this article is published in the seto pana magazine of HWHIC.
Pls go through this article
Nature’s balance
Raghubar Shrestha
Dept of Biology
In the early childhood, not many differences can be seen between male and female baby. In the society, it is realized that the female baby learns fast to speak. The female baby is slightly talkative in comparison to male baby.
Major differences set as they grow. As early as 8 or 9 years of age, in female child, the hormones come into play. The Follicle Stimulating Hormone FSH from the pituitary gland starts the developing of the female reproductive organ like the ovaries. The eggs develop inside the ovaries. The development of the eggs in the ovary is expressed by the onset of menstrual cycle. The developing egg also produces the hormone - Estrogen. This hormone has various effects on the body of girls. There is deposition of fat at different parts of body like thigh and hip. The mammary gland starts being developed. With these, they also develop little shyness. As they grow, they give attention towards the things which can make them pretty.
In case of male child, it is slightly late. Only at about the age of 12 or onward, the Follicle Stimulating Hormone from the pituitary gland starts developing the testis. The Leydig cells inside the testis produce the hormone called Testosterone. The testis starts the production of sperms. The hormone brings the changes like the different pattern of hair distribution in the body, the low pitched voice, and the muscular body. As boys enter puberty, they tend to exhibit more aggressive behaviour, and there is little doubt that the dramatic rise in male sex hormones surging through their blood is responsible for this change. For any hormone to influence behaviour, it must first reach the brain and affect it. Both male and female sex hormones (Testosterone and Estrogen) concentrate selectively in certain regions that play an important role in courtship, sex and mating behaviour and aggressive– behaviour in which the sexes differ most.
In 1973, it was demonstrated for the first time that male and female brains differ structurally in many ways. Castration of male monkeys shortly after birth produced the female hypothalamic pattern while injection of testosterone into female triggered the development of the male pattern. This was the first evidence that there were structural brain differences in the sexes that the sex hormones circulating before, at, or after birth could change the brain. Based on these and later observation, scientists concluded that the basic plan of the mammalian brain in female and stays that way unless “told to do other way” by masculinizing hormone. Females tend to have a longer left temporal lobe and the posterior portion of the corpus callosum is bulbous and wide, while in males the corpus callosum is generally cylindrical and fairly uniform in diameter. This may indicate that there are more communicating fibers between the hemispheres in females.
Both male and female children come up into adolescent with these changes. All these changes are developed to suit the reproduction later on. The effect of the hormones is that, unknowingly, they are being attracted towards the opposite sex. Puberty is the period of life, generally between ages of 10 and 15 years, when the reproductive organs grow to their adult size and become functional. These changes occur in response to rising levels of Gonadial hormones (Testosterone in male and Estrogen in female). It is important that puberty represent the earliest time that reproduction is possible. The eggs are developed earlier in the girls, but the whole body system is fully made ready for the reproduction at about the age of 20 only. Most women reach the peak of their reproductive abilities in their late 20s. After that ovarian function declines gradually, presumably because the ovaries become less and less responsive to gonadotropin signals. Estrogen production declines. Eventually the ovulation and menstruation cease. This normally occurs between the age of 46 and 54 years. This event is called menopause. This signifies that the female is no more capable of reproduction. But there is no equivalent of menopause in males. The male’s reproductive capability seems unending. Healthy men are able to become father of children well into their 80s. However there is noticeable difference in sperm motility with aging.
In the society, the marriage is a legal process to undergo reproduction. In the reproduction, the male partner has very short role. The husband donates the sperms for fertilization. Once the egg/s is/are fertilized, the fertilized egg/eggs are implanted in the uterus of the female or the wife. The fetus develops within the womb in about nine months. This gestation period is much challenging in the life of woman. After nearly nine months period, she gives birth to baby/babies either female or male. After nine month long period of very difficult situation, she can now breathe with peace. The act of giving birth to baby (parturition) is even more challenging and difficult. Parturition is the culmination of pregnancy. The series of events that expel the infant from the uterus are referred to collectively as labor. During this period, the mother may sacrifice herself. This act is much painful to the female but male partner is free from all these troublesome jobs.
After the birth of child, both partners look after the child, but it is mainly the responsibility of the mother to rear the young one/s. The Nature has given the main responsibility to the female counter part.
