CHAPTER 8 REPRODUCTION AND DEVELOPMENT

BASIC UNDERSTANDING OF BIOLOGY FOUNDATION SEM 1: DB014

CHAPTER 8: REPRODUCTION AND DEVELOPMENT

8.1 REPRODUCTION IN PLANT AND ANIMALS

(a) Definition sexual and asexual reproduction

Sexual Reproduction:

• Reproduction that involves fertilization between male and female gametes.
• Occurs in animals and plants

Asexual Reproduction:

• Reproduction that does not involve fertilization between male and female gametes.
• Offspring are derived from a single parent without any fusion of egg and sperm.
• Occurs in animals and plants; especially plants and lower animals. Rarely occur in higher animals
• Types:

 Parthenogenesis
 Sporulation
 Budding
 Binary Fission
 Regeneration
 Vegetative Propagation

8.2 SEXUAL REPRODUCTION IN FLOWERING PLANTS

(a) Structure and function of flower:

Sepal  Enclose and protect unopened floral buds
Petal  Often brightly colored, attract animal pollinators (i.e. birds, bees)
Stamen  The male reproductive organ of a flower. Consist of:

Carpel  Filament (stalk)

 Anther (pollen-producing structure)
 The female reproductive organ of a flower. Consists of:

 Stigma (pollen grain landing site)

 Style (a neck-like structure through which pollen tube grows)

 Ovary (an enlarged structure that contains one or more ovules)

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(b) DEVELOPMENT OF A POLLEN GRAIN AND FORMATION OF MALE GAMETE

Development of a pollen grain and formation of
male gamete

 Pollen grain develops in the anther.
 Each anther consists of 4 microsporangia/ pollen sacs.
 Within each microsporangium/ pollen sac contains many

diploid microsporocytes/ microspore mother cells (2n)
 Each microsporocyte undergoes meiosis to produce 4 haploid

microspores (n)
 Each microspore divides by mitosis (with cytokinesis)

producing a haploid male gametophyte (pollen grain) which
consist of two cells:

(i) generative cell
(ii) tube cell
 Pollen grain has a thick, resistant wall called exine and intine.
 During pollination, pollen grain transferred from anther to
stigma. Pollen grain undergoes germination.
 Tube cells produce pollen tube, which penetrates the

style and grows to reach the micropyle.
 The nucleus of generative cell divides by mitosis into

two sperms (male gamete). Pollen grains now become
mature gametophyte.

(c) DEVELOPMENT OF OVULE, EMBRYO SAC AND FORMATION OF FEMALE GAMETE

Development of ovule, embryo sac and formation of female
gamete

 Female gametophyte/ embryo sac develops in the ovule
(megasporangium) of the ovary. Within ovary, one or more
ovules develop.
 Each ovule attached to ovary wall by short stalk (funicle)
 Main body of ovule is nucellus, which enclosed and
protected by 2 sheaths called integuments.
 Micropyle (small pore) is at one end of the ovule, the
other end is chalaza.

 Each ovule/ megasporangium contain diploid

megasporocyte/ megaspore mother cells (2n)
 Each megasporocyte undergoes meiosis producing 4 haploid

megaspores (n)
 3 of them degenerates and one surviving haploid

megaspore undergoes 3 times mitosis producing embryo
sac containing 8 haploid nuclei.
 2 nuclei move to the centre, forming polar nuclei
 3 nuclei located near the micropyle: one becomes egg cell

and another two become synergid cells. Synergids
function to attract and guide the pollen tube.
 3 nuclei become antipodal cells with unknown function

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(d) DOUBLE FERTILIZATION IN THE FORMATION OF SEED

DOUBLE FERTILIZATION IN PLANT

Double fertilization in flowering plant

1. During pollination, pollen grain is transferred from anther to stigma.
2. The pollination assisted by pollinating agents such as wind, water or insects.
3. Pollen grain absorbs the moisture (water) and germinates.
4. The tube cell produces a pollen tube which grows down the style towards the ovary.
5. As the pollen tube grows, the generative cell divides by mitosis to form two male gametes (sperms).
6. In response to chemical attractant from synergids, the tip of the pollen tube grows toward the micropyle.
7. When the pollen tube reaches the micropyle, the tube nucleus degenerates. The tip of pollen tube burst and

discharges two sperms into the embryo sac.
8. Double fertilization occurs. Both of the male gametes fuse with nuclei in the embryo sac.
9. Double fertilization means that, one sperm cell fuses with the egg cell to produce a diploid zygote (2n).

