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GCSE · Biology

B1b Cell Division and Stem Cells

AQA 8464 · Calculator allowed · about 78 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Chromosomes carry the genetic information of a cell.

(a)Define the term 'chromosome'.(1)

(b)State how many chromosomes are found in a normal human body cell.(1)

(c)Human body cells are described as 'diploid'. State what this means.(1)

(Total for Question 1 is 3 marks)

The cell cycle is the sequence of stages a cell goes through between one division and the next. Its three main stages are: Mitosis; Interphase; Cytokinesis (listed here in the wrong order).

(a)State the correct order in which these three stages occur in one full cell cycle.(2)

(b)During interphase, before mitosis begins, a cell's DNA replicates (is copied). Explain why the DNA must replicate before the cell divides by mitosis.(2)

(Total for Question 2 is 4 marks)

Mitosis is a type of cell division that produces new cells.

(a)State two purposes of mitosis in the human body.(2)

(b)Describe what happens to the chromosomes during mitosis, and state the type of cell produced as a result.(3)

(Total for Question 3 is 5 marks)

A student cuts her finger while cooking. Over the next few days, the skin at the site of the cut heals.

Explain, using ideas about mitosis, how new skin cells are produced to repair the cut.

(Total for Question 4 is 3 marks)

Strawberry plants can reproduce asexually by growing runners: a new, separate plant grows from a stem that touches the ground.

Explain why the new plant produced from a runner is genetically identical to the parent plant.

(Total for Question 5 is 2 marks)

The formula linking magnification, image size and actual size is: magnification = image size / actual size. A student uses a light microscope to observe cells in an onion root tip. In the image produced, one cell has a width of 4.5 mm. The actual width of this cell is 30 micrometres (um).

(a)Calculate the magnification of the image. Give your answer as a whole number.(3)

(b)The student increases the total magnification to x600, without changing the actual size of the cell. Calculate the new width of the image, in mm.(3)

(Total for Question 6 is 6 marks)

Required practical: a student prepares and views a root tip squash slide, in order to observe cells at different stages of the cell cycle in the root tip of an onion or garlic.

(a)Describe how the student should prepare the root tip squash slide, including the equipment/reagents used and one safety precaution.(4)

(b)Explain why the tip of the root, rather than a section further up the root, is used for this practical.(2)

(c)The student views the slide and counts 250 cells in the field of view. Of these, 20 cells are seen to be undergoing mitosis. Calculate the mitotic index (the percentage of cells undergoing mitosis) for this sample.(2)

(d)Suggest one reason why the mitotic index might be higher in cells taken from close to the root tip than in cells taken from further up the root.(1)

(Total for Question 7 is 9 marks)

A stem cell is a type of cell found in both animals and plants.

(a)Define the term 'stem cell'.(1)

(b)State one difference between an embryonic stem cell and an adult stem cell, in terms of the range of cell types each can differentiate into.(2)

(c)State where meristem tissue (which contains plant stem cells) is found in a plant.(2)

(Total for Question 8 is 5 marks)

A gardener takes a cutting from a healthy geranium plant and plants it in soil. Over the next few weeks, the cutting grows roots and shoots, developing into a complete new plant that is genetically identical to the parent plant.

(a)Name the type of cell division responsible for producing the new cells needed for the cutting to grow.(1)

(b)Explain how meristem tissue in the cutting allows it to develop into a complete new plant with roots and shoots.(3)

(Total for Question 9 is 4 marks)

Embryonic stem cells can be grown in a laboratory culture. In one such culture, every cell divides by mitosis into two new cells once every 18 hours.

(a)A culture starts with 500 stem cells. Calculate the number of stem cells present in the culture after 72 hours, assuming every cell continues to divide at this rate.(3)

(b)State one assumption made in this calculation.(1)

(Total for Question 10 is 4 marks)

Stem cells have a number of actual and potential uses in medicine.

(a)Give two examples of medical conditions that scientists are researching treatments for, using stem cells.(2)

(b)Bone marrow transplants, using stem cells from a donor, are already used to treat some blood disorders, such as certain types of leukaemia. Explain how the transplanted stem cells help to treat the patient.(2)

(Total for Question 11 is 4 marks)

Using stem cells to treat patients carries some medical risks.

(a)Give one medical risk associated with using stem cells to treat patients.(1)

(b)Suggest why using a patient's own adult stem cells, rather than stem cells from a donor, might reduce this risk.(2)

(Total for Question 12 is 3 marks)

Higher Tier: therapeutic cloning can be used to produce embryonic stem cells that are a genetic match for a particular patient.

(a)Describe how therapeutic cloning could be used to produce embryonic stem cells that are genetically identical to a patient.(3)

(b)Suggest one advantage of using stem cells produced by therapeutic cloning, rather than stem cells from a donor embryo, to treat this patient.(2)

(Total for Question 13 is 5 marks)

A student writes the following incorrect statement about mitosis: 'Mitosis produces four new cells, and each new cell contains different genetic information from the parent cell.'

