ZERO-IN

Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included supporting the teacher’s understanding of the content being introduced within the CELL.

ANALYZE IT

Instruct students to complete the Analysis Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

Note: Students should place their team’s fossil record from Lab on their table so that they are able to refer to it as they respond to the following questions.

• Study the fossil record and think about the experiment you just completed with the more dense bone and less dense bone penguins and fish. Use your results to explain what may have happened during the time period between Layer 2 and Layer 3? The fossil record clearly demonstrates that the penguins and the fish became extinct sometime in the time between Layer 2 and Layer 3. This suggests that there was some change in the environment. There also seemed to be more penguins found in the fossil recording which had more dense bones so you could theorize that the temperature was getting colder. However, the help of a geologist would be very helpful in this case to obtain supporting data.

• Can a fossil record provide clues to what happened in an environment? Explain. The fossil record provides clues to the nature of life in the past. It is possible to see the change in organisms over time. It can suggest environmental changes but supporting information is necessary.

• Can a fossil record provide information about natural selection? Explain. Yes, at times it can. This occurs if specific traits are found in the fossil record and are able to be identified. For example, in the model fossil record, the impressions left by the bones may give a clue to different densities and would show a “picture” of which trait was more prevalent at each era.

GET FOCUSED

Instruct students to complete the Focus Question in their SDRs then discuss it as a class. Use the suggested response below to guide students’ answers.

• How can an environmental change affect a population? When a new environmental pressure is introduced, some organisms in a population will not survive. The organisms with the genes that are most adapted to the environment will have the highest chance of surviving and passing their genes on to the next generation. In our example, the change in the climate severely reduced the food source of the penguins. The result was that there was not enough food for all of the penguins in the population to survive and only one penguin survived. Because this penguin cannot mate with another penguin and reproduce, the population of penguins will become extinct.

COMPREHENSION CHECK

The Comprehension Check is designed to summarize the Core Experience Learning Lab and provide the teacher with an informal way to assess students’ understanding of the big ideas.

If time permits, ask your students to answer each Focus Question below. Use the suggested responses below to guide students’ answers.

• Why do individuals of a species have different traits? Genes are responsible for all the traits that allow an organism to be adapted to its environment since the genotype of an individual determines their phenotype. Genetic variation ensures the existence within a species of many possible genotypes and therefore many possible phenotypes that individual organisms can possess. This genetic variation is a result of mutations, recombination of genes, and the random mating of individuals. When an environment changes, an individual with a specific phenotype may be better suited to adapt to the new environment. This is important because this species will then be more likely to survive and pass their genes to the next generation. In Investigation One, naturally occurring mutations within the penguin species resulted in some individuals with more dense bones compared to the bone density of other individuals.

• What is the relationship between the survival of the individuals of a species and genetic variations? Genetic variation is the reason why there are many unique individuals of a species in a population. In the cactus population, there were cacti with few spines and some with many spines. All of these individuals would survive if the Sun is not too intense. More intense Sunlight will favor the survival of those cacti with many spines since they would be more shaded. Likewise, in the penguin population, there coexist numerous penguins with different bone densities. Genetic variation allows the entire population of a species to survive different environmental pressures. The naturally occurring variation in bone density allowed some individuals to fish more easily than those individuals with bones of a lesser density.

• How does genetic variation affect the type of traits or the adaptations in the individuals of a species? Genetic variation is responsible for the different traits that an individual possesses. In the example in Investigation Two, genetic variation existed in the trait of bone density. Before the weather turned much colder, all the penguins survived fairly easily. However, when the environment changed, some individuals were more adapted to the environment than others and were more likely to survive and pass on their genes.

• What is the relationship between genetic variation and natural selection? If members of a species did not possess different traits, natural selection could not occur because all the members of that species would be equally adapted to each environmental pressure. However, the genetic variation in a population makes some individuals more adapted to their surroundings than others. The individuals that survive are more likely to pass on their genes, so advantageous genetic variations become more common in a population. The mutation that results in greater bone density represents natural genetic variation that gives those penguins with the variation a survival advantage. This advantage is passed on to their progeny resulting in greater survival and their natural selection.

• How can an environmental change affect a population? Environmental pressures can affect the population because some members of a species are more adapted to the new environment than others. In Investigation Two, penguins with more dense bones survived at a higher rate because they were more equipped to deal with the shortage of food. The environmental pressure can be natural causes (such as temperature and sunlight) or human causes (such as pesticide exposure or antibiotic exposure). When a new environmental pressure is introduced, some organisms in a population will not survive. The organisms with the genes that are most adapted to the environment will have the highest chance of surviving and passing their genes onto the next generation. In Investigation Three, the change in the climate severely reduced the food source of the penguins. The result was that there was not enough food for all of the penguins in the population to survive and only one penguin survived. Because this penguin cannot mate with another penguin and reproduce, the population of penguins will become extinct.