2010
3
(c ) Diagram 3.2 shows the involvement of cells produced by this type of cell
division in the formation of zygote.
When the
nucleus of the sperm(haploid) fuses with the nucleus of an ovum (haploid)
during fertilization, a zygote is formed.
d(i) 45
chromosomes or 44 + X chromosomes
(ii)
Turner’s syndrome
(ii)
The absence
of one X chromosome which is a sex chromosome
(iii) Radioactive radiation can cause
mutation of the chromosomes . As a result, only one chromosome is present
SPM Year 2009
Question
5
Diagram 5 shows a human foetus in his mother’s uterus.
(a) Name
the structures labeled R and S
R
Placenta
S Umbilical cord
(b) Explain
the composition of the blood that flows through the blood vessels in S.
The umbilical artery contains deoxygenated
blood and waste products such as urea whereas the umbilical vein contains
oxygenated blood and nutrients.
The umbilical artery carries blood from the
foetus to the mother whereas the umbilical vein carries blood from the mother
to the foetus.
(c ) The structure R
is needed to maintain the thickness of the uterine wall. Explain the statement.
Structure R will secrete
progesterone and estrogen which stimulate the uterine wall/endometrium to
become thicker to prepare for the implantation of the fertilized egg.
(d)(i) State the type of immunity the foetus gets from his
mother.
Passive natural immunity.
(ii)
Explain the importance of structure R to the body defence of the foetus.
Give protection to
the baby by allowing the diffusion of antibodies from the mother to the foetus
that gives immunity to some
diseases.
(e) Explain
why the foetus has a separate blood circulatory system from his mother?
·
Prevents
the mixing of blood groups of the mother and
the foetus which may be incompatible .Agglutination might occur if the
blood group of the foetus is different from the blood group of the mother.
·
Ensures
that the fine blood vessels of the foetus do not burst as a result of high
blood pressure caused by the flow of the mother’s blood
·
Prevents
certain harmful bacteria & their toxins from endangering the foetus
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