Answer:
2. A change occurs in the environment.
4. Poorly adapted individuals have decreased survivorship.
1. Well-adapted individuals leave more offspring than do poorly adapted individuals.
3. Genetic frequencies within the population change.
Explanation:
The natural selection theory was developed by Darwin to explain how evolution occur within a population. The environment is in constant state of changes and always select for organisms that are better adapted to it.
Poorly adapted organisms gradually reduce from the population as a result of decreased survival while well-adapted individuals multiply and contribute more to successive generation. 
Well-adapted individuals pass on the adaptive alleles to their offspring, eventually leading to a change in gene frequencies within the population.
Hence, the sequence of events is 2, 4, 1 and 3.
 
        
             
        
        
        
<h2>
Answer:  (b) Cholesterol</h2>
Explanation:
As the name suggests, cholesterol is a sterol (a modified steroid). It is biosynthesized by animal cells.
 
        
        
        
Explanation:
eukaryotic glycocalyx is present in prokaryotic cells, eukaryotic cells can also have glycocalyces especially single celled eukaryotic organisms.
 
        
             
        
        
        
Answer:
Symbiosis is a close relationship between two species in which at least one species benefits. 
Explanation: