Grade 12GEN - Week 5 - 4.2. Human Development Before Birth

Human
Development
Before Birth

4.2 Human Development Before
Birth (Lesson number in Inspire
Biology textbook: U6M26L2)

KPI’s covered

Week 5:

+4.2.1 Define the process of fertilization

+4.2.2 Explain why hundreds of sperm are necessary for fertilization to happen

+4.2.3 Recognize the importance of acrosomes during fertilization

+4.2.4 Explain the major events that occur during the first week after fertilization

+4.2.5 Discuss the roles of the extraembryonic membranes and the placenta

Week 6:

+4.2.6 Compare hormonal regulation during the menstrual cycle with the hormonal regulation during pregnancy

+4.2.7 Differentiate between the terms: zygote, embryo, and fetus

+4.2.8 Summarize the development that occurs during each trimester

+4.2.9 Describe the techniques used to diagnose and detect medical conditions of a fetus

LESSON 1

Multiple Choice

In what order does sperm travel through the female reproductive system?

• Vagina > Uterus > Cervix > Fallopian Tubes

• Cervix > Vagina > Uterus > Fallopian Tubes

• Vagina > Urethra > Cervix > Fallopian Tubes

• Vagina > Cervix > Uterus > Fallopian Tubes

Multiple Choice

Process in which a sperm cell is joining with an egg cell is called

• zygote

• implantation

• fertilization

• ovulation

4.2.1 Define the process
of fertilization

Open Ended

Can you describe what is happening in this diagram?

Fertilisation

4.2.1 Define the process of fertilization
4.2.2 Explain why hundreds of sperm are necessary for fertilization to happen

Explain why hundreds of sperm are necessary for fertilization
to take place, and how only one sperm cell can fertilize the
egg.

+About 300 million sperm are released into the vagina during intercourse. Only several
hundred of them will successfully reach the egg. Many never make it out of the vagina,
some are attacked by white blood cells, and many simply die along the way. Only one sperm
can fertilize an egg, but it takes several hundred to participate in the process.

+Connection A single sperm cannot penetrate the plasma membrane of a human egg. Notice
in Diagram, on the last page, that the tip of each sperm is a specialized lysosome called an
acrosome.

- As several hundred sperm bombard the egg, the enzymes inside of the acrosomes weaken the plasma membrane of
the egg.

- Eventually the plasma membrane becomes weak enough that one sperm can penetrate the egg. Immediately, the egg
forms a barrier to prevent other sperm from entering the now fertilized egg.

4.2.3 Recognize the importance of acrosomes during fertilization

Multiple Choice

This part of sperm cell releases enzymes that breaks down the outer membrane of egg cell

• Acrosome

• Zona Pellucida

• Mitochondrion

• Cortical Granule

Poll

My understanding of fertilisation is ...

• not much

• a little

• I understand

• I have full understanding

LESSON 2

4.2.4 Explain the major events that occur during
the first week after fertilization

The first week of human development:

+The fertilized egg, which is called a zygote (ZIgoht), moves through the oviduct propelled by
involuntary smooth muscle contractions and by the cilia lining the oviduct.

+Around 30 hours after fertilization, the zygote undergoes its first mitosis and cell division.

+Cell division continues, and by the third day, the embryo leaves the oviduct and enters the
uterus. At this point, the embryo is described as a morula, a solid ball of cells.

+By the fifth day, the morula has developed into a blastocyst, a hollow ball of cells.

+The blastocyst attaches to the endometrium around the sixth day and is fully implanted by
day 10.

+Figure 8 shows that the blastocyst is not completely hollow. Inside the blastocyst is a group
of cells called the inner cell mass.

+The inner cell mass eventually will become the embryo.

Early Development

Multiple Choice

Embryonic structure of an animal that consists of TWO cell layers

• blastula

• gastrula

• morula

• blastocyst

Multiple Choice

______ implants itself into the lining of the uterus.

• blastual

• blastocyst

• gastrula

• morula

Multiple Choice

The embryo become a solid ball of cell

• morula

• zygote

• gamete

• blastula

4.2.5 Discuss the roles of the extraembryonic
membranes and the placenta

+Extraembryonic membranes

ØThe membranes that extend beyond an embryo are called the extraembryonic membranes.

ØYou also might have learned about the development of the amniotic egg, and how this
enabled animals to reproduce on land.

ØDeveloping humans have these mem- branes, as shown in Figure 9. But because humans
and most other mammals develop inside the mother’s body, these membranes have
somewhat different functions.

+Early in human development, four extraembryonic membranes form.

+These membranes are the amnion, the chorion (KOR ee ahn), the yolk sac, and the allantois
(uh LAN tuh wus), shown in Figure 9.

+The amnion is a thin layer that forms a sac around the embryo. Inside this sac is the
amniotic fluid (am nee AH tihk • FLU id), which protects, cushions, and insulates the
embryo.

+Outside of the amnion is the chorion, which, together with the allantois, contributes to the
formation of the placenta (pluh SEN tuh).

+The yolk sac in humans does not contain any yolk but serves as the first site of red blood cell
formation for the embryo.

Multiple Choice

What are the components of an extraembryonic membranes?

• Amnion, Allantois, Air Cavity, and Yolk Sac

• Operculum, Cuticle, Amnion, and Yolk Sac

• Amnion, Allantois, Chorion, and Yolk Sac

• Allantois, Amnion, Chorion, and Amplexus

The placenta

+About two weeks after fertilization, tiny fingerlike projections of the chorion, called chorionic villi
(VIH li), begin to grow into the wall of the uterus. The placenta, the organ that provides food and
oxygen and also removes waste, begins to form. The placenta has two surfaces—a fetal side that
forms from the chorion and faces the fetus and a maternal side that forms from uterine tissue.
When completely formed, the placenta is 15–20 cm in diameter, 2.5 cm thick, and has a mass of
about 0.45 kg. The umbilical cord, a tube contain- ing blood vessels, serves as the connection
between the fetus and the mother. Figure 10, on the next page, illustrates the connection
between the mother and fetus.

+The placenta regulates what passes from the mother to the fetus and from the fetus to the
mother. Oxygen and nutrients travel from the mother to the fetus. Alcohol, drugs, and the human
immunodeficiency virus (HIV) also can pass through the placenta to the developing fetus.

+Metabolic waste products and carbon dioxide travel from the fetus to the mother. Because the
mother and the fetus have their own separate circulatory systems, blood cells do not pass
through the placenta. However, the mother’s antibodies pass to the fetus and help protect the
newborn until its immune system is functioning.

Figure 10 Visualizing a
Placenta
A growing fetus exchanges
nutrients, oxygen, and
wastes with the mother
through the placenta. The
placenta contains tissue
from both mother and fetus.

Multiple Choice

What is the structure that acts as temporary organ to allow exchange of substances between mother and foetus.

• placenta

• umbilical cord

• uterus

• amniotic sac

Poll

My understanding of early development (embryo and placenta) is ...

• None

• Sort of

• I still need a little help

• I fully understand you may move forward

Lesson 3 – Assigned AFL’s
Differentiated worksheets
Students to download and print for
practice purposes in class and
presentation of answers
Green group – higher order
Yellow group – middle order
Red group – lower order