DEFINITION:
Green chemistry is the utilization of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture and application of chemical products.
GREEN CHEMISTRY IS ABOUT
Waste minimization at source
Use of catalyst in place of reagent
Using nontoxic reagent
Use of renewable resources
Improved atom efficiency
Use of solvent free or recyclable environmentally benign solvent system
INTRODUCTION
Term has been coined by royal society of chemistry based on within department of chemistry, university of York , Helington , York, and administration by Dr. Helen Coombs.
In developing green chemistry two main programmes
1.Environmental Protection Act,(EPA).
2.Pollution Prevention Act,1990.
HISTORY
In January 1999, as a part of Environment movement ,a National symposium on Green Chemistry was organized by the Department of Chemistry, University of Delhi to bring together all who were practicing green chemistry in India for first time.
For Green Chemistry education, a refresher course was organized for college teachers by the centre for professional development in higher education in university of Delhi.
After, an IUPAC International Symposium on Green Chemistry was organized by the Department of Chemistry, University of Delhi, which proved to be excellent event for scientists’ world over to interact on the common platform.
Another symposium was held by Nirma University, Ahemedabad, on 25-26th nov.2005.
GREEN CHEMISTRY RESEARCH ACTIVITY-MAJOR INSTITUTES & LABS
o UICT,mumbai-chemical engineering and technology
o University of Delhi-GCI branch
o IIT-Madras-National Centre for Catalysis Research
o CSIR Laboratories at various locations NCL, IICT, CDRI, NEERI.
o IISC, Banglore
o JNCASR, Banglore
o IIT-Bombay, IIT Guwahati Anna University,Pune University,MS University Baroda
RENEWABLE RESOURCES AS AFEEDSTOCKS
Priority Areas For India
o Biodiesel
o Bioethanol
o Biodiesel base product
o Biosurfactant
o Biopolymers
o Biopharmaceuticals
Prevention
Atom Economy
Less Hazardous Chemical Synthesis
Designing Safer Chemicals
Safer Solvents and Auxiliaries
Design for Energy Efficiency
Use of Renewable Feedstocks
Reduce Derivatives
Catalysis
Design for Degradation
Real-time Analysis for Pollution Prevention
Inherently Safer Chemistry for Accident Prevention.
GREEN STRATEGIES:-
In developing green synthetic strategies Indian scientists are mainly concentrating on avoiding environmentally.
Non compatible reagent
Solid phase synthesis
Modification of synthetic routes
Decrease number of steps
Increase over all yield,
Usage of newer catalysts
Simplification of classical procedures of reaction
Analytical chemistry has been at centre of green chemistry.
Microwave chemists are turning their attention toward microwave assisted in
Dry media reaction
Ultrasonic reaction
Photochemical reaction
Non-conventional reaction
APPLICATION:-
To improve innovative technologies to establish industrials processes .
Development of environmentally improved routes to important products
.
Design new green chemicals and materials.
Use of sustainable resources.
Use of biotechnology alternatives.
Methodologies and test for evaluating environmental impact.
CONCLUSION:-
The future of green India and world is hand of researchers, students as a practices of green chemistry is moral responsibility for them.
Government agencies should enforce the law strictly to practice green chemistry.
Industries should be also understand their moral responsibility toward the fragile environment.
Tuesday, 14 October 2008
Friday, 10 October 2008
SEED
Seed
INTRODUCTION
Seed, term applied to the ripened ovule of a seed plant before germination. Seeds of an angiosperm, or flowering plant, differ from those of a gymnosperm (many woody plants such as the ginkgo and the yew), in being enclosed in the ovary that later forms a fruit; gymnosperm seeds lie exposed on the scales of the cones.
