1. Welcome to AP Biology Saturday Study Session
Macroevolution
Student packets start with a summary of key concepts. Do not review the summary with students because there is not enough time in the session. Begin the session with your introduction and then move on to the multiple choice questions. Students can use the summary as a resource while answering multiple choice and essay questions and/or keep it to study for the AP test.

2. Clue: prior to the formation of K-T boundary
Question 1 c
Clue: prior to the formation of K-T boundary
Fossils are one of several sources that provide evidence for evolution.

3. Fossils show that speciation and extinction have occurred throughout the Earth’s history
Remind students about the law of superposition.

4. Extinction rates are high at times of ecological stress20
800
700 15
600
500
Number of families:
(families per million years):
Total extinction rate 10
400
300 5
200
100
Famous extinctions:
3rd extinction – Permian (251 million years ago) – 96% of marine species died out due to a huge volcanic eruption in current Siberia
5th extinction – Cretaceous (65.5 million years ago) – more than half of marine species, many terrestrial species (including dinosaurs) died out due to an asteroid or large comet?; Yucatan peninsula has 180 km diameter crater
Era
Period
Paleozoic
Mesozoic
Cenozoic E O S D C P Tr J C P N
542
488
444
416
359
299
251
200
145
65.5
Time (millions of years ago)

5. Clue: conditions were sufficient
Question 2 b
Clue: conditions were sufficient

6. Scientific evidence supports several models about the origin of life on Earth
Primitive Earth provided inorganic precursors from which organic molecules could have been synthesized due to the presence of available energy and the absence of oxygen.

7. Clue: DNA replicates with fewer errors
Question 3 d
Clue: DNA replicates with fewer errors
The RNA World hypothesis proposes that RNA could have been the first genetic material. Help students understand that there are several hypotheses about the origin of life on Earth that have been tested or are currently being tested. As scientists gather new evidence, some of these hypotheses may have to be revised.

8. Clue: oxygen accumulated prior to evolution of eukaryotes
Question 4 b
Clue: oxygen accumulated prior to evolution of eukaryotes
The Great Oxygenation Event, also known as Oxygen Revolution, Oxygen Crisis or Great Oxidation occurred 2.5 billion years ago and changed the Earth’s environment dramatically. Evolution of cellular respiration took place and used oxygen to harvest energy from organic molecules.

9. Origin of Life Timeline
Briefly review key events with students.
Remind them that all organisms on Earth share a common ancestral origin of life.
Two of life’s three domains, Bacteria and Archaea, are prokaryotic. They are distinguished from Eukarya by lack of a nucleus and lack of membrane-bound organelles.
Eukaryotes are related to both Archaea and Bacteria and are thought to have formed through endosymbiosis. The endosymbiotic theory proposes that mitochondria and chloroplasts were formerly small prokaryotes that began living within a larger cell.
Accumulation of oxygen in the atmosphere (2.5 bya)

10. Clue: accumulate features rapidly, then change little
Question 5 c
Clue: accumulate features rapidly, then change little

11. Speciation Rates Can Vary
According to the gradualism model, evolution occurs by the gradual accumulation of small changes. Individuals speciation events or major changes in lineages occur over long periods of geologic time, from hundreds of thousands to millions of years. Punctuated equilibrium model argues that evolutionary history consists of geologically long periods of stasis with little or no evolution, “punctuated” by geologically short periods of rapid evolution ranging over tens of thousands of years.

12. b Question 6 Clue: point mutation
Review with students that variation in molecular units provides a wider range of functions.
Processes that increase genetic variation are reviewed in depth in the Microevolution SSS.

13. Gene duplications may provide new phenotypes
Another example of gene duplication is the antifreeze gene in fish. Arctic cod has the antifreeze gene which originated from a duplication of a pancreatic gene aiding in digestion. A new copy of the gene evolved to code for antifreeze glycoproteins, allowing the cod to survive in cold ocean water.

14. a Question 7 Clue: islands
Please review adaptive radiation. Speciation types are reviewed in the 2nd short free response question.

15. Adaptive Radiation Example
Focus on the size and shape of the beak as it relates to a possible food source.
Adaptive radiation is the process in which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available and opens new environmental niches. Starting with a recent single ancestor, this process results in phenotypic adaptation of an array of species exhibiting different morphological and/or physiological traits with which they can exploit a range of environments.

16. Math Grid In 1 The correct answer: 17,190 years 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

17. time required for the radioactive material to decrease by one half
Half-life
time required for the radioactive material to decrease by one half

18. Math Grid In 2
The correct answer: 14 Solution: = 28 (diploid) 28/2 = 14 (haploid)

19. Allopolyploidy Unreduced gamete with 4 chromosomes Unreduced gamete
Hybrid with
7 chromosomes
Viable fertile hybrid
(allopolyploid)
Meiotic error;
chromosome
number not
reduced from
2n to n
Species A
2n = 4
2n = 10
Normal gamete
n = 3
Normal gamete
n = 3
Species B
2n = 6

20. Autopolyploidy Failure of cell division
in a cell of a growing
diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue.
Offspring with tetraploid karyo-
types may be viable and fertile—a new biological species.
Gametes produced by flowers on this tetraploid branch are diploid. 2n
2n = 6
4n = 12 4n

21. Short Free Response 1 4 points possible
For each kind of data, must include description and explanation.
Description of kind of data (1 pt each)
Explanation (1 pt each)
Ability to produce viable seeds/offspring in nature
Consistent with definition of biological species
Ability to cross-pollinate
Production of fertile offspring
Comparison of sequences of DNA/chromosomes or other conserved molecules
Similarity supports single species
Fertile hybrid populations found living between the two other populations of plants
Released Practice Question
Review that the biological species concept distinguishes species on the basis of reproductive isolation while the morphological species concept distinguishes species on the basis of physical similarities.

22. Short Free Response 2 2 points possible
Mechanisms that lead to the development of separate species from a common ancestor (1 point each)
Allopatric speciation takes place when a population of one species becomes physically separated by some geographic barrier such as a river, mountain range, etc. Long-term isolation of two populations eventually leads to reproductive isolation.
Sympatric speciation happens when new species arise as a result of reproductive isolation within the population range - for example, because of polyploidy or switching mating behaviors (fruit flies going from hawthorn to apple to lay eggs). Eventually the two populations are unable to interbreed.
Reproductive isolation by prezygotic barriers such as habitat, temporal, behavioral, mechanical or gametic incompatibility.
Reproductive isolation by postzygotic barriers (e.g., reduced hybrid viability or fertility) leads to speciation.
Released 2011 B Question 4a
Remind students that in order for speciation to take place, reproductive isolation must occur.

23. Modes of Speciation
Allopatric speciation
Sympatric speciation

24. Prezygotic and Postzygotic Isolating Mechanisms