12th Bio-Botany notes
BOARD EXAM
CHAPTER – 1
ASEXUAL AND SEXUAL REPRODUCTION IN PLANTS
1. What are clones?
Morphological & genetically identical are clones.
2. What is polyembryony? Give example.
Occurrence of more than 1 embryo in a seed.
Example: Orchids
3. List out the types of polyembryony.
1. Cleavage polyembryony
2. Formation of embryo by cells of the Embryo sac other than egg
3. Development of more than one Embryo sac within the same ovule
4. Activation of some sporophytic cells of the ovule
4. Define apomixis.
Reproduction does not involve union of male and female gametes.
5. Classify apomixis by Maheswari.
1. Recurrent apomixis
2. Non recurrent apomixis
6 Define – Agamaspory
Embryos are formed by eliminating meiosis and syngamy.
7. What is sporophytic budding?
An Embryo arises directly from the diploid sporophytic cells either from
nucellus or integument.
Example: Citrus
8. What is somatic apospory?
(1)Megaspore mother cell undergoes the normal meiosis and 4
megaspores formed gradually disappear.
(2) A nucellar cell becomes activated and develops into a diploid
embryo sac.
Example: Hieracium
9. Define the term Diplospory.
Diploid embryo sac is formed from megaspore mother cell without regular
meiotic division.
Example: Aerva
10. List out the functions of endosperm
(1)It is the nutritive tissue for the developing embryo.
(2)In majority of angiosperms, the zygote divides only after the
development of endosperm.
(3)Endosperm regulates the precise mode of embryo development.
11. Write a short note on Cicer seed
(1) The mature seeds are attached to the fruit wall by a stalk called
funiculus.
(2) The funiculus disappears leaving a scar called hilum.
(3) Below the hilum a small pore called micropyle is present.
(4) The outer coat is called testa and is hard
(5) The inner coat is thin, membranous and is called tegmen.
(6) The portion of embryonal axis projecting beyond the cotyledons is
called radicle
(7) The other end of the axis called embryonic shoot is the plumule.
(8) Embryonal axis above the level of cotyledon is called epicotyl
(9) Cylindrical region between the level of cotyledon is called
hypocotyl
12. Give a detailed account on parthenocarpy. Add a note on its
significance.
1) Fruit like structures may develop from the ovary without fertilization
– Parthenocarpic fruits.
Example: Banana (Seedless)
2) Significance
a) Great significance in horticulture.
b) Great commercial importance.
c) Used for preparation of jams, jellies etc.
d) High proportion of edible part is available in Parthenocarpic fruits
due to the absence of seeds.
13. Write a short notes on Oryza seed
(1)The seed of paddy is one seeded and is called Caryopsis
(2) It is separated from embryo by a definite layer called epithelium.
(3) The embryo is small and consists of one shield shaped cotyledon known as scutellum present towards lateral side of embryonal axis.
(4) A short axis with plumule and radicle protected by the root cap is
present.
(5) The plumule is surrounded by a protective sheath called coleoptile.
(6) The radicle including root cap is also covered by a protective sheath called coleorhiza.
14. Differentiate the structure of dicot seed and monocot seed.
15. Explain the various stages involved in the development of embryo.
(1) The embryo develops at micropylar end of embryo sac.
(2) The zygote undergoes transverse division to form upper or terminal cell and lower or basal cell.
(3) Further divisions in the zygote during the development lead to the formation of embryo.
(4) Embryo undergoes globular, heart shaped stages before reaching
a mature stage.
(5)The mature embryo has a radicle, two cotyledons and a plumule.
16. What is Endosperm? Explain its types.
1) Primary Endosperm Nucleus divides immediately after fertilization
but before the zygote starts to divide, to form zygote.
2) Types:
a) Nuclear Endosperm:
(i) PEN undergoes several mitotic divisions without cell wall
formation, thus free nuclear condition exists in endosperm.
(ii) Example: Arachis
b) Cellular Endosperm:
(i) PEN divides into 2 nuclei and it is immediately followed by
wall formation.
(ii) Example: Adoxa
c) Helobial Endosperm:
(i) PEN moves towards base of embryo sac and divides into 2
nuclei. Cell wall formation takes place leading to the formation of
➔ Micropylar chamber (Nuclear divisions occurs)
➔ Chalazal chamber (No division)
(ii) Example: Hydrilla
d) Ruminate endosperm:
(i) The endosperm with irregularity and unevenness in its
surface forms ruminate endosperm.
