MCAT Biology : Developmental Physiology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Biology

To form a female zygote, the sperm cell must contribute which chromosome(s)?

Possible Answers:

Both an X- and a Y-chromosome

A Y-chromosome

An X-chromosome

Two Y-chromosomes

Two X-chromosomes

Correct answer:

An X-chromosome

Explanation:

The necessary genotype for a female zygote is XX.

The mother will share this XX genotype (since she is also female) and will contribute one X-chromosome. The father, however, will be male and have the genotype XY. This means he has a 50% chance of passing on an X-chromosome and a 50% chance of passing on a Y-chromosome. If the zygote inherits a Y-chromosome from the father's sperm, then the offspring will be male. If the zygote inherits an X-chromosome from the father's sperm, then the resulting genotype will be XX and the offspring will be female.

Example Question #1 : Embryogenesis

What is a totipotent cell?

Possible Answers:

Stem cells from adult tissues

A cell that has the ability to differentiate into a limited number of tissue types if exposed to the appropriate chemical signals

A cell that has the ability to differentiate into any type of tissue if exposed to the appropriate chemical signals

Stem cells from the inner cell mass

A cell that has the ability to form a complete organism through embryogenesis

Correct answer:

A cell that has the ability to form a complete organism through embryogenesis

Explanation:

Totipotent cells have the ability to propogate and differentiate into any cell types, including the trophoblast. They are different from stem cells, which could be considered multipotent (able to differentiate into multiple tissue types) or pleuripotent (able to differentiate into any major tissue type, but cannot create trophoblast). The only truly totipotent cells are the first two blastomeres.

Example Question #1 : Reproductive System And Development

What is the "common dogma"?

Possible Answers:

All cells come from other cells

Cells lose genetic material over time, becoming less totipotent

None of the other answers

All organisms are made of cells

Most cells in the body contain a complete genome, despite the fact that most of the genes in the genome are not necessary for each cell's specific function

Correct answer:

Most cells in the body contain a complete genome, despite the fact that most of the genes in the genome are not necessary for each cell's specific function

Explanation:

Most cells contain a complete genome, but not all genes are activated in each cell. Activation of particular genes produces appropriate protein function.

Example Question #1 : Biology

Differentiation of the endoderm in a developing human embryo will eventually give the human the ability to __________.

Possible Answers:

circulate blood

produce urine

move

breathe

think

Correct answer:

breathe

Explanation:

The endoderm develops into a number of internal organs, including the lung, which are vital for breathing.

The kidneys (urine production), muscles (movement), and blood vessels (blood circulation) develop from the mesoderm. The brain (thought) develops from the ectoderm.

Example Question #1 : Animal Development

During embryogenesis, the separation of cells into the three individual germ layers first occurs during which of the following?

Possible Answers:

Gastrulation

Neurulation

Organogenesis

Cleavage

Fertilization

Correct answer:

Gastrulation

Explanation:

After fertilization occurs, the zygote undergoes a series of cellular divisions in a process called cleavage. This is followed by the formation of the blastula, a hollow sphere of cells. Gastrulation occurs next, where the embryo is divided into three germ layers: the endoderm, mesoderm, and ectoderm (from inside to outside). Hence, gastrulation is the stage in which this process first occurs. Neurulation and organogenesis occur after gastrulation.

Example Question #1 : Developmental Stages And Events

During embryogenesis, the process in which a committed cell develops distinctive functions and characteristics is known as __________.

Possible Answers:

differentiation

determination

induction

specification

Correct answer:

differentiation

Explanation:

Once a committed cell begins to develop specialized functions, it is known as differentiation. Before a cell differentiates, it makes a commitment to a certain cell type, first by specification, which is reversible, and then by determination, which is irreversible. Once a cell is committed to a cell type, it undergoes differentiation to develop specific cell characteristics.

Induction is a process in which cells induce adjacent cells to commit to a certain cell type. 

Example Question #23 : Reproductive System And Development

In what stage of embryogenesis does the embryo develop the three primary germ layers?

Possible Answers:

The blastocyst

The morula

The neurula

The gastrula

Correct answer:

The gastrula

Explanation:

The gastrula is formed during the second week following fertilization. At this stage, a process called gastrulation takes place. During gastrulation, the three primary germ layers are formed: the ectoderm, the mesoderm, and the endoderm.

Prior to gastrulation, the embryo is a blastocyst, and prior to that it is a morula. The morula forms soon after fertilization and is classified by cleavage divisions, increasing the number of cells without increasing the size of the embryo. The blastocyst is characterized by the formation of the inner cell mass and trophoblast; implantation occurs during this stage. After implantation, gastrulation occurs. After the gastrula stage, the embryo begins the process of neurulation (development of the primitive streak and notochord) and becomes a neurula.

Example Question #1 : Developmental Stages And Events

Which of the following options demonstrates the correct order of embryogenesis?

Possible Answers:

Fertilization  Blastula formation  Gastrulation  Cleavage

Fertilization  Cleavage  Blastula formation  Gastrulation

Fertilization  Cleavage  Gastrulation  Blastula formation

Fertilization  Blastula formation  Cleavage  Gastrulation

Correct answer:

Fertilization  Cleavage  Blastula formation  Gastrulation

Explanation:

The correct order is listed below.

1. Fertilization: the joining of an egg and sperm

2. Cleavage: early cell division in an embryo before a specific structure is formed

3. Blastula Formation: the cells of the embyro form a hollow structure filled with fluid

4. Gastrulation: the cells in the embryo migrate to form the three germ layers; the hole with fluid formed during the blastula stage is now filled with cells

Example Question #1 : Developmental Physiology

What is gastrulation?

Possible Answers:

Phase during embryogenesis in which multiple rapid mitotic divisions occur

Phase during embryogenesis in which a single-layered blastula is reorganized into a three-layered structure

Phase during embryogenesis when the embryo implants into the uterine lining

Phase during embryogenesis in which the single-layered blastula is reorganized into a solid ball of cells

Correct answer:

Phase during embryogenesis in which a single-layered blastula is reorganized into a three-layered structure

Explanation:

Gastrulation is the phase in embryogenesis in which the single-layered blastula is reorganized into a trilaminar structure called the gastrula. These three germ layers are called the endoderm, mesoderm, and ectoderm and give rise to individual organs during organogenesis.

The blastula is implanted into the uterine lining and the morula undergoes rapid cell divisions (cleavage) after fertilization of the zygote.

Example Question #1 : Animal Development

Formation of the primitive streak occurs during what stage of embryogenesis?

Possible Answers:

Blastula

Gastrula

Neurula

Morula

Correct answer:

Blastula

Explanation:

The primitive streak forms in the blastula stage and establishes symmetry (left-right and cranial-caudal body axes). This spatial differentiation determines the site of gastrulation and initiates formation of the three germ layers. The epiblast (precursor to the ectoderm) invaginates to form the primitive streak. Cells from the primitive streak give rise to the mesoderm and the endoderm. Formation of the primitive streak marks the beginning of gastrulation.

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