Download Sexual vs. Asexual Reproduction

Asexual Reproduction
 Asexual reproduction is natural “cloning.” Parts of
the plant, such as leaves or stems, produce roots
and become an independent plant.
Sexual Reproduction
 Sexual reproduction produces a greater chance of
variation within a species than asexual reproduction
would.
 This variation improves the chances that a species will
adapt to his environment and survive.
Sex!
 Asexual Reproduction
 involves only 1 parent
 offspring genetically
identical to parent
 involves regular body
cells
 its quick
 Sexual Reproduction
 involves 2 parents
 offspring genetic mix of
both parents
 involves specialized sex
cells
 its slow
Which is Better?
It depends!
Asexual Reproduction
 advantages
Sexual Reproduction
 advantages
 does not require special
 lots of variation within a
cells or a lot of energy
 can produce offspring
quickly
 in a stable environment
creates large, thriving
population
species
 able to live in a variety of
environmental settings
 able to adapt to changes
in the environment
 disadvantages
 limited ability to adapt
 face massive die-off if
environment changes
 disadvantages
 needs time & energy
 produce small
populations
Terms
to
know:
 Haploid: having a single set of
chromosomes in each cell.
 Diploid: having two sets of chromosomes in
each cell.
 Mitosis: cell division, which produces two
genetically identical cells.
 Meiosis: reduction division, which produces
four haploid reproductive cells.
Flowers
Flower Parts
PARTS of the flower include:
 Sepals: enclose the flower bud and protect it until it
opens
 Petals: attract pollinators
Insect-pollinated flower
Floral structures
Diagram of an insect-pollinated flower
Petal
Stigma
Anther
Filament
Style
Ovary
Ovule
Nectar
Sepal
Wind-pollinated flower
Diagram of a wind-pollinated flower
Bract
Anther
Filament
Ovary
Stigma
Functions of parts of the flower
 sepals
 petals
 Protects the flower during the bud stage
 Attracts insect pollinators by colour and
 Anthers
scent
 produce and release pollen grains
 filament
 positions the anther for effective pickup
 Stigma
 style
 ovaries
of pollen by the pollinating agent
 collects the pollen from the pollinating
agent
 positions the stigma for pollen collection
 site of fertilisation, protects the
developing seeds, aids in seed dispersal
Pollination
 The transfer of
pollen grains from
the male part of
the plant (anther
of stamen) to the
female part of the
plant (stigma).
Agents of pollination
 . . . the means that
moves the pollen
grains from the
anther to the
stigma.
 Agents of
pollination include:
wind; insects; birds;
water & rodents.
Photomicrograph of pollen grains:
Note the spikes that attach pollen grains to insect’s body.
structural adaptations of insect-pollinated
and wind-pollinated flowers
Insect-pollinated flowers
 Petals large & brightly





coloured to attract insects
Stigma located inside the
flower where the insects have
to brush past it
Anthers inside the flower
where the insects have to
brush past them
Stigma usually small & sticky
so that pollen grains can
attach from insect body
Flower often strongly scented
Large sticky or spiky pollen
grains which stick to insects
Wind-pollinated flowers
 Petals small or absent, if





present, not brightly coloured
Stigma exposed to catch pollen
grains blowing in the wind
Anthers exposed outside the
flower so that wind can easily
blow the pollen grains away
Stigma large & feathery to catch
pollen grains blowing in the
wind
Flowers have no scent
Light & smooth pollen that can
be blown in the wind
What happens after pollination?
 pollen grains germinates








forming pollen tube
the pollen tube grows down
style digesting the style tissue
The pollen tube enters ovule
through micropyle
male nucleus moves into ovule
male nucleus (male gamete)
fuses with the ovum or egg cell
(female gamete) i.e.
fertilisation occurs
ovule becomes seed
ovule wall becomes seed coat or
testa
ovary becomes fruit
stigma and the style withers and
dry up
Pollen is produced in
the male organs of the
flowers - anthers.
Pollination occurs
when pollen is
transferred from the
anthers to the female
organs by wind or by
animals. If the female
stigma is receptive to a
pollen grain, the pollen
produces a pollen tube,
which grows through
the female tissue to the
egg, where
fertilization takes
place by the sperm
nucleus.
Sexual Reproduction in
Flowering Plants
(Angiosperm)
External structure of a Seed
Internal structure of a Seed
plumule
radicle
micropyle
cotyledon
testa (seed coat)
 Testa; protects the




embryo from physical
damage & attack from
pathogens
Micropyle; a hole in the
testa that allow water &
oxygen to enter into the
seed
Cotyledons; stores
nutrients (starch, protein
& lipids) required during
germination
Plumule; grows into
shoot after germination
Radicle; grows into root
after germination
Conditions for seed germination
 Seed germination is the
process in which a plant
emerges from a seed & begins
grow
 Conditions needed for seeds
germination are:
 Suitable temperature; for
enzymes to work effectively
 Oxygen; for aerobic respiration
to provide energy to growing
embryo
 Water; for chemical reactions
to occur in solution, dissolve
nutrients for transportation,
activate enzymes & soak testa