BIOLOGY 3 Marks Question

• It is a cost effective method for producing seeds.
• Hybrid seeds can be cultivated.
• It has great use for plant breeding when specific traits of a plant have to be preserved.

1. In coconut Primary Endosperm Nucleus (PEN-3n) undergoes successive nuclear divisions, give rise to free- nuclear endosperm known as coconut water, white kernel is the cellular endosperm, provides nourishment to the growing embryo.
2. Storage/cryopreservation (storage in liquid nitrogen at - 196 o C), to use in crop breeding programmes.

1. Yes, By artificial means.
2. Diagram with following labellings: Stigma Pollen tube, Synergid/Filiform Apparatus, Micropyle.

1. Failed to keep pace with demand, failed to provide fast and efficient system of crop improvement.
2. Large number of plants can be developed in a short duration/production of genetically identical plants/somaclones/healthy plants can be recovered from diseased plants.
3. Tomato/banana/apple.

1. Endosperm formation, there are three types:

1. Nuclear endosperm formation repeated free nuclear division take place, a cell wall formed after cell wall nuclear division referred liquid endosperm. Ex-coconut juice.
2. Cellular endosperm formed with nuclear division, Acoraceal cellular endosperm development while monocot are helobial.
3. Helobial endosperm formation between the first two nuclei after which one half develops endosperm a long the cellular pattern in coconut.

2. Coconut water is considered as a ‘fluid of life’ It increase immunity. lender coconut water is a good source of ‘Laceric acid’.
3. Endosperm internally, consists of two unequal portion of dicotyledonous seed the most common dicot seeds age of gram, pea castor etc. these testa hard end is of different colour in different seeds.

1. Pollen - light/large number/non sticky,

Anther - well exposed,

Stigma - large/feathery/open/sticky.

2. Provides nectar/food for the larvae/pollen grains/safe place to lay eggs.

B. Two ways -

1. In some species, the diploid egg cell is formed without reduction division and develops into embryo without fertilisation.
2. More often, as in many citrus and mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos.

2. Central cell.

• Since reproductive process such as pollination and fertilisation are independent of water, seed formation is more dependable.
• Seeds have better adaptive strategies for dispersal to new habitats and help the species to colonise in other areas.
• As they have sufficient food reserves young seedlings are nourished until they are capable of photosynthesis on their own.
• The hard seed coat provides protection to the young embryo.
• Being products of sexual reproduction, they generate new genetic combinations/variations.
• Dehydration and dormancy of mature seeds are crucial for survival under adverse conditions.

1. Function of Acrosome:

• It contains enzymes that help the sperm to enter and to fertilise the ovum.

2. Function of Nucleus:

• It stores the genetic information. It carries 23 chromosomes, out of which one is sex chromosome (either X or Y). Thus, it is responsible for determining the sex of the individual.

3. Function of Middle piece:

• The middle piece contains several mitochondria, which produce energy for the movement of the tail and motility of the sperm.

1. Wind pollinated: Pollen grains are light non sticky/ well exposed stamens/ Large feathery stigma/ single ovule in each flower/ Small flowers packed in inflorescence.

2. Insect pollinated: Pollen grains sticky/ Floral rewards/ Fragrant/ Nectar rich/ Large Flower/ Foul odour.

1. To preserve the agricultural biodiversity in the form of preservation of valuable genetic resources.
2. These pollens can be used in various crop hybridization breeding programmes, biochemical and physiochemical studies such as the study of allergens etc.

1. A compatible pollen grain starts its germination on the stigma.
2. The intine grows out through one of the germ pores to form a pollen tube; the contents of the pollen grain move into the pollen tube.
3. In those species, where the pollen grains are shed at the two-celled stage, the generative cell divides to form two male gametes.
4. The pollen tube grows through the tissues of style and stigma and reaches the ovary.
5. It enters the ovule through the micropyle and then enters the embryo sac through the filiform apparatus of one of the synergids.
6. All these events, from the deposition of pollen grains on the stigma till the entry of pollen tube into the ovule, are collectively called pollen-pistil interaction.

1. Syngamy, i.e., fusion of male and female gametes to form a zygote.
2. Triple fusion, i.e., fusion of two polar nuclei (secondary nucleus) and a male gamete, to form the primary endosperm nucleus (PEN).

1. The flowers offer floral reward like nectar and pollen grain.
2. In some species floral reward provides safe place to lay eggs.

