Chapter 2 Lesson 3- Animal Life Cycles
VOCABULARY
1. Metamorphosis
2. Complete metamorphosis
3. Larva
4. Pupa
5. Incomplete metamorphosis
6. Nymph
7. External fertilization
8. Internal fertilization
NOTES
What are animal life cycles?

Most animals resemble the adult they will become.

Other animals, such as amphibians and insects, go through metamorphosis.
Complete Metamorphosis

Butterflies, moths, flies, and beetles go through complete metamorphosis.

Complete Metamorphosis-4 DISTINCT STAGES
1) Egg
2) Larva-(see vocabulary)
3) Pupa –(see vocabulary)
4) Adult

Larva has no wings.

Larva eats different food than the adult.

Pupa is thought to be a resting stage, but it is really very active.

The entire body is changing.

When the cocoon opens, an adult butterfly with completely restricted body emerges.
Incomplete Metamorphosis

Grasshoppers, dragonflies, termites, and bedbugs go through incomplete metamorphosis.

Incomplete metamorphosis- 3 DISTINCT STAGES
1) Eggs
2) Nymph-(see vocabulary)
3) Adult

Nymphs have no wings or sex organs.

There may be several different nymph stages before the animal becomes an adult.

Grasshoppers have a rigid exoskeleton.

Must shed its hard skeleton to make room for a larger body size.

Grasshoppers go through 5 separate shedding stages before they reach adulthood.

During each stage, the wings emerge a little bit more.
How does fertilization occur in animals?

Sexual reproduction in animals starts with fertilization.

The problem most animals face is that sex cells are delicate and must be protected for
fertilization to occur.
External Fertilization

Amphibians and most fish release their sex cells into water.

External Fertilization is a high-risk process.

The chances of sperm cells finding and fertilizing the egg cells are decreased in large amounts of
water.

Many sex cells are lost and some are eaten by other animals.

The sex cells can also be exposed to extreme temperatures and pollution.

These animals ensure the production of offspring by releasing a great many sex cells at one
time.

Larger numbers increase the chances of fertilization.

Only 1 or 2 out of every 1000 eggs laid survive to adulthood.
Internal Fertilization

Reptiles, birds, and mammals use internal fertilization (see vocabulary).

Increases the chances of fertilization and the offspring’s survival.

Protects sex cells and fertilized eggs from drying out.

Protects from harsh environments and other organisms.

Since the chances of fertilization are much greater than external fertilization, fewer eggs need to
be produced.
What happens to a fertilized egg?

A successful fertilization produces an egg with a developing embryo inside of it.

Animals have different eggs depending on their structures and environments.

Fish/Frog eggs are somewhat protected by a jellylike layer around the eggs.

These embryos get food from the yolks of the eggs.

Reptile/Bird eggs have tough shells that are filled with watery liquid.

This liquid gives the embryo the wet environment it needs to develop and protects it from
drying out.

Tough outer shell protects embryo from being eaten.

Yolk provides food.

Mammals grow embryos inside the mother.

Embryos are fed by their mothers’ bodies.