🌸 Chapter 1
Sexual Reproduction in Flowering Plants
(3 Marks )
🌸 1. What are the essential
parts of a typical flower involved in reproduction?
Answer:
The essential parts are the stamens (male reproductive organs) and carpels/pistils
(female reproductive organs). Stamens produce pollen grains containing male
gametes, and carpels contain the ovary with ovules that house the female
gametes (egg cells).
2. Define microsporogenesis.
Answer:
Microsporogenesis is the process of formation of microspores (pollen grains)
from microspore mother cells (MMC) by meiotic division in the
anther’s pollen sac.
3. Describe the structure of a
mature anther.
Answer:
A mature anther is bilobed and each lobe has two microsporangia. Each
microsporangium has four layers: epidermis, endothecium, middle layers, and
tapetum. The innermost tapetum nourishes the developing pollen grains.
4. What is the role of the tapetum?
Answer:
The tapetum provides nutrition to developing microspores and secretes
materials for pollen wall formation (sporopollenin). It also releases enzymes
and proteins essential for pollen maturation.
5. Differentiate between
microsporogenesis and megasporogenesis.
Answer:
- Microsporogenesis: Formation of pollen grains
(male gametophyte) in anther.
- Megasporogenesis: Formation of megaspores
(female gametophyte) in ovule.
Both involve meiotic division of a mother cell but occur in different reproductive organs.
6. Explain the structure of an
ovule.
Answer:
An ovule consists of integuments, a nucellus, and an embryo
sac. The opening in the integuments is the micropyle, the opposite
end is the chalaza, and the funicle attaches the ovule to the placenta.
7. What is the embryo sac and how
many nuclei does it contain?
Answer:
The embryo sac is the female gametophyte formed from the functional
megaspore. It contains seven cells and eight nuclei: one egg, two
synergids, three antipodals, and one central cell with two polar nuclei.
8. Differentiate between self-pollination
and cross-pollination.
Answer:
- Self-pollination: Pollen transferred to stigma
of the same flower or another flower on same plant.
- Cross-pollination: Pollen transferred between
flowers of different plants of same species.
Cross-pollination promotes genetic diversity.
9. Name any three agents of
pollination and give one example each.
Answer:
1.
Wind
(Anemophily):
e.g., Maize
2.
Water
(Hydrophily):
e.g., Vallisneria
3.
Insects
(Entomophily):
e.g., Hibiscus
10. Mention any three adaptations of
wind-pollinated flowers.
Answer:
- Produce large quantity of
lightweight pollen
- Feathery stigmas to trap pollen
- Exposed stamens for easy
dispersal
11. What is pollen-pistil
interaction?
Answer:
It is the sequence of events from pollen landing on stigma to pollen tube entry
into ovule. It ensures compatibility and guides the pollen tube to deliver male
gametes.
12. Define double fertilization.
Answer:
Double fertilization is a unique event in angiosperms where one male gamete
fuses with egg (syngamy) forming a zygote, and another fuses with two
polar nuclei forming triploid endosperm.
13. Explain the significance of
double fertilization.
Answer:
It ensures formation of endosperm only when egg is fertilized —
conserving energy. It synchronizes embryo and endosperm development for
successful seed formation.
14. What is triple fusion?
Answer:
Triple fusion is the fusion of one male gamete with two polar nuclei
in the central cell, producing triploid (3n) endosperm nucleus.
15. What are synergids? What is
their role?
Answer:
Synergids are two cells flanking the egg cell in the embryo sac. They secrete chemicals
guiding the pollen tube and help in male gamete release during
fertilization.
16. What is the function of
endosperm?
Answer:
The endosperm provides nutrition (proteins, starch, fats) to the
developing embryo during seed maturation.
17. Define apomixis.
Answer:
Apomixis is the formation of seeds without fertilization, resulting in
offspring genetically identical to the parent (asexual reproduction through
seeds).
18. What is polyembryony? Give an
example.
Answer:
Polyembryony is the formation of more than one embryo in a single seed.
Example: Citrus and mango.
19. Mention the parts of a mature
embryo in dicot plants.
Answer:
A dicot embryo consists of:
- Two cotyledons
- Plumule (shoot tip)
- Radicle (root tip)
- Embryonal axis
20. How does fertilization occur in
flowering plants?
Answer:
Pollen germinates on stigma → pollen tube grows through style → enters ovule
via micropyle → releases two male gametes → one fuses with egg, another with
polar nuclei (double fertilization).
21. Describe the structure of a
pollen grain.
Answer:
A pollen grain has two layers:
- Exine: Outer hard layer of
sporopollenin.
- Intine: Inner pectin-cellulose layer.
Contains vegetative and generative cells.
22. What are the advantages of
cross-pollination?
Answer:
- Increases genetic variation
- Produces healthier and more
adaptable offspring
- Prevents inbreeding depression
23. Name different outbreeding
devices.
Answer:
1.
Dichogamy – anther and stigma mature at
different times
2.
