Reproduction may be defined as the production of new generation of individuals of the same species that are physically independent of their parents.
DNA copying or DNA replication
Creation of a DNA copy is the basic event in the process of reproduction. Cells usually employ chemicals to build copies of their DNA. This process results in the production of two similar copies of their DNA. This process results in the production of two similar copies of DNA in a reproducing cell.
DNA copying is always accompanied by the creation of another cellular apparatus. Finally, the DNA copies are separated into two similar cells, each with its own cellular apparatus.
Types of reproduction
All the reproductive methods of living organisms are broadly categorised into two types:
1. Asexual reproduction
2. Sexual reproduction
Asexual reproduction may be defined as the production of offsprings by a single parent without meiosis, formation of gametes, fertilisation and transfer of genetic materials between individuals.
Asexual reproduction occurs in the following ways:
Fission may be defined as the splitting of a unicellular organism into two or more than two separate daughter cells.
Differences between Binary fission and Multiple fission
|Binary fission||Multiple fission|
|1. It results in the production of two individuals.||1. It results in the production of several individuals.|
|2. It occurs under favourable conditions.||2. It occurs both under favourable and unfavourable conditions.|
|3. Nucleus of the parent cell divides only once to form two nuclei.||3. Nucleus of the parent cell undergoes repeated divisions to form a number of daughter nuclei.|
|4. Cytoplasm divides after nuclear division.||4. Cytoplasm does not divide after each nuclear division.|
|5. No part of parent body is left unused.||5. A part of the body (covering and residual cytoplasm) is left unused.|
Some multicellular organisms have simple body organisation. These organisms are comprised of a random collection of cells without differentiation of specialised tissues and organs. Such organisms reproduce by breaking of their bodies into small pieces. Each of these pieces is called a fragment. These fragments grow into new individuals and the mode of reproduction is called fragmentation.
Regeneration may be defined as the ability of an organism to regenerate its lost parts of the body which have been removed, as by injury or autotomy (self-ampulation of body parts, e.g., some lizards can break off part of the tail).
Budding may be defined as the production of new individual from an outgrowth of the parent individual.
5. Spore formation
A spore is a single or several celled reproductive structure that detaches from the parent and gives rise, directly or indirectly, to a new individual.
6. Vegetative propagation in plants
Vegetative propagation in plants is a method of asexual reproduction in which the parts other than seeds are used as propagules (i.e., the structural unit that is employed in place of seed). In fact, it is a method of propagation in those plants which have lost their capacity to produce seeds or produce non-viable seeds (e.g., banana, seedless grapes, rose, pineapple, etc.).
7. Propagation by plant tissue culture
This method includes propagation of plants by culturing the cells, tissues and organs. In this method, the plant cells or tissues are cultured on a sterilized (free from microorganisms) medium containing necessary nutrients and hormones.
Sexual reproduction may be defined as the production of offsprings (new individual) by the fusion of two gametes (usually one from male parent and the other from female parent) to form a diploid zygote which develops into a mature organism.
Differences between Self pollination and Cross pollination
|Self pollination||Cross pollination|
|1. It is the transfer of pollen grains from anther to the stigma of the same flower.||1. It is the transfer of pollen grains from the anther of one flower to the stigma of another flower.|
|2. It does not require an external agency for the transfer of pollen grains.||2. It requires an external agency for the transfer of pollen grains from one flower to another.|
|3. Such bisexual flowers produce small number of pollen grains.||3. Such flowers produce large number of pollen grains.|
|4. It does not bring variations.||4. It brings about large number of variations.|
Reproduction in human beings
Primary and secondary sex organs
The primary sex organs are gonads, which produce gametes (or sex cells) and secrete sex hormones. The gonads of the male are called testes which produce male gametes-sperms and the male hormone- testosterone. The gonads of the female are ovaries which produce female gametes- ova and female hormones- estrogen and progesterone.
The secondary sex organs include the genital ducts and glands which helps in transportation of gametes and productive process. They do not produce gametes or secrete hormones.
Puberty is the age of human males and females at which the reproductive organs become functional, gonads start producing gametes and sex hormones, and the boys and the girls become sexually mature.
What is menstrual cycle?
The cycle of events taking place in female reproductive organs, i.e., in ovaries and uterus, under the control of sex hormones, in every 28 days and marked by bleeding or menstrual flow, is called menstrual cycle (sexual cycle in human females).
The regulation of conception by preventive or devices to control the number of offsprings is called birth control.
Sexually Transmitted Diseases
The infections (communicable) diseases, which are spread from an infected person to a healthy person by sexual contact, are called sexually transmitted diseases (or STDs).
Q1. What is menstrual cycle.
Q2. Types of Asexual reproduction.
Q3. Define: STDs.