AP Biology : Understanding Embryogenesis and Development

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Reproductive Physiology

During embryonic development, which stage begins after the formation of 128 cells and terminates with germ layer differentiation? 

Possible Answers:

Gastrula stage

Cleavage stage

Blastula stage

Zygote stage

Somitogenesis stage

Correct answer:

Blastula stage

Explanation:

The blastula is defined as beginning following the cleavage stages. Following seven cleavages 128 cells have formed, and will later begin to form the differentiated layers of endoderm, mesoderm and ectoderm before going into the gastrula stage.

Example Question #1 : Reproductive Physiology

From what germ layer does the nervous system develop?

Possible Answers:

Ectoderm

Mesoderm

Epiboly

Endoderm

Somites

Correct answer:

Ectoderm

Explanation:

During gastrulation, the ectoderm begins to fold in on itself following the primitive streak. These neural folds form the basis of the neural tube, later developing into the adult nervous system.

Example Question #1 : Understanding Embryogenesis And Development

What do somites, formed from mesoderm during somitogenesis, go on to form? 

Possible Answers:

The dermis

Skeletal muscle

None of these structures

Vertebrae

All of these structures

Correct answer:

All of these structures

Explanation:

Somites go on to form skeletal muscle, vertebrae, and the dermis. 

Example Question #2 : Understanding Embryogenesis And Development

In humans, fertilization involves the addition of chromosomes from the sperm and the egg. The resulting cell is called a __________.

Possible Answers:

embryo

gamete

blastocyst

zygote

Correct answer:

zygote

Explanation:

The fusion of haploid gametes (sperm and egg) produces a zygote. The addition of the chromosomes from sperm and egg restores the diploid state of the cell and gives rise to a diploid organism.

An embryo refers to the developing organism after the first cellular division, following formation of the zygote. A blastocyst forms during the first stages of embryogenesis, and is defined by cellular replication without cellular growth.

Example Question #3 : Understanding Embryogenesis And Development

What is the product of rapid division, but no overall growth during embryogenesis?

Possible Answers:

Gastrula

Morula

Blastula

Zygote

Correct answer:

Morula

Explanation:

The first stage after fertilization is the single-celled zygote, which quickly begins to divide. These divisions, however, do not increase the overall size of the embryo and are known as cleavage divisions. As the mass of cells divides, it is considered a morula.

Eventually, the morula develops an inner cell mass and associated trophoblast. At this stage, it is considered a blastula or blastocyst. It is during this stage that implantation occurs. After implantation, the cell develops the three germ layers through the process of gastrulation. Once the endoderm, mesoderm, and ectoderm have been established, the embryo is considered a gastrula.

Example Question #4 : Understanding Embryogenesis And Development

Which body part would you not expect to develop from the ectoderm?

Possible Answers:

The eyes

The intestinal lining

The cerebellum

The skin

The spinal cord

Correct answer:

The intestinal lining

Explanation:

The ectoderm is generally credited with the formation of the skin, teeth, nervous system, and sense organs. The lining of the digestive tract is formed from the endoderm.

Example Question #5 : Understanding Embryogenesis And Development

Which of the following would not be expected during pregnancy?

Possible Answers:

Secretion of human chorionic gonadotropin (HCG)

Blastocyst implantation

Maintenance of the corpus luteum

Formation of the corpus albicans

Formation of the placenta

Correct answer:

Formation of the corpus albicans

Explanation:

The corpus luteum is a structure in the ovary that secretes progesterone, and is preserved during pregnancy with the help of human chorionic gonadotropin (HCG). If fertilization does not take place, the corpus luteum will degenerate into the corpus albicans. As a result, corpus albicans formation only takes place if the woman is not pregnant.

Blastocyst implantation is considered the first event of pregnancy, and the placenta will later form in order to secrete hormones crucial for embryonic development.

Example Question #6 : Understanding Embryogenesis And Development

Early in development, the zygote divides via __________.

Possible Answers:

mitosis

meiosis

cloning

fertilization

Correct answer:

mitosis

Explanation:

Mitosis is the process by which diploid cells duplicate and divide to ensure all cells have the same number of chromosomes and genetic material. Meiosis is the process by which haploid gametes are produced by the primary sex organs.  

Example Question #7 : Understanding Embryogenesis And Development

Which of the following type(s) of cell movement are involved in the development of the neural plate into the neural tube?

Possible Answers:

Invagination

Convergence

Neither convergence nor invagination

Convergence and invagination

Correct answer:

Convergence and invagination

Explanation:

During the formation of the neural tube, the neural plate—a thick layer of differentiated columnar cells—change shape and undergo certain cell movements. The formation of the neural tube is called primary neurulation. In a complex process, the cells of the neural plate change shape, invaginating the cell layer to form the neural groove. Convergence moves the cells of the neural folds towards the developing neural groove. Eventually, the two edges of the neural plate touch and join together to form the neural tube. 

Example Question #8 : Understanding Embryogenesis And Development

Which of the following is not a true characteristic of the neural plate?

Possible Answers:

It invaginates to form the neural tube

It is composed of columnar cells 

It is within the primitive streak of the embryo

It develops from ectoderm tissue

Correct answer:

It is within the primitive streak of the embryo

Explanation:

The neural plate is a cell layer opposite of the primitive streak in the developing embryo. It forms from a thickening and flattening of the ectoderm layer. These cells then take a columnar shape. The neural plate develops into the neural tube during primary neurulation.

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