Chapter 4 Form 4

1. REPRODUCTION & GROWTH

2.  Gamete  production cell , sperm, ovum
 Meiosis  cell division
 Mitosis  cell division
 Zygote

3.  Organisms reproduce to ensure the
continuation of the species and to pass
down their genes to the next generation.
 There are two types of reproduction:
sexual reproduction and asexual
reproduction.

4. Sexual reproduction Asexual reproduction
New individual produced as New individual produced
a result of the fertilisation without involving the
between a male and female formation of gamete
gamete
Two individuals are involved Only one individual or parent
as parents is involved
The new individual The new individual is exactly
Inherits characteristics of like its parent
both parents

7.  Inhuman beings, the male gamete is the
sperm while the female gamete is the
ovum.
 Sperms are produced in the testes while
the ovum is produced in the ovary.
 The formation of sperms is called
spermatogenesis.
 Spermatogenesis occurs in the germinal
epithelium of the seminiferous tubules.

9.  Go

10. A spermatozoon or sperm cell consist of
head, the middle piece and the tail.
 Figure 4.4 shows a spermatozoon. The
head contains enzymes to help it penetrate
the ovum. The middle piece contains a
large number of mitochondria to provide
energy for the movement of the tail.

11.  The formation of ovum is called oogenesis.
 Oogenesis is regulated by hormones and
occurs in the germinal epithelium of the
ovary of a female even before birth.
 A cross section of the ovary is shown in
Figure 4.5.

14.  Go

16.  The meaning of menstruation
 The relationship between menstruation
and the menstrual cycle
 The importance of the menstrual cycle
 Hormones involved in the menstrual cycle
 Premenstrual syndrome and menopause

17.  Menstruation is the breakdown of the lining
of the uterus wall and its discharge through
the vagina with a small amount of blood
and some cells.

18.  Menstrual cycle consisting of follicle
development, ovulation, thickening of the
endometrium and menstruation.
 Thus, menstruation occurs during the
menstrual cycle

19.  Firstlyprepares the inner lining of the
uterus to receive a fertilised ovum.
 Secondly, it controls the development of
mature ova and ovulation, and ensures
that they occur simultaneously with the
thickening of the endometrium.
 In enabling the production of the female
gamete, the ovum, the menstrual cycle
propagation of the species.

20.  Two
groups of hormones involved in the
menstrual cycle
Hormones that control Hormones that control
changes in the ovaries changes in the uterus
• Gonadotrophin-releasing • Progesterone
hormone (GnRH) • Oestrogen
•Follicle-stimulating
hormone (FSH)
•Luteinising hormone (LH)

21. Hormone Site of secretion
Gonadotrophin-releasing hormone Hypothalamus
(GnRH)
Follicle-stimulating hormone (FSH) Anterior lobe of the pituitary gland
Luteinising hormone (LH) Anterior lobe of the pituitary gland
Oestrogen Follicle cells of the ovary
Progesterone Corpus luteum

23. 1 day before menstruation begins, the
hypothalamus produces GnRH.
 GnRH stimulates the anterior lobe of the
pituitary gland to secrete FSH and LH.
 FSH stimulates the growth of a follicle in
the ovary.
 The follicle produces the hormone,
oestrogen.

24.  At the beginning of its development, the
follicle is small and produces a small amount
of oestrogen.
 As the follicle grows, its oestrogen production
increases.
 Although rising, the oestrogen level is still
relatively low.
 The low oestrogen level exerts negative
feedback on the pituitary gland.
 This feedback keeps FSH and LH low during
development of the follicle ( days 1-11).

25.  As the time of ovulation draws near, the
maturing follicle increases its oestrogen
secretion and oestrogen levels begin to rise
steeply, and peak about day 12.
 This exerts positive feedback on the
hypothalamus, resulting in increased GnRH
secretion.
 High level of GnRH in turn cause FSH and LH
secterion to rise. Thus, the peak in oestrogen
level is followed by an FSH and LH peak that
occurs just prior to ovulation.

26.  The high LH level has many effect:
• Stimulates the completion of meiosis I by changing the
primary oocyte in the follicle into secondary oocyte.
• It then stimulates ovulation at about the 14th day of a
28 day menstrual cycle.
• It does this by enabling enzymes to break down the
follicle so that ovulation can take place.
• After ovulation, it promotes the development of the
corpus luteum.
• LH also stimulates the corpus leteum to secrete
progesterone and oestrogen.

