‫ االستثنائية‬2013 ‫دورة سنة‬ ‫اهتحانات الشهادة الثانىية العاهة‬ ‫وزارة التربية والتعلين العالي‬

2013 ‫ اّب‬22 ‫الخويس‬ ‫فرع علىم الحياة‬ ‫الوذيرية العاهة للتربية‬

‫دائرة االهتحانات‬
:‫االسن‬ ‫هسابقة في هادة علىم الحياة‬
:‫الرقن‬ ‫ ثالث ساعات‬:‫الوذة‬
Answer the following exercises

Exercise 1 (5 points) Vaccine against AIDS

In the framework of researches concerning AIDS, scientists
followed up 1600 non treated persons that are infected by
HIV (Human Immunodeficiency Virus). They measured, at
the beginning of the infection, the viral concentration in the
blood and recorded the percentage of persons reaching the
phase of AIDS. The results are presented in document 1.
1- Justify, by referring to document 1, the following
statement: “in the absence of treatment, there is a
relation between the onset of the phase of AIDS and the
early evolution of the viral charge”.
In the case of HIV, vaccines that activate only the
production of anti-HIV antibodies don’t protect against all
the known strains of the virus. Currently, the scientific
community agrees on the fact that: to be effective, a vaccine
should also stimulate the production of cytotoxic T
lymphocytes directed against HIV. This allowed the
elaboration of vaccines against HIV. Document 1
Proportion of T8 lymphocytes
2- Indicate how vaccination protects against a given
specific to the virus of AIDS
antigen.
One of these vaccines was tested on two lots of macaques
monkeys that are not infected by the virus of AIDS. The
monkeys of the first lot (lot1) receives a series of five
vaccine injections. The monkeys of the second lot (lot 2) are
not vaccinated. Then, all the monkeys are exposed to the
virus. The proportion of T8 lymphocytes specific to the
AIDS virus is then evaluated in the blood of the monkeys
(document 2). The viral charge is measured in the two lots
of monkeys at the 8th and at the 24th week following the
exposure to the virus (document 3).
3- Show, by referring to document 2, that the immune
response of the vaccinated monkeys is more rapid and Document 2
more amplified then that of the non-vaccinated
monkeys during the first 3 months of the infection. Viral charge ( number
4- Determine if the immune response triggered in lot 1 is Time after of viral RNA copies /
durable. exposure to the ml of plasma)
5- Interpret the results of document 3. virus.
6- Show, by referring to what precedes, that the tested Lot 1 Lot 2
vaccine has a limited efficiency and doesn’t allow the
8th week 5.104 25.104
eradication of the disease.
24th week 5.104 50.104
Document 3

1
Exercise 2 (5 points) Origins of Phenylketonuria
In hepatic cells, the enzyme phenylalanine
hydroxylase, PAH, is responsible for the
transformation of phenylalanine into
tyrosine. Its absence or its inactivity results
in the accumulation (increase in the
amount) of phenylalanine in the blood
which becomes toxic at a dose exceeding
20mg/dL which leads to the destruction of
the nerve cells in individuals affected with
phenylketonuria. This disease has different
origins and is manifested by irreversible
mental retardation.
1- Pick out the consequence of the high
amount of phenylalanine in the blood.
Document 2 represents a part of the gene
coding for the enzyme PAH of a healthy
individual and that of the equivalent
fragment of an individual suffering from
phenylketonuria. Document 1

2- Determine, using the genetic code table Alleles Nucleotide sequence of the
(document 1), the sequence of amino non-transcribed strand of DNA from
acids of the part of the enzyme PAH codon 277 to codon 283
coded by each of these two alleles. Normal TAT ACC CCC GAA CCT GAC ATC
3- Explain how the modification in the Diseased TAT ACC CCC AAA CCT GAC ATC
nucleotide sequence of the allele leads to Document 2
the appearance of phenylketonuria.
Alleles F1 M1 N1 F2 M2 N2
Two normal couples had two newborns with Normal ▬ ▬ ▬ ▬ ■■■■■■
high plasma concentration of phenylalanine Diseased ▬ ▬ ■■■■■■ ▬ ▬
that exceeds 20mg/dL. F: Father M: Mother N: Newborn
Document 3
4- Indicate if the allele of the disease is
dominant or recessive. Justify the answer.
In order to determine the origin of the disease
in these two newborns, N1 and N2, these
couples consulted a doctor who recommended
DNA analysis for all the family members. The
obtained results are presented in document 3.
Moreover, the doctor proposed another test,
where he injected the newborns with
phenylalanine followed by injection of BH4,
an organic substance normally present in the
organism and that is indispensable for the
normal activity of PAH. The obtained results
are presented in document 4.

