Scientists investigated the cell cycle in neoblasts (stem cells) of planarian flatworms (Dugesia tigrina) undergoing regeneration after amputation. Neoblast activity was measured at 6, 24, 48, and 72 hours post-amputation.

Their results are shown in Table 1.

Table 1

Time post-amputation / hours	Percentage of neoblasts undergoing mitosis	Percentage of neoblasts undergoing DNA replication
$6$	$0.4$	$2.1$
$24$	$5.2$	$18.6$
$48$	$12.8$	$6.4$
$72$	$1.9$	$1.1$

Describe and explain the data in Table 1.

The scientists determined the percentage of neoblasts undergoing DNA replication by using a thymine analogue called BrdU (5-bromo-2'-deoxyuridine). Cells use BrdU instead of nucleotides containing thymine during DNA replication.

Describe how BrdU would be incorporated into new DNA during semi-conservative replication.

Cells with BrdU in their DNA are detected using an anti-BrdU antibody with an enzyme attached.

Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have BrdU in their DNA.

Their results are shown in Table 1.

Table 1

Time post-amputation / hours	Percentage of neoblasts undergoing mitosis	Percentage of neoblasts undergoing DNA replication
$6$	$0.4$	$2.1$
$24$	$5.2$	$18.6$
$48$	$12.8$	$6.4$
$72$	$1.9$	$1.1$

Describe and explain the data in Table 1.

Describe how BrdU would be incorporated into new DNA during semi-conservative replication.

Cells with BrdU in their DNA are detected using an anti-BrdU antibody with an enzyme attached.

Use your knowledge of the ELISA test to suggest and explain how the scientists identified the cells that have BrdU in their DNA.

Nucleic acids are important information-carrying molecules

Question 2

Table 1

Markscheme

Nucleic acids are important information-carrying molecules

Question 2

Table 1

Markscheme

Nucleic acids are important information-carrying molecules

Question 2

Table 1

Nucleic acids are important information-carrying molecules Questions

Nucleic acids are important information-carrying molecules

Question 2

Table 1

Nucleic acids are important information-carrying molecules Questions