Chapter 12 Reproduction in Plants

(a) Vegetative propagation
Vegetative propagation is an asexual method of reproduction in plants in which lower plants reproduce vegetatively through various methods like budding, fission, fragmentation, spores, buds etc. With the flowering parts roots, stems, leaves and buds helps in the vegetative propagation. For example: tuberous roots of modified plants can be vegetatively propagated when planted in soil.

(b) Unisexual
A flower may have either male or female reproductive parts. Such a flower is called unisexual flower whereas bisexual flower possess both stamen (male reproductive organ) and pistil. 

(c) Pollination
The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as pollination. This is of two types: self- pollination (it involves the transfer of pollen grains from the anther to the stigma of the same flower) and cross- pollination (it involves the transfer of pollen grains from the plant of one flower to the stigma of another plant).

(d) Fertilization
The process in which the male gamete fuses with the female gamete that is present in ovule to form a new cell called diploid zygote is called fertilization that occurs within the embryo sac or female gametophyte.

(e) Air, water and insects
Seed dispersal takes place by various agent that is responsible for cross pollination. Anemophily (wind pollination) is the mode of transfer of pollen grains from anther to stigma through the agency of wind. Hydrophily is the water pollination in which the transfer of pollen grains from anther to stigma occurs through the agency of water. Wind and water pollination both are the abiotic factors of the pollination. Entomophily is the animal pollinator or biotic category in which the transfer of pollen grains from anther to stigma occurs through the agency of insects like moths, flies etc.

Asexual reproduction is the simplest form of reproduction in which only one parent is involved. It do not involves the meiosis, gamete formation and fusion of gametes. This asexual reproduction is also known as clonal propagation because of their genetically identical products.

The asexual reproduction in plants can take place by the following methods:

1. Vegetative propagation: It is the natural process that is found in many plant species. It is a process by which plant reproduces without the production of seeds and spores. In this growth of new plants from the plant parts (like bulbs, runners, stems cuttings, roots and leaves etc.) occurs. Tissue culture is also the method of vegetative propagation under the sterile conditions.

Examples: Tuber of potato, the rhizome of ginger etc.

2. Budding: In budding process a small part of the body of the parent plant grows as a bulb- like structure called ‘bud’ which then detaches and becomes a new plant or we can say formation of daughter individual from the small projection called the bud that arises on the parent body is known as budding.

Example: Yeast (unicellular fungi), Hydra etc.

3. Fragmentation: The breaking up of the body of a plant into two (or more) pieces on maturing, each of which automatically grows to form a new plant, is called fragmentation. An alga reproduces by the asexual method of fragmentation. An example of common alga is Spirogyra. Spirogyra is a green, filamentous alga plant which is found in ponds, lakes and slow moving streams. Spirogyra reproduces by the asexual method of reproduction called fragmentation.

4. Spore Formation: Propagules which germinate to produce new individuals are known as spores. There are several types of spores: zoospores, sporangiospores, chlamydospores, oidia and conidia.  

Sexual Reproduction:  Meiosis and fertilization; these two are the essential processes in the sexual cycle of the flowering plants Sexual reproduction is the combination of reproductive cells from two individuals to form offspring (with unique characteristics). Sexual reproduction produces offspring with the different combination of genes and as a result it leads to evolution with the new characteristics. It includes the production of gametes which have half the number of chromosomes compared to all other cells in the organisms.

Most of the flowering plants reproduces through the sexual reproduction method involving the fusion of sex cells called gametes. This means that two sexes: male and female that are involved in reproduction in flowering plant. Flowers are the reproductive part of the plant. The sexual reproduction in plants involves the fusion of male and female gametes of the plants which leads to the formation of the seeds of the plant and these seeds can then used to grow new plants.

A flower is modified into complex shoot to carry out sexual reproduction in the higher plants. The terminal or the end part of the axis of the flower that supports all the floral appendages: sepals, petals, stamens and carpels; is known as receptacles. These four whorls of floral appendages attached on the receptacle in which the two lower whorls (calyx and corolla) are sterile; and upper two are (androecium and gynoecium) are fertile or reproductive whorls. The floral parts are explained as below:  

1. Calyx: It is the outermost circle of a floral leaves are called calyx and the individual leaf segment is known as sepal, is green in colour. The function of sepals (Or calyx) is to protect the flower in its starting stages when the bud formation occurs.

2. Corolla: This is the second whorl of the floral leaves arise from the inner part to the calyx, and colourful parts of a flower are called corolla and the individual leaf of corolla is known as Petal. The petals lie inside the sepals and are generally coloured which attracts the insects (for pollination) and to protect the reproductive organs of the flower.

3. Androecium: The little stalk and the third whorl of the floral appendage that arises inner to corolla; individual appendage is stamen. Stamen is the male reproductive organ of the plant and consists of two parts: a filament and an anther. The stalk of stamen is called filament and the swollen top of stamen is called anther and it makes the pollen grains and stores them. Pollen grains appear to be yellow, powder like substance to us. Pollen grains contain the male gametes (or male sex cell) of the plant which is present inside a pollen grain is called ‘male nucleus of pollen grain’.

