Use the figure to answer the following question. In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (15N) and then transferred them to a medium containing 14N (nonradioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?

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#Question id: 16789

#Unit 13. Methods in Biology

The median of number 50, 48, 47, 48.5, 50.5, 52, 48.8, 46 will be: 

TLS Online TPP Program

#Question id: 16790

#Unit 13. Methods in Biology

For the moderately symmetrical distribution of age of the employees, mean = 20 and mode = 25. The approximate value of the median is: 

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#Question id: 16791

#Unit 13. Methods in Biology

The mode of a distribution is 24 and the mean is 60. What is its median? 

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#Question id: 16953

#Unit 4. Cell Communication and Cell Signaling

The ability of any stem cell to self-renew and differentiate depends on the structural organization and cellular function of specialized anatomic microenvironments known as stem cell niches. These sequestered regions are typically populated by a supportive network of stromal cells. Stem cell niche stromal cells express soluble and membrane-bound proteins that regulate cell survival, proliferation, differentiation, and trafficking. Which statements is true about HSCs?

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#Question id: 16954

#Unit 4. Cell Communication and Cell Signaling

match the following

Component	Description
A. endosteal niche	1. versatile cells that both generate bone and control the differentiation of HSCs
B. osteoblasts	2. line the blood vessels and also regulate HSC differentiation
C. reticular cells	3. send processes connecting cells to bone and blood vessels, and unexpectedly
D. sympathetic neurons	4. can control the release of hematopoietic cells from the bone marrow.

TLS Online TPP Program

#Question id: 16955

#Unit 4. Cell Communication and Cell Signaling

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.