While other sperm fuses with two polar nuclei to form a triploid endosperm (3n).
10. After double fertilization, ovule develops into seed; integument becomes the seed coat/ testa while ovary

develops into fruit.
11. Zygote will develop into embryo.
12. Triploid endosperm divides mitotically into nutrient tissue rich in lipids, proteins and carbohydrates. It

functions as food storing tissue that nourishes the growing embryo.

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8.3 HUMAN REPRODUCTIVE SYSTEM

(a) STRUCTURE OF SPERMATOZOA

Structure Description
Head - Contain haploid nucleus and

Neck acrosome
Middle - Acrosome is cap-like structure that
/midpiece
Tail cover the nucleus, contain
hydrolytic enzymes to penetrate
egg
Joins head with middle piece
Contain mitochondria to provide
energy for movement
Contain flagellum for movement

(b) STAGES OF SPERMATOGENESIS AND ITS HORMONAL CONTROL
 Spermatogenesis is the process of sperm formation and development that occurs in the seminiferous

tubule of the testis.
 It begins in male at puberty and continuous throughout life.
 Each primary spermatocyte (2n) undergoes meiosis to produce 4 spermatids (n). Spermatids mature into

spermatozoa (sperms).

Cross section of seminiferous tubules in testis

showing spermatogenesis process.

- Spermatogenesis process begins at the
wall of seminiferous tubules and ends

in the lumen.
- The sperms produced will be stored in

the epididymis.

Spermatogenesis Spermatogenes in the seminiferous tubule of the
testis

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1. Primordial germ cells (2n) in male embryos are divided by mitosis to form spermatogonia (2n)
2. Each spermatogonium(2n) divide by mitosis to produce large amount of spermatogonia (2n)
3. Some spermatogonia (2n) remain near the basement of the seminiferous tubules for future sperm

production. The rest grows, enlarge and differentiate into primary spermatocytes (2n).
4. Primary spermatocytes (2n) undergo meiosis I to form TWO secondary spermatocytes (n).
5. Each secondary spermatocyte (n) undergoes meiosis II to form FOUR spermatids (n).
6. Until this stage, the cell remains in contact by cytoplasmic bridge for synchronized production of sperm.
7. Each spermatid moves to the lumen of the seminiferous tubule to undergo differentiation (spermiogenesis)

to form mature spermatozoa / sperm cell (n).
8. The sperm travel along the tubule into epididymis where they become motile.

THE ROLE OF HORMONES IN SPERMATOGENESIS

Spermatogenesis in the seminiferous tubules of testis

1. At puberty, hypothalamus secretes Gonadotropin-Releasing Hormone, GnRH.
2. GnRH stimulates the anterior pituitary gland to secrete Follicle-Stimulating Hormone, FSH and

Luteinizing Hormone, LH.
3. FSH acts on sertoli cell to facilitate spermatogenesis by support and nourish (provide nutrients)

developing sperm. Sertoli cells also secrete Inhibin, which reduces FSH secretion by negative feedback.
4. LH acts on Leydig cell to secrete testosterone. Function of testosterone:

(i)-Stimulates the maturation of secondary spermatocytes through meiosis and differentiation to
spermatozoa.
(ii)-Develop and maintains the male secondary sex characteristics.
(iii)-Control the growth of vas eferens, epididymis, vas deferens, testis, scrotum and penis.
5. High level of testosterone will exert negative feedback on the secretion of LH by anterior pituitary and
GnRH from hypothalamus respectively.
6. Inhibin from sertoli cell also inhibits secretion of FSH by anterior pituitary.