During the process of fertilization, the pollen tube enters the ovule through a small opening known as the micropyle. One of the two sperm nuclei in the pollen tube unites with the egg cell in the ovule to form a zygote, which develops into the embryo. In flowering plants the other sperm nucleus unites with two polar nuclei present in the embryo sac to form an endosperm nucleus, which later produces the nutritive endosperm tissue surrounding the embryo in the seed. In gymnosperms, the endosperm is formed from the tissue of the embryo sac itself. The nucellus, or megasporangium, is the tissue composing the main part of the ovule; it is partly digested during the development of the embryo and endosperm tissue. Surrounding the seed is a hard, tough seed coat, derived from the integument (outer layer) of the ovule and known as the testa. In flowering plants a second seed coat occurs within the testa; this second coat is thin and membranous and is known as the tegmen. Some seeds, in addition, have projections from the seed coat that serve to aid the absorption of water when the seed is about to germinate (see below) or that merely form an additional protective coating about the seed. In almost every seed, the micropyle through which the pollen tube entered the ovule persists as a small opening in the seed coat. Close to the micropyle in flowering plants, a stalk, or funiculus, attaches the seed to the placenta on the inside of the fruit wall. When the seed is removed, a small scar, known as the hilum, marks the former attachment of the stalk.
In a few plants, such as the orchids, the embryo is a small, undifferentiated mass of cells until after the seed has parted from the parent plant; during the period between separation from the parent plant and eventual germination, the undifferentiated cells develop into an embryonic root, bud, stalk, and leaf. In most other plants this development occurs prior to seed dispersal: the embryonic root, or radicle, usually grows towards the micropyle; the embryonic bud, called a plumule, or epicotyl, is at the end of the embryo opposite to the radicle; the embryonic stem, or hypocotyl, connects the radicle with the seed leaves, or cotyledons. In gymnosperms, several cotyledons are usually present; among angiosperms two groups of plants exist, one group having but one cotyledon in the seed and known as the monocotyledons (or monocots), and the other with two cotyledons and known as dicotyledons (or dicots). The cotyledons serve as centres of absorption and storage, drawing nutritive material from the endosperm. The cotyledons of many plants, such as the sunflower, function as primary photosynthetic organs after germination and before the development of foliage leaves from the plumule.
II SEED VIABILITYSome seeds, such as those of the willow, are viable (capable of growing into healthy organisms) for only a few days after falling from the parent tree. Other seeds are viable for years—for example, seeds of the Oriental lotus have been known to germinate 3,000 years after dispersal. Each species of plant has its specific period of viability; seeds sown after the period of optimum viability may produce weak plants or may not germinate.
III SEED TESTING
In most countries, the law requires dealers to test seeds for viability and purity before putting them on the market. A specific number of seeds are counted out, and the seeds are placed in an environment favourable to development; the percentage of viable seed in the batch of seed being tested is an index of viability of all seeds of the same lot. Seed testing also ensures the marketing of seed that is true to type—that is, seed that does not differ from the variety of plant desired.
IV SEED DORMANCY
Lack of viability of seed is often confused with seed dormancy. Many seeds require a so-called resting period after falling from the parent plant before they are able to germinate into new plants. Among the members of the orchid family, the seeds complete their maturation during this resting period. In other plants, chemical changes take place during the resting period that make the seed ready for germination. Still other seeds have extremely tough seed coats that must soften or decay before water and oxygen can enter the seed to take part in the growth of the embryo, or before the growing embryo is capable of bursting through the seed coat. Plant growers who wish to shorten the period of seed dormancy in seeds with undeveloped embryos can do little; germination may be induced, however, in seeds having mature embryos by abrasion of the hard coat, by soaking in water or in such chemicals as dilute sulphuric acid, by heating to crack the seed coat, or by alternate freezing and thawing.
V I SEED DISPERSAL
Although some seeds simply fall from the parent plant and germinate next to it, most seeds are dispersed further afield to ensure that at least some of the seeds germinate in areas suitable for growth. The main agents of seed dispersal are wind, water, and animals. The wind carries many small angiosperm and gymnosperm seeds that have wing-like structures, such as those of the elm and ash trees, or fine hairs, such as willow seeds. The dust seeds of heathers and orchids are the smallest seeds, weighing no more than a few micrograms, and are easily carried on the wind. Edible coconuts are very large seeds that float in sea water before reaching a shore on which to germinate. Penetration by salt water is prevented by the seed's fibrous outer layer. Seeds dispersed by animals can be carried externally on their feet, fur, feathers, or beaks. Those seeds with hooks or sticky substances rely on the chance that they will attach themselves to a passing animal. Other seeds are eaten by animals and passed out in the faeces. In order to persuade an animal to eat these seeds they are covered in sweet, nutritious flesh—that is, fruit.
