Which of these describe(s) variation within a species or population? A population is defined as members of the same species living together in the same area and who are likely to breed with each other. A) Hummingbirds have beaks able to collect nectar from flowers while woodpeckers have beaks able to collect insects from tree bark

B) Polar bears have differences in the number of hairs per square inch of their skin

C) Evergreen trees have needle-like leaves

D) Fish use gills to obtain oxygen from water

B. Polar bears have variable hair density

Explanation: humming birds and woodpeckers are in different genera. Evergreen trees: the question should actually refer to conifer genera and angiosperm genera such as Casuarina and Exocarpos since many evergreen trees do not have needle like leaves, but in any case this again involves different species from many genera. Gills are a plesiomorphy common to all fish. Polar bears (Ursus maritimus) is a single species and hair density is within-species variation.

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.