5- Indicate the possible origin of the disease in

the case of the newborn (N1). Justify the
answer by referring to documents 3 and 4. Document 4
6- Determine, by referring to documents 3 and 4, the possible origin of the disease in the case of the newborn
(N2).

2
Exercise 3 (5 points) LSD and Hallucinations
Albert Hofmann is best known for discovering a powerful synthetic drug, the LSD. In one of his books, he
described his sensations after he voluntarily took this drug in the frame work of experimental automedication.
« Everything in my field of vision was oscillating and distorted as if seen in a curved mirror. I also had the
sensation that the bike was not moving even though my assistant told me later that we have been moving
fast. When I arrived home, dizziness and weakness sensation were more serious in a way that I couldn’t
stand up and was obliged to lie down on a sofa-bed.
Later, I noticed that the way all acoustic perceptions, such as the sound of a door handle or that of a car
passing by the house, were transformed into visual perceptions. Every sound generated a corresponding
animated image with a particular form and color. »

Document 1
1- Knowing that hallucination is defined as «perception without any object to perceive», show that the LSD is
a powerful hallucinogen.
2- Justify that the LSD doesn’t modify only the visual perceptions of the individual.
To better understand the action of LSD and its effects, the following studies are performed.
Stimulations applied on neurons A produce visual perceptions. Document 2 shows the encephalic visual
pathways involved in these types of perceptions.
Document 3 represents the scheme of the synapse between the two types of neurons A and B at the level of the
cerebral relay.

Document 2 Document 3
Effective stimulations of increasing intensities
(I1< I2< I3) are applied on neuron A. The Frequency of AP Amount of Frequency of AP
amount of serotonin in the synaptic cleft is Intensity at the level of serotonin at the level of
measured and the nervous message at the level the neuron A (in AU) the neuron B
of neurons A and B are recorded. The results are I1 5 1.5 8
shown in document 4 I2 9 2.5 13
I3 12 3 18
3- Explain the steps of synaptic transmission
of the nervous message coming from the Document 4
retina via neurons of type A before reaching the
visual centers.
4- Draw a histogram showing the variation of the
amount of serotonin as a function of the intensity of
stimulation.
5- Analyze the obtained results. Draw out the form in
which the nervous message is coded at the level of
the neuron as well as that at the level of the synapse.
Document 5 shows the molecular structure of serotonin
and that of LSD.
Document 5
6- Suggest, referring to all what precedes, an
explanation of the mode of action of LSD in the genesis of visual hallucinations.

3
Exercise 4 (5 points) Ovaries and Sexual Cycles
Ovaries are active from puberty
till menopause. Groups Conditions Observed Results
In order to understand the Mass of the Uterine cycles
endocrine role of ovaries on the uterus
genital activity, the following 1 Control 710 mg Cyclic variation
experiments are performed. 2 Ablation of two ovaries 120 mg No variation
3 Bilateral ovariectomy + 705 mg No cyclic
Experiment 1: continuous and identical variation
Two lots of female rats which injections of ovarian extracts
did not reach puberty, 2 and 3, Document 1
are subjected to ovariectomy
with or without injection of ovarian extracts: estradiol and Uterus at day 0 Uterus removed
progesterone. The conditions and the results of the experiment on the 11th day
are presented in document 1.
1- Draw out the roles of ovaries and their mode of action as
revealed in this experiment.
Experiment 2:
Four lots (A, B, C and D) of female rabbits that did not reach
puberty receive daily injections of 5 µg of estradiol (E) and/or
200 µg of progesterone (P) during several days. Then,
transverse sections of their uterus are prepared at the end of the
experiment, at day 11. Document 2 presents the experimental
conditions as well as the obtained results.
2- Interpret the results of document 2.
Experiment 3:
Protein receptors for progesterone were revealed at the level of
endometrium cells. The injection of estradiol provokes an
increase in the number of progesterone receptors in the day
following the injection.
3- Explain the obtained results of lot A in experiment 2.
Experiment 4: Document 2
A lot of ovariectomized female mammals are subjected to injections of high amounts of estradiol with or
without progesterone.
The evolution of the plasmatic concentration of the pituitary hormone LH is measure and the obtained results
are shown in documents 3 and 4.

Document 3 Document 4
4- Show, by referring to documents 3 and 4, that “the activity of the pituitary gland is under the control of
ovarian hormones”.
5- Establish, by referring to all what precedes, a functional diagram showing the relations existing between
the ovaries and the two other organs: the pituitary gland and the uterus.

