Doctors do not administer vaccinations to people who are too sick. which best explains why?
a. the weakened or dead form of the pathogen may not have any effect on sick people.
b. the weakened or dead form of the pathogen may have a fatal effect when it is combined with medication that the sick people are taking.
c. the digestive systems of sick people may be negatively affected by the weakened or dead pathogen.
d. the white blood cells of sick people may not be able to efficiently handle the weakened or dead form of the pathogen.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation:

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