REPRODUCTIONREPRODUCTIONPart 1Part 1

OCS BiologyOCS Biology

Mrs. BonifayMrs. Bonifay

Spontaneous GenerationSpontaneous Generation

Many years ago, some people Many years ago, some people thought living things could come thought living things could come from nonliving things. This is called from nonliving things. This is called spontaneous generation.spontaneous generation. For For example, then they saw a frog jump example, then they saw a frog jump out of a muddy pond, they thought out of a muddy pond, they thought the mud made the frog.the mud made the frog.

Spontaneous generation was proved Spontaneous generation was proved to be to be untrue. untrue. Living things come Living things come from other from other living things.living things.

DNADNA

Each organism’s cells contain the Each organism’s cells contain the information needed to make another information needed to make another organism just like itself. Cells store organism just like itself. Cells store this information as a chemical called this information as a chemical called DNA.DNA.

DNA stores information in a DNA stores information in a patternpattern of of chemicals.chemicals.

Your DNA contains all the information Your DNA contains all the information needed to make a human with your needed to make a human with your characteristics or characteristics or traitstraits..

DNA and ReproductionDNA and Reproduction

Each type of organism has its own Each type of organism has its own uniqueunique DNA. Humans have DNA about how to DNA. Humans have DNA about how to make a make a humanhuman. Frogs have DNA about . Frogs have DNA about how to make a how to make a frog.frog.

When living things reproduce, they pass When living things reproduce, they pass exact copiesexact copies of their DNA to their offspring. of their DNA to their offspring.

In some organisms, such as bacteria, In some organisms, such as bacteria, reproduction requires reproduction requires one parentone parent. The . The parent passes copies of parent passes copies of all all of its DNA to its of its DNA to its offspring. Its DNA is offspring. Its DNA is identical identical to the to the parent’s DNA.parent’s DNA.

DNA & ReproductionDNA & Reproduction

Reproduction in animals and plants Reproduction in animals and plants usually involves usually involves two parentstwo parents..

You have traits from both parents, You have traits from both parents, even though you might resemble one even though you might resemble one parent more than the other. This is parent more than the other. This is because your DNA is a because your DNA is a combinationcombination of both parents’ DNA. Therefore, of both parents’ DNA. Therefore, humans and other organisms humans and other organisms produce offspring that are produce offspring that are uniqueunique..

DiversityDiversity Humans and other species that produce Humans and other species that produce

unique offspring are said to have unique offspring are said to have diversitydiversity.. Diversity if the range of Diversity if the range of differencesdifferences found found

in a certain population.in a certain population. If a population’s If a population’s environment environment changes changes

suddenly, the population’s diversity can suddenly, the population’s diversity can help it continue to help it continue to survivesurvive. The population . The population can can adaptadapt because of diversity. because of diversity.

AdaptationsAdaptations are traits that allow organisms are traits that allow organisms to survive in certain environments. They to survive in certain environments. They are found in information on an organism’s are found in information on an organism’s DNA.DNA.

Asexual ReproductionAsexual Reproduction When an organism passes all of its DNA onto its When an organism passes all of its DNA onto its

offspring and the offspring are identical to the offspring and the offspring are identical to the parent, it is called parent, it is called asexual reproduction.asexual reproduction.

One-celledOne-celled organisms usually reproduce organisms usually reproduce asexually.asexually.

Their cells divide to form Their cells divide to form two identicaltwo identical cells. cells. Protists, fungi, and some plants and animals can Protists, fungi, and some plants and animals can

reproduce by asexual reproduction.reproduce by asexual reproduction. SkinSkin cells, cells, bonebone cells, and cells, and musclemuscle cells are cells are

examples of human cells that reproduce examples of human cells that reproduce asexually to form new cells. This allows your asexually to form new cells. This allows your body to body to growgrow, , healheal, and , and replacereplace dead cells. dead cells.

Asexual ReproductionAsexual Reproduction

One advantage of asexual reproduction is that One advantage of asexual reproduction is that an organism does not have to find a an organism does not have to find a matemate..

Another advantage is Another advantage is timetime. One-celled . One-celled organisms can reproduce organisms can reproduce quicklyquickly..