State two corrections that should be made to this statement.

(Total for Question 14 is 2 marks)

Embryonic stem cells could potentially be used to treat a range of medical conditions, such as paralysis caused by damage to the spinal cord. However, obtaining embryonic stem cells currently involves destroying the human embryo from which they are taken.

Evaluate the use of embryonic stem cells to treat medical conditions such as paralysis. In your answer, you should consider: the potential medical benefits of embryonic stem cells; the scientific/practical issues involved; the ethical concerns raised by their use; and possible alternatives.

(Total for Question 15 is 6 marks)

Cell division by mitosis is normally tightly controlled by the body.

(a)State what is meant by a tumour.(1)

(b)Explain how uncontrolled mitotic cell division can lead to the formation of a tumour.(2)

(Total for Question 16 is 3 marks)

In most animals, cells lose the ability to differentiate at an early stage of development. In contrast, many plant cells retain the ability to differentiate throughout the life of the plant, at meristems.

Explain how this difference accounts for the fact that gardeners can grow a complete new plant from a small cutting, but doctors currently cannot grow a complete new organ from a small piece of adult human tissue.

(Total for Question 17 is 3 marks)

A laboratory stem cell culture contains 240 cells. After being left to grow for 60 hours under ideal conditions, the culture contains 7680 cells. Assume every cell in the culture divided the same, fixed number of times during the 60 hours.

Calculate how long it took for the cells in this culture to double in number (i.e. the length of one division/doubling cycle).

(Total for Question 18 is 3 marks)

Mark scheme · B1b Cell Division and Stem Cells

Question 1

(a) B1 a long, coiled structure made of DNA, found in the nucleus, that carries genetic information (organised into genes), oe
(a) Answer: A long, coiled structure made of DNA, found in the nucleus, which carries genetic information organised into genes.
(b) B1 46 (23 pairs) cao
(b) Answer: 46 chromosomes (23 pairs).
(c) B1 the cell contains chromosomes in pairs / two complete sets of chromosomes, oe
(c) Answer: The cell contains its chromosomes arranged in pairs (two complete sets of chromosomes).

Question 2

(a) B1 correctly identifies Interphase as the first stage of the cycle
(a) B1 correctly identifies Mitosis as the second stage and Cytokinesis as the third (last) stage
(a) Answer: Interphase, then Mitosis, then Cytokinesis.
(b) B1 each new (daughter) cell produced by mitosis needs a complete copy of the DNA/full set of chromosomes, oe
(b) B1 so that each daughter cell is genetically identical to the parent cell (and to each other), oe
(b) Answer: Each daughter cell needs a complete copy of the DNA (full set of chromosomes) so that it is genetically identical to the parent cell.

Question 3

(a) B1 growth (production of new cells so the body/an organ can grow), oe
(a) B1 repair of damaged tissue (allow: replacement of dead or worn-out cells), oe
(a) Answer: Growth (producing new cells for the body to grow), and repair of damaged tissue.
(b) B1 before mitosis begins, each chromosome is copied/duplicated (so it consists of two identical strands), oe
(b) B1 during mitosis, one copy of each chromosome is pulled to each end (pole) of the cell, and the cell then divides into two, oe
(b) B1 producing two genetically identical (diploid) daughter cells, each with the same number of chromosomes as the parent cell, oe
(b) Answer: Each chromosome is copied before mitosis. During mitosis, one copy of each chromosome moves to each end of the cell, which then divides, producing two genetically identical diploid daughter cells with the same number of chromosomes as the parent cell.

Question 4

B1 cells at the edge of the wound divide by mitosis, oe
B1 producing new cells that are genetically identical to the original skin cells, oe
B1 the new cells fill the gap and repair the damaged tissue, oe
Answer: Cells at the edge of the wound divide by mitosis, producing new cells that are genetically identical to the original skin cells. These new cells fill the gap, repairing the damaged tissue.

Question 5

B1 the new plant's cells are produced by mitosis from the parent plant's cells, oe
B1 mitosis produces cells that are genetically identical (exact copies) to the parent cell, oe
Answer: The new plant's cells are produced by mitosis from the parent plant's cells, and mitosis produces cells that are genetically identical to the parent cell.