All these are due to the fact that the females have a pair of X chromosomes in the nucleus of the cells together with 22 pairs of Autosomes. Unlike, in the males, there is only one X chromosomes and one Y chromosome in addition to 22 pairs of chromosomes. The very thing here to notice is that the females are much safer as they have a pair of X chromosomes. It is a boon for the females as they do not generally develop the different types of genetic diseases like hemophilia, color blindness etc. In human beings, about fifty X chromosome linked defects have been reported up to now. The most important and common defects in man are :
1. Color or red - green blindness 2. Haemophilia
3. Anhidrotic ectoderma ( non functional sweet gland) 4. Night blindness
5. Myopia ( short sightedness) 6. Juvenile glaucoma
7. White fore lock etc.
Hemophilia is most serious and notorious disease which is more common in man than in woman. It is also known as Bleeder’s disease. The person which contains recessive gene for hemophilia lacks in normal clotting substance in blood. So, normal and minor injuries cause continuous bleeding and ultimate death due to the hemorrhages. This hereditary disease was first reported by John Cotto of Philadelphia in 1803 in man. This disease has been most common in Royal families of Russia and England. Queen Victoria and her further generation were having hemophilic disease. The males are easily victimized to these diseases because of only one X chromosome. The defects in the X chromosome are frequently expressed in males. When one of the X chromosomes is defective, the women are not affected by any deadly disease as it is dominated by another X chromosome. The women in this condition is said to be carrier of the defective X chromosome. They can transmit the defective X chromosome to daughters and sons. However the sons are easily affected by it. Knowing the fact that the daughters transmit the recessive genes to their sons, the Royal families in those days got their daughters married in other countries.
The daughters are affected by such deadly diseases only when both of the X chromosomes are defective. It is possible only when there is marriage between the diseased man and woman or diseased man and carrier woman. Generally diseased men and women do not get married easily. In case of the marriage between diseased man and carrier woman, only half of the daughters will get both defective X chromosomes and other half will get one defective X chromosome. When there is only one defective X chromosome, these daughters are not affected, they will just become carrier of defective X chromosome and transmit it to sons.
There are certain other cases which are linked to the Y chromosome. The Y chromosome is only present in males. So these Y chromosome linked defects are directly transmitted from father to son. One of the simple examples of this can be taken as ichthyosis hystrix gravis hypertrichosis (excessive development of hairs on pinna or ear). Still others are both X-Y linked. In human beings, several diseases are X-Y linked such as total colour blindness, skin diseases (Xeroderma pigmentosum and Epipermolysis bullosa), Retinitis pigmentosa, Spastic paraplegia etc. From all these, it is now clear that the females are much safer from all these notorious and deadly inheritable genetic diseases.
At the end, it can be said that the Nature is looking both the males and females equally without any discrimination. Any one of the males and females is not important for the Nature. Both are needed and both can contribute to the continuity of the race. Both should go together for the betterment of the race.
Saturday, August 29, 2009
Monday, July 20, 2009
BLAS questions
Natural Science VI semester
Questions for the Pre board exam 2065
Time 3 hours
Long question (attempt any two) 2X20=40
Describe the Oparin Haldane theory of origin of life.
Describe the theory of Natural selection with its limitation.
Discuss the strategies in the management of wildlife in Nepal.
Short questions (attempt any five) 5X8= 40
How is Chemistry related with Biology?
Describe Miller Urey experiment about origin of life.
Illustrate the use and disuse of organ in Lamarckism.
Give the meaning of a) Punnet Square b) Genotype
Why did Mendel select pea plant for his experiment.
Write down the role of forest.
Why are mountains important to us?
Write consequences of deforestation.
Model Questions for the Practice during Dashain vacation
Long question 20 Marks each
Describe the Oparin Haldane theory of origin of life.
Describe the Mendel’s Laws of Inheritance.
Describe the theory of Natural selection with its limitation.
Discuss the various scopes of Natural science.
Discuss the strategies in the management of wildlife in Nepal.
What is Law of Independent Assortment? Describe it with dihybrid cross of Mendel’s experiment.
Short questions (attempt any five) 8 marks each
How is Chemistry related with Biology?
Write short notes on spontaneous generation.
Describe Miller Urey experiment about origin of life.
Illustrate the use and disuse of organ in Lamarckism
Write a short note on survival of the fittest.
Describe Redi’s experiment. How does it prove Biogenesis?
