12 lab exercise - citrus · pdf filethe right to familiarize yourself with these three ......

Exercise 12Exercise 12Reproduction and Development

INTRODUCTIONINTRODUCTION

The fertilization of an egg and the subsequent development ofgg q pan organism is a most remarkable process.

The fusing of the sperm and egg creates a cell, the zygotezygote, whichmay undergo a series of cell divisions to create the adult.

Although the specifics of development vary among organisms,h iki i il i i f d ll d l i bthere are striking similarities found among all developing embryos.

In this lab, we will examine patterns of development among animal forms and look at a plant embryo as well as the structuresanimal forms and look at a plant embryo as well as the structuresthat ensure its survival.


The development of an animal embryo can be divided into fiveThe development of an animal embryo can be divided into fivemajor processes:

1) gametogenesisgametogenesis: the process of gamete production.2) fertilizationfertilization: the fusion of male and female gametes

to form a single-celled zygote capable ofundergoing development.g g p

3) cleavagecleavage: the mitotic divisions that divide the cytoplasminto increasingly smaller cells, without an increase in the total size of the cell massincrease in the total size of the cell mass.


4) t l tit l ti t f ll t d t4) gastrulationgastrulation: a stage of cell movement and rearrangement resulting in three different germ layers of cells. The three germ layers have different potentials for tissue specialization and development. As you will observed in lab, the amount of yolk greatlyinfluences gastrulation and the development ofinfluences gastrulation and the development of these three germ layers: ectodermectoderm, endodermendoderm, andmesodermmesoderm.

5) ii th h b d l f th5) organogenesisorganogenesis: the process whereby organs develop from the three germ layers.


A t f thi l b t ill b lid f thAs a part of this laboratory you will observe slides of thefollowing:

mammalian ovarymammalian ovary and testistestisdevelopmental stages of the starfish embryostarfish embryodevelopmental stages of the chick embryochick embryo (33 and 72 hour)

In addition, you will observe the embryonic plantembryonic plant and the structures that surround it.


REPRODUCTIVE ANATOMY

I hi i ill i h f h liIn this section you will examine the anatomy of the mammalianovary and testis.

Follicles within the ovary mature each month to form aFollicles within the ovary mature each month to form a graafian folliclegraafian follicle. After ovulation, the remnant of the folliclebecomes the corpus luteumcorpus luteum which is responsible for the secretionof progesterone and estrogen.

The ovaries, the uterus and the brain are linked in a complexand integrated system that uses hormones as chemical messengersand integrated system that uses hormones as chemical messengers,communicating the status of the systems and initiating changes which must occur.


Refer to the following picture to review ovarian structure.

Note the graafian follicle and the corpus luteum.

Refer to Figure 12.2Refer to Figure 12.2in your lab manualin your lab manual

graafian follicle for comparison.for comparison.

corpus luteum


The structure of the male testis is composed of hundreds of tinyseminiferous tubulesseminiferous tubules, where sperm cells form from special cellstermed spermatogoniaspermatogoniatermed spermatogoniaspermatogonia.The spermatogonia cells divide to form the primary spermatocyteprimary spermatocytewhich is still diploid.p

The primary spermatocytes divide by meiosis to form two new haploid cells termed secondary spermatocytessecondary spermatocytes which undergo asecond meiotic division to form spermatidsspermatids.

Once formed, the spermatids develop tails and mature to becomellllsperm cellssperm cells.


The picture below represents a cross section of a seminiferoustubule.

Refer to Figure 12.1Refer to Figure 12.1in your lab manualin your lab manualfor comparisonfor comparisonfor comparison.for comparison.


STARFISH DEVELOPMENT

The starfish is an animal which practices external fertilizationexternal fertilization and offers no support or protection for the young. Since the young mustprovide for their own survival, they mature quickly into embryonicforms which can feed themselves and are mobile enough to avoid o s w c ca eed t e se ves a d a e ob e e oug to avo dcertain predators.

The following stages of starfish development occur in the water g g pcolumn and lead to the production of a larval larval form responsible for feeding before maturation into an adult starfish.


The following pictures represent various stages of starfish development.UNFERTILIZED EGGUNFERTILIZED EGG

h f ili d i l l-The unfertilized egg may or may not contain a clearlyvisible nucleus. Immature eggs, like this one, will contain a large nucleus and nucleolus.

FERTILIZED EGGFERTILIZED EGG-The fertilized egg (zygote) will have a denseThe fertilized egg (zygote) will have a dense cytoplasm, without an obvious nucleus. A fertilization membrane may be seen wrapped around the zygote in some instances.yg


MORULAMORULA-The zygote undergoes rapid cell division withoutcell growth (termed cleavagecleavage) until a solid ball ofcell growth (termed cleavagecleavage) until a solid ball of cells is produced termed the morulamorula. The cells that make up the morula are termed blastomeresblastomeres.

BLASTULABLASTULA-The center of the morula “hollows out” and creates

blastulablastula. The space inside the blastula is termedthe blastocoelblastocoel.


GASTRULAGASTRULAGASTRULAGASTRULA-Cell migration results in the formation of the gastrulagastrula. The gastrula containsthree layers of cells termed germ layers.

The three germ layers include the ectoderm, endoderm and mesoderm.

EctodermEctoderm - Cells of the ectoderm will form the outer skin and nervous systemyof the adult starfish.

Endoderm Endoderm - Cells of the endoderm form the digestive tract and associatedorgansorgans.

MesodermMesoderm - Cells of the mesoderm give rise to muscle, connective tissue and reproductive tissues.


