CHAPTER – 5
Short
Question Answers – Growth and Development
Q.1. What is
the type of hen’s egg? In which form it is released from the ovary?
Ans. The egg of hen is polylecithal type, which has large
quantity of yolk. It is released from the ovary as primary oocyte with a
diameter of about 3cm.
Q.2. What is
blastodisc? When the oocyte becomes the secondary oocyte?
Ans. Cytoplasm and nucleus is restricted to small area
called blastodisc or germinal disc. After release from ovary, the oocyte
undergoes first maturation division to become secondary oocyte.
Q.3. Where
fertilization occur in the oviduct and how egg is formed?
Ans. Fertilization is internal which occurs in terminal
part of oviduct. The secondary oocyte after fertilization undergoes second
maturation division to become mature ovum gathers albumen makes two egg
membranes and a porous proteunous calcarious shell. This fertilization ovum is
laid in 24 hours after fertilized.
Q.4. What is
incubation?
Ans. Cell division in fertilized egg required temperature
of 36oC – 38oC either naturally by hen or artificially in meubaton. At this
temperature complete development and hatching takes place in 21 days.
Q.5. What is
cleavage and what type of cleavage occur in hen’s egg?
Ans. Immediately after fertilization, the egg undergoes a
series of mitotic division, called cleavage. Cleavage is restricted to the
blastodisc, hence called discoidal cleavage. The first two cleavage planes vertical
while the third runs horizontal. The rest of the cleavages are irregular and
blastodise transformed into blastoderm.
Q.6. What is
morulla?
Ans. Cleavage result in the formation of rounded closely
packed mass of blastomeres. This is morulla it consists of disc shaped mass of
cells two or more layers in thickness lying closely to the yolk.
Q.7. What is
blastula and how it is formed?
Ans. Morulla changes into blastula stage. It contains a
fluid filled cavity called blastocoel cavity. It appears when the blastodermal
cells split into two layers, the upper of epiblast and the lower layer
hypoblast. In between these layers blastocoel appears. The marginal cells of
blastoderm lie unseparated from the yolk and from the zone of junction or area
opaca, while the central region is termed as area pellucida. The egg is laid at
this stage.
Q.8. What is
gastrulation?
Ans. Blastula changes into gastrula and the process is
called gastrulation. During this process formation, migration and rearrangement
of cells occurs in embryo. These cells begin to differentiate into definite
layers, the ectoderm, the mesoderm andthe endoderm.
Q.9. How
endoderm is formed?
Ans. Some cells of hypoblast of the area pellucida
migrates downward and spread over the yolk. This newly formed layer is called
endoderm which enclosing yolk and stalk connecting the yolk mass to the embryo.
Q.10. How
mesoderm and ectoderm are formed?
Ans. Mesoderm
Formation – Cells of epiblast for
the middle of blastodisc move downward in the direction or yolk. As a result of
the movement of the cell at the blastodisc, a groove the primitive streak is
produced. Number of cells of epiblast pass through the primitive streak to the
blastocoel to form a new layer of cells called mesoderm. Primitive streak has a
swelling at its anterior end called primitive knot or Hessen’s node.
Ectoderm Formation –
The remaining layer of epiblast after the formation of mesoderm formed as
ectoderm.
Q.11 Describe
the mechanism of formation of notochord.
Ans. Notochord
Formation and Differentiation of Mesoderm
After the formation of endoderm cell from the region of
Hessen’s node push into a form a rod like structure called notochord in the mid
line beneath the ectoderm. The mesoderm on each side of the notochord gives
rise metamerically arranged somites or epimeres, which later give rise muscles,
axial skeleton and connective tissues. Below epimere mesomere is produced which
gives rise to kidneys. The rest of the mesoderm is the hypomere. after 24 hours
of incubation hypomeres are differentiated into and outer somatic layer and
inner splanchnic layer. The space between two layers is called coelom.
Q.12. Define
neuralation? What is its mechanism of formation and significance?
Ans. Neurulation – The whole process of formation of
central nervous system is called neurulation. Some cells of ectoderm above the
notochord divide quickly to form neural plate on the dorsal surface. During the
course of cell division the neural plate sinks inside the embryo to form the
neural groove. Both the edges of neural groove are called neural folds. Neural
folds after fusing together form neural tube. The embryo now called neurula.
The neural tube gives rise to nervous system.
Q.13. What is
cell differentiation?
Ans. The process in which cells arise from zygote
morphologically and physiologically different from each other is called cell
differentiation.
The embryo arise from single fertilized ovum, so all the cells of embryo have
same number and kind of genes but during gastrulation some genes are activated
and some are inactivated due to which cells are differentiated form each other.
