Sexual Reproduction in Flowering Plants full note

BIOLOGY UNIT BIOLOGY SB015
KOLEJ MATRIKULASI MELAKA SEMESTER 1
SESSION 2020/2021

CHAPTER 9:

REPRODUCTION AND
DEVELOPMENT

9.1 SEXUAL REPRODUCTION IN FLOWERING

PLANTS

9.2 HUMAN REPRODUCTIVE SYSTEM

9.3 FERTILIZATION AND FOETAL DEVELOPMENT

9.4 ROLES OF HORMONES DURING PREGNANCY

AND PARTURITION

JPU PSPM SEMESTER I:

Paper 1 Paper 2

7 marks 17 marks

CHAPTER : MOLECULES OF LIFE BIOLOGY SB015
SEMESTER 1
SESSION 2020/2021

9.1 SEXUAL REPRODUCTION IN FLOWERING
PLANTS

LEARNING OUTCOMES

a) State and define the terminologies involve in
gamete formation in flowering plants

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

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

d) Explain double fertilization in the formation of
seed.

Male gamete formation : Terminologies

1. Microsporangium @ Pollen Sac

Microsporangia @ pollen sac contains diploid
microsporocytes (2n) which develops into pollen

grains.

Male gamete formation : Terminologies

2. Microsporocyte @ Microspore Mother Cell

• Diploid cells within the
microsporangia which
undergoes meiosis,
forming four haploid
microspores (n) @
tetrad.

Male gamete formation : Terminologies

3. Microspore @ Tetrad
• Haploid spore which then develops

into pollen grain (male
gametophyte)

4. Male gametophyte (pollen grain)
• In seed plants, a pollen grain is a microscopic

structure that contains generative cell and tube cell
enclosed within thick resistance wall (sporopollenin)

Male gamete formation : Terminologies

5. Generative cell

Haploid cell tha divides by
mitosis forming two male
gametes (sperm cells)

6. Tube cell

Haploid cell that develops into
pollen tube, which delivers the
male gametes to the egg cell.

Female gamete formation : Terminologies

1. Megasporangium @ ovule

• A structure that develops within the
ovary of a seed plant and contains
diploid megasporocytes (2n)

2. Megasporocyte @ Megaspore mother cell

• A diploid cell that divide by meiosis producing four
haploid megaspores (n).

Female gamete formation : Terminologies

3. Megaspore
• Haploid spores in flowering

plants that develops into female
gametophyte (embryo sac).

4. Female Gametophyte/Embryo Sac
• formed from the growth and division of the megaspore

into a multicellular structure that typically has eight
haploid nuclei.

• consist of one egg cell (n),

2 synergid cell (n),
3 antipodal cell (n) and
a polar nuclei (n+n)

Egg cell (n)

Female gamete formation : Terminologies

5. Antipodal Cell, Polar Nuclei, Egg Cell,
Synergid Cell

Antipodal Cell
• 3 haploid cells with unknown function.

Polar Nuclei
• 2 haploid nuclei are share the cytoplasm of the large
central cell of the embryo sac
Synergid cells
• 2 haploid cells help attract
and guide the pollen tube
to the embryo sac.

Egg cell (1)

Overview Of Gamete Formation : Basic concepts

Sporocyte/ Sporangium (2n)
Spore mother
cell (2n) MEIOSIS

Spores (n)

Gametophyte (n) MITOSIS
Gametes (n)

Development of Male Gametophyte (Pollen Grain)

● Microsporangium (pollen
sac of anther) consists of
microsporocyte/
microspore mother cell
(2n)

● Each microsporocyte
undergoes meiosis to
produce 4 haploid
microspores (n) @ tetrad

Development of Male Gametophyte (Pollen Grain)

● Each microspore
undergoes mitosis,
producing a
generative cell & a tube
cell

● This two-cell structure is
encased in a thick,
resistant wall known as
pollen grain (male
gametophyte)

Development of Male Gametophyte (Pollen Grain)

Microsporocyte/ Mitosis
microspore mother
4 haploid
cell (2n) microspores (n) /

Generative tetrad
cell
Tube cell

Development of Male Gametophyte (Pollen Grain)

● The pollen grain / male

gametophyte becomes

mature when the generative

cell divides by mitosis into

two male gametes (sperm

cells)

→ Mostly after it has lands on

stigma and the pollen tube

begins to form (after

pollination) into
→ The tube cell develops

pollen tube, which delivers the

male gametes to the egg cell.

