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					Reproduction       Year 04   Paper I   8(6)

Questions:

8

(a)




(i) Relate the location of the mitochondria to their function

                                                           (2 marks)

(ii) It is known that in mammals, less than 0.01% of the

      mitochondrial DNA is inherited from males

      (1) What is the major source of mitochondrial DNA in the

         zygote?                                            (1 mark)
    (2) What can the mitochondrial DNA in the zygote tell us about

       human inheritance?                                    (1 mark)



(b) It is known that the nuclei from two sperms of the same

    individual can be made to combine inside an anucleate ovum

    (ovum withoust cucleus) to form a diploid cell which can further

    develop into an embryo. Explain the sex(es) of the embryo that

    can be produced by this method.                         (2 marks)




Answers:

8

(a) (i) ․ mitochondria close to the tail

       ․ provide energy for motility of the tail of sperm

    (ii) (1) ․ from the ovum / female

       (2) Any one:

           ․ trace genetic line from female

           ․ parentage identification

(b) ․ male sperm contains X or Y chromosomes, when 2 nuclei are

       combined,
    ․ the result is either female, when the nuclei of two sperms containing

       X chromosome are used, or male, when the nucleus of one sperm

       containing X chromosome and one sperm containing Y chromosome

       are used




Reproduction      Year 03    Paper II    8(20)

Answers:

8

(a) Significance of the cyclic pattern in females

    1 role of females is to bear foetus (1) for viviparous

       reproduction (1)

    2 ovum takes time to accumulate nutrients to grow and

       mature (1)

    3 enables the discharge of one mature ovum at a time,

       another oocyte will undergo development only if the

       ovulated ovum is not fertilized (1) This would result in better

       survival of the foetus (1), and avoid expenditure of a large

       amount of energy if simultaneous growth of a large number

       of follicles were to take place (1)
    ․ FSH stimulates the growth of follicles (1) within the ovary in

        each cycle

    ․ LH stimulates ovulation (1)

    ․ oestrogen inhibits FSH and LH secretion at early phase of

        menstrual cycle by negative feedback to prevent the

        development of another follicle (1)

    ․ progesterone inhibits FSH / LH after ovulation to prevent the

        maturation of another follicle (1)



4 make provisions and preparations for bearing the foetus

    require changes to the uterine lining (1), this takes time ∴

    cyclical (1) and needs co-ordination with ovulation (1)

    ․ thickening of uterine lining under progesterone / oestrogen

    stimulation (1), to prepare for implantation of the foetus (1),

    ․ vascularization of the uterine lining under progesterone /

        oestrogen stimulation (1), to provide nutrients for growth of the

        foetus (1)

5   ․ If no fertilization takes place, uterine wall sheds (1), this saves

        energy and resources in maintaining the uterine wall (1)

        > progesterone production decreases (1)
         ․ If no fertilization takes place, needs to prepare for the next cycle

              of events (1), to create new opportunity for fertilization (1)



(b) Significance of non-cyclic pattern in males

    ․ males do not have to bear the foetus (1), role of males is to provide a

         continuous supply (1) of sperms for fertilization (1)

         > FSH / testosterone stimulate the formation and maturation of the

              sperms (1) in the testes

(Bonus: if both female and male have cyclical events, it is more difficult to

achieve synchronization of the release of gametes for successful

reproduction, this reduces chance to produce offspring (1))




                               Reproduction- animal
0225c(4)
Q: Explain why milk flow eventually stops after a nursing mother has discontinued
   breast-feeding her baby.                                                     (4 marks)
A:
 cessation of suckling stops nervous stimulation to the *hypothalamus (1)
 prolactin secretion from pituitary is inhibited (1) milk synthesis at the breast glands is
   inhibited (1)
 secretion of oxytocin from the pituitary is inhibited (1), no milk ejection from the
   breast (1)



0224b(5)
Q: Describe how the mammalian foetus obtains amino acids from proteins in the
     maternal diet.                                                        (5 marks)
A:
  maternal digestion: protease breaks down proteins to amino acids (1)/ peptides, in
  stomach and small intestine (1)
 absorbed into the maternal blood stream at the ileum (1)
 a.a. carried via veins to hearts, then along artery to uterine wall (1)
 a.a. diffuse across the *placenta into foetal blood circulation (1)



