MUKHLiS TANVEER JAN KURD

Tanveer Kurd Biology concepts.

sweat is evaporated for cooling.

In Cold temperature

The cold receptors send the impulses to hypothalamus to inhibit heat loss mechanisms, and activate the heat conservation mechanisms. This includes constriction of superficial blood vessels and stimulating shivering and non-shivering mechanisms.

Temperature in fever (Pyrexia)

In bacterial and viral infections mainly, leukocytes increase in number. These pathogens and the blood cells produce chemicals called as pyrogens

Pyrogens displace the set point of hypothalamus above the normal point 37° ?.

Importance.

Fever or high temperature helps in stimulating the protective mechanisms against the pathogens.

Animal cells require more critical balance of water and solutes in the body as they cannot survive a net water gain or loss. Water continuously leaves and enters the cell; however, the quantity of the water and the solutes is kept is balance. There are two aproaches in maintaining this balance.

Osmoconformers.

Animal body fluids are kept isotonic to the external environment even for marine saltwater environment. These animals thus do not require actively to adjust their internal osmotic state, so are known as osmoconformers.

Example.

Most marine invertebrates are osmoconformers. Among the vertebrates hagfishes are isotonic with the surrounding sea’s water.

Osmoregulators

The animals whose body fluid concentrations differ noticeably the outside environment actively regulate to

discharge excess water in hypotonic and

excrete salts in hypertonic conditions

Therefore, are called as osmoregulators

Examples.

Cartilaginous fishes, Terrestrial mammals etc. Animals inhabiting different environments have distincet adaptations to regulate osmotic balance, e.g. marine, fresh water and terrestrial environments.

Osmoregulation has enabled the animals and plants to distribute themselves in wide range of habitats.

Osmoregulation in Different Environments

Marine:

Osmoconformers.

Most marine invetebrates are osmoconformers. Among the vertebrates hagfishes are isotonic with the surrounding sea’s water

Osmoregulators.

Most cartilaginous fishes

maintain lower internal salt concentration than that

of sea’s water.

 Their kidneys for osmoregulation excrete slats through gills and

 also possess salt excreting organs such as rectal glands.

These employ active transport mechanism to remove salt against osmotic gradient.

Some fishes such as sharks have relatively low salts in body fluids but have rendered these hypertonic to that of sea’s water by retaining urea in adequate concentration. Because urea in high concetration is damaging so these fishes retain another chemical trimethylamine oxide for protection against urea.

Bonyfishes , ( the descendants of fresh water ancestors )

but later became marine constantly lose water from their hypotonic body fluids to hypertonic environments. These fishes have adapted themselves to drink large amount of seas water and excrete concentrated urine resulting in maximum salt excretion and minimum water loss.

Fresh Water

Fresh water animals are constantly facing the osmotic flooding of body fluids and loss of salts.

Fresh water protozoa ,

Amoeba and Paramecium pump out excess water by structures contractile vacuoles.

Many fresh water animals

including fishes remove excess water by producting large valumes of vary dilute urine. The loss of salts is compensated by prefernce of salt containing food and by active uptake of salts by gills and skin

Terrestrial

The evaporative loss of water leading to dehydration is the major problem for terrestrial life.

Adaptations.

Arthropods and vertebrates have successfully adapted to terrestrial mode of life. These animals have structural, metabolic and behavioral adaptations.

Structural

Terrestrial animals are covered by body surface, which prevents loss of water as

 the waxy exoskeletons of insects and

 Multi-layered dead keratinized skin cells of most terrestrial vertebrates.

 Terrestrial animals produce concentrate urine in their kidneys that reabsorb most filtered water in the process of excretion.

Behavioral.

Drinking and eating moist foods compensate the loss of water.

Metabolic.

Some desert mammals e.g. Kangaroo rat survives without drinking water by feeding on seeds of desert plants containing more carbohydrates, which produce water of metabolism.