V SEED GERMINATIONThe term germination is applied to the resumption of the growth of the seed embryo after the period of dormancy. Germination does not take place unless the seed has been transported to a favourable environment by one of the agencies of seed dispersal. The primary conditions of a favourable environment are adequate water and oxygen, and a suitable temperature. Different species of plants germinate best in different temperatures; as a rule, however, extremely cold or extremely warm temperatures are not good for germination. Some seeds also require adequate exposure to light before germinating.During germination, water diffuses through the seed coat into the embryo, which has been almost completely dry during the period of dormancy, thus causing a swelling of the seed; the swelling is so great that the seed coat is ruptured. With the absorption of oxygen by the seed, energy is made available for growth. The foodstuffs stored in the endosperm or in the cotyledons are broken down by enzymes into simpler substances which are transported through the embryo to the various centres of growth. The radicle (embryonic root) is the first portion of the embryo to break through the seed coat. It develops root hairs that absorb water and attach the embryo to particles of soil. The hypocotyl (embryonic stem) then lengthens, bringing the plumule and often the cotyledon or cotyledons above the surface of the soil. If the cotyledons are brought into light, they develop chlorophyll and carry out photosynthesis until the true foliage leaves develop from the plumule. In many plants, especially members of the grass family, the cotyledons never appear above the surface of the soil, and photosynthesis does not occur until true leaves develop; the plant meanwhile subsists on food stores in the seed. From the time of germination until the plant is completely independent of food stored in the seed, the plant is known as a seedling.
See also Horticulture; Plant Breeding.
INTRODUCTION
Seed, term applied to the ripened ovule of a seed plant before germination. Seeds of an angiosperm, or flowering plant, differ from those of a gymnosperm (many woody plants such as the ginkgo and the yew), in being enclosed in the ovary that later forms a fruit; gymnosperm seeds lie exposed on the scales of the cones.
During the process of fertilization, the pollen tube enters the ovule through a small opening known as the micropyle. One of the two sperm nuclei in the pollen tube unites with the egg cell in the ovule to form a zygote, which develops into the embryo. In flowering plants the other sperm nucleus unites with two polar nuclei present in the embryo sac to form an endosperm nucleus, which later produces the nutritive endosperm tissue surrounding the embryo in the seed. In gymnosperms, the endosperm is formed from the tissue of the embryo sac itself. The nucellus, or megasporangium, is the tissue composing the main part of the ovule; it is partly digested during the development of the embryo and endosperm tissue. Surrounding the seed is a hard, tough seed coat, derived from the integument (outer layer) of the ovule and known as the testa. In flowering plants a second seed coat occurs within the testa; this second coat is thin and membranous and is known as the tegmen. Some seeds, in addition, have projections from the seed coat that serve to aid the absorption of water when the seed is about to germinate (see below) or that merely form an additional protective coating about the seed. In almost every seed, the micropyle through which the pollen tube entered the ovule persists as a small opening in the seed coat. Close to the micropyle in flowering plants, a stalk, or funiculus, attaches the seed to the placenta on the inside of the fruit wall. When the seed is removed, a small scar, known as the hilum, marks the former attachment of the stalk.
In a few plants, such as the orchids, the embryo is a small, undifferentiated mass of cells until after the seed has parted from the parent plant; during the period between separation from the parent plant and eventual germination, the undifferentiated cells develop into an embryonic root, bud, stalk, and leaf. In most other plants this development occurs prior to seed dispersal: the embryonic root, or radicle, usually grows towards the micropyle; the embryonic bud, called a plumule, or epicotyl, is at the end of the embryo opposite to the radicle; the embryonic stem, or hypocotyl, connects the radicle with the seed leaves, or cotyledons. In gymnosperms, several cotyledons are usually present; among angiosperms two groups of plants exist, one group having but one cotyledon in the seed and known as the monocotyledons (or monocots), and the other with two cotyledons and known as dicotyledons (or dicots). The cotyledons serve as centres of absorption and storage, drawing nutritive material from the endosperm. The cotyledons of many plants, such as the sunflower, function as primary photosynthetic organs after germination and before the development of foliage leaves from the plumule.
