CHAPTER 27: INTRODUCTION TO
ANIMALS
Section 2: Animal Body Systems
TISSUES AND ORGANS
 Digestion
Single celled
organisms and sponges
digest their food
within their body cells.
 All other animals
digest their food
extracellularity
(outside of their body
cells) within a
digestive cavity.

TISSUES AND ORGANS
 Simple
animals,
such as the hydra
and flatworms,
have a
gastrovascular
cavity, a digestive
cavity with only
one opening.
TISSUES AND ORGANS
 Other
animals
have a
digestive
tract (gut)
with two
openings, a
mouth and an
anus.
TISSUES AND ORGANS
 Respiration

In simple animals, oxygen gas and
carbon dioxide gas are exchanged
directly with the environment by
diffusion.
TISSUES AND ORGANS
 The
uptake of
oxygen and the
release of
carbon dioxide,
called
respiration,
can take place
only across a
moist surface.
TISSUES AND ORGANS
 Some
aquatic (and a few terrestrial)
animals respire with gills – very thin
projections of tissue that are rich in
blood vessels.
TISSUES AND ORGANS
 In
more
advanced
animals, lungs
are the
respiratory
organs used to
transfer oxygen
into the blood
and remove
carbon dioxide
from blood.
TISSUES AND ORGANS
 Circulation

In complex animals, oxygen and
nutrients must be transported to the
body cells by a circulatory system.
TISSUES AND ORGANS
 Two
types of circulatory systems:
 Open circulatory system: heart
pumps fluid containing oxygen and
nutrients through a series of
vessels out into the body cavity.
TISSUES AND ORGANS
 Closed
circulatory
system: a heart
pumps blood
through a
system of
blood vessels.
TISSUE AND ORGANS
 Conduction
of Nerve Impulses
 Nerve cells (neurons) are specialized for
carrying messages in form of electrical
impulses.
 Bilaterally symmetric animals have
clusters of neurons called ganglia.
TISSUE AND ORGANS

More complex
invertbrates,
such as the
grasshopper,
have brains
with sensory
structures.
TISSUE AND ORGANS
 Support
Many soft-bodied
invertebrates have
a hydrostatic
skeletal systems.
 Hydrostatic
skeleton - consists
of water that is
contained under
pressure in a closed
cavity.

TISSUE AND ORGANS

Other
invertebrates,
such as insects,
have an
exoskeleton,
which is a rigid
external
skeleton that
encases the
body of an
animal.
TISSUE AND

ORGANS
An endoskeleton
is composed of a
hard material,
such as bone,
embedded within
an animal.
TISSUE AND ORGANS
 Excretion

The term
excretion
refers to the
removal of
wastes
produced by
cellular
metabolism.
TISSUE AND ORGANS
 Simple
aquatic
invertebrates
and some fishes
excrete ammonia
into the water
through their
skin or gills by
diffusion.
TISSUE AND ORGANS
Other animals, especially
terrestrial animals,
convert ammonia to
nontoxic chemicals, like
urea.
 As the excretory system
eliminates these wastes,
water and other useful
substances are returned to
the body.

REPRODUCTIVE STRATEGIES
 Asexual
Reproduction
 Reproduction that does not
involve the fusion of two
gametes is called asexual
reproduction.
 An unusual method of
asexual reproduction is
parthenogenesis, in which a
new individual develops
from an unfertilized egg.
REPRODUCTIVE STRATEGIES

Animals that reproduce asexually
are usually able to also reproduce
sexually.
REPRODUCTIVE STRATEGIES
 Sexual
Reproduction
 In sexual reproduction, a new
individual is formed by union of a
male and a female gamete.
REPRODUCTIVE STRATEGIES
Gametes are
produced in the
sex organs.
 Males have
testes that
produce sperm.
 Males produce
sperm until
death.

REPRODUCTIVE STRATEGIES
Females have
ovaries that
produce eggs.
 At birth,
females have
produced all
the eggs they
will ever have.

REPRODUCTIVE STRATEGIES

Some species of
animals, called
hermaphrodites,
have both testes
and ovaries.
REPRODUCTIVE STRATEGIES
 Most
aquatic
animals simply
release the male and
female gametes near
one another in the
water, where
fertilization occurs.
 This is known as
external
fertilization.
REPRODUCTIVE STRATEGIES
Most terrestrial
animals sexually
reproduce by means
of internal
fertilization.
 Internal fertilization
occurs when the
sperm and egg unite
inside of the female’s
body.
