Explain about Growth in Plants

Definition of Growth - Growth is a permanent increase in length or volume of an organism that brought upon by an increase in its dimensions due to synthesis of new protoplasmic material.

Growth in multicellular organisms occurs by both increase in the number of cells and it causes Irreversible change in the external structure which continuous throughout the life.

As we all know growth is very essential feature of all living organisms and this is a physiological process which is affected by different external and internal factors. Growth helps a seedling to grow into a tree, an embryo to a matured man. By this physiological process it is manufactured by permanent increase in length or volume and is normally possible.

Definition of Differentiation - Differentiation is the process of formation of specialized cells from the existing undifferentiated cells during the initial stages of development and discount as differentiation.

Growth in higher organisms is mediated by two main processes those are-Cell elongation and cell multiplication. Cells in such cases during interface and is followed by multiplication of cell. Then the cell is aggregate and is formed by repeated division and tissue is formed. Which is again aggregate together to form organs and different organs are associated and involved in specific functions to form different systems in the body. Different types of systems are observed in the organisms body switch together constitute a plant or animal body. This entire process cannot be explained by cell growth and division as it involves growth differentiation morphogenesis and development and latter this is why organisms enters the functional state of life.

Types of growth according to region and the area of  growth can be classified in various ways of plants and animals-

1. Growth on the basis of nature-this type of growth can be classified as vegetative growth, reproductive growth and regenerative growth.

* Vegetative or somatic growth - This type of growth occurs due to the division of somatic cells and is called vegetative growth as life starts with the formation of zygote that undergoes repeated mitotic division to form a multicellular embryo that develop into an adult plant or animal individual.

* Reproductive growth - After the completion of vegetative growth organisms develop the reproductive organs which include the development of flowers in angiospermic plant, development of gonads in higher animals and this type of growth is called reproductive growth which is useful for the perpetuation of an organism.

* Regenerative growth - Regenerative growth is a type of growth which are outside in plants and animals during the repairing or lost or damaged of part.

2. Growth on the basis of development of organs - basis of growth on the organs it can be divided into isometric or allometric by nature.

Isometric growth- this type of growth is uniform in all respect and the development is professional for all sides so there is no change in the external structure of the organisms. Fish is the example of this type of organism.

Allometric Growth - This type of growth is not uniform in all respect as a some of the organs developed at a later stages like the development of reproductive organs in the later stage in case of mammals.

3. Growth on the basis of multiplication of cells in this type of growth it can be classified into auxetic, multiplicative and accretionary according to its nature.

Auxetic growth - This type of growth takes place mostly by increase in the volume of cytoplasm but it does not increase the number of cells. This is observed in case of the growth of nematodes and tunicates.

Multiplicative growth - This type of growth takes place  by the multiplication of cells  as if the newborn baby has only 2 trillion cells which increases to 80 trillion cells in adult individuals.

Accretionary growth - This type of growth are observed in the post embryonic stage of higher animals where the cells do not divide but only the totipotent cells of mesenchyme and chondrocyte divide to cause the growth in individual.

4. Growth on the basis of duration - This type of growth can be either unlimited, orlimited according to the duration of the growth-

* Unlimited growth - in this type of growth the process continuous all through the life cycle and it is called continuous growth or positive growth which is observed in perineal Woody plants and some fishes.

* Limited growth- growth in this case is limited for a particular period in the life cycle of the organism and mainly observed in Hibiscus plants ;and is called discontinuous growth as it is seen in insects where maximum growth is observed during  metamorphosis. As this growth is observed during senescence, degrowth, thus it is also called negative growth.

5. Growth on the basis of tissue types - This type of growth are commonly observed in plants which includes apical intercalary and Lateral.

Apical growth - Growth of the shoot apex of the root Apex is called typical or primary growth which is observed due to epical meristems.

Intercalary growth - Growth of the shoot apex also take place due to the division of intercalary meristem and are also called intercalary growth.

Lateral growth - Lateral growth refer to the secondary growth which takes place from the cambium and that increase the thickness of a plant which is commonly observed in woody angiospermic plant.

Phases of growth - Phases of growth can be divided into three distinct phases-

1. Phases of cell division - In phase of cell division cells divide mitotically that helps in the growth of a tissue and is also called hyperplasia that is commonly observed in the meristematic regions of plants and actively growing regions of animals.

2. Phase of cell elongation - Cells originating from cell division is observed to be increase in the amount of Protoplasm and followed by its enlargement in size known as hypertrophy.

3. Phase of cell maturation - Cell differentiation is the enlargement of cells that get modified and helps them to perform the diverse functions of a multicellular organisms and once the cell changes its shape it has​ a permanent change.

