This is because toxins are ingested by organisms and accumulate in the fatty tissues. Theses toxins then become more concentrated in successive trophic levels of a food web biological magnification. Magnification occurs because the biomass at any given trophic level is produced from a much larger biomass ingested from the level below and therefore, top-level carnivores tend to be the organisms most severely affected by toxic compounds. 
        
             
        
        
        
A chromosome consists of a single, double-stranded DNA molecule. Chromatids are two molecules of double-stranded DNA joined together in the center by a centromere. Chromosomes have a thin ribbon-like structure. Chromatids have a thin and long fibrous structure.
 
        
             
        
        
        
Answer:
Deforestation is the major problem causing lack of rich species in Costa Rica. This is due to over grazing by cattle.This may lead to flooding which affect fertility of the soil.These animals graze on  the plants without regulations,and cause erosion as their hoofs percolate the soil,  further reducing soil fertility.
In addition to sustain the beef production,  trees were fell to for cattle ranching.This ultimately contributed to loss of the forest species.
Banana plantation is an  additional factor.Forest were cleared to cultivate banana, which affects forest population.
Explanation:
 
        
             
        
        
        
 
 
How day length affects crop production most plant donot grow when day length is less than 10 hours . Even if the temperature is kept within the optimum range _ For example in a climate _ controlled greenhouse _ most plant will just sit dormat until the magic 10 hours of light perday arrives