BIOLOGY IN HUMAN WELFARE

The world’s human population, which was only one billion during
1850, had reached 6.1 billion around year 2000. This dramatic increase in population, otherwise called ‘population explosion’ has created its impact not only on the environment but also on food production.

Half of this 6.1 billion people live in poverty and one fifth of this
population suffer due to malnutrition. Increase in population, unplanned industrialization and migration towards cities and urban areas has resulted in the degradation of the environment. The present agricultural practices have polluted cultivable land physically, chemically and biologically.

The net productivity is gradually being reduced. These factors lead to the shrinkage of the agricultural lands and a fall in agricultural production.

Food production

In order to fight the menace of hunger and malnutrition, we need
crops with greater yield and better nutritive value. The quantity and
quality of crops can be improved by modern scientific methods through genetic manipulation called genetic engineering. However, the time old concept of breeding plants either interspecific or intraspecific to bring out the best hybrid plant in plant breeding programmes still remains in vogue even today. Efforts are being made by ICAR – Indian Council of Agricultural Research and other related organisations in our country to increase food production.

A plant breeder strives to get a group of plants or a variety with
suitable combination of genes that gives better yield and improved quality under a particular set of environmental conditions. A single species is a group of assemblage of innumerable number of genetic types such as lines, strains, etc. The strains are tested in various climatic conditions, successful ones are named, multiplied and distributed as a variety or cultivar eg. Oryza sativa Co.15, ADT. 16.

Breeding experiments

Increase in population has forced us to carry out continuous scientific experiments for the following reasons viz.

1. To develop more food crops.
2. For increase quality in food crops.
3. To have sustainable food quality in food crops and assured food
supply.

By introducing specialized technology, plant breeder are now able
to develop more crops, which they multiply and supply them to the growers. Improvement in the genetic make up of plants is called plant breeding.

Major aspects of plant breeding include

1. creation of useful variation in the cultivable crops.
2. selection of better crops.
3. conducting / carrying out breeding experiments to assess the quality of the crop and
4. release of a variety after their extensive multiplication.

Other links 

Plant physiology – photosynthesis and its significance

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Aims of plant breeding

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Aspects of plant breeding and Types

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Hybridization in plant breeding

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Polyploid breeding, Mutation breeding, Breeding for disease resistance

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Genetic engineering, Improved varieties, Role of biofertilizers

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Green manuring, Mycorrhiza as biofertilizer

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Benefits from biofertilizers

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Crop diseases and their control, Rice – Oryza sativa

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Groundnut or peanut – Arachis hypogea

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Citrus canker, Tungro disease of rice

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Biocontrol of insect pests Bacterial pesticides

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Genetically modified food

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Bio war, Genetically Modified Organisms (GMO) in biological warfare

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Biopiracy, Bioresources, Biomolecules, Biopatent, Biotechnology

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Sustainable agriculture

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Medicinal plants including microbes

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Commonly Available Medicinal Plants

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Microbes in medicine

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Economic importance of Food plant Rice

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Oil plant Groundnut Economic importance

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Fibre plant – Cotton Economic importance

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Timber yielding plant Teak Economic importance

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Photoperiodism and vernalization

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The response of a plant to the relative lengths of light and dark periods is known as photoperiodism. In plants, most significant photoperiodic response is the initiation of flowering. It has been first observed in Maryland Mammoth variety of tobacco (Nicotiana tabacum). From the observation of Garner and Allard all the plants do not require the same length of light and dark periods for flowering. Plants require specific period of light and darkness for flowering. It is known as critical period.

Plants are classified into three classes

1. The plants requiring longer exposure to light than their critical period are known as long day plants eg. wheat and oats.
2. The plants requiring light for a shorter period than their critical period are known as short day plants eg. tobacco and Chrysanthemum.
3. The plants in which flowering is unaffected by the photoperiod are
known as day neutral plants eg. sunflower and maize.

Phytochromes and flowering

In 1959, Butler et al. were able to discover a photoreceptor flower
inducing pigment in plants which they name phytochromes. It is believed to be widely present in all green plants. Chemically, phytochrome is a biliprotein and exists in two forms. One form absorbs red with the wave length of 660 nm called Pr and the other form absorbs far red with the wave length of 730 nm called Pfr. The two forms of phytochrome are interconvertible as shown below:

Based on the absorption spectra, Pr is also called P 660 and Pfr is P 730. In short day plants, Pr promotes flowering while Pfr suppresses it , while it is viceversa in long day plants.