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1. In high levels of testosterone:
(a) Impulse send to hypothalamus to reduce
secretion of GnRH
(b) Impulse send to anterior pituitary glands to
block the action of GnRH

2. Therefore, decrease in GnRH will inhibit LH secretion.
3. FSH secretion also subject to negative feedback.
4. Once the degree of spermatogenesis required is

achieved, Sertoli cells secrete inhibin.
5. Inhibin acts on anterior pituitary gland to reduce FSH

secretion.

Role of hormones in spermatogenesis

(c) STRUCTURE OF THE SECONDARY OOCYTE

 Size: 100-120µm diameter. Structure of secondary oocyte
 Consists of plasma membrane, cytoplasm and nucleus.
 The haploid nuclei (arrested at metaphase II) sits

inside a cell with a large volume of cytoplasm.
 The secondary oocyte is produced along with the first

polar body as a result of the first meiotic division.
 There are cortical granules just beneath the plasma

membrane that serves a critical function during

fertilization (contain enzyme that prevent polyspermy

during fertilization)
 Secondary oocyte is covered by a thick glycoprotein

shell called the zona pellucida (jelly-like coat).
 First polar body is located in zona pellucida.
 Around the outside are the follicular cells called

corona radiata. Corona radiata is made up of the

granulosa cells of the follicle.
 Cells of corona radiata protect the secondary oocyte as

it passes through the ruptured follicular wall

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OOGENESIS
-The process of secondary oocyte production in ovary.
-Is not a continuous process:

1. Begins before birth but arrested at prophase I.
2. Resumes under hormonal control at puberty but until metaphase II.
3. Only completed the meiosis II if fertilized by sperm

(d) THE STAGES OF OOGENESIS (FORMATION OF EGG CELL IN OVARY)
a) Oogenesis takes place in the ovary.
During fetus development, primordial
germ cell of female embryo divides by
mitosis to form oogonia (2n).

b) Each oogonium (2n) divides by mitosis
and differentiates into primary oocytes
(2n) and then begins meiosis I but
arrested at prophase I before birth.

Oogenesis process c) Beginning at puberty, anterior pituitary
gland secretes FSH to stimulate the
development of follicles in the ovary.

d) Of these follicles, only one matures at
each menstrual cycle which is known as
Graafian follicle.

e) Primary oocyte completing meiosis I.
Unequal cytokinesis after meiosis I
produces bigger haploid secondary
oocytes (n) and first polar body.

f) Secondary oocyte continues meiosis II,
but stop at metaphase II.

g) Thus, secondary oocyte released from
ovary during ovulation is arrested in
metaphase II.

h) Penetration of the secondary oocyte by
the sperm triggers completion of
meiosis II.

i) This produces an ovum and secondary
polar body. The first polar body may
divide to form two polar bodies. All
polar bodies are eventually degenerate.
If the secondary oocyte is not fertilized
within a short time, it degenerates in the
fallopian tube.

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(e) FEMALE REPRODUCTIVE CYCLE AND ITS HORMONAL CONTROL

Ovarian cycle Uterine/ menstrual cycle
 A series of event in the ovaries that occurs during  Concurrent series of changes in the endometrium

and after maturation of oocyte. of uterus to prepare it for the arrival of fertilized
 Average 28 days each cycle
 3 phases: ovum until birth
 Average 28 days each cycle
 3 phases:

Phases Event Phases Event

Follicular Follicle begins to develop Menstruation Rupture of endometrial wall

Ovulation Release of secondary oocyte from phase

matured follicle Proliferative Regeneration of endometrial wall

Only one secondary oocyte is released phase

each month by one of the ovaries Secretory Thickening and maintenance of

Luteal Development/ degeneration of corpus phase endometrial wall

luteum

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Roles of hormone in both cycles

1. The reproductive cycle begins with the release of GnRH from the hypothalamus.

2. GnRH stimulates the anterior pituitary to secrete FSH and LH.

3. FSH stimulates one of primary follicle in the ovary to become Graafian follicles.

4. The cells of the growing follicles secrete estrogen. There is slow rise in estrogen secreted during the

follicular phase. Estrogen stimulates the thickening of uterine wall.

