A. Individuals migrate between 2 populations that have the same gene pool. b. The thickness in fur coat for particular small mammal is determined by the average temperature in its environment. Over time, the environment gets warmer. c. A mutation introduces a new wing color in a group of butterflies. d. A flood washes away 3/4 of a population of ground squirrels. e. Within a lizard population, there is genetic variation in the length of the tail. The neighborhood cats chase the lizards, and have an easier time catching the ones with long tails.

frogs. the lower the ph the higher the acid content. frogs have the highest tolerance in this scenario.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.