 Similarly, salts removed by animals of hypertonic environment are the excretory products for these animals.

 Otherwise, overhelmingly, nitrogenous waste metabolite constitutes the excretory products.

Nitrogenous Wastes.

Productions.

Primarily, in the catabolism of animo acids the amino group (---NH2) is released (deamination) or tranferred to another molecule for removal or resuse.

Excretion.

Amino group not reused for recycling of aminoacids is essentially dissoloved in water and excreted to avoid toxic rise in the plasma. Elevated levels of these wastes can cause convulsions, coma and eventually death.

Mostly excess nitrogen is excreted by animals as ammonia, urea or uric acid.

Lower quantities of nitrogen are excreted in the form of other compunds such as creatinine, creatine or trimethylamine oxide and

in very small quantities as amino acids, purines and pyrimidines.

Metabolism of purine and pyrimidine bases

It produces significant amount of nitrogenous wastes of hypoxanthine, xanthine, uric acid, allantoin, urea and ammonia.

 uric acid, from nucleic acids

 Bilirubin, end products of haemoglobin breakdown and metabolites of various hormones.

 Metabolic wastes also include the toxins produced within the body and ingested into the body such as pesticides, drugs and food additives.

The presence of wastes in the body causes serious hazards, thus are eliminated by excretory system.

Excretory Organs:

Liver and kidneys are the primary structure for eliminating waste prodtubule.

Types of nephron.

The functional units, nephrons, in human kidneys are arranged along two distinct regions, an outer cortex and an inner medulla.

Cortical Nephron.

The nephrons arranged along the cortex are called as cortical nephrons.

Juxtamedullary nephrons

These are arranged along the border of cortex and medulla with their tubular system looping deep in inner medualla are juxtamedullary nephrons.

These juxtamedullary nephrons are specifically instrumental in the production of concentrated urine.

Structure of nephron.

Nephron consists of mainly three parts, renal corpuscle, tubular system and a collecting duct.

Renal Corpuscle.

It consist of Bowman capsule and glomerulus.

In each nephron inner end forms a cup-shaped swelling, called Bowman’s capsule.

 Capsule is around a ball of capillaries called glomerulus.Glomerulus circulates blood through capsule as it arrives through afferent arteriole and leaves the capsule by efferent artoeriole.

 The blood vessel subdivides again into another network of capillaries, the peritubular capillaries.

Tubular system.

 Bowman capsule continues as extensively convoluted proximal tubule,

 loop of Henle and

 the distal tubule,

Collecting duct.

Tubular system empties into collecting tubules. The collecting tubules open into pelvis.

Vasa recta.

The peritubular capillaries intermingle with proximal and distal tubules of the nephron. In juxtamedullary nephrons additional capillaries extend down to from a loop of vessels, vasa recta.

The filtrate from glomerulus passes through these sturctures and is processed ultimately for urine formation.

Urine Formation.

Blood passing through glomerulus is filtered into Bowman’s capsule. It is specifically filtered here, unlike at the other parts of the vessels, because

Glomerulus wall are porous, and

The fraction of the blood pressure reaching here provides the filtration pressure.

Glomerular filtrate.

The filtrate appearing in glomerulus is called as glomerular filtrate, which contains numerous useful substances such as glucose, amino acids, salts etc. in aqueous solution.

Reabsorption:

All the useful constituents of the glomerular filtrate are reabsorbed in proximal tubules and when filtrate leaves proximal tubules, it mostly contains nitrogenous wastes

Secretion

The tubular epithelium also secretes substances into the lumen, this secretion is very selective and is mainly of hydrogen ions to balance pH value of the filtrate passing through the tubule.

matching donor’s kidney is transplanted.

Kidney Transplant:

Dialysis may be used as a temporary measure. In high degree renal failure also called as uremia or end-stage renal disease, the dialysis cannot be done hence thus the surgical transplantation of a matching donor kidney is the only option left for as the permanent treatment.