0013(7)
Q: Photomicrographs P, Q and R (below) show a structure at different developmental
stages observed in a mammalian organ. They are not arranged according to the
sequence of development of this structure.
(a) Show the correct sequence of development of the structure by listing the letters of
    the photomicrographs.                                                     (1 mark)
(b) The normal development of the structure can be artificially interrupted. Suggest one
    way to bring about this interruption and explain the mechanism involved. (4 marks)
(c) Name the structure in P and state its function.                           (2 marks)
Photomicrographs Q and R from:
P.R. Wheater, H.G. Burkitt & V.G. Daniels, Functional Histology Low-Priced Edition,
    pp.258
A:
(a) RQP (1)
(b) - oral contraceptive pill contains oestrogen and progesterone (or just progesterone)
      (1), / skin implant of progesterone and / or oestrogen, / injection of progesterone
      of progesterone and / or oestrogen.
    - oestrogen and progesterone can decrease/ inhibit FSH (1) and LH release (1),
       follicle will not mature / develop (1)/ prevents production of ova
(Other correct alternatives that work to affect the reproductive hormones are accepted.)
(c) corpus luteum/ yellow body (1)
    function: produce progesterone to maintain uterine wall thickening (1)/ vascularity to
    prepare for/ maintain pregnancy


9913(3.5)
Q: The following photomicrographs, A and B, were taken from two groups of mice. One
of the photomicrographs was taken from the group that had been treated with a drug that
caused sterility and the other was taken from the control group.
(a) Identify the organ where the photomicrographs were taken.                     (1 mark)


(b) Which photomicrograph, A or B, shows the result of the drug-treated group? Give
    one reason for your choice.                                       (1.5 marks)


(c) Deficiency of a certain hormone in mice will also produce the same effect as that
    caused by this drug. Name the hormone.                                (1 mark)
A:
(a) *testis (1)
(b) B (0.5)
    -     no spermatozoa (0.5) in centre of seminiferous tubule in B (0.5)
(c) *follicle stimulating hormone (1)/ *testosterone/ *luteinising hormone/ *interstitial cell
    stimulating hormone
    N.B. FSH/ LH/ ICSH (0.5)



9521c(6)
Q: Compare and contrast gaseous exchange in a human adult and a foetus. (6 marks)

A: Comparison:
 Both are affected by the diffusion of respiratory gases along their respective
   concentration gradients.
 Both exchange surfaces maintain steep diffusion gradients of gases by mass flow
   (ventilation or circulation) of exchange media.
 Both have thin, moist, richly vascularized and large surface area for gaseous
   exchange.


    Contrast                    Adult                       Foetus
    Exchange surface            Lung/ alveoli               Placenta/ chorionic villi
                                                            formed by maternal and
                                                            foetal tissues
    Exchange media              Gaseous and liquid          Both sides liquid
    Exchange direction          Oxygen from air to blood; Oxygen from maternal
                                reverse for carbon        blood tofoetal blood;
                                dioxide                   reverse for carbon
                                                          dioxide. Foetal
                                                            haemoglobin with higher
                                                            oxygen affinity
9517(9)
Q: (a) The following flow chart shows the sequence of gamete transfer in the human
    male and female reproductive systems prior to fertilization. List the contraceptive
    methods indicated by (i) to (vi).                                       (6 marks)




(b) Explain the principles underlying the use of porgesterone and oestrogen in oral
    contraceptives.                                                     (3 marks)


A: (a)       (i)   vasectomy (cut and tie of sperm duct)
     (ii)(iii)     condom/ coitus interruptus/ rhythmic method/ withdrawal method/ female
              condom (any two)
      (iv)(v) spermicide/ diaphragm/ cervical cap (any two)
      (vi)    tubal ligation/ ovidectomy (cut or tie oviduct)
      N.B. 1 mark each, wrong spelling, no mark


(b) Both (0.5) oestrogen and progesterone inhibit the release of follicle stimulating
    hormone (0.5) and luteinzing hormone (0.5) from the pituitary (0.5), thus inhibit
    follicular maturation (0.5) and ovulation (0.5).



9413(6)
Q: Draw an annotated diagram of a sperm and show how its structure is related to its
function.                                                               (6 marks)
A: Diagram: clear and accurate (1)
Annotations: (1 mark each for correct structure-function, total 4 marks)
Labels: head, neck, middle piece, tail, end piece (any two, 0.5 mark each, not to repeat
annotated structures below)
(0.5 mark deducted for each spelling mistake on structure)




9317(20)
Q: Two experiments were conducted on mature female mice with similar body weights.


In experiment I, the effects of surgical removal of the two ovaries (OVX) and subsequent
treatment with hormone A on the uterine weight were examined. The results are
presented in Table I.




