Chapter 34 - ANIMALS34-1 The Nature of Animals

34.1

•Vertebrate•An animal with a backbone

•Invertebrate•An animal without a backbone

CHARACTERISTICS

Animals are:•Multicellular•Heterotrophic•Lack cell walls•Most reproduce sexually•Most have movement

Multicellular Organization

Body of adult human contains 50 trillion cells.

Cells of multicellular organisms do not live independently.• Each cell depends on the presence and functioning of

other cells.• They cooperate and work together…

Cells – tissues – organs – organ systems – organism Specialization is the adaptation of a cell for a

particular function. Cell junctions are connections between cells.

• The formation of tissue from many individual cells occurs because of cell junctions.

• Cell junctions hold the cells together as a unit.

Heterotrophy

Ingestion is the taking in of organic material.

Digestion then takes place:•Carbohydrates, lipids, amino acids, and other organic molecules are extracted from the material or cells the animal eats.

Sexual Reproduction and Development

Sexual:•Most animals reproduce sexually.

•This allows for more genetic variability, since with male and female contributions, there are more genes introduced into the gene pool.

Sexual Reproduction and Development Asexual:

• Hydra – budding• Sponges – internal budding (gemmules)• Planaria – fragmentation (head / tail), although

most reproduce sexually• Echinoderms (starfish) – regeneration

zygote: 1st cell of a new individual (diploid)• Will undergo repeated mitotic divisions

Differentiation: cells become different from each other, i.e.:• Blood cells• Bone cells• The process of differentiation is the path to cell

specialization.

Movement

Attachment:• Barnacles attach to a surface, aka

substrate.• Life Cycle:• Egg – larva – then leaves parent's shells,

spends youth swimming, sticks to rocks for all adulthood.

Neurons

Neurons are cells of nervous tissue.

Nervous tissue… through electrical signals (impulses), allows animals to detect stimuli.

Muscle tissue allows animals to respond to the stimuli.

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Origin and Classification

Page 669 The 1st animals probably originated in the

sea. The structural characteristics of invertebrates

suggest they were the first multicellular animals.

It also suggests that they evolved from protists.

Protists are both heterotrophic and eukaryotic.

Because of this, scientists have inferred that multicellular invertebrates may have developed from colonies of loosely connected, flagellated protists.

Origin and Classification

Cell specialization during early period of evolution…

Colonial protists may have lost their flagella as individual cells in the colony became more specialized.

They may have been similar to modern colonial protists that do show some degree of cell specialization.• In these species, the gametes are distinct from non-reproductive cells.

Origin and Classification

A similar division of labor in early protists may have been the 1st step toward multicellularity.

Many taxonomists recognize 30+ animal phyla.

Some phyla contain a very small # of species.