Annotated Article from the June 2013 Unit 5 Exam

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Scientific Article Notes, Question and answers, June 2013 Unit 5,
by Stafford Valentine Redden (M.Sc.; M.Ed.; M.A.; Ph.D)
Scientific article for use with Question 7
Naked and ugly: The new face of lab rats
1. In a small room in the lab-animal wing of the University of Illinois at Chicago, biologist Thomas
Park peers into a plastic box full of naked mole rats. "You guys are so cute," he says softly, in a voice Comment [S1]: To look intently or searchingly
usually reserved for babies or puppies.
2. Park is mistaken. Naked mole rats are not cute. They are bald, wrinkled and purply pink, with tiny
near-blind eyes and huge yellow teeth. Ranging from the size of a large mouse to that of a small
rat, these odd rodents are among the strangest looking mammals on the planet. But don't judge a Comment [S2]: Mice measure between 3 and 14
naked mole rat by its unfortunate appearance. These bizarre creatures could help us tackle all sorts inches in length and weigh up to 2 ounces. Rats
may be as long as two feet and weigh more than
of human maladies, from cancer and stroke to pain relief and ageing. mice. The snout of the rat is more pointed.
Comment [S3]: mammals, characterised by a
Paragraph 2 single pair of continuously growing incisors in
each jaw which must be kept short by gnawing.
SAQ1. Explain the formation of tumors (cancers).
Comment [S4]: Strikingly unconventional and
Cancer is caused by gene mutations (in tumor suppressor genes or oncogenes: which are far-fetched in style or appearance
responsible for regulation of the cell cycle) which cause uncontrolled cell division. The rate of cell Comment [S5]: To make a determined effort to
proliferation is greater than the rate of cell death. deal with a difficult problem or situation.
Comment [S6]: Any undesirable or disordered
SAQ2. Explain how stroke may be caused.
Comment [S7]: Known medically as a malignant
Atheroma formation and thrombosis in cerebral arteries (or other arteries in the brain) lead to neoplasm, is a broad group of various diseases,
ischaemia (lack of blood flow and oxygen supply) in the brain. This leads to necrosis (death) of all involving unregulated cell growth
neurons in the brain. This is the main cause of stroke. High blood pressure can also cause Comment [S8]: A stroke is the rapid loss of
brain function due to disturbance in the blood
rupture of arteries in the brain, leading to necrosis of brain cells. supply
Comment [S9]: the gradual biological
SAQ3. State the risk factors for stroke. impairment of normal function.
High blood pressure, high LDL levels, lack of exercise, ageing, gender, smoking, genetic factors
and diet.
SAQ4. Explain the causal link between ageing and stroke.
Ageing makes the arteries less elastic. This increases blood pressure and causes endothelial
damage. T cells and monocytes migrate into the smooth muscle layer of arteries and facilitate the
deposition of Ca2+ ions, LDL cholesterol and cells debris to form atheroma or plaque. This
narrows the lumen of arteries in the brain and increases the risk of stroke.
SAQ5. Pain is caused when specific receptors called A (delta) receptors and C fiber receptors
are stimulated. Using your knowledge about ion movement in a neurone, explain how an action
potential will be initiated in these neurons.
The stimulus will cause the Na+ ion channels to open. The influx of Na+ ions into the neuron will
initiate the formation of an action potential.
SAQ6. Suggest mechanisms by which the mole rat may provide relief from pain.
They may produce some chemicals (analgesics) which may block pain receptors at the synapses
and prevent post synaptic potentials from forming in the neurons that are responsible for the
sensation of pain.
3. A dozen species of mole rat exist, all native to sub-Saharan Africa. Naked mole rats stand out, Comment [S10]: living naturally in a particular
though, not least because they appear completely bald. They are also extremely social, living region
underground in elaborate networks of tunnels and chambers in groups of up to 300. Here in the Comment [S11]: to be prominent or special
lab, Park mimics their burrow system by connecting several dozen plastic boxes with long tubes. Comment [S12]: To copy or imitate closely
The animals spend their days pushing bedding around the tubes and nibbling on bits of sweet Comment [S13]: Take small bites
Author of A Level biology text books and practical workbooks, global academic consultant and Head of Institution, Republic of Maldives.
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Paragraph 3
SAQ7. Explain why the mole rat populations may be termed as endemic.
This is because all species of mole rats are found in sub-Saharan Africa alone.
SAQ8. Potato contains a lot of starch. Suggest the importance of potato in the diet of mole rats.
Starch can be digested by the mole rat to produce glucose. The glucose is a good respiratory
SAQ9. Explain what is meant by a population.…read more

