Question 1
1
During the development of multicellular organisms, cells differentiate into specific cell lines. A study was carried out on the early stages of differentiation in cells from mouse embryos that were grown in cultures. Two differentiated cell lines were studied, one of inner embryonic tissue (endodermal cells) and the other of external embryonic tissue (nerve cells) after 48 and 96 hours of incubation in cell cultures. A culture of undifferentiated cells was used as a control group. Cell population growth was measured by changes in cell density in all three cell lines.
13 marks
Question 1(a)
1(a)
Distinguish between the changes in cell numbers in the three cell lines that occur during the 96 hour period.
Mediumstructured2 marks
Answer
a. nerve cells increase the least OR control cells the most b. «endodermal and control cells are the same at 48 hours» but the control cells increase exponentially/much more than endodermal cells by 96 hours OR last 48 hours/from 48 hours to 96 hours, constant «small» increase in cell numbers for nerve, but greater/increased change for control and endodermal c. from 48 to 96 hours much more increase in cell number in control than in endodermal Do not accept numbers without distinguishing terms. Award [1 max] if all three (nerve, endodermal and control cells) not mentioned at some point in the answer as stem requires all three. 2 max
Question 1(b)
1(b)
Using the data in the graph, deduce the relationship between cell differentiation and population growth.
Mediumstructured1 marks
Answer
cell differentiation slows down/retards/decreases population growth OR population growth is slower in differentiating/differentiated cell lines Accept converse eg: nondifferentiation accelerates growth.
Question 1(c)
1(c)
There are three phases of interphase in the cell cycle: - the growth phase with the synthesis of RNA and proteins (G1) - the phase of DNA replication (S) - and the pre-mitotic phase of rapid growth (G2). The graph shows the percentage distribution of the three cell lines in the different stages of interphase after 96 hours of incubation. Compare and contrast the percentage of control and nerve cells in each of the three phases after 96 hours of incubation.
Mediumstructured2 marks
Answer
a. the percentage of «cells in» G1 in nerve is greater than in control OR the S phase has greater «percentage of cells» in control than in nerve b. G2 phase is similar in both OR least/lower percentage of cells of the phases in both lines Do not accept numbers without distinguishing terms.
Question 1(d)
1(d)
Using the data of both graphs, deduce the relationship between the percentage of cells in each cell cycle phase and the population growth.
Hardstructured2 marks
Answer
a. more cells in G1 «of cell lines/nerves» with slow population growth b. more cells in S «of cell line/control» with fast population growth/«significantly» fewer cells in S in both slow growth lines/nerves and endodermal cells c. G2 seems not to be related with pop growth as it is very similar in the three cell lines Accept converse statements. 2 max Answers Notes Total
Question 1(e)
1(e)
Interphase is followed by mitosis. State the final product of the mitotic cell cycle.
Easystructured1 marks
Answer
two genetically identical daughter nuclei/cells OR two identical daughter nuclei
Question 1
1
Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of \(0 \mu \mathrm{~mol}\). In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.
10 marks
Question 1(a)
1(a)
0 marks
Question 1(a)(i)
1(a)(i)
Deduce the concentration of ZDV that would cause a 50 % reduction in root growth compared to the control.
Mediumstructured1 marks
Answer
\(75 \mu \mathrm{~mol} \) Deduce Allow answers in the range of \(70 \mu \mathrm{~mol}-80 \mu \mathrm{~mol}\)
Question 1(a)(ii)
1(a)(ii)
Identify the root length, as a percentage of the control, resulting from a ZDV concentration of \(400 \mu \mathrm{~mol}\).
Easystructured1 marks
Answer
24 \% Identify Allow answers in the range 23\%-25\%
Question 1(b)
1(b)
Compare and contrast the effect of ZDV and NVP on the growth of Allium roots.
Mediumstructured2 marks
Answer
Similarities: a. reduce root length (compared to the control) b. (ZDV and NVP) have greatest change (in growth) at lowest concentrations (of ZDV and NVP) c. same effect at \(200 \mu \mathrm{~mol} \) d. above/at about \(400 \mu \mathrm{~mol}\) effect levels off Differences: e. the change/differences become significant after \(200 \mu \mathrm{~mol}\) f. ZDV has a (slightly) larger effect / NVP has a (slightly) smaller effect / WTTE OR above \(400 \mu \mathrm{~mol}\) effect of ZDV remains higher / NVP remains lower / Compare and contrast Answer must contain one similarity and one difference Credit may be given for numeric differences when accurately stated 2 max
Question 1(c)
1(c)
Both ZDV and NVP are believed to have a damaging effect on the process of mitosis but ZDV in particular is believed to block the formation of the spindle. Based on this information, suggest with a reason which of the labelled cell types will become more common in Allium root tips treated with ZDV.
