Reproduction and Development How Animals Reproduce Sexual Reproduction Asexual Reproduction Animal Development

How Animals Reproduce Reproduction in animals is either sexual or asexual Reproduction is characterized by certain adaptations Eggs are an important adaptation in reproduction for many animal groups

Sexual Reproduction In sexual reproduction, sperm from a male unite with one or more eggs produced by a female in a process called fertilization In animal groups, fertilization may be external or internal

External Fertilization Many animal species may produce one or many new individuals at one time Water-inhabiting animals may produce huge numbers of eggs and sperm at one time. These organisms depend on water to carry out fertilization

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

Internal Fertilization A female produces one or more eggs that are kept in the body The male deposits sperm in a fluid into the female’s body The sperm swim to and unite with the eggs.

that undergo development in the female’s body generally produce Organisms that have fertilized eggs that undergo development in the female’s body generally produce smaller numbers of offspring. Organisms that undergo internal fertilization are not restricted to living in or near water to accomplish fertilization

Asexual Reproduction Asexual reproduction is the production of a new organism from just one parent No eggs or sperm are exchanged Asexual reproduction occurs in manly invertebrates

Two types of Asexual Reproduction Budding– a new organism breaks off from the parent Regeneration– regrowth of a new organism from a portion of the original body.

Animal Development Development of a fertilized egg into an adult varies in the animal world. Birds and mammals have young that look very similar to the adult form of their species Some animals at first look nothing like their parents and undergo extensive changes in their form

Metamorphosis Metamorphosis is the change in form that organisms undergo in their life cycle Organisms change form completely as they grow from egg to adult Two types of metamorphosis are known in insect life cycles Complete metamorphosis Incomplete metamorphosis

Complete Metamorphosis in Butterflies Stage 1 Egg Stage 2 Larva Stage 3 Pupa Stage 4 Adult

Stage 1 Egg Complete metamorphosis begins about seven days after an egg is fertilized. The caterpillar egg develops into a larva

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

In the pupa stage the caterpillar spins a covering from a silken thread it produces. During this time, chemicals called hormones cause vast changes to take place that result in a complete change in form inside the pupa

In the adult stage, the insect splits open its covering and emerges. The adult insect—a butterfly—unfolds its wings and flutters them, thus pumping blood into its veins

Survival During Development Animals evolve a variety of adaptations to survive to adulthood Some of these adaptations involve: Reproducing in large numbers Shells Internal development

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

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

Internal Development Most mammals develop within the female’s body. Internal development provides protection for the embryo.