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Embryology Review KEY
1. Define embryology: Branch of biology that studies the formation and early development of living things.
2. There are four main processes to early embryonic development. Finish the statement about each process.
(a) Fertilization: This is the process when the __EGG___ and the sperm come together to form a _ZYGOTE_.
(b) Implantation: This is the process when the blastocyst implants into the wall of the ____UTERUS_. This
implantation ensures that the baby will have a home for the next 9 months.
(c) Gastrulation: This is the process where the blastocyst folds in to become a ball of cells with __3___ layers.
These layers are known as the germ layers.
(d) Cell differentiation: This is the process when the cells of the three germ layers are given specific
___JOBS/FUNCTIONS___. In other words, this is the time when stem cells become different from each other.
They become nerve cells, blood cells, muscle cells, etc.
3. When an embryo is going through the 4 processes from number 2, it takes on different shapes and looks along the
way. For each of the following stages of an embryo, explain its structure and draw a picture of it.
(a) Zygote: Single Cell- Diploid
(b) Morula: Solid ball of cells (day 3)
(c) Blastocyst: Hollow ball of cells (day 5)
(d) Gastrula: Three distinct layers (after implantation)
4. Gastrulation: Below is an image of a gastrula. For each arrow, state the name of the germ layer (endoderm,
mesoderm, and ectoderm) and state the types of cells that that layer will become.
Ectoderm
Skin and Nerves
Endoderm
Digestive Tract
Mesoderm
Organs
5. Extraembryonic membranes are membranes around the growing embryo that do not become a part of the baby, but
instead help to nourish and protect baby during development. Complete the statements about each
extraembryonic membrane.
(a) Amnion: This membrane forms the ______Amniotic Sac______, which is a fluid filled sac that _____Cushions
and protects_____ the embryo.
(b) Chorion: This is the outer-most membrane that combines with the uterine lining to for the
_____Placenta________.
6. What is the placenta?
Site of nutrient, waste, and gas exchange.
7. What is in vitro fertilization (IVF)?
When fertilization happens outside of the organism. Once the embryo reaches the blastocyst stage it will be placed
in the uterus with hopes of implantation.
8. What are stem cells?
Unspecialized or undifferentiated cells that can give rise to various types of cells.
9. What is the main goal of stem cell research?
To cure/treat diseases
Create a Venn diagram comparing oogenesis to spermatogenesis using the following statements:
Produces 1 viable gamete
Haploid cells
Produces 1 cell per month (cycle)
Genetic recombination
Ends at menopause
Includes meiosis
Involves millions of cells daily
produces 4 viable gametes
begins at puberty continues till death
Females
Males
Fertilization to Implantation
The following pictures trace the development of an embryo from a zygote to a gastrula. Label each
stage in the diagram below:
Zygote
Morula
Blastula
Gastrula
1. How does the process of cleavage differ from a cell cycling through the normal cell cycle
(MITOSIS)?
Cells undergoing cleavage do not grow before they divide. Because of this the cells decrease in size
after each division.
2. What is the difference between the following: morula, blastula, and gastrula?
Morula is a solid ball of cells, a blastula is hollow, and a gastrula has begun differentiation with 3
distinct germ layers.
3. When and where does implantation take place (be specific)?
Implantation takes place at around day 7. The blastula (DAY 5) implants into the uterus.
Gastrulation
Gastrulation produces a three-layered embryo. Each of the three layers gives rise to particular
structures. Label each of the body systems and parts with the germ layer from which they originated.
1. Bladder
3. Heart
5. Skin
7. Spinal Cord
9. Nails
11. Femur
EndoMesoEctoEctoEctoMeso-
2. Muscles
4. Nerves
6. Esophagus
8. Lungs
10. Hair
12. L Intestine
MesoEctoEndoMesoEctoEndo-
Twinning
Twins are a natural phenomenon. Answer the following question in a complete sentence.
13. What is the difference between fraternal and identical twins?
Fraternal twins come from 2 embryos while identical twins come from 1 embryo
14. When identical twins split late in the embryonic development what can occur?
The later they split the more they share – they can share the placenta, amniotic sac, etc.
Conjoined twins