REPRODUCTION IN ORGANISMS
Reproduction is a biological process in which an organism produces offspring of their own kind.
The period of birth to the natural death of an organisms represents its life span. The life span of an organism may vary from species to species. The life span of an organism is not necessarily correlated with their body size, it can vary from less than one day to more than 400 years.
Reproduction is a biological process by which an organism gives rise to young ones of their own kind.
Significance of reproduction
Reproduction enables the continuity of the species, generation after generation.
Sexual reproduction is responsible for variation in a population and its inheritance to future generations.
Modes of reproduction;
A type of reproduction by which offspring is produced from s single parent with or without the involvement of gamete formation. (uniparental).
Offsprings are morphologically and genetically identical to their parents (clones).
Asexual reproduction is common among unicellular organisms, and in plants and animals with relatively simple organizations.
Types of asexual reproduction
1. Fission: a mode of asexual reproduction in which a parental cell splits up into two or more daughter cells.
a. Binary fission:
A parental cell divides into two equal daughter cells and each rapidly grows into an adult.
It occurs in single-celled organisms like bacteria, amoeba, and paramecium.
It can be simple or irregular, longitudinal. Oblique or transverse, depending on the plane of division.
b. Multiple fission:
The splitting of a parental cell into numerous daughter cells, each of which grow into an adult. E.g., Plasmodium.
Under unfavourable conditions, organisms like Amoeba cover themselves with a three-layered hard covering or cyst. This phenomenon is called encystation. On return of favourable conditions, it divides by multiple fission within the cyst and produces many Amoebae or pseudopodiospores. The cyst bursts and spores are liberated to develop into adults. This is called sporulation.
2. Fragmentation: It is a mode of asexual reproduction in which the parental body breaks into two or more fragments and each fragment grows into a new individual, e.g., Spirogyra.
3. Budding: It is a mode of asexual reproduction in which one or more outgrowths (buds) are produced which initially remain attached to the parent cell and eventually get separated from it to grow into a new individual, e.g., yeast, Hydra.
4. Regeneration: It is a mode of asexual reproduction in which the missing parts of an organism is repaired by proliferation of cells, e.g., Planaria.
5. Spore formation:
Zoospores: These are endogenously produced unicellular, naked and motile spores with one or two flagella. Zoospores are produced in a sac-like structure called zoosporangium, e.g., Chlamydomonas.
Conidia: Asexual non-motile spores cut off externally either singly (e.g., Phytophthora) or in chains (e.g., Penicillium) from the tip of a special hyphae called conidiophore.
Gemmules: Internal asexual reproductive units or buds are called gemmules, e.g., sponges. These develop within the parental body and are released during germination.
6. Vegetative propagation: It is a mode of reproduction in which new plants are formed from vegetative parts (vegetative propagules) of the plant like root, stem, etc.
It is very common in higher angiosperms.
Following are some units of vegetative propagation:
Bulbil – Agave
Bulbs – Onion, Garlic
Eyes – Potato
Leaf buds – Bryophyllum