When a child touches a hot surface, receptors in the hand send a signal to the nervous system. The nervous system then sends a signal to the muscles in the arm to contract and move the hand from the hot surface.

This is an example of how
A.
cells in the body work independently of each other and have no need to coordinate or communicate.
B.
a behavioral response requires coordination and communication between different parts of the body.
C.
an internal stimulus does not require the communication between different parts of the body.
D.
a behavioral response triggered by an internal stimulus does not require communication between cells.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

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