Cells become variable in morphology and function in different regions of the embryo. The process is
After formation of three primary germ layers (i. e., ectoderm, mesoderm and endoderm), cells of these three layers become variable in morphology, shape, size and more specified to form organs so as to meet out the future functional needs of the foetus, this process is called differentiation.
What is true about cells during cleavage?
No growth of the embryo occurs during cleavage because there is an increase in the number of cells and progressively they decrease in size.
Meroblastic cleavage is a division which is
Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic (total or entire cleavage) ormeroblastic (partial cleavage). In the presence of a large amount of yolk in the fertilized egg cell, the cell can undergo partial or meroblastic cleavage. Two major types of meroblastic cleavages are discoidal e.g. birds and superficial e.g. arthropods.
Eye lens is formed from
Ectoderm forms : Eye (conjunctiva, cornea, lens, retina, iris, ciliary muscles) Mesoderm forms : Sclera & choroid of eye.
Blastopore is the opening by which the cavity of the gastrula (gastrocoel), communicates with the exterior. It is formed as a result of invagination of endoderm during embryonic development. During maturation of some animals it evolves into the anus or the mouth; in others it is covered over and contributes to the canal joining the primitive gut with the cavity of the neural tube.
Termination of gastrulation is indicated by
Termination of gastrulation is indicated by obliteration of blastocoel.
In telolecithal egg, the yolk is found
Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals.
Amount of yolk and its distribution are changed in the egg. Which one is affected?
A change in the amount of yolk and its distribution in the egg will affect pattern of cleavage. The pattern of cleavage is influenced by the amount of yolk in the egg. In eggs with less yolk, cleavages are equal, and the resulting blastomeres are of similar size. If the yolk is licalized, such as in frog eggs, then cleavages are unequal, the cells derived from the yolky region (the vegeal pole) are larger than those derived from the region without yolk (the animal pole).
What is true about cleavage in fertilized egg of humans?
After ovulation egg comes in fallopian tube where it is fertilized by the sperm & cleavage starts here only.
In an egg, the type of cleavage is determined by
The amount of yolk and how it is distributed determines the type of cleavage. On this basis cleavage is of two types:
(a) Holoblastic - where the segmentation line passes through the entire egg. It occurs in alecithal (without yolk), microlecithal (with very little amount of yolk) and mesolecithal (little amount of yolk) egg.
(b) Meroblastic - where segmentation line does not pass through the egg and remained confined to a part of the egg. It occurs in megalecithal (large amount of yolk) egg.
The correct sequence in the process of development of human embryo is 
Fusion of male and female gamete produces a zygote. Repeated division of the zygote is called cleavage forming a solid morula. After further division and rearrangement a fluid filled cavity surrounded by blastomeres - blastula is formed. The appearance of germ layers mark the gastrula.
Which of the following processes is associated with a change in the cellular DNA amount?
Cytokinesis involves division of the cytoplasm of the parent cell into its daughter cells. Fertilization involves the fusion of two haploid gametes. Blastulation refers to the process of cleavage in the zygote to form a blastula.
Exponential growth of cells is a characteristic feature of
Embryo growth graph is ‘J’ shaped.
Blastopore is the opening of
Blastopore is the transitory opening on the surface of gastrula through which the internal cavity archenteron) communicates with the exterior. It is formed by invagination of superficial cells during gastrulation.
During regeneration, modification of an organ to other organ is known as
A. Morphogenesis – Formation of organs from the embryo is called Morphogenesis or organogenesis.
B. Epimorphosis - Regeneration of limbs or tail is an epimorphosis regeneration. Replacement of lost organ of the body by proliferating new cells from the surface of the injured part is called Epimorphosis.
C. Morphallaxis - The reconstruction of an entire animal from a small fragment by reorganizing the existing cells, is called Morphallaxis.
D. Accretionary growth – It involves a cell secretion to increase the volume of the extracellular spaces. Many adult tissues will only divide when induced by injury or other stimuli. It occurs in cartilage and bone.
What is true for cleavage?
Cleavage involves repeated cell division without increase in size. But cell size decrease.
Vegetative propagation in mint occurs by:
Vegetative propagation in mint occurs through sucker. Sucker is a non-green underground specialised stem developing from the underground base of an erect shoot or crown.
The “Eyes” of the potato tuber are
The axillary buds of the potato tuber are called “eyes” in common language. They are found at the nodes of the stem tuber.
What is common between vegetative reproduction and apomixis?
Vegetative reproduction and apomixis both are asexual methods of reproduction, which gives the progeny genetically similar to parent.
Which one of the following is correctly matched?
Onion - Bulb - Undeground stem, Ginger - Rhizome, Chlamydomonas - Zoospore Yeast - ascospores
Select the wrong statement :
In oomycetes female gamete is large and non motile while male gamete is small & motile.
Monoecious plant of Chara shows occurrence of :
Monoecious or homothallic condition in Chara (green algae) is used to denote upper oogonium and lower antheridium on the same plant. The organisms, which possess both the reproductive organs are called bisexual. Unisexual condition represents both male or female organs in same organism.
Meiosis takes place in :
In diploid organisms, specialised cells called meiocytes(gamete mother cell) undergo meiosis. Conidia and gemmules are asexual reproductive structures found in penicillium and sponge respectively. Megaspores are female gametes in plants, which undergo sexual reproduction.
Syngamy can occur outside the body of the organism in
[NEET Kar. 2013]
In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water) i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation.