The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes.

 Which of the following is the most likely explanation for failure of overexpression of the integrin alpha subunit to alter the rate of fibroblast migration?

#Question id: 9253

#Unit 9. Diversity of Life Forms

#Question id: 9182

#Unit 9. Diversity of Life Forms

Imagine that a deep temperate zone lake did not turn over during the spring and fall seasons. Based on the physical and biological properties of limnetic ecosystems, what would be the difference from normal seasonal turnover?

#Question id: 9174

#Unit 9. Diversity of Life Forms

Use the following figures to answer the question below.

Based on the data in the figures, which of the following statements is accurate?

#Question id: 9173

#Unit 9. Diversity of Life Forms

Use the following figure to answer the question below

In the figure, which number would designate the arctic tundra biome?

#Question id: 9171

#Unit 9. Diversity of Life Forms

Suppose that the number of bird species is determined mainly by the number of vertical strata found in the environment. If so, in which of the following biomes would you find the greatest number of bird species?

#Question id: 9169

#Unit 9. Diversity of Life Forms

In areas of permafrost, stands of black spruce are frequently observed in the landscape, while other tree species are noticeably absent. Often these stands are referred to as "drunken forests" because many of the black spruce often "lean over" (that is, they are displaced from their normal vertical alignment). What is the most likely explanation for the unusual growth of these forests in this marginal habitat?