Growth and Development
Growth:
Growth is a permanent and irreversible
increase in size that occurs as an organism mature.
Development:
The changes in shape and degree of
complexity in an organism are called development.
Development is a programmed series of
stages from a simpler to more complexes from. As a
result of development cellular
differentiation of structure and function take place.
Growth and Development in plants:
Growth and development in plants are
two successive integrated physiological processes.
Growth is quantitative increase in the
plant body. Because during growth permanent change
occurs in the size and overall dry
weight of plant is increased.
Development on the other hand is
qualitative changes in the plant body.
Growth and development therefore,
cannot be separated but one follows the other.
Mostly plants show indeterminate growth
i.e. show continue growth throughout their life.
But some plants and animals show
determinate growth i.e. they stop growth after reaching a
certain size.
Growth Points:
In lower plants the whole body takes
part in growth.
In higher plants the growth occurs only
in certain region called growth points.
In these regions the cells divide
rapidly
These cells are known as meristems.
These meristems are of three types
(i) Apical Meristems:
These cells are present at the tip of
root and stem.
They take part in the formation of
branches, flowers and leaves.
They increase the length of plant at
both the stem and root sides.
(ii) Intercalary Meristems:
They are present at the base of
internodes in many plants.
They also increase the length of
plant.
(iii) Lateral Meristems:
These cells are present in the form of
ring between xylem and phloem.
They increase the thickness of plant
body.
These are present in dicots and
gymnosperms.
Growth Rate:
Plants differ in their growth rates.
Bamboo plant grow up to 60 cm per day.
Most of the cultivated plants grow 1-2
cm per day.
The rate of growth is not uniform
throughout the plant body.Phase of Growth
There are three phases of growth in
root and stem tips:
(a) Phase of cell Division:
Cell division is the first phase of
growth.
This phase is present at the tips of
root and stem.
In this phase the number of cells
increases by mitosis.
The cells have dense cytoplasm, central
nuclei and thin cell wall.
These cells are non-vacuolated or
having small vacuoles.
(b) Phase of Cell Elongation:
The second phase of growth is cell
elongation.
It lies just behind the phase of cell
division.
Here the cells simply elongate to
attain their maximum size.
During elongation the cell volume
increases up to 150 times due to uptake of water.
The cells synthesize new cytoplasm,
cell wall material and a large central vacuole is formed.
Thus cells show increase in weight and
attain different shapes.
(c) Phase of cell Maturation:
This phase is present behind the phase
of cell elongation.
Here the cell walls become thicker and
cells attain their final size and shape.
The cells modified into different
tissues according to their location and function.
Some cells form parenchyma,
collenchymas, xylem and phloem.
CONDITIONS FOR GROWTH:
There are certain factors which affect
the process of growth. These factors are;
(a) External factors (b) Internal
factors
(a) External Factors:
(i) Temperature
Normally rate of growth increases with
rise of temperature and decreases with decrease of
temperature.
Very high or low temperature affects
growth.
Optimum temperature for maximum growth
is 25 - 37 o C.
Because all hormones and enzymes work
best at this temperature.
At very high temperature (40 – 45oC )
growth stops and the plants dies.
(ii) Light
Most plants grow in light while some
grow in shade. Light affect growth in three ways:
Light Intensity: Increases cell
division and chlorophyll formation.
Light Quality: Red light increases cell
elongation. Ultra violet light also reduces cell
elongation. In complete darkness plant
become pale and show stunted growth.
Light Duration: Duration of light
effects the growth of vegetative and reproductive
organs. It also plays a role in
inducing or suppressing flowering.(iii) Supply of Oxygen:
Growing cells need energy for their
growth.
This energy is released by the
oxidation of food.
The oxidation or breakdown of food
needs oxygen.
Thus healthy growth require regular
supply of oxygen.
(iv) Nutrients:
Plants require sixteen essential
element for their normal growth.
Their deficiency may cause certain
abnormal conditions.
(b) Internal Factors:
(i) Supply of Water:
Water keeps the growing cells turgid.
By absorbing water the cells elongate.
Plants can use nutrients only in
solution form.
Plants under shortage of water show
suppressed growth.
