Biology Answer the following questions in detail.

1. Mature embryo sac is 7-celled and 8 nucleate.
2. Egg apparatus at micropylar end – with 2 synergids and egg cell.
3. Central cell with secondary nucleus formed by 2 polar nuclei
4. Antipodal cells at chalazal end – 3 cells.
5. Pollen tube enters the synergids, Synergids guide the growth of pollen tube towards egg.
6. Male gamete fuses with female gamete, i.e. syngamy to form zygote which develops into embryo.
7. One male gamete fuses with secondarynucleus to form primary endosperm nucleus (PEN) which forms endosperm, nutritive tissue for embryo.

The oospore undergoes a transverse division to form a large basal cell towards the micropyle and a small apical or terminal cell towards the chalaza of the embryo sac. This two celled structure is called proembryo. The basal cell or suspensor initial undergoes repeated transverse divisions to form a multicellular structure called suspensor. The suspensor pushes the embryo towards the endosperm to draw its nutrition.

1. The development of embryo from a zygote is called embryogenesis.
2. The fusion of male gamete and an egg cell during fertilization results in the formation of a diploid zygote. The zygote develops a wall around it and is converted into oospore.
3. The apical cell or embryonal initial of the proembryo undergoes a transverse division followed by two vertical divisions at right angles to form an octant stage.
4. From octant, the lower four cells form hypocotyl and radicle while four cells of upper side form plumule with two cotyledons.
5. The lowermost cell of suspensor is hypophysis and by its further division forms part of radicle and root cap.
6. The cells from upper side of octant divide repeatedly to form heart shaped which elongated further to form two lateral cotyledons.
7. Enlargement of hypocotyl and cotyledon results into curved embryo which appears horse shoe shaped.

1. Microspore or pollen grain is first cell of male gametophyte.
2. The protoplast of pollen grain divides mitotically to form two unequal cells – a small thin walled generative cell and a large naked vegetative or tube cell.
3. The generative cell possesses thin cytoplasm and a nucleus. It separates and floats in the cytoplasm of vegetative cell.
4. The vegetative, possesses thick cytoplasm, irregular shaped nucleus and the reserved food.
5. In majority of the angiosperms, the pollen grains are liberated at two-celled stage after the dehiscence of the anther.
6. The generative cell of the pollen grain divides by mitosis to form two male non-motile gametes.

(2) During double fertilization, the pollen tube on reaching the ovule enters the embryo sac through micropyle and bursts in one of the synergids. Owing to this, the two male gametes contained in the pollen tube, are set free.

(3) Out of the two male gametes, one unites with the egg or female gamete and the other unites with the secondary nucleus of the embryo sac, forming a triploid or triple fusion nucleus, called the primary endosperm nucleus. The process involving the fusion of one of the male gametes with the egg nucleus, resulting in the formation of a diploid zygote is called syngamy.

(4) The reproductive process in which non-motile male nuclei are carried to the egg cell through a pollen tube is called siphonogamy.

(5) After fertilization, zygote develops into an embryo. Certain changes take place in the ovule leading to the development of a seed.

(i) Apomixis : The phenomenon of formation of embryo(s) by asexual methods without formation of gametes and fertilization is termed as apomixis.
(ii) There are three main categories of apomixis.

1. Recurrent
2. Non-recurrent and
3. Adventive embryony.

1. Recurrent apomixis : In this diploid sporophytic cell, archesporial cell or nucellus form embryos, When diploid megaspore mother cell forms embryo sac it is known as diplospory. It is also called apospory.
2. Non-recurrent apomixis : Haploid embryo sac is formed but the embryos arise either from egg cell or any other haploid cell. It is also known as apogamy.
3. Adventive Embryony : In this in addition to normal zygotic embryo, additional embryos develop from nucellus or integuments. It results in polyembryony.

There are three types of endosperm, viz., nuclear, cellular and helobial.
(i) Nuclear endosperm:

1.Nuclear endosperm is the most common type of endosperm.
2.During the formation of nuclear endosperm, the primary endosperm nucleus (PEN) undergoes free nuclear division forming a large number of triploid nuclei which remain freely suspended in the common cytoplasm of central cell.
3.A central vacuole pushes the nuclei towards periphery.
4.Later on wall formation takes place around these nuclei to form a cellular mass.
5.It is seen in plants like maize, sunflower, wheat, coconut, etc.
(ii) Cellular endosperm:
1.In this type of endosperm, the triploid primary endosperm nucleus undergoes nuclear divisions followed by cytokinesis.
2.Owing to this, the development of endosperm occurs in cellular form.
3.It is less common and seen in dicot plants like Datura, Petunia, Balsam, Adoxa.

