Question 1

The "quality" of human eggs and sperm declines as people age. One possible reason for this is
A)accelerated apoptosis of sperm and egg precursor cells.
B)acquired harmful mutations in egg and sperm precursor cells.
C)declining levels of morphogens.
D)lower levels of oxytocin and prostaglandins.

Accepted Answer

As people age, the likelihood of acquiring harmful mutations in egg and sperm precursor cells increases. This can lead to chromosomal abnormalities in the resulting embryos, affecting their viability and increasing the risk of genetic disorders.

Question 2

By the end of a normal first trimester, the zygote has
A)not yet developed visible limbs.
B)recognizable arms and legs.
C)reached its birth length.
D)gained about 50 percent of its birth weight.

Accepted Answer

By the end of the first trimester, the embryo has developed recognizable arms and legs, along with other major organs and structures.

Question 3

In humans, the yolk sac
A)does not contain yolk.
B)produces blood cells.
C)contains cells that will eventually produce gametes.
D)all of the above

Accepted Answer

The human yolk sac does not contain yolk but is involved in early blood cell production and contains primordial germ cells that will develop into gametes.

Question 4

Human females probably evolved the ability to live beyond their reproductive years because
A)women once preferred to mate with men known to come from families with long life spans.
B)the hormones produced by the female reproductive system slow the aging process.
C)the contribution of grandmothers to child rearing increases the survival rate of children.
D)in early human cultures, women who produced children later in life were more likely to survive to raise their children.

Accepted Answer

The contribution of grandmothers to child rearing increases the survival rate of children. Studies have shown that the presence of grandmothers in a community increases the survival rate of children, as they often help with child care and provide resources such as food and protection. As humans evolved, the ability to live beyond reproductive years may have been selected for because it allowed older women to contribute to the survival of their grandchildren, thus increasing the overall fitness of the group.

Question 5

Disruptions to the development of a zygote can occur at any time during pregnancy. Among the time periods mentioned below the most vulnerable period of development for a zygote/fetus/embryo would be the
A)first week.
B)twentieth week.
C)thirtieth week.
D)fortieth week.

Accepted Answer

The first week of pregnancy is the most vulnerable period of development for a zygote/fetus/embryo as this is the time when the fertilized egg is implanting in the uterine wall and beginning to differentiate into different cell types. Any disruptions during this time can result in miscarriage, chromosomal abnormalities or birth defects.

Question 6

Which of the following would not be exchanged between a mother and her fetus through the umbilical cord?
A)enzymes
B)carbon dioxide
C)antibodies
D)oxygen

Accepted Answer

Enzymes are not typically exchanged between mother and fetus through the umbilical cord. The other options (carbon dioxide, antibodies, and oxygen) are commonly exchanged.

Question 7

Stem cells
A)play a large role in directing apoptosis.
B)can differentiate into specific cell types.
C)develop as apoptosis continues during development.
D)develop from epithelial cells in the lining of the small intestine.

Accepted Answer

Stem cells have the ability to differentiate into specific cell types, such as muscle cells, nerve cells, or blood cells. They are important for tissue repair and regeneration, as well as for normal tissue maintenance. Stem cells can be found in various tissues in the body, such as bone marrow, adipose tissue, and the umbilical cord.

Question 8

Why does an embryo undergo the process of gastrulation?
A)Gastrulation separates the cells of the inner cell mass and the trophoblast so that the trophoblast is free to develop into the placenta.
B)During gastrulation, the cells of the embryo move around to create the four extraembryonic membranes that protect the membranes.
C)The rapid cell division that occurs during gastrulation allows the embryo to increase quickly in cell number without using much energy for cell growth.
D)Cells in the blastocyst differentiate to form embryonic tissues, but are not originally located in the right place. Gastrulation moves these cells to the proper position in the embryo.

Accepted Answer

Gastrulation is the process that rearranges cells within the blastocyst to form the three germ layers, which give rise to all the tissues and organs in the body. During this process, cells move to their proper positions in the embryo, allowing for proper differentiation and formation of tissues and organs. Thus, option D is the correct choice.

