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Name of Board | AHSEC |
Class: | Assam Board Class 12 |
Subject: | AHSEC Class 12 Biology |
Number of Chapter: | 01 |
Chapter Name | Sexual Reproduction in Flowering Plants |
Content Type: | Text, Images and PDF Format |
Academic Year: | 2024-25 |
Medium: | English |
Available Solution Link: | AHSEC Class Biology Notes |
AHSEC Class 12th Biology Chapter: 1 Sexual Reproduction in Flowering Plants
(A) Questions for 1 mark
1. Define reproduction?
Ans: Reproduction is a biological process in which an organism gives rise to young ones of its own kind.
2. What is incompatibility?
Ans: Incompatibility is the inability of viable gametes to fuse with each other and produce fertile offspring.
3. What is malacophily?
Ans: Malacophily is cross pollination performed through the agency of snails.
4. What types of flowers favours cross pollination?
Ans: Unisexual flowers.
5. What type of pollination is found in a self incompatible plants?
Ans: Cross pollination.
6. Why sunflower is best suited for insect pollination?
Ans: Sunflower is large in size and petals are brightly coloured which attracts insects for pollination.
7. What do you understand by double fertilisation? Who discovered it?
Ans: Double fertilisation is the phenomenon in which two fusions, i.e. syngamy and triple fusion occur in an embryo sac. It was discovered by S.G. Nawaschin (1897)
8. What is sporopollenin?
Ans: Sporopollenin is one of the most resistant organic material present in the exine layer of pollen grain.
9. What is the first cell to develop male and female gametephyte of flowering plants?
Ans: Male gametophyte Microspores
Female gametophyte – Megaspores.
10. Name two plants in which pollination occurs with the help of (i) Bird (ii) Bats
Ans: (i) Bird→ Bombax (Red Silk cotton)
(ii) Bats → Anthocephalus (Kadam)
11. What is triple fusion?
Ans: Triple fusion is a fertilisation that involves fusion of one male gamete and two polar nuclei in the central cell of embryo
12. What do you mean by parthenogenesis and Parthenocarpy?
Ans: Parthenogenesis is the phenomenon in which the unfertilised female gamete or ovum develops into an adult individual.
Parthenocarpy is the phenomenon of formation of fruits without fertilisation.
13. Arrange the following terms in correct developmental sequence: Pollen grain, sporogenous tissue, Microspore tetrad, Pollen mother cell, Male gametes.
Ans: Sporogenous tissue → Pollen mother cell → Microspore tetrad Pollen grain Male gamete
14. How does endosperm in angiosperms become triploid?
Ans: Endosperm become triploid as it is formed by the fusion of one male gamete with two polar nuclei in the central cell.
15. Mention the scientific term used for modified form of reproduction in which seeds are formed without fusion of gametes.
Ans: Apormixis.
16. A bilobed dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes this anther can produce?
Ans: 1600 male gametophytes.
17. Why should a beekeeper keep beehives in crop fields during flowering periods?
Ans: Bees help in pollination so beehives are kept in the crop fields during flowering periods.
18. If the chromosome number of somatic cell of a plant is 24. What would be the chromosome number of male gamete and endosperm cells of the plant?
Ans: Male gamete → 12
Endosperm cell → 36.
19. What are the constituent cells of the egg opparatus in an embryo sac?
Ans: Two synergids and one egg cell.
20. What are the three cells found in a pollen grain when it is ready to shed?
Ans: One vegetative cell and two male gamete.
21. Name the parts of the pistil which develop into fruits and seeds.
Ans: Ovary develop into fruits and ovule into seed.
22. Name the cultivated plant in which neither fruits nor seeds are formed.
Ans: Rose.
23. Name the activities
(i) Removal of anthers from the bisexual flower bud to male it a female flower.
(ii) Sprinkling of desired pollen grains over the stigma of a plower.
Ans: (i) Emasculation (ii) Dusting.
24. What are archesporial and tapetum layers?
Ans: Archesporial cells divide to form the sporogenous tissue that further divides to form the microspore mother cell.
Tapetum is the inner layer of microsporangium that nourishes the developing pollengrains.
25. Differentiate true fruits from false fruits.
Ans: True fruit develops from ovary whereas false fruits develops from some other parts of the flower like thalamus instead of the ovary.
