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SNAB edexcel A-level biology > Voice of the Genome > Flashcards

Voice of the Genome Flashcards

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1
Q

What is the structure and function of the Golgi apparatus?

A

A group of fluid-filled membrane-bound flat sacs surrounded by vesicles. Processes and packages new proteins and makes lysosomes and vesicles.

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2
Q

What is the structure and function of Golgi vesicles?

A

small fluid-filled sacs that store proteins and lipids processed by the Golgi apparatus through the cell surface membrane.

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3
Q

What is the structure and function of a flagellum?

A

a long ‘tail’ attached within the cell membrane that aids in locomotion for prokaryotes.

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4
Q

How is DNA stored in prokaryotes?

A

In plasmids or free-floating in the nucleus.

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5
Q

Why does Bacteria contain infolding areas of the cell surface membrane?

A

To allow or photosynthesis or to carry out nitrogen fixation

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6
Q

Why do Bacteria contain pilli

A

For attachment to other cells or surfaces and also involved in sexual reproduction.

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7
Q

What is the basic structure of a virus?

A

some genetic material in the form of DNA or RNA surrounded by a capsid and attachment proteins.

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8
Q

What are the limitations of light microscopes?

A

Low resolution- around 250nm

Low relative magnification- around 1500x max

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9
Q

What are the pros of light optical microscopes?

A

specimen and can dead or alive
can view natural or stained samples
cheaper

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10
Q

What are the stages of a light microscope?

A

Light passes through the specimen
into the condenser lens
into the objective viewing lens
then into the observers eye.

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11
Q

How to electron microscopes work?

A

Use electrons to form images, which are smaller than light photons.

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12
Q

What is the maximum magnification and resolution of an electron microscope?

A

Resolution: 0.002 micrometers
Magnification: 500 000

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13
Q

How do you extract cell organelles from a sample of cells or tissue?

A
  • must be put in isotonic and must be very cold
  • sample is homogenized in a homogenizer (like a blender)
  • cells are filtered
  • Ultracentrifuged- spun at very high speeds and organelles are then separated by mass.
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14
Q

What is the order of organelles by mass? (heaviest to lightest)

A

Nucleus, mitochondria, and chloroplasts, lysososmes.

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15
Q

define a nucleosome.

A

Double-helix of DNA wrapped around a positively charged histone protein.

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16
Q

What is a histone protein?

A

a protein that provides structural support for a chromosome

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17
Q

What is Chromatin?

A

the normal form of DNA in the nucleus- many nucleosomes, but not yet very coiled.

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18
Q

What are the steps of interphase? explain what happens in each stage

A

G1- cell growth and performing its function
S- DNA gets replicated
G2- continues growth and DNA is checked for errors.

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19
Q

What are the stages of mitosis in order?

A

Prophase
Metaphase
Anaphase
Telophase

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20
Q

Describe what happens in prophase

A
  • chromosomes condense and coil, becoming visible under a microscope
  • nuclear envelope starts to disintegrate
  • centrosomes start to form spindle fibers which are made of microtubules
  • centrosomes move to opposite poles of the cell
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21
Q

Describe what happens in Metaphase

A
  • nuclear membrane breaks down
  • spindle fibers continue to extend and centrosomes reach opposite ends of the cell.
  • chromosomes line up at the equator of the cell
  • each sister chromatid is joined to a spindle fibre.
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22
Q

Describe what happens in anaphase

A
  • spindle fibers contract and pull chromatids to opposite poles of the cell.
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23
Q

describe what happens in telophase

A
  • spindle fibers detach
  • each chromatid is now a chromosome
  • nuclear envelope forms again around each group of chromosomes
  • chromosomes uncoil into chromatin
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24
Q

What are the parts of a mammals sperm?

A

Acrosome
Nucleus
Distil centriole
Mitochondria

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25
Q

Describe the cortical reaction

A

fusion of sperm cell membrane with egg cell membrane
- cortical granules release contents into zona pellucida
- zona pellucida thickens/hardens
- fusion of sperm + egg haploid nuclei
-

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26
Q

Describe the role of the golgi apparatus and rough ER in the formation and transport of extracellular enzymes.

