The Biology Topics of ecology involve studying the relationships between living organisms and their environment.
What is Reproduction? What are the Different Types of Reproduction?
Now, all living organisms grow old with time and ultimately die. In fact, every living organism remains alive on this earth for a limited period of time and then dies. So, new organisms have to be produced in place of those who die. The production of new organisms from the existing organisms of the same species is known as reproduction. In simple words, we can say that reproduction is the creation of new living things (from the existing living things). Actually, one of the most important characteristics of living organisms is their ability to reproduce more members of their species. Reproduction is essential for the survival of a species on this earth. So, living organisms produce more organisms of their kind to maintain the life of their species on this earth.
The process of reproduction ensures the continuity of life on Earth. For example, human beings reproduce by giving birth to babies (sons and daughters). These babies grow and ultimately become adults. So, when the old parents die, their sons and daughters keep living on this earth. These sons and daughters also reproduce by giving birth to more babies, and this process goes on and on. Thus, reproduction by human beings ensures that the human species will continue to exist on this earth for all time to come.
(a) Humans reproduce by giving birth to babies
(b) Dogs reproduce by giving birth to puppies
(c) Most of the plants reproduce by producing seeds to grow more plants
The process of reproduction ensures continuity of life for various species
Similarly, cats reproduce by giving birth to kittens so that their species may live forever. And dogs reproduce by giving birth to puppies so that their species may continue to live on this earth. Most plants reproduce by producing seeds to grow more plants so that their species may continue to live on this earth.
It is clear from the above discussion that for a species of plant or an animal to continue living on this earth, it must reproduce itself. Reproduction gives rise to more organisms with the same basic characteristics as their parents. For example, human beings always produce human babies; cats always produce kittens; and sunflower seeds always produce sunflower plants. If, however, some species of living organisms cannot reproduce due to certain reasons, then the organisms of this species will gradually die out and disappear from this earth one day. In this chapter, we will discuss the various methods of reproduction in plants and animals.
Please note that the existing organism or organisms are called parents and the new organisms produced by them are called offspring. For example, our father and mother are parents and we (their children) are the offspring. The parent or parents of organisms can be animals as well as plants. Sometimes, the word daughter (or daughter cells) is also used for the offspring of an organism.
Types of Reproduction
There are many different ways in which new organisms are produced from their parents. Some organisms like Amoeba just split into two parts to produce new Amoebae; some organisms like Hydra and yeast grow out of the parent’s body in the form of a bud; some organisms like birds and snakes hatch out of the eggs laid by their parents; whereas some organisms like human babies, cubs, kittens, and puppies are born from their mother. This means that each species of organism reproduces in a different way. All the different ways of reproduction can be divided into two main groups: asexual reproduction and sexual reproduction. Thus, there are two main methods of reproduction in living organisms asexual reproduction, and sexual reproduction.
Reproduction is the fundamental characteristic of living organisms. It involves the transmission of genetic material from one generation to the next, ensuring that the species survive over long periods of time.
Classification of different types of Reproduction:
The maximum diversity of each organism in this bio-logical world arises from their multiplication mechanism and production of offspring. According to their habitat, internal physiology, and other important factors, two basic patterns of reproduction have been observed among living beings. These are asexual and sexual. Asexual reproduction does not involve gamete formation and gamete fusion. It is uniparental. Sexual reproduction consists of the formation of gametes and the fusion of gametes of opposite sexes. It is biparental involving two types of parents of different sexes.
Reproduction in living beings mainly takes place in the following four ways:
- Asexual reproduction
- Vegetative reproduction
- Sexual reproduction
|Types of Reproduction||Definition||Example|
|1. Asexual Reproduction||The process by which reproduction takes place without the formation of gametes and produces offspring simply by cell division or by spore formation is called asexual reproduction.||Mucor, Agaricus, Amoeba, Hydra etc.|
|2. Vegetative Reproduction||The process by which new individuals are formed directly from the vegetative parts of living organisms without any change in protoplast is called vegetative reproduction.||Potato, Rose, Yeast, Bacteria etc.|
|3. Sexual Reproduction||The process by which reproduction takes place by the union of two different gametes, i.e., male gamete and female gamete is known as sexual reproduction.||Higher groups of plants and animals, e.g., Rice, Wheat, Mango, Cat, Cow, Man, etc.|
|4. Parthenogenesis||The process by which young ones develop from the eggs without fertilization is known as parthenogenesis.||Spirogyra, Mucor, Bees, Ants, etc.|
(a) An Amoeba reproduces just by splitting into two parts to form two Amoebae
(b) Chicken is hatched from the egg
(c) Tiger cubs are bom from their mother tigress
There are many different ways in which new organisms are produced from their parents
We can now say that living organisms reproduce mainly by two methods ‘asexual reproduction’ and ‘sexual reproduction’. This means that new living organisms (new plants and animals) can be made either by the method of ‘asexual reproduction’ or by the method of ‘sexual reproduction’. We will now discuss the meaning of asexual reproduction and sexual reproduction. In order to understand this, please keep in mind that certain organisms contain ‘reproductive cells’ (called ‘sex cells’, ‘gametes’ or ‘germ cells’) in their bodies whereas some other organisms do not contain ‘reproductive cells’ (‘sex cells’, ‘gametes’ or ‘germ cells’) in their bodies.