(B) Fill Up The Blanks:
1. Morphologically flower is a modified _____.
Ans: Shoot.
2. Transfer of pollen grains from anther to the stigma of another flower of the same plant is called _______.
Ans: Geitonogamy
3. The wind pollinated flowers are generally______ sexual in nature.
Ans: abi
4. Entry of pollen tube into ovule through micropyle is known as _______.
Ans: porogamy.
5. Pollen grains are able to tolerate extremes of temperature and desication as its exine is made up of _______.
Ans: sporopollenin
6. Anthesis is a condition in which______takes takes place.
Ans: pollination
7. The ovule is attached to the placenta by ______.
Ans: funicle
8._______ is the first cell of embryo sac.
Ans: Megaspore
9. Hilum is the point at which _____ of _____ remain attached.
Ans: funicle, ovule
10._______ is the formation of embryo from vegetative cells derived from zygote.
Ans: Embryogenesis
(C) SELECT THE TRUE AND FALSE STATEMENT
1. In angiosperms, a mature male gametophyte is formed from a pollen mother cell through one meiotic and two mitotic divisions.
Ans: False
2. Tapetum is the innermost layer of pollen sac which help in protection of sporogenous cells.
Ans: False
3. Endosperms developed from secondary nucleus which is present in the middle of embryosac is diploid in chromosome set.
Ans: False
4. Pomixis is an event where a new plant is develop without the fusion of gametes.
Ans: False
5. Xenogamy, the type of pollination brings genetically different types of pollen grains to the stigma.
An: True
6. Fruits are formed in all phanerogams.
Ans: False
7. Commonly in a mature fertilized ovule n, 2n and 3n, condition is respectively found in synergids, zygote and endosperm cells.
Ans: True
8. A bisexual flower which never opens up in its life span is known as homogamy,
Ans: False
9. Wind pollinated flowers are small producing large numbers of pollen grains.
Ans: False
10. The egg apparatus of an angiosperm embryosac comprises of an egg cell and two antipodal cells.
Ans: False
(II) QUESTIONS FOR 2 MARKS
1. Draw a diagram of LS of angiospermic ovule and label the different nuclei present in it.
Ans :
2. What do you mean by sporogenesis? Differentiats microsporogenesis from megasporogenesis.
Ans: Sporogenesis is the process of formation of microspores and megaspores-
✓Microsporogenesis is the process of formation of microspores in microsporangia whereas megasporogenesis is the process of formation of megaspores in megasporangia.
3. What is triple fusion? Where it takes place? Name the nuclei involved in this event.
Ans: Triple fusion is a fertilisation that involves fusion of one male gamete and two polar nuclei in the central cell of embryo sac.
✓ It takes place in the central cell of embryo sac.
The nuclei involved in this event are one male nucleus and two polar nuclei.
4. What is bagging technique? Mention its usefulness in the programme of plant breeding.
Ans: Bagtging is the covering of emasculated flowers with a bag, generally made of butter paper to prevent contamination of its stigma with unwanted pollen.
Uses in plant breeding-
(i) Prevents contamination of stigma of female flowers with foreign pollens.
(ii) Prevents germination of foreign pollens over the stigma.
5. Why apple is called a fales fruit? Mention the parts of the flower from which this false fruit is develop.
Ans: Apple is called a false fruit because it develops from some other accessory floral parts instead of the ovary. In apple the thalamus develops into fruit.
6. Define emasculation? When and why the plant breeder employ this technique?
Ans: Emasculation is the process of removal of stamens / anthers before the anther dehisces from bisexual flowers.
A plant breeder employ this technique in the bud condition before the anthers dehisces. It is required to prevent self pollination.
7. ‘Angiosperms perform double fertilisation.’ Explain the statement.
Ans: In angiosperms one of the male gamete moves towards the egg cell and fuses with it to form the diploid zygote; this fusion is called syngamy. The second male gamete fuses with the secondary nucleus in the central cells to form the primary endosperm nucleus, this fusion is called triple fusion. Since in angiosperms two fertilisation, syngamy and triple fusion occurs it is called double fertilisation.
