Plant and Animal Development - Exercise 10
Objectives
-Identify Starfish Development using the models and
microscope slides.
-Understand when sperm penetrates the egg, it
creates a membrane barrier.
-Understand purpose of umbilical cord and placenta
in mammals.
-Know primary germ layers.
Pages 1 - 4 is skipped unless your instructor
wants you to know this stuff, you have to
do this on your own. You will learn more
about this in BI108, if you take the class.
• All multicultural, sexually reproducing animals utilize
gametes to transmit genetic information to their
offspring.
• The contribution to the offspring is limited to their
nuclear contends - I.e., a haploid set of chromosomes.
Egg cells are typically much larger than sperm cells.
They, too, contribute a haploid set of chromosomes to
the offspring; however, they may also provide
nutrients (for energy and growth), in the form of yolk,
to sustain the development of the offspring to the point
that it can obtain its own food. There are several
different types of eggs with respect to the amount
and distribution of yolk.
• Those organisms that live independently will
usually pass through one or more immature
larval stages before reaching their final mature
form. The more yolk that an egg possess, the
more time the embryo has to develop tissues
and organs that will enable it to live indecently.
Organisms that develop on land must be
protected from desiccation (drying out) by
remaining in mother’s body or have a protective
barrier. Also, there must be enough yolk to
support a considerable amount of development,
as occurs in bird and reptile eggs, for example.
• The fusion of the haploid sperm nucleus with the
haploid egg nucleus at fertilization produces a diploid
zygote, which is the beginning of new organism. The
first stage of development is cleavage, during which the
cells rapidly dividing by mitotic cell division without
increase their mass.
• Each of the cells is called a blastomere. The embryo,
therefore, increases its cell number, but it does not
grow in overall size.
• As cleavage progresses, the blastomeres tend to
become peripherally located, leaving a space or cavity
(the blastocoel) in the center of the embryo. Cleavage
ends with the formation of a hollow ball of cells called a
blastula.
• The next process is called morphogenesis.
During this, the shape and body form of the
organism will be produced and the embryo
will begin to grow an enlarge. Some cells will
migrate to other locations in the embryo.
This movement of embryonic cells is referred
to as morphogenesis movements. The
movements coupled with the continued
multiplication of cells will produce three
layers of cells. The three specialized cell
layers are called the primary germ layers.
• Ectoderm: Outermost layer. It gives rise to the
skin and associated structure and the nervous
system.
• Mesoderm: Middle layer. It gives ruse to muscle,
bone, tendons, blood, and other connective
tissues. The kidney, gonads and the heart.
• Endoderm: Inner layer. It gives rise to the lining
of the organs of the digestive system, the lining of
the lungs, liver, cell of the pancreas and produce
digestive enzymes.
• Morphogenesis is initiated by the inward migration of a
group of cells towards the interior of the embryo into
the blastocoel. The particular morphogenesis
movement is referred to as an invagination, and during
this time the embryo is called a gastrula. The
invagination (aka gastrulation) creates an opening to
the outside of the embryo which is called the
blastopore. As gastrulation progresses, the inward
moving cells from an internal cavity called the
archenteron, which is continuous with the blastopore.
• Once the primary germ layers have formed,
differentiation of these cells into mature tissues begin
to occur.
Starfish Development Models
Cleavage
• Early cleavage stage embryos (2,4, and 8 cell
stages)
Early cleavage stage embryos (2,4, and 8 cell stages)
Cleavage
Gastrula
Development in placental mammals
• Nearly unique to most mammals in the animal
kingdom is the protection and nourishment of the
embryo (fetus) within the uterus of the mother by
assistance of a complex organ called the placenta.
There is no active, feeding larval stage in
mammals, because the mother and the placenta
provide food for embryonic growth through the
umbilical cord.
• Embryos are attached to the umbilical cord with
the placenta.
• Various mammals in their
placenta.
• -What’s the thing cord that
attaches the placenta to the
animal for nutrients?
