Biology 9700 · AS & A Level
Replication and division of nuclei and cells
100 practice questions on Replication and division of nuclei and cells, with worked solutions and instant marking.
Which statements regarding the cell cycle are correct?
Feb/March 2016
Some stem cells undergo division and produce phagocytes. In which part of the human body do these stem cells divide?
Feb/March 2017
Which is the correct order of the stages in the mitotic cell cycle?
Feb/March 2017
Telomerase is an enzyme that maintains telomeres. It prevents telomeres from becoming shorter each time a chromosome is replicated. In human body cells, telomerase is usually inactive, although it can be switched on in some diseases. In which disease is the enzyme telomerase activated?
Feb/March 2017
The statements refer to events in the mitotic cell cycle. Which is the correct sequence for three of these events in the mitotic cell cycle?
Feb/March 2017
Meselson and Stahl carried out an investigation on DNA in bacteria. First, they cultured the bacteria in a medium containing only heavy nitrogen, $^{15}\text{N}$, until every bacterial DNA molecule had heavy nitrogen only. The bacteria were then transferred out of the heavy-nitrogen medium and grown in a medium containing only light nitrogen, $^{14}\text{N}$. Samples of bacteria were taken from each of the next three generations and the DNA was examined. Hybrid DNA has both heavy and light nitrogen. Which row indicates the correct DNA for the first and third generations?
Feb/March 2017
At the beginning of each of these stages of the mitotic cell cycle, how many copies of each distinct DNA molecule are present in a cell? The stages shown are $G_2$ of interphase, prophase and cytokinesis.
Feb/March 2018
A bacterial culture was grown so that it replicated with nucleotides containing the heavy nitrogen isotope ($^{15}\text{N}$). After a number of generations, every bacterial DNA molecule contained heavy nitrogen. A DNA sample was removed from the culture, combined with caesium chloride solution and then centrifuged at high speed. During this procedure, DNA molecules with different masses separate into bands at different places in the centrifuge tube. The greater the mass of the DNA molecules, the nearer the bottom of the centrifuge tube the band appears. The diagram shows where the DNA molecules containing heavy nitrogen are located in the centrifuge tube. The bacterial culture was then grown using nucleotides containing the light nitrogen isotope ($^{14}\text{N}$). DNA samples were collected and separated by centrifugation after the bacteria had divided once and then again after they had divided twice. At which positions would the DNA be present after one cell division and after two cell divisions?
Feb/March 2018
What causes the white blood cell count to rise in people with leukaemia?
Feb/March 2019
Which statements about complementary base pairing are true?
Feb/March 2021
What substances are formed when a DNA molecule replicates?
Feb/March 2021
Which letter labels the cell structures in which semi-conservative replication of DNA takes place?
Feb/March 2021
For what reason are spleen cells fused with myeloma cells in monoclonal antibody production?
Feb/March 2021
The protein p53 is made in a cell when DNA has been damaged. It temporarily halts the cell cycle just before DNA is replicated, allowing the DNA to be repaired. In which phase of the cell cycle does this halt take place?
Feb/March 2022
Which row is the correct one for the replication of a DNA molecule?
Feb/March 2022
Which of these events occur in the mitotic cell cycle?
Feb/March 2023
The human body is estimated to contain a total of $2.5 \times 10^{13}$ red blood cells. Each day, about $2.5 \times 10^{11}$ red blood cells are taken out of the circulation and substituted by stem cells in the bone marrow. What percentage of the overall number of red blood cells is replaced per day?
Feb/March 2023
DNA polymerase catalyses condensation reactions between molecules during semi-conservative replication of DNA. Which molecules are joined by DNA polymerase?
Feb/March 2023
In mammals, while sperm are being formed, a portion of each chromosome is exchanged for proteins called protamines. As a result, the DNA can be compressed much more tightly than it otherwise could be. Which component of the chromosome is replaced by protamines?
Feb/March 2024
Which of the following statements accurately describe features of stem cells that are vital for cell replacement and tissue repair?
Feb/March 2024
Which statements concerning complementary base pairing are correct?
Feb/March 2024
In the mitotic cell cycle, chromosomal DNA is copied. The particular positions in DNA molecules at which copying is taking place are called replication forks. A typical human chromosome contains about 150 million base pairs of DNA. Replicating the DNA of a typical human chromosome takes about 1 hour. When only one replication fork is used, the replication rate is about 50 base pairs per second. Approximately how many replication forks are needed during DNA replication in a typical human chromosome?
