Program Base Learning (pbl)

Program Base Learning (PBL) Stage 1: Group setting. Group members: 1) Muhammad Shakir bin Che Soh 2) Nur ‘Ain bt Ibrahim 3) Raja Nur Aimi bt Raja Ibrahim 4) Siti Aishah bt Abd Latiff 5) Syadida bt Zakaria Rules: 1) Everyone have to contributes ideas. 2) Be punctual. 3) Every task have three meetings. 4) Give cooperation. 5) Enjoy doing the work. Roles of tutor: 1) Guide the group members in solving the problems. 2) Discuss with the group members about the problems. 3) Follow up the groups’ progress. Roles of the students: 1. Each members have their own responsibilities 2. Each members have to complete their task 3. Each members must contribute some ideas to complete the tasks 4. Each members should find the sources of information to give the best answers. 5. All members should prepare their report according to their task

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Stage 2: Problem identification Pn Laila is senior laboratory assistant at biological science Institute, University of Malaya. One day, she received a set of model claimed to be animal’s

embryonic

development. The model obtained from Carolina Biological, one of scientific equipments supplier. She was interested to know how the cleavage process occurs does. For the next day, she asks a lecture who is expert about embryonic development. The lecturer said the cleavage pattern and the type of cleavage of different animal’s groups are correlated with the amount and distribution of yolk in their eggs and polarity of eggs. During explanation the lecture gave also an example the cleavage process in amphibian. After having some discussion we have identified the problems that have been given in the task. -

We have to confirm the model as a series of cleavage.

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We have to identify and describe a series of cleavage

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We have to explain about the cleavage pattern

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We have to explain the types of cleavage

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We have to describe the process of the cleavage of the amphibian.

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Stage 3: Idea generation

After discussing, we have generated some ideas that can be guideline from the question.These ideas can help the students to more understand about the process in human development and how the formation of twins. The ideas from the question are: 1. Cleavage is the division of zygote to form the muticellular embryo 2. The cleavage pattern of different animals groups are correlated with the amount and distribution of yolk and polarity of egg. 3. The amount of yolk will affect the size of blastomere. 4. There are four term of yolk distribution which are isolecithal, mesolecithal, telolecithal, and centrolecithal. 5. The polarity of egg consists of animal pole and vegetal pole. 6. There are two type of cleavage which are holoblastic and meroblastic. 7. Holoblastic cleavage patterns indicates that entire egg is cleaved during cytokinesis. 8. Holoblastic cleavage pattern include radial, bilateral, rotational and spiral cleavage. 9. Meroblastic cleavage is include the egg that partially cytokinesis 10. Two major types of meroblastic cleavage are discoidal cleavage and superficial cleavage. 11. The different animals have the different types of cleavage patterns.

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Stage 4: Learning issues

We have determined the conflict that we should let the student know. The issues are: •

What is cleavage or blastulation?

•

How the cleavage process occur?

•

What is blastomeres?

•

What are the types of cleavage?

•

What are the cleavage patterns?

•

What are factors that correlated with cleavage patterns?

•

What is yolk distribution ?

•

How many types of yolk distribution?

•

What are the differences between the term of yolk distribution?

•

How does the amounts of yolk affect the size of blastomere?

•

What is polarity of egg?

•

What is the differences between animal pole and vegetal pole?

•

What is the holoblastic cleavage pattern and their types?

•

What is the meroblastic cleavage pattern and their types?

•

What are the differences between holoblastic and meroblastic?

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What is the cleavage pattern of the sea urchin’s, molluscs, amphibians, chick, fish and mammals?

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Why the cell divisions more rapidly in the animal pole in amphibians?

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Stage 5: Self-Directed Learning FACTS IDEAS LEARNING ISSUES ACTIONS ● She claimed that the • Pn Laila is • How she can claimed • refer senior

model is the series of

that the model is the

laboratory

cleavage.

series of cleavage?

assistant

at

biological

to

internet •

book

•

lecture note

•

discussion

science Institute, University of Malaya •

received

a

set of model claimed

to

be animal’s embryonic •

development Stages of •

Cleavage

cleavages

division of zygote

is

the •

What is cleavage or blastulation?

