​In the pulmonary circuit, pulmonary ____ carry oxygen-poor blood to lungs and pulmonary ____ return oxygenated blood to the heart.

A) ​veins; arteries
B) ​venules; capillaries
C) ​capillaries; arteries
D) ​arterioles; venules
E) ​arteries; veins

During which epoch did the first major extinction occur?

A) Eocene
B) Oligocene
C) Miocene
D) Pleistocene
E) Ordovician

_________________ are divided into three distinct phyla: mosses, liverworts, and hornworts.

According to the endosymbiotic theory, early eukaryotic cells became the mitochondria and chloroplasts found in prokaryotic cells.

Which of the following is NOT considered a lymphatic structure?

A) pancreas
B) tonsils
C) spleen
D) Peyer's patches of the intestine

Blockage of the ileocecal valve would prevent

A) pancreatic juice from entering the duodenum.
B) bile from entering the duodenum.
C) lymph from entering the jejunum.
D) chyme from entering the ileum.
E) chyme from entering the large intestine.

Muscles exhibit the property of excitability. This means that the muscle

A) shortens its length.
B) recoils to its original resting length.
C) stretches beyond its normal length.
D) responds to stimulation by the nervous system.
E) excites itself.

T tubules are invaginations of the

A) sarcoplasmic reticulum.
B) sarcomere.
C) myofibril.
D) sarcoplasm.
E) sarcolemma.