Question 9

In humans, the exchanges of materials between the embryo and its mother occur through the
A)umbilical cord.
B)amnion.
C)yolk sac.
D)endometrium.

Accepted Answer

The umbilical cord connects the developing embryo to the placenta, which is responsible for nutrient and gas exchange between the embryo and its mother.

Question 10

Examine this close-up of the placenta (on the left of the figure below). 
Why do the chorionic villi have the shape of a tree?
A)The branches of the chorionic villi create a large amount of surface area for the exchange of nutrients and gases between maternal and fetal blood.
B)The branches of the chorionic villi allow blood to flow back and forth more rapidly between the capillaries of the mother and her fetus.
C)The branches of the chorionic villi create more locations where fetal capillaries can fuse directly with maternal capillaries.
D)The branches of the chorionic villi create more surface area for the production of the amniotic fluid.

Accepted Answer

The branches of the chorionic villi create a large amount of surface area for the exchange of nutrients and gases between maternal and fetal blood. This allows for efficient transfer of oxygen and nutrients from the mother to the fetus, and carbon dioxide and waste products from the fetus to the mother. The tree-like shape of the chorionic villi allows for maximum surface area within the limited space of the uterus.

Question 11

In mammals, the trophoblast layer in a blastocyst will become part of the
A)uterus.
B)primary oocyte.
C)oviduct.
D)placenta.

Accepted Answer

The trophoblast layer in a blastocyst develops into the placenta in mammals.

Question 12

The human embryo develops in a fluid-filled sac called the
A)uterus.
B)endometrium.
C)yolk sac.
D)amnion.

Accepted Answer

The amnion is the membrane that surrounds the developing embryo in the uterus and is filled with amniotic fluid. The yolk sac, while also present in early development, is not the primary fluid-filled sac that surrounds the embryo. The uterus and endometrium are the location where implantation occurs, but they are not the sac itself.

Question 13

Embryonic stem cells have the greatest potential for creating medical treatments because they
A)contain less DNA than other types of stem cells so they are easier to manipulate.
B)are more common than other types of stem cells in the bodies of adults.
C)do not undergo transcription.
D)can become any type of body cell and, therefore, can be used to treat many different conditions.

Accepted Answer

Embryonic stem cells can become any type of body cell, making them useful for generating a wide range of tissues and organs for transplantation and for studying human development and disease. This potential gives embryonic stem cells an advantage over other types of stem cells, which are more limited in their ability to differentiate into various cell types.

Question 14

In the last few weeks of pregnancy, the level of estrogen in a woman's blood rises. This causes
A)the fetus to develop more rapidly.
B)the amount of prostaglandin secreted by the placenta to decrease.
C)the muscles of the uterus to become more sensitive to the hormone oxytocin.
D)even more estrogen to be released from the pituitary.

Accepted Answer

The rise in estrogen levels during the last weeks of pregnancy causes the muscles of the uterus to become more sensitive to the hormone oxytocin. This ultimately leads to contractions and the start of labor.

Question 15

During the rapid cell division that occurs after fertilization, cells increase rapidly in number, but the embryo stays the same size. The cells of this very early embryo must
A)undergo gastrulation before rapid cell division begins.
B)undergo rapid meiosis.
C)have a very short interphase.
D)contain a large yolk sac.

Accepted Answer

The statement "During the rapid cell division that occurs after fertilization, cells increase rapidly in number, but the embryo stays the same size" suggests that the cells are undergoing a lot of cell division without much growth in size. This can only happen if the cells have a very short interphase, the period between cell divisions where cells grow and replicate their DNA. Therefore, Option C is the most accurate answer. The other options are not relevant to the given statement.

Question 16

The graph below shows the rate of cell division in a developing frog embryo. 
Why does the rate of growth decrease dramatically after the point indicated by the arrow?
A)At this point, development switches from rapid cell growth to cell differentiation and migration.
B)The arrow indicates when the embryo begins to run out of its internal food source and must find another source to continue developing.
C)This is when fertilization occurs. Before this point, the single-celled egg was growing quickly as it stored food. After this point, growth slows for the more deliberate process of development.
D)At the time indicated by the arrow, the trophoblast separates from the inner cell mass and the two tissues begin to divide at different and slower rates.