Development of Male Gametophyte (Pollen Grain)

OVERVIEW : FORMATION OF MALE GAMETE

(POLLEN Microsporangium (2n)
SACS)
consist of

Microsporocyte @ microspore mother cell

(2n)

undergo

meiosis

4 haploid

microspores (nd)evelop

into

(POLLEN Male gametophyte (n) mitosis

GRAINS)

produc

((SSPPEERRMMSC)ELLS) Male gameetes

Development of Ovule

● Ovule develop from carpel
tissue, i.e. the placenta
which is held by a funicle

● The young ovule is a
cluster ofparenchyma cells
called nucellus

● The nucellus is encased
within 2 layers of
integuments
→ form tiny hole at one end

called micropyle
→ other end is called chalaza

Development of Ovule

ovary

ovary

Development of Female Gametophyte
(Embryo Sac) and Formation of Female Gamete

● Megasporangium in ovule
contains megasporocytes/
megaspore mother cells
(2n)

● Each megasporocyte
undergoes meiosis to
produce 4 haploid
megaspores (n)

Development of Female Gametophyte
(Embryo Sac) and Formation of Female Gamete

• 3 of megaspores Egg cell (1)
degenerates

• One surviving
megaspore divides by
mitosis three times
without cytokinesis
producing 8 haploid
nuclei (within embryo
sac)

Development of Female Gametophyte
(Embryo Sac) and Formation of Female Gamete

● Two groups of 4 nuclei move to both ends of
the embryo sac

● One nucleus from both ends move to the
centre, forming 2 polar nuclei ( not partitioned into
separate cells but share cytoplasm of the large
central cell of embryo sac

● 3 nuclei located near the micropyle:
- one becomes egg cell
- two become synergid cells (help attract and
guide the pollen tube to embryo sac)

Development Of Female Gametophyte
(Embryo Sac) And Formation Of Female Gamete
● 3 nuclei on the opposite ends:
✔all become 3 antipodal cells (unknown

function)
● Eventually one embryo sac/ female gametophyte

consists of 8 nuclei contained within 7 cells

Egg cell (1)

OVERVIEW : FORMATION OF FEMALE GAMETE

(within Megasporangium (2n)
ovule)
consist of

Megasporocyte @ megaspore mother cell (2n)

undergo meiosis

4 haploid megaspores (n)

develop into

(EMBRYO Female gametophyte (n) mitosis

SAC)
produce

(E(GOGVUCME)LL) Female gametes (n)

Summary: Formation of Male and Female Gametes

Double Fertilization
DEFINITION

• Process of fusion between one of the sperm cell
(n) with an egg cell (n) to form diploid zygote (2n).

• The other sperm cell (n) fuses with two polar
nuclei to form triploid endosperm (3n).

• The zygote develop into embryo.

cells

Double Fertilization

● Pollen grains land on
stigma.

● Stigma secrete
chemicals (sugary
solution) to stimulate
germination of
pollen grain.

● The pollen absorbs
water and
germinates by
forming pollen tube.

Double Fertilization

• Pollen tube grows
through the length of
the style towards the
embryo sac

● Nucleus tube cell
move down the
pollen tube followed
by generative cell

● Generative cells
divides by mitosis to
form 2 male gametes /
sperm cells.

Double Fertilization

● Pollen tube cells
penetrates the wall
of embryo sac
through micropyle

● Nucleus tube cell
degenerate and
sperm cells enter
the embryo sac

Double Fertilization

● One of the sperm (n)
fertilizes the egg cell (n)
to form a diploid zygote
(2n) which develop into
embryo

● The other sperm (n)
fuses with 2 polar nuclei
(n) to form triploid (3n)
nucleus and develop to
triploid endosperm(3n)
(a food storing tissue of
the seed)

Double Fertilization

● The union of two sperm
cells with different nuclei
of the female gametophyte
is called DOUBLE
FERTILIZATION

• Importance of double
fertilization:

- Ensure that endosperm
develops only in ovules
where the egg has been
fertilized

- Preventing from squandering
nutrients on infertile ovules

Double Fertilization

Triploid

cells Diploid zygote
cells

Functions Of Endosperm

❖ to provide a source of nutrients for
developing embryo and germinating seed

❖ to provide growth stimulating hormone for
developing embryo

Seed Development

❖ After double fertilization:

→ Ovule develops into seed
▪ as the embryo
develops from diploid
zygote by mitosis, the
seed accumulate
nutrients (starch,
protein and oils)

→ Ovary develops into fruit
enclosing the seed and
aids in their dispersal by
wind or animals

Seed Development

→ The integuments becomes the seed coat
• outer integument  testa
• inner integument  tegment

Tegment and testa is lignified, strong and durable
for the seed coat protection.

Different Between Dicot And Monocot Seed

DICOTS MONOCOTS
Two cotyledons One cotyledon

Seed Structure: Dicots

Mature embryo consists of:

✔2 cotyledons: store nutrient

✔Epicotyl: portion of
embryonic axis above where
cotyledon attached.

At the tip of epicotyl is the
plumule @ embryonic shoot

✔Hypocotyl: portion of
embryonic axis below where
cotyledon attached

The hypocotyl terminates in
the radicle @ embryonic root

Seed Structure: Dicots

Seed Structure: Dicots

Example 1: Common bean
❑ Thick cotyledon

❑Fleshy cotyledon store food absorbed from
endosperm before the seed germinates.

Seed Structure: Dicots

Example 2: Castor bean
❑ Thin cotyledon

❑ Narrow membranous cotyledon absorbed
food from the endosperm when the seed
germinates.

Seed Structure: Monocots

Mature embryo consists of:

✔ e.g. maize

✔ 1 cotyledon

Maize has a large cotyledon called a scutellum

Seed Structure: Monocots

9/19/12

References

• Campbell, N. A. & Reece, J.B. (2014). Biology (10th
Ed.), Pearson, The Benjamin Cummings
Publishing Company, Inc., 638-640.