Types of Reproduction

One of the basic characteristics of living things is their ability to reproduce. Reproduction is a biological process by which living things produce their young ones which are similar to the parents. Reproduction ensures the continuity of a species and also helps the organism to adapt itself to the changing environment.

There are two principal types of reproduction, asexual and sexual. The organisms produced through asexual reproduction are genetically identical among themselves and also to their parents. These organisms fail to cope with the changing environment and if continue to reproduce this way, ultimately become extinct/ asexual reproduction is advantageous for the organisms as this method is efficient, a shorter time is taken for the species to inhabit or colonize the habitats. In the long term the organisms must reproduce by sexual reproduction to become successful over longer periods of time.

“A population of genetically identical individuals produced from a single parent is called a clone”

Definition of Types of Reproduction — Types of Reproduction

In asexual reproduction no gametes are involved, all the offspring’s are produced from single parent by mitotic cell division.

The most important difference between asexual and sexual reproduction is that in the former, there is no mixing of hereditary material prior to the formation of new organism, but in the latter there is always mixing of hereditary material, either between two cells of the same organism or between two cells of different organisms of the same species.

Different types of asexual reproduction — Types of Reproduction

The none mixing of hereditary material in asexual reproduction does not improve the genetic make up and does not produce variety among the descendents. So if environmental conditions, to which these organisms are well adapted, are changed, this would affect all the members of that species. Suppose if asexually produced plant has no resistance to a particular disease the whole population could be wiped off. In contrast the genetic variability is produced by sexual reproduction, which results in most cases by meiosis and mixing of hereditary material. This genetic variability helps the organisms to live successfully in changing environment.

So some of the offspring would survive, even if most of them are wiped off by a particular disease, because the surviving organisms have the resistance to that disease. Some of the common methods of reproduction in plants and animals are binary fission, multiple fission, budding, spore formation, vegetative propagation, regeneration, parthenogenesis and sexual reproduction.

Asexual means without sex and this method does not involve the fusion of gametes in most cases. There are many different forms of asexual reproduction employed by different kinds of organisms including plants. Some of these methods are:

Binary fission in bacteria

It is a type of asexual reproduction in which one unicellular organism divides into two by simple division (fig 16.1). Bacteria belong to kingdom monera and exhibit binary fission. Under favorable conditions one bacterium would divide into two bacteria after about every 20 minutes. They gave a single circular chromosome made of DNA. Steps involved in binary fission are:

(1) when the DNA molecule replicates, it results in the formation of two chromosomes.

(2) These two chromosomes move towards opposite sides.

(3) The middle portion of the cell membrane invigilates inwards from the two sides and when meet in the centre it separates the two halves of the bacterial cell.

(4) New cell wall is deposited between two cross cell membranes.

(5) The daughter bacteria grow to their normal size, and then separate from one another.

Budding in yeasts

Yeast, a fungus, consists of a single microscopic spherical cell. The cells of yeast reproduce by budding. It is a special type of asexual reproduction, in which a small bud or out-growth is formed on one side of cell. The nucleus divides by mitosis into two nuclei, and one of the two nuclei is passed on to the bud. Bud enlarges and is finally cut off as an independent cell. When the process of budding is rapid, the individual cells so formed do not separate at once and as a result, small groups of attached cells may some times be seen.

al-qasim-trust-yeast — Fig. 16.2. budding in yeast

“Practical work: observation of budding in yeast using prepared slides”

1. How many buds are present on a single yeast cell?

2. Can you find nucleus in any bud?

Spore formation in Rhizopus

You have already studied the structure of Rhizopus. Asexual reproduction in Rhizopus is by the formation of spores in sporangia which are borne on the tips of sporangiophores. Spores are single celled, thick walled, and are produced in sporangium without sexual process. These spores are released from the sporangium and are carried by wind. Each spore when exposed to suitable conditions forms new Rhizopus mycelium.

al-qasim-trust-rhizopus — Fig. 16.3 sporangium and spore formation in rhizopus

(Fig.16.3 Sporangium and spore formation in Rhizopus)

“Practical work examination of sporangia and spores of Rhizopus, from prepared slides and fresh material”

Study the prepared slides of Rhizopus showing sporangia and spores under the microscope.

In chapter 5, you have already learned to prepare slide of Rhizopus from fresh material. Make a slide and study it under microscope.

Draw labeled diagrams of sporangia and spores.

What is the shape of sporangium?
What is the shape of spores?
How many spores are present within a sporangium?

Sexual Reproduction in Flowering Plants

The reproductive part of flowering plants is the flower. You have already studied the structure and functions of floral parts of Brassica in chapter.

Pollination

The transfer of pollen grains (also called pollen) from anthers of a stamen to the stigma of a carpel of a flower is called pollination.

Types of pollination

There are two types of pollination, self pollination and cross pollination.

“Hay fever, is an allergic response to pollen; which are in the air, and are inhaled by us during inhalation”

The transfer of pollen in the same flower or between two flowers of the same plant is called self pollination.

Cross pollination is the transfer of pollens from one plant to another plant of the same species. The transfer of pollens may be by wind, water or by insects ( or other animals).

The characteristics of wind pollinated, insect pollinated and water pollinated flowers is given in the table 16.1.

Table 16.1 Differences among wind pollinated, insect pollinated and water pollinated flowers.

Wind pollinated flowers	Insect pollinated flowers	Water pollinated flowers
1. Flowers are small anad without bright coloured petals.	The flowers are large and have brightly coloured petals	The flowers are small and without brightly coloured petals.
2. Pollens produced in enormous numbers and are light in weight.	Pollens are not produced in enormous numbers and are sticky.	The pollen grains neither sink nor float on the surface of water, due to their peculiar specific gravity. They float under water.
3. The flowers have long feathery stigmas.	The stigmas are variously shaped so that pollen grains are attached or entangled there.	The flowers have long stalks. The styles are long and the stigmas are sticky.
4. The filaments of stamens are long and have versatile anthers.	Stamens have short filaments and anthers are not versatile.	Stamens have short filaments and anthers are not versatile.
5. The flowers do not produce nectar.	The flowers produce nectar by glands called nectarines.	Do not produce nectar.
6. Examples are the flowers of maize, wheat and rice.	Examples are the flowers of most dicots e.g. Bougainvillea, rose and calotropis.	Examples are the flowers of plants such as potamogeton and Vallisneria.