ASEXUAL REPRODUCTION AND SEXUAL REPRODUCTION In asexual reproduction, a new individual develops or...

ASEXUAL REPRODUCTION AND

SEXUAL REPRODUCTION

• In asexual reproduction, a new individual develops or grows from a single parent.

• There is no fusion of cells from two different parents.

The two modes of Reproduction

• In sexual reproduction, new individuals are formed by the fusion of a male reproductive cell (male gamete) and a female reproductive cell (female gamete).

• This fusion is known as fertilization.

SEXUAL REPRODUCTION

• How about asexual reproduction?

• Since there is only one parent, the new individual would be identical in characteristics to the one parent which produced it.

• Can you think of advantages of sexual reproduction and advantages of asexual reproduction?

Asexual Reproduction Sexual Reproduction

Adult parent Adult parent Adult parent

Detached portion of Parent

New Adult

Male gamete Female gamete

fertilization

zygote

New Adult

• Plant parts : roots, stem, leaves, flowers and fruits.

• Reproductive Structures : – flowers and fruits

• Vegetative Structures:– roots, stem and leaves

• Some plants can reproduce both ways – reproductively as well as vegetatively.

Reproductive vs Vegetative Structures

• Two types : Natural Vegetative Propagation and Artificial Vegetative Propagation

• Natural Vegetative Propagation:– They are also flowering plants– But they can reproduce through underground storage organs e.g.

rhizomes, bulbs, corms, tubers, roots– Or shoots e.g. runners, offsets, suckers

• Essentially, same principle :– These organs have a store of food. Shoots grow from these organs

bearing leaves and flowers. In the process, food is withdrawn from the underground storage organ which shrivels. As the leaves manufacture food, food is transported to the buds which gradually swell to become new underground stems.

Vegetative Reproduction

• Rhizomes (e.g. canna, lallang, ginger)– Stem that grows horizontally above or below

surface of soil

Natural Vegetative Reproduction

• Rhizomes (e.g. canna, lallang, ginger)

Natural Vegetative Reproduction

• Corms (e.g. water chestnut, cocoyam,)

– Thick, short underground stem swollen with food reserves.

– Protected by dry scale leaves

– New corms grow on top of old corms

Natural Vegetative Reproduction

Natural Vegetative Reproduction

• Bulbs (e.g. onion)– Flattened, disc-like

stem with closely set nodes bearing fleshy scale leaves surrounded by some dry scale leaves.

– Buds are in the axils of the fleshy scale leaves.

Natural Vegetative Reproduction

• Tubers (e.g. potato)– Swollen underground stem bearing a number of

scale leaves.

Natural Vegetative Reproduction

• Tubers (e.g. potato)Natural Vegetative Reproduction

• Runners (e.g. strawberry plant)Natural Vegetative Reproduction

• Runners (e.g. strawberry plant)Natural Vegetative Reproduction

• Offsets (e.g. water hyacinth and water lettuce)

– Like runners but shorter and thicker

Natural Vegetative Reproduction

• Suckers (e.g. pineapple, banana, chrysanthemum)

– A shoot arising either from the underground portion of the stem or from an adventitious bud on the root.

Natural Vegetative Reproduction

Advantages and Disadvantages of Natural Vegetative Propagation

• Advantages– No need external agencies

e.g. insects, wind etc– Food is usually present in

the vegetative structures, a rapid development of buds into daughter plants can take place.

– New plants resemble parent plant in every way.

– Involves only one parent

• Disadvantages– Lack of dispersal

mechanism may lead to overcrowding.

– New plants are less varied

– New plants may be less adaptable to changes in environmental condition.