Feb/March 2024
A nucleus in a body cell of a species of fruit fly contains 8 chromosomes. How many strands of DNA are found in the nucleus at the end of interphase?
Feb/March 2025
What percentage of the chromosomal DNA in a cell during $G_1$ is still present in that same cell later in the same mitotic cell cycle in prophase and in telophase?
Feb/March 2025
The statements refer to two genes and the proteins they produce, both of which may contribute to tumour development. • The protein encoded by the $PTEN$ gene stops cells from increasing in size and dividing too quickly. • The protein encoded by the $p53$ gene stops cells from moving on through the mitotic cell cycle when those cells contain damaged DNA. Which pair of mutations in these two genes in one individual is most likely to lead to tumour formation?
Feb/March 2025
Telomerase is an enzyme that stops telomeres from becoming shorter. It is absent from most normal cells, but it is active in an estimated 85% to 95% of human tumour cells. Which statement explains the effect of telomerase on human tumour cells?
Feb/March 2025
DNA is known to copy itself in a semi-conservative manner. The results from Meselson and Stahl’s experiments provided very strong support for this theory. They worked with $E.\ coli$, which has a generation time of 50 minutes. The stages in their experiment are listed below, but the order is incorrect. P All bacteria contain $^{15}\text{N}$ DNA. Q All bacteria contain hybrid DNA ($^{15}\text{N}$ DNA and $^{14}\text{N}$ DNA). R Bacteria contain either all $^{14}\text{N}$ DNA or hybrid DNA. S Bacteria were grown in a $^{15}\text{N}$ medium for many generations. T Bacteria were moved to a $^{14}\text{N}$ medium and sampled every 50 minutes. Which sequence of letters shows the correct order of the steps in the experiment?
May/June 2010
DNA is described as replicating in a semi-conservative manner. Meselson and Stahl’s experimental results provided very strong evidence for this theory. They worked with E. coli, which has a generation time of 50 minutes. The steps in their experiment are listed below, but they are not in the right order. P: Every bacterium contains $^{15}\text{N}$ DNA. Q: Every bacterium contains hybrid DNA ($^{15}\text{N}$ DNA and $^{14}\text{N}$ DNA). R: Bacteria contain either only $^{14}\text{N}$ DNA or hybrid DNA. S: Bacteria were grown in a $^{15}\text{N}$ medium for many generations. T: Bacteria were moved to a $^{14}\text{N}$ medium and taken as samples every 50 minutes. Which sequence of letters gives the correct order of the experimental steps?
May/June 2010
Which statement is always correct about cytokinesis?
May/June 2011
The diagram illustrates how genetically identical frogs may be produced from unfertilised frog eggs. The diploid number $(2n)$ in frogs is $26$. Which set of numbers correctly shows the number of chromosomes in each type of cell in the diagram?
May/June 2011
The mode of action for four drugs that block DNA replication is given here. Aphidicholine blocks DNA polymerase. Cytarabine is changed into a molecule that can replace a DNA nucleotide and it also blocks DNA repair mechanisms. Epirubicin blocks an enzyme needed for DNA unwinding and strand separation. Hydroxycarbamide blocks an enzyme involved in making deoxyribonucleotides. Which row pairs a drug with the correct explanation of its mechanism of action?
May/June 2011
The graph shows how the amount of DNA in one nucleus varies at different points in the life cycle of a mammal. At which stage does $X$ occur?
May/June 2011
In which process does only mitosis take place?
May/June 2011
Which statement is always true during cytokinesis?
May/June 2011
The diagram illustrates how genetically identical frogs may be produced from unfertilised frog eggs. In frogs, the diploid number (2n) is 26. Which set of numbers correctly shows the chromosome number in each type of cell in the diagram?
May/June 2011
The mechanism of action of four drugs that inhibit DNA replication is shown below. Which row correctly pairs a drug with an explanation of the mechanism of action?
May/June 2011
In organisms that reproduce sexually, a reduction division takes place before fertilisation. Which reasons explain why this is needed?
May/June 2012
What conditions are present in a human cell immediately before it enters prophase?