Vernalization

The term vernalization was first introduced by a Russian scientist
T.D. Lysenko in 1920. Many species, especially biennials and perennials are induced to flower at low temperature range of 1oC to 10oC. This is known as vernalization.

The response to the cold temperature stimulus is not uniform in all
plants. Plants, which are vernalized, are called inductive types. Those nonvernalized are called noninductive types.

Techniques of vernalization

The following are the steps to be taken to induce vernalization. Seeds are allowed to germinate and subjected to cold treatment for varying period of time depending on the species. Germinated seeds after this treatment are allowed to dry for sometime and then sown.

Devernalization

Reversal of the effect of vernalization is called Devernalization.
Subjecting the plants to higher temperature after a cold treatment brings about devernalization.

Practical application of vernalization

Russian scientists have used vernalization to shorten the time of crop maturity by hastening the flowering processes which are brought about by cold treatment.

Advantages

Crops can be produced earlier by vernalization. They can be cultivated in places where they naturally do not grow. Vernalization helps to accelerate the plant breeding.

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Other links 

Plant tissue culture – origin and techniques

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Plant physiology – photosynthesis and its significance

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Site of photosynthesis and Mechanism of photosynthesis

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Electron transport system and photophosphorylation types

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Dark reaction

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C3 and C4 pathways

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Photorespiration or C2 cycle

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Factors affecting photosynthesis

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Test tube and funnel experiment, Ganong’s light screen experiment

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Mode of nutrition – Autotrophic, Heterotrophic

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Chemosynthesis

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Mechanism of Respiration – Glycolysis

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Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

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Mechanism of Respiration – Electron Transport Chain, Energy Yield

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Ganong’s respiroscope, Pentose phosphate pathway

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Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

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Plant growth and Measurement of plant growth

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Phytohormones Auxins

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Phytohormones Gibberellins

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Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

 

Phytohormones Cytokinin

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Cytokinin is a plant growth substance, which stimulates cell division.
This was isolated by Miller and Skoog in 1954 from Herring fish.
Following the discovery of kinetin many other compounds showing similar activity were discovered. These are collectively called cytokinins. The cytokinin found in the zea mays is called zeatin. Cytokinin is also found in theendosperm of coconut. Cytokinin occurs in various seed plants. They are
found particularly in embryos, developing fruits and roots. Varying
mixtures of auxin and cytokinin influence plant growth and differentiation.

Physiological effects of cytokinin

1. The most important function of cytokinin is the promotion of cell
   division.
2. In association with IAA, cytokinin initiates bud and root formation in callus tissue.
3. External application of cytokinin promotes the growth of lateral buds even if the apical bud is intact.
4. Cytokinin breaks the dormancy of many seeds and also promotes
   germination.
5. Application of cytokinin delays the process of ageing in plants. This is also known as Richmond Lang effect.

Ethylene

Ethylene is a simple gaseous hormone. It is usually present in a
minute quantity. It is synthesised in large amounts by tissues undergoing ageing and acts as a natural plant growth hormone.

Physiological effects of ethylene

Ethylene prevents elongation of stem and root in longitudinal direction. Simultaneously, the tissue enlarges radially resulting in thickening of plant parts.

1. Ethylene promotes positive geotropic growth of roots.
2. A ethylene inhibits the growth of lateral buds in pea seedlings.
3. Ethylene is involved in the ripening of fruits.
4. The ethylene stimulates the formation of abscission zone in leaves, flower sand fruits. This causes leaves, flowers and fruits to shed prematurely.
5. Flowering can be induced by application of ethylene in plants like
   pineapple and mango.
6. Ethylene stimulates rooting of cuttings, initiation of lateral roots and growth of root hair.
7. The ethylene is responsible for breaking the dormancy of buds and seeds.

Abscisic acid

Abscisic acid (ABA) was originally discovered for its role in regulating abscission and bud dormancy. Like other plant hormones, it has multiple functions in the growth of plants.