4
 ‫ االستثنائية‬2013 ‫دورة العام‬ ‫اهتحانات الشهادة الثانىية العاهة‬ ‫وزارة التربية والتعلين العالي‬
‫فرع علىم الحياة‬ ‫الوديرية العاهة للتربية‬
‫اسس التصحيح‬ ‫دائرة االهتحانات‬

Part Answer Grade

Exercise 1
1 The percentage of untreated patients in the AIDS phase five years after the infection 1
increases from 9% to 60% when the viral charge one year after the infection increases
from 1000 up to 10000 copies of mRNA/mL. This shows that the onset of the AIDS
phase and the early evolution of the viral charge vary in parallel to each other.

2 Vaccines immunize the organism against a specific antigen by inducing a durable 0,5
immunological memory.

Or
Vaccines protect the organism by sensitizing the immune system against the pathogens in
order to recognize and destroy them in a more rapid and more efficient manner upon a
second contact with the same pathogen.

3 In vaccinated monkeys, the proportion of T8 lymphocytes increases from 0 to 6.5 greater 1

than that of non-vaccinated monkeys which is 2. This shows that the response triggered
in vaccinated monkeys is more amplified. (0,5 pt)

After the exposure to the virus, the increase of the proportion of T8 lymphocytes in
vaccinated monkey begins after a latency time of one week, less than that in the
vaccinated monkeys which is 2 weeks. This shows that the response in vaccinated
monkeys is more rapid than that of the non-vaccinated ones. (0,5 pt)

4 Between the fourth and the 12th week, the proportion of T8 lymphocytes, in both lots 1 0,5
and 2 decreases while remaining higher in vaccinated monkeys and reach the same value
of 2 at week 12. After the 12th week, the variations of these proportions remain identical.
This shows that the immune response triggered by the vaccine is not durable, it does not
last except for 12 weeks.
5 Document 3 shows that the viral charge at the 8th week in vaccinated macaques is 5. 1
104viral RNA copies/ml inferior to that of the non-vaccinated ones 25. 104viral RNA
copies/ml . At the 24th week it increases (doubles) to 50.104viral RNA copies/ml in
the non-vaccinated macaques while it remains constant at 5.104viral RNA copies/ml
in vaccinated macaques value that is 10 times smaller than 50.104viral RNA copies/ml.
This shows that vaccine maintains the viral charge weak and constant at the beginning of
the infection.

6 The chance of reaching the phase of AIDS diminishes in the case where the viral charge 1
is weak at the beginning of the infection (doc.1). The vaccine maintains the viral charge
low at the beginning of the infection (doc.3). This diminishes the evolutions of the
disease toward the phase of AIDS thus extending the asymptomatic phase. Therefore
there is a greater chance to prolong the life of seropositive individuals. From this point
the vaccine is efficient. The vaccine amplifies the specific cell mediated immune
response the first three months after infection (doc.2) however this amplification is not
durable thus the efficiency is limited. In addition the vaccine doesn’t ensure a total
recovery and the disease is not eradicated.
Part of Answer Grade
the ex.
Exercise 2
1 It is toxic, leads to the destruction of the nerve cells and is manifested by irreversible 0,5
mental retardation.

2 Portion of the amino acids sequence of the enzyme: 1

We establish the mRNA sequence by replacing T by U
Normal mRNA: UAU ACC CCC GAA CCU GAC AUC
Amino acids sequence : Tyr-Thr-Pro-Glu-Pro-Asp-Ile
Diseased m RNA: UAU ACC CCC AAA CCU GAC AUC
Amino acids sequence : Tyr-Thr-Pro-Lys-Pro-Asp-Ile

3 The mutation by substitution at the level of the first nucleotide of the 280th codon of the 1
DNA where G is replaced by A is transcribed at the level of mRNA by a new codon
which is translated into a new amino acid, lysine instead of the glutamic acid. This new
amino acid sequence affects the tridimensional structure of the enzyme PAH which
becomes inactive (nonfunctional). Since this enzyme is responsible for the
transformation of phenylalanine into tyrosine. This transformation doesn’t occur any
more leading thus to the accumulation of phenylalanine which in high amount becomes
toxic and causes phenylketonuria.

4 The allele of the disease is recessive with respect to the normal allele. Since normal 0,5
parents gave birth to an affected child, thus they carry the allele of the disease that is
masked in the parents.
Let N be the symbol of the normal allele.
Let m be the symbol of the allele coding for the disease.