8. What is sexuality of plants? Give one example each from both monoecious and diosecious plants.
Ans: Sexuality of plants mean whether male and female reproductive structure are produced in the same plant i.e. bisexual or two different plants i.e. unisexual.
Eg of monoecious plant → Coconut dioccious plant → Papaya
9. What are the cells present in a developed embryo sac of angriosperms. Name them and mention the chromosome set found in them.
Ans: The cells present in a developed embryo sac are (i) Two synergids and one egg cell in the micropylar end
(ii) Three antipodal cells towards the chalazal end.
(iii) One large central cell which contains two polar nuclei.
The chromosome set found in them is haploid.
10. What is pollination? Briefly discuss its need and significance in angiosperms.
Ans: Pollination is the transfer of pollen grains from anthers to the stigma of a flower.
Pollination is a need for angiosperms because pollen grains continue their development only when they fall on a suitable stigmatic surface. It is quite significant for angiosperms otherwise fertilisation and events after fertilisation like endosperm development, seed and fruit formation will not take place.
11. Give one example from each of the following character-
(a) Flowers having both androecium and gynoecium
(b) A plant bearing both male and female flowers in the same body.
(c) A plant where fruit is not formed from ovary.
(d) An angiosperm where neither fruit nor seeds are formed.
Ans: (a) China rose
(b) Cucurbits
(c) Apple
(d) Rose
12. Which part of a seed is called the first food for the developing embryo? What is the primary sources of this food?
Ans: Food stored in cotyleodons are the first food for the developing embryo. The primary sources of this food is the endosperm.
13. What are functions of the cells present in a developed pollen grain which is ready to shed?
Ans: The functions of the cells present in a developed pollen gram are
(i) The vegetative cell is bigger and has abundant food reserve (starch, protein, fats etc)
(ii) The function of the generative cell is to divide mitotically to give rise to two male gametes.
14. Draw the L.S. of a pistil of angiosperms which is ready to take part in the process of fertilization. Label the different structure present there.
Ans:
L.S of Post Pollinated Pistil
15. Distinguish between cutting and layering. Give one example from each of them practiced in the crop plants.
Ans: Cutting: In this method suitable branches are cut to small pieces in growing season and are then placed in suitable moist soil with a portion of the stem inserted in soil. eg. Lemon. Layering: It is a type of rooting cutting in which adventitious roots are induced to develop on a soft stem while it is still attached to the plant. eg. Jasmine.
(III) QUESTIONS FOR 3 MARKS
1. What is self incompatibility? Why does self pollination does not lead to seed formation in self incompatible flower?
Ans: Self incompatibility is the inability of a bisexual plant to produce viable seeds on self pollination in spite of producing functional male and female gametes.
Self incompatibility is genetically controlled by multialleltic S- gene. Occurrence of similar allele in pollen grain and stigma results in failure of pollen grain to complete its growth and effect fertilisation. As a result no seed is formed.
2. What do you mean by pollination. Discuss its importance in flowering plants. Describe the role of various agencies responsible for the phenomenon.
Ans: Pollination is the transfer of pollen grains from anther to the stigma of a flower. Pollination is important is flowering plants because without it fertilisation cannot take place.
The various agencies that play important role in this phenomenon are wind, water, various insects, animals etc. If the pollen grains are light it is carried away by wind, water helps in pollination of aquatic plant and if the flowers are specifically adapted and produces nectar or sticky pollen grains then they were pollinated by insects and other animals.
3. What is vegatative propagation? State the importance of vegetative propagation in horticulture practices, giving examples.
Ans: Vegatative propagation is a mode of reproduction in which new plants are formed from vegetative parts of the plant like root, stem etc.
Importance of vegetative propagation-
(i) Characters of parents are maintained eg. Jasmine
(ii) Plants with reduced power of sexual
(iii) Plants having poor viability of seeds can be grown. eg. Banana.
4. Define triple fusion. What is the product of this process. What does the product develop into?
Ans: Triple fusion is a fertilisation that involves fusion of one male gamete and two polar nuclei in the central cell of embryo sac.
The product of this process is triploid primary endosperm nucleus that further develops in to the endosperm which provides nourishment to the developing embryo.
