CHAPTER 8 : REPRODUCTION and DEVELOPMENT

112 BIOLOGY STUDENT’S COMPANION RESOURCES [SES DB014]

CHAPTER 8 : REPRODUCTION and DEVELOPMENT

SUBTOPIC 8.1: Types of Reproduction

LEARNING OUTCOMES:

a) Define sexual and asexual reproduction.

SUBTOPIC 8.2: Sexual Reproduction in Flowering Plants

LEARNING OUTCOMES:

a) State the general structures and functions of the reproductive organs in flowering plants

b) Describe the development of a pollen grain and formation of male gamete

c) Describe the development of ovule, embryo sac and formation of female gamete

d) Explain double fertilization in the formation of seed

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KEY POINT EXPLANATION NOTES

Definition of

sexual and

asexual

reproduction

Definition of asexual reproduction

• A process by which an individual inherits all of its genes from a

single parent thus, being genetically identical to the parent

Definition of sexual reproduction

• A process in which new organisms are created by combining the

genetic information from two individuals of different sexes via

fertilization

General

structures and

functions of the

reproductive

organs in

flowering plants

• The flower is a unique structure that is specialized for sexual

reproduction.

• The four types of floral organs are sepal, petal, stamen and carpel


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Floral organ Structure and function

Sepal • Sepal forms the outer and lower ring of

flowers

• Usually green and more leaf-like in

appearance

• Enclose the flower before it opens

• The group of sepals is called calyx

• Function is to cover and protect the young

flower bud

Petal • Petal are broad, flat and thin but vary in

shape and brightly colored

• The group of petals is called corolla

• Function is to attract animals pollinators to

the flower

Stamen • The male reproductive organs of flower that

consists of :

• Anther

• Filament

Functions :

• Anther contain pollen sacs that produce

pollen grains (male gametophyte)

• Filament is the stalk that holds the anther

Carpel • The female reproductive organs of flower

that consists of :

• Stigma (sticky structure on top)

• Style (neck like structure)

• Ovary

Functions :

• Stigma act as a landing platform for pollen

grains

• Style is the structure in which pollen tube

grows

• Ovary is the structure that contains one or

more ovules. Female gamete develops in its

ovule

Terminologies used :

• Microsporangium refers to the diploid (2n) pollen sac of anther

• Megasporangium refers to the diploid (2n) ovule in ovaries

• Male sporocyte : Diploid (2n) microsporocyte or microspore

mother cell

• Female sporocyte : Diploid (2n) megasporocyte or megaspore

mother cell

• Male spore : Haploid (n) microspore

• Female spore : Haploid (n) megaspore


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• Male gametophyte refers to haploid (n) pollen grain

• Female gametophyte refers to haploid (n) embryo sac

• Male gamete refers to haploid (n) sperm cell

• Female gamete refers to haploid (n) egg cell

Development of

a pollen grain

and formation of

male gamete

❖ Pollen grain (male gametophyte) forms in the pollen sac of

anther (microsporangium)

❖ Each anther contains four pollen sacs

❖ Each pollen sac contains numerous diploid (2n) microspore

mother cells (microsporocytes)

❖ Each diploid (2n) microsporocyte undergoes meiosis

❖ Produce 4 haploid (n) microspores (tetrad)

❖ Each microspore (n) undergoes mitosis

❖ Producing a generative cell (n) and a tube cell (n)

❖ Both cells are encased in haploid (n) immature pollen grain

❖ Pollen grain is surrounded by exine (the outer wall) and intine

(the inner layer)

❖ When pollination occur (pollen grains land on stigma), the

generative cell (n) divides by mitosis into two haploid (n)

sperm cells and now, pollen grain (n) is matured


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Development of

the ovule,

embryo sac and

the formation of

the female

gamete

❖ Diploid, 2n ovule (megasporangium) develop from carpel tissue

which is held by funicle.