II SEED VIABILITYSome seeds, such as those of the willow, are viable (capable of growing into healthy organisms) for only a few days after falling from the parent tree. Other seeds are viable for years—for example, seeds of the Oriental lotus have been known to germinate 3,000 years after dispersal. Each species of plant has its specific period of viability; seeds sown after the period of optimum viability may produce weak plants or may not germinate.
III SEED TESTING
In most countries, the law requires dealers to test seeds for viability and purity before putting them on the market. A specific number of seeds are counted out, and the seeds are placed in an environment favourable to development; the percentage of viable seed in the batch of seed being tested is an index of viability of all seeds of the same lot. Seed testing also ensures the marketing of seed that is true to type—that is, seed that does not differ from the variety of plant desired.
IV SEED DORMANCY
Lack of viability of seed is often confused with seed dormancy. Many seeds require a so-called resting period after falling from the parent plant before they are able to germinate into new plants. Among the members of the orchid family, the seeds complete their maturation during this resting period. In other plants, chemical changes take place during the resting period that make the seed ready for germination. Still other seeds have extremely tough seed coats that must soften or decay before water and oxygen can enter the seed to take part in the growth of the embryo, or before the growing embryo is capable of bursting through the seed coat. Plant growers who wish to shorten the period of seed dormancy in seeds with undeveloped embryos can do little; germination may be induced, however, in seeds having mature embryos by abrasion of the hard coat, by soaking in water or in such chemicals as dilute sulphuric acid, by heating to crack the seed coat, or by alternate freezing and thawing.
V I SEED DISPERSAL
Although some seeds simply fall from the parent plant and germinate next to it, most seeds are dispersed further afield to ensure that at least some of the seeds germinate in areas suitable for growth. The main agents of seed dispersal are wind, water, and animals. The wind carries many small angiosperm and gymnosperm seeds that have wing-like structures, such as those of the elm and ash trees, or fine hairs, such as willow seeds. The dust seeds of heathers and orchids are the smallest seeds, weighing no more than a few micrograms, and are easily carried on the wind. Edible coconuts are very large seeds that float in sea water before reaching a shore on which to germinate. Penetration by salt water is prevented by the seed's fibrous outer layer. Seeds dispersed by animals can be carried externally on their feet, fur, feathers, or beaks. Those seeds with hooks or sticky substances rely on the chance that they will attach themselves to a passing animal. Other seeds are eaten by animals and passed out in the faeces. In order to persuade an animal to eat these seeds they are covered in sweet, nutritious flesh—that is, fruit.
V SEED GERMINATIONThe term germination is applied to the resumption of the growth of the seed embryo after the period of dormancy. Germination does not take place unless the seed has been transported to a favourable environment by one of the agencies of seed dispersal. The primary conditions of a favourable environment are adequate water and oxygen, and a suitable temperature. Different species of plants germinate best in different temperatures; as a rule, however, extremely cold or extremely warm temperatures are not good for germination. Some seeds also require adequate exposure to light before germinating.During germination, water diffuses through the seed coat into the embryo, which has been almost completely dry during the period of dormancy, thus causing a swelling of the seed; the swelling is so great that the seed coat is ruptured. With the absorption of oxygen by the seed, energy is made available for growth. The foodstuffs stored in the endosperm or in the cotyledons are broken down by enzymes into simpler substances which are transported through the embryo to the various centres of growth. The radicle (embryonic root) is the first portion of the embryo to break through the seed coat. It develops root hairs that absorb water and attach the embryo to particles of soil. The hypocotyl (embryonic stem) then lengthens, bringing the plumule and often the cotyledon or cotyledons above the surface of the soil. If the cotyledons are brought into light, they develop chlorophyll and carry out photosynthesis until the true foliage leaves develop from the plumule. In many plants, especially members of the grass family, the cotyledons never appear above the surface of the soil, and photosynthesis does not occur until true leaves develop; the plant meanwhile subsists on food stores in the seed. From the time of germination until the plant is completely independent of food stored in the seed, the plant is known as a seedling.
See also Horticulture; Plant Breeding.
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