Download Lesson 1-AsexualInPlants

The two modes of Reproduction
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.
SEXUAL 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.
• 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
Adult parent
Detached portion of
Parent
Sexual Reproduction
Adult parent
Male gamete
Adult parent
Female gamete
fertilization
New Adult
zygote
New Adult
Reproductive vs Vegetative Structures
• 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.
Vegetative Reproduction
• 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food is withdrawn from the underground storage organ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.
Natural 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.
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.