Download Asexual and Sexual Reproduction

Asexual vs. Sexual
Reproduction
Part 2 of 3
Sexual Reproduction
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Sexual
Reproduction
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1. 2 parents
2. Sex cells: sperm and
egg
3. Sperm and egg join=
fertilization
4. Offspring look different
from parent (mixed DNA)
Sexual Reproduction

Sexual
Reproduction
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Examples
– Humans, some plants,
mammals, fish, reptiles, etc.
Read:
Sexual Reproduction: Gametes, External/Internal Fertilization, Male/Female
Sexual Reproduction
Sexual Reproduction in Animals
• involves specialized sex cells called gametes
• the union of a male and female gamete results in
the formation of a zygote that develops into a
new individual
Sexual
Reproduction in
Plants
Female Parts
Male Parts
(Pistil)
pollen (male) + ovule (female) → single-celled zygote → multi-celled
embryo (contained in a seed) → new individual
Sexual Reproduction in Plants
• The stamen is the male part and contains
pollen
• The carpels or pistil is the female part
and contains the ovule (eggs)
• Pollen grains from the anther are
transferred to the stigma by the process of
pollination
– self pollination (plant pollinates its own eggs)
– Assisted Pollination of a Flower (1:11)
– cross pollination (pollen from one plant
pollinates another plants eggs)
Pollination
• Flowers are designed (bright colors, stripes,
sweet smell, food) to attract insects to help
with the pollination process
– also wind, animals, birds can transport pollen
Plant Reproduction (1:30)
Plant Reproduction:
Methods of Pollination
(3:58)
Sexual Reproduction Summary
Male
Gamete
Female
Gamete
Type of
Union
Result of
Union
Final
Result
Plants
pollen
ovule
(egg)
pollination
single cell
zygote
multi-cell
embryo
(in seed)
Animals
sperm
egg
fertilization
single cell
zygote
multi-cell
embryo
Asexual vs. sexual reproduction
Organisms that reproduce through asexual reproduction tend to grow in number exponentially.
However, because they rely on mutation for variations in their DNA, all members of the species
have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of
offspring, but the large amount of variation in their genes makes them less susceptible to
disease.
Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea
anemones, some species of starfish (by fragmentation), and many plants are examples. When
environmental factors are favorable, asexual reproduction is employed to exploit suitable
conditions for survival such as an abundant food supply, adequate shelter, favorable climate,
disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these
organisms increase exponentially via asexual reproductive strategies to take full advantage of
the rich supply resources.
When food sources have been depleted, the climate becomes hostile, or individual survival is
jeopardized by some other adverse change in living conditions, these organisms switch to
sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the
species. The variations found in offspring of sexual reproduction allow some individuals to be
better suited for survival and provide a mechanism for selective adaptation to occur. In addition,
sexual reproduction usually results in the formation of a life stage that is able to endure the
conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae,
cysts or other "over-wintering" stages of sexual reproduction ensure the survival during
unfavorable times and the organism can "wait out" adverse situations until a swing back to
suitability occurs.
Some Organisms do Both
• Most plants that produce seeds (sexual
reproduction) can also reproduce
asexually by things like cuttings or runners
• This gives them an advantage for survival
sponges and hydra
mosses
onions
Asexual and Sexual
Reproduction - I can do both!
Aphids
Asexual and Sexual
Reproduction - I can do both!
Fuligo septica, the "dog vomit"
slime mold
Slime mold growing out of a bin
of wet paper
Mycetozoa from Ernst Haeckel's
1904 Kunstformen der Natur
(Artforms of Nature)
Mycetozoa is a grouping of
slime molds.
Slime mold (Physarum polycephalum)
Sea anemone
Asexual Reproduction – Grade Six
Attachment
Organisms and
Types
of EAsexual Reproduction
Asexual Reproduction Resource Page
Any of the following could be used in the science lab to reinforce content.
Organism
Whiptail
lizards
Type of
Asexual
Reproduction
Parthenogenesis
Bacteria
Fission
Spider plant
Vegetative
Propagation
Strawberries
Vegetative
Propagation
Fragmentation
Some
flatworms
Paramecium
Mint
Blue-green
algae
Protists
Hydra
Fission
Vegetative
Propagation
Fission
Fission
Budding
Description
A female whiptail lizard may produce eggs that develop into
genetically identical versions of itself. In some species, there
are entire clonal populations of this lizard. Most whiptail lizard
species do reproduce sexually, though.
A single-celled organism that has no nuclei or cell walls and
reproduce by splitting in two.
Spider plants reproduce new plants by the division of cells from
roots or runners. These can be placed in water or soil to
produce another plant. Spider plants also reproduce sexually.
Strawberries reproduce new plants by the division of cells from
runners or roots. Strawberries also reproduce sexually.
Some flatworms can grow by cell division from a fragmented
section of its body.
Paramecium is a single-celled organism that reproduces by
splitting in two.
Division of the roots reproduces new mint. Mint also
reproduces sexually.
A single celled organism that reproduces by splitting in two.
Protists have a nucleus and are therefore eukaryotic. Some
protists contain chloroplasts and make their own food, and
others don't. But all reproduce by fission-the process of
splitting in two.
Cell division forms a bud that is an identical copy of its single
parent that separates from the parent and becomes independent.
Which is Better?
It depends!
Asexual Reproduction
• advantages
– does not require special
cells or a lot of energy
– can produce offspring
quickly
– in a stable environment
creates large, thriving
population
• disadvantages
– limited ability to adapt
– face massive die-off if
environment changes
Sexual Reproduction
• advantages
– lots of variation within a
species
– able to live in a variety
of environmental
settings
– able to adapt to changes
in the environment
• disadvantages
– needs time & energy
– produce small
populations