Reproduction and Development

1.1. How Animals ReproduceHow Animals Reproduce

2.2. Sexual ReproductionSexual Reproduction

3.3. Asexual ReproductionAsexual Reproduction

4.4. Animal DevelopmentAnimal Development

How Animals ReproduceHow Animals Reproduce Reproduction in animals is either Reproduction in animals is either sexual or asexualsexual or asexual

Reproduction is characterized byReproduction is characterized by certain adaptationscertain adaptations

Eggs are an important adaptation inEggs are an important adaptation in reproduction for many animal groupsreproduction for many animal groups

Sexual ReproductionSexual Reproduction

In sexual reproduction, spermIn sexual reproduction, sperm from a male unite with one orfrom a male unite with one or more eggs produced by a female more eggs produced by a female in a process called fertilizationin a process called fertilization

In animal groups, fertilizationIn animal groups, fertilization may be external or internalmay be external or internal

External FertilizationExternal Fertilization

Many animal species may produce oneMany animal species may produce one

or many new individuals at one timeor many new individuals at one time

Water-inhabiting animals may Water-inhabiting animals may

produce huge numbers of eggs and produce huge numbers of eggs and

sperm at one time.sperm at one time.

These organisms depend on water toThese organisms depend on water to

carry out fertilizationcarry out fertilization

During External fertilization, the During External fertilization, the female releases eggs into the water. female releases eggs into the water. The male then releases sperm, The male then releases sperm, which swim to the eggswhich swim to the eggs

Internal FertilizationInternal Fertilization A female produces one or moreA female produces one or more eggs that are kept in the bodyeggs that are kept in the body

The male deposits sperm in aThe male deposits sperm in a fluid into the female’s bodyfluid into the female’s body

The sperm swim to and unite withThe sperm swim to and unite with the eggs.the eggs.

Organisms that have fertilized eggsOrganisms that have fertilized eggs that undergo development in thethat undergo development in the female’s body generally producefemale’s body generally produce smaller numbers of offspring.smaller numbers of offspring.

Organisms that undergo internalOrganisms that undergo internal fertilization are not restricted tofertilization are not restricted to living in or near water to accomplishliving in or near water to accomplish fertilizationfertilization

Asexual Reproduction

Asexual reproduction is the Asexual reproduction is the production of a new organism fromproduction of a new organism from just one parentjust one parent

No eggs or sperm are exchangedNo eggs or sperm are exchanged

Asexual reproduction occurs in manlyAsexual reproduction occurs in manly invertebratesinvertebrates

Two types of Asexual Reproduction

Budding– a new organism breaksBudding– a new organism breaks

off from the parentoff from the parent

Regeneration– regrowth of a newRegeneration– regrowth of a new

organism from a portion of theorganism from a portion of the

original body.original body.

Animal Development

Development of a fertilized egg into anDevelopment of a fertilized egg into an

adult varies in the animal world.adult varies in the animal world.

Birds and mammals have young that Birds and mammals have young that

look very similar to the adult form oflook very similar to the adult form of

their speciestheir species

Some animals at first look nothing likeSome animals at first look nothing like

their parents and undergo extensivetheir parents and undergo extensive

changes in their formchanges in their form

Metamorphosis

Metamorphosis is the change inMetamorphosis is the change in form that organisms undergo inform that organisms undergo in their life cycletheir life cycle

Organisms change form completely asOrganisms change form completely as they grow from egg to adultthey grow from egg to adult

Two types of metamorphosis are knownTwo types of metamorphosis are known in insect life cyclesin insect life cycles

Complete metamorphosisComplete metamorphosis Incomplete metamorphosisIncomplete metamorphosis

Complete Metamorphosis in Butterflies

Stage 1 Stage 1 EggEgg

Stage 2 Stage 2 LarvaLarva

Stage 3 Stage 3 PupaPupa

Stage 4 Stage 4 AdultAdult

Stage 1 Egg

Complete metamorphosis Complete metamorphosis

begins about seven days afterbegins about seven days after

an egg is fertilized.an egg is fertilized.

The caterpillar egg developsThe caterpillar egg develops

into a larvainto a larva

Stage 2 Larva The larva chews the egg case openThe larva chews the egg case open and stretches out.and stretches out. In fact the larva can eat severalIn fact the larva can eat several times its body weight in one day.times its body weight in one day. As it grows, the larva molts—its As it grows, the larva molts—its exoskeleton splits and a new oneexoskeleton splits and a new one formsforms Just before its last molt, the matureJust before its last molt, the mature larva attaches itself to a twig or leaflarva attaches itself to a twig or leaf

In the pupa stage the caterpillarIn the pupa stage the caterpillar

spins a covering from a silkenspins a covering from a silken

thread it produces. thread it produces.

During this time, chemicalsDuring this time, chemicals

called hormones cause vast called hormones cause vast

changes to take place thatchanges to take place that

result in a complete change inresult in a complete change in

form inside the pupaform inside the pupa

In the adult stage, the In the adult stage, the insect splits open its insect splits open its covering and covering and emerges. emerges.

The adult insect—a The adult insect—a butterfly—unfolds its butterfly—unfolds its wings and flutters wings and flutters them, thus pumping them, thus pumping blood into its veinsblood into its veins

Survival During Development

Animals evolve a variety of Animals evolve a variety of adaptations to survive to adulthoodadaptations to survive to adulthood

Some of these adaptations involve:Some of these adaptations involve:

Reproducing in large numbersReproducing in large numbers

ShellsShells

Internal developmentInternal development

Reproducing in large numbers

Animals that Animals that develop through develop through the process of the process of metamorphosis metamorphosis seem to seem to reproduce in reproduce in large numbers.large numbers.

Shells

Birds and reptiles reproduce in Birds and reptiles reproduce in smaller numbers. These species smaller numbers. These species have adapted ways to protect their have adapted ways to protect their young as they develop outside the young as they develop outside the female’s body.female’s body.After fertilization, a protective shell After fertilization, a protective shell forms around an egg.forms around an egg.The shell keeps the egg from drying The shell keeps the egg from drying out.out.

Internal Development

Most mammals Most mammals develop within the develop within the female’s body.female’s body.

Internal development Internal development provides protection provides protection for the embryo. for the embryo.