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Paragraph 5
SAQ20. Melanin is a pigment found in the skin and fur of mammals. Explain the environmental
influence on the phenotype with reference to melanin production.
High exposure to UV radiation stimulates the increased production of Melanocyte Stimulating
Hormone (MSH) and MSH receptor on melanocytes. This triggers the increased production of
melanin. The melanin is packed into melanosomes and transferred to other epidermal cells. This
protects the nuclei from UV damage and reduces mutations in DNA.
SAQ21.…read more

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9. According to this theory, oxygen-containing free radicals damage the molecules of the body, causing Comment [S39]: a highly reactive atom or group
them to deteriorate over time until they stop functioning altogether. This oxidative damage, as it of atoms with an unpaired electron
is known, is apparent as extra molecules that attach to DNA and proteins "like chewing gum stuck Comment [S40]: become worse
to the bottom of a shoe", Buffenstein says.…read more

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10. To her surprise, Buffenstein found the opposite: more telltale oxidative damage in 6-month-olds
than in mice of the same age. Remarkably, however, the damage had no obvious impact on their
Keeping in shape
11. Why is this? To find out, Buffenstein took a closer look at the 3D structure of proteins, which is
critical to their functioning. Mouse proteins begin misfolding very quickly after suffering oxidative
damage ­ a kind of anti-origami that causes them to stop working properly.…read more

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from both mice and humans multiply until they form a single dense layer. At that point, they stop
dividing, halted by a process called contact inhibition. In cancerous tissues, however, the abnormal
cells continue to multiply, piling up and growing out of control.
Paragraph 15
SAQ43. State three physical conditions that must be controlled while culturing cells in a Petri dish
to ensure rapid growth.
Temperature, Nutrients, pH, Oxygen
SAQ44.…read more

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a). G1 (First Gap phase): During this stage
there is rapid synthesis of RNA and proteins
and rapid cell growth occurs during this phase.
The cell has only one copy of the genome.
b). Synthesis (S) phase: DNA replication
occurs. The quantity of DNA doubles in the
cell. Nucleus usually gets larger during this
stage. The cell now has two copies of the
c).…read more

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25. When Gorbunova and her team began specifically investigating mole rat cells, they were surprised
at how difficult it was to grow the cells in the lab for study. The cells simply refused to replicate once
a certain number of them occupied a space. Other cells, such as human cells, also cease replication
when their populations become too dense, but the mole rat cells were reaching their limit much
earlier than other animals' cells.
Paragraph 25
SAQ57.…read more

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makes transcription factors the largest group of human proteins. The general transcription factors have
been highly conserved in evolution, with the same factors occurring in different organisms from humans
to simple single-cell organisms.
Mammalian hormones are chemical messengers carried by the blood from endocrine glands to all parts
of the body. They affect specific cells, called target cells. Many hormones activate transcription factors in
the target cells.…read more

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32. This finding is particularly significant because the nerve fibres associated with chemical pain are
also involved in post-traumatic pain in people ­ precisely the type of discomfort researchers would Comment [SVR69]: Post-traumatic stress
like to eliminate. "It's OK to have pain sensation to tell you to get your hand off the stove, or to disorder (PTSD) is a real illness.…read more


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