Reproduction in organisms mitosis and meiosis
Sexual Reproduction in plants
Sexual Reproduction In Animals
Reproduction
Reproduction
means
organism replicate themselves. Reproduction mainly divided in to two 1. Sexual
and 2. Asexual reproduction.
Asexual reproduction: in this processes only one parent
produce off springs. Gene flow from one generation to other generation from
single parent . all prokaryotes reproduce by asexual reproduction. In
prokaryotes involve in lateral gene flow means transduction, conjugation etc.
Some plants and fungi also reproduce asexually. Asexual reproduction helps population
growth in short time . In asexual reproduction nucleus divide by mitosis
process.
Asexual reproduction absent in invertebrates and
vertebrates.
Characteristics
of Asexual Reproduction:
(a) A single parent is involved (uni-parental
condition)
(b) Gametes are not formed
(c) No fertilization
(d) There is only mitotic cell division
(e) Daughter organisms are genetically identical to
parent
(f) Multiplication occurs rapidly
1.fission , 2. budding,
3. fragmentation, 4.regeneration 5.vegetative propagation and 6.spore
formation.
1.Fission: fission is the division of a cell into two or more parts into separate
cells.
Fission are two types:
Binary fission.
Multiple fission.
Binary Fission:
In this process of asexual reproduction, the parent organism
act as single reproductive cell and divides into two halves(almost equal ), each
half forming an independent daughter organism. Binary fission involves mitosis.
The resultant offspring are genetically identical to the parent and to each
other . That means we observe in nucleus and cytoplasm. Depending on the
division of cytoplasm binary fission again divided in to 3 types.
Simple binary fission.
Transverse binary fission.
Longitudinal binary fission.
Longitudinal binary fission.
Simple
binary fission: cytoplasmic
division passes through any plane, the fission is called simple binary fission .example
amoeba.
Transverse
binary fission: The plane of division runs along the transverse
axis of the individual, e.g., Paramecium, Planaria, diatoms and bacteria.
Longitudinal
binary fission: The plane of division runs along the
longitudinal axis of individual, ex : Euglena.
Processes
of Binary fission:
Replication of the circular DNA molecule inside the
cell.( karyokinesis)
Replicated DNA move to either poles of the cell.
The cell lengthens.
The equatorial plate of the cell constricts and
separates the plasma membrane so each new cell has exactly the same genetic
material. That means cytoplasm division take place called as cytokinesis.
This process takes around 20 minutes at room temperature,
meaning a single cell can produce millions of cells in the space of a few
hours. Note that not all bacterial cells undergo binary fission in 20 minutes;
it can sometimes take as long as 24 hours.
Multiple Fission
It is that type of asexual reproduction in which
the parental body divides into many daughter cells simultaneously during the unfavorable conditions to increase the chances of survival of daughter cells.
Residual cytoplasm will left. In this, the reproductive u;nit is whole parental
body. e.g., Amoeba , plasmodium.
2.Budding :
an outgrowth from the body which develops into a new individual. It is a form
of asexual reproduction limited to animals or plants of relatively simple
structure. In this process a portion of the wall of the parent cell softens and
pushes out. In this processes a new organism grows on another one. The new
organism remains attached as it grows, separating from the parent organism only
when it is mature. Some times buds don’t separate ,so it forms interconnected
colonies.
Example:
yeast, hydra in animals, In animals we observe internal and external budding.
Hydra is external budding . annelids (Syllis) and tunicates (Salpa) among animals.
3.Fragmentation:Fragmentation occurs in
multi-cellular organisms with simple body organization. In fragmentation, an organism breaks into pieces and each piece
develops into new individual. No specialized cells are involved in fragmentation. It is
found in some flat worms (Microstomum), sea anemones among coelenterates, and
echinoderms. In starfish, even one arm with a part of central disc can develop
into whole animal
4.Regeneration: Regeneration occurs in fully
differentiated multi-cellular organisms with complex body organization. In
regeneration, specialised cells proliferate and form a mass of cells. The cells
from the mass differentiate to form different cells types and tissues.
In regeneration organisms if breaks into pieces, each piece
may or may not develop into new individual .Example: Regeneration of blood
cells in mammals.
5.Vegetative propagation: The ability of
plants to reproduce without sexual reproduction( seeds or spores), by producing
new plants from existing vegetative structures. does not involve flowers, pollination
and seed production. Instead, a new plant grows from a vegetative part, usually
a stem, of the parent plant. Plant propagation is the process of increasing the
number of plants of a particular species by asexual reproduction. The principal types of vegetative reproduction structures are bulbs, corms, rhizomes and runner
By Stem: main plant send out side branches to the ground, called runners,they creeps along the ground and develops some roots and give rise to new plant .
Ex: strawberry and species of grass.
Underground stem: some of the plant organs stores food and they also for reproduction. Bulb (onion), rhizome(ginger) stem tuber(potato) in unfavorable conditions plant will die ,but these organs stores food and survive in unfavorable conditions then produce new plant.
By leaves: in bryophyllum new plant produced from leaves,buds are at leaf edges, that buds produces new plants.
By roots: in plants such as carrot, turnip and radish ,that taproot may become swollen with food since they are biennial plants they grow vegetatively during first year and store food .in second year of the growth they produces flowers and seeds, at the end of which they die .buds present at the base of the old stem just above the taproot acct as organs of perennaion and vegetative propagation.
6.Spore formation: A mode of reproduction
resembling multiple fission, common among Protozoa, in which the organism
breaks up into a number of pieces, or spores, each of which eventually develops
into an organism like the parent form . The nucleus divides many times and then
the daughter nuclei are surrounded with protoplasm bits to form daughter cells
called spores. The spores are covered with a thick wall called the cyst. On
maturation, the sporangium bursts and releases the spores. The spores germinate
on getting favorable conditions. For example, fungi such as Mucor and Rhizopus
and non seed bearing plants such as mosses and
ferns
