lab 3: embryology

Question 1

embryology

Answer 1

the study of the processes in the early development of an organism

Question 2

fertilization

Answer 2

the initial event in development in sexual reproduction (sperm -> egg)

Question 3

cleavage

Answer 3

-after fertilization, the period of rapid cell division without growth
-produces the morula (a solid ball of cells), then it forms blastula, a hollow sphere of many cells with a fluid-filled cavity (blastocoel), cells are called blastomeres

Question 4

gastrulation

Answer 4

-rearranges the cells of a blastula into a 3-layered embryo (gastrula)

Question 5

germ layers

Answer 5

-the three layers produced by gastrulation

Question 6

ectoderm

Answer 6

-outer layer of the germ layers

Question 7

endoderm

Answer 7

-lines the digestive tract
-layer of germ layer

Question 8

mesoderm

Answer 8

-partly fills the space between the endoderm & ectoderm

Question 9

organogenesis

Answer 9

-when various regions of the germ layers develop into organs

Question 10

cell polarity

Answer 10

-refers to spatial differences in shape, structure & function within a cell
-polarity is defined by the heterogeneous distribution of substances like mRNA, proteins & yolk
-yolk is most concentrated at the vegetal pole & least at animal pole

Question 11

fertilization in sea stars

Answer 11

-zygote divides to form 2 cells
-yolk is holoblastic (only a small amount of yolk is present)
-cleavage forms a ball of 16-32 cells called a morula, which forms a hollow sphere of many cells called blastula
-the fluid filled cavity within blastula is blastocoel, & the cells are called blastomeres

Question 12

gastrulation in sea star

Answer 12

-occurs after blastula matures
-cells invaginate into blastocoel & form gastrula & new cavity called archenteron
-formation of germ layers [endoderm: digestive tract, ectoderm: skin & nervous system, mesoderm: muscular tissue & parts of reproductive & circulatory systems]

Question 13

organogenesis

Answer 13

-formation of motile & feeding larval stage called the bipinnarial larva
-this stage is followed by the (brachiolaria larva: attach to the substrate & undergo metamorphosis)
-sea star arms grow -> juvenile sea star

Question 14

in conclusion (reproduction & development of sea stars)

Answer 14

-first is meiosis where the adult male & female sea stars produce haploid gametes (sex cells)
-second is the sperm & egg fuse forming diploid zygote
-third is mitosis that produces a blastula
-fourth is continued mitosis & changes in shape to produce a gastrula
-fifth is the gastrula develops into a larva
-sixth is the larva undergoes metamorphosis & becomes an adult
-then the cycle repeats

Question 15

fertilization in frogs

Answer 15

-cytoplasm becomes specialized in certain regions [animal pole: less yolk, more cytoplasm; vegetal pole: more yolk, less cytoplasm]
-eggs are telolecithal: vegetal pole contains significant amount of yolk, unevenly distributed

Question 16

cleavage in frog

Answer 16

-holoblastic: small amount of yolk present resulting cells not equal in size, but total division
-morula -> blastula
-asymmetric blastula: vegetal pole cells of blastula have more yolk & divide slower than animal pole cells

Question 17

gastrulation in frogs

Answer 17

-involution: layer on animal pole cells moves & grows down over vegetal cells. moves inward at blastopore
-yolk cells are enveloped, some produce a yolk plug through blastopore
-mesodermal layer develops
-formation of neural tube [neurulation: the process of formation of neural tube or nerve cord]

Question 18

organogenesis

Answer 18

-producing functioning larva

Question 19

in conclusion (development of frog)

Answer 19

-gametogenesis
-sperm & egg cells fertilize
-fertilized egg goes through cleavage which becomes the blastula
-gastrulation happens & the blastocoel & blastopore develops
-then the ectoderm, mesoderm & endoderm develop
-then the neurula & neural tube
-then organogenesis happens & produces functioning larva

Question 20

fertilization in chicks

Answer 20

-occurs before hard shell is produced
-egg cell is large mass of yolk & small area of cytoplasm on its surface = germinal disk (contains egg nucleus)
-cells formed from germinal disk become the embryo
-albumen surrounds egg cell & supplies embryo w food & water
-albumen is surrounded by 2 shell membranes & a shell porous to gas

Question 21

cleavage in chicks

Answer 21

-confined to germinal disc (abundance of yolk)
-blastodisc (blastoderm) consists of 2 layers: epiblast & hypoblast
-layers are separated by blastocoel; epiblast forms endoderm & mesoderm
-cells on surface of embryo form ectoderm

Question 22

gastrulation in chicks

Answer 22

-cells migrate across surface of blastodisc & into the primitive streak (becomes midline of developing chicks)
-embryo is surrounded by a network of arteries & veins -> to extra-embryonic membranes
-[amnion: surrounds embryo; yolk sac: surrounds yolk; allantois: waste disposal sac; chorion: surrounds the entire embryo or yolk]

Question 23

summary (starfish)

Answer 23

-amount of yolk: holoblastic
-distribution of yolk: isolecithal
-blastulation: holoblastic
-gastrulation: ectoderm, endoderm, mesoderm
-larval stage: motile, free floating
-egg size: microscopic

Question 24

summary (frog)

Answer 24

-amount of yolk: holoblastic
-distribution of yolk: telolecithal
-blastulation: holoblastic
-gastrulation: nerurulation, open cavity
-larval stage: tadpole, motile
-egg size: small but visible to naked eye but clearer beneath microscope

Question 25

summary (chick)

Answer 25

-amount of yolk: meroblastic
-distribution of yolk: partial merblastic
-blastulation: meroblastic
-gastrulation: primitive streak
-larval stage: nonmotile, inside egg, surrounded by yellow yolk
-egg size: very large, no need for microscope

Question 26

meroblastic

Answer 26

partial cleavage of the zygote in chicks; produces a flat blastodisc of developing cells lying atop the bulky yolk

Question 27

holoblastic

Answer 27

cleavage of the zygote: only a small amount of yolk is present, divides evenly in the sea star. in frog zygote, the resulting cells are not equal in size

Question 28

telolecithal

Answer 28

vegetal pole contains significant amount of yolk, unevenly distributed

Question 29

isolecithical

Answer 29

yolk is distributed evenly