(ii) Supply of Food:
Growth is an anabolic process and
require food supply which can be converted to body.
For not only provide building material
but also energy to the newly formed cells for their growth.
(iii) Hormones:
Some hormones also play important role
in plant growth such as, Auxin and Gibberilins.
GROWTH CORRELATIONS
The relationship of growth among
different organs of a plant is called Growth correlation. OR
The relationship between the organs of
plant in which the activity of one organ influence the
growth of other organ is called growth
correlation.
In plants the growth of various parts
is correlated with each other.
Examples:
Growth of vegetative part is sharply
checked during fruiting.
Similarly formation of flower may be
controlled by the activity of leaves.
Types:
There are two types of growth
correlation in plant.
Inhibitory Correlation:
When the activity of apical bud
inhibits or control the growth of lateral buds (branches) is called
inhibitory correlation.
It is also called Apical dominance.
In apical dominance the apical buds
dominate and control the growth of lateral buds.
Apical dominance depends upon the
distance between apical and lateral buds.
Apical dominance is of two types:(a)
Complete Apical Dominance:
When the apical bud completely inhibits
the growth of lateral bud is called complete apical
dominance.
In this case only the main shoot grows
and the growth of lateral bud is completely inhibited e.g.
sunflower.
(b) Incompletely Apical Dominance:
When the apical bud cannot fully
inhibit the growth of lateral buds is called incomplete apical
dominance.
In this case the apical bud is weak and
lateral buds grow out.
This results in bushy appearance of
plants. e.g. Tomato
Inhibitory Factor:
In 1934 Thiman and Skoog discovered
that Auxin (IAA) causes apical dominance.
COMPENSATORY CORRELATION:
When the removal of one part enhance
(increase) the growth of other part is called compensatory
correlation.
Example:
Thinning of fruits can cause the
remaining fruits to grow larger in size.
In chrysanthemum removal of all buds
except one results in the development of one large single
flower.
EMBRYONIC INDUCTION
When one body part differentiates in
response to a signal from an adjacent body part is called
embryonic induction. OR
The interaction between two embryonic
cells types in which one cell stimulate the other cell to
produce a structure is called embryonic
induction.
The embryonic tissue which produce
inductive influence is called embryonic induction.
The tissue on which inductor acts is
called responsive tissue.
The inductor transmits some chemical
substance called morphogen or messenger.
Thus induction occurs by the transfer
of morphogen from inductor to responsive tissue.
History
The idea of embryonic induction was
first introduced by Hans Spemann in 1924.
He was awarded Nobel Prize in 1935 for
this discovery.
Experiment No#1
Spemann cut out a piece of ectoderm
form an embryo.
This ectoderm have the power to develop
into a nerve tube and then form central nervous
system.
He placed this piece of ectoderm in a
dish. The embryo healed and lived but it never develops a
normal nervous system. The isolated
piece of ectoderm also did not develop into nervous
system.Conclusion:
Spemann concluded that:
The piece of ectoderm is required by
the embryo in order to develop a proper nervous system.
Experiment No#2
Spemann removed the ectoderm from the
top of an embryo.
Then he removed the mesoderm and
discarded it. He again put the ectoderm on its original place.
The ectoderm healed and looked quite
healthy. But it did not develop into nervous system.
Conclusion:
He concluded that of Mesoderm influence
the ectoderm to differentiate into nervous system.
Experiment No#3
In this experiment Spemann used two
embryos in early gastrula stage. From one embryo he
removed a piece of mesoderm from the
dorsal lip of blastophore.
From the second embryo he removed a
similar sized piece from ventral or lateral side of
mesoderm of dorsal lip. He transplanted
the piece of first embryo into the ventral or lateral
position of second embryo. The
transplanted embryo formed blastophore and moved inside the
embryo. The embryo healed and survived
this surgery. This embryo developed normally but it
had tow nervous systems. First nervous
system was at the normal position. Second nervous was
away from the normal position. This
second nervous system was in response to the transplanted
dorsal lip of blastophore. This embryo
developed into a Siamese twin with two heads and one
trunk.