A
  • vesicles fuse with golgi apparatus
  • proteins are modified inside GA
  • secretory vesicles are pinched off with the modified protein packaged inside.
  • vesicle fuses with the cell membrane and protein is released through exocytosis.
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27
Q

Glucosaminoglycans (GAGs) are the by-products of chemical reactions inside cells. GAGs
are broken down by enzymes inside lysosomes in cells.
Mucopolysaccharidosis type I (MPS I) is a genetic condition that results in the build-up of
GAGs inside cells.
MPS I affects the production of enzyme G that breaks down GAGs inside lysosomes.
Describe what happens to lysosomes once their contents have been digested.

A
  • fuse with the cell membrane
  • contents are transported outside the cell via exocytosis.
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28
Q

Plasmodium falciparum is a single-celled eukaryotic organism. P. falciparum causes the
disease malaria when it invades red blood cells.
If untreated, malaria can result in a shorter than normal life span.
The high mortality rate of people with malaria has been claimed to be one of the greatest
selection pressures on the human genome in recent history. Describe how scientists could have determined that P. falciparum is a eukaryotic organism
and not a prokaryotic organism.

A
  • DNA is in a nucleus and not linear like in eukaryotes
  • Have membrane bound organelles which eukaryotes don’t have.
  • No plasmids are present
  • Have membrane bound RER
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29
Q

what is an amyloplast?

A

An organelle found in plant cells that stores and forms strach.

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30
Q

Scientists took blood samples from infected red squirrels and analysed them using an
electron microscope.
Describe the features that could be used to identify the prokaryotic cells in the blood
sample.
(4)

A
  • small size ribosomes
  • presence of plasmids
  • presence of pilli
  • presence of a slime capsule
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31
Q

Explain why the nucleus cannot be observed at the end of prophase in a eukaryotic cell.

A
  • because nuclear envelope breaks down
  • and DNA is condensed into individual chromosomes
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32
Q

Give two functions of the Golgi apparatus.

A
  • modify proteins
  • forms vesicles
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33
Q

Anti-freeze glycoprotein (AFGP) is one type of anti-freeze protein.
Messenger RNA coding for AFGP is translated at a ribosome to produce a polypeptide.
Describe how this polypeptide is then processed to make AFGP.

A
  • polypeptide moves to RER and then to the golgi
  • where it assumes a 3d shape
  • a carbohydrate group is added in the golgi to the protein
  • protein packed into secretory vesicle to transport around the cell.
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34
Q

Many of the proteins synthesised become extracellular enzymes.
Describe what happens to these proteins following the process of translation until they
are released from the cell.

A
  • protein goes into golgi
  • it’s modified
  • packaged into secretory vesicles
  • vesicles fuse with cell membrane and are transported out of the cell via exocytosis.
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35
Q

) Cells in people with these diseases produce incorrectly folded enzyme molecules.
Explain why enzymes that are incorrectly folded cannot carry out their function

A
  • active site would be of a diff shape due to dff tertiary structure
  • so won’t be complementary to substrate
  • therefore no enzyme-substrate complex will form and reaction wont catalyse.
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36
Q

what is a plasmodesmata?

A
  • a cytoplasmic connection between plant cells that allow the movement and exchange of molecules in between plant cells.
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37
Q

Which of the following describes the acrosome reaction?
A the ovum releases enzymes that digest the egg cell membrane

B the ovum releases enzymes that digest the zona pellucida

C the sperm cell releases enzymes that digest the egg cell membrane

D the sperm cell releases enzymes that digest the zona pellucida

A

D

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38
Q

Devise an investigation to determine the effect of exposure time to Agil on the rate of
mitosis in onion root tips.

A
  • Use roots from the same onion
  • cut off the tip and soak in HCl, then rinse with H2O
  • then stain with toluidine blue
  • expose each of the
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39
Q

Describe the stages of meiosis

A

Prophase 1: nuclear envelope breaks down, chromosomes, spindles move, and chromosomes duplicated.
Metaphase 1: chromosomes line up next to each other- this is where independent assortment can happen- completely random.
Anaphase 1: Pulls apart full chromosome to opp poles of the cell

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40
Q

name the part of a chromosome that is occupied by a gene

A

a Locus

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41
Q

Explain which chromosome shows the weakest linkage between genes 1 and 2.