27.  Oestrogen and progesterone are the two
female sex hormones that induce the
changes to the endometrium.
 Between 1 – 5 of the menstrual cycle:
• Low level of oestrogen and progresterone
• Causes the endometrium to break down and its
blood vessels to burst.
• Menstruation occurs

28.  Between days 5 – 13, higher oestrogen secretion by a
growing follicle in the ovary causes repair and growth of the
endometrium.
 Increasing level of progesterone secretion by the corpus
luteum between days 15 – 21 causes the endometrium to
further vascularised and thicken to 2 – 3 mm.
 The endometrium is now ready for implantation of the
embryo.
 If no implantation occurs, the corpus luteum begins to
degenerate after day 21 and the resulting of low level of
progesterone causes breakdown of the endometrium and
menstruation.
 If implantation occurs, the progesterone level continues to
rise and endometrium is further developed to support the
growing embryo.

29.  The menstrual cycle refers to the changes in
the uterus wall of a woman that take place
every 28 days, beginning from puberty (11
years old) until menopause (45-50 years old).
 The menstrual cycle is regulated by
hormones.
 The hormones involved in the menstrual cycle
are Follicle stimulating hormone (FSH),
oestrogen, luteinising hormone (LH) and
progesterone.

31.  The menstrual cycle occurs every 28 days.
 A girl starts to menstruate when she reaches
puberty.
 Menstruation is the blood discharged from the
vagina when the uterine lining breaks down.
 Menstruation occurs when there is no
fertilisation, and it lasts from 3 to 5 days. During
this period, FSH stimulates the development of the
follicle and the production of oestrogen to repair
the uterus lining.
 From day 5 to 13, the FSH and oestrogen level
continue to increase and a Graafian follicle is
formed.

32.  On day 13, the LH level increases rapidly
causing ovulation to take place on the day 14.
 From day 15 to 25, the corpus luteum formed
secretes progesterone which stimulates the
endometrium of the uterus to become even
thicker and filled with blood vessels.
 If the ovum is not fertilised, the uterus lining
breaks down and the corpus luteum
degenerates. This causes the progesterone level
to drop even further, followed by more
breakdown of the uterine lining, which is
discharged as menstrual flow.

33.  If the ovum is fertilised, the zygote
develops into an embryo, which implants
itself into the endometrium of the uterus.
 The corpus luteum continues to secrete
until the placenta is formed.
 Progestrone inhibits the production of FSH
and LH causing the menstrual cycle to
stop during pregnancy.

34.  Some woman suffer from PMS a few days
before menstruation, due to the imbalance
in the oestrogen and progesterone level.
 During this period, they are often
depressed, irritable and tired.
 Some suffer from headaches and
backaches while others gain weight easily.

35.  Menopause occurs when the menstrual cycle
stops.
 It occurs usually when a woman reaches 45
to 50 years of age.
 During the time, very little FSH is
produced, resulting in lower levels of
oestrogen.
 The follicles and the uterus walls do not
develop; there is no ovulation and the
menstrual cycle is disrupted. The
menstruation eventually stop.

36.  Millions of sperms are ejaculated into the
vagina during sexual intercourse.
 The sperms swim up pass the cervix into the
uterus towards the fallopian tubes.
 Once a sperm penetrates the ovum, it
discards its tail, and its nucleus moves
towards the nucleus of the ovum, fertilisation
occurs.
 Fertilisation is the fusion of the sperm nucleus
with the ovum nucleus to produce a zygote. It
occurs in the Fallopian tube.

38.  The development of the zygote begins after two
days, the zygote divides several times by mitosis
to form a solid mass of cells called the morula
followed by a blastula which is a fluid-filled sphere
with hundreds of cells around it.
 One end of the blastula is made up of a mass of
cells which continue to develop into embryo, while
the remaining cells surrounding the fluid becomes
the trophoblast which later develop into the
placenta.
 Once the blastula reaches the uterus, implantation
occurs.

