AS1 Chapter 5 - Continuity of Cells Flashcards
Past Paper Question - June 2017 Q4 c) AS1 (Revised Spec. + Legacy Material)
Q4 c) Describe and explain two features of meiosis that contribute to genetic variation. [4]
Q4 c) Independent assortment/ random alignment of homologous chromosomes; resulting in new chromosome combinations in gametes.
Exchange of genetic information (crossing over)/ recombination of genes between two chromatids/ non sister chromatids/ homologous chromosomes/ new allelic combination; [4]
Past Paper Question - June 2017 Q4 d) AS1 (Revised Spec.)
Q4 d) The cell cycle can be targeted by anti-cancer drugs such as 5’ Fluorouracil. State the stage of the cell cycle which is affected by this drug. [1]
Q4 d) DNA synthesis/ S-phase [1]
Past Paper Question - June 2017 Q4 d) AS1 (Legacy Material)
Q4 d) Nuclear division by mitosis or meiosis is followed by cytokinesis. Describe precisely how cytokinesis occurs in animal cells. [1]
Q4 d) Cleavage furrow/ invagination/ cytoplasm splits to form two daughter cells. [1]
Past Paper Question - June 2016 Q5 a)i) AS1 (Legacy Material)
Q5 The diagram below represents the eukaryotic cell cycle.
Mitosis -----> Stage X Stage X ----> G1 G1 ------> S S -------> G2 G2 ------> Mitosis (Circle)
a)i) Identify process X. [1]
Q5 a)i) Cytokinesis; [1]
Past Paper Question - June 2016 Q5 a)ii) AS1 (Legacy Material)
Q5 a)ii) Describe two changes that take place in cells during the G1 phase. [2]
Q5 a)ii) Any two from:
• Cell increases in size/volume/mass
• Protein synthesis/RNA/enzymes synthesis
• Organelles replicate/are synthesised
Past Paper Question - June 2016 Q5 a)iii) AS1 (Legacy Material)
Q5 a)iii) Describe two differences between the cell cycle in animal and plant cells. [2]
Q5 a)iii) Centrioles involved in animal cells (or converse); Cleavage furrow (by description) in animal cells/formation of cell plate (by description) in plant cells; [2]
Past Paper Question - June 2016 Q5 b) AS1 (Legacy Material)
Q5 b) Onion root tip cells require 12 hours to complete the cell cycle. The time spent in a particular stage can be estimated using the following formula:
Time in stage = Number of cells in stage
——————————— x time in minutes for cell cycle
Total number of cells counted
Actively dividing onion tissue was examined using a microscope. The table below shows the number of cells observed to be in different stages of the cell cycle. The time spent in each stage has been calculated except for metaphase.
Stage Number of cells Time in stage/mins
Interphase 20 389
Prophase 10 195
Metaphase 3 X
Anaphase 2 39
Telophase 2 39
Total number of cells 37
Using the formula and the table, calculate the time spent in metaphase by these onion cells.
(Show your working). [2]
Q5 b) 3 divided by 37
Multiply by 720 (12x60=720)
Answer = 58 minutes [2]
Past Paper Question - June 2015 Q4 c)ii) AS1 (Legacy Material)
Q4 c) Cancer occurs when cells divide more frequently than normal, resulting in a mass of cells called a tumour. One type of treatment for cancer is chemotherapy, which involves drugs which interfere with the cell cycle in cancer cells.
Two chemotherapy drugs, A and B, are effective because they prevent DNA replication within the cancer cells. This reduces the rate of cell division within a tumour.
Drug A contains platinum, a metallic element, that forms strong cross-links between the two strands in a DNA molecule.
Drug B is similar in structure to a nucleotide but contains three phosphates instead of one.
ii) Identify the precise stage of the cell cycle which is affected by both these drugs. [1]
Q4 c)ii) S/synthesis phase; [1]
Past Paper Question - June 2015 Q8 Section B AS1 (Legacy Material)
Q8 The process of meiosis results in haploid daughter cells which show genetic variation.