Herkogamy – physical barriers
3.
Self-incompatibility
4.
Unisexuality
24. What are unisexual and bisexual
flowers? Give examples.
Answer:
- Unisexual: Either stamen or carpel
present (e.g., papaya).
- Bisexual: Both present (e.g., hibiscus).
25. Explain megasporogenesis.
Answer:
It is the formation of four haploid megaspores from a diploid
megaspore mother cell (MMC) in the ovule by meiosis. Usually, only one
megaspore is functional and forms the embryo sac.
26. What are the three types of
ovules based on orientation?
Answer:
1.
Orthotropous
(straight) – e.g.,
Polygonum
2.
Anatropous
(inverted) – common
type
3.
Campylotropous
(curved) – e.g.,
Capsella
27. What happens to the following
after fertilization – ovary, ovule, integuments, and zygote?
Answer:
- Ovary → fruit
- Ovule → seed
- Integuments → seed coat
- Zygote → embryo
28. How does pollen develop in the
anther?
Answer:
Each microsporangium has MMCs → undergo meiosis → form microspores → tetrads →
separate → mature into pollen grains.
29. What are the pre-fertilization
events in plants?
Answer:
Pre-fertilization events:
1.
Gametogenesis
(formation of gametes)
2.
Pollination
(transfer of pollen)
30. What are post-fertilization
events?
Answer:
- Zygote → embryo
- Primary endosperm nucleus →
endosperm
- Ovule → seed
- Ovary → fruit
31. What is the economic importance
of apomixis?
Answer:
Apomixis helps produce hybrid seeds without repeated hybridization,
maintaining hybrid vigour and reducing cost.
32. Describe the types of
pollination based on flower relationship.
Answer:
- Autogamy: Same flower
- Geitonogamy: Different flower, same plant
- Xenogamy: Flower of another plant
33. What are pollen viability and
pollen storage?
Answer:
Pollen viability is the ability of pollen to fertilize. Pollen can be stored
for years in liquid nitrogen (-196°C) using cryopreservation.
34. What are the characteristics of
insect-pollinated flowers?
Answer:
- Brightly coloured petals
- Fragrant
- Nectar present
- Sticky pollen and stigma
35. Describe the structure of a mature
embryo sac.
Answer:
Egg apparatus (1 egg + 2 synergids) at micropylar end, 3 antipodals at chalazal
end, and 2 polar nuclei in center → total 8 nuclei, 7 cells.
36. Why are pollen grains of some
species preserved for long years?
Answer:
Due to sporopollenin in the exine, which is resistant to chemicals,
enzymes, and high temperatures.
37. What is emasculation and why is
it done?
Answer:
Emasculation is removal of anthers before pollen release to prevent
self-pollination during artificial hybridization.
38. What is bagging and its purpose?
Answer:
Bagging is covering of emasculated flowers with paper bags to prevent unwanted
pollination before introducing desired pollen.
39. Distinguish between monocot and
dicot seed.
Answer:
- Monocot: One cotyledon, e.g., maize
- Dicot: Two cotyledons, e.g., bean
40. Define fertilization and
syngamy.
Answer:
Fertilization is fusion of male and female gametes.
Syngamy refers specifically to fusion forming the zygote.
41. Explain the term “endosperm
development.”
Answer:
After triple fusion, the primary endosperm nucleus divides repeatedly to form
endosperm, which nourishes embryo (can be nuclear, cellular, or helobial).
42. What are the differences between
true fruit and false fruit?
Answer:
- True fruit: Developed from ovary only
(e.g., mango)
- False fruit: Also involves other floral
parts (e.g., apple)
43. Explain the function of pollen
tube.
Answer:
The pollen tube carries two male gametes from pollen grain through style to
embryo sac, ensuring fertilization.
44. Describe the stages of embryo
development.
Answer:
Zygote → pro-embryo → globular → heart-shaped → mature embryo with cotyledons
and axis.
45. What are the types of endosperm?
Answer:
1.
Nuclear – free-nuclear divisions (e.g.,
coconut)
2.
Cellular – cell wall forms after each
division (e.g., Datura)
3.
Helobial – both characters (e.g., monocots)
46. Define parthenocarpy and give
one example.
Answer:
Formation of fruit without fertilization; results in seedless fruits like
banana or grapes.
47. What is the role of antipodal
cells?
Answer:
They are nutritive in function and may help in embryo sac maintenance though
they degenerate later.
48. What are the conditions
necessary for successful pollination?
Answer:
Pollen must be viable, stigma must be receptive, and both must be
compatible genetically and physiologically.
49. Define seed dormancy and give
its advantage.
Answer:
Seed dormancy is a period when seed cannot germinate even under favourable
conditions. It helps in dispersal and survival during unfavorable conditions.
50. Explain the role of hormones in
fruit and seed formation.
Answer:
After fertilization, auxins, gibberellins, and cytokinins stimulate
fruit and seed development. Synthetic hormones can induce parthenocarpic
fruits.
