Grade 9 Science
Unit #3: Reproduction
Topic #3 – Asexual and Sexual Reproduction
Lesson
1
Topic
Asexual
Reproduction
2
Sexual
Reproduction
What you will learn:
- Asexual reproduction involves only one parent
- Plants can reproduce asexually by binary fission, spore
production, vegetative reproduction, fragmentation, or grafting.
Animals can reproduce asexually by budding or parthenogenesis
- Asexual reproduction can produce lots of identical individuals
very quickly but produces entire populations of individuals that
may not survive if the environmental conditions are not optimal
- Asexual reproduction is a fundamental part of the agriculture
and forestry sectors in Saskatchewan
- Sexual reproduction in animals is achieved by the union of male
and female gametes
- Gametes are produced through the process of meiosis
- Sexual reproduction produces individuals with many variations of
characteristics, so they are very rarely identical; this form of
reproduction may require a large amount of energy to produce
only a small number of offspring
A. Asexual Reproduction
Asexual reproduction is a method of reproduction where a single parent reproduces its offspring. There
is no genetic recombination; therefore the DNA of the offspring is identical to that of its parent.
Offspring that are identical copies of each other are called clones. In some cases, asexual reproduction
can produce lots of identical individuals very quickly. Over a 12-hour period, a single bacterium can
divide to produce 10 million copies of itself. This is a great advantage in environments that do not
change very much. Ex. Bacteria that live in the gut of an animal will always have a warm, moist
environment to live in while the animal is alive. Producing many copies of a bacterial cell that is suited
to that environment is a safer bet for survival than producing a smaller number of bacteria with many
variations that may never be needed. The main disadvantage of asexual reproduction is that all the
offspring are identical to the parent. Any factor that negatively affects the parent, such as disease or
drug, will also affect all the offspring. Also, if the environmental conditions become unfavorable, the
entire population may be wiped out.
Grafting
Budding
Definition/Process
The parent produces a small bud, or a
miniaturized clone. In some parents,
the buds eventually detach and
become separate individuals. In other
animals, the offspring remain attached
to the parent, forming a large
structure composed of many identical
individuals.
One plant is joined with another plant,
called the parent tree or the root
stock. The two plants heal together
and grow as a single plant, but the two
plants maintain their own
characteristics. Can be used to
strengthen the stem of a plant to
ensure that it grows and develops a
strong, healthy stem.
Diagram
Examples of plants
Hydra
Yeast
Coral
This is commonly
used by gardeners
to produce flowers
with
certain
colours or trees
that grow different
types of apples on
different branches.
Binary Fission
Occurs when single-celled organisms
divide into two identical daughter cells
to produce two new individuals that
are identical to each other and are
clones of the parent cell.
Bacteria
Amoeba
algae
Spore Production
Spores are haploid cells that can
develop into new organisms. Spores
are similar to seeds because they
contain and protect the DNA of the
organism against unfavourable
conditions. Spores remain alive, but
they do not grow until environmental
conditions are suitable for growth.
Fungi
Green algae
Mould
Non-flowering
plants
Fragmentation
New individuals are formed from a
piece of the existing parent organism.
Some animals can grow two identical
individuals after being cut into two
pieces.
Worms
Starfish
Many plants
Vegetative
Reproduction
Method 1 – take a cutting from a
coleus plant and place it in water, the
cutting will grow roots and eventually
develop into a whole new plant.
Method 2 – Plant produce modified
stems that run horizontally over the
ground (runners) or under the ground
(rhizomes) and produce new plants
along their length.
Coleus plants
Strawberries
Spider plants
Potatos
Onions
Tulips
Parthenogenesis
An unfertilized haploid egg matures
into new organisms. In some species
unfertilized eggs become male drones
and fertilized eggs become female
workers and queens.
Ants
Bees
Snakes
Lizards
Plant Tissue Cultures
Plant cells are placed in a petri dish or
a bottle containing nutrients and other
chemicals and grown into a new
individual. Once the cells develop into
seedlings, they can be transplanted
into soil and grown like a normal plant.
Often happens
with plants that
have desirable
features such as
disease resistance
or good fruit
production. Or to
conserve
endangered plant
species.