5. Match the items of column ‘A’ with the items of column ‘B’ of the following.
Column ‘A’
1. Autogamy
2. Apomixis
Column ‘B’
(i) Female gametophyte
(ii) Self pollination
6. What is agamospermy? How is agamospermy different from parthenogenesis and parthenocarpy?
Ans: The phenomenon of asexual reproduction that mimics sexual reproduction by formation of seed without fertilisation is called agamospermy. Whereas parthenogensis is the development of unfertilised ovule into an adult individual and parthenocarpy is the phenomenon of formation of fruits without fertilisation.
7. What is meant by emasculation? When and why does a plant breeder employ this techique?
Ans: Emasculation is the process of removal of stamens / anthers before the anther dehisces from bisexual flowers.
A plant breeder employ this technique in the bud condition before the anthers dehisces. It is required to prevent self pollination.
Plant breeders use emasculation for several reasons:
1. Controlled pollination: By removing the male reproductive organs, breeders can ensure that only desired pollen is used for fertilization. This helps in maintaining genetic purity and controlling the traits passed on to the offspring.
2. Prevention of self-pollination: Some plants have mechanisms for self-pollination, which can limit genetic variation. Emasculation prevents this and encourages cross-pollination, leading to greater genetic diversity.
3. Elimination of unwanted pollen: Emasculation allows breeders to eliminate unwanted pollen sources, such as pollen from inferior or wild varieties, thus improving the quality of the resulting offspring.
4. Hybridization: In hybridization programs, emasculation is often used to prevent self-pollination and ensure successful cross-breeding between two different varieties or species.
Overall, emasculation is a crucial technique in plant breeding for controlling pollination, ensuring genetic purity, and developing new cultivars with desired traits.
8. What is polyembryony and how it can be commercially exploited?
Ans: Presence of more than one embryo in a seed is called polyembryony.
For commercial purposes hybrid varieties of crops are extensively cultivated which increases productivity. But hybrid vigour is not maintained beyond single generation as segregation of genes takes place so to over come this seeds are developed through apomixis. Since the embryo in apomictic seeds often develops from diploid cells, segregation of traits will not occur and the new seeds will contain all the traits of the hybrid variety.
9. Write the characteristic features of anther, pollen and stigma of wind pollinated flowers. Discuss briefly how to flowers reward their insect pollinators.
Ans: The characteristics are
(i) Pollen grains are light in weight, non- sticky dry and winged.
(ii) Well exposed stamens for easy dispersal of pollen grains in the wind.
(IV) QUESTIONS FOR 5 MARKS (EXPLANATORY)
1. What is embryo? Discuss the stages of development of a dicot embryo. How you can differentiate a dicot embryo from a monocot embryo?
Ans: Embryo is the early stages of development of an offspring from the zygote.
Stages of development of a dicot embryo :-
1) The zygote undergoes transverse division to form a large basal cell and a small terminal cell.
2) Basal cell enlarges further and undergoes transverse division to form a group of 6-10 cells called suspensor.
3) The first cell of the suspensor towards the micropyle is called haustorium whereas the last cell towards the chalazal end is called hypophysis that later develop into radicle.
4) The terminal cell undergoes one transverse and two vertical divisions to produce 8-celled proembryo. Four cells of this proembryo towards the apex give rise to plumule and two cotyledons and another four gives rise to hypocotyl and part of radicle.
Difference between dicot and monocot embryo-
Dicot embryo
1) Consists of an embryonal axis and 2 cotyledons.
2) Portion of embryonal axis above cotyledons is epicotyl, which terminated with plumule
3) Portion below the levels of cotyledon is hypocotyl that terminates to radicle or root tip; covered with root cap.
Monocot embryo
1) Consists of only one cotyledon called scutellum
2) Portion of embryonal axis above the level of attachment of scutellum is epicotyl. Epicotyl has shoot apex and few leaf primordia as coleoptile.
3) Lower end of embryonal axis has radical and root cap enclosed in an undifferentiated sheath called coleorrhiya.
2. ‘Incompatibility is as natural barrier in the fusion of gametes.” Justify the statement.
Ans: Incompatibility is a natural barrier due to the following reasons
(i) It prevents inbreeding & outbreeding
(ii) Pollen promotion or inhibition occurs only after pollen recognition of pollen pistil interaction.
(iii) Only right mating type of pollen will germinate and fertilize.
