Download A-3 Notes

Science 9: Unit A – Biological
Diversity
Topic 3: Passing It On
The Function of Reproduction



Adaptations are passed on through
reproduction.
Any trait that is passed on through
reproduction (hair color, eye color) is
called a heritable trait.
Reproduction among different kinds of
organisms takes on a variety of forms
or REPRODUCTIVE STRATEGIES.
Asexual Reproduction



Occurs when only one organism passes on their
genetic material. They basically clone themselves.
This method of reproduction is common among
bacteria and fungi
Benefits – You don’t need to spend energy finding
and attracting a mate. Another benefit is that you
can produce much more rapidly, producing many
more offspring.
Drawbacks – Since all of your genetic material is
identical, there is little or no variability in a
population. One disease, or a change in the
ecosystem could wipe out the entire population or
species.
Binary Fission

Binary Fission – Occurs in unicellular
organisms and our own cells. The cell itself
divides creating two cellular organisms.
The cell first duplicates its entire inside
structure: the organelles. The nucleus
stores the genetic material and it splits off
into two clones with the exact same
genetic material. Eventually the cell
membrane closes off and splits the cell
into two identical daughter cells.
Spores

Asexual Spores – Occurs in some
fungi. Single cells called spores are
formed in the fungus. Millions of
spores are then released into the
environment. The spores are
genetically identical to the parent
fungus.
Zoospores – Spores with
Flagella

Zoospores – Are a special type of
spore produced by some fungi and
algae. They are equipped with a
flagellum which allows them to swim
in water and therefore spread their
genetics over a larger area.
Asexual Reproduction in Plants

Vegetative Reproduction – Plants can
reproduce through asexual
strategies. Special cells called
meristem cells act as stem cells:
blank cells that can reproduce
themselves and specialize into any
kind of cell. By taking a cutting of the
plant, you can activate the meristem
cells and produce a clone of the
parent plant.
Budding


Budding – Occurs with sea sponges, yeast
and hydra. A bud cell, like the spore, is
produced and then attaches itself to the
outside of the organism. When it is
completely developed, it detaches itself
and becomes its own organism.
Some buds may remain attached to each
other and form a superorganism: a
collection of organisms which act together
as a single organism.
Most asexual reproducers also
reproduce sexually.

Note that in each of the above kinds of
organisms, they will routinely reproduce
sexually in addition to asexually. Why
would they do this?
Sexual Reproduction

Sexual reproduction usually involves
two individuals. Most plants and
animals reproduce sexually. The
offspring of sexual reproduction will
have the characteristics of both parents
(ie. a lion cub will share 50% of its
genes with each parent). The main
benefit of sexual reproduction is
increased variation.
Gametes are Sex Cells

Sexual reproduction happens through
the joining of gametes. Gametes are
the reproductive cells that join together
to form the zygote. For animals the
gametes are the sperm cell from the
male, and the egg cell from the female.
Sexual Reproduction in Animals



Occurs when the sperm cell from the male
and the egg cell from the female join
together. This process is called fertilization.
After fertilization the two gametes are now
one cell called a zygote which will divide
repeatedly very quickly. Once it starts dividing
we call the new organism an embryo.
Mammals have the structural adaptation of
internal fertilization and gestation (the growth
of the embryo). This helps protect the
gametes and embryo until it is mature
enough to survive in the environment.
Gametes Must Live in Liquid
environments

Gametes, like all cells, must live in a
liquid environment; therefore
fertilization must either occur in water
(amphibians, and fish) or inside an
internal liquid environment (everything
else).
Sexual Reproduction in Plants




Most plants have both male and female sex
organs and produce both kinds of gametes.
Plants that flower have their reproductive
organs in the flower area.
Stigma contains the male gametes, and is
produced in the STAMEN, the male
reproductive organ of the plant.
Ovary contain the female gametes, and they
are found in the PISTIL, which is the female
sex organ in the plant.
Pollination is for plants what fertilization is for
animals: the joining of the two gametes.
Sexual Reproduction in Plants
Cont’d



Self-pollination occurs when the pollen
reaches the pistil of the same plant. This
allows a plant to reproduce sexually even if
there are no other plants of the same species
nearby.
Cross pollination occurs when the pollen from
plant is carried by wind or insect to another
plant of the same species. The advantage
here is that maximum variation is achieved.
The embryo of the plant is produced in a
seed and remains in the seed until the
conditions are right.
Sexual Reproduction in Bacteria

Bacterial conjugation is a primitive form
of sexual reproduction between two
bacteria cells (unicellular organisms).
Two bacteria cells form a connection
with each other and transfer genetic
material to each producing two new
organisms without producing any
offspring.