4. Gynoecium (or pistil): In the centre of a flower, there is a flask-shaped organ called pistil and it represents female reproductive organ of the plant. A pistil is constitutes of three parts: stigma, style and ovary. Ovary is the present on the base and is swollen part of the carpel that bears various ovules. Stigma lodges pollen grains. Style is the connection between ovary and stigma.

Pollination is the transfer of pollen grains from the anther to the stigma of the flower which can be achieved by biotic (insects, birds etc.) and abiotic (wind, water etc.) pollinating agents. On the basis of pollinating mechanism, plants can be grouped into two mating systems: self- pollinated and cross- pollinated.

The process of fusion of gametes of male and female (egg) to form the diploid zygote in the embryo sac is called fertilization.

Fertilization takes place as follows: The pollen generally germinates on the stigma. When a pollen grains falls on the stigma of the pistil then the pollen grains grows a pollen tube into downward direction through the style towards the female gametes in the ovary. A male gamete are carried to the egg by the pollen tube and enters the ovule in the ovary. The tip of pollen tube bursts out and male gametes comes out of pollen tube or gets spreads out. In ovary, the male gametes of pollen fuses with the female gamete present in ovule to form the ‘zygote’ then zygote develops into the embryo sac; this process is known as siphonogamy. Embryo is that part of a seed that develops into the new plant.

Seed dispersal takes place by various agent that is responsible for cross pollination; and this means to scatter seeds over a large area. The seeds of some of the plant disperse as seeds and some are dispersed in the form of fruits because they contain seeds inside them. There are various methods of seed dispersal that have been categorised into two main categories: Abiotic (like wind, gravity, water etc.) and Biotic (animal pollinators like insects).

Anemophily (wind pollination):                                                                                                                                                                                                      It is the mode of transfer of pollen grains from anther to stigma through the agency of wind. The flowers that are wind pollinated are anemophilous. These flowers contains some adaptations like flowers are colourless, odourless and nectar-less; pollen grains are small, dry, dusty and sometimes saccate so that they can blow away easily to the long distances etc.

Hydrophily (water pollination):                                                                                                                                                                                                      It is the mode of transfer of pollen grains from anther to stigma occurs through the agency water. The flowers that are water pollinated are hydrophilous flowers. These flowers contains some adaptations like flowers are small, colourless, odourless and nectar-less; pollen grains are unwettable, stigma are long and sticky etc. Dispersal by water takes place in some aquatic plants which is very rare and in some that grows near a water body. For example: Zostera, Hydrilla, Ceratophyllum etc.

Entomophily (insects pollination):                                                                                                                                                                                                It is the animal pollinator or biotic category in which the transfer of pollen grains from anther to stigma occurs through the agency of insects. The flowers that are insect pollinated are entomophilous flowers. These flowers contains some adaptations like flowers are usually large, brightly coloured and slowly to attract insect pollinators etc. The most common insect pollinators are as follows: moths, flies, butterflies, bees, beetles etc.

Dispersal by Humans: Human beings also help in dispersal of seeds during the farming.                                                                                                          

There are much more methods for the dispersal of seeds like Ornithophily (pollination by birds), Chiropterophily (pollination by bats) etc.  

Here are the correct matches; 

Column I                             Column II
(a) Bud                                  (iii) Yeast
(b) Eyes                                (v) Potato
(c) Fragmentation                 (ii) Spirogyra
(d) Wings                              (i) Maple
(e) Spores                             (iv) Bread mould

Budding is a process of asexual reproduction in which bud is arise from the parent body and when it mature, it get detached from the parent body and makes a new individual. Eyes (as bud) potato's vegetative part that also shows budding process. fragmentation is the asexual mode of reproduction. spirogyra is an algae which shows reproduction through this fragmentation method. Maple have seeds which have wings, which is very light weighted so that pollination is being easy or the transfer of pollen grains from anther to stigma is easy. Bread mould is the most common fungi, found in tropical and sub- tropical regions. Spores are asexual reproductive bodies, are light in weight and covered by hard protective covering which protects them from unfavourable condition like high temperature and low humidity.  
                                             

(a); (iv) Flower                                                                                                                                                                                                                              Flowers are the reproductive part of a plant that contains Stamens and pistils which are the male and the female reproductive part of a plant respectively.

(b); (i) Fertilization
The process of fusion of gametes of male and female (egg) to form the diploid zygote in the embryo sac is called fertilization.

(c); (iv) Fruit
Ovary contains ovules that develop into seeds after the fertilization process. After that the zygote differentiates to form an embryo sac inside the ovule. The ovary matures to turn into the fruit which can either be fleshy or dry, in which the seeds are embedded in them. A fruit is mainly formed as the result of cell division, expansion and differentiation in the ovary; or the results of stimuli received from pollination as well as from the seeds that are developing. 

(d); (ii) Bread mould
Spore is a unit of reproduction in plants which may also be used for dispersal as well as for survival in unfavourable conditions spore- producing plants include ferns, mushroom, liverworts, hornworts and mosses etc.

(e); (ii) Leaves
Bryophyllum is a group of plant species of the family Crassulaceae and can reproduce by its leaves, i.e. reproduces asexually.