(iii) Helobial endosperm:

1. In helobial type of endosperm, the first division of the primary endosperm nucleus is followed by the formation of cell wall.
2. Owing to this, the central cell is divided into a large micropylar cell and a small chalazal cell.
3. In both micropylar and chalazal chamber, the further development of the endosperm is of nuclear type.
4. Walls develop between nuclei in micropylar chamber.
5. This type of embryo development is seen in plants belonging to order Helobiales of Monocots. e.g. Asphodehis.

1. Megasporogenesis : The process by which . the diploid megaspore mother cell of nucellus undergoes meiosis to form a tetrad of haploid megaspores is known as megasporogenesis.
2. Development of female gametophyte:
(i) The diploid megaspore mother cell undergoes meiosis to form a linear tetrad consisting of four-haploid megaspores. Generally, the chalazal megaspore becomes the functional megaspore. The other three megaspores degenerate.
(ii) The chalazal megaspore (fertile megaspore) is the first cell of the female gametophyte. It undergoes enlargement and develops into the female gametophyte. The haploid nucellus of chalazal megaspore undergoes three successive free nuclear mitotic divisions to produce eight nuclei. Of these, the first mitotic division results in the formation of two nuclei.
(iii) Both these nuclei undergo two successive mitotic divisions resulting in the formation of four nuclei at both the poles. In the meantime, one nucleus from each pole called polar nucleus moves towards the centre of the embryo sac and fuse to form a diploid nucleus called secondary nucleus.
(iv) The three nuclei at the micropylar end are organised to form a three-celled structure called egg apparatus, while the other three nuclei at the chalazal end reorganise to form three antipodal cells. The egg apparatus consists of a central cell called egg cell or female gamete which is flanked by two lateral cells called synergids.
(v) The female gametophyte consists of an egg apparatus, a secondary nucleus and three antipodal cells, A7 celled 8 nucleated structure.

1.A typical angiospermic pollen grain (mature) is a unicellular, uninucleate, spherical or oval haploid structure.
2.The pollen grain is also called microspore.
3.It is covered and protected by a double layered wall called sporoderm.

"
1.The outer layer of the wall is thick. It is known as exine. The inner layer of the wall is thin. It is known as intine.
2.The exine is made up of a complex substance called sporopollenin. The sporopollenin protects the pollen grain from physical and biological decomposition.
3.The exine is spiny in insect pollinated plants, with sculptured pattern or smooth in wind pollinated plants.
4.The exine is not continuous throughout. It is interrupted, very thin at one or more places by small pores called germ pores.
5.The intine which is composed of cellulose and pectin encloses the protoplasm with a single haploid nucleus.

1. The ovule which has a bent axis and downwardly directed micropyle is called anatropous ovule.
   It is the most common type of ovule in angiosperms.
2. The matured anatropous ovule consists of two parts, viz., the stalk and the body. The stalk of the ovule is called the funicle or funiculus. The funicle attaches the ovule with the placenta.
3. The point at which the funicle is attached to the body of the ovule is called hilum.
4. Nucellus : It is made up of diploid parenchymatous cells.
   The basal part of the nucellus is called chalaza.
   The protective coverings of the nucellus are called integuments.
5. Micropyle : The integuments do not completely cover the nucellus. They leave a small opening called micropyle at the tip.
6. Embryo sac : In a mature ovule, the nucellus shows an oval-shaped structure towards its micropylar end called embryo sac or female gametophyte.

1. Internally it shows four chambers called microsporangia or pollen sacs.
2. The anther consists of two main parts, viz., anther wall and microsporangium or pollen sac.
3. The wall of the anther can be differentiated into four layers, viz., epidermis, endothecium, middle layers and tapetum.
4. The epidermis is the outermost layer of the anther wall. It is made up of flattened cells which are protective in function.
5. The endothecium lies internal to the epidermis. It is made up of a single layer of cells. The cells of endothecium show fibrous thickenings on radial walls.
6. Internal to the endothecium, lie 1 to 3 layers of parenchymatous cells forming middle layers of the anther wall. The cells of middle layers degenerate at maturity during the formation of microspores.
7. The tapetum is the innermost nutritive layer of the wall of the anther, consisting of a single layer of cell surrounding the sporogenous tissue.