May/June 2012
In eukaryotic cells, during semi-conservative replication of DNA, these events take place. Which option gives the correct sequence for some of the events?
May/June 2012
The diagram illustrates the cell cycle. If radioactive nucleotides are added to cells that are dividing, at what stage will they be incorporated into the chromosomes?
May/June 2012
In organisms that reproduce sexually, a reduction division takes place before fertilisation. Which reasons account for this requirement?
May/June 2012
What is the state of a human cell immediately before it enters prophase?
May/June 2012
In semi-conservative replication of DNA in eukaryotic cells, these processes take place. Which option gives the correct sequence of some of them?
May/June 2012
Which statement best describes a cell from a haploid organism that can reproduce?
May/June 2013
Some chemicals, which are used to halt tumour growth, act by stopping the DNA double helix from uncoiling and separating. At which stage of the cell cycle do they act?
May/June 2013
When cancer cells divide without control, tumours are produced. Which statement explains how a cancer cell differs from a normal cell?
May/June 2013
Mutations in either the $\text{BRCA1}$ gene or the $\text{BRCA2}$ gene account for most inherited breast cancer in humans. The proteins made by these two genes move into the nucleus, where they interact with other proteins, including those encoded by the tumour suppressor gene, $\text{p53}$, and the DNA repair gene, $\text{RAD51}$. Which pattern of gene activity is most likely to lead to breast cancer?
May/June 2013
During which processes does mitosis take place?
May/June 2014
Two batches of bacteria were cultured in different nitrogen-containing growth media. For one batch, the medium contained the ‘heavy’ isotope of nitrogen, $^{15}\text{N}$, and the bacteria were kept there until every DNA molecule became labelled. The other batch was cultured in a medium containing the ‘light’ isotope of nitrogen, $^{14}\text{N}$, until all the DNA was labelled. DNA was taken from each batch of bacteria and then centrifuged. The diagram indicates where this DNA appeared in the centrifuge tubes. Bacteria whose DNA was labelled with $^{15}\text{N}$ were moved into a medium containing $^{14}\text{N}$ and allowed to divide once. DNA was then extracted from the resulting generation of bacteria and centrifuged. Which tube shows where the DNA from this new generation of bacteria is found?
May/June 2014
The statements concern the disease tuberculosis (TB). Which factor explains why antibiotic treatment for TB takes such a long time?
May/June 2014
Which statement about cell and nuclear division is correct?
May/June 2014
Diploid ($2n$) organisms that reproduce sexually form haploid ($n$) gametes. However, some plants, including wheat, are able to make diploid or haploid gametes. These gametes may then fertilise diploid or haploid gametes from another plant. Which of the following statements are correct for plants of this type? 1. Diploid gametes may arise from an error during reduction division (meiosis). 2. The offspring will always have a higher chromosome number. 3. The offspring could be either $2n$, $3n$ or $4n$. 4. In theory, the chromosome number could rise in every generation.
May/June 2014
A hole may be present between the right atrium and the left atrium in some babies. These babies have a higher count of red blood cells. What explains this rise?
May/June 2014
In a primary immune response, the following stages take place. 1 Certain B-lymphocytes differentiate into plasma cells. 2 B-lymphocytes with the matching cell surface receptors undergo repeated mitotic division. 3 A specific antibody is synthesised. 4 T-helper cells release cytokines. 5 T-helper cells recognise a particular antigen. In what order do these stages happen?
May/June 2014
In which process does mitosis alone take place?
May/June 2014
The information given concerns genes and proteins that play a role in breast cancer. • The protein encoded by the $\text{BRAC1}$ gene slows the growth of breast cancer cells. • The protein encoded by the $\text{RAD51}$ gene is needed to repair damaged DNA. Which pair of genes is most likely to lead to breast cancer?
May/June 2014
The diagram illustrates some links among different nucleic acid bases. Which row is the correct one?
May/June 2014
The diagram illustrates the structures of several drugs that are similar in structure to nucleotides. The presence of these drugs lowers nucleic acid synthesis. Which statement explains how the drugs reduce nucleic acid synthesis?
May/June 2014
A scientist observed that each root cell in a xerophytic plant contained 22 chromosomes. What are the diploid and haploid chromosome numbers for this species?