Conclusion:
He concluded that: if the mesoderm of
the dorsal lip region is removed the animal produces no
nervous system. If it is put in a
strange place, the animal develops an extra nervous system. This
area of mesoderm seems to control or
induce the differentiation.
ROLE OF NUCLEUS AND CYTOPLASM IN
DEVELOPMENT:
We know that genes are present in all
cells. But each cell differentiates and functions differently.
For example
(i) Stomach cells produces enzymes
which help in digestion.
(ii) Cells on the tips of fingers and
toes produces keratin protein for the formation of nail.
This indicate the presence of some
controlling mechanism within the cells.
This controlling mechanism allows only
certain genes to express itself.
Both the nucleus and cytoplasm play
important role in the normal development.
The nucleus determines the
characteristics of the individual.
While the cytoplasm selectively “turn
on” some genes and “switches off” others.
ROLE OF NUCLEUS IN DEVELOPMENT:
Hamerling performed an experiment to
explain the role of nucleus in development. In this
experiment an alga plant Acetabularia
is used.
Habitat: Acetabularia is found in
European sea water
Size: Acetabularia is unicellular and 2
– 3 cm in length.
Structure: Acetabularia consists
of:Acetabularia attached with the ground by a base which contain a
single nucleolus.
Stalk is long and arises from the base.
A cap like structure is present at the tip of stalk.
There are two species of Acetabularia
which differ in shape and structure of their cap.
(1) Acetabularia mediterrancea: Which
has an umbrella like cap.
(2) Acteabularia crentulata: Which has
irregular cap.
If the caps of these algae’s are
removed, a new one is regenerate.
Experiment:
(1) When caps were removed from both
types.
Result: each plant again produced the
cap of its own type.
(2) Then he cut the caps and stalks
from both alga plants. Each alga was grafted with stalk of
other type.
Result: Each type again produced the
cap of its own shape inspite of having separate stalk.
(3) Finally he cut the nucleus
containing base from both types. He grafted the base of A.
Mediterranean into A. cranulata.
Result: He found that the new
regenerated cap had the shape of A Mediterranean.
Conclusion:
Only the nucleus present at the base
determined the shape of cap. Nucleus exerts a strong
influence on the development of cap
through mRNA.
Stalk do not play any role in the
formation of cap.
ROLE OF CYTOPLASM IN DEVELOPMENT:
Cytoplasm is also important in the
development of an embryo. To explain the role of cytoplasm
experiment was performed on frog
embryo. In unfertilized egg of frog the upper half part is
pigmented. While the lower half part is
non-pigmented and contain yolk. After fertilization some
pigments are migrated in the upper
part. AS a result a less pigmented part is formed in the
middle which is called grey crescent.
Experiment:
In this experiment frog’s zygote was
used.
During normal cleavage the first
division is vertical.
Zygote divide into two equal parts
through the middle of grey crescent.
In this way each cell contain half
amount of grey crescent.
If these two cells are carefully
separated then such cells will grow to form a normal tadpole.
If these two cells are separated in
such a way that one cell contain complete grey crescent.
Then only that cell will develop into
normal tadpole which contain grey crescent.
While cell without grey crescent will
develop into an undifferentiated mass of cells.
Conclusion:
The cytoplasm in the grey crescent
directs embryonic development.AGING
The natural phenomenon of getting old
is called aging. OR The negative changes both structural
and functional in our body are called
aging.
The negative changes both structural
and functional in our body are called aging.
The study of aging is known as
“Gerontology”.
Every organism on the earth has a
limited period of life.
No one can live for ever. During the
life cycle the living organism passes through various stages
such as:
Growth
Maturation
Physical and Mental
deterioration
Finally
Death.
After adult stage some physical changes
occur in the bodies which are degenerative in nature.
Aging Rate:
life span varies greatly depending on
diseases and accidents. Aging rate is different in different
animals.
E.g. Frog
12-y 15 years,
Dog
15
years
Crow
100 years
Human
70 years
Sign of Aging:
Hair become colourlesss (white) Poor
vision, weak memory
Hearing impairment, Loss of
reproductive capacity.
Dryness and wrinkling (folding) of
skin, arthritis.
Decreased body immunity.