The Umbilical cord…
Chicken Embryonic Stages
Sperm
Identify: Sperm head & flagellum
Starfish embryos, various stages Fig 110a - Rust
Early Starfish Development
Females and males shed their gametes into water where fertilization occurs. These
slides contain a mixture of all of the various embryonic stages in whole mounts.
Single Egg cell – Unfertilized egg
Before sperm penetration of the
egg occurs, the nucleus and a
single nucleolus are clearly
visible in the unfertilized egg
cell.
Label: nucleus, nucleolus,
nuclear membrane, cytoplasm
Zygote
Fertilized egg: Once the sperm penetrate the egg, the egg cell (which was
actually a secondary oocyte) completes meiosis. The nucleus will no longer be
visible. A fertilization membrane is formed, which prevents any other sperm
cells from entering the egg.
Label: Fertilization membrane
Two Cell Stage Fig. 110C - RUST
When a sperm has
gotten into the egg,
the egg will create a
membrane barrier to
prevent other sperm
from entering.
Cleavage
Early cleavage stage embryo
(2,4, and 8 cell stages)
Early Blastula Figure 110g - RUST
Late Blastula Figure 110h - RUST
Cleavage Figures 110i – 110k - RUST
Label: Blastopore & Blastocoel
Gastrula Figure 110l - RUST
Late gastrula
Label: Blastocoel, archenteron, blastopore, ectoderm, endoderm, & mesoderm..
Larva of Starfish Figure 110m - RUST
Label mouth, esophagus, stomach, intestine, and anus
Chick
Page 10 – Lab Book - Questions
• 1. What stage of development is characterized by
an increase in the number of cells but no overall
increase in the mass of the embryo?
• 2. Which of the starfish stages that you drew marks
the beginning of morphogenesis?
Page 10 – Lab Book - Questions
• 1. What stage of development is characterized by
an increase in the number of cells but no overall
increase in the mass of the embryo? Cleavage
• 2. Which of the starfish stages that you drew marks
the beginning of morphogenesis? Gastrula
Page 11 – Lab Book - Questions
6. Yolk in animal eggs is used for food energy for
growth of the embryo until the embryo hatches or
becomes a large larva. The starfish egg has almost no
yolk and develops into a larva with a complete digestive
tract fort eight hours after fertilization. A frog egg has a
moderate amount of yolk and develops into a larva
(tadpole) 10 days after fertilization. A bird egg has a very
large amount of yolk and doesn’t hatch for three weeks.
Does there seen to be any connection between the
amount of yolk present in a starfish egg and the rate at
which the larval stage and its digestive system develops in
the starfish embryo? Explain.
Page 11 – Lab Book - Questions
6. Yolk in animal eggs is used for food energy for growth of the
embryo until the embryo hatches or becomes a large larva. The
starfish egg has almost no yolk and develops into a larva with a
complete digestive tract fort eight hours after fertilization. A frog egg
has a moderate amount of yolk and develops into a larva (tadpole) 10
days after fertilization. A bird egg has a very large amount of yolk
and doesn’t hatch for three weeks. Does there seen to be any
connection between the amount of yolk present in a starfish egg and
the rate at which the larval stage and its digestive system develops in
the starfish embryo? Explain. The more yolk, the longer it takes
to develop into a larva and your digestive system isn’t fully
developed.
Page 12 – Lab Book - Questions
• 7. Name several functions of the placenta.
• 9. Compare how the sperm is transported
to the egg in a flowering plant and how the
sperm travels to the egg of a starfish.
Page 12 – Lab Book - Questions
• 7. Name several functions of the placenta.
Provides protection, nutrients (food & oxygen). It
helps to remove carbon dioxide and wastes from
fetus.
• 9. Compare how the sperm is transported to the
egg in a flowering plant and how the sperm travels
to the egg of a starfish. In starfish the sperm is just
thrown to the water and it swims towards the egg
to fertilize it.