Hardstructured2 marks
Answer
a. Y (will become more common) b. spindle not formed yet OR cells x and z have spindles c. cells in Y cannot progress (into Z/into metaphase) Suggest 2 max
Question 1(d)
1(d)
Allium root tips continue to show some growth even at high concentrations of NVP. Suggest a possible reason for the growth seen in root tips with \(800 \mu \mathrm{~mol}\) NVP.
Hardstructured1 marks
Answer
a. still some mitosis b. individual cells grow/elongate (expand by absorbing water) c. NVP is not 100 % effective / does not enter all of the cells / not all cells have come in contact with NVP d. roots have reached maximum saturation of NVP and are no longer functionally affected e. some cells are resistant to the drug Suggest Accept reasonable suggestions. If in doubt contact your team leader. 1 max
Question 1(e)
1(e)
Mitosis plays an important role in tissue regeneration and can be an important factor in recovery from surgery. The hormone leptin has been shown to promote mitosis in certain circumstances. The bar chart shows the mitotic indices of liver tissue exposed to leptin and control tissue during 72 hours after surgery. Deduce the change in mitotic index after 72 hours compared to the control.
Mediumstructured1 marks
Answer
0.3 / 100\% increase / doubling \(\) Deduce Do not penalize errors in significant figures. For example, 0.34 would be acceptable.
Question 1(f)
1(f)
Based on the data, evaluate the evidence for leptin promoting regeneration of liver tissue.
Hardstructured3 marks
Answer
a. mitotic index in treatment greater than in control/leptin appears to promote mitosis b. mitotic index increases with time suggests ongoing regeneration/growth OR positive correlation between exposure to leptin and increased mitotic index c. but experiment limited to 72 hours/regeneration/recovery may take longer than 72 hours d. no error bars shown/no information on significance/sample size Evaluate Acknowledge WTTE 3 max
Question 1
1
Mitosis in cancerous tissues is uncontrolled and the number of cells undergoing mitosis increases exponentially. Rapidly dividing cells in root tips can be used as a model for studying the effects of anticancer drugs. Aqueous extracts of the fruit of avocado (Persea americana) and the leaves of crepe jasmine (Tabernaemontana divaricata) have been shown to be toxic to some human cancer cell lines. Root tips of the broad bean (Vicia faba) were exposed to these aqueous plant extracts over a range of concentrations. The mitotic index is the percentage of cells examined undergoing mitosis. The table shows the numbers of broad bean root cells examined and the mitotic indices over a range of plant extract concentrations.
14 marks
Question 1(a)
1(a)
0 marks
Question 1(a)(i)
1(a)(i)
Calculate the number of cells undergoing mitosis using 100 ppm of crepe jasmine extract.
Easystructured1 marks
Answer
240 Reject 'about 240' and any answer other than 240
Question 1(a)(ii)
1(a)(ii)
Describe the effect of avocado extract on mitotic index.
Easystructured1 marks
Answer
reduces it
Question 1(b)
1(b)
Compare and contrast the effect of increasing extract concentration on the mitotic indices for the two plant extracts.
Mediumstructured3 marks
Answer
similarities a. both extracts reduce the mitotic index/percentage of cells undergoing mitosis OR mitotic index decreases as concentration of both extracts increases / negative correlations differences b. avocado (extract) more effective/reduces MI more (at higher concentrations) OR lower MI with avocado (than jasmine) above 2500/at 5000 to 20000/at 20000 c. at lower concentrations jasmine (extract) more effective/reduces MI more OR lower MI with jasmine (than avocado) below 5000/at 100 to 2500 Accept MI for mitotic index and accept crepe or jasmine for T. divaricata. For similarities in mpa the answer must refer to the different extracts together, not in separate parts of the answer. For mpb or mpc the differences can be expressed in the reverse, for example jasmine less effective at higher concentrations for mpb. Do not award marks for quoting figures without a statement of the similarity or difference. For the first alternatives of mpb and mpc, do not accept 'greater rate' instead of 'more'. 3 max
Question 1(c)
1(c)
The percentage of cells in different stages of mitosis in the root tips was also recorded. Outline the effect of avocado extract concentration on the percentage of cells in the different stages of mitosis.
Mediumstructured2 marks
Answer
a. \% in prophase increased (at higher extract concentrations) b. \% in metaphase decreased (slightly) c. \% in anaphase with telophase decreased Do not award mpa for 'prophase percentage is highest' The initial rise of metaphase \% is unlikely to be significant so this and other fluctuations are not included in the mark scheme. 2 max
Question 1(d)
1(d)
Using both the table of mitotic indices and the bar charts, deduce whether these extracts contain chemicals that block mitosis in broad bean root tips.
