Mutations (changes) to the DNA within the cells.
Answer: (B)
Explanation: DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies.
Predators possess usually good senses to find their prey and special abilities to trap the prey. Predatory birds, for example, had an outstanding eyesight and sometimes hearing, for the case of the owls while other predators, like many species of mammals, have a very high sense of smell that helps them locate prey. Many predators are very fast, and use their speed to help capture their prey, some are fastest runners, fast fliers and fast swimmers.
A signal cascade is a series of chemical reactions which are triggered by a stimulus acting on a receptor that is then transduced to the intracellular space through second messengers. Finally, effector molecules receive the signal causing a cellular reaction to the initial stimulus. A signal cascade is very useful because it facilitates and accelerates the communication between cells that could be in different parts of a living organism. This communication is vital for cell processes in complex multicellular organisms.
B. It allows some molecules to enter the cell and blocks entry to others.