Q.14.
Describe the mechanism of cell differentiation with the help of experiment.
Ans. Experiment – John Gurdon in his experiment
removed the nucleus from the unfertilized egg of frog. Then he obtained nucleus
from the intestinal cell of tadpole and implanted into the egg. Surprisingly
the transplanted zygote developed into complete from indicating that nucleus of
he differentiated cell does not lose any genetic information and remain
totiopotent.
Mechanism –
During the differentiation process genetic expression is influenced by
cytoplasmic chemical composition. During cleavage cytoplasm of ovum is divided
into cells containing mRNA, protein and other molecules for the future
differentiation of cells into tissues.
Q.15. What is
embryonic induction?
Ans. When an embryonic tissue influences upon the other
embryonic tissue through transmitting some chemical stimulus the primary
organizer, this phenomenon is called embryonic induction.
Q.16.
Describe the process of embryonic induction with the help of experiment.
Ans. Experiment – Hans Spemann and Hilde Mangold in
1924 performed an experiment. They cut the presumptive nervous tissue and
transplanted into the belly region of another embryo. They found that neural
tissue failed to develop into nervous system. In another experiment, they cut
away the presumptive notochord tissue and grafted it under the belly ectoderm.
Surprisingly, the belly ectoderm developed into neural tissue.
Q.17. What is
aging? Give the name of the branch of biology that deals with the study of
aging?
Ans. The progressive process of deterioration in the body
is called aging. The science of aging is called gerontology.
Q.18.
Describe the process of aging and give its main causes.
Ans. In the process of aging the cells starts to breakdown
structurally and functionally which lead to structurally changes and ultimately
the loss of different functions of body. The exact cause of aging is yet
unknown. However there are following interesting lines to think about.
(i) Genetic
Origin –
Experiment of Leonard Hay flick and paul moor Head, that the cells of the
tissues have only a finite number of cell divisions. By the time the tissues or
organs is fully grown. For example in the case of nervous system mental
activity and memory deteriorate and there are fewer nerve cells in old age.
(ii) Gene
Mutation –
During the passage of time due to the accumulation of gene mutation the
capacity of self repair of DNA during its replication is lost. This results in
progressive inadequate functioning of cells that cause the aging.
Q.19. What is
regeneration? In which type of animals the potential for regeneration is
higher?
Ans. It is the ability of a living organism to reconstruct
its lost part of the body. Some animals retain this power after maturity and
adulthood while other looses it. It is much more common in invertebrates than
in vertebrates. Simpler animals have greater power of regeneration than the
higher ones. Sponges have greater power of regeneration. An adult hydra of
star-fish if chopped into many parts. Each part can regenerate into complete
organism. Among arthropods usually appendages can be regenerated. Salamanders
and lizard can regenerate their tails. In birds and mammals the regeneration is
mostly limited to the small wounds by the formation of a new tissue called
Scar.
Q.20. What is
the degree for regeneration?
Ans. The regeneration potential is generally related to
the differentiation of cells. Thus greater the differentiation among the cells
at the body the lesser will be regeneration.
Q.21. What is
abnormal development? Which branch of science deals with study of abnormal
development?
Ans. Deviation in the normal structure and functions of an
organism occur under unfavourable conditions during the embryological
development and are called abnormal development. The study of abnormal
development is called Teratology.
Q.22. What
are the causes of abnormal development?
Ans. Sometimes due to mutation radiation. Some drugs during
the pregnancy, abnormal secretory functions of glands etc. Some kind of
structure for biochemical abnormalities, which may be lethal, develop in new
individual.
Q.23. Give
examples of abnormal development.
Ans. Some abnormal conditions are listed belowl
DISORDERS
1. Microcepahly
2. Cleft Lip and Palate
3. Polydactyl
4. Dextrocardia
5. Sickle Cell Anemia
6. Turner’s Syndrome
7. Klinefelter’s Syndrome
8. Down’s Syndrome
9. Haemophilia
10. Thalassemia
MAJOR
SIGNS AND SYMPTOMS
1. Individual with small skull in proportion to the normal
body size.
2. Splitr in upper lip and gap in the roof of the mouth.
3. Excessive number of fingers or toes.
4. Heart towards the right side of the chest.
5. Abnormal sickle shaped RBC’s.
6. Female Sexual Defect.
7. Male Sexual Defect.
8. Mental and Physical Retardation
9. Decreased ability or inability of the blood to clot.
10. Fragile RBC’s cause hemolytic anemia.
these notes are realy very helful for us .. (Y) :)
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