A
  • chromosome C
  • genes are furthest apart
  • so more likely to be separated during crossing over.
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42
Q

) Extracellular enzymes are produced by specialised cells.
Explain how groups of cells can produce the same enzyme.

A
  • the genes can be activated in all cells, for the enzyme as all of them will receive the same stimulus.
  • so the m-RNA will be produced for the enzyme.
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43
Q

) The population may recover quickly as saiga antelopes usually produce twins.
(i) Even though both offspring are from the same father and the same mother,
they may be genetically different.
Explain why the offspring may be genetically different.

A
  • since each offspring will be formed from different gametes
  • because Meiosis produces gametes that are genetically different due to crossing over
  • so each gamete contains a different combination of alleles
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44
Q

During fertilisation, only one sperm cell can fertilise an egg cell.
Explain why a second sperm cell cannot fertilise the egg cell.

A
  • Enzymes in the egg thicken the zona pellucida in the cortical reaction.
  • which prevents other sperm from reaching the cell membrane.
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45
Q

This is a more recent classification diagram based on a study of the
mitochondrial genomes of antelopes.

Deduce how this study led to different opinions about the relationship
between Saiga and Antilope.

A
  • New evidence discovered
  • showing they’re less closely related
  • through DNA analysis
  • so more genetic differences detected in mitochondrial genome.
46
Q

) Explain why an individual may have a greater adult height than their
biological parents.

A
  • height is polygenic inheritance
  • so offspring might inherit a diff mix of alleles from each parent
  • might also have a diet high in calcium than parents
  • height is also an affect of both genes and environment
47
Q

Scientists took blood samples from infected red squirrels and analysed them
using an electron microscope.
Describe the features that could be used to identify the prokaryotic cells in
the blood sample.

A
  • prokaryotes have plasmids
  • smaller ribosomes
  • have a cell wall
  • slime capsule
48
Q

) The mean distance between the two sets of chromatids in the photograph of
cell A is 1.5 cm.
Calculate the actual distance in ȝm.
magnification is 800x

A
  • 15 x 10^4 /800
    = 18.75
49
Q

Devise an investigation to study the effect of temperature on the rate of
nuclear division in a plant meristem. (6)

A
  • take sample of meristem tissue from same plant’s tip of roots.
  • rinse with HCl, and then water.
  • place each different temperature water bath up to around 50 degrees celcius
  • stain with toluidine blue
  • squash under cover slip
  • place at lowest objective lens first, increasing as you go, then compare number of condensed chromosomes to see how temp affects nuclear division.
50
Q

Teratozoospermia is a condition that causes sperm cells to have an abnormal
structure. This condition reduces fertility.
The diagram shows an abnormal sperm cell with two flagella.
(a) Explain why the production of these abnormal sperm cells may reduce fertility

A
  • 2 flagella may result in slower mobility
  • so prevents the sperm from reaching the egg
  • so prevent fertilisation
51
Q

Discuss the potential use of vitamin E as a fertility treatment for people with
teratozoospermia.
(6)

A
  • vit E shows positive effect on normal swimming sperm
  • compared to control, MMS+ E produces more motile sperm- around 3% more
  • increased motility may increase the chance sperm reaches the egg
  • so higher chance of fertilisation
  • but data is from rats, so might not apply to people
  • However, MMS and E produces lower sperm counts, suggesting lower number of sperm might not be the cause of infertility
  • did not include ONLY Vit E as a trial, and only involved it with combo of MMS.
52
Q

explain what is meant by a sex-linked disorder

A
  • a disorder caused by a faulty allele
  • located on a sex chromosome
  • more likely to affect one sex than another
53
Q

) Explain how crossing over and independent assortment can produce gametes
with new combinations of the alleles shown on the diagram of the two pairs
of chromosomes.

A

crossing over: chromatids with different combinations of alleles can be formed during meiosis 1, eg: aB

Independent assortment: different combinations of chromosomes are produced during prophase 1, so alleles A and B could be in the same gamete as C or c

54
Q

) Explain how crossing over may differ in sex chromosomes.

A

crossing over cannot occur in sex chromosomes because they may not be homologous due to them being a different size.

55
Q

Cell division in a plant such as an onion can be observed using a light microscope.
Explain why the following techniques are used when producing a root tip squash
to observe cell division.
(4)
Adding hydrochloric acid to the root tip

Adding a stain

A
  • HCl can help observe a single layer of cells so light passes through easier
  • makes condensed chromosomes visible to identify stages of mitosis.
56
Q

Explain the role of the cell cycle (2)

A
  • to allow the cells to grow and replace older cells
57
Q

Name one environmental factor that can cause a cell to become cancerous except UV

A
  • ionising radiation
58
Q

Suggest how the cell cycle will be affected in cells that have become cancerous (2)

A
  • the G phase will shorten
  • resulting in uncontrollable cell division
59
Q

Describe the process in which cells usually become specialised following cell division (3)

A
  • some genes are turned on or off
  • the genes that are on are the only ones that get transcribed
  • so they make the protein that determines the cell’s function.
60
Q

Describe how insulin is modified, packaged and secreted by the cell. (4)

A
  • RER makes insulin hormone in its tertiary structure
  • RER packs them into vesicles to transport to golgi
  • vesicles fuse with golgi and protein is modified
  • packaged into secretory vesicles
  • transported out of cell via exocytosis.
61
Q

Explain the importance of meiosis in the production of gametes (4)

A
  • Meiosis produces cells that are haploids
  • so gametes can form diploid zygote at fertilisation
  • also produce genetic variation in gametes
  • due to crossing over and independent assortment.
62
Q

Describe how the acrosome reaction allows fertilisation to take place

A
  • acrosome of the sperm swells, attaches to zona pellucida and releases enzymes to digest through the zona pellucida and reach the ovum cell membrane
  • sperm nucleus then joins with the egg nucleus and forms diploid zygote.
63
Q

Explain why an individual may have a greater adult height than their biological parents.
(4)

A
  • height example of polygenic inheritance
  • so can inherit mixture of alleles for height.
  • but also affected by environment and genotype
  • eg the kid might have had a diet more high in protein than parents
64
Q

Alleles of a gene linked to the development of lupus have been located on the X chromosome. Scientists tested 13 different alleles of the IRAK1 gene, which is located on the X chromosome. Five of these alleles were associated with lupus. If these five alleles are recessive, explain how this could affect the ratio of males to females who develop lupus.

A
  • males more likely to develop lupus
  • because females have 2 X and males only have 1
  • so males only need one copy to have lupus
  • because they could only inherit one allele
65
Q

Ash trees are threatened with extinction due to a fungal disease called ash dieback. This disease has the potential to destroy 95% of the ash trees in the UK.
Suggest how the effects of ash dieback fungal disease on biodiversity could be measured. (3)

A
  • measure species richness by counting number of species in the area
  • count in areas with and without ash dieback and without over time
  • compare loss of ash trees to to loss of biodiversity.
66
Q

define genetic diversity

A

the number of alleles in a population.

67
Q

Outline how an egg cell is adapted for its function

A
  • lipid droplets to provide energy for growing fetus.
  • haploid nucleus to make diploid nucleus during fertilisation.
  • cortical granules to help thicken zona pellucida to prevent entry of more sperm
68
Q

This man produces gametes. Each gamete only contains one allele of each gene.

Describe how each each gamete only receives one allele of each gene.

A
  • During meiosis, homologous chromosomes are separated from each other.
  • and then sister chromatids are pulled apart.
69
Q

Assess the relative chances of this man’s gametes containing these combinations of alleles.

E and K
e and K
h and i
H and i
(look at diagram)

A

combination on same chromosome more likely

but { e+K / H+i } can result from crossing over

H+i are closer together than e+K on the same locus.

greater distance between loci gives greater likelihood
of { crossing over / e+K }

the relative chances, from most likely to least likely,
are: h+i, E+K, e+K, H+i (1)

70
Q

explain how preventing the shortening of spindle fibres can affect mitosis

A
  • sister chromatids wouldn’t be pulled apart to opposite poles
  • so mitosis would have stopped at metaphase.
71
Q

deduce the effect of the P21 gene on the cell cycle when treated with gamma radiation.

A
  • cells with faulty p21 gene have high cell cycle overall
  • cells with functioning p21 gene have lower mitotic index
  • shows that p21 gene regulates the cell cycle
  • and that radiation causes damage to chromosomes.
72
Q

Fibrosis of the liver is a chronic condition that can lead to cirrhosis of the liver and liver failure.
In fibrosis of the liver, liver cells secrete excess collagen.
There is an association between fibrosis of the liver and alcohol consumption in humans.
Scientists have investigated the effects of alcohol intake on collagen synthesis in rats.
The results are shown in the table.

None: 14
small vol each day: 16
one large volume on day 1: 19
one large vol on day 1, one small vol from day 2 and 7: 27

A
  • larger the volume, the larger the secretion of collagen
  • largest collagen production when combined volumes of alcohol consumed on diff days.
  • so a larger volume of alcohol indicates a greater the risk of fibrosis.
73
Q

The scientists have suggested that epigenetic events are involved in regulating collagen
synthesis in rats given alcohol.
Explain how epigenetic events might be involved in regulating collagen synthesis in rats given
alcohol.

A
  • alcohol may acted as stimulus for activating certain genes through histone modification or DNA methylation.
  • so the gene for collagen production more likely to be transcribed.
74
Q

State what is meant by the term stem cell.

A
  • an unspecialised cell with no Hayflick limit
  • can specialise into other cell types
75
Q

Type 1 diabetes occurs when beta cells in the pancreas do not produce insulin.
Stem cells produced from skin cells can be used to replace these beta cells in mice. The skin
cells can be stimulated to become pluripotent stem cells.
The pluripotent stem cells were injected into the mice. After eight weeks, these cells had
developed into insulin-secreting beta cells.
Describe how these pluripotent stem cells became specialised beta cells.

A
  • stimulus may have resulted in certain genes being activated.
  • therefore these genes are transcribed to make m-RNA
  • and then translated to produce a protein
  • this then determines the cell’s function.
76
Q

Scientists predicted that the snails exposed to both UV light and water from a tank of
predator fish would have 80% shell pigmentation.
Explain how this prediction was made.

A
  • calculating the increase above the control
  • then adding the ‘fish’ and ‘UV’ effects to it.
77
Q

) It is thought that an increase in shell pigmentation levels provides protection against UV
light. UV is a form of radiation that can damage DNA.
Explain how the DNA of the snail could be damaged.

A
  • might interfere with DNA replication
  • which could lead to mutations
78
Q

Some fish live in very cold parts of the sea where ice can form.
Many of these fish produce anti-freeze proteins, which help to stop ice forming inside the fish.
Some fish produce another anti-freeze protein, called AFP II.
The tissues of these fish were tested for the presence of AFP II and the mRNA coding for AFP II.
The results are shown in the table.
Explain the distribution of the AFP II protein and AFP II mRNA.
(4)

A
  • genes for AFP ii only activated in liver cells.
  • so transcribed to make m-RNA
  • then translated to produce AFP II protein
  • this is then transported from liver cells to the rest of the body to prevent freezing in all parts of the body.
79
Q

Recently, scientists have shown an interest in using plant tissue culture techniques to
produce large numbers of genetically identical cotton plants. Cotton plants provide fibres used
for clothing.
Plant tissue culture techniques depend on the totipotent properties of the cells used.
(a) Describe how you could use a plant tissue culture technique to show totipotency in cotton
plant seedlings.

A
  • Use aseptic technique
  • use agar jelly plates
  • with growth hormones and other nutrients
  • grow the plants until roots/small shoots are observed growing.
80
Q

Human stem cell research involves the use of both totipotent and pluripotent stem cells.
Describe the differences between a totipotent stem cell and a pluripotent stem cell.
(2)

A
  • totipotent stem cells can differentiate into any cell type that can make up an entire organism.
  • pluripotent stem cells can differentiate into most cell types, but can’t give rise to an organism.
81
Q

Explain how these stem cells become specialised and develop into heart muscle cells.

