NEET Important Chapter - Sexual Reproduction in Flowering Plants

This article includes the notes of the chapter sexual reproduction in flowering plants as per the NEET syllabus for biology. This article will help out the NEET aspirants as it explains sexual reproduction in flowering plants and its important topics for the last minute revision.

The following document contains all of the important topics and provides insight into the exam pattern. By going through this document one can find out all the answers to the important questions related to the chapter such as what is a flower and describe its different parts of the flower, what is pre fertilisation events: microsporogenesis and megasporogenesis, what is pollination and its types, what is fertilisation, why double fertilisation is observed in angiosperms, what are post-fertilisation events, what is apomixis and polyembryony. 

Important Topics of Reproduction in Organisms

• Flower: its different parts and functions

• Microsporogenesis and megasporogenesis

• Structure of pollen grain

• Types of ovules

• Pollination and types of pollination

• Artificial hybridization

• Inbreeding and outbreeding devices

• Pollen pistil interaction 

• Double fertilization

• Post fertilization events like endosperm formation, embryo formation, seed formation and fruit formation

• Apomixis 

• Polyembryony

Important Concepts

Flowers: The Attractive Parts of the Plant

The flowers are the charming parts of the plants. Those are colourful elements which attract insects and are referred to as the reproductive organs of the plant. The flower possesses essential and non-essential whorls. The essential whorls are androecium and gynoecium and the non-essential whorls are the calyx and corolla

The Four Whorls of the Flower

1. Calyx 

These are the outermost layer of the flower which is referred to as sepals. This calyx covers the opposite floral elements in the course of bud. Mostly green in shade however in a few cases it is petaloid as they may be coloured as petals. They either can be absent or distinguished.

2. Corolla  

It is the second whorl of the flower that possesses three or more than three petals which might be fragrant every so often. Those are helpful in pollination as they are colourful and appealing which entice animals.

3. Androecium  

It is the third whorl of the flower that possesses stamen and so it's far referred to as the male reproductive part. Stamen is made of two components, particularly anther and filament.

• Anther: These are the structures responsible for pollen production, these are four-lobed and the tapetum is the inner layer which nourishes the developing pollen grain.

• Filament: These are long thread like shape which can be beneficial in maintaining anther in an area

• Microsporangia: These are made up of four layers: tapetum, central layer, endothecium and epidermis.

• Tapetum: Innermost layer of Microsporangium(anther) which nourishes the developing pollen grains

• Central/Middle layer: Those are observed simply next to the endothecium, made up of thin-walled layers.

• Endothecium: These are innermost to the epidermis made of thin-walled cells.

• Epidermis: These are the outermost layer that is surrounded externally.

• Microsporogenesis: The formation of microspore from microspore mother cells by way of the meiotic division.

4. Gynoecium 

The closing whorl of the flower which is also called the female reproductive element, the important position of the thalamus is occupied by the gynoecium. The pistil is made up of stigma, style and ovaries. Ovules are produced in the ovary. Megaspores are produced by using ovules which eventually produce female gametophytes after which egg cells are produced.

Events in Sexual Reproduction

There are three events in sexual reproducion Pre-fertilisation, Fertilisation, Post-fertilisation.

1. Pre-Fertilisation: It involves the processes called Gametogenesis and gamete transfer. 

• Gametogenesis: The production of male and female gametes is known as gametogenesis. Gametes are haploid cells with a structure that might be similar or distinct. 

Isogametes: Both the gametes have a similar structure.

Heterogametes: Both the sexes have distinctly structured gametes.

In fungi and plants, the bisexual condition is denoted by terms like homothallic and monoecious and for the unisexual condition, it is heterothallic and dioecious. In flowering plants, the unisexual male flower is staminate, i.e., bearing stamens, while the female is pistillate or bearing pistils.

• Gamete Transfer: It can be described as the transfer of gamete which leads to fusion. In the majority, only male gametes are motile while fungi and algae have both gametes motile.

2. Fertilisation: It is also called Syngamy, wherein the fusion of male and female gametes occurs. 

Pollination: Pollination is the transmission of pollen from a plant's anther to its stigma. Pollination may be self (anther to the stigma of the same flower) or cross (anther to the stigma of a different flower). Factors affecting: wind, water, rain and pollinators. 

• The process of the development of new organisms without fertilisation of female gametes is called parthenogenesis. For example: banana.

• External fertilisation happens when syngamy occurs outside the body of the organism and internal fertilisation happens when the syngamy occurs inside the body of the organism.

3. Post Fertilisation Events: Events in the sexual reproduction after the formation of the zygote.

Embryogenesis: It is the process of the development of the embryo from the zygote wherein the zygote undergoes mitotic division and cell differentiation. 

• In flowering plants, the zygote is formed inside the ovule. After fertilisation, sepals, petals and stamens of flowers fall off. The zygote develops into embryos and ovules into seeds. The ovary develops into fruits which develop a thick wall called the pericarp, protective in function.

Artificial Hybridisation 

This includes 2 steps: Emasculation and Bagging.

