1. A closer look - Muscles and their role in health and energy needs of athletes Skeletal muscles, which move bones, consist of cells fused into long fibers. These muscle fibers can increase in size when contracted, which is what happens as a result of some exercise. This animation shows the structure of vertebrate skeletal muscles. It starts at a large scale, showing the muscles of a human upper arm, and then gradually zooms in to smaller and smaller levels, labeling each structure along the way. Watch the animation and then answer the question that follows. An individual muscle fiber is one long muscle cell . An increase in skeletal muscle size, resulting in increased strength is known as

the right side of the picture going down is:

polymerase

protein

transport vesicle

modified protein

the left side of the picture going down is:

dna helix

single-stranded rna

endoplasmic reticulum

ribosome

golgi apparatus

protein released from vesicle

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-lavira : )

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.