Potatoes are an excellent example of how different methods of asexual reproduction are used in
agriculture in Saskatchewan. A parent plant with desirable features is selected, cuttings are taken and
either planted and grown or used to create plant tissue cultures. The clones are grown and produce
seed potatoes. Seed potatoes are potatoes that are grown for replanting, not eating. The plants grown
from seed potatoes produce potatoes sold for eating.
Assignment: Page 23 # 1 – 6, 8, 11, 12
B. Sexual Reproduction
Sexual reproduction is a method of reproduction that typically involves two parents, a male and female
such as with humans and other animals, but can occur with species that we wouldn’t consider male and
female, such as in plants and coral. Sexual reproduction is the combination of two gametes, male and
female sex cells, to produce an offspring. Gametes in females are called eggs or ova, whereas sex cells
from a male are called sperm. These cells are produced through meiosis. The union of the sperm cell
with the egg cell occurs during mating and is called fertilization.
DNA recombines to create offspring with a combination of characteristics from both parents. So
offspring are not clones of their parents. Variation helps a species survive by giving it the ability to
survive changes in its environment. Although, a major disadvantage or sexual reproduction is that the
gametes need to meet. Flowering plants must have wind or attract insects to move pollen to the
stigma. Also, the embryo must be protected and nurtured during development. In mammals, the
embryo grows within the body of the female parent. Because this takes a large amount of time and
energy needed for this development, only a limited number of offspring can be produced.
Flowering Plant Structures
Pollination – is the transfer of pollen grains to the stigma. Pollen transferred to the stigma of
the same flower is called self-pollination. If pollen grains are transferred to the stigma of
another flower, it is called cross-pollination.
Cross-pollination can be caused by various sources, such as: wind, water, bees, birds, bats or
other animals (including humans).
Fertilization – is the process that occurs after pollination. If the pollen grain has landed on a
compatible stigma, a pollen tube grows to transport the pollen to the egg. Once the pollen
reaches the egg, the two gametes fuse and create a zygote. The zygote then forms into a seed.
Germination – is the process a plant undergoes as the seed grows into a new plant. Once the
seed absorbs water, it begins to expand and open as the new plant grows within it.
Sexual Reproduction in Animals
In animals, sexual reproduction uses eggs (female gamete) and sperm (male gamete) as the
reproductive cells. After the two gametes fuse, a zygote is formed. Fertilization can occur
within and exterior to the animal body depending on the specific animals form of reproduction.
Once the zygote has undergone cellular division, it forms an embryo, which is a multi cellular
structure. The embryo will begin to form small organs and appendages. Once the organs begin
to function, it is called a fetus this occurs at approximately the nine week mark in humans. The
fetus is final structure an organism will take before birth.
Hermaphrodites can produce both male and female gametes. Worms and slugs are examples
of hermaphrodites. Although hermaphrodites usually mate with other individuals of their
species, in time of environmental stress, members of some species can fertilize themselves.
Sequential hermaphrodites are species that are born as one sex, but then become the opposite
sex. One example is the clownfish. Clownfish travel in packs that consist of a large
reproductive female, a smaller reproductive male as well as numerous smaller nonreproductive males. If the female dies or leaves, the large reproductive male becomes a female
and the largest of the non-reproductive males becomes the new reproductive male.
Organisms that Reproduce Both Sexually and Asexually
Some species have the ability to reproduce both sexually and asexually. Most plants that
produce seeds by sexual reproduction can also reproduce asexually, either from cuttings or by
producing structures such as bulbs or runners.
Some plants can use their seeds to reproduce both asexually and sexually. In the asexual
method, embryos develop in the seeds without the contribution of sperm cells. These offspring
are genetically identical to their parent.
Some animal species can also reproduce both ways. Aphids are small insects that feed on the
sap of certain plants. Throughout the growing season, females produce live female young
through asexually. Over the summer, several generations are produced. In the fall, when days
shorten and the temperature drops, the females produce a generation that includes both males
and females. These males and females reproduce sexually and lay eggs that will hatch in the
spring to produce new colonies. Sponges can also produce sexually and asexually.
Assignment: Page 34 #3, 4, 6 – 9, 11, 12