Grand period of growth-

Grand period of growth means the internal period in which the organisms grows and it included different phases like zero phase, lag phase, log phase, reducing phase and stationary phase.

Zero phase - It is the short preparatory phase just after the formation of zygote when the organisms does not grow.

Lag phase - This is the short preparatory phase of growth in the cells only show changes in dimension but very little  division is observed. As this time to the growth rate is very slow.

Log phase - This is the actual green face when the growth rate is very fast due to maximum division of cells and the savings also known as exponential face. This phasevarries from one organism to other.

Reducing phase - After the log phase when there is very fast rate of division then it comes the rate which becomes gradually reduced in various organisms and this phase is known as reducing phase.

Stationary phase - Stationary phase is the last phase of growth when the growth rate become more or less constant and this phase may continues till the end of life cycle in plants but in animals it may stop.

Factors affecting growth-

Factors affecting growth in living organisms can be broadly classified into two major headings called the external factors and the internal factors which are described below-

A. External factors - External factors are generally environmental factors , a biotic factors which influence the growth of plant by affecting different physiological activities in plants. These are-

Temperature - Temperature is the external factors which controls the metabolic activity of a living cell and varies from organism to organism.

Light - Light is a factor that influence the growth of plants because it controls the process of photosynthesis. In high intensity there any wheat plant growth because it damages photosynthetic machinery and the duration of flight mainly controls the reproductive growth or flowering there may be three types of plants according to the disposal of light hair short day plants long day plants and day neutral plants. The source of light also induced the phototropic movement for the branch and leaves are positive phototropic and roots are negative phototrophic.

Generally plants that grow in unlighted place are called photophillic plants. Examples of this type of plants are – sunflower. The Shade loving plants are called photophobic plants and the plants which like to grow both in enlighted condition and also in dark conditions are called photo neutral plants. Examples of photophobic plants are – moss, fern etc.

Oxygen - This gas causes respiration and release energy which is required for metabolic activity of a living cell and this influence the growth.

Carbon dioxide - Carbon dioxide promotes photosynthesis in plant and the amount of food within cell increases due to this process directly to give rise in the rate of growth but in some cases high concentration of carbon dioxide mainly ​returded growth in plants.

Soil conditions - Texture of soil availability of nutrients soil PH and the soil water really influence the plant growth.

Wound - rate of cell division increases at the regions of wounds in a plant which can be promoted regenerative growth.

Gravitational force - Gravitational force may induce the growth of the underground parts of the plants specially the roots.

B. Internal factors - Internal factors that affect growth of plants are mainly by their cell activities ,metabolism .

Nutrition - Nutrition is a physiological process which helps the plants to accumulate materials in their Protoplasm and that causes cell to grow and divide which give rise of overall growth in plants.

Hormone - Hormones are the most important factors that control growth in living organisms mainly observed in barely cytokinin that promotes cell elongation and cell division as they act as growth regulators.

Enzymes - There are different growth promoting enzymes and they work by increase the metabolic activities.

Vitamins - Portland describes that vitamins are only required as trace amount but in animals vitamin D directly promotes growth while Vitamin B complex influences growth by promoting metabolism.

Water - Entry of water in plants within the cell increases stability and thereby increase plant growth.

Chromosomal inheritance - Individual characteristics including growth and cell division are controlled by genes and chromosomes as the inheritance of these characters by the four genius from the parents controls their rate of growth this is transmitted to the subsequent generations and the established the trend of growth.

Growth Curve -

Definition of growth curve - The growth curve can we get by the plotting of rate of growth against time.

Types of growth curve - S growth curve illustrate the differential rate of growth in different organisms for these the growth card may vary from one organism to other there are mainly two types of growth curve that is found. They are-

Sigmoid growth curve - Sigmoid growth curve are the most common growth curve which are commonly observed in plants and also in some animals. In this graph it is almost is shaped where initially the growth rate is very slow during the leg phase then the growth rate picks up during logphase , it is then gradually reduced and ultimately in stationary phase it is parallel to the base line.

Parabolic growth curve - This type of curve is observed mainly in bacteria and also in some animals. Here five phases are observed lag phase, log phase, reducing phase, short plateau, reducing phase two and zero phase. Due to this phases this curve appears Bell shaped or parabolic curve.

Growth in Plants - The growth process which is a variable Processing Unicellular organisms and growth are primarily occurs by increasing the volume of cells.

In case of multicellular organisms growth occurs both due to increase in the number of cells and Irreversible changes that occurs in the external structure throughout the life.

Growth cycle -

Definition of growth cycle- group cycle is a cyclical events which occurred sequential in the life cycle of a plant which included two phases that are vegetative phase and reproductive phase.