Causes of Aging:
The exact process of aging is still
unknown. But the following two causes are very important;
(i) Genetic Origin:
It is the main cause of aging.
Mitosis is genetically programmed which
decline at a particular stage of the life cycle.
Some scientists also believe that cells
gradually lose the capacity for DNA self repair.
(ii) Gene Mutation:
Sometime changes occur in the genes and
DNA replications affected.
Mutation in the DNA replication leads
to nonfunctional protein production.
Thus function of the cells become weak
causing aging.
AGING AFFECTS:
(i) Limited cell Division:
The dividing capacity of aging cell is
gradually decreases.
After birth the muscle and nerve cells
of human do not divide.
These non-dividing cells die off
leading to memory loss and weakness.
Accumulation of lipofuscin pigment in
the cells also decline cells division.(ii) Loss of hormonal
Activities:
Diabetes mellitus is common in old age
due to less secretion of insulin.
In women menopause occur due to loss of
estrogen and progesterone.
(iii) Cross linkage of protein:
During aging changes in intra cellular
substances take place.
Elastic tissue loss their elasticity
with the passage of time. Aging is an inevitable process, no one
can stop it.
Following can slow down aging process
(1) Balance diet
(2) Regular exercise
(3) No smoking
(4) Proper rest
(5) Relaxed life
ABNORMALITIES IN DEVELOPMENT
Any interference or error in the normal
process of development of an organism is called
abnormal development.
Development is pre planned programme.
In all organisms development occur in
systematic and an accurate way. This embryonic
development is under strict control of
genes.
Any error in normal gene function can
lead to the formation of abnormal body parts.
Such a development is called abnormal
development.
The study of abnormal development is
known as teratology.
Example: common examples are;
Microcephaly: individual born with
abnormal small skull.
Cleft Plate: individual born with an
upper lips folded or hare lip.
Polydactylism: More than fingers in the
hands or feet.
Syndactylism: individual born with
webbing of the fingers.
CAUSES OF ABNORMAL DEVELOPMENT
Abnormal developments occur due to some
faults in the control mechanism.
Mutation:
Any change in the genetic material is
known as mutation.
Mutation changes the appearance and
function of the organisms.
Teratogen:
Environmental factors causing abnormal
development are called Teratogens. Such as UV rays, x
– rays and certain drugs bring
changes in the genes of the developing sperm and egg.
Sex Chromosomes:
Abnormal development is also related to
the presence of defective genes on sex chromosomes.
It leads to colour blindness,
haemophilia etc.
Non – Disjunction:
When a pair of homologous chromosomes
in meiosis fail to separate from one another is called
non-disjunction.This process occur
during gametes formation. When these abnormal gametes unite to form
a
zygote.
Then the individual will have less or
more than the normal number of chromosomes.
Klinefelter’s syndrome: this is due
to one extra sex chromosome in male (xxy)
Turner’s syndrome: When one sex
chromosome is missing in female (Xo)
Down’s syndrome: one extra chromosome
in pair number 21.
Uncontrolled Cell Division:
It leads to a kind of abnormal
development called cancer.
In leukemia there is abnormally
increased WBC’s which leads to abnormal blood function.
Abnormal Gland Functioning:
Malfunctioning of the body glands also
caused abnormal development such as gigantism,
dwarfism, sterility etc.
STRUCTURE OF HEN’S EGG
Shape:
Fully mature egg of a hen is elliptical
in shape.
Egg of hen is broader at one end and
pointed at another.
Size: Hen’s egg is about 5cm in
length and 3 cm in breath.
Colour: Egg is white brownish in
colour.
Hen’s egg contain large amount of
yolk and is called polylecithal egg. This yolk is unevenly
distributed in the egg forming two
poles.
(1) Vegetal Pole – Having greatest
concentration of yolk.
(2) Animal Pole – Having smallest
concentration of yolk.
The egg of hen consists of the
following parts.
(1) Egg Shell: It is the outer most
covering of egg. It is composed of calcium carbonate (CaCo 3 ).
This shell is hard, porous (7000 small
pores) and protective.
