Muscle tone is a) the feeling of well-being following exercise b) the condition of athletes after intensive training c) the ability of a muscle to efficiently cause skeletal movements d) a state of sustained partial contraction

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.