Give an account of the process of meiosis. Your account should include the stage at which the haploid number of chromosomes is formed and two ways in which the process results in genetic variation in daughter cells. [13]
Quality of written communication [2]
Q8 Three essential points and any ten other points from:
• at prophase 1 homologous chromosomes pair up/form bivalents
• chromosomes shorten and thicken/become visible/condense
• chiasma/chiasmata/crossing over occurs
• between non-sister chromatids/homologous chromosomes
• leads to recombinants/new allelic combinations/non-parental allelic
combinations
• which is one cause of variation (essential point)
• spindle fibres develop
• at metaphase 1 the bivalents (homologous pairs) attach to the spindle fibres
• by their centromeres
• orientation of the bivalents (homologous pairs) is random/independent assortment occurs
• which is another cause of variation (essential point)
• at anaphase 1 the spindle fibres contract
• pulling whole chromosomes to opposite poles of the cell/separating
homologous chromosomes
• this is the point at which the haploid number of chromosomes is formed (essential point)
• nuclear membranes form/two cells produced
• in prophase 2 two sets of spindle bres form at right angles to the original
• in metaphase 2 individual chromosomes (within each group) attach to the spindle fibres
• by their centromeres (allow once)
• in anaphase 2 the spindle fibres contract (allow once)
• pulling the chromatids (do not accept chromosomes) to opposite poles
• resulting in four groups of (new) chromosomes
• nuclear membranes form/four cells produced (allow once)
• chromosomes decondense/become thinner/less visible
Past Paper Question - January 2014 Q3 a)i)+ii)+iii)+b)i)+ii) AS1 (Legacy Material)
Q3 Photograph 1.3 shows six photomicrographs of animal cells at different stages of mitosis. These are labelled A–F.
(a) (i) Identify the stages shown in photomicrographs A–D.
A ____________________
B ____________________
C ____________________
D ____________________ [4]
ii) Identify the structures labelled X and describe fully their role in the
process of mitosis. [3]
iii) The photomicrographs A–F do not show the stages of mitosis in the correct sequence. Rearrange the letters A–F to show the correct sequence of the stages. [2]
b)i) Identify the process that is beginning to happen in E. [1]
ii) Outline how this process would be different in a plant cell. [1]
(Go do this past paper)
Q3 i) A: telophase;
B: anaphase;
C: prophase (not interphase, as question concerns mitosis);
D: metaphase; [4]
(ii) Spindle fibres;
spindle fibres attach to the centromeres (at the start of metaphase); contraction of the spindle fibres pulls the chromatids apart (during anaphase); [3]
(iii) C, D, F, B, A, E; [2]
b) i) Cytokinesis; [1]
(ii) A cell plate would form (instead of a cleavage furrow); [1]
Past Paper Question - June 2014 Q2 a)+b) AS1 (Legacy Material)
Q2 The diagram below shows two stages in the process of nuclear division by meiosis. The diploid number of the cell shown in stage A is 4.
a) Identify stage B. [1]
b) Describe the behaviour of the chromosomes between stage A and stage B. [4]
(Go do this past paper question)
Q2 a) Telophase I/Prophase II; [1]
b) Any four from:
• homologous chromosomes pair up/bivalents form
• chiasmata form/crossing over occurs
• (homologous pairs/bivalents) line up at the equator of the cell
• spindle fibres attach to centromeres
• homologous chromosomes are separated/pulled apart (as a result of
spindle fibres shortening)
• chromosomes may be enclosed in a new nuclear envelope [4]
Past Paper Question - January 2013 Q3 a)ii) AS1 (Legacy Material)
Q3 a)ii) Identify the specific stage in the cell cycle when DNA replicates to form the two chromatids. [1]
Q3 a)ii) S/synthesis phase (of interphase); [1]
Past Paper Question - January 2013 Q3 a)i)+b)i)+ii)+c) AS1 (Legacy Material)
Q3 a) The diagram below represents a chromosome as it would appear during prophase of mitosis.
i) Name the structure labelled X. [1]
b)i) The diagram below shows a cell at a stage of mitosis.