❖ Young ovule contain nucellus. Nucellus is encased within two

layers of integuments

❖ Integuments form tiny hole at one end known as micropyle and

the other end is called chalaza

❖ In nucellus, diploid (2n) ovule

(megasporangium) contain one

megasporocyte / megaspore mother cell (2n)

❖ Each megasporocyte (2n) undergoes meiosis

❖ Producing four haploid (n) megaspores

❖ Three of the megaspores (n) degenerate


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❖ The one surviving megaspore (n) undergoes three times mitotic

division (without cytokinesis)

❖ Producing eight haploid nuclei within the haploid embryo sac

(female gametophyte)

❖ Eight haploid nuclei are arranged in groups of four nuclei at two

opposite poles

❖ One nucleus from each pole moves to the center, forming polar

nuclei (2n)

❖ Three haploid nuclei at the pole near to micropyle form 1

haploid egg cell (female gamete) and 2 haploid synergid cells

❖ 3 haploid nuclei at the pole away from micropyle, form the

antipodal cells

❖ Embryo sac thus consist of 8 haploid nuclei contained within 7

cells

Double

fertilization in

the formation of

seed

Definition of double fertilization :

The union of the 2 sperm cells (n) with different nuclei of the

embryo sac.

One haploid (n) sperm cell fertilize the egg cell (n) forming diploid

(2n) zygote. Other one sperm cell (n) fuses with polar nuclei (2n)

forming triploid (3n) primary endosperm

After double fertilization

each ovule develops into

seed. Ovary develops

into fruit. Endosperm

become food-storing

tissue of the seed.


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✓ Pollen grains land on stigma

✓ At the time of pollination, the pollen grain typically consists of

only 1 tube cell (n) and 1 generative cell (n)

✓ Pollen grain absorbs water and germinates by producing a

pollen tube (a long tube that delivers sperm cell to the embryo

sac).

✓ As the pollen tube elongates through the style, generative cell

(n) divides by mitosis and forms 2 sperm cells (n)

✓ The tube nucleus leads ahead of the 2 sperm cells as the tip of

pollen tube grows toward micropyle in response to chemical

attractants produced by the synergid cells.

✓ The arrival of pollen tube at micropyle initiates the death of one

of the two synergid cells, providing a passageway into embryo

sac.

✓ Tube nucleus and the 2 sperm cells (n) are then discharged from

pollen tube.

✓ Double fertilization occur after the 2 sperm cells (n) reach the

embryo sac.

✓ Near the time of double fertilization, tube nucleus, the other one

synergid cell and the antipodal cells degenerate

✓ In double fertilization, one haploid (n) sperm cell fertilize the

egg cell (n) forming diploid (2n) zygote.

✓ Other one sperm cell (n) fuses with polar nuclei (2n) forming

triploid (3n) primary endosperm.

polar nuclei



SUBTOPIC 8.3 : Human Reproductive System

LEARNING OUTCOMES:

a) Describe the structure of spermatozoa.

b) Describe the stages of spermatogenesis.

c) Describe the structure of the secondary oocyte.

d) Describe the stages of oogenesis.

e) Outline female reproductive cycle and its hormonal control:

i. Ovarian cycle

ii. Uterine/menstrual cycle

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Male Reproductive Organ : Testes (singular: testis) consist of many highly

coiled tubes called seminiferous tubule.

Seminiferous tubule is the site of spermatogenesis or sperms production.

Once produced, sperm cells swim inside the lumen of seminiferous tubule.

Structure of

spermatozoa

Four major parts of

spermatozoa :

✓ Head

✓ Neck

✓ Midpiece / middle

piece

✓ Tail


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Structure

of sperm

Characteristics

Head • Composed of a haploid nucleus

Acrosome • Located at the tip of head

• Consist of special vesicle that contain hydrolytic

enzyme (that help the sperm penetrate an ovum)

Neck • Short and have one pair of centriole

Midpiece • Contain mitochondria (provide ATP for the

movement of the sperm’s tail)

Tail • Is the sperm flagellum that move the sperm to the

ovum

Stages in

spermatogenesis

❖ Spermatogenesis begins during puberty

❖ Occurs in the seminiferous tubule of testes

1) In embryonic testis, diploid (2n) primordial germ cell differentiate into

spermatogonia (2n)

2) At puberty, each spermatogonia (2n) divide by mitosis forming type A

and type B spermatogonia (2n)

3) Type A spermatogonia (2n) remains at basement membrane to maintain

the layer of germinal cells – continue divide by mitosis producing large

number of spermatogonia (2n)

4) Type B spermatogonia (2n) differentiate into primary spermatocytes (2n)

5) Each primary spermatocyte (2n) undergo meiosis I forming 2 haploid (n)

secondary spermatocyte

6) Each secondary spermatocyte (n) undergo meiosis II forming 2 haploid

(n) spermatids – there are 4 spermatids (n) from 1 primary

spermatocytes (n). Spermatids are rounded, non-motile cells.

