Animals need to take in food and oxygen from the external environment. Plants need to take in the raw materials necessary to carry out the photosynthesis, as well as , mineral nutrients and oxygen front hr external environment. Both animals and plants have to vet rid of waste products from their bodies to the exterior.
A simple unicellular organism, like the amoeba, carries out these material exchanges through its external body surface by diffusion. The Amoeba, however, can only do this up yo a certain body size. Beyond this size, its external body surface cannot cope with its material exchange requirements. when this happens, the Amoeba stops growing and divides into two.
What happens as the Amoeba increases in size?
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