(2) Shell Membrane: shell membrane is a
double layered membrane. It lies below the shell and
surrounding albumen. At the broader end
of egg the two membrane separate from each other
forming a cavity called air space. Air
space provide intermediate zone for respiration between
the embryo and porous shell. At the
time of hatching the young one prickles the air space.
(3) Albumen:
It lies under the shell membrane. It is
also known as white of egg. It is secreted by glandular
oviduct of the hen. Albumen contain
about 85% water and 15% various protein.
Albumen consists of two zones:
(i) Water Albumen: thin outer layer or
zone
(ii) Thick albumen: dense inner layer
or zone.
Thick albumen forms two spirally coiled
strands at the sides called chalazae.
Chalazae keeps the ovum in the centre
of albumen.Functions:
Provide nutrition to developing
embryo.
Serve as a water store. Acts as shock
absorber for embryo. Albumen also has bacterial qualities.
(4) Ovum:
The mature ovum is present in the
middle of egg. The ovum is large because it contains large
quantity of yolk.
The yolk has a central mass of white
yolk. This white yolk is surrounded by alternate circular
layers of yellow and white yolk.
On yolk surface a disc of active
cytoplasm and zygote nucleus is present called blastodisc.
A column or pillar of white yolk is
present below he blstodisc called letebra
(5) Vitteline Membrane:
DEVELOPMENT OF CHICK
Fertilization:
The fusion of sperm nucleus with the
egg nucleus is called fertilization. In hen fertilization is
internal and occurs in the oviduct. The
egg is laid 24 hours after fertilization.
Incubation:
Development occurs when the egg is
incubated by the female. Optimum temperature for
development ranges from 36 – 38 o C.
This temperature is obtained from mother body or
incubator. The normal time for hatching
is about 21 days.
Cleavage:
After fertilization the egg undergoes a
series of mitotic division called cleavage.
In hen’s egg cleavage is confined to
blastodisc. This type of cleavage is called discoidal
cleavage. In this process the yolk do
not cleaved. The cleavage furrows start in the clear
cytoplasmic region. The first two
cleavages are vertical while the 3 rd one is horizontal. Thus the
zygote divide into 8 – cells called
blastomers.Morula:
The conversion of zygote into a solid
ball of cells is called morula. In morula the central cells are
smaller called micromeres. While the
outer cells are larger called megamers. Morula lies closely
to yolk.
Blastalation:
The conversion of morula into blastula
is called Blastalation. A hollow cavity appears inside
morula called blastocoels. These
blastocoels are filled with a fluid. The cap of cells above the
blastocoels is known as blastoderm.
After Blastalation the egg is laid and gastrulations start.
Gastrulation:
The process by which the blastula
become three layered embryo is called gastrulation. During
gastrulation the blastoderm divides
into two layers;
(i) Epiblast: The upper layer of cells
is called epiblast. It is the future ectoderm and mesoderm.
(ii) Hypoblast: the lower layer of
cells is called hypoblast. It is the future endoderm.
The central cells of blastoderm is
called area pellucid. The peripheral cells of blastoderm are
called area opaca. The epiblast cells
form a thick central longitudinal band or line called
primitive streak. The upper end of
primitive streak has a swelling called Hensen’s node. In
gastrulation the cells are migrated and
arranged at suitable places in the embryo. These cells take
part in the formation of three layers;
(i) ectoderm (ii) endoderm and (iii) mesoderm.
Organogenesis:
The formation of organs from the three
germinal layers of gastrula is called organogenesis.
Ectoderm:
It gives rise; epidermis, nervous
system, parts of eyes, ear and inner parts of mouth and anus.
Mesoderm:
It forms; Heart, blood vessels,
excretory organs, Skeleton, Notocard.
Endoderm:
It gives rise; Alimentary canal (except
mouth and anus), liver, pancreases, lungs. Hensen’s node
forms a notocard. The cells of ectoderm
become thick to form a band called neural plate. Neural
plate is then converted into neural
tube. At this stage the embryo is called neurula. The upper
part of neural tube forms brain. The
remaining tube forms spinal cord. Mesoderm form compact
masses of cells called somites. Organs
formed from the germinal layers are smaller in size called
organs rudiments.