Give the meaning of a) Punnet Square b) Genotype
Describe the monohybrid cross of Mendel’s experiment.
Describe the dihybrid cross of Mendel’s experiment.
Why did Mendel select pea plant for his experiment.
Write down the role of forest.
Write down the role of the river.
Write short account of any one National Park of Nepal.
What are the causes of Flood.
What are the strategies in the management of landslides
What are the protective measures to be carried out at the time of earth quake?
Why are mountains important to us?
How are the Himalayas different from mountains?
Write short note on mountain ecosystem
Write consequences of deforestation
Write short notes on special creation regarding origin of life.
The giraffe has long neck and long fore limb. What do this prove.?
Why have snakes lost legs?
Give name of four endangered animals of Nepal.
Questions for the Pre board exam 2065
Time 3 hours
Long question (attempt any two) 2X20=40
Describe the Oparin Haldane theory of origin of life.
Describe the theory of Natural selection with its limitation.
Discuss the strategies in the management of wildlife in Nepal.
Short questions (attempt any five) 5X8= 40
How is Chemistry related with Biology?
Describe Miller Urey experiment about origin of life.
Illustrate the use and disuse of organ in Lamarckism.
Give the meaning of a) Punnet Square b) Genotype
Why did Mendel select pea plant for his experiment.
Write down the role of forest.
Why are mountains important to us?
Write consequences of deforestation.
Model Questions for the Practice during Dashain vacation
Long question 20 Marks each
Describe the Oparin Haldane theory of origin of life.
Describe the Mendel’s Laws of Inheritance.
Describe the theory of Natural selection with its limitation.
Discuss the various scopes of Natural science.
Discuss the strategies in the management of wildlife in Nepal.
What is Law of Independent Assortment? Describe it with dihybrid cross of Mendel’s experiment.
Short questions (attempt any five) 8 marks each
How is Chemistry related with Biology?
Write short notes on spontaneous generation.
Describe Miller Urey experiment about origin of life.
Illustrate the use and disuse of organ in Lamarckism
Write a short note on survival of the fittest.
Describe Redi’s experiment. How does it prove Biogenesis?
Give the meaning of a) Punnet Square b) Genotype
Describe the monohybrid cross of Mendel’s experiment.
Describe the dihybrid cross of Mendel’s experiment.
Why did Mendel select pea plant for his experiment.
Write down the role of forest.
Write down the role of the river.
Write short account of any one National Park of Nepal.
What are the causes of Flood.
What are the strategies in the management of landslides
What are the protective measures to be carried out at the time of earth quake?
Why are mountains important to us?
How are the Himalayas different from mountains?
Write short note on mountain ecosystem
Write consequences of deforestation
Write short notes on special creation regarding origin of life.
The giraffe has long neck and long fore limb. What do this prove.?
Why have snakes lost legs?
Give name of four endangered animals of Nepal.
BLAs notes
Kingdom Monera
Characters
Unicellular, microscopic, prokaryotic and found greatest in number on earth
Lack of well organized nucleus, not surrounded by nuclear membrane, nucleus consists of double stranded DNA, nuclear contents lie any where scattered in protoplasm.
Most of them rigid cell wall
Various mode of nutrition, autotrophic, parasitic, symbiotic or saprophytic known as decomposers which convert complex organic matter into simple and soluble forms.
Can tolerate extreme environmental conditions like temperature pH absence of O2.
Bacteria were first discovered by Dutch naturalist Anton Van Leeuwenhoek (1632-1723). He discovered the first microscope in the 17th C. He observed Bacteria in June 10, 1675. The term bacteria was given by Ehrenberg in 1838. The study of Bacteria is called Bacteriology. Bacteria can withstand temp up to 78 oC and -190 oC. There are two types of Bacteria Gram +ve and Gram –ve based on stain.
Kingdom Protista
Characters
Unicellular microscopic eukaryotic organism with well organized nucleus. Besides nucleus, mitochondria , endoplasmic reticulum, golgi bodies plastids etc present.
Both autotrophic and heterotrophic mode of nutrition.
Photosynthetic protists are chief prodders of ocean, fresh water bodies and known as phytoplankton .
The non photosynthetic protists are called zooplankton which are primary consumers.
Some act as decomposers
Reproduce both sexually and asexually. Some like Euglena exhibit flexible life style. In absence of light ingest food and in he presence of light show autotrophic mode of nutrition.