A
  • have some genes activated
  • so only these genes are transcribed to make m-RNA
  • therefore they are then translated to make proteins
  • these proteins then determine the function of the cell as a heart muscle cell.
82
Q

Explain the advantages of using stem cells from the patient instead of using stem cells from
a donor.

A
  • these stem cells will be genetically identical to patient
  • so stem cells won’t be rejected.
83
Q

Suggest why this form of stem cell therapy is less controversial than embryonic stem cell
therapy.

A
  • does not involve destruction of embryos
  • which reduces ethical objections to stem cell therapy.
84
Q

The photograph below shows an X-ray of a dachshund. The dachshund is a breed of
dog that is at higher risk of paralysis due to spinal injury.
Scientists have successfully used stem cells to reverse this paralysis.

(a) Suggest why stem cells can be used to reverse this paralysis.

A
  • because stem cells are undifferentiated and can give rise to specialised cells.
  • have no hayflick limit
  • can form new nerve cells
85
Q

The trial experiment was carried out on a dog that was paralysed due to a spinal
injury and was unable to use its back legs.
The scientists extracted stem cells from the lining of the dog’s nose. These cells
were cultured for one month to increase their numbers. The stem cells were then
injected into the injury site of this dog.
Suggest why stem cells were taken from this dog and not from another dog.

A
  • stem cells will be genetically identical to dog itself
  • so no risk of rejection.
86
Q

A further investigation was carried out on 34 dogs with spinal injuries. Some had
stem cells injected into the site of the spinal injury. The others were injected with
a fluid containing no stem cells. This fluid is called a neutral fluid.
Neither the scientists nor the owners knew which dogs had been given stem cells
and which had been given the neutral fluid.
The dogs that were given stem cells recovered the use of their back legs.
(i) Explain the reason for giving some of the dogs a neutral fluid instead of stem
cells.

A
  • as a control
  • to compare to stem cells
87
Q

Suggest why neither the scientists nor the owners knew which dogs had been
given stem cells and which had been given the neutral fluid.

A
  • to prevent bias
88
Q

Induced pluripotent stem cells (iPS cells) are a new type of stem cell.
(a) To produce iPS cells, four genes that code for different transcription factors are
added to the genome of somatic (body) cells. The transcription factors produced
cause the somatic cells to be converted into iPS cells.
(i) Suggest why it may be better to produce differentiated cells from iPS cells
than from pluripotent stem cells.

A
  • no stem cells will be extracted from embryos
  • no immune response with ips cells- so no rejection.
89
Q

Explain how these transcription factors may cause the somatic cells to be
converted into iPS cells.

A
  • transcription factors bind to promoter regions
  • so no genes are switched off/deactivated
  • so the gene is transcribed by RNA polymerase to make m-RNA
  • which will produce protein- allowing the somatic cells to become unspecialised.
90
Q

In 2013, it was discovered that a mixture of seven chemicals could be added to
somatic cells to cause them to develop into iPS cells rather than the need to add
genes to their genome.
Suggest how a valid comparison of these two techniques could be carried out to
discover which may be more effective for converting somatic cells into iPS cells.

A
  • use same source of somatic cells
  • run for the same amount of time
  • measure the concentration of m-RNA produced by each method to determine efficacy in converting to ips cells.
91
Q

Stem cells can differentiate into specialised cells and tissues.
(a) There are about 23 000 genes in a human body cell. The table below shows the
number of genes that have not been switched off, in three different cells, A, B and C.
Cell Number of genes that have not been switched off
A 11 000
B 18 000
C 23 000
Suggest which of these cells is a totipotent stem cell.
Give reasons for your answer.

A
  • C
  • because no genes have been deactivated
  • so can specialise into any specialised cell.
92
Q

A fertilised egg can be used as a source of human pluripotent stem cells.
(i) Explain what is meant by the term pluripotent stem cell.

A
  • an unspecialised cell with no hayflick limit that can specialise into most other differentiated cells, but cannot give rise to an entire organism.
93
Q

Describe how a fertilised egg can be used as a source of human pluripotent
stem cells.