39.  Implantation is the attaching of the blastula
onto the endometrium of the uterus.
 The embryo becomes the foetus after eight
weeks.
 The foetus is enclosed in an amniotic sac
filled with amniotic fluid to protect it from
any physical shock.

40.  There are three kinds of twins which are
identical twins, fraternal twins and
Siamese twins.

41. Formation of identical twins Formation of fraternal twins

42. Formation of identical twins Formation of fraternal twins
Formed when a sperm fertilises an Formed when two ova are released at
ovum to produce a zygote. The zygote the same time, and fertilised by two
formed divides into two zygotes which different sperms
develop into two foetuses in the uterus
The foetuse are identical as they were The foetuses are not identical as they
from the same zygote are formed from different sperms and
ova
The two foetuses share the same The two foetuses do not share the
placenta but have their own umbilical same placenta. They each have their
cord own placenta and their own umbilical
cords
They are genetically identical. They are genetically not identical.
Therefore they are always the same Therefore they can be the same or
sex different sex

43.  Siamese twins are formed when the mitotic
division that occurs during the formation of
identical twins is incomplete.
 As a result, the twins are joined at the
parts of the body where the incomplete
division occurs.

44.  During foetal development, the foetus
depends on the mother for food and
oxygen, and to get rid of its waste
products.
 The placenta helps in the exchange of
substances between the foetus and the
mother.
 The foetus is connected to the placenta by
the umbilical cord.

46.  The placenta arises from the chorion
(trophoblast at the embryo stage) which
extends fingerlike projection called villi, into
the endometrium to make contact with the
uterine blood.
 The finger-like villi help to increase the
surface area for the exchange of nutrients.
 The membrane of the chorionic villi separates
the foetal blood from the mother’s blood.

47.  Diffusion of nutrients occur across the
membrane of the chorion.
 The umbilical arteries carry deoxygenated
blood, carbon dioxide and waste products
from the foetus to the placenta while the
umbilical vein carries oxygenated
blood, nutrients, antibodies and hormones
from the mother’s artery to the placenta.

48.  Newly married couples should start family
planning to prepare themselves for
parenthood. Family planning helps them
decide when to start a family and how
many children they want to have.
 If they do not want to start a family yet,
they can prevent pregnancy by using the
various method of contraception available
today, made possible by the advancement
in science and technology.

49.  Avoid sex during the fertile period
 Insert an intrauterine device (IUD) into the uterus (by a
doctor)
 Place diaphragm (domestic shaped structure that is
made of rubber) at the cervix
 Use a condom
 Take oral contraceptives pills (prescribed by a doctor)
 Apply spermicides to the vagina to kill the sperms
 Vasectomy for men where the vas deferens in a man’s
body are cut surgically.
 Tubal ligation in woman, where the Fallopian tubes are
surgically cut off to pevent pregnancy.

50.  Blocked Fallopian tubes
 Difficulty in implantation of zygote
 Inability to produce an ovum due to
hormonal imbalance
 Low sperm count

51.  Sperm bank
 a sperm bank is a place where sperms are frozen and
stored in liquid nitrogen under -2000C.
 Artificial insemination
 sperms are collected and injected into the uterus of a
female during her fertile period.
 In vitro fertilisation
 This method is used for females with blocked Fallopian
tubes. The ovum is extracted from the ovary during
ovulation and placed in a Petri dish containing the
husband’s sperms. After fertilisation, the embryo is
implanted into the uterus where it continues its
development. The baby is called a test tube baby.

52.  Surrogate mother
 a surrogate mother is a woman who
gives birth to a baby for another woman
who is unable to conceive due to
abnormalities in the uterus. In vitro
fertilisation is carried out using the ovum
and sperms of the parents but the embryo
is implanted into the uterus of the
surrogate mother.

53.  Sexually-transmitted diseases are
transmitted by sexual contact. They are
also known as venereal diseases.
 Example of sexually transmitted diseases
are syphilis, gonorrhea and AIDS.