Physiological effects of abscisic acid

1. Abscisic acid acts as growth inhibitor and induces bud dormancy in a variety of plants.
2. ABA is a powerful growth inhibitor. It causes 50 per cent inhibition
   of growth of oat seedlings.
3. As the name suggests abscisic acid is an hormone that stimulates
   abscission.
4. ABA controls geotropic responses of roots. It stimulates positive
   geotropism in roots.
5. Abscisic acid causes closure of stomata.

Growth inhibitors

Some organic substances produced in the plant inhibit the plant growth.
These substances are called growth inhibitors. They inhibit the elongation in roots, stems and leaves. For example, ethylene is a potent inhibitor of bud growth. ABA inhibits lateral bud growth in tomato.

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Other links 

Plant tissue culture – origin and techniques

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Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

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Chemosynthesis

---

Mechanism of Respiration – Glycolysis

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Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

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Mechanism of Respiration – Electron Transport Chain, Energy Yield

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Ganong’s respiroscope, Pentose phosphate pathway

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Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

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Plant growth and Measurement of plant growth

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Phytohormones Auxins

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Phytohormones Gibberellins

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Photoperiodism and vernalization, Phytochromes and flowering

 

Phytohormones Gibberellins and Physiological effects of gibberellin

Phytohormones Gibberellins and Physiological effects of gibberellin are illustrated with notes.

Gibberellins

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Gibberellin was first discovered in Japan by Kurusowa.

He observed from his field that some of the rice seedlings had grown much taller than the others.

On further observation, he found that such taller rice plants had shown unusual internodal elongation.

This internodal elongation is known as the ‘bakanae’ or ‘foolish seedling’ disease of rice.

Later, it was discovered that the elongation was due to the action of a substance produced by a fungus, Gibberella fujikuroi.

This substance was successfully isolated from the fungus and it was named as gibberellic acid.

There are over 90 different gibberellins isolated from fungi and from
higher plants.

Gibberellins occur in various plant organs.

They are named as GA1, GA2, GA3, etc. These phytohormones occur in all groups of plants.

Physiological effects of gibberellin

1. Gibberellins produce extraordinary elongation of stem. The elongation of stem is caused by the cell division and cell elongation induced by gibberellic acid.
2. One of the most striking effects of the gibberellins is the reversal of
   dwarfism in many genetically dwarf plants. For e.g. ‘Rosette’ plant
   of sugar beet, when treated with GA undergoes marked longitudinal
   growth of axis attaining the normal size.
3. Rosette plants usually show reduced internodal growth. These plants
   exhibit excessive internodal growth when they are treated with
   gibberellin. This sudden elongation of stem followed by flowering is
   called bolting.
4. Many biennials usually flower during the second year of their growth.
   For flowering to take place, these plants should be exposed to cold
   season. Such plants could be made to flower without exposure to
   cold season in the first year itself, when they are treated with
   gibberellins.
5. Formation of seedless fruits without fertilization can also be induced
   by gibberellin treatment in many plants. eg. Tomatoes, apples,
   cucumbers, etc.,
6. Some of the light sensitive seeds can germinate by the treatment of
   gibberellic acid even in complete darkness. eg. barley,
   m Gibberellin breaks dormancy in potato tubers.

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For more details about Phytohormones Gibberellins and Physiological effects of gibberellin click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Phytohormones Auxins and Physiological effects of auxin

Phytohormones Auxins and Physiological effects of auxin are explained with detail notes.

Phytohormones Auxins

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Auxin was the first plant hormone to be discovered.

They were isolated initially from human urine.

The term auxin is given to generally IAA and other natural and synthetic compounds having similar structure and growth regulating properties.

Generally, auxins are produced in the growing apices of stem and root where from they migrate to the other parts of the plant. Auxins such as IAA and phenyl acetic acid (PAA) are natural auxins.

Synthetic auxins are chemicals synthesised in the laboratory.

They are considered as plant growth regulators. eg. Naphthalene acetic acid, 2,4 – Dichlorophenoxy acetic acid.

