Answer:
e. horizontal transfer of genes from a marine bacterium
Explanation:
Horizontal gene transfer is the transfer of genetic material from one independent mature bacterium to another and creates new gene combinations in the recipient bacterium. It mostly occurs between the bacterial of different species and is responsible for the spread of new genetic traits such as antibiotic resistance, digestion of specific substances, virulence, etc. 
Transfer of genetic material from the donor to host bacteria can occur in three ways: transformation, transduction, and conjugation. According to the given information, marine Bacteroidetes have enzymes required to digest porphyran and agarose. <em>B. plebeius</em> might have acquired the genes for these enzymes from marine Bacteroidetes by horizontal gene transfer. This resulted in its ability to digest the marine seaweed while its close relative species cannot do so. 
 
        
             
        
        
        
Answer: Genetic variation describes naturally occurring genetic differences among individuals of the same species. Gene duplication, mutation, or other processes can produce new genes and alleles and increase genetic variation. New genetic variation can be created within generations in a population, so a population with rapid reproduction rates will probably have high genetic variation. And there are the reasons.
 
        
             
        
        
        
Fishes and bottom dwelling worms cope with the fluctuating salinity within estuaries over the tidal cycle with the use of transport system such as active and passive transport. 
<h3>How active and passive transport system are used?</h3>
In salty water, fish and other marine organisms used active transport in which energy is used to remove salts from the body of these marine organisms because excess salts are harmful for them.
So we can conclude that Fishes use transport system such as active and passive transport to cope with the fluctuation of salt concentration.
Learn more about salinity here: brainly.com/question/20283396
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Lichens are the photosynthetic organisms.
        
             
        
        
        
Answer:
The most effective experimental approach to assess the effects of elephant impact on vegetation is to assess plant responses under differences in elephant density. It is important that other factors, such as soils or habitat structure are held constant so that the only factor which varies is elephant density.
Explanation:
source: Studying Elephants icun.org