Name the stage of mitosis shown in the diagram. [1]
ii) Describe how the arrangement of the chromosomes would differ in a cell at the same stage of the first division of meiosis. [2]
c) An outline of a cell-surface membrane is shown below. Within this outline draw the cell shown in b)i) as it would appear at the next stage of mitosis. [2]
(Go do this past paper question)
Q3 a)i) Centromere/kinetochore; [1]
b) i) Metaphase; [1]
ii) Paired homologous chromosomes/bivalents attached to spindle; chiasmata/crossing over (that formed during prophase) visible; [2]
c) Chromatids pulled apart [chromatids shown as V-shaped, with centromeres pointing towards poles];
with attached spindle fibres missing the sections between the chromatids (with other spindle fibres complete); [2]
Past Paper Question - January 2012 Q3 a) AS1 (Legacy Material)
Q3 Yew trees have been used as a source of a group of drugs called taxanes. Taxanes interfere with the normal functioning of the microtubules in the cell, and so inhibit mitosis. They are used to treat certain types of cancer since they prevent cell division and therefore reduce tumour growth.
The effect of various concentrations of a taxane drug on percentage inhibition of mitosis is shown in the graph below.
a) Describe, as fully as possible, the effect of increasing taxane concentration on the % inhibition of mitosis. [3]
(Go do this past paper question)
Q3 a) At low levels (0–4), a rise in taxane causes a small rise in inhibition/inhibition is low;
Not just inhibition is slow.
at medium levels (3–6/4–5), a rise in taxane causes a large increase in inhibition;
Not just inhibition increases more rapidly.
at high levels of taxane (6–8), there is little further rise in inhibition/inhibition levels off/inhibition is nearly complete;
Not just inhibition increases less rapidly/stops. [3]
Past Paper Question - January 2012 Q3 b) AS1 (Legacy Material)
Q3 Yew trees have been used as a source of a group of drugs called taxanes. Taxanes interfere with the normal functioning of the microtubules in the cell, and so inhibit mitosis. They are used to treat certain types of cancer since they prevent cell division and therefore reduce tumour growth.
The effect of various concentrations of a taxane drug on percentage inhibition of mitosis is shown in the graph below.
b) Cells which have been treated with taxanes begin mitotic division, but cannot complete it. Suggest which phase of mitosis is prevented by taxanes, and give a reason for your answer.
Phase of mitosis ___________________________
Reason ___________________________________________
___________________________________________________ [2]
Q3 b) Metaphase;
taxane will interfere with the spindle formation/prevents attachment of centromere (of chromatids/chromosome);
or
Anaphase;
taxane will interfere with spindle shortening/prevents chromatids from
being pulled apart;
Must link name of phase with correct reason. [2]
Past Paper Question - June 2012 Q5 a)i)+ii) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
a) The image below shows a karyotype of mouse chromosomes.
i) Using the karyotype, determine the haploid number for mouse cells. [1]
ii) Identify the sex of the mouse, assuming that sex determination in mice and humans follows the same model. [1]
(Go do this past paper question)
Q5 a)i) 20; [1]
ii) Male; [1]
Past Paper Question - June 2012 Q5 b)i) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
b) Gametes in mammals are produced by meiotic cell division. Two important properties of mammalian gametes are that:
• they are haploid;
• there is genetic variation in the gametes produced by any one individual.
i) Identify the precise phase of meiosis which results in the haploid condition and describe what happens during this phase. [2]
Q5 b)i) Anaphase I;
homologous chromosomes are separated; [2]
Past Paper Question - June 2012 Q5 b)ii) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
b) Gametes in mammals are produced by meiotic cell division. Two important properties of mammalian gametes are that:
• they are haploid;
• there is genetic variation in the gametes produced by any one individual.
ii) There are two ways in which genetic variation arises. In each case, identify the precise phase of meiosis which results in genetic variation and describe what happens during the phase.
