<span>It took over 200 years for the "cell theory" to be formalized and accepted. Hooke and Leeuwenhoek were early microscopist's.... but at the time the nature of matter, the belief in spontaneous generation, and the idea there were little worlds within little worlds ad infinitinum was popular. The discovery of the periodic table and establishment that atoms were real, the demolishing of spontaneous generation, all happened at the time that Schwann and Schleiden (and others) were working with better microscopes, better ideas about the material world, and better observations...... thus the cell theory.
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Telomeres are protective sequences of nucleotides found at the ends of chromosomes,Which become shorter every time a cell divides.
A gradual degeneration of an organism occurs, resulting in ageing.
However, some cells are able to replenish their telomeres using the enzyme telomerase. 
Hope this helps! :)
        
             
        
        
        
Past climate changes led to extinction of many species, population migrations, and pronounced changes in the land surface and ocean circulation. The speed of the current climate change is faster than most of the past events, making it more difficult for human societies and the natural world to adapt.
        
             
        
        
        
When an object<span> is speeding up, the </span>acceleration<span> is in the same direction as the velocity. Thus, this </span>object has<span> a positive </span>acceleration<span>. In Example , the </span>object<span> is moving in the </span>negative<span> direction ( </span>has<span> a </span>negative<span> velocity) and is slowing down.</span>