THERMOREGULATION

Control system operate in organisms to cope with environmental stresses including temperature extremes. Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different.

regulation and these are of structural, physiological and behavioral nature.

Structural Adaptions

These may be long term changes in sub dermal fatty layer insulation and pelage.

The presence of sweat glands and lungs modified for panting.

Physiological Adaptions:

These regulate blood flow to the skin specifically greater blood flow in warmth to dissipate heart and lower in colds to economize heart loss,  Also the activation of certain muscles causes plumage fluffing.  Similarly activation of sweat glands is done for evaporative cooling.

Behavioral Adaptations

These include moving of the animal an environment where heat exchange between these is minimal e.g.

Ground squirrels move to burrows in midday heat and

Lizards bask in sun to gain heat.

Animals also control the amount of surface area available for heart exchange by adjusting their postures.

Introduction.

Every species of organisms can reproduce new individuals of that species. In organisms, methods of reproduction are varied and some are quite complex. In one respect, reproduction differs from all other functions of animals- it is not necessary for the well-being of the individual.

Although reproduction has nothing to do with the survival of the individual, it is very important to the survival of a species or a population.

Reproduction is the mechanism that produces new generations and maintains a species.

Types of reproduction.

Reproduction is of two types, asexual reproduction and s****l reproduction.

Asexual reproduction

It requires only single parental organisms which gives rise to offspring by mitotic cell division, during which the total chromosomes content of the cell is exactly replicated and passed on to daughter cells, so that the offspring are genetically identical to the parent.

Methods of asexual reproduction

vegetative propagation, artificial propagation, parthenogenesis and apomixis etc.

Significance.

Rapid Type of Reproduction. In asexual reproduction, although increase in number of genetically alike individuals from a parent is very rapid Less adaptive. This is not an adaptive method and may at some stage jeopardize the survival of a species.

Beneficial for Human.

• Man has favoured this type of reproduction for his own needs, commonly in plants but now tissue culturing in plant and cloning in animals are being adopted for producing organisms of valuable characteristics, without a change in their genetic makeup.

Limitations

Cloning has been practiced successfully but its disadvantages like rapid aging and low resistance to environmental stress and diseases limitations for commercial ventures. Also it is still not being accepted socially and morally in general.are still the

Sexual reproduction

It usually involves two parents. A fertilized egg is produced through the union of meiotically produced specialized s*x cells (egg and sperm) from each parent. Meiosis or reduction division gives rise to gametes (gametogenesis) in which not only the chromosome number is halved haploid) but reshuffling of genes leads to recombination of genes.

Significance

This not only maintains the chromosome number in a species but also produces genetic variations, an important factor in the survival and adaptation of species or a population

In plants,

if there is alternation of generations namely a diploid sporophyte and a haploid gametophyte, meiosis occurs during spore formation (sporogenesis).

Differentiate between s****l and Asexual Reproduction.

REPRODUCTION IN PLANTS

Plants both s****l and asexual reproduction are found.

In asexual reproduction layering, grafting, budding etc. are the artificial modes.

In s****l reproductionplants have diplohaplontic life cycle with alternating diploid sporophyte and haploid gametophyte generations. If the two generations are vegetatively similar, such alternation of and generations is referred to as isomorphic, and if they are dissimilar it is called heteromorphic.

Dominancy of Spermatophytes.

modification of flower and inflorescence for pollination,

involving gamete transfer by pollen tubes,

food storage for developing embryo, protection by seed coats and

Dispersal with the help of fruit formation (angiosperms).

Seeds are capable of enduring unfavourable conditions in dormant form (seed dormancy) and as soon as, conditions become favourable for establishing the seedling, it germinates. (Importance Of Seed Formation?)

Importance of Pollen Tube.

Evolution of pollen tube is an important step in land adaptation by the spermatophytes. Pollen tube acts as vehicle for male gametes for their safe transport to female gamete in ovule in hostile land environment. Evolution of pollen tube is parallel to the evolution of seed and is a tool of success for seed plants.

