Stage thymocytes express neither CD4 nor CD8, markers associated with mature T cells. They are therefore called double negative (DN) cells. DN cells first travel to the region under the thymic capsule, a region referred to as the ________, where they proliferate and begin to generate their T-cell receptors. Thymocytes that successfully express TCRs begin to express both CD4 and CD8, becoming double positive (DP) cells, and populate the cortex, the site where most (85% or more) immature T cells are found.

#Question id: 12112

#Unit 10. Ecological Principles

#Question id: 7151

#Unit 5. Developmental Biology

In developmental biology, what is meant by the concept of "growth"?

a) Growth occurs through increases in cell size.

b) Growth occurs through increases in cell number.

c) Growth can result from increases in the volume of extracellular matrix between cells.

d) Cell death is an important determinant of overall growth.

Which of the following is correct?

#Question id: 11169

#Unit 10. Ecological Principles

The viceroy butterfly (limenitis archippus) resembles the queen butterfly (danaus gilippus), a species toxic to birds because of alkaloids it stores during larval development from the milkweeds it feeds upon. The viceroy butterfly is an example of what kind of defense against predation?

#Question id: 14824

#Unit 2. Cellular Organization

#Question id: 4308

#Unit 3. Fundamental Processes

Most repressor proteins are allosteric. Which of the following molecules binds with the repressor to alter its conformation and therefore affect its function?