1. The flowers are small and inconspicuous.
2. The pollen grains are light and non-sticky so that they can be easily transported by wind.
3. They have well-exposed stamens so that pollens get easily dispersed.
4. They often have feathery stigma to catch the pollens grains.
5. The pollen grains are dry and unwettable to prevent pollens from gaining moisture from air.
6. The pistil usually has single ovule in each ovary.

1. Pollen grains are light in weight, non-sticky, dry and winged.
2. Well-exposed stamens for easy dispersal of pollen grains in the wind.
3. The stigma is sticky, large, feathery to trap pollen grains in air.

1. Select two pea plants one with white and other with purple flower.
2. Label them as male (white flowered) and female (purple flowered) plant.
3. Cut anthers from purple flower with the help of scissors before their dehiscence to avoid self-pollination and cover it with white paper bag.
4. Now, collect pollens from the white flower (male plant) with the help of brush.
5. Dust the pollens on the stigma of female (purple flower) flower.
6. Cover it again with paper bag till seed formation.

1. In some species, the diploid (2n) egg cell is formed without reduction division and develops into embryo without fertilisation.
2. In many varieties of Citrus and mango fruits, some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and then develop into embryos.

1. One of the male gametes moves towards the egg cell and fuses with it to complete syngamy to form the zygote.
2. The other male gamete fuses with the two polar nuclei and forms triploid Primary Endosperm Nucleus (PEN).

This is termed as triple fusion.

3. Since, two kinds of fusion-syngamy and triple fusion take place, the process is known as double fertilization and is charactedstic of flowering plants.

• Autogamy: In this type, pollination is achieved within the same flower. Transfer of pollen grain from the anther to the stigma of the same flower. In a normal flower which opens and exposes the anthers and stigma complete autogamy is rather rare. Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.
  
• Geitonogamy: Transfer of pollen grains from the anther to the stigma of another flower of the same plant.
  
• Xenogamy: Transfer of pollen grains from anther to the stigma of a different plant.
  

A diagrammatic representation of the mature embryo sac.

1. Time of pollen release and stigma receptivity are different (not synchronised). This prevents self-pollination.
2. Anther and stigma are placed at different positions, so the pollens cannot come in contact with the stigma of the same flower.
3. Self incompatibility, which is a genetic mechanism to prevent the pollen germination on the stigma of the same flower.

1. Megaspore is the first cell of the female gametophyte.
2. The megaspore increases in size and its nucleus divides mitotically into two nuclei which move apart to opposite poles. Thus, a 2-nucleate embryo sac is formed.
3. The two daughter nuclei undergo another mitotic division giving rise to the 4-nucleate stage.
4. The third mitotic division gives rise to 8-nucleate 7-celled embryo sac.
5. The central cell contains 2 nuclei known as polar nuclei.
6. The three nuclei at the micropylar region form the egg apparatus.
7. In the egg apparatus, the middle cell is the largest and is called oosphere/ egg/ ovum, while other two naked cells adjoining the egg cell are called synergids.
8. The three nuclei at the chalazal end are surrounded by cytoplasm and cellular wall. These are called antipodal cells.

A diagrammatic representation of the mature embryo sac.

1. Zygote and the primary endosperm nucleus are the products of double fertilisation.
2. Zygote is formed by the fusion of the female gamete and one of the male gametes, i.e. syngamy.
3. Primary endosperm nucleus is formed by the fusion of two polar nuclei (into a secondary nucleus) and one of the male gametes, i.e. triple fusion.
4. The endosperm development from the primary endosperm cell precedes that of the zygote, to provide assured nutrition to the embryo.
5. The zygote develops into the embryo after some amount of endosperm is formed.

1. In plants bearing bisexual flowers, the anthers are removed from the flower before they dehisce. This is called emasculation. The emasculated flowers are covered with a bag of butter paper to prevent contamination of stigma with unwanted pollen. This process is called bagging. When this stigma attains receptivity, mature pollen grains are dusted on the stigma and the flowers are rebagged to allow the fruits to develop.
2. If the female parent produces unisexual flowers, emasculation is not done. The flower buds are bagged before the flowers open. When the stigma becomes receptive, pollen is dusted on stigma and the flower is rebagged.

1. Unisexuality (Dicliny): Flowers are unisexual, so that self-pollination is not possible. The plants may be monoecious (bearing both male and female flowers, e.g. maize) or dioecious (bearing male and female flowers on different plants, e.g. mulberry, papaya).

