C, when mutations are not always predictable they are random
Cell membranes serve as barriers and gatekeepers. They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot.
The type of stimulus following a behavior removes something that is unpleasant is the negative reinforcer.
Stimulus is any signal. This can be in the form of touch, smell, taste, etc. This stimulus triggers the nerve cells of the body that send to signals to the brain to generate a response. For example, when one person touches a hot utensil, the touch of heat acts as a stimulus, where the brain sends response in the form of instantly removal of the hand.
Negative reinforcement is the response towards a stimuli that has not yet been received. For example, taking a medicine before any disease appears is the acts of negative reinforcement.
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A cell theory.
Since cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
Decomposers break down dead animals and plants. They usually benefit producers by releasing nutrients back in the soil.
