The answer is A.
Why: The heart is part of an organism, so that doesn't exactly count. Soil is not alive, and neither is clay. Therefore, Bacteria must be it. Bacteria is a living thing, and can function by itself.
Answer:
D it is taken in from the air
Explanation:
Carbon dioxide is in the air and plants use it to make food.
The neuron releases chemical messengers. Otherwise, there would be no 'signal transduction' in the postsynaptic cell. So, your answer is B.
Individual, population, community, biome, ecosystem