1. Embryo sac develops inside the nucellus of ovule from megaspore.
2. Megaspore mother cell is diploid structure which undergoes meiosis.
3. After meiosis, tetrad of haploid cells are produced.
4. The upper three megaspores degenerate and the lower one of the tetrad is functional.
5. The entire embryo sac is developed by elongation and then three mitotic divisions of this single megaspore take place hence the development is described as monosporic.

1. riple fusion is also called second fertilization.
2. Out of the two male gametes in angiosperms, the first one fuses with the egg to form the zygote, while the second one fuses with the secondary nucleus to form primary endosperm nucleus. This is called triple fusion. Since each of the polar nuclei is a sister nucleus of the egg, it is called second fertilization.
3. First fusion involves the fusion of a male gamete with the egg; the second fusion involves the fusion of two polar nuclei to form the secondary nucleus and the third fusion involves the fusion of the other male gamete with the secondary nucleus.

1. Endosperm is a nutritive tissue. It nourishes the developing embryo.
2. The endosperm develops from the primary endosperm nucleus (PEN).
3. The endosperm is a post fertilization tissue.
4. There are two types of seeds depending upon the presence or absence of endosperm, viz., endospermic and non-endospermic.
5. Castor, coconut, maize, etc. are endospermic seeds, while bean, pea, gram, etc. are non-endospermic seeds.

1. Pollination with the help of insects is called entomophily.
2. The insect pollinated flowers are called J entomophilous flowers.
3. Entomophilous flowers show the following adaptations:
4. Flowers are large and attractive.
5. Flowers are brightly coloured with i pleasant smell.
6. Flowers produce nectar which is food for the insects.
7. Pollen grains are spiny and sticky for easy adherance to the rough and sticky stigma.
8. Entomophily is seen in plants like rose, Jasmine, Oestrum, Salvia, etc.

1. Egg apparatus is a three celled structure lying at the micropylar end of the embryo sac.
2. The egg apparatus consists of a median egg cell called oosphere and two lateral cells called synergids.
3. The embryo sac also consists of three antipodal cells or antipodals towards the chalazal end which degenerate after fertilization.
4. In the centre, the embryo sac consists of a large central cell consisting of two haploid polar nuclei.
5. The polar nuclei at a later stage fuse with each other forming a diploid secondary nucleus.
6. The secondary nucleus develops into endosperm.

1. When stamens and carpels mature at different times in a bisexual flower, the condition is known as dichogamy.
2. Owing to dichogamy self-pollination is avoided and cross pollination is favoured.
3. Dichogamy is of two types, viz., protandry and protogyny.
4. Protandry is seen in sunflower in which pollen grains are released much before stigma becomes receptive.
5. In protogyny, stigma becomes ready to receive the pollen grains before the anthers mature. It is seen in plants like Gloriosa.

1. The transfer of pollen grains through birds is called ornithophily.
2. Bird pollinated plants are called ornithophilous plants.
3. Ornithophilous plants bear large and showy flowers.
4. Flowers brightly coloured to attract birds for pollination.
5. Ornithophilous flowers lack fragrance as birds have poor sense of smell.
6. Pollen grains are sticky and spiny e.g. Callistemon, Bignonia, Bombax, Butea, etc.

1. The transfer of pollen grains with the help of water is called hydrophily.
2. Plants that are pollinated by water are called hydrophilous plants.
3. Hydrophilous plants possess small, inconspicuous unisexual flowers.
4. Flowers lack fragrance, nectar and bright colour.
5. Pollen grains and other floral parts are protected from getting wet.
6. Stigma is long and sticky, e.g. Zostera, Vallisneria, etc.

1. The transfer of pollen grains through wind is called anemophily.
2. Plants that are pollinated by wind are called anemophilous plants.
3. Anemophilous plants bear small and inconspicuous flowers without any bright colours, fragrance and nectar.
4. Flowers are produced in large numbers.
5. Stamens are long with versatile anthers.
6. Stigma is feathery, exposed to receive the pollen grains coming along with the wind, e.g. Grasses, maize, Jowar and Palms.

1. It is a condition when more than one embryos are developed inside the seed.
2. It was first noticed in Citrus by Leeuwenhoek.
3. When embryos develop from diploid cells of nucellus or integuments, it is described as adventive polyembryony.
4. When zygote divides into small units which develop into embryos then it is called cleavage polyembryony.
5. It results in multiple seedlings and is of significance in horticulture.

