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

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

3. 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.

4. Stages of Succession Pioneer stage, with fireweed dominant Dryas stage60 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.

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

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

7. 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.

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

9. 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.

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

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

12. 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.

13. 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.

14. 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

15. 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.

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

17. mRNA from DNA
RNA is less stable and one sided.

18. 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.

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

20. Math Grid In solution Step 1: 100% ÷ 8 = 12.5%
Step 2: Time = 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

21. 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.

22. 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.)