Mediumstructured3 marks
Answer
a. yes / extracts (do contain chemicals that) block mitosis (in broad bean root tips) evidence from table of mitotic indices b. lower MI shows (both) extracts prevent cells from undergoing/entering/starting mitosis evidence from bar charts c. avocado increases prophase \% indicating progression to metaphase/through mitosis slowed/blocked OR avocado decreases metaphase and anaphase-telophase \% indicating progression from prophase/through mitosis slowed/blocked d. jasmine increases metaphase \% so progression to anaphase/through mitosis slowed/blocked OR jasmine reduces prophase \% so (entry to/start of) mitosis slowed/blocked Do not award mpa if no attempt at deduction is presented in the answer. This is a deduce question so mpb to mpd not awarded for only describing of the data. 3 max
Question 1(e)
1(e)
The mechanism of action of vinblastine, an anticancer drug, was investigated over a range of concentrations. Vinblastine is an alkaloid isolated from the periwinkle plant (Catharansus roseus). The percentage of cells in mitosis and ratio of anaphase to metaphase in cells exposed to this drug in vitro for a fixed time were recorded. The data are displayed in two graphs. By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.
Hardstructured3 marks
Answer
evaluation of evidence in graph on left a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) b. supports hypothesis that cells get stuck in/cannot complete mitosis evaluation of evidence in graph on right c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase d. cells not progressing from metaphase to anaphase/get stuck in metaphase Do not allow mpa if the candidate is arguing that the hypothesis is not supported. 3 max
Question 1(f)
1(f)
Some anticancer drugs inhibit mitosis by blocking the formation of the spindle. Suggest one other way in which vinblastine could block mitosis.
Mediumstructured1 marks
Answer
a. causes microtubules/spindle fibres to break up / tubulin molecules to depolymerize b. prevents contraction of spindle microtubules/fibres c. disrupts/damages kinetochores/centromeres/microtubule motors/centrioles/centrosomes d. prevents separation/pulling apart of (sister) chromatids/chromosomes/centromeres e. prevents microtubules/spindle binding to chromatids/chromosomes/centromeres/DNA Mark the first suggestion only in the answer. Do not allow answers about DNA replication or other processes that precede mitosis. 1 max
Question 1
1
0 marks
Question 1(a)
1(a)
The photomicrograph shows a section of onion (Allium cepa) root tip cells.
structured0 marks
Question 1(a)(i)
1(a)(i)
Describe how a mitotic index could be obtained from this image.
MediumPractical2 marks
Answer
a. count all cells in any stage of mitosis; b. divide by total number of cells; c. convert to percentage OR multiply by 100 ; Do not accept other terms than cells. 2 max
Question 1(b)
1(b)
Cadmium is a heavy metal that can cause environmental problems. Cadmium ions are released from various human activities such as the release of sewage sludge, mining and industrial processes. Plants take up cadmium ions and they enter food chains. A study was carried out to look at the effect of various concentrations of cadmium ions on the mitotic index of the apical meristem of root cells from 4-day-old wheat (Triticum aestivum) seedlings.
0 marks
Question 1(b)(i)
1(b)(i)
State the effect of cadmium ion concentration on the mitotic index of root cells from wheat seedlings.
Mediumstructured1 marks
Answer
as concentration increases mitotic index decreases OR negative effect/correlation/relationship;
Question 1(b)(ii)
1(b)(ii)
Suggest the effect the change in mitotic index would have on the wheat plant.
Mediumstructured1 marks
Answer
decreased growth/cell proliferation;
Question 2
2
What is the sequence of stages during the cell cycle?
Mediummcq1 marks
Answer
A
Question 3
3
Which of the following does not occur during interphase? A. Replication B. Translation C. Cytokinesis D. An increase in the number of mitochondria
Mediummcq1 marks
Answer
C
Question 3
3
The cell theory states that cells come from pre-existing cells. What biological process allows this to occur? A. Ovulation B. Differentiation C. Cytokinesis D. Exocytosis
Easymcq1 marks
Answer
C
Question 3
3
Which processes are involved in the development of cancer? I. Mutations occur in oncogenes. II. Oncogenes prevent cancer. III. Oncogenes affect cell cycle regulatory proteins. A. I and II only B. I and III only C. II and III only D. I, II and III
Mediummcq1 marks
Answer
B
Question 3
3
The image shows a micrograph of a cell. in_prophase,_metaphase,_anaphase,_telophase).jpg by Doc. RNDr. Josef Reischig, CSc.] What explains the appearance of the cell in the micrograph? The cell is dying. The DNA is replicating. The cell is in metaphase. The cell is in telophase.
Mediummcq1 marks
Answer
C
Question 3
3
This micrograph is from a dividing cell. What is shown in this image? Two condensed chromosomes consisting of four chromatids A chromosome from a cell in telophase of mitosis A chromosome from a cell in G1 of interphase A chromosome from a cell in metaphase
Mediummcq1 marks
Answer
D