2. Dichogamy: Anthers and stigmas mature at different times in a bisexual flower for preventing self-pollination.

• Protandry: Anthers mature earlier than stigma of the same flower. The pollen thus become available to stigmas of the older flowers, e.g. sunflower, Salvia.

• Protogyny: Stigmas mature earlier, so that they get pollinated before the anthers of the same flowers develop pollen grains, e.g. Mirabilis jalapa, Gloriosa, plantago.

3. The third device to prevent self-pollination is self-incompatibility. It is a genetic mechanism that prevents self-pollen from fertilising the ovules by preventing pollen germination or pollen tube growth in the pistil. All these methods encourage cross-pollination thus, causing genetic variations among them.

L.S. of pistil showing path of pollen tube growth;

Enlarged view of an egg apparatus showing entry of pollen tube into a synergid.

A diagrammatic view of a typical anatropous ovule.

Geitonogamy will lead to inbreeding depression because the pollen grains are genetically similar, which results in inbreeding. Continued inbreeding will thus reduce fertility and productivity.

1. Unisexuality: Male and female flowers are present on different plants.
2. Dichogamy: The condition in which the stamens and stigma of a bisexual flower mature at different times.
3. Protandry: This is the condition where anthers mature earlier than the stigma and release pollens.

1. Endothecium.
2. Middle layers.
3. Tapetum.

2. The cells of tapetum possess.

1. Dense cytoplasm and.
2. More than one nucleus.

They nourish the developing pollen grains.

1. Self-incompatibility is the genetic mechanism that prevents self-pollen from fertilising the ovule by inhibiting pollen germination or retarding the growth of pollen tube.
2. Certain plant species produce male and female flowers on different plants, i.e. the plants are dioecious; this prevents both autogamy and geitonogamy.
3. Pollen release and stigma receptivity are not synchronised, either the anthers mature first on the pistil/ gynoecium matures first.
4. The anthers and stigma of a flower are placed in such a way that the pollen of the flower cannot fall on the stigma of the same flower.

1. Pollen grains cause severe allergies, bronchial respiratory disorders, asthma, bronchitis, etc.
2. Parthenium (or carrot grass) came into India as contaminant with imported wheat and causes pollen allergy.

Endothecium performs the function of protection and help in dehiscence of anther to release the pollen.

1. The endosperm development starts from the primary endosperm cell (PEC).
2. In the most common type of endosperm development, the primary endosperm nucleus (PEN) undergoes repeated mitotic divisions to give rise to a number of free nuclei in the primary endosperm cell.
3. The number of free nuclei formed varies greatly with the species.
4. At this stage of development, the endosperm is called free-nuclear endosperm.
5. Subsequently, cell wall formation occurs and the endosperm becomes cellular.
6. The cells are filled with reserve food materials. Endosperm development precedes that of embryo development as an adaptation to provide assured nutrition to the embryo.

1. The smaller daughter cell with dense cytoplasm is situated towards the chalazal pole. It is called terminal cell or apical cell or embryonal cell.
2. Another comparatively larger daughter cell situated towards the micropylar cell, is called basal cell. This cell divides transversely and gives rise to suspensor cells.
3. The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.

1. Insect pollinated flowers are large, colourful, fragrant and rich in nectar.
2. A number of flowers are clustered into an inflorescence to make them conspicuous, when the flowers are small.
3. Flowers have nectar glands and are highly fragrant to attract insects.
4. The surface of pollen grains is sticky due to exine layer and stigma is sticky due to mucilaginous layer.
5. In some species, floral rewards are to provide safe place for laying eggs, e.g. amorphophallus.

1. Emasculation refers to the practice of removal of anthers/ stamens from a bisexual flower before the pollen grains mature.
2. It is necessary to prevent the self-pollen from contaminating the stigma.
3. Bagging refers to the covering of the emasculated flowers with a suitable bag made of butter paper; it is essential to prevent contamination of the stigma of the emasculated flower with unwanted pollen grains.
4. When the stigma becomes receptive, the pollen grains from the selected flowers are dusted on it and the flower is rebagged for the development of fruits and seeds. - If female parent bears unisexual flowers, there is no need for emasculation; but the female flower buds are bagged before they open.
5. When the stigma becomes receptive, pollination is carried out with the desired pollen and the flowers are rebagged.

