One sarcomere a. extends from z line to z line. b. is composed of many myofibrils. c. contains only actin fibers. d. is composed of many muscle fibers. e. surrounds each muscle in the body.

a. extends from Z line to Z line.

Explanation:

A sarcomere refers to the region between two consecutive Z lines. Sarcomere serves as functional units in skeletal muscles as the shortening of individual sarcomeres results in shortening of myofibrils and muscle cells.

Each sarcomere extends from one Z line to the next one and consists of one complete A band and two half parts of an I band. The two halves of the I band are present one either side of A band in a sarcomere.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.