Question 6

(a) M1 converts 4.5 mm to um: 4.5 * 1000 = 4500 um, oe
(a) M1 magnification = image size / actual size = 4500 / 30, oe
(a) A1 150 cao
(a) Answer: x150
(b) M1 rearranges to image size = actual size * magnification, oe
(b) M1 30 * 600 = 18000 (um), oe
(b) A1 18 mm cao
(b) Answer: 18 mm

Question 7

(a) B1 cuts a few mm from the very tip of the root using a scalpel or mounted needle, oe
(a) B1 places the root tip in warm, dilute hydrochloric acid for a few minutes, to soften/macerate the tissue, oe
(a) B1 adds a stain (e.g. acetic orcein or toluidine blue) to stain the chromosomes, then squashes the tip gently under a cover slip (using a mounted needle or thumb) to spread the cells into a single layer, oe
(a) B1 safety precaution, e.g. wears eye protection and gloves when handling the dilute acid and stain, oe
(a) Answer: Cut a few mm from the root tip; place it in warm, dilute hydrochloric acid for a few minutes to soften the tissue; add a stain such as acetic orcein; squash gently under a cover slip to spread the cells into a single layer. Wear eye protection and gloves when handling the acid and stain.
(b) B1 the root tip contains meristem tissue, where cells are actively dividing by mitosis, oe
(b) B1 sections further up the root contain far fewer actively dividing cells, as the cells there have already differentiated, oe
(b) Answer: The root tip contains meristem tissue, where cells actively divide by mitosis. Further up the root, most cells have already differentiated, so far fewer are dividing.
(c) M1 (20 / 250) * 100, oe
(c) A1 8% cao
(c) Answer: 8%
(d) B1 the root tip contains meristem tissue, where a much higher proportion of cells are actively dividing (undifferentiated) compared with tissue further from the tip, oe
(d) Answer: Close to the tip is meristem tissue, where a much higher proportion of cells are actively dividing, compared with tissue further from the tip, which contains mostly differentiated (non-dividing) cells.

Question 8

(a) B1 an undifferentiated cell that can divide (by mitosis) to produce more cells, and that can differentiate into one or more types of specialised cell, oe
(a) Answer: An undifferentiated cell that can divide by mitosis and can differentiate into one or more types of specialised cell.
(b) B1 embryonic stem cells can differentiate into almost any type of cell in the body, oe
(b) B1 adult stem cells can only differentiate into a limited/smaller range of cell types, e.g. bone marrow stem cells can only produce different types of blood cell, oe
(b) Answer: Embryonic stem cells can differentiate into almost any type of cell in the body, whereas adult stem cells can only differentiate into a limited range of cell types (e.g. bone marrow stem cells can only produce different types of blood cell).
(c) B1 at the tips of roots, oe
(c) B1 at the tips of shoots, oe
(c) Answer: At the tips of roots and at the tips of shoots.

Question 9

(a) B1 mitosis
(a) Answer: Mitosis.
(b) B1 meristem tissue contains unspecialised (stem) cells that can divide repeatedly by mitosis, oe
(b) B1 these new cells can then differentiate into different types of specialised plant cell, oe
(b) B1 forming the specialised tissues needed for new roots and shoots (e.g. root hair cells, xylem), oe
(b) Answer: Meristem tissue contains unspecialised stem cells that divide repeatedly by mitosis. The new cells then differentiate into different types of specialised plant cell, forming the tissues needed for new roots and shoots.

Question 10

(a) M1 number of divisions in 72 hours = 72 / 18 = 4, oe
(a) M1 500 * 2⁴, oe
(a) A1 8000 cao
(a) Answer: 8000 cells
(b) B1 e.g. assumes no cells die during the 72 hours / assumes every cell divides at exactly the same rate / assumes nutrients, oxygen and space do not become limiting, oe
(b) Answer: Assumes that no cells die and that every cell continues to divide at exactly the same, constant rate (e.g. nutrients and space do not become limiting).

Question 11

(a) B1 any one condition, e.g. type 1 diabetes / paralysis (spinal cord injury) / damaged retina / heart disease (damaged heart muscle)
(a) B1 a second, different condition from the list above
(a) Answer: Any two of: type 1 diabetes; paralysis (spinal cord injury); damaged retina; heart disease.
(b) B1 the transplanted (healthy) bone marrow stem cells can divide by mitosis, oe
(b) B1 and differentiate to produce new, healthy blood cells, replacing the patient's faulty/cancerous blood cells, oe
(b) Answer: The transplanted, healthy bone marrow stem cells divide by mitosis and differentiate into new, healthy blood cells, replacing the patient's faulty blood cells.

Question 12

(a) B1 e.g. transfer of a viral infection from the donor/culture to the patient, or rejection of the transplanted cells by the patient's immune system, oe
(a) Answer: The transplanted cells could be rejected by the patient's immune system (or a viral infection could be transferred from the donor).
(b) B1 the patient's own stem cells are genetically identical to the patient's own cells, oe
(b) B1 so they are less likely to be recognised as foreign and rejected by the patient's immune system, oe
(b) Answer: The patient's own stem cells are genetically identical to the patient, so they are less likely to be recognised as foreign and rejected by the immune system.

Question 13

(a) B1 the nucleus is removed from an egg cell, oe
(a) B1 a nucleus (or the whole cell) from one of the patient's own body cells is inserted into the empty egg cell, oe
(a) B1 the egg cell is stimulated to divide by mitosis to form an early embryo, from which embryonic stem cells can then be extracted, oe
(a) Answer: The nucleus is removed from an egg cell and replaced with a nucleus from one of the patient's own body cells. The egg cell is then stimulated to divide by mitosis to form an early embryo, from which embryonic stem cells can be extracted.
(b) B1 the stem cells produced are genetically identical to the patient (contain the same genetic information), oe
(b) B1 so they are less likely to be rejected by the patient's immune system when used in treatment, oe
(b) Answer: The stem cells are genetically identical to the patient, so they are less likely to be rejected by the patient's immune system when used in treatment.

Question 14

B1 mitosis produces two daughter cells, not four, oe
B1 the daughter cells are genetically identical to the parent cell, not different, oe
Answer: 1) Mitosis produces two daughter cells, not four. 2) The daughter cells are genetically identical to the parent cell, not different.

Question 15

Level 3 (5-6): A detailed and balanced evaluation that accurately covers medical benefits, scientific/practical issues and ethical concerns, and reaches a justified overall conclusion. Correct scientific terminology is used throughout and the answer is logically structured.
Level 2 (3-4): Some accurate points are made, covering at least two of the three areas (benefits, practical issues, ethical concerns), with mostly correct scientific terminology. The answer has some structure but the evaluation may be incomplete or one-sided.
Level 1 (1-2): Basic, isolated statements are given about stem cells or ethics, with little or no evaluation or linking of ideas. Scientific terminology may be limited or only partly correct.
Level 0 (0): No relevant content.
Indicative content:
- Embryonic stem cells are pluripotent: they can differentiate into almost any type of human cell, unlike adult stem cells, which can only differentiate into a limited range of cell types.
- This means embryonic stem cells could potentially be used to grow replacement nerve cells or tissue, to repair damage caused by paralysis, or to treat other conditions such as type 1 diabetes or heart disease.
- Obtaining embryonic stem cells currently requires the destruction of the early embryo from which they were taken.
- Some people believe an embryo should be treated as a potential human life, and therefore object, on ethical or religious grounds, to embryos being destroyed for research or treatment.
- Others argue the potential medical benefits to seriously ill or paralysed patients justify the use of spare embryos (e.g. those donated from fertility clinics that would otherwise be discarded).
- There are also scientific/practical risks: transplanted stem cells could be rejected by the patient's immune system, or could transfer a viral infection.
- Embryonic stem cells are also harder to control in culture than adult stem cells, and there is a risk that transplanted cells could divide uncontrollably and form a tumour.
- Adult stem cells (e.g. from bone marrow) avoid the ethical concerns around embryo destruction, but can only differentiate into a limited range of cell types, so may not be able to treat every condition.
- Research into other alternatives, such as therapeutic cloning or reprogramming adult cells, may reduce reliance on embryonic stem cells in future, but is not yet fully developed.
- A balanced judgement should weigh the significant potential medical benefits against the ethical concerns and current scientific limitations/risks.

Question 16

(a) B1 a mass/lump of cells resulting from uncontrolled cell division (by mitosis), oe
(a) Answer: A mass of cells resulting from uncontrolled cell division (mitosis).
(b) B1 normally, the rate of cell division (mitosis) in the body is tightly controlled, oe
(b) B1 if cells divide by mitosis in an uncontrolled way, this produces an increasing mass of cells, forming a tumour, oe
(b) Answer: Cell division is normally tightly controlled. If cells divide by mitosis in an uncontrolled way, this produces a growing, abnormal mass of cells, forming a tumour.

Question 17

B1 in plants, cells in the meristem remain able to differentiate into any type of plant cell throughout the plant's life, oe
B1 in mature animals, most cells have already differentiated and lost the ability to change into a different cell type, oe
B1 so a plant cutting can develop all the specialised cells/tissues of a whole new plant, but a piece of adult human tissue does not contain enough cells still able to differentiate into all the different cell/tissue types needed for a whole organ, oe
Answer: Plant meristem cells stay able to differentiate throughout the plant's life, so a cutting can grow all the specialised tissues of a new plant. Most mature animal cells have already differentiated and cannot change type, so a piece of adult human tissue cannot regrow a whole new organ.

Question 18

M1 calculates the number of times the population has doubled: 7680 / 240 = 32, oe
M1 recognises 32 = 2⁵, so the population doubled 5 times in 60 hours, oe
A1 60 / 5 = 12 hours cao
Answer: 12 hours

Cell Division and Stem Cells - Worksheets, Questions and Revision