Parthenocarpy

Definition.

In some cases fruit development proceeds without fertilization and thus no seed formation takes place e.g. banana, pineapples and some varieties of oranges and grapes. Such development is called parthenocarpy.

Cause.

It is due to hormonal imbalance; usually high auxin levels occur in these ovaries. Parthenocarpy is sometime artificially induced for commercial purposes, by adding auxins as in tomato, peppers etc.

Seed Dormancy

Definition.

It is the special condition of rest, which enables an embryo to survive the long periods of unfavourable environmental conditions, such as water scarcity or low temperature. During this period of rest the embryo ceases or limits growth.

Significance.

This a is of great survival importance to the plant in that it prevents the dormant seed from germinating in response to conditions such as a warm spell in winter, which, although apparently favourable, are only temporary.

Germination

Germination or resumption of normal growth by a dormant embryo requires certain, very precise combinations of environmental cues, to avoid any accidental stimulus which may prove fatal later on.

Fruit set and Fruit ripening

Fruit setting.

It is the process of retention of the ovary, which becomes the fruit after fertilization.

Role of Auxin.

Germinating pollen grain is not only an important structure for safe transfer of gametes and insurance for fertilization but also a rich source of auxins as well as commonly stimulating the tissues of the style and ovary to produce more auxin. This auxin is necessary for fruit setting. Without it abscission of flowers normally occurs, leading to low fruit yields.

Fruit Development.

After fertilization, the ovary and the ripe seeds continue to produces auxins which stimulate fruit development. Developing seeds are not only a rich source of auxins and gibberellins, but also of Cytokinins. These growth substances are mainly associated with development of the embryo and accumulation of food reserves in the seed and some times in the pericarp (fruit wall).

Fruit Ripening.

Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green, and softer as it ripens.There are two types of mechanism for fruit ripening.

Climacteric Fruits

In these fruits, ripening is often accompanied by a burst of respiratory activity called the climacteric. This is associated with ethane production, which helps in ripening of the fruit. Mangoes, Apples, bananas, melons, apricots, tomatoes (among others) are climacteric fruit.

Non. Climacteric Fruits

They ripen without ethylene and respiration bursts. Citrus fruits like orange, grapes, strawberry are example.

Photoperiodism

Definition

The phenomenon in which light exerts its influence on living organisms is through variations in day length called photoperiod. In plants, photoperiod and temperature affect flowering, fruit and seed production, bud and seed dormancy, leaf fall and germination.Photoperiod affects flowering, when shoot meristems start producing floral buds instead of leaves and lateral buds.

Studied by.

Effect of Photoperiodism was first studied in 1920 by Garner and Allard. They studied that tobacco plant flowers only after exposure to a series of short days. Tobacco plant naturally flowers under same conditions, in autumn, but flowering could be induced by conditions artificially to short days exposing.

Classification of Plants on the basis of Photoperiodism

With further studies they were able classify flowering plants into

Short day plants which requires short days for flowering.

Long-day plants, which require long days for flowering and

Day-neutral plants flower without being influenced by photoperiod

Modified Classification.

Later on, further studies indicated that it is really the length of the dark period which is critical. Thus

Short day plants are really long-night plants. If they are grown short days, but the long night is interrupted by a short light period, flowering prevented.

Long-day plants will flower in short days if the long night period interrupted.

Effect of Quality of Light.

Further experimentation also revealed that quantity of light is also influenced by the quality of light. Cocklebur, a short day plant, will not flower if its long night is interrupted but experiments revealed that red light was effective in preventing flowering and far-red light reversed the effect of red light

Last Light Effect.

It was also demonstrated that the last light treatment always determines te response. This response to light intensity and quality led to the discovery of blue light sensitive protein pigments, the phytochromes.

Role of Phytochromes.

Phytochromes exist in two forms i.e. P 660 and P 730.

