MCAT Biology : Developmental Physiology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Developmental Stages And Events

An experimental birth control method for women uses a chemical to directly prevent pregnancy by altering the protein coating on sperm. The changed protein coating on the sperm is likely to disrupt which of the following biological processes?

Possible Answers:

Fertilization

None of these

Oogenesis

Ovulation

Spermatogenesis

Correct answer:

Fertilization

Explanation:

Fertilization is the complete fusion of egg and sperm. If the chemically-altered sperm are unable to fertilize an egg, there will be no resulting pregnancy. Oogenesis is the process of ovum production. Spermatogenesis is not correct because the chemical is altering the protein coating after production, as the birth control is taken by the woman.

Example Question #1 : Developmental Stages And Events

Which of the following defines the process by which the entry of one sperm into an oocyte prevents other sperms from fertilizing the same egg?

Possible Answers:

Differentiation

Determination

The induction reaction

The cortical reaction

Correct answer:

The cortical reaction

Explanation:

Cortical reaction occurs in fertilization when a sperm enters the cytoplasm of an oocyte. The reaction causes a change in the zona pellucida that prevents polyspermy. Determination refers to the point at which a cell becomes committed to a certain developmental path during embryogenesis, and differentiation refers to the process by which that cell actually becomes a specialized tissue cell. Determination occurs very early during embryogenesis, whereas differentiation occurs later in the developmental process.

Example Question #1 : Animal Development

A new species found by scientists exhibits indeterminate cleavage up to the third cleavage.  If all of the cells in the embryo are separated and incubated in healthy conditions on their own after the third cleavage, how many organisms will develop?

Possible Answers:

8

0

2

4

1

Correct answer:

8

Explanation:

After the third cleavage, the embryo would be composed of 8 cells. If every cleavage step up up to this point was indeterminate, then each cell still has the necessary components to develop into a complete organism. The result would be 8 genetical identical organisms.

Example Question #1 : Developmental Stages And Events

Mishaps in cell cleavage events can result in which of the following?

Possible Answers:

Conjoined twins

Mosaicism

All of these

Tetraploidy

Monozygotic twins

Correct answer:

All of these

Explanation:

The series of mitotic divisions that convert a zygote to a multicellular blastocyst is known as cell cleavage. All of the listed answers are possible as a result of cleavage mishaps. Tetraploidy can result from cells that fail to cleave at the end of mitosis. Monozygotic twins are a result of unexpected cleavage events where the zygote splits into two identical halves. Depending on the timing of a cleavage event in a zygote, the split can result in conjoined twins. Mosaicism is a result of improper chromosome segregation during cleavage that can result two distinct karyotypes in a single embryo.

Example Question #11 : Developmental Stages And Events

What is embryonic cleavage?

Possible Answers:

DNA replication

Division of cells in the early embryo

Division of the zygote into germ layers

Growth of the cell cytoplasm and organelles

Correct answer:

Division of cells in the early embryo

Explanation:

Embryonic cleavage is the division of cells without cell growth. Once an ovum is fertilized by a sperm cell, it is called a zygote. The zygote undergoes multiple rapid cell cycles (rounds of mitosis) without significant growth, producing a dense cluster of cells that is the same size as the original zygote. This process is called cleavage.

Example Question #33 : Reproductive System And Development

Which stage of embryogenesis if the first to allow cell growth?

Possible Answers:

Morula

Blastula

Gastrula

Zygote

Correct answer:

Blastula

Explanation:

Embryogenesis is the process by which an embryo forms, and begins with fertilization of an ovum by a sperm cell. Once an ovum is fertilized, it is referred to as a zygote. The zygote undergoes rapid mitotic divisions without any significant cell growth, a process called cleavage. After four cell divisions occur, a ball of sixteen cells is produced, which is called the morula. After the seventh cleavage, a ball of 128 cells called the blastula is produced. The blastula allows the addition of the G1 and G2 phases into the cell cycle, permitting the cells to grow in size before dividing. The blastula develops an inner cell mass and trophoblast, and becomes implanted in the uterine lining. A gastrula is formed when cells migrate to the interior of the blastula and form three germ layers: the endoderm, mesoderm, and ectoderm. A neurula forms after differentiation of the ectoderm forms the primitive central nervous structures.

Example Question #12 : Developmental Stages And Events

Which of the given embryonic events occurs first?

Possible Answers:

Neurulation

Cleavage

Gastrulation

Implantation

Correct answer:

Cleavage

Explanation:

The correct order of the early development is: cleavage, implantation, gastrulation, neurulation.

Cleavage occurs when zygote undergoes many mitotic divisions without cellular growth, becoming a morula and then a blastula. Only after becoming a blastula will the cells begin to grow in size.

Implantation occurs during the blastula stage when the embryo becomes implanted in the uterine lining.

Gastrulation occurs when the three germ layers (endoderm, mesoderm and ectoderm) arise from the blastula. At this stage, the embryo is considered a gastrula.

Neurulation occurs when the germ layers develop a primitive nervous system, transitioning the embryo from a gastrula to a neurula.

Example Question #35 : Reproductive System And Development

Which of the following is false regarding cleavage?

Possible Answers:

It leads to multiple tiny cells, whose volumes all add up to the original cell size

It results in multiple cells that are each the same size as the original cell

Cleavage happens rapidly after fertilization, but does not continue indefinitely

It is the first step of embryogenesis after fertilization

Cleavage occurs regardless of the sex of the fetus

Correct answer:

It results in multiple cells that are each the same size as the original cell

Explanation:

Cleavage occurs immediately after fertilization. It is a rapid process that increases cell number without increase cell size. Essentially, cells divide without any G1 or G2 phase of the cell cycle. The result is several very small cells that take up the same volume as the original singular zygote.

Cleavage generates the morula and, later, the blastula during development. At the blastula stage, the cells develop the G1 and G2 phases of the cell cycle and begin more comprehensive development. At this stage, the embryo begins to differentiate the inner cell mass and trophoblast regions.

Example Question #12 : Developmental Stages And Events

During what stage of embryogenesis does implantation of the embryo occur?

Possible Answers:

Gastrula

Zygote

Morula

Blastula

Correct answer:

Blastula

Explanation:

Implantation of the embryo occurs during the blastula stage.

The zygote is initially formed by the process of fertilization in the fallopian tube. As the zygote travels within the tube, it begins to undergo cleavage, developing into a morula and eventually a blastula. By this point, it has entered the uterus and can become implanted in the uterine lining. The blastula then begins to differentiate, developing the three germ layers, and becoming a gastrula via the process of gastrulation.

Example Question #3 : Animal Development

The inner cell mass (or embryoblast) of the blastocyst gives rise to all of the following layers except __________.

Possible Answers:

the primitive endoderm

the epiblast

the mesoderm

the trophoblast

Correct answer:

the trophoblast

Explanation:

The blastula, or blastocyst, is made up of blastomere cells and a fluid-filled cavity called the blastocoel. 

There are two regions of the blastocyst: the inner cell mass and the trophoblast. The inner cell mass gives rise to the primitive endoderm and the epiblast, which later gives rise to the three germ layers during gastrulation. The trophoblast is the layer of cells forming the outer ring of the blastocyst. It secretes factors to make the blastocoel and is kept separate from the inner cell mass. All fetal structures eventually develop from the inner cell mass, while the trophoblast helps maintain the fetal environment and placenta.

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