Accepted Answer

The graph shows a rapid increase in cell division rate followed by a dramatic decrease. This corresponds to the change from the early stages of development where the embryo is rapidly dividing cells to later stages where cells are differentiating and migrating to form tissues and organs.

Question 17

The shape of the beak of a hummingbird (very long and thin)and that of a finch (short and fat)is controlled by the same set of genes. Which of the following could account for the differences between these two bird beaks?
A)Apoptosis occurs in the beak of the finch, but not in the beak of the hummingbird.
B)Although development is controlled by the same genes, the genes produce different proteins and those proteins cause development to occur in different ways.
C)The hummingbird retains stem cells for a longer period of time during development than does the finch.
D)The genes involved in determining beak shape stay on for different lengths of time in each bird.

Accepted Answer

The differences in beak shape can be attributed to the duration for which the genes are active during development, affecting the growth and final shape of the beak.

Question 18

In mammals, the blastocyst consists of the trophoblast and the
A)placenta.
B)inner cell mass.
C)zygote.
D)embryo.

Accepted Answer

The blastocyst is composed of two main parts: the trophoblast and the inner cell mass. The trophoblast eventually gives rise to the placenta, while the inner cell mass develops into the embryo. The zygote is the single cell that results from fertilization, which then divides and undergoes differentiation to form the blastocyst.

Question 19

Which of the following could have an effect on the development of a fetus or embryo?
A)alcohol
B)certain prescription drugs
C)drug use
D)all of the above

Accepted Answer

All of the above choices can have an effect on the development of a fetus or embryo. Alcohol consumption during pregnancy can lead to fetal alcohol syndrome, while certain prescription medications and drug use can also result in developmental abnormalities or other health issues for the fetus.

Question 20

The body retains stems cells after embryonic development is complete because
A)stem cells give rise to gametes throughout the life of a mature male.
B)stem cells are responsible for the production of the various cells in our blood, which can be easily lost as a result of injury.
C)in many tissues, cells must be regenerated and replaced as they wear out.
D)all of the above

Accepted Answer

A) Stem cells do give rise to gametes, but this is not the only reason why the body retains stem cells.
B) Stem cells do produce cells in our blood, which can be lost due to injury, but this is not the only reason why the body retains stem cells.
C) In many tissues, cells must be regenerated and replaced as they wear out, which is one of the reasons why the body retains stem cells. Thus, all of the choices are correct, making D the best choice.

Quiz 33: Reproduction and Development

The "quality" of human eggs and sperm declines as people age. One possible reason for this is

By the end of a normal first trimester, the zygote has

In humans, the yolk sac

Human females probably evolved the ability to live beyond their reproductive years because

Disruptions to the development of a zygote can occur at any time during pregnancy. Among the time periods mentioned below the most vulnerable period of development for a zygote/fetus/embryo would be the

Which of the following would not be exchanged between a mother and her fetus through the umbilical cord?

Stem cells

Why does an embryo undergo the process of gastrulation?

In humans, the exchanges of materials between the embryo and its mother occur through the

Examine this close-up of the placenta (on the left of the figure below) . Why do the chorionic villi have the shape of a tree?

In mammals, the trophoblast layer in a blastocyst will become part of the

The human embryo develops in a fluid-filled sac called the

Embryonic stem cells have the greatest potential for creating medical treatments because they

In the last few weeks of pregnancy, the level of estrogen in a woman's blood rises. This causes

During the rapid cell division that occurs after fertilization, cells increase rapidly in number, but the embryo stays the same size. The cells of this very early embryo must

The graph below shows the rate of cell division in a developing frog embryo. Why does the rate of growth decrease dramatically after the point indicated by the arrow?

The shape of the beak of a hummingbird (very long and thin) and that of a finch (short and fat) is controlled by the same set of genes. Which of the following could account for the differences between these two bird beaks?

In mammals, the blastocyst consists of the trophoblast and the

Which of the following could have an effect on the development of a fetus or embryo?

The body retains stems cells after embryonic development is complete because