• Emasculation: If the maternal parent plant bears a bisexual flower, the elimination of anthers from the flower bud before the anther dehisces by the usage of a couple of forceps is referred to as Emasculation.

• Bagging: Emasculated flowers need to be covered with a bag of appropriate size, generally made from butter paper, to save from contamination of its stigma with unwanted pollen. This manner is referred to as bagging. When the stigma matures the pollen grains of desired or selected quality, are dusted at the stigma and are rebagged and the fruits are left to develop.

Double Fertilisation

In this process, the 2 male gametes within the pollen grain enter the embryo sac through a pollen tube, one gamete fuses with egg cells and another fuses with polar nuclei. This process may be determined in angiosperms.

Apomixis

The asexual formation of a seed from the maternal tissues of the ovule heads off the techniques of meiosis and fertilisation, and leads to the development of the embryo.

Polyembryony

A condition in which a single fertilised egg leads to the development of two or more embryos.

Solved Examples from the Chapter: Sexual Reproduction in Flowering Plants

1. Where do the male and female gametophytes develop in an angiosperm flower?

Ans: The male gametes inside the angiosperm flower are evolved within the anther and the female gametophyte in the angiosperm flower develops within the ovules.

Key point to remember: Anther = male gametes, Ovules= female gametophyte

2. Differentiate between microsporogenesis and megasporogenesis. 

Ans:

3. Why is a mature embryo sac called 7-celled, 8 nucleated?

Ans: In angiosperms, the mature female gametophyte or the embryo sac consists of an egg apparatus with two synergids at the micropylar end and 3 antipodals at the chalazal end and also two polar nuclei in a single cell are present at the centre now according to the count 3 antipodals + 3 egg apparatus with synergids + 1 polar nuclei cell, it is 7 celled but as the polar nuclei consist of 2 nuclei it is 8 nucleated.

Key point to remember: 3 Antipodals + 3 Egg apparatus with synergids + 1 Polar nuclei cell

Solved Problems of Previous Years’ Question Based on the Chapter: Sexual Reproduction in Flowering Plants

1. Dioecy in plants prevents: 

a) Autogamy but not geitonogamy 

b) Geitonogamy but not autogamy 

c) Both autogamy and geitonogamy 

d) Neither autogamy nor geitonogamy 

Ans: (c) Both autogamy and geitonogamy

Autogamy: The pollen grains are transferred to the stigma of the same flower then it is referred to as Autogamy also called self-fertilisation.

Geitonogamy: The pollen grains are transferred to the unique flower stigma of the identical plant.

These techniques may prevent dioecious plant life. The dioecious flowers are the ones which own the male and female flowers at the other plants. 

Trick: Papaya is an instance of a dioecious plant, as the male and female plant life are observed in the unique vegetation, each autogamy and geitonogamy are averted on this plant.

2. Which one of the following may require pollinators, but is genetically similar to autogamy? 

a) Geitonogamy

b) Xenogamy 

c) Apogamy

d) Cleistogamy 

Ans: (a) Geitonogamy 

Geitonogamy: In this form of pollination the pollen grains of the unique plant however from different flowers reach the stigma, which is as equal to autogamy because the zygote gets the gene pool of the same plant.

Trick: Auto = same plant same flower, Geitono = same plant different flower.

3. Functional megaspore in an angiosperm develops into 

a) Ovule

b) Endosperm 

c) Embryo sac

d) Embryo 

Ans: (c) Embryo sac

The functional megaspore is the first cell of the female gametophyte. When there is the enlargement of the cell, it undergoes the free nuclear mitotic division. After first division 2 nucleate embryosac is produced.  The 2 nuclei pass closer to the other ends and divide two times to form 4 nucleates after which eight nucleate structures are formed. From each facet, one nucleus acts towards the middle and are referred to as polar nuclei. At the 2 ends ultimately three cells with nuclei and at the micropylar give up three celled egg apparatus and at the chalazal end, three antipodal cells formed. The cell in the centre is organised with binucleate. A single megaspore gives rise to the embryo sac being monosporic.

Practice Questions

1. The male gametophyte (microgametophyte) in case of monocots is:

a) Tetrad

b) Nucellus

c) Megaspore

d) Microspore

2. In a somatic cell, there are 16 chromosomes. What will be the number of chromosomes in the pollen mother cell of the plant?

a) 16

b) 8

c) 24

d) 32

1. Ans: (a) Tetrad

Microspore is the beginning of the male gametophyte. In the case of monocots, the male gametophyte is tetrad. 

2. Ans: (c) 24

Triple fusion results in the angiospermic endosperm, so when the 2n=16 in an angiospermic plant has the endosperm 3n=24.

Conclusion

This article contains all the important information as per the NEET aspirant. Sexual reproduction in flowering plants neet notes can be really very helpful for a quick and at the same time effective revision. It includes all the important concepts and topics, questions from previous years’ NEET question papers, NEET mock tests and Biology NCERT. Make sure to try the Practice question on your own to test your learnings.