How do Organisms Reproduce? / The Life Cycle – Summary
- Reproduction – A process by which a living organism is able to produce more of its own kind.
It is of two types- asexual reproduction and sexual reproduction.
- Asexual reproduction – Production of an offspring from body parts other than the reproductive organs. In this, only one organism is involved, no gametes are produced and no fertilization takes place.
- Sexual reproduction – Production of an offspring by the fusion of egg and sperm which are the sex cells or gametes. In this, both male and female gametes are produced and fertilization occurs.
- Some methods of asexual reproduction are – fission, budding, fragmentation and spore formation.(i) Binary fission – Process in which two individuals are formed from a single parent.
(ii) Multiple fission – Process in which many individuals are formed from a single parent.
(iii) Vegetative propagation – Method in which any vegetative part of the plant, such as leaf, stem or root, develops into a new plant.
- Some artificial methods of propagation of plants are grafting, cutting, layering and tissue culture.
- A typical flower has four whorls—calyx, corolla, androecium and gynoecium.
- Androecium – The male part of a flower. Each member of the androecium is called stamen.
- Gynoecium – The female part of a flower. Each member of the gynoecium is called pistil.
- Most animals and some plants reproduce sexually. Sexual reproduction involves two main processes, i.e. meiosis and fertilization (the process of fusion of the egg and the sperm).
- Placentation – The arrangement of ovules in the ovary of a flower.
- Autogamy is self pollination whereas allogamy is cross pollination.
- Spermatogenesis – The process of formation of sperms in the testes of an organism.
- Oogenesis – The process of formation of eggs or ova in the ovaries of an organism.
- Semen – The sperms along with the secretions.
- Zygote – The product of the fusion of the egg and the sperm.
- Puberty – The age at which the reproductive organs become mature and functional in human beings. The puberty age is 13–14 years in males and 11–12 years in females in human beings.
- Placenta – It is an association between maternal and foetal tissues meant for physiological exchange.
- Twins are of two types—fraternal and identical twins.
Identical twins – When two embryos are formed from the same egg due to division of the fertilized egg into two sets of cells.
Non-identical or fraternal twins: When two embryos are formed from two different eggs produced at the same time and fertilized by two different sperms.
- Fertility control methods can be preventive or corrective. We can control the rising population by fertility check.
- Diseases that spread through sexual contact are known as sexually transmitted diseases.
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Reproduction is a process in which a living organism duplicates itself or produces new individuals of the same species resembling it in all essential features. It means, it is a new generation of the species from an existing individual i.e. parents.
Significance of Reproduction
1. All living organisms reproduce to maintain the continuity of the species.
2. Reproduction maintains the numbers of individuals of a species.
3. It helps in evolution by transmitting favourable variations over many generations.
During reproduction, the organism uses its own body material. A simple cell duplicates its genetic material (DNA copying) and passes it on from generation to generation. In the process of DNA copying, some variations take place every time. Thus, DNA copies (next generation) are similar but not identical (subtly different) to the original. This tendency of variation during reproduction leads to evolution.
The importance of Variations
Drastic alteration in ecological system due to uncontrolled conditions such as variation in earth temperature, water levels, meteorite hit etc. can extinct a species. However, if some variations were to be present in a few individuals in the population which are suitable for new environment, there would be some chance of survival of that species. Thus, variation is useful for the survival of species over time.