Page 152 - SUBSEC October 2017_Neat

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02107020/CAPE/SPEC/KMS 2017
BIOLOGY
UNIT 1 – PAPER 02
KEY AND MARK SCHEME
Question 3 cont’d

(b) Structure of oocyte

1. Follicle cells – form a protective layer around the oocyte
2. Zona pellucida – a clear jelly-like protective layer through
which spermatozoa must penetrate
3. Oocyte – contains chromosomes which still have to complete their
meitotic divisions

1 mark for each part annotated = 3 marks
[3 marks]

(c) (i) Fertilization

1. The pH of the vagina is low and tends to kill sperms. They
are able to move as a mass through the cervix because the
semen coagulates immediately after ejaculation.
2. The sperms must travel a far distance to the ovarian end of
the oviduct. They are aided by the contractions of the
cervix, uterus and oviduct.
3. During the fertile period, the cervical mucus forms channels
for the mass of sperms to swim through.
4. Sperms must go through a process called capacitation –
glycoproteins are removed from the outer surface and the
membranes become more permeable to calcium ions
5. The calcium ions increase their motility, and help the
release of enzymes from the acrosome.
6. The enzymes digest a pathway through the follicle cells to
the surface membrane of the oocyte.
7. The membranes of the sperm and oocyte fuse.

1 mark each = 7 marks [7 marks]

(ii) Contraceptives

1. Barrier – condom/femidom placed over the penis/into the
vagina which prevents sperms from entering the vagina during
intercourse
2. Diaphragm/cap – placed over the cervix to prevent sperms
from entering the cervix
3. Intrauterine device – releases progesterone which prevents
implantation of the fertilized egg (controls the lining of
the uterus)
4. Spermicides – chemicals that destroy the sperms to prevent
them from reaching the egg
5. Contraceptive pill – contains one or both ovarian hormone to
prevent ovulation

3 marks for each of 4 methods = 12 marks
[12 marks]

Total 30 marks