(ii) Example: Areca catechu
Diagram
17. With a suitable diagram explain the structure of an ovule.
1. Ovule is protected by one or two covering called integuments.
2. The stalk attaches the ovule to the placenta.
3. The point of attachment of funicle to the body of the ovule is known
as hilum.
4. In an inverted ovule, the funicle is adnate to the body of the ovule
forming a ridge called raphe.
5. The body of the ovule is made up of a central mass of
parenchymatous tissue called nucellus.
6. The nucellus is enveloped by one or two protective coverings called
integuments.
7. Integument encloses the nucellus completely except at the top
where it is free and forms a pore called micropyle.
8. The ovule with one or two integuments are said to be unitegmic or
bitegmic ovules.
9. The basal region of the body of the ovule where the nucellus, the
integument and the funicle meet is called as chalaza.
10. There is a large, oval, sac-like structure in the nucellus toward the
micropylar end called embryo sac
11. The inner layer of the integument may become specialized to
perform the nutritive function for the embryo sac and is called as endothelium.
12. If the sporogenous cell is hypodermal with a single layer of
nucellar tissue around it is called tenuinucellate type.
13. Ovules with subhypodermal sporogenous cell is called
crassinucellate type.
14. Group of cells found at the base of the ovule between the chalaza
and embryo sac is called hypostase.
15. The thick -walled cells found above the micropylar end above the
embryo sac is called epistase.
18. List out the advantages and disadvantages of natural vegetative reproduction.
Advantages
1) Only 1 parent is required for propagation.
2) The new individual plants produced are genetically identical.
3) In some plants, this enables to spread rapidly. Example: Spinifex
4) Horticulturists and farmers utilize these organs of natural vegetative
reproduction for cultivation and to harvest plants in large scale.
Disadvantage
1) New plants produced have no genetic variation.
19. What is tapetum? List out its types and write its functions.
It is the innermost layer of anther wall and attains its maximum
development at the tetrad stage of microsporogenesis.
TYPES
Secretory tapetum
Invasive tapetum
Functions of Tapetum
• It supplies nutrition to the developing microspores.
• It contributes sporopollenin through ubisch bodies thus plays an
important role in pollen wall formation.
• The pollenkitt material is contributed by tapetal cells and is later
transferred to the pollen surface.
20. Explain the various types of ovules
Orthotropous
(1)Micropyle is at the distal end
(2) Micropyle,the funicle and the chalaza lie in one straight vertical
line. Example: Piperaceae
Anatropous
(1)The body of the ovule becomes completely inverted
(2)Micropyle and funiculus come to lie very close to each other.
Example: dicots
Hemianatropous
(1) Body of the ovule is placed transversely and at right angles to the
funicle.
(2)Example: Primulaceae.
Campylotropous
(1)The body of the ovule at the micropylar end is curved
(2)Bean shaped. Micropyle oriented towards the placenta.
Example: Leguminosae
Amphitropous
(1)The distance between hilum and chalaza is less.
(2)The curvature of the ovule leads to horse-shoe shaped nucellus.
Example: Alismataceae.
Circinotropous
(1)Funiculus is very long and surrounds the ovule.
Example: Cactaceae
21. Discuss the steps involved in microsporogenesis.
1) The stages involved in the formation of haploid microspores from
diploid microspore mother cell through meiosis is called Microsporogenesis.
2) The primary sporogeneous cells directly, or may undergo a few
mitotic divisions to form sporogenous tissue.
3) The last generation of sporogenous tissue functions as
microspore mother cells.
4) Each microspore mother cell divides meiotically to form a tetrad of
four haploid microspores.
5) Microspores soon separate from one another and remain free in
the anther locule and develop into pollen grains.
6) In some plants, all the microspores in a microsporangium remain
held together called pollinium. Example: Calotropis.
7) Pollinia are attached to a clamp or clip like sticky structure called
corpusculum.
8) The thread like part arising from each pollinium is called
retinaculum.
9) The whole structure looks like inverted letter 'Y' and is called
translator.
22. Write a note on heterostyly
(1) Some plants produce two or three different forms of flowers that
are different in their length of stamens and style.
(2) Pollination will take place only between organs of the same length.
23. Explain – Lever mechanism in Salvia
(1)When a bee visits a flower, it sits on the lower lip which acts as a
platform.
(2)It enters the flower to suck the nectar by pushing its head into the
corolla.
(3)During the entry of the bee into the flower the body strikes against
the sterile end of the connective.
(4)This makes the fertile part of the stamen to descend and strike at
the back of the bee.
(5)The pollen gets deposited on the back of the bee.
(6) When it visits another flower, the pollen gets rubbed against the
stigma and completes the act of pollination in Salvia
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