1. Asexual Reproduction
In asexual reproduction, the offspring arises from a single parent. The production of a new organism from a single parent without the involvement of sex cells (or gametes) is called asexual reproduction. It is called asexual reproduction because it does not use special cells called ‘sex cells’ (or gametes) for producing a new organism. In asexual reproduction, a part of the parent organism separates and grows into a new organism. Thus, in asexual reproduction, only one parent is needed to produce a new organism. But no sex cells are involved in asexual reproduction. Some of examples of asexual reproduction are binary fission in Amoeba; budding in Hydra; spore formation in Rhizopus fungus (or bread mould); regeneration in Planaria (flatworm); fragmentation in Spirogyra and vegetative propagation in flowering plants (like rose plants).
Please note that asexual reproduction is the simplest method of reproduction. It takes place mainly in those organisms whose bodies have a simple structure. So, simple animals, simple plants, and microorganisms (like bacteria) reproduce by asexual reproduction methods. Actually, asexual reproduction takes place in unicellular animals and plants, micro-organisms (like bacteria) and simple multicellular animals (like Hydra and Planaria), and some multicellular plants (like Bryophyllum and rose plants, etc.).
Hydra is a tiny animal that lives in freshwater. Hydra grows a bud on its side which then separates off and becomes a new Hydra. Only one parent (only one Hydra) is needed in this asexual reproduction by budding.
2. Sexual Reproduction
In sexual reproduction, the offspring arises from two parents of different sexes: a male sex and a female sex. The male parent contains male sex cells (or male gametes) and the female parent contains female sex cells (or female gametes). The production of a new organism from two parents by making use of their sex cells (or gametes) is called sexual reproduction. In sexual reproduction, the sex cell of one parent fuses with the sex cell of the other parent to form a new cell called a ‘zygote’. This zygote then grows and develops to form a new organism. Thus, in sexual reproduction, two parents are needed to produce a new organism.
Two parents called male and female (man and woman or father and mother) are involved in the sexual reproduction of a human being (or baby).
The two parents who are involved in sexual reproduction are called male and female. Our father is a male and our mother is a female. The male and female parents have special organs in them which produce male sex cells and female sex cells respectively (which are required in sexual reproduction). Humans, fish, frogs, hens, cats, dogs, cows, horses, deer, rabbits, lions, and tigers all reproduce by the method of sexual reproduction. Most of the flowering plants also reproduce by sexual reproduction. As we will study after a while, some organisms use both methods (asexual and sexual) for reproduction whereas other organisms use only one of these methods for reproduction.
The basic difference between asexual and sexual reproduction is that only one parent is needed in asexual reproduction whereas two parents are needed in sexual reproduction. Another difference is that no sex cells (or gametes) are involved in asexual reproduction but sex cells (or gametes) take part in sexual reproduction. We will now study asexual reproduction and sexual reproduction in detail, one by one. Let us start with asexual reproduction.
Life Span of Organisms
The period from birth to natural death is the life span of an organism. It may be a few minutes to several years. The life span of some microorganisms is a few minutes while the redwood tree stands as the longest-living plant (3000-4000 yrs.). The life span of the Mayfly is one day only and that of the giant tortoise is 260 years.
Life Span of Some Living Beings:
|Organism||Maximum Life Span|
|1. Some Microorganisms||Few minutes to a few hours|
|2. Mayfly||1 day|
|3. Cicada||1 day|
|4. Butterfly||1 – 2 weeks|
|5. Fruit fly||30 days|
|6. Rice Plant||3 – 4 months|
|7. Wheat Plant||5 months|
|8. Rat||4 years|
|9. Rose Bush||5 – 7 years|
|10. Rabbit||13 years|
|11. Crow||15 years|
|12. Cow||20 – 25 years|
|13. Banana Tree||25 years|
|14. Monkey||26 years|
|15. Dog||20 – 30 years|
|16. Cat||35 – 40 years|
|17. Whale||37 years|
|18. Horse||60 years|
|19. Crocodile||60 years|
|20. Elephant||60 – 90 years|
|21. Eagle||90 years|
|22. Man||100 years|
|23. Parrot||140 years|
|24. Tortoise||200 years|
|25. Banyan Tree||200 years|
|26. Peepal||2000 – 3000 yrs.|
|27. Sequoia (Red Wood Tree)||3000 – 4000 yrs.|
|28. Larrea tridentata (Oldest plant of S.W. California, U.S.A.)||11300 yrs.|
An organism’s life span consists of four stages:
- Juvenility: In this stage, the organism becomes capable of reproduction.
- Maturity: In this stage, reproduction begins.
- Ageing: In this stage progressive deterioration proceeds.
- Death: In this stage, the cessation of all biological functions, that sustain a particular living organism, occurs.
The change over from one stage to another is determined by genetic as well as environmental factors. It is not essential that the life span of organisms should be correlated with their sizes. For example, the sizes of crows and parrots are not very different but their life spans show great difference.
Life span can also denote an estimate of the maximum amount of time that a member of a given species could survive birth and death, provided circumstances that are optimal to that member’s longevity.
Differences between Ageing and Senescence:
|1. It Is a progressive deterioration and general decline in metabolic processes of the body.||1. It is the terminal irreversible stage of ageing.|
|2. It leads to senescence.||2. It leads to death.|
Basic Features of Reproduction
All types of reproduction have some common basic features which are as follows:
- Synthesis of protein, RNA, and other biochemicals.
- DNA replication.
- Cell division.
- Growth of cells.
- Formation of reproductive units – male and female gametes.
- Formation of new individuals from reproductive units.