Vegetative phase - Vegetative phase stars with the formation of zygote that divides mitoticallyto form the embryo and remains in dormant condition for sometime then again it starts growing after the germination of seed. Vegetative phase starts with the formation of zygote that divides my critical uniform the in and remains in government condition for sometime then Indian starts growing after the germination of seed. This process can be triggered by a multiple steps of plant growth regulators auxin, gibberellin and cytokinin and the growth of plants occurs rapidly to form the seedling and soon the plants grows to its normal height.

Reproductive phase - After the vegetative faces completed the plant passes on creates reproductive phase which is initiated by gibberellin and during this time the plants develop flowers which produce male and female reproductive units. Due to the fusion of the male reproductive cell and female reproductive cell zygote is formed and the cycle is continue.

Site of growth - in case of unicellular plant there is no specific site of growth as the cell here only grows by volume but in higher plants growth primarily occurs at the shoot tip by the help of apical meristem. In case of shoot apical growth is also helped by intercalary Meristem. Secondary growth occurs in transverse plane with the help of Lateral Meristem for cambium.

Types of growth - Growth in plants are divided mainly in two types primary growth and secondary growth.

Primary growth - In this type of growth it is initiated by the primary meristematic tissue and can be of two types typical growth and adventitious growth.

* Apical growth - This growth brought about by the British connective tissue of shoot Apex or root Apex and it helps the shoot and root to grow. These tissues are of 3 types protoderm that form the epidermis procambium which found the muscular strength and ground meristematic tissue that form the ground tissue.

* Adventitious Growth - This growth of the primary tissue please send one characteristic feature and foliar buds of bryophyllum or root buds of sweet potato are example of this type of growth.

Secondary growth - Secondary growth takes place after the primary growth is complete and this occurred by the help of cambium. This can be of two types intraxylary growth and extraxylary growth.

Intraxylary growth - This growth takes place within the vascular tissue and due to the joining of fascicular and interfascicular cambium it forms the annual rings by that cutting of secondary xylem towards the centre and secondary phloem towards the periphery.

Extraxylary growth - This growth takes place outside the vascular region and it occurs by the modification of epidermal tissue that form the periderm   and is consist of phelloderm,  phellogen or cork cambium and phellem or thescale bark.

Measurement of Growth in Plants -

Growth of root differential growth of root can be measured by Space Marker Wheel method. The germinating radical he is not that fast at equal intervals with waterproof by space marker wheel and these are placed on wet cotton packed bulb of a thistle funnel where the stem of the funnel is dipped in a bottle that contains water. After 24 hours to 48 hours the marking are observed to be separated unequally which indicates the differential growth of root.

Growth of stem - Fruit of steam can also be measured by the process called horizontal microscope and are also by an instrument called Arc indicator.

Horizontal microscope - A specific portion of the shoot Apex is marked with waterproof 8 and observed that make a horizontal microscope slides on a graduated article stand. After the initial observation the same marking is observed after 48 hours and then the stand must be brought to a new height for this experiment. The difference in the initial and final reading gives the actual growth of the plant part.

Arc indicator - Arc indicator is also known as of auxanometer and this is an ideal instrument to measure the growth of shoot Apex. This instrument is consist of graduated Steel quadrant which is attached to a small heel corresponding to the centre of the circle. A long pointer is attached towards the centre of the field and this is free to move up and down on the graduated arc that placed on the quadrant. Which division of the Earth is corresponding to the linear measurement. A potted plant is first placed below the wheel and the shoot Apex is tied with a thread where as the other end is tied to a small width and the trade is placed on the pulley at the centre of the wheel. This increase in height of the show causes the downward movement of the weight and the pulley moves download as the pointer is also attached to the pulley it also moves downward over the graduated arc. As a result the reading is obtained and it gives the measurement of the  plant growth. Suppose the diameter of the pulley is 4 inch and the length of the pointer is 20 inches then the growth is said to be magnified by 10 times.

Difference between the growth in plants and animals -

* In case of plants growth takes place throughout the life and it is indefinite or in determinant but in animals growth occurs after certain stage of life and it is definite .

* In animal secondary growth is absent but in higher plants secondary growth is observed after the primary growth.

* In plants growth takes place by the tissue in some restricted area instead of whole body but in animals growth occurs throughout the body.

* In plants growth are not well organised but in animals it is well organised.

* In animals growth occurs equally in all parts of the body but in plants growth does not take place equally in all parts of the body.

* In plants annual rings are observed due to the secondary growth by which the age of plant can be determined but it is absent in animal.

* Implant meristematic tissue in growing regions growth take place but in animals growth occurs in all tissues and all regions.

Eleventh Grade

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