Which statement accurately states what happens when a muscle contracts?
a) calcium combines with atp to produce sarcomeres
b) myosin head attach to and pull on a series of actin-binding sites
c) actin produces myosin and atp
d) calcium produces contractions

The observations of hooke and van leeuwenhoek documenting the existence of microscopic cells formed the basis of what important theory? a. the cell theory stating that all living things are composed of cellsb. the theory of spontaneous generation, which held that life forms could arise spontaneouslyc. the theory of chemotherapy, or use of antimicrobials to destroy pathogenic organismsd. the germ theory of disease and causative agents

Consider the model of the oxygen cycle on earth. the majority of earth's oxygen reservoirs are found in the a) atmosphere. b) biosphere. c) hydrosphere. d) lithosphere.

Why are common names a problem for scientist?