A disadvantage of asexual reproduction is that A disadvantage of asexual reproduction is that the offspring are the offspring are exact copiesexact copies of their parent. of their parent. The offspring The offspring lack diversitylack diversity and are likely to and are likely to respond to changes in environment. If change respond to changes in environment. If change kills one offspring, it will likely kill them all.kills one offspring, it will likely kill them all.

MitosisMitosis

In cells that have a nucleus, asexual In cells that have a nucleus, asexual reproduction occurs in the form of reproduction occurs in the form of mitosismitosis..

Mitosis is the dividing of the cell’s Mitosis is the dividing of the cell’s nucleusnucleus..

Before a cell undergoes mitosis, it makes Before a cell undergoes mitosis, it makes a copy of its a copy of its DNADNA..

DNA is found in the nucleus in rod-shaped DNA is found in the nucleus in rod-shaped structures called structures called chromosomeschromosomes. When . When DNA is copied, the chromosomes form DNA is copied, the chromosomes form pairspairs..

Sexual ReproductionSexual Reproduction

Humans and many other organisms Humans and many other organisms have two parents. This is called have two parents. This is called sexual reproduction.sexual reproduction.

During sexual reproduction, a cell During sexual reproduction, a cell from one parent from one parent joinsjoins with a cell from with a cell from the other parent.the other parent.

A disadvantage of sexual reproduction A disadvantage of sexual reproduction is that an organism must find a is that an organism must find a matemate..

Sexual ReproductionSexual Reproduction

Another disadvantage is sexual Another disadvantage is sexual reproduction is that it usually takes reproduction is that it usually takes longerlonger to produce offspring.to produce offspring.

A big advantage to sexual reproduction is A big advantage to sexual reproduction is that it leads to that it leads to greater diversitygreater diversity in a in a population because each offspring is population because each offspring is unique.unique.

Sexual reproduction involves both a Sexual reproduction involves both a female, who produces female, who produces egg cellsegg cells, and a , and a male, who produces male, who produces sperm cellssperm cells..

Sexual ReproductionSexual Reproduction

The The gametesgametes, or sex cell, of certain , or sex cell, of certain species contain species contain one-halfone-half the number the number of chromosomes found in the species of chromosomes found in the species non-sex cells.non-sex cells.

For example, human sex cells have For example, human sex cells have 23 23 chromosomes in their nucleus. chromosomes in their nucleus. Human body cells have Human body cells have 4646 chromosomes.chromosomes.

MeiosisMeiosis

Gametes form by a division of the Gametes form by a division of the nucleus called nucleus called meiosismeiosis..

Meiosis begins after the cell’s Meiosis begins after the cell’s chromosomes have been chromosomes have been copiedcopied..

During meiosis, the nucleus During meiosis, the nucleus disappearsdisappears..

The pairs of chromosomes line up in The pairs of chromosomes line up in the center of the cell and then the center of the cell and then separate. A nucleus forms around separate. A nucleus forms around each seteach set of chromosomes. of chromosomes.

MeiosisMeiosis

Next, the cell Next, the cell dividesdivides into two new into two new cells, and each new cell cells, and each new cell dividesdivides once once again. Therefore, each original cell again. Therefore, each original cell produces produces four four sex cells.sex cells.

Since cell division occurs twice, each Since cell division occurs twice, each sex cell contains sex cell contains one-halfone-half the number the number of chromosomes of the original cell.of chromosomes of the original cell.

FertilizationFertilization FertilizationFertilization is the process by which a is the process by which a

sperm cell and an egg cell join to form one sperm cell and an egg cell join to form one cell. This cell is called a cell. This cell is called a zygotezygote, which has , which has a complete set of chromosomes: half from a complete set of chromosomes: half from the egg cell and half from the sperm cell.the egg cell and half from the sperm cell.

When a female fish has laid her eggs When a female fish has laid her eggs under the water, a male fish swims above under the water, a male fish swims above the eggs and releases billions of sperm the eggs and releases billions of sperm into the water. One of the sperm will into the water. One of the sperm will attach to one of the eggs, and its nucleus attach to one of the eggs, and its nucleus enters the egg joining with the nucleus of enters the egg joining with the nucleus of the egg cell. This is called the egg cell. This is called external external fertilization.fertilization.

FertilizationFertilization

Most fish and amphibians use Most fish and amphibians use external fertilization.external fertilization.

All reptiles, birds, and mammals use All reptiles, birds, and mammals use internal fertilization.internal fertilization.