Kingdom Animalia
Characters
Includes multi cellular, eukaryotic animals.
Heterotrophic mode of nutrition.
They are called consumers as they depend on others
Great variety ranging from invertebrates to vertebrates.
Lack of green pigment chlorophyll, cell wall.
Holozoic, parasitic
Reserve food in the form of glycogen
Have locomotory organ and sense organ.
Kingdom plantae
Characters
Includes multi cellular eukaryotic plants found on land, sea water or freshwater. They can be alga, bryophytes, pterydophytes, gymnospersm and angiosperm. All are photosynthetic hence called autotrophs and producers of ecosystem.
Cell wall is made up of cellulose
Some are parasitc(Cuscuta). Some insectivorous like Pitcher plant and others symbiotic( leguminous plants.
Fixed on land and no locomotory organ.
Have chlorophyll and can synthesize food.
Kingdom Fungi( Mycota)
Characters
Includes multi cellular eukaryotic plants with heterotrophic mode of nutrition. Size vary from microscopic to bracket fungi, toadstools. Puffballs which are seen
with unaided eye.
Mostly saprophytes feeding on dead and decaying organic matter also known as decomposers.
Cell wall is made up of chitin or cellulose or both
Exists as a mycelium made of network of branching multi cellular threads called hyphae
Some are parasitic eg. Puccinia
Body is thallus( not differentiated into root, stem and leaf.
Lack chlorophyll, cannot manufacture food
Non vascular
Reproduce by spore forming, asexual and sexual method
Reserve food in the form of glycogen and oil globules.
Some harmful, causes diseases
Some beneficial, used in industry like alcohol, enzymes. Vitamins, bread and antibiotics, some as food.
Found in almost all habitat where organic material is available.
Characters
Unicellular, microscopic, prokaryotic and found greatest in number on earth
Lack of well organized nucleus, not surrounded by nuclear membrane, nucleus consists of double stranded DNA, nuclear contents lie any where scattered in protoplasm.
Most of them rigid cell wall
Various mode of nutrition, autotrophic, parasitic, symbiotic or saprophytic known as decomposers which convert complex organic matter into simple and soluble forms.
Can tolerate extreme environmental conditions like temperature pH absence of O2.
Bacteria were first discovered by Dutch naturalist Anton Van Leeuwenhoek (1632-1723). He discovered the first microscope in the 17th C. He observed Bacteria in June 10, 1675. The term bacteria was given by Ehrenberg in 1838. The study of Bacteria is called Bacteriology. Bacteria can withstand temp up to 78 oC and -190 oC. There are two types of Bacteria Gram +ve and Gram –ve based on stain.
Kingdom Protista
Characters
Unicellular microscopic eukaryotic organism with well organized nucleus. Besides nucleus, mitochondria , endoplasmic reticulum, golgi bodies plastids etc present.
Both autotrophic and heterotrophic mode of nutrition.
Photosynthetic protists are chief prodders of ocean, fresh water bodies and known as phytoplankton .
The non photosynthetic protists are called zooplankton which are primary consumers.
Some act as decomposers
Reproduce both sexually and asexually. Some like Euglena exhibit flexible life style. In absence of light ingest food and in he presence of light show autotrophic mode of nutrition.
Kingdom Animalia
Characters
Includes multi cellular, eukaryotic animals.
Heterotrophic mode of nutrition.
They are called consumers as they depend on others
Great variety ranging from invertebrates to vertebrates.
Lack of green pigment chlorophyll, cell wall.
Holozoic, parasitic
Reserve food in the form of glycogen
Have locomotory organ and sense organ.
Kingdom plantae
Characters
Includes multi cellular eukaryotic plants found on land, sea water or freshwater. They can be alga, bryophytes, pterydophytes, gymnospersm and angiosperm. All are photosynthetic hence called autotrophs and producers of ecosystem.
Cell wall is made up of cellulose
Some are parasitc(Cuscuta). Some insectivorous like Pitcher plant and others symbiotic( leguminous plants.
Fixed on land and no locomotory organ.
Have chlorophyll and can synthesize food.
Kingdom Fungi( Mycota)
Characters
Includes multi cellular eukaryotic plants with heterotrophic mode of nutrition. Size vary from microscopic to bracket fungi, toadstools. Puffballs which are seen
with unaided eye.