A
  • fertilised egg, obtained from IVF leftover embryo will divide into a blastocyst
  • this contains pluripotent stem cells- which can then be extracted and cultured to use in research.
94
Q

Stem cells are considered to be a potential treatment for many conditions. However,
research on stem cells needs to be regulated.
*(a) Explain the meaning of the term stem cell.

A
  • an unspecialised cell that has no hayflick limit
  • that can give rise to other specialised cell types.
95
Q

(b) State three potential sources of human stem cells.

A
  • embryos left over from IVF
  • adult bone marrow
  • umbilical chord
96
Q

Suggest two reasons why there are regulating authorities for human embryo
research.

A
  • to make sure ethical guidelines are followed
  • to stop cloning of humans
97
Q

Suggest why these regulating authorities should include people involved in
human embryo research and people not involved in embryo research.

A
  • People involved: to fully understand risks
  • People not involved: might not given an unbiased view of embryo research in terms of ethics vs science.
98
Q

a gene therapy trial involved taking bone marrow stem cells from the child to be
treated. A virus was then used to transfer DNA with the dominant allele into the
stem cells. These modified stem cells were then injected into this child.
(i) Suggest how these modified stem cells can result in the prevention of MLD. (3)

A
  • modified stem cells will have the normal gene activated without MLD
  • so this gene will be transcribed to make mRNA
  • translated to make normal functioning
    protein
99
Q

There are some risks associated with somatic gene therapy.
Suggest why the parents of these children gave consent for their children to be
involved in the gene therapy treatment for MLD.

A
  • more benefits than risks
  • they want their child to have a better quality of life.
100
Q

Following mitosis, some cells undergo differentiation to become specialised tissues,
such as xylem.
Explain how cells differentiate to become specialised tissues.

A
  • stimulus provided
  • this activates certain genes
  • so that only these activated genes are transcribed to make m-RNA
  • then translated to make protein
  • this determines the function of the cell.
101
Q

Explain how differential gene expression could result in the specialisation of cells.
(3)

A
  • stimulus
  • some genes activated
  • so only these genes transcribed to make m-RNA and translated to make protein which determines the function of the cell.
102
Q

Epigenetic modifications are involved in the development of an embryo.
The graph shows the changes in DNA methylation during the development of an embryo
from a zygote.

(i) State the meaning of the term DNA methylation.

A
  • adding on a methyl group
  • to a cytosine base
103
Q

Describe the differences between totipotent, pluripotent and multipotent
stem cells during the development of an embryo.

(3)

A
  • totipotent cells are at the very beginning of development- zygote- can specialise into any cell type and can give rise to an organism
  • multipotent are in blastocyst stage- can specialise into most other cell types
  • developing embryo has multipotent stem cells because they can only give rise to some specialised cell types.
104
Q

Analyse the graph to explain why DNA methylation is involved in the development of an
embryo.

A
  • DNA methylation increases the most after blastocyst stage of development
  • shows that some genes are activated/deactivated
  • causing cells to be specialised
105
Q

Epigenetic modification is involved in the formation of the antibody-producing cells.
Describe epigenetic modification.

A
  • changes that affect the activation of genes
  • eg histone modification or DNA methylation
  • involved in specialisation of cells.
106
Q

Where do some bacteria have a capsule?

A
  • outside the cell wall
107
Q

Explain why the interferon made by genetically modified bacteria is different from the
interferon made by animal cells. (id made by bacteria, it is a PROTEIN, and is INCORRECTLY folded and needs to be refolded before use)

A
  • Bacteria don’t have RER
  • so protein cannot be folded properly
108
Q

The eel egg cell is larger than the human egg cell, yet an adult eel is smaller than an
adult human.
Analyse the data in the table to explain why it is advantageous for the eel to have a larger
egg cell. (fertilised in open water)

A
  • larger size= more lipid droplets so more energy for development
  • larger size also means there’s a larger target for sperm to hit, so increased chances of fertilisation.
109
Q

why is HCl added to root tip squash practical?

A
  • to make sure the layers of cells are separated and there’s a thin layer of cells
  • to allow light through.
110
Q

Why is a stain added to the root tip squash practical?

A
  • to make the condensed chromosomes visible
  • to identify the different stages of mitosis.

SNAB edexcel A-level biology (8 decks)

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