•

How

the

cleavage

process occur •

What is blastomeres?

•

What are the types of cleavage?

•

cleavage patterns

•

The

cleavage •

What are the cleavage

pattern of different

patterns?

animals groups are •

What are factors that

correlated with the

correlated

with 5

amount

•

and

cleavage patterns?

distribution of yolk •

How the amount of

and polarity of egg.

yolk

There are four term

cleavage pattern?

of yolk distribution •

What

which

distribution ?

are

isolecithal,

•

mesolecithal,

is

the yolk

How many types of yolk distribution?

telolecithal, •

affect

and •

What

are

the

centrolecithal.

differences

The polarity of egg

the

consists of animal

distribution?

pole

How does the amounts

and

vegetal •

pole.

between

term

of

yolk

of yolk affect the size of blastomere? •

What is polarity of egg

•

What

is

the

differences animal •

between

pole

and

There are two type •

vegetal pole? What is the holoblastic

cleavage

of cleavage which

cleavage pattern and

patterns

are holoblastic and

their types?

Types

of •

•

meroblastic. •

Holoblastic cleavage

pattern

indicates that entire

types?

is

is

meroblastic patterns

egg •

What

cleaved •

the cleavage

and

their

are

the

What

during cytokinesis.

differences

between

Holoblastic

holoblastic

and

cleavage

pattern

meroblastic 6

include

radial,

bilateral, rotational and spiral cleavage. •

Meroblastic cleavage the

include

egg

that

partially cytokinesis. •

Two major types of meroblastic cleavage

are

discoidal cleavage and •

superficial

cleavage.. The different •

What is the cleavage

animals have the

pattern

amphibians

different types of

urchin’s,

and

cleavage patterns.

amphibians,

•

Cleavage patterns

in

others

animals.

of

the

sea

molluscs, chick,

fish and mammals? •

How

the

cleavage

occur in amphibians? •

Why the cell divisions more rapidly in the animal

pole

in

amphibians?

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STAGE 6: Synthesis and Application CLEAVAGE

Cleavage process also known as blastulation is the process after fertilization when early mitotic cell divisions occur that progressively reduce cell size which known as blastomere. During cleavage, the total embryonic mass remains constant. In mammals, zygote divides into 2, 4, 8 and more smaller. When the embryo has about 16 cells, its individual cells begin to adhere to one another and it coalesces to form into a morula.

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Morula is the solid ball. At day 7, blastocyst (blastocyst cavity) forms in the morula when it enters into the uterus. Blastocyst consist of the fluid-filled cavity called the blastoceol. This cavitation is an important transition from homogeneous cells to differentiated cell function. This new structure is called a blastocyst which consists of an outer layer, the trophoblast, and an inner cluster of cells referred to as the inner cell mass that will become the embryo. Implantation is the process in which the blastocyst attaches to and penetrates into the uterine wall.

The cleavage patterns of different animals group are correlated with the amount and distribution of yolk in their eggs and the polarity of eggs. This affects the pattern of cleavage divisions in the embryo. If the little yolk (lancelet), holoblastic cleavage produces similar sized blastomere while if the lot of yolk in vegetal pole (frog), holoblastic cleavage produces different sized of blastomeres. The amount of distribution of yolk in the egg have the major impact on its cleavage pattern. The terms used for the yolk distribution are isolecithal, mesolecithal, telolecithal and centrolecithal. The first term of yolk distribution is the isoletichal which is the egg that have the a small amountof evently distributed yolk in the cytoplasm. For example, type of egg in most echinoderms, molluscs, ascidians and mammals. The second type of the yolk distribution is mesolicithal which egg with moderate amount of yolk present mostly in the vegetal hemisphere. The vegetal pole mostly is the yolk while the animal pole mostly is the cytoplasm. In the vegetal cleavage, the cleavage slower than the animal pole. For example in the amphibian egg. Next, the egg with a large amount of yolk filling the entire egg except for a small area near the animal pole are called telolecithal. For example in most fish, reptiles and bird eggs. The last type of the cleavage pattern is the centrolecithal

