stem cells exam questions Flashcards
Callus is a mass of undifferentiated plant cells. Plantlets are small plants.
(a) Explain the evidence from the table that cells from the stem tip are totipotent. (2)
plantlets
so must be able to develop into different tissues
Papaya plants reproduce sexually by means of seeds. Papaya plants grown
from seeds are very variable in their yield. Explain why. (2)
crossing over
random fusion of gametes
Explain the advantage of growing papaya plants from tissue culture rather
than from seeds. (1)
they are clones
SCID is a severe inherited disease. People who are affected have no immunity.
Doctors carried out a trial using gene therapy to treat children with SCID. The doctors who
carried out the trial obtained stem cells from each child’s umbilical cord.
Give two characteristic features of stem cells. (2)
can continually divide
form other type of cells
The doctors mixed the stem cells with viruses. The viruses had been genetically modified
to contain alleles of a gene producing full immunity. The doctors then injected this mixture
into the child’s bone marrow.
The viruses that the doctors used had RNA as their genetic material. When these viruses
infect cells, they pass their RNA and two viral enzymes into the host cells.
(b) One of the viral enzymes makes a DNA copy of the virus RNA. Name this enzyme.
reverse transcriptase
The other viral enzyme is called integrase. Integrase inserts the DNA copy anywhere in
the DNA of the host cell. It may even insert the DNA copy in one of the host cell’s genes.
(c) (i) The insertion of the DNA copy in one of the host cell’s genes may cause the
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cell to make a non-functional protein. Explain how. (2)
alters the base sequence
alters the primary structure/specific sequence of amino acids
Some of the children in the trial developed cancer. How might the insertion of
the DNA have caused cancer? (2)
-affects tumour suppressor gene
-inactives gene
Five out of the 20 children in the trial developed cancer. Although the cancer was
treated successfully, the doctors decided to stop the trial in its early stages. They
then reviewed the situation and decided to continue. Do you agree with their
decision to continue? Explain your answer. (2)
high risk of developing cancer
cancer may return
Myelodysplastic syndromes (MDS) are a group of malignant cancers. In MDS,
the bone marrow does not produce healthy blood cells.
Haematopoietic stem cell transplantation (HSCT) is one treatment for MDS. In
HSCT, the patient receives stem cells from the bone marrow of a person who
does not have MDS. Before the treatment starts, the patient’s faulty bone
marrow is destroyed.
(a)
(b)
For some patients, HSCT is an effective treatment for MDS.
Explain how. (3)
produces healthy cells
stem cells divide/replicate
no tumour formed
(d)
The control patients were treated with conventional drugs.
Give two reasons why (2)
unethical to not treat patients
to compare to see effect of AZA
Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of
both men and women. Affected individuals have proteinuria (high quantities of
protein in their urine).
Scientists investigated the use of transplanted stem cells to treat AS in mice.
The scientists set up four experimental groups.
Group A – 40 wild type* mice
Group B – 40 AS mice
Group C – 40 AS mice that received stem cells from AS mice
Group D – 40 AS mice that received stem cells from wild type mice
*Wild type mice are mice not affected by AS.
After 20 weeks, the scientists measured the quantity of protein in the urine using
a scale from 0 (lowest quantity) to +++++ (highest quantity).
The results the scientists obtained are shown in below table.
Group
Maximum quantity of
protein in urine at 20
weeks
Percentage of mice
with this quantity of
protein
all the information, evaluate the use of stem cells to treat AS in
humans.
(4)
no data for after 20 weeks
only tested in mice, not humans
rejection may occur
do not known actual quantity of protein
The scientists carried out further work to investigate how the transplanted
stem cells developed after transplantation.
* The scientists transplanted stem cells from wild type male mice into
AS female mice.
* After 20 weeks, they found that the quantity of protein in the urine of
these female mice had significantly decreased.
* They examined cells from glomeruli in the female mice. Some of
these cells contained a Y chromosome.
Suggest how the transplanted stem cells reduce proteinuria. (2)
transplanted stem cells divide
reduced loss of protein at glomerulus
Sickle cell disease (SCD) is a group of inherited disorders. People with SCD
have sickle-shaped red blood cells. A single base substitution mutation can
cause one type of SCD. This mutation causes a change in the structure of the
beta polypeptide chains in haemoglobin.
Haematopoietic stem cell transplantation (HSCT) is a long-term treatment for
SCD. In HSCT, the patient receives stem cells from the bone marrow of a person
who does not have SCD. The donor is often the patient’s brother or sister. Before
the treatment starts, the patient’s faulty bone marrow cells have to be destroyed.
(b)
Use this information to explain how HSCT is an effective long-term
treatment for SCD. (3)
stem cells divide
health red blood cells formed
no more SCD red blood cells formed
Complete achromatopsia is a form of complete colour blindness. It is caused by
having only rods and no functional cone cells. People with complete
achromatopsia have difficulty in seeing detail. Complete achromatopsia is
caused by an autosomal recessive allele and is usually very rare in populations
with only one in 40 000 being affected. However on the Pacific
island of Pingelap ten percent of the population are affected.
One form of red-green colour blindness is caused by a sex-linked recessive
allele which affects more men than women. People with this red-green colour
blindness are unable to distinguish between red and green, and also between
other colours. They have green-sensitive cones but the
photoreceptive pigment they contain does not function.
Scientists investigated the use of gene therapy to correct red-green colour
blindness in monkeys. They injected viruses containing the gene for the
green-sensitive pigment directly into the eyes of the monkeys. Although the
monkeys maintained two years of colour vision, there is debate on
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whether this form of gene therapy is worthwhile. No clinical trials of this
procedure have been carried out on humans. Current research into the treatment
of red-green colour blindness involves the use of induced pluripotent stem cells
(iPS cells). The use of iPS cells could have advantages over the use of gene
therapy.
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Use the information in the passage and your own knowledge to answer the
following questions.
(e)
Current research into the treatment of red-green colour blindness involves
the use of induced pluripotent stem cells (iPS cells) (lines 17–19).
Suggest how iPS cells could correct red-green colour blindness. (2)
ips cells divide
differentiate into cone cells
Scientists have investigated the use of different types of stem cell to treat
damage to the heart after a myocardial infarction. During a myocardial infarction,
a number of different cell types in the heart die. This includes cardiomyocytes
which are heart-muscle cells.
Embryonic pluripotent stem cells (ESCs) can divide and differentiate into a wide
range of different cell types.
(a)
(b)
Using the information given, suggest one reason why ESCs might be
suitable to treat damage to the heart. (1)
can replace any type of heart cell