57.  Inflowering plants or angiosperms, both
male and female gametes are produced in
flowers.

58.  The male reproductive structures in a
flower are the stamens.
 Each stamen consists of two parts that is:
•The filament: a little stalk which holds the anther
•The anther: the place where the pollen grains are
produced

59. The female reproductive structures are the carpel
which consists of three parts, that is
• A stigma  a sticky surface at the apex of the
style
• A style  a stalk that join the stigma to the
ovary
• An ovary  the structure that carries the ovule

61.  The anther has four pollen sacs
 Each pollen sac contains hundred of cells
called pollen mother cell.
Pollen mother cell (2n)
meiosis
4 Microspores, (n)
mitosis
Tube nucleus and generative nucleus
develop
Pollen grains
* Microspores  male gametophyte

63. (a) Embryo sac mother cell in the ovule undergoes meiosis and forms
four haploid megaspores.
(b) Three of the four megaspores die, leaving one megaspore in the
ovule.
(c) The functional megaspores enlarges to many times its original size,
filling up most of the ovule.
(d) The nucleus of the megaspores then undergoes three mitotic
division and form eight haploid nuclei.
* Megaspores  female gametophyte

64.  Three of the eight nuclei migrate to one
end of the cell forming antipodal cells.
 Another two move to the centre to form
polar nuclei.
 The last three nuclei at the other end,
nearest the ovule opening, form an egg
cell clamped by two synergid cells.
 The structure thus formed is known as the
embryo sac.

66.  Pollination: the process in which ripe
pollen from an anther are transferred into a
stigma.
 The landing of a pollen grain on a stigma
starts the fertilisation process.
 Sugar in the stigma stimulate the pollen
grain to germinate and form a tube known
as a pollen tube.
 The pollen tube grows into the style
towards the ovule.

67.  At the same time, the generative nucleus
divides by mitosis into two male gamete
nuclei.
 Led by the nucleus tube, the male nuclei
move down the pollen tube.
 When the pollen tube reaches the ovary, it
penetrate the ovule through the micropyle.
 The nucleus tube disintegrates leaving a clear
passage for the male nuclei to enter the
embryo sac.

68.  One of the male nuclei fuses with the egg cell to
form a diploid zygote (2n).
 The other male nucleus moves further in to fuse
with the two polar nuclei forming a triploid nucleus
(3n).
 The triploid nucleus then divides to form a special
nutritive tissue called the endosperm.
 The zygote itself divides and grows into an
embryo.
 The outer layer of the ovule loses moisture and
develops a hard seed coat.
 The seed coat protects the embryo and its
endosperm.

70.  The process of fertilisation in the ovule
mostly happen twice in flowering plants.
 The first time it happens, a diploid zygote
is formed.
 The second time it happens, a triploid
nucleus is formed.
 Thus, the process is known as double
fertilisation.

71.  After
fertilisation, the ovary and its
constituents develops as shown below:
• Ovule  seed
• Wall of ovule  seed coat
• Zygote  embryo
• Ovary wall  fruit wall
• Ovary  fruit

72.  Double fertilisation helps flowering plants
to survive because each new generation
carries its own temporary food store in the
endosperm of the seed.
 The endosperm provides the nutrition and
energy that is needed by the embryo for its
growth.

73.  Learning outcomes:
• The parameter for measuring growth
• The sigmoid growth curve of an organism
• The growth curve of humans
• The growth curve of an insects

74.  The meaning of growth:
• It can be described as the irreversible increase in
body size, mass and number of cells in an
organisms.
• The latter are quantitative changes that occurs
during growth.
• However, growth also involves qualitative changes
to cells.

75.  Growth in multicellular organism can be estimated by
measuring some parameters of organism like
length, height, volume, fresh mass and dry mass over
a certain period of time
 Height or length, is convenient but the problem is
inaccurate. A tree for example while not increasing in
height, may continue to grow in diameter by growing
sideways.
 Volume: more accurate but is frequently not practical to
measure.
 Fresh mass: the measurement is inaccurate because
involve temporary changes in water content.
 Dry mass: mass of organism after all moisture has
been removed by heating.

76.  When a growth parameter such as height
or mass of an organism is plotted against
time, a growth curve is obtained.
 The pattern of growth is about the same
for most organisms.
 The curve is S-shaped and known as a
sigmoid curve.
 Link

78. • When the length of insects is
plotted against the time, it
shows very unusual, intermittent
growth.
• The graph has a staircase shape.
• The horizontal part indicate zero
growth. It correspond to the time
when the insect stops growing.
• The five vertical lines of curve are
sudden growth spurts. This
correspond to the time when the
nymphs cast away their old
external skeleton and new, larger
ones. This process is called
moulting or ecdysis.
• Each young stage between moults
• is called an instar.