In experiment II, the effects of surgical removal of the pituitary (PX) and subsequent
treatment with either hormone A or hormone B on ovarian and uterine weights were
studied. The results are presented in Table II.
(a) Why was it necessary to conduct the experiments using animals with similar body
    weights?                                                            (2 marks)
(b) With reference to Table I,
    (i) What conclusions can be drawn?                                     (2 marks)
    (ii) Name hormones A and B suggest one other function which was not studied in
         this experiment.                                                    (2 marks)
(c) Based on your knowledge of the sexual cycle, explain the results of group 6 and 7
    mice (Table II), given that hormone B is secreted by the pituitary.      (7 marks)
(d) Describe one histological change that you would expect in the ovaries of group 5
    mice compared with those of group 4 mice.                                (1 mark)
(e) Suggest a medical use of hormone B. Explain your answer.                 (2 marks)
(f) What would be the effect on the remaining ovary if only a single ovary was removed
    in group 2 mice? Explain your answer.                                    (4 marks)
A: (a)   Similar body weights → similar ovarian and uterine weights for comparison1,1
     (b) (i) Hormone A promotes the growth of the uterine wall                      1
              Hormone A is secreted by the ovary                                    1
              OR
              The secretion of hormone A requires the presence of the ovary
         (ii) Estrogen                                                              1
              stimulation of female secondary sexual characteristics                1
     (c) In the group 6 mice, with the pituitary removed, no gonadotrophic hormones
         could be produced                                                          1
         both ovarian growth and uterine growth should be inhibited            0.5, 0.5
         but externally applied hormone A (estrogen resulted in normal uterine growth
         but not ovarian growth because ovarian growth is dependent on gonadotrophic
         hormone (FSH).                                                       0.5, 0.5
         In group 7 mice, with the pituitary removed, no gonadotrophic hormones could
           be produced too, but externally applied gonadotrophic hormone (hormone B)
           stimulated the growth of the ovary and hence and increase in ovarian weight.
                                                                                 1, 0.5
           It also stimulated the ovary to increase production of estrogen            1
           which stimulated uterine growth and hence an increase in the uterine weight.
                                                                                    1.5

     (d) diminished number of mature follicles                                        1
         OR
         increased number of atretic / degenerating / regressing follicles

     (e) to improve fertility                                                         1
         by stimulating ovulation                                                     1

     (f)   The removal of a single ovary would decrease estrogen production      1
           This would decrease negative feedback on pituitary gonadotrophic hormone
           (FSH) secretion                                                       1
           Increased pituitary gonadotrophic hormone (FSH) production            1
           stimulates ovarian growth and hence the remainign ovary underwent
           compensatory hypertrophy                                              1
                                                                                (20)



92213(20)
Q: Discuss recent medical advances in the treatment of human infertility.
                                                                              (20 marks)
A: Female infertility :

     Disorders of ovulation -
         Various factors may Lead to irregular interval between successive ovulations or
         complete failure of the release of ovum from the ovary.
         The time of ovulation is associated with an increase of body temperature (luteal
         phase of the menstrual cycle). Also, the cervical mucus increases at the time of
         ovulation. Measurement of serum progesterone level (increases during
         ovulation) also helps to identify ovulation. Recently, ultrasound examination of
         ovaries is used to monitor the time of ovulation (with increase in follicular
         diameter). These indicate the ideal time of copulation.

           Abnormal hormonal levels preclude ovulation. Administration of anti-oestrogen
           drugs (stimulate the release of FSH and LH) can enhance the release of ovum.
           Progesterone also aids ovum release.

     Malfunction of the fallopian tube -
     Difficulty in ovum pick-up or transport of the ovum or the fertilized gamete along
     the tube (may due to tubular obstruction).
     Radio-opaque dye is injected into the uterine cavity and fallopian tubes. In
     X-rays, the dye should outline the cavity and will demonstrate any filling defects.
     The main treatment for tubular obstruction is by surgical intervention.
     Recent developments of in vitro fertilization and embryo transfer have provided
     an excellent alternative method of treatment for tubal damage. Oocytes
     harvested by micro-surgery are fertilized in vitro and the zygote is transferred
     into the uterine cavity for implantation. This technique can be used for both
     self-oocytes or donor-oocytes.

Abnormality of the uterine cavity -
   Lesions of the uterine cavity may interfere with implantation and conception.
   Pathological conditions are irreversible. In some cases, administration of
   hormone (e.g. oestrogen) may help the process of implantation.

Implication of surrogate mothers.

Male infertility :

Semen contents -
   Abnormal volume may indicate androgen deficiency or abnormal male
   accessory gland function or small testes. Sperm concentration and motility are
   good indications of male fertility. Treatment is possible in only a small
   proportion of infertile males. Reducing the testicular temperature by surgical
   operation on the veins of the spermatic cord may improve semen quality.
   Androgen therapy may be effective but is not reliable.
   Modern technique using chromosome analysis may identify the presence of
   abnormal karyotype, e.g. XXY or XYY.

Abnormal hormonal levels -
   Measurements of FSH level may differentiate between testicular damage and
   ductal obstructive disease. Abnormal LH and testosterone levels may indicate a
   pituitary or hypothalamic disorder. In some cases, hormone treatment may
   rectify the situation.

In cases when there is no prospect of improving the fertility of the male partner,
donor insemination may be explored. The establishment of frozen semen banks (i.e.
donor sperm) may be an alternative.
                                                                              (20)

				
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posted:8/17/2011
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