Introduction to
Animals
The Nature of Animals
• Animal are multi-cellular
heterotrophic organisms
that lack cell walls.
• Allows for variety in animal
life
• Specialization is the adaptation
of a cell for a particular function.
• Cell junctions – connections
between cells that hold the cells
together as a unit
• Single celled organisms cannot
grow large
• Plants are autotrophic animals
are heterotrophic
Animal reproduction can be
sexual or asexual
Zygote – the first cell of a new
individual
Differentiation – cells become
different from each other
• Most animals move around
• Interaction of muscles and
nerves
• Nervous tissue – made of
neurons – conduct electrical
signals through body – allows
animals to detect stimuli in
environment and in body
How did the first animals develop?
• Perhaps from
colonies of loosely
connected
flagellated protists
• Later developed a
division of labor
Animal Bodies
• Symmetry – overall pattern of
structure
• Radial symmetry – similar
parts branch out in all
directions from a central line
• Bilateral symmetry – two
similar halves on either side of
a central plane
• Dorsal – top
• Ventral – bottom
• Anterior – head
• Posterior – end
• Cephalization – concentration
of sensory and brain structures
in the anterior end of the animal
Germ Layers