Physiological effects of auxin

1. Auxins are well known to promote elongation of stem and coleoptile.It promotes the growth by cell enlargement in stems, particularly by elongation of cells behind the apical meristem.
2. Growth in lateral bud is inhibited when the apical bud of a tall plant
   remains intact. However, the lateral bud grows rapidly on removal
   of apical bud.
3. Suppression of growth in lateral bud by apical bud due to auxin
   produced by apical bud is termed as apical dominance. The reason for this is due to auxin produced in growing tip and it stimulates growth but as it moves downward, suppresses growth in the stems below.
4. Auxin is responsible for initiation and promotion of cell division in
   cambium, which is responsible for the secondary growth. This
   property of induction of cell division has been exploited for tissue
   culture techniques and for the formation of callus.
5. Auxin promotes growth of root only at extremely low concentrations. At higher concentrations, it always inhibits growth of root.
6. When leaves and fruits mature, they shed from the stem. This is
   called abscission. Auxin prevents abscission.
7. Seedless fruits are produced in tomato and apple, by external
   application of auxin on flowers. Such seedless fruits are called
   parthenocarpic fruits.
8. 2,4 – Dichlorophenoxy aceticacid, a synthetic auxin is used to eradicate weeds in the field.

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For more details about Phytohormones Auxins and Physiological effects of auxin click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Plant growth and Measurement of plant growth

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Plant growth and Measurement of plant growth

Plant growth and Measurement of plant growth are explained.

Plant growth

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Growth is one of the most fundamental and conspicuous characteristics of living organisms.

Growth may be defined as an irreversible increase in mass, weight and size of a living organisms.

In most cases, it results in increase in dry weight and the amount of protoplasm.

Growth in higher plants includes cell division, enlargement and differentiation.

Increase in the number and size of cells by itself cannot account for the development of an organized plant.

For example, when a seed is sown, it does not become a larger seed but it grows as a seedling.

Thus, growth is always accompanied by differentiation.

Differentiation is the transformation of identical cells into different tissues.

Depending upon the various structural, functional and physiological needs of the plant the tissues are of different types.

Growth and differentiation results in development, which leads to gross form of the plant.

Meristematic cells present in the plant body viz., root, shoot apices, and the cambium are responsible for growth in plants.

Phases of growth

The growth in length of the plant is due to the meristematic activity
of the apical meristems that takes place in the root and shoot apices.

Whereas increase in thickness of stem and root is due to the activity of lateral meristem.

You have already learnt in chapter 2 about different types of meristems.

The period of growth is generally divided into three phases viz., formation, elongation and maturation.

In the first phase, new cells are continuously formed by the apical meristem.

In the second phase known as phase of elongation, the newly formed cells enlarge in size.

In the third phase, phase of maturation, cells start maturing to attain permanent size and form.

The rate of plant growth is slow in the initial stages and this phase is called lag phase.

It is followed by a rapid growth phase called log phase.

In the third and final phases, the growth slows down and the organism maintains the size it has already attained.

This phase is known as stationary phase or steady state phase.

The growth in size or increase in number of cells if plotted against time the graph shows ‘S’ shaped curve known as sigmoid growth curve as shown in the figure.

In the annual plants the last phase i.e. steady state phase is followed by senescence i.e. arrest of growth and death.

However, in the case of large trees each growing season exhibits a sigmoidal pattern of growth.

Measurement of growth in plants

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You have already known that the growth in length of the plant is due
to the activity of the apical region of shoot and root.

So in any plant the growth in length can be measured in ordinary measuring scale at an interval of time.

For precise measurement, an instrument called ‘Lever Auxanometer’ is used. It measures the rate of growth of plant in terms of short length.

The auxanometer cons ists of a movable pointer attached to a pulley and a graduated arc fixed to a stand.

A thread passes around the pulley.

One end of the thread is tied to the growing tip of the potted plant.

The other end is tied to a small weight.

As the plant grows in length the pulley rotates and needle attached to the pulley moves down the scale.

From this, growth in length of the plant can be measured at a given interval of time.

The actual growth in the length of a plant is measured as follows.

Plant growth substances

The growth of a plant is regulated through gene action and
environmental conditions.

There are substances, which are produced by plants themselves, which regulate their growth and many physiological and biochemical activities.

These are called plant growth substances.
Regulation of plant growth through chemical mechanisms frequently involves certain molecules known as hormones.

Based on the origin and biological activities plant growth substances are grouped into three – growth regulators, phytohormones and growth inhibitors.

Growth regulator

It is a hormone like synthetic organic compound.

In small amounts, it modifies the growth and development either by promoting or inhibiting the growth. eg. Naphthalene acetic acid (NAA).