- _____________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________ - _____________________________________________________________________
_______________________________________________________________________
______________________________________________________________________ [3]
Q5 b)ii) Prophase I, crossing over takes place (between homologous chromosomes);
Metaphase I, bivalents assort independently/line up randomly (before being separated); [3]
Past Paper Question - June 2012 Q5 c)i) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
c) One stage of meiosis involves sister chromatids being pulled to opposite ends of the cell. In order to allow this, a protein called cohesin, which binds sister chromatids together, must be hydrolysed by an enzyme called separase.
(i) Identify the stage of meiosis during which sister chromatids are pulled to opposite ends of the cell.
Q5 c)i) Anaphase II; [1]
Past Paper Question - June 2012 Q5 c)ii) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
c) One stage of meiosis involves sister chromatids being pulled to opposite ends of the cell. In order to allow this, a protein called cohesin, which binds sister chromatids together, must be hydrolysed by an enzyme called separase.
ii) Explain the term ‘hydrolysed’. [2]
Q5 c)ii) The breakdown of large molecules into sub-units;
where water is added; [2]
Past Paper Question - June 2012 Q5 c)iii) AS1 (Legacy Material)
Q5 Chromosomes are visible during mitosis and meiosis in eukaryotic cells.
c) One stage of meiosis involves sister chromatids being pulled to opposite ends of the cell. In order to allow this, a protein called cohesin, which binds sister chromatids together, must be hydrolysed by an enzyme called separase.
iii) State the products of the hydrolysis of cohesin. [1]
Q5 c)iii) Amino acids/peptides; [1]
Past Paper Question - June 2011 Q1 AS1 (Legacy Material)
Q1 The following statements describe events within stages of meiosis.
Identify the stage in each case.
• Bivalents are formed when homologous chromosomes pair
______________________________________
• Chromatids separate and are pulled to opposite poles
______________________________________
- Four haploid nuclei are formed
______________________________________ - Chiasmata occur
______________________________________ [4]
Q1
Prophase I;
anaphase II;
telophase II;
prophase I;
Must refer to relevant I and II divisions [4]
Practical Work - Preparing and staining root tip squashes
What species of plant is best used for this experiment and why?
The root tips of broad beans are a good source as they are relatively easy to manipulate.
Practical Work - Preparing and staining root tip squashes In plants (unlike animals), cell division takes place in ...
Specific areas
Practical Work - Preparing and staining root tip squashes
Actively dividing regions in plants are called …
Meristems
Practical Work - Preparing and staining root tip squashes
Where are meristems located in plants?
Shoot and root tips
Practical Work - Preparing and staining root tip squashes to observe mitosis
Describe the procedure used to prepare and stain root tip squashes
- Harvest broad beans 7 – 10 days after planting in a seed tray.
- By this stage the beans will have germinated and the young shoots will have extended through the top of the soil.
• Short lateral roots about 1 cm in length growing out from the main tap root are the best to use for observing mitosis.
Procedure:
• Add a small section of root containing lateral roots to a boiling tube containing acetic orcein.
• Place the boiling tube in a water bath at 60°C for 30 minutes.
• After 30 minutes remove a section of root from the boiling tube and use a scalpel to remove the last few mm or so from one of the lateral roots. Add this short section to a microscope slide and add more acetic orcein if necessary to stop the root tip from drying out.
• Add a cover slip and gently tap with a blunt end of a pointed needle. This will ‘squash’ the root tip into a single layer of cells.
• Observe under a microscope.
Practical Work - Preparing and staining root tip squashes to observe mitosis
“After adding the cover slip, gently tap the cover slip with a blunt end of a pointed needle (or something similar). This will ideally ‘squash’ the root tip into a single layer of cells.”
Why must gentle vertical ‘taps’ be used as opposed to circular grinding movements?
In order to preserve the general arrangement of cells.
Also, it is better to tap gently as you can repeat the tapping process if necessary; you cannot work ‘backwards’ if you tap too hard, or for too long.
Practical Work - Other staining techniques
Name another stain used in practical investigations and name the plant species it is commonly used on.
Toluidine blue
Onion or garlic root tips
Practical Work - Other staining techniques
What are the common features between practical investigations involving staining?
