Bacterial endosymbionts have lost much of their genome and are dependent upon their aphid hosts for survival. Similarly, the aphids depend on the endosymbiotic bacteria for the supply of amino acids that they provide. This interdependence is the result of

Cells a and b are the same size and shape, but cell a is metabolically quiet and cell b is actively consuming oxygen. oxygen will diffuse more quickly into cell because . b the oxygen molecules inside cell b have a higher kinetic energy b. a its membrane transport proteins will not be saturated c. a the diffusion gradient there is shallowerd. b the diffusion gradient there is steeper