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which is egg in which the yolk is concentrated in the central cytoplasm. For example the egg of all insect and many other arthropods belong to this type. The cleavage patterns of different animals groups are correlated with the polarity of eggs. Polarity of egg can be divided into animal pole and vegetal pole. In developmental biology, the term animal pole refers to the upper hemisphere of a blastula embryo (as it is conventionally drawn, in reality the animal pole may not be the upper hemisphere). The animal pole consists of small cells that divide rapidly. The animal pole draws its name from its liveliness relative to the slowly-developing vegetal pole. In some cases, the animal pole is thought to differentiate into the later embryo itself, forming the three primary germ layers and participating in gastrulation. On the other hand, the term vegetal pole refers to the lower hemisphere of a blastula embryo (as it is conventionally drawn, in reality the vegetal pole may not be the lower hemisphere). The vegetal pole contains large yolky cells that divide very slowly. The vegetal pole draws its name from its inactivity relative to the lively animal pole. In some cases, the vegetal pole is thought to differentiate into the extraembryonic membranes that protect and nourish the developing embryo, such as the placenta in mammals and the chorion in birds. Animal pole

Vegetal pole

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Types of cleavage There is much variation in how different deuterostomes carry out their earliest cell divisions. Types of cleavage depending on the amount of yolk distribution and correlated with polarity off egg. The divison can be reduced to two different categories which is holoblastic and meroblastic cleavage.

Holoblastic In the absence of a large concentration of yolk, four major cleavage types can be observed in isolecithal cells and mesolechital. Isolecithal cells are cells with a small even distribution of yolk and mesolechital cells are moderate amount of yolk in a gradient which are can be found in bilateral holoblastic, radial holoblastic, rotational holoblastic, and spiral holoblastic, cleavage.

•

Bilateral The first cleavage results in bisection of the zygote into left and right halves. The following cleavage planes are centered on this axis and result in the two halves being mirror images of one another. In bilateral holoblastic cleavage, the divisions of the blastomeres are complete and separate; compared with bilateral meroblastic cleavage, in which the blastomeres stay partially connected.

•

Rotational Mammals display rotational cleavage, and an isolecithal distribution of yolk . Because the cells have only a small amount of yolk, they require immediate implantation onto the uterine wall in order to receive nutrients. In the first division

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the cells divide in half with the plane from top to bottom. However, in the second cleavage, one of the two blastomeres divides the same as the first cleavage and the other divides at the equator. It also unique to mammalian cleavage is that the cells do not always divide at the same time producing the 2, 4, or 8 cell stages but sometimes divide at different times so that odd numbers of cells may be present such as a 5-cell embryo. •

Radial Radial cleavage is characteristic of the deuterostomes, which include some vertebrates and echinoderms, A developing embryo has radial cleavage if as it undergoes cell division (cleavage) and changes from a four-cell embryo to an eight-cell embryo, the cells divide such that each cell in the top four cell plane is directly over one other cell in the bottom plane.

•

Spiral In spiral cleavage, the cleavage planes are oriented obliquely to the polar axis of the oocyte. A developing embryo has spiral cleavage if as it undergoes cell division (cleavage) and changes from a four-cell embryo to an eight-cell embryo, the cells divide at slight angles to one another, so that the none of the four cells in one plane of the eight-cell stage is directly over a cell in the other plane. At the third cleavage the halves are oblique to the polar axis and typically produce an upper quartet of smaller cells that come to be set between the furrows of the lower quartet. All groups showing spiral cleavage are protostomia, such as annelids and mollusks.

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Meroblastic In the presence of a large amount of yolk in the fertilized egg cell, the cell can undergo partial, or meroblastic, cleavage. All large eggs have meroblastic cleavage, because large masses of yolk intefere with cytokinesis. Two major types of meroblastic cleavage are discoidal and superficial. •

Discoidal In discoidal cleavage, the cleavage furrows do not penetrate the yolk. The embryo forms a disc of cells, called a blastodisc, on top of the yolk. Discoidal cleavage is commonly found in birds, reptiles, and fish which have telolecithal egg cells (egg cells with the yolk concentrated at one end).