Common features between each process are that:
- the chromosomes are stained
- the procedure softens/breaks up the root tissue allowing it to be easily ‘squashed’ into a single layer
Practical Work - Finding cells undergoing mitosis
Describe the structure of a plant root (or shoot) tip
Zone of cell elongation
Zone of cell division
Protective root cap (at the tip of the root)
Practical Work - Finding cells undergoing mitosis
Describe the procedure used to find cells undergoing mitosis in a root (or shoot) tip
Finding cells undergoing mitosis:
- Using low / medium power (for example, x100), scan the root tip section and look for the zone of division.
- Before looking for the zone of division, check that the sample is a good ‘squash’, with the cells neatly arranged in columns and the preparation being only one cell thick.
- Cells in the zone of division are characteristically small and cuboidal (square) in shape with the nucleus appearing relatively large, (i.e. a high nucleus : cell size ratio).
- Once the zone of division is located switch to high power (x400) to observe cells at different stages of mitosis.
Practical Work - Drawing cells undergoing mitosis
Describe the steps necessary to draw cells undergoing mitosis
Drawing cells undergoing mitosis:
- Select a group of two or three cells together, including at least one that is undergoing mitosis and draw.
- Only draw what you see; not what you think is there.
- It is important that proportionality (relative scale) and shape are correct, (i.e. the relative size of chromosomes compared to cell size should be the same in you drawings as it is in the specimen).
Practical Work - Finding cells undergoing mitosis
The staining process will have …
Killed the cells so the cells in the specimen will shows cells ‘arrested’ at a particular stage of mitosis.
Practical Work
You see a photograph of a cell undergoing meiosis.
You see paired chromosomes in a range of strange shapes or twists.
This is likely to be a photograph of what stage of meiosis?
Late prophase I (or metaphase I) of meiosis
Most living organisms grow by …
Increasing cell number
Most living organisms grow by increasing cell number. It is relatively straightforward for cells to …
Divide in two (thereby increasing cell number).
Most living organisms grow by increasing cell number. It is relatively straightforward for cells to divide in two (thereby increasing cell number). The complex part is …
Ensuring that the DNA is duplicated and then accurately distributed between the new cells
Most living organisms grow by increasing cell number. It is relatively straightforward for cells to divide in two (thereby increasing cell number). The complex part is ensuring that the DNA is duplicated and then accurately distributed between the new cells. What processes ensure that this takes place?
Mitosis and meiosis
Mitosis ensures that …
The daughter cells procured during cell division have exactly the same chromosome makeup as the parent cell.
Mitosis ensures that the daughter cells procured during cell division have exactly the same chromosome makeup as the parent cell. Mitosis is only part of the sequence of events called …
The cell cycle
Mitosis ensures that the daughter cells procured during cell division have exactly the same chromosome makeup as the parent cell. Mitosis is only part of the sequence of events called the cell cycle, that includes …
A cell’s formation, it’s growth, mitosis and the cell physically dividing into two (cytokinesis).
What is mitosis?
A nuclear division during which the chromosomal material is partitioned into daughter nuclei.
What is cytokinesis?
Cytokinesis is the division of the cell into two daughter cells
Draw a diagram showing a summary of the cell cycle
Textbook page 91 + 93
In the cell cycle, what do G and S stand for?
G stands for gap (or growth) and S stands for synthesis.
What changes take place during the G1 phase?
Organelles and other cytoplasmic components replicate or are formed. The cell increases in size. Synthesis of macromolecules, including proteins and nucleotides, occurs.
What changes take place during S phase?
DNA duplicated and chromatids form within the nucleus. Histones (proteins that bind to and support the DNA within the chromatids) form. Chromatin is doubled. The DNA and chromatids formed are identical and remain attached until separated during mitosis (or meiosis).
What changes take place during the G2 phase?
Spindle proteins (such as tubulin) are synthesised. Tubulin forms the microtubules of the spindle fibres. Chromosomes checked for error and repaired as necessary. Second growth/gap phase. Energy stores are increased. Cell continues to increase in size.
Comment on the period of time that mitosis occurs for in the cell cycle
Mitosis itself may only be a relatively short part of the cell cycle (perhaps as little as 10%).
What is interphase?