Compare the picture on the left with the diagram onCompare the picture on the left with the diagram onthe right to familiarize yourself with these threegerm layers.

ectodermectoderm

mesodermmesoderm

endodermendoderm


As mesoderm is developed a primitive gutis created termed the archenteronarchenteron. The openingto the archenteron is known as the blastoporeblastoporeto the archenteron is known as the blastoporeblastoporeand will become the anus in the adult animal.

archenteronarchenteron

blastoporeblastopore


Following the gastrula stage, two larvallarval stages develop. As the starfish egg does not contain enough yolk to support development, theembryo uses the strategy of feeding as a free-living larval form toembryo uses the strategy of feeding as a free living larval form toobtain sufficient nutrition to complete development.

NOTE: You are not responsible for starfish larvalNOTE: You are not responsible for starfish larvalNOTE: You are not responsible for starfish larval NOTE: You are not responsible for starfish larval identification.identification.

f ffi i l l d l f hMetamorphosisMetamorphosis occurs after sufficient larval development for changeinto the adult form.


A NOTE ON GASTRULATION-Compare the models of the chick and starfish gatrula.

Notice that both models have the same colors representing endodermectoderm and mesoderm, but the overall appearance of the gastrula differs.

Why is this the case?Why is this the case?

Think about the difference in developmental environmentand the role of yolk in the chick eggand the role of yolk in the chick egg.


CHICK DEVELOPMENT

The chicken has certain features common with all other vertebrateanimals. Since all vertebrates are classified within the same largetaxonomic group (Phylum ChordataPhylum Chordata), they all demonstrate shared features.eatu es.These features need not be present during the entire life of the animalbut must be found during at least some stage of the life cycle.

Features common to all chordates include a dorsal hollow nervedorsal hollow nervecordcord, a cartilagenous rod known as a notochordnotochord, gill slitsgill slits found inthe pharyngeal area and a postpost anal tailanal tailthe pharyngeal area, and a postpost--anal tailanal tail.


33 HOUR CHICK33 HOUR CHICK-Use the diagram on the left to review location of the following:

1) optic vesicles2) heart3) notochord4) d l h ll d4) dorsal hollow nerve cord5) somites6) neural ridges7) remnant of the primitive7) remnant of the primitive

streak


72 HOUR CHICK72 HOUR CHICK-On the right is a picture of a 72 hourhi k bchick embryo.

Refer to the magnified photosh lid ion the next slide to review

features of the 72 hour chick.

Use the diagram on the right andUse the diagram on the right andreview the location of the following:

1) forebrain2) idb i2) midbrain3) hindbrain4) eye5) otic opening5) otic opening6) somites7) heart8) pharyngeal gill slits8) pharyngeal gill slits9) allantois

Refer to Figure 12.3 in the labgmanual for reference.


PLANT DEVELOPMENTPLANT DEVELOPMENT

Just as animals undergo embryonic development, plants alsoexhibit an embryonic condition In animals the embryo isexhibit an embryonic condition. In animals the embryo is typically enclosed within a complex of supportive and protective structures. The same can be said for the embryonicplant.

A seed is much more than just a young plant. For example, the ordinarypinto bean seed is covered by a protective coat that acts as a bufferpinto bean seed is covered by a protective coat that acts as a buffer between the seed’s contents and the environment.


With the seed coat stripped away, a line can be seen which divides the seed into two equal halves along the longitudinal axis. Th f ti f th t t (th t l dt l d ) bThe function for these structures (the cotyledonscotyledons) becomes more apparent when the two are separated, exposing the tiny embryonic plant which was sandwiched in between the two cotyledons.

Filled with starch, the cotyledons nourish the developingFilled with starch, the cotyledons nourish the developingembryo until, or even after, it has produced leaves in embryo until, or even after, it has produced leaves in preparation for photosynthesispreparation for photosynthesispreparation for photosynthesispreparation for photosynthesis.


PROCEDURE

1) Obtain a soaked pinto bean seed and remove the seed coat.) p2) Carefully separate the two cotyledons and examine with the

dissecting microscope.3) Draw and label the cotyledons and the embryonic plant3) Draw and label the cotyledons and the embryonic plant


When the two cotyledons have been separated the seed should appear similar to the picture depicted below:

Compare this specimen to the illustration in Figure 12.4 of yourl b llab manual.


Plants, like the pinto bean, containing two cotyledons are termeddicotsdicots. However, not all plants contain two cotyledons. For example,the corn seed depicted below only contains one cotyledon and isthe corn seed depicted below only contains one cotyledon and istermed a monocotmonocot.

Dicot

MonocotMonocot

Refer to Figure 12.4Refer to Figure 12.4f l b l ff l b l fof your lab manual forof your lab manual for

a comparative diagram.a comparative diagram.


CONCLUSIONS

1) Specialized cells are formed in the process of developing 1) Specialized cells are formed in the process of developing the sperm and egg cells that unite to form new individualsthe sperm and egg cells that unite to form new individuals.

2) Plants and animals employ similar strategies during their2) Plants and animals employ similar strategies during their2) Plants and animals employ similar strategies during their2) Plants and animals employ similar strategies during theirdevelopment.development.

3) Each organism has a set of specific developmental stages 3) Each organism has a set of specific developmental stages that they must pass through in order to developthat they must pass through in order to developthat they must pass through in order to develop.that they must pass through in order to develop.

4) Embryos that provide nourishment for their young develop4) Embryos that provide nourishment for their young developin a manner that is different from that of embryos resultingin a manner that is different from that of embryos resultingfrom external fertilization.from external fertilization.

12 lab exercise - citrus · pdf filethe right to familiarize yourself with these three ......

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