Transcript File

2.2 Reproduction
• Reproduction is
critical for the
survival of a
species. There are
2 types of
reproduction.
1. Asexual
2. Sexual
What is Asexual Reproduction?
• Asexual
Reproduction:
involves only one
parent and doesn’t
require the fusion
of sex cells
– The offspring is
identical to its
parent
4 Types of Asexual Reproduction
1. Binary Fission:
when cell splits
in 2, producing
2 identical
individuals
http://bioweb.wku.edu/courses/BIOL115/Wyatt/Micro/Monera.htm
2. Budding: When a unicellular parent cell
produces an offspring by forming a
protrusion of itself.
http://www.rgs.edu.sg/bio2000/video/yeastbud.mov
3. Spore Production: Producing reproductive
cells through cell divisions of parent cells
Spores are
similar to seeds,
but are produced
when the parent
cells split apart,
rather than when
they are joined.
Spores develop
into plants
IDENTICAL to
the parent plant.
Reproduction Without Seeds
• Vegetative Reproduction:
reproduction of seed plants that does
not involve the production of seeds
• Reproduce from:
•Stems and roots
•Runners: long stems that grow
along the soil of the surface and
produce new plants (ex) raspberries
•Rhizomes: stems that grow
underground stems and produce new
plants
Cuttings
• A piece of a
plant that is used
to make a new
plant
• usually a stem
and few leaves
Grafting
• A technology to
reproduce plants
that involve
attaching part of
one plant to a
second plant
What is Sexual Reproduction?
• Sexual Reproduction:
reproduction involving
the exchange of
genetic material
between two
individuals resulting in
offspring that are
genetically different
from the parents.
Sexual Reproduction
• Sexual reproduction
•
relies on the union of
sex cells called
gametes
Offspring of the
parents will have
mixed characteristics
Sexual Reproduction in Animals
• Male gametes are called sperm
• Female gametes are called egg cells or
ova
• When a sperm and egg cell come together
this is called fertilization
– Only 1 sperm cell can fertilize an egg cell
• The cell created
through fertilization is
called a zygote
– A zygote is formed right
when the 1 sperm cell
enters the egg
– The egg then gives off a
chemical that keeps the
other sperm from
fertilizing it
• The zygote is the first
cell of a new individual
• The zygote then divides into
2 cells
– Divisions are repeated through
a process called cleavage
• The zygote then turns into a
multi-cellular embryo
– Depending on the species the
development of the embryo
can occur inside the female
parent or outside the parents
in an egg
What is pollination?
• Pollination: The transfer of pollen
from the male pollen sacs to the female
stigma
Function of flower
• To attract pollinators with colorful petals,
scent, nectar and pollen
The Parts of a Flower
Reproductive floral organs:
female
• Stigma – is where pollen
•
•
•
sticks to
Style – is the long tube
that connects stigma to
ovary and contains the
pollen tube
Ovary – enlarged
structure at the base of
style that protects the
ovule.
Ovules – contains female
part of the seed plant that
becomes the seed
Sexual reproduction
• In animals is easy because you have
separate male and female individuals.
• In flowering plants it’s not so easy, because
most flowers have both male and female
parts in them, called perfect flowers.
Strategies to avoid selfpollination
• Perfect flowers have both male and female
organs, so plants have strategies to avoid
self-pollination:
• 1. Timing – male and female structures
mature at different times
• 2. Structure –male and female organs
prevent
self-pollination (imperfect flower)
• 3. Biochemical – chemical on surface of
pollen and stigma that stops the pollen tube
from being formed in the same flower
Pollination and Fertilization
• For pollen to successfully
•
•
fertilize the egg, there
must be crosspollination
Pollen sticks to the
stigma, starts growing a
pollen tube
Cross-Fertilization
begins when
tube begins to grow
toward the egg
How do plants get pollen from
one plant to another?
• Because plants are rooted in the ground,
they must use different strategies:
• WIND POLLINATION
• ANIMALS
ANIMAL POLLINATORS
• Many flowering plants rely on animals for
cross-pollination:
• Insects – bees, wasps, flies, butterflies,
moths
• Birds – hummingbirds, honey creepers
• Mammals – bats, mice, monkeys
• Even some reptiles and amphibians!
A word about pollen…
• The shape and form of pollen is related to its
method of pollination…
• Insect-pollinated species
have sticky of barbed
pollen grains
• Wind-pollinated species
is lightweight, small and
smooth (corn pollen)
Advantages and Disadvantages of
Asexual Reproduction
• Are able to reproduce rapidly
– (ex) strep
– (ex) white blood cells
• Limited variation
• If conditions become unfavourable whole
populations can be wiped out
• Puts all energy into reproduction of itself
Advantages and Disadvantages of
Sexual Reproduction
• Reproduce a lot slower
– (ex) human’s
• Provides lots of variation
• Takes a lot of energy into making enough
gametes so that fertilization can occur
– Have a limited amount of offspring
– (ex) sperm and pollen
Organisms that reproduce
Asexually AND Sexually
• Some species can reproduce
both sexually and asexually
– (ex) aphids
• During the growing season,
females reproduce asexually
producing more females (asexual)
• Over the summer these female
young mature
• in the fall asexually produce male
and female offspring
• Males and females mate and lay
eggs for a new colony that
hatches in the spring