7) Spermatids (n) undergo spermiogenesis – Spermatid elongates, discard

excess cytoplasm to become lighter and form tail. Spermatids become

mature and motile spermatozoa / sperm cells


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Structure of

secondary

oocyte

❖ Female has a pair of ovaries.

❖ The outer layer of each ovary is packed with follicles

❖ Each follicle consist of an oocyte surrounded by a group of support cells.

❖ Every month, one primary follicle containing a primary oocyte develops

and matures into Graafian follicle.

❖ Secondary oocyte is found

inside matured Graafian follicle.

❖ During ovulation, secondary

oocyte is released from ovary.


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❖ Structures of secondary oocyte :

✓ Corona radiata (a group of granulosa cells) :

- Secretory cells in Graafian follicle that surrounds the

secondary oocyte.

- Supply nutrients to the developing oocyte.

✓ Zona pellucida

- A layer of glycoprotein that surrounds the plasma membrane

of secondary oocyte

✓ First polar body

- One small cell that is produced in meiosis I during the

development of an oocyte and finally degenerates

Stages of

oogenesis

The development of mature oocytes in ovaries starts during the

embryonic development

1) In embryonic ovaries, diploid (2n) primordial germ cells differentiate

into oogonia (2n)

2) Oogonia (2n) undergo mitosis forming large numbers of oogonia (2n)

3) Oogonia (2n) differentiate by increasing in size forming primary

oocyte (2n)

4) Each primary oocyte (2n) starts meiosis I but stop at Prophase I.

Primary oocyte (2n) enter resting stage until puberty

5) At puberty, primary oocytes (2n) complete Meiosis I forming small

haploid (n) first polar body and large secondary oocyte (n)

6) Secondary oocyte undergo Meiosis II but stop at metaphase II –

During ovulation, secondary oocyte is released from ovary into

Fallopian tube.

7) If secondary oocyte (n) is fertilized by sperm cell (n) then, meiosis II

is completed forming one large ovum (n) and small second polar

body (n). The second polar body will finally degenerate.


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Female

reproductive

cycles and its

hormonal

control


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❖ Ovarian Cycle (relate with ovaries) is divided into :

- Follicular phase (Day 1 – 13)

development of follicles

- Luteal phase (Day 15-28)

development and degeneration of corpus luteum

• Menstrual/Uterine Cycle (relate with endometrial wall of uterus)

is divided into :

- Menstrual flow phase (Day 1 – 5)

rupture of endometrial wall

- Proliferative phase (Day 6 – 14)

repairing of endometrial wall

- Secretory phase (Day 15 – 28)

maintain thickening of endometrial wall

• Follicular phase correspond with menstrual flow phase and

proliferative phase

• Luteal phase correspond with secretory phase


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Ovarian Cycle

1. Ovarian cycle begins when hypothalamus secrete gonadotropin-releasing

hormone (GnRH), which stimulate anterior pituitary

2. to secrete small amounts of follicle stimulating hormone (FSH) and

luteinizing hormone (LH)

3. FSH stimulate follicle growth, aided by LH

4. Follicles start to secrete estrogen. Estrogen concentration slowly rise during

most of the follicular phase. Low levels of estrogen inhibit secretion of

pituitary hormones, keeping levels of FSH and and LH relatively low.

5. Estrogen secretion by the follicles begin to rise steeply

6. The FSH and LH levels increase markedly. High level of estrogen

stimulates GnRH secretion by causing hypothalamus to increase the

secretion of GnRH. High level of estrogen also increases the secretion of

LH

7. LH surge (peak in LH level) stimulate maturation of follicle into Graafian

follicle. In response to FSH and LH surge, ovulation occur releasing the

secondary oocyte.

