The biological levels of organization of living things arranged from the simplest to most complex are: organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere. 
SO CELLS, ORGANS, SYSTEM AND ORGANISMS I GUESS? 
 
        
             
        
        
        
Answer:
Earth's tilted axis causes the seasons. Throughout the year, different parts of Earth receive the Sun's most direct rays. So, when the North Pole tilts toward the Sun, it's summer in the Northern Hemisphere. And when the South Pole tilts toward the Sun, it's winter in the Northern Hemisphere.
 
        
             
        
        
        
Answer:
Chemical bonds include covalent, polar covalent, and ionic bonds. Atoms with relatively similar electronegativities share electrons between them and are connected by covalent bonds. Atoms with large differences in electronegativity transfer electrons to form ions. The ions then are attracted to each other.
Two of the strongest forms of chemical bond are the ionic and the covalent bonds. Chemical bonds form between two atoms, each with its own electron environment.
Hope it helps!!!
 
        
                    
             
        
        
        
 they are a threatened species