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What organs comprise the respiratory system of a bird

Substances that can pass through cell membranes by diffusion include a. na ions. b. proteins c. glucose. d. oxygen.

Which of the following is a feature of all cells? o a. all cells have a nucleus. o b. all cells have dna for at least part of their life cycle. het . o c. all cells are spheres. o d. all cells have a rigid cell wall.