(iv) Interaction of chemical substance of pollen and style act as natural barrier
(v) Pollens of other mating types are discarded.
3. “Pollination is an important phenomenon in the life cycle of a flowering plant.” Discuss the statement and describe briefly about the role of different agencies responsible for the events.
Ans: Pollination is an important phenomenon because without it the pollen grains will not reach the stigma and the male gametes will not reach the ovule to fertilise with the egg. Thus production of seeds and fruits to ensure continuity of the plant species will not take-place.
For effective pollination various pollinating agents are necessary. They are categorised into two types biotic & abiotic.
(i) Biotic agencies Different biotic agents like birds, bats, snails, etc help in pollination but most common are the insects. They visit the flowers in search of nectar or a safe position to lay eggs. While picking up food the insect visitor deposits pollen grains brought from some other. flower over the stigma and gets dusted afresh with pollen grains from the present flower. Thus insect act as very good pollinators.
(ii) Abiotic agencies Some plants do not produce nectars so they have to develop some other mechanisms for pollination. These plants produce light, non sticky pollens so that it can be easily carried away by wind. Thus wind also play an important role as a pollinator.
4. Describe the sequence of the events that lead to the development of a 3 celled pollen grain from microspore mother cell in angiosperms.
Ans: The process of formation of pollen grain from microspore mother cell is called microsporogenesis. Each cell of the sporogenous tissue in a microsporangium acts as a microspore mother cell which undergoes meiotic division to form cluster of four cells called microspore tetrad. On maturity the anther dehydrates and the microspores separate from each other to form pollen grains.
The newly differentiated pollen grain has a central nucleus and dense cytoplasm. Vacuoles develop, pushing the nucleus towards the periphery. On maturity the pollen grain contains two cells, the bigger vegetative cell which is rich in food reserve and smaller spindle shaped generative cell with dense cytoplasm and a nucleus. This is called 2- celled stage. But in some plants the generative cell further divides to form two male gametes which represents the 3- celled stage.
5. What is allogamy? Discuss the contrivances of allogamy stating the most convenient method of achieving allogamy?
Ans: Allogarty is the transfer of pollen grain from anther of one flower to stigma of another flower of different plant.
Contrivances for Allogamy are –
1. Unisexuality: Male and female flowers are present on different plants.
2. Dichogamy: Stamens and stigma of a bisexual flower mature at different times i.e. pollen release and stigma receptivity is not synchronised.
3. Self incompatibility: This is a genetic mechanism that prevents self pollen from fertilising the ovules by inhibiting pollen germination in the pistil.
4. Heterostyly The anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower.
Out of all these contrivances the most convenient method of achieving allogamy is unisexuality as this condition prevents both autogamy and geitonogamy.
6. What do you mean by fertilization? Discuss the significances of the event giving traces on post fertilization changes leading to the formation of seeds in ongrosperm.
Ans: Fertilisation is the fusion of haploid male and female gamete to give rise to diploid zygote.
Significance – 1) It ensures formation of endosperm only when the egg has been fertilised and embryo development is to start.
2) Due to its triploid nature, endosperm shows high physiological activity, grows faster and accumulates nutrients.
Formation of seed: In angiosperms, the seed is the final product of sexual reproduction. It is called the fertilised ovule. A seed consists of seed coat, one or two cotyledons and an embryonal axis. The seed coat is often double layered, formed by the integuments; the outer integument forms the outer layer of seed coat, the testa and the inner integument forms the inner layer of seed coat, the tegmen. Micropyle is a small opening found on the seed coat; it facilitates the entry of water and oxygen into the seed during germination. Hilum remains as a scar on the seed coat. The cotyledons are generally thick and swollen with food materials. A seed may be endospermic or non endospermic. The embryonal axis has hypocotyl and radicle on its lower end and epicotyl and plumule on its upper end.
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Last Words on AHSEC Class 12 Biology Chapter: 1 Sexual Reproduction in Flowering Plants
The Chapter 1 of AHSEC Class 12 Biology deals with sexual reproduction in flowering plants for a brief understanding. It includes essential topics such as reproduction, types of pollination and double fertilization in angiosperms. This involves processes like microsporogenesis and megasporogenesis to understand the structure and function of reproductive parts of the plant like pollen grains and embryo sac.