•

Superficial In superficial cleavage, mitosis occurs but not cytokinesis, resulting in a polynuclear cell. With the yolk positioned in the center of the egg cell, the nuclei migrate to the periphery of the egg, and the plasma membrane grows inward, partitioning the nuclei into individual cells. Superficial cleavage occurs in arthropods which have centrolecithal egg cells (egg cells with the yolk located in the center of the cell).

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CLEAVAGE PATTERN OF REPRESENTATIVE ANIMALS AMPHIBIANS Amphibians typically exhibit mesolecithal eggs, having an intermediate amount of yolk. The amphibian egg is larger than that of the starfish due to the larger quantity of yolk. It is distinctly divided into a dark pigmented hemisphere (the animal hemisphere) and a lightly or unpigmented hemisphere (the vegetal hemisphere). The pigment granules reside in the cortical cytoplasm of the egg within the plasma membrane and are more abundant in the animal hemisphere. The yolk is distributed throughout the cytoplasm of the egg but is much more concentrated toward the vegetal pole end of the egg. Hence, the yolk offers resistance to cleavage in the vegetal hemisphere. The amount of yolk is still sufficiently small to allow complete cleavage of the egg cell. 8 Cell Frog Embryo •

The first cleavage was vertical through the animal and vegetal poles.

•

The second cleavage was also vertical, but at right angles to the first.

•

The third cleavage was horizontal but unequal.

•

The embryo now consists of four smaller blastomeres (micromeres) at the animal pole and four larger blastomeres (macromeres) at the vegetal pole

AP = animal pole, VP = vegetal pole.

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EARLY FROG BLASTULA (SURFACE VIEW) AP = animal pole, VP = vegetal pole

Early Frog Blastula - Sagittal Section

 MAMMALS •

Holoblstic cleavage except concentrated at one pole (inner cell mass analogous to blastodisc)

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•

Cells surrounding inner cell mass (trophoblast) become part of the placenta.

 BIRD •

Egg is telolecithal like fish

•

See discoidal meroblastic cleavage

•

Cleavage only in the blastodisc - small disc of cytoplasm 2-3 mm in diameter at the animal pole

•

First cleavage furrow appears centrally in the blastodisc

•

Other cleavages follow and create a single layered blastoderm

•

They do not extend into the yolky cytoplasm Later equatorial and vertical cleavages divide the blastoderm into a tissue five to six cell layers thick

•

Cells linked by tight junctions

•

Between the blastoderm and the yolk is space - subgerminal cavity

•

This is created when the blastoderm cells absorb fluid from the albumin & secrete it between themselves and the yolk

 FISH •

Cleavage occurs in the blastodisc, yolk-free cytoplasm at the animal cap of the egg

•

Meroblastic cleavage occurs only in the cytoplasm of the blastodisc called discoidal

•

Calcium waves started at fertilization stimulate contraction of actin squeezes non-yolky cytoplasm into the animal pole of the egg

•

Divisions are rapid - about every 15 minute

•

Discoidal Cleavage in a Zebrafish

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First 12 divisions occur synchronously - forms mound of cells atop a single large yolk cell

•

These cells are called the blastoderm

•

At the 10th division - mid-blastula transition - zygotic gene transcription begins

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Now cells divisions slow & cell movement becomes evident 16

STAGES 7: Reflection and Feedback This is the second PBL for us. We use the same method to complete this task. To do this PBL, we search the information, discuss, write the report and present it together. So from this PBL, we know more details about how to do Problem Based Learning process according to the right process. We also gain and learn more details about cleavage process. By doing this activity, we know the definition of cleavage, the steps, types, pattern, factor that affect the cleavage process and also the cleavage patterns of representative animals like mammals, mollusks, amphibians, chick or birds, fish or zebrafish and sea urchins. In doing this PBL, we faced some problem such as we do not understand clearly about the problem that we got and about the cleavage process. So, to settle this problem, we make the discussion with our group members and ask Dr Hayati. From our discussion and the explanation from Dr Hayati, we more understand and can do this task. Because this PBL is the second one, so we do not get the same problem like before which is on how to do PBL like in the first PBL that we did before. Therefore, we can do this PBL smoothly and we hope that it will be better than before. Besides, we also hope that by doing this PBL we can more understand about this topic.

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