Download REPRODUCTION Part 1

REPRODUCTION
Part 1
OCS Biology
Mrs. Bonifay
Spontaneous Generation
Many years ago, some people thought
living things could come from nonliving
things. This is called spontaneous
generation. For example, then they saw a
frog jump out of a muddy pond, they
thought the mud made the frog.
 Spontaneous generation was proved to be
untrue. Living things come from other
living things.

DNA
Each organism’s cells contain the
information needed to make another
organism just like itself. Cells store this
information as a chemical called DNA.
 DNA stores information in a pattern of
chemicals.
 Your DNA contains all the information
needed to make a human with your
characteristics or traits.

DNA and Reproduction
Each type of organism has its own unique DNA.
Humans have DNA about how to make a human.
Frogs have DNA about how to make a frog.
 When living things reproduce, they pass exact
copies of their DNA to their offspring.
 In some organisms, such as bacteria,
reproduction requires one parent. The parent
passes copies of all of its DNA to its offspring.
Its DNA is identical to the parent’s DNA.

DNA & Reproduction
Reproduction in animals and plants usually
involves two parents.
 You have traits from both parents, even
though you might resemble one parent
more than the other. This is because your
DNA is a combination of both parents’
DNA. Therefore, humans and other
organisms produce offspring that are
unique.

Diversity
Humans and other species that produce unique
offspring are said to have diversity.
 Diversity if the range of differences found in a
certain population.
 If a population’s environment changes suddenly,
the population’s diversity can help it continue to
survive. The population can adapt because of
diversity.
 Adaptations are traits that allow organisms to
survive in certain environments. They are found
in information on an organism’s DNA.

Asexual Reproduction
When an organism passes all of its DNA onto its
offspring and the offspring are identical to the parent, it
is called asexual reproduction.
 One-celled organisms usually reproduce asexually.
 Their cells divide to form two identical cells.
 Protists, fungi, and some plants and animals can
reproduce by asexual reproduction.
 Skin cells, bone cells, and muscle cells are examples of
human cells that reproduce asexually to form new cells.
This allows your body to grow, heal, and replace dead
cells.

Asexual Reproduction
One advantage of asexual reproduction is that
an organism does not have to find a mate.
 Another advantage is time. One-celled
organisms can reproduce quickly.
 A disadvantage of asexual reproduction is that
the offspring are exact copies of their parent.
The offspring lack diversity and are likely to
respond to changes in environment. If change
kills one offspring, it will likely kill them all.

Mitosis
In cells that have a nucleus, asexual
reproduction occurs in the form of mitosis.
 Mitosis is the dividing of the cell’s nucleus.
 Before a cell undergoes mitosis, it makes a
copy of its DNA.
 DNA is found in the nucleus in rod-shaped
structures called chromosomes. When
DNA is copied, the chromosomes form
pairs.

Sexual Reproduction
Humans and many other organisms have
two parents. This is called sexual
reproduction.
 During sexual reproduction, a cell from
one parent joins with a cell from the other
parent.
 A disadvantage of sexual reproduction is
that an organism must find a mate.

Sexual Reproduction
Another disadvantage is sexual reproduction is
that it usually takes longer to produce offspring.
 A big advantage to sexual reproduction is that it
leads to greater diversity in a population
because each offspring is unique.
 Sexual reproduction involves both a female, who
produces egg cells, and a male, who produces
sperm cells.

Sexual Reproduction
The gametes, or sex cell, of certain
species contain one-half the number of
chromosomes found in the species nonsex cells.
 For example, human sex cells have 23
chromosomes in their nucleus. Human
body cells have 46 chromosomes.

Meiosis
Gametes form by a division of the nucleus
called meiosis.
 Meiosis begins after the cell’s
chromosomes have been copied.
 During meiosis, the nucleus disappears.
 The pairs of chromosomes line up in the
center of the cell and then separate. A
nucleus forms around each set of
chromosomes.

Meiosis
Next, the cell divides into two new cells,
and each new cell divides once again.
Therefore, each original cell produces four
sex cells.
 Since cell division occurs twice, each sex
cell contains one-half the number of
chromosomes of the original cell.

Fertilization
Fertilization is the process by which a sperm cell
and an egg cell join to form one cell. This cell is
called a zygote, which has a complete set of
chromosomes: half from the egg cell and half
from the sperm cell.
 When a female fish has laid her eggs under the
water, a male fish swims above the eggs and
releases billions of sperm into the water. One of
the sperm will attach to one of the eggs, and its
nucleus enters the egg joining with the nucleus
of the egg cell. This is called external
fertilization.

Fertilization
Most fish and amphibians use external
fertilization.
 All reptiles, birds, and mammals use
internal fertilization.
 Internal fertilization is when the male
places sperm inside the female’s body
where fertilization occurs.

Growth and Development
A new animal begins as a zygote (a single
cell that contains a complete set of
chromosomes).
 Eventually, the zygote divides into millions
of cells that make up an embryo. An
embryo is an early stage in the
development of an organism. In this
process, the same DNA is copied in each
cell.

Differentiation

An embryo’s cells gradually take on
different shapes and functions. This is
called cell differentiation.
Development
The embryos of many animals, such as
fish, reptiles, and birds, develop inside an
egg.
 When young insects look like the adult,
they are called nymphs. Nymphs cannot
reproduce until they are adults.

Mammal Offspring
Mammals produce few offspring compared
to fish and other kinds of animals.
 Mammal parents often take care of their
young for long periods of time, protecting
them from danger and increasing their
chances of survival. Because of this,
fewer offspring are needed to ensure
survival of a mammal species.

Mammal Offspring
Most animals do not lay eggs; the exceptions
are the duck-billed platypus and the spiny
anteater.
 All other mammals carry their young inside their
bodies, at least for part of the time.
 Marsupials are mammals that give birth to
young that are undeveloped. After being born,
the tiny marsupial crawls into its mother’s
external pouch, where it continues to develop.
 All other mammals give birth to young ones that
are more fully developed.

Food for Young Mammals
Most mammals embryos get food from inside
their mother’s body.
 Most female mammals have a uterus, an organ
that holds and protects the developing embryo.
 Inside the uterus, the embryo forms protective
tissues around itself. Part of these tissues form
a placenta which provides food and oxygen from
the mother’s body.
 Once a young mammal is born, it feeds on milk
produced by its mother’s mammary glands.

Food for Young Mammals
The embryos of most marsupials do not obtain
food through a placenta. When inside the
mother, it gets food from the fertilized egg for a
short time, and then feeds on milk in the
mother’s pouch after it is born.
 For mammals that lay eggs, the mammal eggs
do not contain a large food supply, so the young
feed on milk from their mother’s mammary
glands after they are born.

Gestation
Different mammals have different gestation
times, depending on the size of the animal.
 Gestation time is the period of time from the
fertilization of an egg until birth.
 The larger the mammal, the longer the gestation
times.
 The gestation time for an elephant is almost two
years; for a mouse, it is only 20 days.
