Question

1. What is the most noticeable difference between the egg cells of sea stars and those of birds?

2. compare gastrulation in a sea star to gastrulation in a chick

Answer 1

1 ans Differences Egg cell of Sea star

a)Due to high diversity in the egg cells of sea star which can be observed during fertilization,Male and female sea stars have gametes that releases gonophores which are located on dorsal side of thr sea star as well as fertilization occurs in seawater externally which can be spawn by investigators in lab by spawning the sea star.

b)Sea star are consider as echinoderm in nature.Oocytes which are found in sea star are prophase of meiosis as they are known as 1- methyladenine. Egg cells of sea star are induced during meiotic maturation is complete as individual or in a group.

Difference - Cells of bird egg

a) Cells of bird egg are considered as single cell because they are unfertilized in nature, also known as the largest cell in the world. Yolk and albumin makes the egg a single cell.

b) When sperm and ovum fused together which forms zygote, completely covered by organic shell,which makes the cells of egg semipermeable as it can mimic a single cell.

Gasturlation in Sea star

Early gasturlation -After blastula stage, certain cells are involved in embryo development and are formed into blastocoel which is known as gasturlation.Further,blastopore is formed i.e the site of indentation. More cells lead to formation of new celll and cavity.

Gasturlation - Further , cavity are open up and form third layer of cells during embryo development. Three layer which are ectoderm,endoderm and mesoderm are consider as brick and the mortar of the egg cell which are used in differentiation of organ embryo system.

Gasturlation in chick
Gastrulation is initiated within four or five hrs when the onset of incubation is completed, which is requires a incubation time of 22 hours. Gastrulation in chick embryo are divided into two phases-
a) Endoderm formation & b). Primitive streak formation
a) Formation of endoderm - Endoderm of hypoblast are developed into single layer of cells which are present inside the blastocoel. After forming endoderm, upper layer which is ascalled epiblast.
b) Primitive streak Formation-
At the posterior
region of area pellucida which is present in the mid dorsal line of primitive streak is initiated aftert eight hours of incubation. Convergence of cells are observed between
blastoderm towards the centre region. After eighteen to nineteen hours of
incubation are completed, primitive streak is Completely developed which is known as definite primitive streak. Having a narrow region known as Primitive groove.
Edges of grooved and thick known as primitive folds. At the anterior end are packed of cells known as "hensen's node" also known as
primitive knob. Centre region of nod pit called as primitive pit.Further lromotove streak develops into immigrated cells as they become prechordal plate, notochord, and
mesoderm.