Interphase (G1, S, G2 phases) is an active phase, with many metabolic processes taking place that prepare the cell for its role and also for division. This is an intense period of metabolic activity as the cell synthesises new components such as organelles and membranes, and new proteins and DNA.
How is control maintained in the cell cycle?
There are a number of checkpoints within the cell cycle.
What is the role of checkpoints in the cell cycle?
These check and monitor that the previous stages have been carried out correctly before the process can continue to the next stage.
Name the checkpoints which occur in the cell cycle
G1 checkpoint
G2 checkpoint
Metaphase (spindly assembly) checkpoint
When is the G1 checkpoint?
At the end of the G1 phase
The formation of new cells, for example …
In the development of a multicellular organism
The formation of new cells, for example in the development of a multicellular organism, involves …
The production of additional cell contents before a cell can divide
The formation of new cells, for example in the development of a multicellular organism, involves the production of additional cell contents before a cell can divide. The pattern of events is called …
The cell cycle
What is the cell cycle?
The cell cycle is a sequence of events that actively dividing eukaryotic cells pass through. These events include:
- Interphase: two gap (growth) phases (G1 and G2) separated by a synthesis (S) phase.
- Mitosis
- Cytokinesis
What are the four different stages of mitosis, in chronological order?
Prophase
Metaphase
Anaphase
Telophase
Knowledge check 49
When during the cell cycle does DNA replication take place?
S phase of interphase
When is the G2 checkpoint?
Towards the end of the G2 phase
What does the G1 checkpoint ensure?
This checkpoint is at the end of the G1 phase. Before DNA duplication (the next stage, S) can begin this checkpoint ensures that:
- The cell has reached a critical size.
- There are enough nutrients available for the next stages to take place.
- Necessary growth (regulatory) factors are in place.
- There is no DNA damage. (If damage is detected the DNA is repaired).
What does the G2 checkpoint ensure?
The cell checks that DNA replication (during the S phase) has taken place accurately (if not, the cell cycle is stopped) and that there is no DNA damage (if damage is detected the cell cycle can be delayed to repair the DNA). The cell starts the process of mitosis if there are no problems at this stage. Cell size is checked once again.
What does the Metaphase (spindle assembly) checkpoint ensure?
The cell checks that all the chromosomes have attached properly to spindle fibres before anaphase proceeds.
If the checkpoint requirements are met in the G2 checkpoint, the cell starts the process of …
Mitosis
If the G1 checkpoint requirements are met, the cell starts the process of …
DNA duplication (S phase, DNA synthesis phase)
It is essential that a cell only divides when:
- Sufficient macromolecules and organelles have been assembled so that the cell has grown to an appropriate size.
- The DNA is error-free (or is repaired) and accurately replicated.
- The chromosomes have been positioned correctly during mitosis.
If the G1 checkpoint requirements are not met, the cell …
Enters a resting state or phase (G0).
How long do cells usually spend in G0?
Cells can remain in G0 for a short time, very long periods of time or remain in G0 permanently. What happens depends on a range of internal and external factors. The majority of human cells are in G0 and so are not actively dividing.
What happens to the cell during G0?
Although cells in G0 have suspended activities linked to cells division, they may still be very active in terms of carrying out normal cellular function.
What is the role of the nutrients and growth (regulatory) factors in cells before DNA synthesis (S) phase?
They promote the synthesis of proteins and other macromolecules
Give some examples of cells which are in G0
The majority of human cells are in G0 and so are not actively dividing.
Highly differentiated cells in G0 (such as neurones) do not return to the cell cycle whereas cells in epithelial tissue may not enter G0 at all.
Many lymphocytes (white blood cells involved in antibody production) are in G0. They only move out of G0 and back into the cell cycle (and start the S phase) if triggered to do so by the presence of specific antigens.
The G1 checkpoint is a logical position for cells that normally become very differentiated (for example, neurones) to move out of the cell cycle. There is little point in them entering the S phase and duplicating chromosomes if they will not undergo mitosis in the future.
When does the metaphase (spindle assembly) checkpoint occur?
At the end of metaphase
