Sexual reproduction in flowering plants

 Introduction 

Reproduction is one of the most important event help in the survival and growth of every organism. The initial phase of all the organisms is the growth phase or the juvenile phase (In plants it is called vegetative phase) where individuals grow physically to prepare themselves for the reproductive phase which is the next phase. During the reproductive phase, many changes occur within the plant. Plant reproduction is the collective process used for the production of new offspring. Plant reproduction is accomplished by sexual or asexual reproduction while the majority of the flowering plants undergoes sexual reproduction. Sexual reproduction produces offspring by the fusion of gametes which results in offspring having genetically different traits from the parents. On the other hand, sexual reproduction produces new individuals without the fusion of gametes and the resulted progeny is genetically identical to the parent plants, except when mutations occur. In this post, let us be specific to the sexual reproduction in a flowering plant.

 

 

Prerequisites for sexual reproduction

Sexual reproduction is the most common mode of reproduction in the majority of the eukaryotes. Sexual reproduction requires certain conditions to be met, such as age, sexual maturation, hormonal levels and health status of the 2 individual parents. Sexual reproduction involves 2 parents with a male and a female. Sexual reproduction results in the gamete formation with the help of fertilization which is gradual and lengthy. One of the fundamental features of sexual reproduction is the occurrence of variation among offspring as most of the progeny are different from their parents both genetically and physically.

 

 

Sexual reproduction in flowering plants

Sexual reproduction results in the formation of one or more slightly identical or non-identical offsprings due to the sexual contact between the male and female parts of the flowering plant. Flowering plants are the most dominant type of plants as the majority of the plant population on the earth belong to this group. Non-flowering plants accommodate asexual reproduction, while the flowering plants are not hence they are unique. Irrespective of a plant or animal, sexual reproduction produces a diverse range of features due to the genetic variation that occurs at the time of exchanging the gametes. In a flowering plant, sexual reproduction can happen in 2 scenarios; an individual flower has both male and female parts that come in contact to form a fused product or a plant can have either male or female part which comes in contact with the flowering parts of other plants. In order to understand the sexual reproduction, it is essential to understand the parts of the flower.

 

 

Parts of a flower 

In most of the cases, an individual plant contains both male and female reproductive organs within it. The flowers of such plants are called bisexual flowers which makes sexual reproduction easy due to the easy access between the male and female flowering parts. On the other hand, if the flower is monosexual having either male or female parts, the chances of reproduction are not by direct contact, but they take the help of vectors like honey bees, wind or animals.

 

 

 

 

  1. The fundamental parts of a flower which supports reproduction in flowering parts are stamen which is the male reproductive part and pistil , female reproductive part.

  2. Some other parts that aids in reproduction are calyx, Corolla, Androecium, and Gynoecium.

  3. The calyx is the collection of sepals found at the first layer from the base of the flower which is usually green in colour but they can rarely differ. The set of coloured sepals are called petaloids that help in protecting the flower through the budding stage. 

  4. Corolla, the second layer from the bottom is the orderly arranged collection of petals found just above the sepals while the petals are the most colourful part of a flower aids in attracting the insects and birds for pollination. In the middle of many sepals, a pollen tube has arisen. Corolla is used to indicate the male parts of the sexual reproduction of a plant hence they are absent in some flowers.

  5. Androecium, the third layer of the flower settled just above the corolla and has a bunch of stamens with each stamen containing an anther and a filament. The anther is at the tip of the filament inside which the pollen grains are stored. The filament is a stalk-like extension that holds the anther straight. 

  6. The gynoecium is the 4th layer from the bottom of a flower possessing a collection of carpels. It again has three parts namely stigma, style, and ovary. Stigma is a small and sticky landing spot on which pollen grains stick. Style is a thin stalk-like structure assist in holding the stigma and Ovary. At the base of the style, many ovules are present. Ovules contain the female gametes.

 

 

Mechanism of reproduction in a flowering plant   

As mentioned above, the flower can be unisexual or monosexual. Plants such as papaya and watermelon are best examples where they contain either carpel or stamens. In a bisexual plant,  both stamen and carpels are found . Plants such as Hibiscus, mustard belong to this group. Stamen, the female part of a flower produces yellowish pollen grains, which stick to your hand when you touch the yellowish surface of a flower. On the other hand, carpel is the female part present in the middle of the flower.  A carpel has bottom part called the ovary, the middle elongated portion is the style and the top portion is the sticky stigma. The ovary contains ovules or egg cells.

 

 

Stages of  reproduction

  1. The male germ-cell produced by the pollen grain comes in contact with the ovule resulting in the fusion of their germ cells and the process is called fertilization.

  2. In order for the fusion of male and female parts, the pollen must be carried from the stamen to the stigma and the process is called Pollination. If the transfer of pollen occurs within the same flower, it is  called self-pollination. But some times the pollen contact happens between 2 different flowers called cross-pollination. 

  3. Pollen makes use of several vehicles for its transfer to the target place. Some of the most common vehicles are wind, rain, insects, birds, and animals.

  4. As the pollen lands on a suitable stigma, it reaches eggs; the female germ-cells found in the ovary. To facilitate this transfer, a small tube-like structure is developed out of the pollen called style through which the grains travel. 

  5. After the fusion (fertilization), the zygote multiplies several times to form an embryo inside the ovule. In order to protect the embryo, the ovule develops a tough covering layer which later becomes the seed. 

  6. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals, sepals, stamens, style, and stigma may shrivel and fall off. The seed contains the future plant or embryo which develops into a seedling under appropriate conditions. The formation of the seed is known as the germination.

 

 

Stages of sexual reproduction in plants

 

 

 Fruit and seed formation

Followed by the fusion of male and female gametes (fertilization), the ovary gets ripened to become fruit. The seeds develop from the ovules of the ovary with each seed containing an embryo enclosed in protective covering layers around the seed. The fruits can be soft like mango, orange, or they can be hard nuts like almond and walnuts.  The outermost layer is the epicarp while the middle portion is the mesocarp. At the centre comes the seed which is surrounded by a layer of the endocarp.

 

 

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