1. The endosperm will have 30 chromosomes and the embryo will have 20 chromosomes.
2. The meiocyte is a diploid cell(with 20 chromosomes) and it undergoes meiosis; hence, the haploid cells of maize will have 10 chromosomes.
3. The endosperm develops from the primary endosperm cell, where the primary endosperm nucleus (PEN) is formed by triple fusion, i.e., fusion of three haploid nuclei-two polar nuclei (fuse to form a diploid secondary nucleus) and a haploid male gamete.
4. So the endosperm cells are triploid with 30 chromosomes.
5. The embryo develops from the zygote, which is formed by the fusion of a female gamete with a male gamete; so it is diploid with 20 chromosomes.

1. The stamens are well-exposed, so that pollen grains are easily dispersed in wind currents.
2. The stigma is large and often feathery, to easily trap the air-borne pollen grains.
3. The pollen grains are light and non-sticky, to be transported in wind currents.
4. There is a single ovule in the ovary of these flowers.
5. Numerous small flowers are packed into an inflorescence.
6. Pollen grains are produced in enormous quantity.

1. There is synchromy between pollen release and stigma-receptivity; i.e. the anthers and pistil mature simultaneously.
2. The anthers and stigma lie close to each other in such a way that pollen from the anther can fall on the stigma.
3. Cleistogamous flowers (the bisexual flowers which do not open at all) are produced by some plants.

Pollination in Vallisneria:

• In Vallisneria, the male flowers (later pollen grains) are released on the surface of water; the female flowers reach the surface of water by uncoiling of the long stalk.
• When the passively floating male flowers/pollen grains meet the female flowers, pollination is effected, and the stalk of the female flower coils and the flower is drawn back inside the water column.

Pollination in Water lily:

• Since the flowers emerge above the level of water, they are pollinated by insects.

Enlarged view of one microsporangium showing wall layers.

Tapetum, the innermost wall layer provides nourishment to the developing pollen grains.

1. A seed is defined as an embryonic plant covered in a seed coat containing some food. On the other hand, a grain is a small edible fruit, usually hard on the outside, harvested from grassy crops.
2. Maize grains are formed from female flowers after the fertilisation.
3.  

4. Amit is attentive, inquisitive and wants to gain knowledge.

1. Yes, there are some plants with closed flowers, e.g. Oxalis.
2. Yes, such flowers undergo self-pollination. The pollen from the anthers of same flower are transferred to the stigma of the same flower.
3. Such flowers are called cleistogamous flowers.
4. Kanchan is very curious about nature, active and lively in her life.

1. The farmer was spraying auxins or gibberellins in low concentration which have been found to induce parthenocarpy in several plants, e.g. tomato, cucurbits, strawberry, fig, etc.
2. This is called chemically induced parthenocarpy, which is not harmful for the consumers. However, pesticide sprays are harmful for our health.
3. In parthenocarpy, fruit formation occurs without fertilisation. It can be of three types, i.e. genetical, environmental and chemically induced (as done by the farmer).
4. Ram is an intelligent, observant, inquisitive boy who is concerned about the day-to-day activities that happen around him.

1. The crossing of different plant species and genera leads to combination of desirable characters to produce commercially superior varieties.
2. Artificial hybridisation.
3. In artificial hybridisation, only desired pollen grains should be used for pollination. The stigma should be protected from unwanted pollen. This can be achieved by emasculation and bagging techniques.
4. Rohan is attentive, observant, inquisitive and wants to gain knowledge.

Cross-pollination can be prevented by exhibiting:

1. Cleistogamous flowers: These are bisexual closed flowers which never open and the anthers dehisce inside these closed flowers, e.g., Commelina.
2. Homogamy: It is the condition of the maturity of anther and stigma at the same time, e.g., Catharanthus (Vinca).
3. Close association between anther and stigma, e.g., Mirabilis.

Chasmogamous and cleistogamous flowers.

1. Meiosis.
2. Mitosis.
3. Mitosis.

1. Yes, a plant flowering in Mumbai can be pollinated by pollen grains of the same species growing in New Delhi, It is mainly because there are certain agents of pollination that can carry pollen grains to long distance.

It is believed that pollidation by wind (anemophily) is more common because transport by wind-current can take pollens to distant places.

2. The parts involved in transferring the male gametes to its desired destination are stigma, style, micropyle, filiform apparatus and synergids.

