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FSc Notes Biology Part 2 Chapter 19 Growth and Development Notes

FSc Notes Biology Part 2 Chapter 19 Growth and Development Notes


Growth is a permanent and irreversible increase in size that occurs as an organism mature.


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
  1. 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.
  2. Intercalary Meristems: They are present at the base of internodes in many plants. They also increase the length of plant.
  3. 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:
  1. 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.
  2. 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.
  3. 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:
  1. External factors
  2. Internal factors
External Factors:

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 degree Celsius. Because all hormones and enzymes work best at this temperature. At very high temperature (40 – 45 degree Celsius) growth stops and the plants dies.

Most plants grow in light while some grow in shade. Light affect growth in three ways:
  1. Light Intensity: Increases cell division and chlorophyll formation.
  2. Light Quality: Red light increases cell elongation. Ultra violet light also reduces cell elongation. In complete darkness plant become pale and show stunted growth.
  3. Light Duration: Duration of light effects the growth of vegetative and reproductive organs. It also plays a role in inducing or suppressing flowering.
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.

Plants require sixteen essential element for their normal growth. Their deficiency may cause certain abnormal conditions.

Internal Factors:

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.

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.

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:
  1. 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.
  2. 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.

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
  1. Stomach cells produces enzymes which help in digestion.
  2. 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 are removed, a new one is regenerate.


(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.

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.

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.


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:
  1. Hair become colorless (white) Poor vision, weak memory
  2. Hearing impairment, Loss of reproductive capacity.
  3. Dryness and wrinkling (folding) of skin, arthritis.
  4. Decreased body immunity.

Causes of Aging:
The exact process of aging is still unknown. But the following two causes are very important:
  1. 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.
  2. 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:

  1. 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 lipo fusion pigment in the cells also decline cells division.
  2. 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.
  3. 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:
  1. Microcephaly: individual born with abnormal small skull.
  2. Cleft Plate: individual born with an upper lips folded or hare lip.
  3. Polydactylism: More than fingers in the hands or feet.
  4. Syndactylism: individual born with webbing of the fingers.

Causes of Abnormal Development

Abnormal developments occur due to some faults in the control mechanism.
  1. Mutation: Any change in the genetic material is known as mutation. Mutation changes the appearance and function of the organisms.
  2. 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.
  3. Sex Chromosomes: Abnormal development is also related to the presence of defective genes on sex chromosomes. It leads to colour blindness, haemophilia etc.
  4. 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.
  5. Klinefelter's syndrome: This is due to one extra sex chromosome in male (xxy)
  6. Turner’s syndrome: When one sex chromosome is missing in female (Xo)
  7. Down’s syndrome: one extra chromosome in pair number 21.
  8. 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.
  9. 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.

Egg Shell: 
It is the outer most covering of egg. It is composed of calcium carbonate (CaCO3). This shell is hard, porous (7000 small pores) and protective.

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.

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:
  1. Water Albumen: thin outer layer or zone
  2. 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 center of albumen.
Functions: Provide nutrition to developing embryo. Serve as a water store. Acts as shock absorber for embryo. Albumen also has bacterial qualities.

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 blastodisc called letebra

Vitteline Membrane:

Development of Chick

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.

Development occurs when the egg is incubated by the female. Optimum temperature for development ranges from 36 – 38 degree Celsius. This temperature is obtained from mother body or incubator. The normal time for hatching is about 21 days.

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 3rd one is horizontal. Thus the zygote divide into 8 – cells called blastomers.

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.

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.

The process by which the blastula become three layered embryo is called gastrulation. During gastrulation the blastoderm divides into two layers:
Epiblast: The upper layer of cells is called epiblast. It is the future ectoderm and mesoderm.
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.

The formation of organs from the three germinal layers of gastrula is called organogenesis.

It gives rise; epidermis, nervous system, parts of eyes, ear and inner parts of mouth and anus.

It forms Heart, blood vessels, excretory organs, Skeleton, notochord.

It gives rise" Alimentary canal (except mouth and anus), liver, pancreases, lungs. Hensen’s node forms a notochord. 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.

Written by: Asad Hussain