79.  Learning outcomes:
• The meaning of growth
• The types of growth in plants
• Primary growth tissue
• Secondary growth tissue
• The importance of primary and secondary growth
• The economic importance of plants that undergo
secondary growth

80.  Growth can be described as the irreversible
increase in body size, mass and number of cells in
an organism.
 Quantitative changes : changes in the number of
cells.
 Qualitative changes : changes in shape, function
and complexity specialized with specialisation.
 The process of growth can be divided into three
stages:
• Cell division stage
• Cell enlargement stage
• Cell differentiation stage

82.  There are two types of growth in plants, namely
primary growth and secondary growth.
 Primary growth : the growth that occurs after
germination
 Secondary growth
 the growth in diameter of the stem, root and
trunk of plants
 the growth pattern is an annual series of
sigmoid curves
 such plants show unlimited growth, that is, they
grow continuously throughout their lives, and thus,
their growth curves never flatten out.

83.  Perennials  plants that continue their
growth from year to year
 Annuals  plant that complete their whole
life cycle in a year
 Biennials  plants that have two-year life
cycle

84.  There are some
plants that do not
show secondary
growth and live as
annuals and
biennials, for
example, the pea
plant, Pisum
sativum.

85.  Primary growth begins by rapid cell division in
a group of cells at the extreme tip of the stem
and root.
 This group of cells divides by mitosis and
forms the apical meristem.
 Growth at apical meristem leads to the
formation of mature primary tissue of the
stem and root such as the cortex and primary
phloem and primary xilem in the vascular
bundle.
 This results in an increase in length of the
stem and root.

87.  After primary growth complete, secondary
growth continues in woody plants like trees
and shrubs.
 In non-woody plants like herbs, no
secondary growth occurs.
 Secondary growth is the result of cell
divisions in the lateral meristems of both
stem and the root.
 The lateral meristem are the vascular
cambium and cork cambium.

88.  The vascular cambium located between
primary phloem and primary xilem in
vascular bundles
 The cork cambium  located immediately
below the epidermis.

89. Parenchyma cells divide actively
The vascular cambium join up to form ring
The cell of cambium ring divide
Outer cells become the secondary phloem
tissue and secondary xylem tissue
Smaller ring in the rings form medullary rays
connecting the cortex with the pith

92.  Secondary xylem develops thick walls
with deposition lignin. It then becomes
wood.
 Similarly, the cork cambium beneath the
epidermis divides actively to form the outer
cork and the inner secondary cortex.
 The external cork layer forms a protective
bark at the surface of the woody stem.

93.  In trees of temperate climates, the activity of
the vascular cambium is not uniform
throughout the year.
 In spring  the cambium is more active and
form larger and thinner-walled xylem vessels
(spring wood)
 In autumn  the cambium is less active and
forms narrower vessels and fibers (autumn
wood)
 These two kind of wood are seen together in
transverse sections of the stems, as
concentric rings called annual growth rings.

94.  Each annual ring
indicates one year’s
growth.
 Hence, by counting the
total number of annual
rings, the age of the tree
can be determined.
 Trees in tropical countries
like Malaysia, however,
do dot show clear annual
rings because the climate
is not distinctly seasonal.

95.  Primary growth:
• Responsible for the increase in height of a plant
• It anchors the plant firmly to the soil
 Secondary growth:
• Enables the plants to live longer and grow throughout
their life
• They are able to support their increasing weight
• The thickened cork and bark reduce the evaporation of
water from the surface of the stem
• Protect the plants attack by insects and parasitic fungi
• They also guard the plant body against variation in
external temperature.

96.  The plant have commercial value and produce the
most valuable timber, eg: meranti, kapur, keriung
and cengal.
 The timber may be used as beams for buildings,
for durable fencing and high-quality furniture.
 The wood and bark of plants can be used to
produce useful resins and oils.
 Hibiscus, yellow bells and bougainvillea are
valuable as ornamental plants in gardens and
parks.
 Durian tree, mango tree and rambutan tree
produce a substantial quantity of fruits for local
consumption and for export.