What respiratory challenge do land animals face that aquatic animals do not?

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

What causes eclipses? check all that apply. earth's rotation on its axis moon's shadow covering the sun earth's shadow covering the moon earth's orbit and moon's orbit occasionally aligning the moon and sun's gravity pulling in the same direction

Easy 6th grade work! 100 points! i need fast! compare the parts of a cell and the cell as a whole to another common nonliving system (i. e., a car, a city, describe the parts of a cell and their primary function.