May/June 2015
The protein p53 is synthesised in a cell when DNA damage occurs. A scientist exposed three sets of cells, X, Y and Z, to different conditions. In which sets of cells would the scientist expect to find large amounts of p53 mRNA?
May/June 2015
Lung cancer and chronic obstructive pulmonary disease (COPD) have several symptoms in common. Which symptom is characteristic of lung cancer but not COPD?
May/June 2015
Protein p53 is made within a cell when DNA damage occurs. It briefly halts the cell cycle immediately before DNA is copied, allowing the DNA to be repaired. During which phase of the cell cycle does this halt take place?
May/June 2016
What characteristic of stem cells allows them to replace cells in tissues such as the skin?
May/June 2016
The photomicrographs display cells at different stages of the cell cycle. Which cells have twice the number of DNA molecules as a cell from the same organism following cytokinesis?
May/June 2016
Mitosis is a vital process in organisms. Which characteristics of mitosis matter for single-celled organisms?
May/June 2016
Bacteria were cultured in a medium that contained $^{15}\text{N}$. After a number of generations, every DNA molecule contained $^{15}\text{N}$. Some of these bacteria were then moved into a medium containing the usual nitrogen isotope, $^{14}\text{N}$. They were permitted to divide once. The DNA from some of these bacteria was removed and examined. It was entirely hybrid DNA, with equal proportions of $^{14}\text{N}$ and $^{15}\text{N}$. The rest of the bacteria were kept in the $^{14}\text{N}$ medium and allowed to divide once again. The DNA from some of these bacteria was then extracted and analysed. What is the composition of this DNA?
May/June 2016
The graph illustrates the diameter of a tree trunk at various times. Which statement is correct?
May/June 2016
Which processes take place in bone marrow cells during the mitotic cell cycle? 1 phosphate groups attach to ADP molecules to make ATP 2 bonds are formed between nucleotides in a DNA strand 3 tRNA anticodons form hydrogen bonds with codons on mRNA
May/June 2016
An individual has two blood tests taken one month apart. For each test, the number of each cell type in a fixed sample volume is counted. What might this indicate about the individual from the findings after one month?
May/June 2016
Bacterial cells divide by a process known as binary fission. Which macromolecules need to be synthesised for binary fission?
May/June 2017
The diagram illustrates the mitotic cell cycle. In which phase does DNA replication occur?
May/June 2017
The table outlines the roles of four different proteins involved in DNA replication. Which option states the function of these proteins?
May/June 2017
The bacterium Escherichia coli splits once every 50 minutes at $36^\circ\text{C}$. E. coli were cultured on a medium that had only heavy nitrogen, $^{15}\text{N}$, until every part of the bacterial DNA contained heavy nitrogen (0 minutes). Some of the bacteria were transferred from the heavy nitrogen medium and then grown in a medium containing only light nitrogen, $^{14}\text{N}$. A sample of bacteria was taken after each of three generations. The DNA was removed and spun in a centrifuge. Hybrid DNA includes both heavy and light nitrogen. The diagram indicates the possible band positions (upper, middle and lower) of the DNA. The real band positions in the first two samples are shown. What fraction of the DNA in the sample collected at 150 minutes will be in the upper position?
May/June 2017
The diagram illustrates the cell cycle of a mammalian cell. Checkpoints in the mammalian cell cycle stop the cycle from carrying on if errors occur or DNA is damaged. Four checkpoints are given below. 1 Mitosis is prevented when DNA replication is not complete. 2 Anaphase is prevented if chromatids fail to attach correctly to the spindle. 3 DNA replication is prevented when DNA has been damaged. 4 DNA replication ceases if DNA damage has still not been repaired. At which phases of the cell cycle do these checkpoints occur?
May/June 2017
Meselson and Stahl studied DNA replication by culturing bacteria in a medium containing heavy nitrogen, $^{15}\text{N}$, until all the DNA had been labelled. These bacteria, called the parental generation, were then moved to a culture containing only light nitrogen, $^{14}\text{N}$, and allowed to replicate for two generations. DNA was removed from each bacterial generation and its relative mass was measured. The flow diagram shows the results. Which row accounts for the relative mass of the DNA in the second generation grown in $^{14}\text{N}$?
May/June 2017
In which stage of the cell cycle does DNA replication occur?