1. It is a condition in which fruit is developed without event of fertilization.
2. It is a natural process observed on Pineapple and Banana.
3. A chemical stimulus in the form of auxin (IAA) is given by placental tissues of unfertilized ovary.
4. Due to the stimulus, enlargement of ovary takes place to form a fruit.
5. Parthenocarpic fruits are without seeds.

1. It is a state of metabolic arrest which helps in survival of organism in unfavourable environmental conditions.
2. Structure or physiological adaptive measures of seed that are helpful in adverse conditions is called dormancy.
3. Seeds are dispersed during their dormancy.
4. When dormancy period of seeds is completed then only the viable seed germinate.

1. It is a functional ability of pollen grain to form male gametophyte by its germination.
2. Viable pollen grains germinate on stigmatic surface,
3. Environmental factors mainly temperature and humidity influence its germination.
4. Viability is low up to 30 minutes in plants like rice and wheat.
5. Duration of viability is up to months in some plants of family Leguminosae, Rosaceae and Solanaceae.

1. It is type of artificial vegetative propagation.
2. In this method two different plants are joined together.
3. The part of stem containing one or more buds is scion which is joined on a rooted plant stock.
4. They grow as one plant, e.g. Apple, Pear, Mango.
5. When a single bud is grafted on a stock plant it is known as bud grafting or budding, e.g. Rose.

1. It is asexual method of reproduction.
2. Plants reproduce through their vegetative plant parts.
3. New plants produced are genetically identical to their parents.
4. It is very useful in agriculture and horticulture.
5. Artificial methods like cutting and grafting are useful for propagation of desired varieties as per human needs.

(i) Apomixis : The phenomenon of formation of embryo(s) by asexual methods without formation of gametes and fertilization is termed as apomixis.

(ii) There are three main categories of apomixis.

1. Recurrent
2. Non-recurrent and
3. Adventive embryony.

1. Recurrent apomixis : In this diploid sporophytic cell, archesporial cell or nucellus form embryos, When diploid megaspore mother cell forms embryo sac it is known as diplospory. It is also called apospory.

2. Non-recurrent apomixis : Haploid embryo sac is formed but the embryos arise either from egg cell or any other haploid cell. It is also known as apogamy.

3. Adventive Embryony : In this in addition to normal zygotic embryo, additional embryos develop from nucellus or integuments. It results in polyembryony.

1. Megasporogenesis : The process by which . the diploid megaspore mother cell of nucellus undergoes meiosis to form a tetrad of haploid megaspores is known as megasporogenesis.

2. Development of female gametophyte:
(i) The diploid megaspore mother cell undergoes meiosis to form a linear tetrad consisting of four-haploid megaspores. Generally, the chalazal megaspore becomes the functional megaspore. The other three megaspores degenerate.

(ii) The chalazal megaspore (fertile megaspore) is the first cell of the female gametophyte. It undergoes enlargement and develops into the female gametophyte. The haploid nucellus of chalazal megaspore undergoes three successive free nuclear mitotic divisions to produce eight nuclei. Of these, the first mitotic division results in the formation of two nuclei.

(iii) Both these nuclei undergo two successive mitotic divisions resulting in the formation of four nuclei at both the poles. In the meantime, one nucleus from each pole called polar nucleus moves towards the centre of the embryo sac and fuse to form a diploid nucleus called secondary nucleus.

(iv) The three nuclei at the micropylar end are organised to form a three-celled structure called egg apparatus, while the other three nuclei at the chalazal end reorganise to form three antipodal cells. The egg apparatus consists of a central cell called egg cell or female gamete which is flanked by two lateral cells called synergids.

(v) The female gametophyte consists of an egg apparatus, a secondary nucleus and three antipodal cells, A7 celled 8 nucleated structure.

1. The pollination that occurs with the help of bats is called chiropterophily.
2. In chiropterous plants the flowers are large and stout enough in such a way that bats can hold onto the flowers.
3. Chiropterous flowers are nocturnal, i.e., they open during the night time only.
4. Flowers emit rotten fruits like fermenting fruity odours which attract bats.
5. Flowers produce copious nectar.
6. Flowers possess large number of stamens which produce large amount of edible pollen grains.
7. Anthocephalus, Kigellia and Adansonia are chiropterous flowers.