P 660 quiescent form

It absorbs red light at a wave length of 660 nm and is converted to active P 730.In nature this conversion takes place in dark.

It promotes flowering in short day plants.

It inhibits flowering in long day plants.

P 730 (Active form)

It absorbs far red light at 730 nm and is converted to P 660. In nature, the P 660 to P 730 conversion takes place in day light an P 730 to P 660 conversion occurs in the dark.

Interconversion of P730 and P660 ( Clock for Plants)

Thus during the day a plant has P 730 phytochromes while during the night it contains more phytochromes in the form of P 660. The presence of either form provides the plants with a means of detecting whether it is in a light of dark environment. The rate at which P730 is converted to P 660 provides the plant with a “clock” for measuring the duration of darkness.

Hypothesis based on Phytochromes Interconversion.

It has been found that red light inhibits flowering in the short day plants but promotes flowering in long day plants, under conditions during which flowering normally takes place. This observation led to hypothesize that “The P730-P660 interconversion might be the plant time – regulator for flowering.”According to this hypothesis,

P 730, converted from P 660 by the absorption of far-red light, would inhibit flowering in short day plants but promotes flowering in long day plants.

Because P 730 accumulates in the day and diminishes at night, short day plants could flower only if the night were long enough, during which a great amount of P730 would not be completely inactivated, so that enough P 730 would remain at the end of the night to inhibit flowering.

Established Phenomenon.

But now it is generally agreed that the time measuring phenomenon of flowering is not totally controlled by the interconversion of P 660 to P 730. Other factors, like presence or absence of light and length of dark or light period also play an important role in flowering. Phytochromes seem to be responsible for the detection of either light or darkness.

Role of Hormones.

The biological clock once stimulated causes production of florigen hormone in leaves, which travels through phloem to the floral buds, initiating flowering.

Vernalisation

Definition.

Biennials and perennial plants are stimulated to flower by exposure to low temperature. This is called Vernalisation.

Stimulus Reception.

The low, temperature stimulus is received the shoot apex of a mature stem or embryo of the seed but not by the leaves as Photoperiodism.

Requirement For Plants.

For some plants, vernalisation is an absolute requirement or in some cases it simply assists in inducing flowering.

Conditions.

The duration of low temperature (chilling) treatment required varies from four days to three months. Temperature around 4^o C is found to be very effective.

Vernaline Release.

It stimulates at production of “vernalin” hormone which induces Vernalisation. It is now believed that vernalin is nothing special but actually is gibberellin.

Significance.

Photoperiodism and vernalisation serve to synchronise the reproductive behaviour of plants with their environment, ensuring reproduction at favourable times of year. They also ensure that members of the same species flower at the same time, encouraging cross pollination for genetic variability.

REPRODUCTION IN ANIMALS

Animals like plants also reproduce both asexually as well as sexually. But asexual reproduction is less common in animals as compared to plants. Binary fission, multiple fission (animal like protoctists) budding (Hydra) parthenogenesis, tissue culturing, cloning and identical twins are the common asexual methods of reproduction.

Parthenogenesis.

Parthenogenesis is defined as the development of an egg without fertilization, ants, bees and wasps are good examples. There are two types of parthenogenesis.

Haploid Parthenogenesis.

It is development of an haploid egg without fertilization into complete animals.

Example

In the honeybees, males (or drones) develop from unfertilized eggs. The queen bee, though carrying male gametes from male, has the ability to lay eggs that have not been fertilized. The sperms she receives from drone bee are sorted in a pouch closed off by a valve. The eggs may be fertilized or may not be fertilized from the stored sperms. The haploid egg develop into haploid offspring, it is called haploid parthenogenesis.

In honey bee males are haploid and produce sperms by mitosis.

Diploid parthenogenesis.

It is development of an haploid egg without fertilization into complete

Example.

