Answer:
There are prion-like particles in the brain normally, and when these become abnormal they can cause disease. (Ans. A)
Explanation: 
Prions are proteins which can trigger normal proteins to fold abnormally, and they are present in the brain. They are causing many types of neurodegenerative diseases in both humans and animals. Which are known as transmissible spongiform encephalopathies.
Prions can enter the brain with the help of infection, also can arise from the gene mutation that encodes the proteins, and sometimes this affects humans by infected meat.
If a person infected from prion disease, it affects central nervous system tissues like brain, eye tissues and spinal cord.
 
        
             
        
        
        
No muscle contraction will be observed.
<h3>What is the effect of calcium concentration on muscle contraction?</h3>
The concentration of calcium ions in the muscle cells help in contraction and relaxation of muscles fibers.
Release of calcium ions initiate muscle contraction.
Therefore, there will be no contraction of muscle if calcium ions are not transported out from the sarcoplasm.
Learn more about muscle contraction and calcium ions at: brainly.com/question/14760686
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The answer is the plant growth, because the dependent variable is what responds to the independent variable.