8. The luteal phase follows ovulation. LH stimulates formation of corpus

luteum from the ruptured follicle. Stimulated by LH, corpus luteum secrete

progesterone and estrogen. High level of estrogen and progesterone, exert

negative feedback on hypothalamus and anterior pituitary. Results in, low

level of FSH and LH in order to prevent maturation of another oocyte if

pregnancy occur.

If pregnancy does not occur, low level of GnRH at the end of luteal phase

cause corpus luteum to disintegrate, triggering sharp decline in estrogen and

progesterone. Low level of estrogen and progesterone cause the

hypothalamus and anterior pituitary is no longer inhibited. Anterior

pituitary secrete enough FSH to stimulate the growth of new follicles,

initiating next ovarian cycle.


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Uterine / Menstrual Cycle

9. Prior to ovulation, estrogen secreted in increasing amounts by growing

follicles stimulates the endometrium to thicken. This is the proliferative

phase of uterine cycle.

After ovulation, estrogen and progesterone secreted by corpus luteum

stimulate maintenance and further development of the uterine lining,

enlargement of arteries and growth of endometrial glands. This is the

secretory phase of uterine cycle. If an embryo has not implanted in

endometrium by the end of secretory phase, corpus luteum disintegrates.

10. Low level of estrogen and progesterone causes arteries in endometrium to

constrict and uterine lining disintegrates, releasing blood that is shed along

with endometrial tissue and fluid. The result is menstruation (menstrual

flow phase of uterine cycle). During this phase, a new set of ovarian

follicles begin to grow. The first day of menstrual flow is designated day 1

of the new female reproductive cycle.



SUBTOPIC 8.4 : Fertilization

LEARNING OUTCOMES :

a) Describe briefly the stages that lead to fertilization.

i. Capacitation

ii. Acrosomal reaction

iii. Fusion of sperm head membrane and oocyte

iv. Cortical reaction

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Stages that lead

to fertilization

➢ Haploid (n) secondary oocyte / ovum is fertilized by sperm cell (n) forming a

diploid (2n) zygote

➢ Occurs in the Fallopian tube

➢ Fertilization occurs in 4 stages :

i. Capacitation

ii. Acrosomal reaction

iii. Fusion of sperm head membrane and oocyte

iv. Cortical reaction

1) Capacitation

❖ Sperm activating process.

• Several changes in the outer surface of the sperm occur :

✓ Removal of glycoprotein layer, cholesterol and plasma protein

• Effects of capacitation :

✓ Motility of sperm cells increase

✓ Removal of glycoprotein layer allows the binding of sperm cell to

secondary oocyte / ovum

✓ Removal of cholesterol increase membrane fluidity

✓ Easier to release hydrolytic enzymes


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2) Acrosomal Reaction

• Before sperm cell reach the secondary oocyte,

– It moves through the layers of granulosa cells (corona radiata) and

reach zona pellucida

• Head of sperm cells bind to receptors on zona pellucida

– triggers the acrosome to burst, releasing hydrolytic enzyme

• The enzyme digest a path through zona pellucida to the surface of

secondary oocyte.

acrosomal vesicle hydrolytic enzyme

3) Fusion of Sperm Head Membrane and Oocyte

• Membrane proteins of sperm head bind to receptors on plasma membrane

of the secondary oocyte

• The two membrane fuse

– Releasing the nucleus and centrosome of sperm cells into the

cytoplasm of secondary oocyte


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4) Cortical Reaction

• Immediately after the penetration of one sperm cell into secondary oocyte,

cortical granules release enzymes into zona pellucida via exocytosis to

destroy the sperm cell receptor

• These enzymes also thicken and harden the zona pellucida forming

fertilization envelope

• The entry of sperm cell triggers the completion of meiosis II forming

haploid (n) ovum and second polar body (n)

• At this stage, the nuclei of the sperm cell and ovum is known as pronuclei

• Fusion of male pronuclei and female pronuclei produce a diploid (2n)

zygote.

CHAPTER 8 : REPRODUCTION and DEVELOPMENT

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