May/June 2018
Meselson and Stahl studied DNA in bacteria. They first grew bacteria in a culture containing only heavy nitrogen, $^{15}\text{N}$, until every bacterial DNA molecule was heavy. The bacteria were then transferred out of the heavy nitrogen culture and grown in a medium containing only light nitrogen, $^{14}\text{N}$. A sample of bacteria was taken from the first generation in the light nitrogen medium and their DNA was examined. Hybrid DNA consists of both heavy DNA and light DNA. Which row gives the percentage of heavy DNA strands and the percentage of hybrid DNA molecules in the first generation produced in the medium containing light nitrogen?
May/June 2018
Radioactively-labelled nucleotides are added to a cell. In which cell structures would the radioactivity be concentrated first?
May/June 2018
Which of these statements concerning cytokinesis is always correct? 1. Cell structures are duplicated. 2. Cell structures are distributed between two cells. 3. The nuclear envelope re-forms.
May/June 2018
Which statement accounts for DNA replication being described as semi-conservative?
May/June 2018
Which statement correctly explains how carcinogens affect lung tissue and lead to tumour formation?
May/June 2018
Which characteristics of an organism are influenced by a drug that prevents mitosis?
May/June 2018
DNA polymerase catalyses condensation reactions between molecules during semi-conservative replication of DNA. Which two molecules does DNA polymerase join?
May/June 2018
Which row shows the cells that can keep dividing continuously and take part in monoclonal antibody production?
May/June 2019
The enzyme telomerase stops telomeres from being lost after many mitotic cell cycles. Which cells need to transcribe telomerase enzyme?
May/June 2019
The diagram illustrates some of the stages that occur in the cell cycle. Which two stages occur during interphase?
May/June 2019
Which of the following statements concerning complementary base pairing are correct?
May/June 2019
The diagram illustrates the possible arrangement of DNA molecules following one replication. Which arrangement is correct?
May/June 2019
The enzyme telomerase stops telomeres from being lost after many mitotic cell cycles. Which cells are required to transcribe telomerase enzyme?
May/June 2019
A gene directs the synthesis of a protein, p53, which attaches to damaged DNA during interphase and stops it from being copied. A carcinogen in cigarette smoke alters this gene. Which statement explains why this mutation may cause cancer?
May/June 2019
What function does DNA polymerase carry out?
May/June 2019
Meselson and Stahl studied DNA in bacteria. They first grew the bacteria in a medium containing only heavy nitrogen, $^{15}\text{N}$, until every DNA molecule in the bacterial cells was heavy. The bacteria were then transferred from the heavy nitrogen medium to a medium containing only light nitrogen, $^{14}\text{N}$. A sample of bacteria from the second generation was taken and the DNA was analysed. Hybrid DNA includes both heavy and light DNA. Which row gives the percentage of heavy DNA strands and the percentage of hybrid DNA molecules in the second generation produced in the medium containing light nitrogen?
May/June 2019
Which characteristic of stem cells allows them to replace cells in tissues such as the skin?
May/June 2020
Bacteria were cultivated in a medium in which heavy nitrogen, $^{15}\text{N}$, was the only nitrogen source. After many generations, every bacterial DNA molecule contained heavy nitrogen. The bacteria were then transferred from the heavy nitrogen medium to a medium containing only light nitrogen, $^{14}\text{N}$. Bacteria were taken from each of the following three generations and their DNA was examined. Hybrid DNA includes both heavy and light nitrogen. Which row gives the correct DNA for the first and third generations?
May/June 2020
Which processes make use of mitosis?
May/June 2020
How many of the following statements are correct about semi-conservative replication of DNA in a eukaryotic cell?
May/June 2020
The diagram indicates how long each stage of the cell cycle takes relative to the others. Which row gives the stages of the cell cycle in the correct order?
May/June 2020
DNA replication takes place in a number of stages. Which of the following statements about DNA replication are correct?
May/June 2020
A person has two blood tests taken one month apart. The number of each cell type in a fixed sample size is counted. What might this indicate about the person from the results after one month?
May/June 2020
The jellyfish $\textit{Turritopsis dohrnii}$ is said to be immortal. Provided that $T.\ dohrnii$ is not consumed by predators or affected by disease, it appears capable of living forever. There is no method for finding the biological age of an individual $T.\ dohrnii$. Which property of the cells in $T.\ dohrnii$ might account for these observations?
May/June 2021