When an external stimulus crosses the threshold, a muscle fibre will respond.
<h3>The level of the threshold</h3>
- For the identification of the electrical activity carried out by the active muscles, the threshold level is a crucial consideration. 
- A portion of the electrical activity carried out by the target muscles may be excluded if the chosen threshold level is higher than the overall activity.
<h3>What is the stimulus threshold for muscle contraction?</h3>
- A certain stimulus magnitude is necessary for muscle contraction. 
- The threshold stimulus is the smallest amount of force needed for a stimulus to cause a muscle to contract in response.
- If the stimulus intensity is less than this threshold value, there is no response.
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My guess is that fat-soluble toxins that may occur in freshwater ecosystems would most affect apex species in these ecosystems. This is because fat-soluble toxins are stored in the fat reserves of animals, and then bioaccumulate up the food chain. So in this case, most of the toxin is not secreted, but stored within the food chain, and bioaccumulates, with the concentration becoming higher the further up the food chain. 
        
                    
             
        
        
        
Answer:
completed by the formation of a cytoplasma
 
        
             
        
        
        
Answer:
The correct answer will be- Crop rotation
Explanation:
When the growth of a type of crop which uses soil nutrients in abundance and then growing another crop in the same filed led to the decrease in the production of the next crop.
Thus farmers adapted to avoid such farming practices and developed a new practice which allowed the land to become fertile again so that the growth of next crop will not be affected.
The practice involved the planting of a crop on a piece of land then leaving the soil ploughed and unsown for a longer period of time and growing corp on another piece of land allowing the time to restore the nutrient content. This practice is known as "crop rotation".
Thus, crop rotation is the correct answer.