5 The origin of the disease in the case of N1 is a mutation that leads to the synthesis of an 1
inactive PAH (non-functional).
Document 3 shows that affected N1 is homozygous of genotype m//m. And document 4
shows that a slight decrease in the plasma level of phenylalanine in N1 from 80 to 70
mg/dL after the injection of 20 mg/Kg of BH4. This implies that even in the presence of
functional BH4, the PAH remains nonfunctional.
6 1
Document 3 shows that the affected newborn N2 is homozygous of genotype N//N. His
allele codes for a normal PAH. Document 4 shows that in N2, the constant plasma level
of phenylalanine of 80 mg/dL decreases after the injection of 20 mg/Kg of BH4to 15
mg/dL value that is inferior to the reference level of 20 mg/dL. Thus BH4 acts in N2 by
decreasing the plasma level of phenylalanine toward its normal value. The PAH in the
newborn N2 is functional but needs the presence of BH4 to be activated. Hence, his
disease in N2 can be due to the absence of BH4 or to the presence of non-functional
BH4.
Part Answer Grade
Exercise 3
1 “Every sound generated a corresponding animated image”. The “acoustic perceptions 0,5
such as the sound of a door handle or a passing automobile became transformed into
optical perceptions”. Sounds are generating visual perceptions. Thus LSD is a powerful
hallucinogen since it provokes perceptions without objects to perceive.

2 LSD doesn’t modify only the visual sensations, but it also causes general disturbance. 0,5
Hoffmann didn’t realize that the bike was moving, he felt dizzy and weak he couldn’t
stand up and was forced to lie down on a sofa bed.

3 The nerve message coming from the retina towards the extremity of the axon of 1
presynaptic neuron A, leads to the influx of calcium in the terminal knob, this causes
vesicles filled with neurotransmitters, serotonin, to migrate to the cell’s surface and to
release their contents of serotonin into the synaptic cleft by exocytosis. Then, serotonin
fixes on specific receptors of the membrane of the postsynaptic neuron B. the binding of
the neurotransmitter to its specific receptor generates an EPSP in the postsynaptic
neuron inducing the birth of a nerve message that is transmitted by neuron B towards
the nerve centers.

4 Histogram : variation of the amount of serotonin as a function of the intensity of 1,25

stimulation

5 The frequency of AP at the level of the neuron A and at the level of neuron B increases 0,75
respectively from 5 to 12 AP and from 8 to 18 AP as the intensitiy of stimulation
increases from I1 to I3. Meanwhile, the amount of serotonin increases from 1.5 to 3 au.
Thus the nerve message at the level of neuron is modulated by frequency of AP and at
the level of the synapse by the amount of neurotransmitter.

6 the molecule of serotonin and that of LSD have an identical part in their molecular 1
structures, and this common part allows the serotonin to fix on its specific receptor. We
can suggest that molecules of LSD fix on serotonin receptors due to their
complementary form. Being agonist to serotonin, the LSD fixation on serotonin
receptors generates an EPSP at the level of neuron B in absence of any message at the
level of the presynaptic neuron A, and consequently the induced nerve message
propagates towards the visual centers even though eyes don’t detect any object. This
explains the visual hallucinations described by Hoffmann.
Part Answer Grade
Exercise 4
1 Ovaries are responsible for the development of the uterus and the cyclic variation of the 0.75
uterine cycle.
Ovaries act by secreting estradiol and progesterone in the blood in a variable or cyclic
manner.

2 There is development in the endometrium of the uterus following the injection of 2

estradiol for 6 days followed by an injection of progesterone for 4 days (lot A).
However this development is less important following the injection of estradiol for 6
days alone ( lot B). Thus estradiol stimulates the development of the endometrium and
progesterone amplifies this action. While there is no development of the endometrium
following the injection of progesterone alone from day 7 till day 10 (lot C). Hence,
progesterone alone doesn’t have any effect on the endometrium. On the other hand the
endometrium shows a weak development less important than that in lot A following the
injection of progesterone for 4 days followed by an injection of estradiol for 6days.
Thus progesterone does not act on the endometrium unless it is preceded by estradiol.

3 In lot A, the injection of estradiol at the beginning of the cycle ensures slight 0.75
development of the endometrium and increases the number of progesterone specific
receptors. This increases the concentration of the progesterone bound to its receptors in
the nucleus of target cells. this increases the synthesis of proteins and ensures the
thickening of the endometrium, leading to the important development of the
endometrium in lot A.
4 The amount of LH increases from 0.5ng/mL to 9ng/mL between the days 8 and16 0.75
following the injection of estradiol alone on day8. This shows that estradiol exerts a
positive feedback on the pituitary gland. On the contrary, the amount of LH decreases
from 60ng/mL to 10ng/mL between day 12 and 28 after the injection of estradiol and
progesterone at day 12. This shows that estradiol with progesterone exert a negative
feedback on the pituitary gland.
This shows that the activity of the pituitary gland is under the control of ovarian
hormones.

5 Functional diagram showing the relations existing between the ovaries and the two 0.75
other organs: the pituitary gland and the uterus

+ _
Pituitary gland

High
LH
dose
Ovaries

Estradiol Estradiol +
Progesterone

Secrete
Lead to Weak development Important
Feedback of the endometrium development of the
endometrium