Mostly saprophytes feeding on dead and decaying organic matter also known as decomposers.
Cell wall is made up of chitin or cellulose or both
Exists as a mycelium made of network of branching multi cellular threads called hyphae
Some are parasitic eg. Puccinia
Body is thallus( not differentiated into root, stem and leaf.
Lack chlorophyll, cannot manufacture food
Non vascular
Reproduce by spore forming, asexual and sexual method
Reserve food in the form of glycogen and oil globules.
Some harmful, causes diseases
Some beneficial, used in industry like alcohol, enzymes. Vitamins, bread and antibiotics, some as food.
Found in almost all habitat where organic material is available.
Friday, July 17, 2009
BLAS notes
Classification
Grouping of living organisms according to their similarities and dissimilarities is known as classification. It is the important part of modern taxonomy. There are millions of living organisms on earth. No systematic study can be done without classifying them.
The classification is not only for identification but also to know the evolutionary trend. Different systems of classification
Artificial classification
It is the classical type of classification. Ancient people tried to classify plants and animals according to use to mankind. This type of classification is based on one or few characters. It is not based on natural characters and phylogenetic relationship. Artificial classification is put forwarded by different workers in pre Darwinian era.
Natural system of classification
Natural system is based on truly natural characters such as characters of resemblance or correlation, affinities among them etc. this system considers all aspects by which closely related plants and animals come together. The best and highly recognized natural system of natural classification was proposed by George Bentham (1800 to 1894) and Joseph Dalton Hooker (1817-19110). They made the thorough observation of the plants and presented classification.
Phylogenetic system of classification
The study of history of development of a race or simply evolutionary history is called phylogeny. It includes he knowledge of ancestor, place and time of origin. This is the most advanced type of classification. This system classifies the plants and animals according to their evolutionary sequence and genetic relationship. This system was put forwarded by A Engler(1844-1893) this system enables the taxonomists to trace out ancestor and evolutionary trend.
Hierarchic system in classification
Hierarchy is a system of arrangement where taxonomic categories are placed in major units of classification
Kingdom
This is the highest caterory. There are kingdoms like Monera, Protista, Fungi or Mycota, Plantae and Animalia etc.
Division or Phylum
The division or phylum includes classes of different organisms having common characters.
Class
It is the group of orders.
Order
Group of related Families
Family
Group of related genera
Genus
Aggregation of two or more species
Species
This is the basic unit of classification. The closely resembling individuals of same kind constitute species. They can freely interbreed and produce fertile offspring. Among the member of species, there may be presence of minor differences in color, form and size etc
Two Kingdom classification
Carolus Linnaeus (1707-1778) divided all living things into two Kingdoms for the first time.
Kingdom Plantae or Plant kingdom
Some characters
Autotrophic mode of nutrition
Immobility
Rigid cellulosic wall
Less sensitive
Includes all plants
Kingdom Animalia or Animal kingdom
Some characters
Heterotrophic mode of nutrition
Mobility
Made up of cells without rigid cellulosic wall.
More sensitive because of presence of nerve cell
Includes all animals
The two kingdom classification is appreciable effort. However it could not address a great variety of animals and plants. So, it is inadequate and unsatisfactory in modern age.
Five kingdom classification
RH Whittaker of USA (1969) gave five kingdom system of classification (Science,163:150-160)
This system focuses on
Complexities of cell structure and body organization
Mode of nutrition
Phylogenetic relationship
Features of five kingdom classification
Advancement over the two kingdom classification
Based on phylogenetic relationship
Solves many problems of two kingdom classification.
Characters of five kingdom classification
Separated prokaryotes from eukaryotes
Removed anomaly of positions of many transitional and intermediate forms
All multi cellular, photosynthetic, eukaryotic with cellulosic wall included in kingdom Plantae
All multi cellular, non photosynthetic, eukaryotic with cellulosic wall included in Animal kingdom
All multi cellular, non photosynthetic plants separated from photosynthetic plants and kept in kingdom Fungi.
Brought out phylogenetic relationship amongst the primitive forms
Grouping of living organisms according to their similarities and dissimilarities is known as classification. It is the important part of modern taxonomy. There are millions of living organisms on earth. No systematic study can be done without classifying them.
