Reproduction

• Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.

• The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death.

• Reproduction enables the continuity of the species, generation after generation.

Reproduction- Types

• All living organisms reproduce. Sexual reproduction occurs when two individuals are involved. Asexual reproduction occurs when a single individual is involved.

Difference in the reproduction in unicellular & multicellular organisms

• In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc.

• whereas in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc.

• In more complex multicellular organisms such as human beings and plants, the mode of reproduction is sexual reproduction.

Types of asexual reproduction

• Fission

• Fragmentation

• Budding

• Regeneration

• Vegetative propagation

• Spore formation

Fission

It occurs in single-celled organisms, belonging to the kingdom Protista and Monera. It is further divided into two types:

• 1. Binary fission

• 2. Multiple fission

Binary fission

• In binary fission, the single cell divides into halves. A few organisms that divide by binary fission are bacteria and Amoeba.

• In Amoeba, cell division or splitting of cells can take place in any plane.

• Binary fission can also occur in one particular axis. For example, Leishmania (a parasitic flagellated protozoan), which causes kala azar in humans, divides only longitudinally.

• Leishmania has whip-like flagella at one end of the cell. Cell division occurs in relation to these flagella.

Multiple fission

• In multiple fission, a single cell divides into many daughter cells simultaneously. Examples:

• Plasmodium and Amoeba

Fragmentation

• It is a form of asexual reproduction in which an entirely new organism is formed from a fragment of the parent.

• It occurs in multicellular organisms, whose body organization is fairly simple such as annelids, starfish, fungi, lichens, and some algae such as spirogyra.

• The filaments of spirogyra, upon maturation, break into small pieces or fragments, which grow into new individual.

Regeneration• Simple organisms such as Hydra and Planaria are capable of

producing new individuals through the process of regeneration. • The process of regeneration involves the formation of new organisms

from its body parts. Simple organisms can utilize this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth and development.

• However, complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.

Regeneration

• If the tail of a house lizard is cut, the missing part develops again from the remaining part of the tail. In some cases, regeneration is so advanced that an entire multicellular body is reconstructed from a small fragment of tissue. Our body spontaneously loses cells from the surface of the skin and replaced by newly formed cells. This is due to regeneration.

• Regeneration can be defined as the natural ability of living organisms to replace worn out parts, repair or renew damaged or lost parts of the body, or to reconstitute the whole body from a small fragment during the post embryonic life of an organism. Regeneration is thus also a developmental process that involves growth, morphogenesis and differentiate

Regeneration in lizard

Budding• It is seen in certain fungi and

multicellular animals. In budding, the parent cell or body gives out a lateral outgrowth called the bud.

• The nucleus divides and one of the daughter nuclei passes into the daughter cell. The bud grows in size while being attached to the parent body.

• It then gets separated from the parent by the formation of a wall. It then falls off and germinates into a new individual.

• Thus budding results in the formation of daughter cells of unequal sizes that later grow to adult size. For example, yeast, a fungus and Hydra, a multicellular animal.

• In case of Hydra, the daughter hydra even develops mouth and tentacles develop around the mouth before being detached from the parent body.

Budding in yeast

Budding in Hydra

Difference between regeneration & fragmentation

• Both regeneration and fragmentation are the type of asexual reproduction. They both stands for the same meaning i.e growth of an organism from a part of the body. Regeneration is mainly associated with the animals whereas fragmentation is mainly associated with the plants.

• Regeneration is of two types, in the first type, a part of the body that gets broken off or cut is regenerated. For example, lizards cast off their tails to escape predators and then regenerate them. The other type of regeneration involve the capacity to give rise to an entire organism from a cut part. It is seen in small invertebrates such as planaria and Hydra.

• Fragmentation is also a mode of asexual reproduction. It is the unintentional cutting up of the body of an organism which each grows into different organism. It is most commonly seen in some algae.

Spore formation in Rhizopus

• The thread-like structures that developed on the bread in are the hyphae of the bread mould

(Rhizopus).

• On the other hand, the tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can develop into new Rhizopus individuals

• The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.

Vegetative reproduction

• There are many plants in which parts like the root, stem and leaves develop into new plants under appropriate conditions

Advantages of Vegetative reproduction

• Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from

seeds.

• Such methods also make possible the propagation of plants such as banana, orange,rose and jasmine that have lost the capacity to produce seeds.

• Another advantage of vegetative propagation is that all plants produced are genetically similar to the parent plant.

Vegetative reproduction by leaf

• Similarly buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants

Vegetative reproduction by stem

1. Runners are stems that grow horizontally above the ground. They have nodes where buds are formed. These buds grow into a new plant.

Vegetative reproduction by roots

• New plants will grow out of swollen, modified roots called tubers. Buds develop at the base of the stem and then grow into new plants

Stem cutting

• Cuttings: Cuttings are part of the plant that is cut off of the parent plant. Shoots with leaves attached are usually used. New roots and leaves will grow from the cutting. The shoot is cut at an angle.

Layering

• In layering a shoot of a parent plant is bent until it can be covered by soil. The tip of the shoot remains above ground. New roots and eventually a new plant will grow. These plants can then be separated.

Grafting

• In grafting 2 plants are used to develop a new plant with combined traits from the 2 parent plants. In grafting the scion is the above ground part of one plant. The scion is attached to the stock which is the rooted part of the second