a Chapter Summary: Sexual Reproduction in Flowering
Plants
1. Introduction
" Flowering plants (angiosperms) reproduce sexually through flowers.
"Sexual reproduction includes meiosis, gamete formation, and
fertilization.
2. Flower: A Reproductive Unit
" Structure of a flower:
o Calyx (sepals) - protective
o Corolla (petals)- attract pollinators
o Androecium (stamens) - male reproductive part
o Gynoecium (carpels) - female reproductive part
3. Pre-fertilization: Structures and Events
a. Male Reproductive Part - Stamen
" Anther: Bilobed with two thecae
" Filament: Stalk-like structure
b. Microsporogenesis
" Microspore mother cells (2n) undergo meiosis ’ Microspore tetrad
(n)
" Microspore mother cells (2n) undergo meiosis ’ Microspore tetrad
(n)
" Microspores separate and form pollen grains
Structure of Mature Pollen Grain:
" Two-layered wall:
oExine - thick, sporopollenin
o Intine - thin, cellulose and pectin
" Two cells:
o Generative cell(divides into 2 male gametes)
o Vegetative cell (forms pollen tube)
Diagram: Structure of pollen grain
C. Female Reproductive Part - Carpel (Pistil)
" Ovary (contains ovules), style, and stigma
d. Megasporogenesis
"Megaspore mother cell (2n) in ovule undergoes meiosis ’ 4
megaspore (n) (only 1 survives)
"f Embryo Sac (Female Gametophyte):
" Develops from functional megaspore by 3 mitotic divisions ’ 8
nuclei
" Cell arrangement:
o 3 Antipodal cells (chalazalend)
o 2 Polar nuclei (central cell)
o 1Egg cell+2 Synergids (micropylar end)
Diagram: Embryo sac structure
4. Pollination
" Transfer of pollen from anther to stigma.
Types:
1. Autogamy: Same flower
2. Geitonogamy: Different flower, same plant
3. Xenogamy: Different plant
Agents of Pollination:
" Abiotic - Wind, water
" Biotic- Insects, birds, bats
Adaptations in pollinated plants:
" Sticky pollen, nectar, colorful petals (entomophily)
5. Pollen-Pistil Interaction and Fertilization
" Germination of pollen grain on stigma ’ pollen tube
" Pollen tube enters ovule via micropyle
" Double fertilization:
o Syngamy: One male gamete + egg’ zygote
o Triple fusion: Other male gamete + polar nuclei ’ endosperm (3n)
Diagram: Fertilization and pollentubeentry
6. Post-fertilization Events
a. Development of Endosperm
" Provides nutrition to embryo
" Types: Nuclear, Cellular, Helobial
b. Development of Embryo
" Zygote divides ’ embryo with:
o Radicle
o Plumule
oCotyledons
c. Seed and Fruit Formation
" Ovule’ Seed
Ovary -’ Fruit
Diagram: Parts of mature see
7. Apomixis and Polyembryony
a. Apomixis
Seed formation without fertilization
" Common in grasses
" Advantage: Produces clones of parent plant
b. Polyembryony
" More than one embryo in a seed
" Occurs in citrus, mango
+ Key Points Recap
" Sexual reproduction involves meiosis, gamete formation, pollination,
fertilization, and embryo formation.
" Double fertilization is unique to angiosperms.
" Pollination types and their agents are critical to reproductive
SUccess.
" Endosperm and embryo develop post-fertilization.
" Apomixis helps in producing genetically identical offspring without
seeds.
Important Diagrams (You can request them visually
if needed)
1. Structure of mature pollen grain
2. Structure of ovule and embryo sac
3. Double fertilization process
4. Development of seed and fruit
5. L.S. of flower showing reproductive parts
One-Liner Questions (Very Short Answer)
1. What is the function of the tapetum in anther?
2. Define double fertilization.
3 What is the ploidy of endosperm in angiosperms?
4 Name the type of cell in the pollen grain that forms the pollen tube.
5 Define emasculation.
6 What is meant by apomixis?
7. Name the common pollinating agent in water plants like
Vallisneria.
8. What is the role of synergids during fertilization?
9 What is polyembryony? Give one example.
10. Which part of the ovule develops into the seed coat?
MCQs (0bjective Type)
1. Inangiosperms, double fertilization involves:
" a) Syngamy and triple fusion
o b) Syngamy and mitosis
oc) Fertilization and zygote formation
o d) Triple fusion only
Answer: a) Syngamy and triple fusion
2. Pollen grains are preserved in fossil form due to the presence of:
o a) Sporopollenin
ob) Pectin
o c) Cellulose
o d) Lignin
|Answer: a) Sporopollenin
3. The functional megaspore in an angiosperm develops into:
oa) Embryo sac
o b) Endosperm
o c) Ovule
o d) Embryo
Answer: a) Embryo sac
4. Pollination in water hyacinth and water lily is by:
o a) Water
o b) Insects or wind
o c) Both aand b
o d) None
Answer: b) Insects or wind
5. What willbe the ploidy of the following: (i) Pollen grain, (i)
Endosperm, (ii) Zygote?
oa) n, 3n, 2n
o b) 2n,n, 3n
o c) 2n, 3n, n
od) n, 2n, 3n
Answer: a) n, 3n, 2n
6. Which of the following shows polyembryony?
o a) Mustard
o b) Citrus
o c) Banana
o d) Mango
Answer: b) Citrus
7. Emasculation is essential in:
o a) Self-pollinated crops
o b) Apomictic plants
oc) Cross-pollinated crops
o d) Asexual plants
Answer: c) Cross-pollinated crops
Long-Answer Questions (LAQ- 5 Marks)
1. Describe the structure of a mature embryo sac of an
angiosperm.
Answer:
"Embryo sac (female gametophyte) is 7-celled and 8-nucleate.
" Three cells at micropylar end: 1egg cell and 2 synergids
" Three cells at chalazal end: antipodal cells
" Two nuclei in center: polar nuclei, later fuse ’ central cell
" Develops from a single functional megaspore via three mitotic
divisions
" Diagram recommended.
2. Explain the process of double fertilization in angiosperms.
Answer:
" Pollen tube enters ovule through micropyle.
" Discharges two male gametes into embryo sac.
o One gamete + egg cell ’ zygote (syngamy)
o Other gamete + 2 polar nuclei ’ endosperm nucleus (3n) (triple
fusion)
Syngamy + Triple fusion = Double Fertilization (unique to
angiosperms)
" Results in diploid zygote and triploid endosperm.
3. What is microsporogenesis? Describe the development of male
gametophyte.
Answer:
" Formation of microspores from pollen mother cells (PMC)
" PMC (2n) undergoes meiosis ’ Microspore tetrad (n)
" Each microspore ’ pollen grain
" Pollen grain:2 cells - generative cell (divides into 2 male gametes),
vegetative cell
" Generative cell divides during pollen tube growth.
4. What is apomixis? How can it be commercially beneficial?
Answer:
" Apomixis: Seed formation without fertilization
" No fusion of gametes, bypasses sexual reproduction
" Offspringgenetically identical to parent (clone)
" Used to maintain hybrid vigour in hybrid seeds
" Reduces need for repeated hybridization and high seed cost
5. What is pollination? Describe the various types and their agents.
Answer:
" Pollination: Transfer of pollen from anther to stigma
Types:
" Autogamy - same flower
" Geitonogamy - different flower, same plant
" Xenogamy - different plant
Agents:
" Biotic: Insects (entomophily),birds, bats
" Abiotic: Wind (anemophily), water (hydrophily)
" Adaptations: Colorful petals, nectar, sticky stigma/pollen