In some cases e.g. in aphids, diploid parthenogenesis may occur, in which the which the egg production cells of the female undergo a modified form of meiosis involving total non-disjunction of the chromosomes, the retain the diploid umber of chromosomes. Egg (diploid) develops into young females.

Significance.

Parthenogenesis has the advantage of accelerating the normal reproductive rate.

Apomixes in Plants.

In flowering plants, one form of parthenogenesis is called apomixis. In this a diploid cell of the ovule, either from the nuccellus or megaspore, develops into a functional embryo in the absence of a male gamete. The rest of the ovule develops into the seed and the ovary into the fruit.

Tissue Culture Technique.

Definition.

Development of plant from tissue or cell by growing in liquid medium is called as tissue culture technique.

Procedure.

In tissue culturing technique in plants, cambium tissue excised from plants can be stimulated by the addition of nutrients, Cytokinins, and IAA (indole acetic acid). These cells show continued growth and differentiate into a new plant, genetically identical o their parents.Tissue culture is now widely used for the rapid propagation of desired varieties clones.

Cloning

Definition.

. Production of genetically identical copies of an organism or cell by asexual reproduction is called as cloning.

Procedure.

In animals and especially among vertebrates, a nucleus from the somatic cell is removed and introduced into an egg cell, whose own nucleus has been destroyed by ultra violet radiation. The egg with transplanted diploid somatic cell nucleus develops into an organism, genetically identical to the parent who has contributed the nucleus.

Importance of Cloning.

The cloning of desirable animals such as prize bulls; race horses etc. might be as useful as cloning of useful varieties of plants.

The use of cloned cells allows the quantitative study of the action of hormones, drugs and antibodies to be made on cells.

Such a technique is a useful substitute for investigating the effect of drugs, cosmetics and pharmaceutical products on animal cells without exposing laboratory animals to these chemicals.

Limitations.

Cloning has the advantage that all the offspring behave similarly, but should an environmental hazard develop (like an outbreak of a disease), non-resistant strains are present to lessen the impact.

Also the degree to which environment influences clone development is not fully known and

Any cloned cell would have to go through all the phases of development once again including embryo, fetus, baby and child hood (in case of human beings).

Human Cloning. However, the application of the technique to humans would be open to serious moral questions. Theoretically any number of genetically identical copies of the same man or woman might be made.

Introduction.

Types of reproduction.

Methods of asexual reproduction Significance.

Rapid Type of Reproduction.

Development

The progressive changes which are undergone before an organism acquires its adult form constitute embryonic development. Development is also a programmed series of stages from a simpler to more complex form.

Growth

Growth is the permanent and irreversible increase in size that occur as an organism mature. As development proceeds, all sorts of the changes take place. The most obvious change is growth.

GROWTH AND DEVELOPMENT IN PLANTS

In plants growth and development involve cell division, elongation and differentiation of cells into tissues and then organs.

Growth is an irreversible increase in size while

Development is a programmed series of stages from a simpler to more complex form. As development proceeds, cellular differentiation of structure and function takes place.

Open GrowthAs plant has growth pattern called open growth. Throughout life, the plant adds new organs such as branches, leaves and roots, enlarging from the trip of roots and shoot

Rate of growthis not uniform throughout the plant body. At the beginning, the growth is slow, but gradually it becomes rapid, attains a maximum, and then gradually slows down.

In vascular plants,growth occurs through the activity of meristems. Meristems are young tissues or group of cells that retain the potential to divide. In lower plants, the entire plant body is capable of growing,

In higher plants, the entire plant body is not capable of growing but growth is limited to certain regions known as growing points. These growing points consist of groups of cells which are capable of division, these growing points are called meristems.

Kamiabi Qismat se nai Mehnat se Milti ha.

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Try again and again than you will be success.

Failure is key of Success.

Naakami Kamiabi ki chabi ha.

DEVELOPMENT IN PLANTS

In plants growth and development involve cell division, elongation and differentiation of cells into tissues and then organs.

Growth is an irreversible increase in size while

Development is a programmed series of stages from a simpler to more complex form. As development proceeds, cellular differentiation of structure and function takes place.

Open GrowthAs plant has growth pattern called open growth. Throughout life, the plant adds new organs such as branches, leaves and roots, enlarging from the trip of roots and shoot

Rate of growthis not uniform throughout the plant body. At the beginning, the growth is slow, but gradually it becomes rapid, attains a maximum, and then gradually slows down.

In vascular plants,growth occurs through the activity of meristems. Meristems are young tissues or group of cells that retain the potential to divide. In lower plants, the entire plant body is capable of growing,

In higher plants, the entire plant body is not capable of growing but growth is limited to certain regions known as growing points. These growing points consist of groups of cells which are capable of division, these growing points are called meristems.

GROWTH AND DEVELOPMENT IN PLANTS

In plants growth and development involve cell division, elongation and differentiation of cells into tissues and then organs.

Growth is an irreversible increase in size while

Development is a programmed series of stages from a simpler to more complex form. As development proceeds, cellular differentiation of structure and function takes place.

Open GrowthAs plant has growth pattern called open growth. Throughout life, the plant adds new organs such as branches, leaves and roots, enlarging from the trip of roots and shoot

Rate of growthis not uniform throughout the plant body. At the beginning, the growth is slow, but gradually it becomes rapid, attains a maximum, and then gradually slows down.

In vascular plants,growth occurs through the activity of meristems. Meristems are young tissues or group of cells that retain the potential to divide. In lower plants, the entire plant body is capable of growing,

In higher plants, the entire plant body is not capable of growing but growth is limited to certain regions known as growing points. These growing points consist of groups of cells which are capable of division, these growing points are called meristems.

TYPES OF MERISTEMS

Apical Meristems

The apical meristems are found at the tips of roots and shoot and are primarily concerned with the extension of plant body. These perpetual growth zones found at the apices of roots and stems.

Importance

They are responsible for increase in the number of cells at the tips of roots and stem, so they play important role in primary growth

Intercalary Meristems

These are the parts of apical meristem which get separated from apex by permanent tissues. They are situated at the bases of internodes in many plants

Importance They play important role in the production of leaves and flower. These of temporary nature.

ypes of Growth.

Determinate Growth

Certain growths are determinate i.e. they grow to certain size and then stop e.g. leaves, flowers and fruits; while others

Indeterminate Growth

Some growth patterns are indeterminate i.e. they grow by meristems that continually replenish themselves, remaining youthful e.g. vegetative root and stem.

Primary Growth:

Primary tissue is added by the apical meristem and leads to increase in length of plants.

Secondary Growth

Secondary tissue is added by the intercalary or vascular cambium leading to increase in thickness.

Phases of Growth.

Growth of multicellular plant is divided into four phases, cell division, elongation, maturation and differentiation.

Cell Division

During cell division, the number of cells increase by mitosis. It occurs at the tip of root and shoot where

Cells are small, have spherical nuclei laying in the center of cytoplasm, which is non-vacuolated.

As a result of cell division, each daughter cell proceeds to enlarge.

Synthesis of cytoplasm and cell wall material also takes place in this zone.

Cell Elongation.

During elongation the cell volume increase up to 150 fold due to uptake of water.

Plasticity of the cell wall increases and wall pressure is reduced.

Synthesis of new cytoplasm and cell wall material proceeds on.

Cell Maturation

During maturation, the final size of a given type of a cell is attained.

When the cell enlargement ceases, the process of differentiation starts

Cell Differentiation

During this growth phase the walls of cells become thicker, the walls of many kinds of cells and tissues become pitted; thickening appear on the walls of xylem vessels, cells of various tissues differ in spatial dimensions and may new structural features develop.

Tanveer Kurd.

Professor Bilil Kurd Behramshahi Mastung.

Jalal Kurd Behramshahi Mastung.

Abdul Raziq Kurd Behramshahi Mastung.

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