Combining the genes of two parents in offspring increases in the population, which is valuable for a species because it provides more characteristics for natural selection to operate on.

The correct answer will be- variation

Explanation:

Natural selection is the process in which an organism becomes adaptable to its environment by changing the genotype which changes the phenotype of the organism. The phenotype trait is selected by the organisms and passed on to the generation to become permanent. Nature selects the fittest species to survive the environment.  

Since the organism reproduces either through asexual or sexual mode in which sexual mode increases the chances of natural selection as sexual mode involves the mixing of genes from different parents which increases the chances of "variation" in the genotype thus phenotype.

Thus, variation is the correct answer.

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.

the missing space is phylum