Phytohormones

These are organic substances produced by the plant.

They are active in very minute quantities.

They are synthesised in one of the parts of the plant and translocated to another part where they influence specific physiological, biochemical and morphological changes.

The phytohormones are broadly grouped under five major classes namely auxins, gibberellins, cytokinins, ethylene and abscisic acid.

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For more details about Plant growth and Measurement of plant growth click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering

 

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment

Anaerobic respiration

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Anaerobiosis means life in the absence of oxygen.

Certain organisms can survive in the absence of oxygen.

The respiration which takes place in the absence of free oxygen molecules is called anaerobic respiration.

It occurs in yeast and some bacteria.

Hence, they are known as anaerobes.

Glycolysis alone occurs in these organisms.

The splitting of glucose into two molecules of pyruvic acid is given in the following equation.

In anaerobic respiration, the respiratory substrate is not completely
oxidized to release energy.

Glucose is split into two molecules of pyruvic acid.

The pyruvic acid is further converted into either ethanol or organic acids like lactic acid.

Fermentation is a good example for anaerobic respiration.

Respiratory quotient

Respiratory quotient may be defined as “the ratio between the volume of carbondioxide given out and oxygen consumed during respiration”.

This value depends upon the nature of the respiratory substrate and its rate of oxidation.

Respiratory quotient for anaerobic respiration

In anaerobic respiration, carbondioxide is evolved but oxygen is not
consumed.

Therefore, the respiratory quotient in such case is infinity.
For example,

Compensation point

At a given low concentration of carbondioxide and nonlimiting light
intensity, the photosynthetic rate of a given plant will be equal to the total amount of respiration, which includes both dark respiration and
photorespiration.

The concentration of CO2 at which photosynthesis just compensates the respiration is referred to as carbondioxide compensation point.

At carbondioxide compensation point, the amount of CO2 uptake for photosynthesis is equal to that of CO2 generated.

Through respiration including photorespiration, so the net photosynthesis is zero under these conditions.

Fermentation

Fermentation literally means a chemical change accompanied by
effervescence.

The anaerobic breakdown of glucose to  carbondioxide and ethanol is a form of respiration referred to fermentation.

It is normally carried by yeast cells and accounts for the production of alcohol in alcoholic beverages.

In fermentation process, if glucose is converted into ethanol then it is called ethanolic fermentation.

When glucose is converted into organic acids such as lactic acid,
then this type of fermentation is known as lactic acid fermentation.

It is carried out by the bacterium Bacillus acidilacti.

Kuhne’s fermentation tube experiment

Kuhne’s fermentation tube consists of an upright glass tube and a
side tube with a bulb.

10 per cent glucose solution mixed with baker’s yeast is taken in the Kuhne’s tube and the tube is completely filled.

After some time, the glucose solution is fermented and gives out an alcoholic smell.

The level in the upright tube will fall due to the accumulation of CO2 gas.

It is because yeast contains the enzyme zymase which converts glucose solution into alcohol and CO2.

When a crystal of KOH is introduced into the tube, the KOH will absorb CO2 and the level of the solution will rise in the upright tube.

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For more details about Anaerobic respiration, Respiratory quotient, Compensation point, Kuhne’s fermentation tube experiment click here

Other links 

Plant tissue culture – origin and techniques

---

Plant physiology – photosynthesis and its significance

---

Site of photosynthesis and Mechanism of photosynthesis

---

Electron transport system and photophosphorylation types

---

Dark reaction

---

C3 and C4 pathways

---

Photorespiration or C2 cycle

---

Factors affecting photosynthesis

---

Test tube and funnel experiment, Ganong’s light screen experiment

---

Mode of nutrition – Autotrophic, Heterotrophic

---

Chemosynthesis

---

Mechanism of Respiration – Glycolysis

---

Mechanism of Respiration – Oxidative decarboxylation , Krebs cycle

---

Mechanism of Respiration – Electron Transport Chain, Energy Yield

---

Ganong’s respiroscope, Pentose phosphate pathway

---

Plant growth and Measurement of plant growth

---

Phytohormones Auxins

---

Phytohormones Gibberellins

---

Phytohormones Cytokinin, Ethylene, Abscisic Acid, Growth Inhibitors – Physiological Effects

---

Photoperiodism and vernalization, Phytochromes and flowering