5. When estrogen secretion rises steeply, it exerts a positive feedback on hypothalamus. It causes the

hypothalamus to increase secretion of GnRH while anterior pituitary produces large amount of LH.

6. It causes the LH levels increase markedly.

7. Surge increase of LH stimulates ovulation. Ovulation is a process in which the Graafian follicle will

burst, releasing the secondary oocyte into the Fallopian tube.

8. After ovulation, LH also stimulates transformation of the ruptured follicle into corpus luteum.

9. Two events that may occur:

If pregnancy occur (implantation occur) If pregnancy does not occur (no implantation)

 LH also stimulates the corpus luteum to secrete  Corpus luteum degenerates
 Estrogen and progesterone level decline, cause
progesterone and little estrogen to continued
constriction of artery in endometrium, thus
development and maintenance of the uterine
lower the supply of blood and oxygen
lining.  Cells of the endometrium die and
 This process is continued if pregnancy occurs to
disintegrate. Blood and endometrial tissue is
ensure the zygote can implant.
 Actually, hCG from developing placenta maintain shed/ discharged through menstruation
 Decrease in estrogen & progesterone level will
the corpus luteum until placenta is fully
also cause anterior pituitary to secrete enough
developed
 By the time placenta is fully developed, it FSH to stimulate the growth of new follicle in

begins to secrete estrogen and progesterone the ovary
 Corpus luteum is degenerated
 High concentration of estrogen and progesterone

has a negative feedback effect on the

hypothalamus/anterior pituitary. It Inhibits

secretion of FSH and LH.

Graph of the hormone if pregnancy occur:

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8.4 FERTILIZATION

FERTILIZATION
 The process of the fusion of a male and female gametes or fusion of sperm and egg. The fusion takes place in

the oviduct/ fallopian tube.
 During fertilization, genetic material from a haploid sperm cell and haploid secondary oocyte merge to form a

single diploid zygote.

(a) THE STAGES THAT LEAD TO FERTILIZATION

Stage 1: Capacitation
1. Sperm that reach oocyte within minutes after ejaculation are not able to fertilize it until about 7 hours

later. During this time, it undergoes capacitation.
 Undergoes maturation process
 a series of functional changes in sperm’s head and prepare its plasma membrane to fuse with

secondary oocyte’s plasma membrane.
 Sperm acts upon secretion in the female reproductive tract that result in removal of cholesterol,

glycoproteins and proteins from the plasma membrane of the sperm’s head.

Stage 2: Acrosomal reaction
2. Strong tail movement of sperm penetrates corona radiata.
3. When the sperm head penetrates the corona radiata, it will come in contact with zona pellucida.
4. Sperm will bind to receptor molecules (ZP3) in zona pellucida.
5. It will trigger acrosomal reaction
6. Acrosome at sperm head will released acrosomal enzymes (hyaluronidase and proteolytic enzyme) to

digest glycoprotein of zona pellucida

Stage 3: Fusion of sperm head membrane and oocyte membrane
7. Only the first sperm that penetrate the entire zona pellucida and reach the plasma membrane of secondary

oocyte’s fuses with the oocyte
8. The sperm nucleus taken into the cytoplasm of the secondary oocyte. (This is NOT the fertilization)
9. Once sperm cell enters secondary oocyte, secondary oocyte complete meiosis II forming ovum and

second polar body
10. Sperm nucleus develop to male pronucleus and ovum nucleus develop into female pronucleus
11. Male pronucleus and female pronucleus fuse to form single diploid nucleus
12. The fertilized ovum now called zygote (2n).

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Stage 4: Cortical reaction
13. Within a few seconds, fusion causes the plasma membrane of secondary oocyte to be depolarized which

acts as a fast block to polyspermy
14. Depolarization triggers cortical reaction - Cortical granules inside plasma membrane released enzymes

by exocytosis.
15. Enzymes from cortical granules cause cross-linking of glycoprotein in the zona pellucida, harden the

zona pellucida
16. Thus, preventing the entry of any more sperm/ polyspermy. Secondary oocyte completes its second

meiotic division
17. The male nucleus and the female nucleus will fuse together to form a diploid zygote

END OF TOPIC

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