Correct Answer: (4) mitosis and the differentiation of cells after fertilization has occurred

Right after the female gamete is fertilized by one or more male gametes, successive cell divisions (by mitosis) occur to increase the number of cells that will form into an embryo. After the cells undergo different stages (cleavage, blastula formation, gastrulation, etc.), the cells will differentiate to form cells with different structures and functions. This usually happens during the organogenesis stage of development. For example, the outer cells of the zygote will further develop as the epidermis and nervous system of the organism.

Incorrect Answers:

Fertilization is the union of male and female gametes during mating of the animals. It stops eventually and then the development of the zygote occurs.

Mitosis is a process of cell division in eukaryotic cells wherein the different stages conserve chromosome number by equally allocating replicated chromosomes to each of the daughter cells.

Correct Answer: (2) Materials are exchanged between fetal and maternal blood.

Placenta functions for the delivery of oxygen and food from the mother to the fetus. Aside from that, it also aids in disposal of the fetus' waster through the mother's kidney.

Incorrect Answers:

Oxygen diffuses from the maternal blood to the fetal blood.

Maternal blood is not converted into fetal blood. The fetal blood is developed from the fetus itself through the process of differentiation of cells during embryonic development.

Digestive enzymes do not pass on from the maternal blood. Just like blood, the digestive enzymes needed by the fetus are formed in the fetus during development.

Correct Answer: (3) being vaccinated against chicken pox

Vaccines are applied to individuals to develop immunity to a specific ailment. Vaccines usually have a little amount of an agent that is similar to a microorganism. This agent stimulates the individual's immune system to identify the agent as foreign, obliterate it, and retain its information so that when the system encounters it again, it will be able to recognize it and destroy it.

Incorrect Answers:

Antibiotics replace one of immune system's functions.  Antibiotics act by inhibiting certain enzymatic processes of bacteria, and by changing mineral balances.  Normal cells, however, are also affected.  This may be one reason why antibiotics weaken the immune response.  Other toxic effects of antibiotics, such as the effect upon the normal bowel flora, may also be a cause.

A healthful diet may keep the person fit but if a strong virus or bacterium goes in the system, the food eaten will not be able to protect the organism.

Colostrum, or the mother's first milk has many antibodies needed  by the newborn baby in order to be healthy. However, it is not completely effective to protect the baby from all diseases. It is still recommended that individuals must be vaccinated to prevent specific diseases.

Correct Answer: (1) The phrase is correct for both Individual A and Individual B. Individual A produces male gametes, while individual B produces female gametes.

Correct Answer: (4) The phrase is correct for Individual B, only

Fertilization in humans occurs when the male gamete (sperm cell) penetrates the female gamete (egg cell) in the ovary of the female individual (Individual B).

Correct Answer: (4) The phrase is correct for Individual B, only

After fertilization in the ovary, the fertilized egg transfers to the uterus by passing through the fallopian tube. The development of the embryo happens there which is characterized bu successive mitotic divisions.

In asexual reproduction, a single organism is passes copies of its entire genetic make up onto its offsprings. This occurs by mitotic cell division, in which DNA is copied and allocated equally to two daughter cells. Thus, the chromosome number of the parent is conserved and the same number is acquired by the daughter cells.