the soil layer thicker.

Primary succession As birds bring in larger plant species seeds a transition occurs. The shrubs will grow taller than the grasses and shade them out. They also make the soil deeper.

Primary Succession Climax Community (Hawaii today) Trees of all kind develop over time. They shade out the shrubs and increase the soil depth.

Clue: shallower = more recent Question 2 A Clue: shallower = more recent

Fossil Formation using water, sediment, and long periods of time Please help students understand the oldest rock layers are deeper down. The more recent are closer to the surface.

Question 3 C Please stress to students that a reducing environment (one with out free oxygen) favors molecules coming together. An oxidizing environment promotes the degrading (tearing apart) of molecules.

Stanley Miller and Harold Urey experimental set up CH4 Water vapor Electrode NH3 H2 Condenser Cold water Please help students that this was to represent the gases believed, by volcanic gas analysis, to be in the Earth’s early atmosphere. The electricity represented the lightning and the fire/boiling solution represented warm oceans. Cooled water containing organic molecules H2O Sample for chemical analysis

Question 4 D Please help students see that DNA is more stable than RNA because it is double sided using base pairing; where as, RNA is single side.

DNA Chromosomes Double sided and more stable due to base pairing.

mRNA from DNA RNA is less stable and one sided.

B Clue: took advantage Question 5 Please remind students that oxygen is needed in Cellular respiration utilizing mitochondria. Oxygen is a by-product of photosynthesis. So the cyanobacteriaof the world’s oceans were the creators of the free oxygen within the atmosphere of early earth.

Question 6 A Please walk students through the series of events and stress the need to think logically about the events.

Math Grid In solution Step 1: 100% ÷ 8 = 12.5% Step 2: Time 0 = 100% = 0 years First Half life = 50% = 5,730 years Second Half life = 25% = 5,730 years Third Half life = 12.5% = 5,730 years Adds up to: 17,190 years

Short Free Response 1 4 points possible Possible points awarded for: Discussion of the Endosymbiotic Hypothesis proposing a method for eukaryotic cells to evolve, over time, from prokaryotic cells that formed symbiotic relationships. (1 pt.) 3 Possible facts : Each possesses its own DNA 1 pt. each Reproduces by binnary fission Each has its own ribosomes Each can generate energy.

Short Free Response 2 4 points possible Discussion of amino acids needed to make proteins (work horse molecules) and nucleic acids storing information. (1 pt.) Discussion of using environments energy to make larger complex molecules for building structures. (1 pt.) Discussion of RNA/DNA being used for reproduction and information storage. (1 pt.) Discussion of membranes needed to hold cell together and form a separate internal space. (1 pt.)