Mutations that block expression of the E-cadherin gene are thought to be an important step in metastasis. To better understand how loss of E-cadherin contributes to metastasis, scientists created two cell lines that differed in their expression of E-cadherin. One cell line expressed normal E-cadherin, but at 10% of the usual levels. The other cell line expressed normal E-cadherin at the usual levels, and also, at high levels a mutant form that included the cytoplasmic domain but lacked the rest of the protein. Both cell lines exhibited strongly reduced cell adhesion in culture. However, only the cell line with reduced expression of normal E-cadherin metastasized when introduced into mice.

Which of the following hypotheses is most consistent with the observations on cell adhesion and metastasis in these cell lines?

TLS Online TPP Program

#Question id: 12099

#Unit 10. Ecological Principles

According to the competitive exclusion principle, two species cannot continue to occupy the same

TLS Online TPP Program

#Question id: 12100

#Unit 10. Ecological Principles

Prairie dogs once covered the expanses of the Great Plains. Their grazing made the grass more nutritious for the huge herds of bison, and a variety of snakes, raptors, and mammals   preyed on the rodents. In fact, the black- footed ferret (now endangered) specialized in prairie dog predation. Today, growing housing and agricultural developments have covered many prairie dog towns. Which of the following statements about prairie dogs is true?

TLS Online TPP Program

#Question id: 12101

#Unit 10. Ecological Principles

The sum total of an organism's interaction with the biotic and abiotic resources of its environment is called its

TLS Online TPP Program

#Question id: 12102

#Unit 10. Ecological Principles

Use the following diagram of Joseph Connell's study of barnacle distribution in Scotland to answer the following two questions

Which of the following is the most logical conclusion about the distribution of the two species of barnacle, Chthamalus and Balanus?

TLS Online TPP Program

#Question id: 12103

#Unit 10. Ecological Principles

Which of the following is a good description of an ecological niche? 

TLS Online TPP Program

#Question id: 12104

#Unit 10. Ecological Principles

Two barnacles, Balanus and Chthamalus, can both survive on the lower rocks just above the low-tide line on the Scottish coast, but only Balanus actually does so, with Chthamalus adopting a higher zone. Which of the following best accounts for this niche separation?