1. No; the pollen grains of different species remain viable for different periods of time.

e.g. pollen grains of cereals remain viable for less than 30 minutes whereas some members of Rosaceae, Leguminosae and Solanaceae retain the pollen viability for months.

2. In the pollen banks, pollen grains are stored. In liquid nitrogen (at -196°C). Such stored pollen grains can be used for breeding programmes whenever necessary.

1. .

• Coleoptile protects the plumule.
• Coleorrhiza protects the radical.
• Endosperm stores food materials to be used by the embryo during germination of the grain.

1. The organic material of exine of pollen grain is sporopollenin. This is the most resistant biological material known so far. It protects pollen grains from damages.
2. Exine on pollen grain is not a continuous layer. It is thin at places and pollen tube germinates by growth of intine through these thin parts of exine called germ pores.
3. Pollen banks can be used for storing pollen grains for years and for crop breeding programmes.

2. It is through the micropylar end the pollen tube enters the ovule. The micropyle helps in absorbing the water at the time of germination of seed.

1. Albuminous seedCastor, Coconut, Sunflower.

Non-albuminous seed-Pea, groundnut.

2. ​​​​​​​

1. Nucellus.
2. Integuments.
3. Primary endosperm cell.
4. Zygote.

1. On the exine of pollen grains while in the microsporangia.
2. In the central cell of embryo sac of the ovule.
3. From the pollen tube into one of the synergids of the embryo sac.
4. In the nucellus of the ovule.

1. No, it cannot be assumed like that because double fertilisation does occur in legumes.

• The primary endosperm cell undergoes mitoses and forms the endosperm, whose cells are filled with reserve food materials.
• But it is completely consumed by the developing embryo before the seed matures and there is no residual endosperm left in the seed; so the seeds are non-albuminous.

2. Similarity

• In both autogamy and geitonogamy, the pollen grains are genetically similar to the pistil.

Difference:

• In autogamy, pollen grains of a flower fall on the stigma of the same plant; no pollinating agent is involved.

1. No, not all pollen grains remain viable for the same length of time.

Two suitable examples of the same are:

• Some cereals like rice have pollen grains that lose viability within 30 minutes of their release.
• Some members of family Leguminoseae, have pollen grains that have viability for a few months.

2. 'Pollen Banks' store pollen grains for a period of time in viable conditions. These can be used for different studies and crop breeding techniques. It preserves the biodiversity by preserving genetic material.

The pollen grains can be stored by two methods:

• Short term storage of pollen grains.
• Long term storage of pollen.

• Double fertilisation occurs in legumes and there is also endosperm formation.
• But, the developing embryo consumes the endosperm completely and there is no residual endosperm in the mature seed; hence the seeds of legumes are non-albuminous.

• In plant breeding experiments, pollen from the selected male parent only, are used for pollination.
• To prevent contamination of the stigma by any other pollen grain, the pistillate flowers are bagged.

2. Continued self-pollination leads to inbreeding depression; hence to discourage self-pollination, outbreeding devices are developed by flowers.

1. Development of Pollen grain:

1. Microsporocytes undergo mitotic divisions to increase the number of functional microspore mother cells.
2. Each microspore mother cell undergoes meiosis to form a microspore tetrad.
3. All the four microspores remain enclosed in a common wall.
4. As the anther matures and dehydrates, they start separating from one another and each develops into a pollen grain.
5. The nucleus undergoes a mitotic division resulting in the formation of a large vegetative cell and a small generative cell.
6. The pollen grain develops a wall of two layers-the outer exine of sporopollenin and inner intine of pectin and cellulose.
7. At this stage, the pollen grains are liberated; but in some cereals the generative cell undergoes mitosis to form two male gametes and the pollen grain is 3-celled, at the time of liberation.

2. Mature Pollen Grain:

1. A mature pollen grain has a wall of two layers.
2. The outer layer called exine is thick, and is made of sporopollenin.
3. The exine has prominent apertures, called germ pores, where sporopollenin is absent.
4. The inner layer, called intine is thin and is made pf pectin and cellulose.
5. A mature pollen grain is two-celled with a large vegetative cell and a small generative cell floating in the cytoplasm of the vegetative cell.

2. Functions of micropyle:

1. It is the passage through which the pollen tube enters the ovule.
2. It remains as a small pore in the seed coat and facilitates the entry of water and oxygen during seed germination.