Question
(a) Mitosis is a type of nuclear division.
Fig. 5.1 is a series of photomicrographs showing a cell dividing by mitosis.
(i) State the change that has occurred to the mass of DNA immediately before mitosis in
Fig. 5.1.
(ii) Estimate the time when the chromosomes shown in Fig. 5.1 begin to separate.
(b) Meiosis is another type of nuclear division.
Describe how the nuclei in cells produced by meiosis differ from the nuclei in cells produced
by mitosis.
(c) Stem cells divide by mitosis during the growth of an embryo.
Describe the role of stem cells in the growth of an embryo.
(d) An embryo develops into a fetus.
Outline the processes of labour and birth.
Answer/Explanation
Answer:
(a)
(i) doubles ;
(ii) 34–39 minutes ;
(b) are genetically different (from each other and the parent cells) ;
(produce) haploid (nuclei) ;
ref. to reduction division / chromosome number being halved ;
(c) ref. to unspecialised cells ;
that can become specialised ;
ref. to expression of genes in specialised cells ;
AVP ; e.g. continually divide
(d) breaking of the amniotic sac ;
amniotic fluid is released ;
contraction of (the muscles in the) uterus (wall) ;
dilation of the cervix ;
passage through the vagina ;
(tying and) cutting the umbilical cord ;
delivery of the afterbirth / placenta ;
AVP ;