Receptors detect changes in the environment. For a stimulus to elicit a response, certain cells must have an appropriate receptor. Stimulation of the receptor initiates a specific signal pathway.
        
             
        
        
        
Answer:
The nerves in the integumentary system (skin) sense the irritation and send the signal to the brain. The brain then sends impulses through the nervous system to scratch the itch.
Explanation:i hope this helps u :)
 
        
             
        
        
        
Answer:
Anaerobic respiration
Explanation:
Anaerobic respiration occurs releasing the ATP per molecule of glucose for immediate use by the cell. Anaerobic respiration is carried out in absence of oxygen. There are two forms of fermentation, alcoholic and lactic acid fermentation. In humans, lactic acid fermentation occurs in muscle cells during intense muscular activity.
C6H12O6    →     2C3H6O3 + 150 kJ
 
        
             
        
        
        
Closely related but different, distantly related but similar
        
             
        
        
        
Answer:
An organism with five pairs of chromosomes can have 32 genetic possibilities from a variety independent of its single gamete.