Animal Evolution, Symmetry, and Skeletal Systems: Key Concepts for Biology

What evolutionary relationships suggest that the earliest animals were simple, multicellular, ocean-dwelling, and coordinated?

Close evolutionary relationships between choanoflagellates and animals.

What type of symmetry do protostome animals exhibit?

Bilateral symmetry.

Name three examples of protostome animals.

Annelid worms, mollusks, and arthropods.

What are the four main groups of arthropods?

Insects, arachnids, myriapods, and crustaceans.

Which group of animals is known for having jointed legs and includes the most diverse group?

Arthropods, specifically insects.

What is a significant characteristic of insects regarding their eggs?

All insects have desiccation-resistant eggs.

What type of symmetry do deuterostome animals exhibit?

Bilateral symmetry.

Which three main phyla are included in deuterostome animals?

Hemichordata, echinodermata, and chordata.

What are well-known examples of echinoderms?

Sea stars and sea urchins.

What defines vertebrates in terms of their anatomy?

They have a bony cranium and typically a vertebral column.

What are the two types of muscle tissue?

Striated (skeletal and cardiac) and smooth muscle.

What is the basic contractile unit of a skeletal muscle?

Sarcomere.

How does smooth muscle differ from striated muscle?

Smooth muscle lacks regular sarcomere organization and appears smooth.

What factors affect the force generated by a muscle?

Muscle size, degree of actin-myosin overlap, shortening velocity, and stimulation rate.

What are the three types of skeletons found in animals?

Hydrostatic, exoskeleton, and endoskeleton.

What is a hydrostatic skeleton?

An incompressible fluid within a body cavity used to support the body and change shape.

What is the advantage of an endoskeleton?

It allows for growth and repair and transmits muscle forces across joints.

What are the two basic structures of bone?

Compact bone and spongy bone.

What role do osteoblasts and osteoclasts play in bone health?

Osteoblasts form bone, while osteoclasts remove bone, allowing for growth, shape change, and repair.

What is the function of cartilage in the skeletal system?

It forms the embryonic skeleton, remains as growth plates, and provides rapid growth after birth.

What is the significance of the shape of a bone's joint surfaces?

It largely determines the range of motion and stability of a joint.

Sponges

widespread in the oceans, simple organization, feed by drawing water containing food particles and dissolved organic molecules into their interiors

Cnidarians

form multiple tissues, differentiate nerve and muscle cells, and feed as predators by means of specialized stinging cells.

Ctenophores

resemble cnidarians but move by beating cilia, have an anal pore for waste, and have a rudimentary mesoderm germ layer.

Placozaons

simple organization, but genomic data support the hypothesis that they are the sister group to cnidarians and bilaterians