Internal fertilization is when the male Internal fertilization is when the male places sperm places sperm inside inside the female’s the female’s body where fertilization occurs.body where fertilization occurs.

Growth and DevelopmentGrowth and Development

A new animal begins as a A new animal begins as a zygotezygote (a (a single cell that contains a complete single cell that contains a complete set of chromosomes).set of chromosomes).

Eventually, the zygote divides into Eventually, the zygote divides into millions of cells that make up an millions of cells that make up an embryoembryo. An embryo is an early stage . An embryo is an early stage in the development of an organism. in the development of an organism. In this process, the same DNA is In this process, the same DNA is copied copied in each cell.in each cell.

DifferentiationDifferentiation

An embryo’s cells gradually take on An embryo’s cells gradually take on different shapes and functions. This different shapes and functions. This is called is called cell differentiationcell differentiation. .

DevelopmentDevelopment

The embryos of many animals, such The embryos of many animals, such as fish, reptiles, and birds, develop as fish, reptiles, and birds, develop inside an inside an eggegg..

When young insects look like the When young insects look like the adult, they are called adult, they are called nymphsnymphs. . Nymphs cannot Nymphs cannot reproduce reproduce until they until they are adults. are adults.

Mammal OffspringMammal Offspring

Mammals Mammals produce few offspring produce few offspring compared to fish and other kinds of compared to fish and other kinds of animals.animals.

Mammal parents often take care of their Mammal parents often take care of their young for long periods of time, young for long periods of time, protectingprotecting them from danger and them from danger and increasing their chances of increasing their chances of survivalsurvival. . Because of this, fewer offspring are Because of this, fewer offspring are needed to ensure survival of a mammal needed to ensure survival of a mammal species.species.

Mammal OffspringMammal Offspring Most animals Most animals do notdo not lay eggs; the lay eggs; the

exceptions exceptions are the duck-billed platypus are the duck-billed platypus and the spiny anteater.and the spiny anteater.

All other mammals carry their young inside All other mammals carry their young inside their their bodiesbodies, at least for part of the time., at least for part of the time.

MarsupialsMarsupials are mammals that give birth to are mammals that give birth to young that are young that are undevelopedundeveloped. After being . After being born, the tiny marsupial crawls into its born, the tiny marsupial crawls into its mother’s external mother’s external pouchpouch, where it , where it continues to develop.continues to develop.

All other mammals give birth to young All other mammals give birth to young ones that are ones that are more fully developedmore fully developed..

Food for Young MammalsFood for Young Mammals Most mammals embryos get food from Most mammals embryos get food from insideinside

their mother’s body.their mother’s body. Most female mammals have a Most female mammals have a uterusuterus, an , an

organ that holds and protects the developing organ that holds and protects the developing embryo.embryo.

Inside the uterus, the embryo forms Inside the uterus, the embryo forms protectiveprotective tissuestissues around itself. Part of these around itself. Part of these tissues form a tissues form a placenta placenta which provides food which provides food and oxygen from the mother’s body.and oxygen from the mother’s body.

Once a young mammal is born, it feeds on Once a young mammal is born, it feeds on milk produced by its mother’s milk produced by its mother’s mammary mammary glandsglands..

Food for Young MammalsFood for Young Mammals

The embryos of most marsupials do not The embryos of most marsupials do not obtain food through a placenta. When obtain food through a placenta. When inside the mother, it gets food from the inside the mother, it gets food from the fertilized eggfertilized egg for a short time, and then for a short time, and then feeds on milk in the mother’s feeds on milk in the mother’s pouchpouch after it after it is born.is born.

For mammals that lay eggs, the For mammals that lay eggs, the mammal mammal eggseggs do not contain a large food supply, so do not contain a large food supply, so the young feed on milk from their mother’s the young feed on milk from their mother’s mammarymammary glandsglands after they are born. after they are born.

GestationGestation

Different mammals have different Different mammals have different gestation times, depending on the gestation times, depending on the sizesize of of the animal.the animal.

Gestation timeGestation time is the period of time from is the period of time from the fertilization of an egg until birth.the fertilization of an egg until birth.

The The larger larger the mammal, the the mammal, the longerlonger the the gestation times.gestation times.

The gestation time for an elephant is The gestation time for an elephant is almost almost two yearstwo years; for a mouse, it is only ; for a mouse, it is only 20 20 daysdays..