The classification is not only for identification but also to know the evolutionary trend. Different systems of classification
Artificial classification
It is the classical type of classification. Ancient people tried to classify plants and animals according to use to mankind. This type of classification is based on one or few characters. It is not based on natural characters and phylogenetic relationship. Artificial classification is put forwarded by different workers in pre Darwinian era.
Natural system of classification
Natural system is based on truly natural characters such as characters of resemblance or correlation, affinities among them etc. this system considers all aspects by which closely related plants and animals come together. The best and highly recognized natural system of natural classification was proposed by George Bentham (1800 to 1894) and Joseph Dalton Hooker (1817-19110). They made the thorough observation of the plants and presented classification.
Phylogenetic system of classification
The study of history of development of a race or simply evolutionary history is called phylogeny. It includes he knowledge of ancestor, place and time of origin. This is the most advanced type of classification. This system classifies the plants and animals according to their evolutionary sequence and genetic relationship. This system was put forwarded by A Engler(1844-1893) this system enables the taxonomists to trace out ancestor and evolutionary trend.
Hierarchic system in classification
Hierarchy is a system of arrangement where taxonomic categories are placed in major units of classification
Kingdom
This is the highest caterory. There are kingdoms like Monera, Protista, Fungi or Mycota, Plantae and Animalia etc.
Division or Phylum
The division or phylum includes classes of different organisms having common characters.
Class
It is the group of orders.
Order
Group of related Families
Family
Group of related genera
Genus
Aggregation of two or more species
Species
This is the basic unit of classification. The closely resembling individuals of same kind constitute species. They can freely interbreed and produce fertile offspring. Among the member of species, there may be presence of minor differences in color, form and size etc
Two Kingdom classification
Carolus Linnaeus (1707-1778) divided all living things into two Kingdoms for the first time.
Kingdom Plantae or Plant kingdom
Some characters
Autotrophic mode of nutrition
Immobility
Rigid cellulosic wall
Less sensitive
Includes all plants
Kingdom Animalia or Animal kingdom
Some characters
Heterotrophic mode of nutrition
Mobility
Made up of cells without rigid cellulosic wall.
More sensitive because of presence of nerve cell
Includes all animals
The two kingdom classification is appreciable effort. However it could not address a great variety of animals and plants. So, it is inadequate and unsatisfactory in modern age.
Five kingdom classification
RH Whittaker of USA (1969) gave five kingdom system of classification (Science,163:150-160)
This system focuses on
Complexities of cell structure and body organization
Mode of nutrition
Phylogenetic relationship
Features of five kingdom classification
Advancement over the two kingdom classification
Based on phylogenetic relationship
Solves many problems of two kingdom classification.
Characters of five kingdom classification
Separated prokaryotes from eukaryotes
Removed anomaly of positions of many transitional and intermediate forms
All multi cellular, photosynthetic, eukaryotic with cellulosic wall included in kingdom Plantae
All multi cellular, non photosynthetic, eukaryotic with cellulosic wall included in Animal kingdom
All multi cellular, non photosynthetic plants separated from photosynthetic plants and kept in kingdom Fungi.
Brought out phylogenetic relationship amongst the primitive forms
BLAS notes
Nature of Biology
The word Biology comes from Greek words, Bios = life, logos= study, knowledge or discourse. It is the branch of Natural Science which deals with various aspects of living beings (animals and plants). Biology tries(seeks) to understand how animals and plants perform their life activities , how they interact with each other and with non living things. So, it is most appropriately called as the life science.
Though the definition of Biology is very simple, it is equally complex and extensive as it deals with various aspects of enormous number of living organisms spread in time and space.
This branch of science deals with structural organization of living organisms, functions of their body parts, habitat, relationship and interaction among themselves and surrounding. How they pass their specific characters to the next generation ? How do they evolve from simple or primitive to more advanced forms ?
Biology must have born very early in the remote past out of simple curiosity of man about himself and the living world around him. The study have begun in search of different articles of human use from living world so as to lead comfortable life. The science of living organism is as old as the history of man himself. However the first conceivable evidence of the study of living organisms comes from the work of great Greek philosopher Aristotle ( 384 – 322 BC) . He arranged all living organism in a hierarchy placing the simplest organism at the bottom and man at the top. Due to this creditable work, Aristotle is known as the Father of Biology. He is also known as the Father of Zoology and Founder of Embryology.
The term Biology was first used by French Naturalist Lamarck and Treviranus in 1801.
Scope of Biology
Biology is very much important branch of Natural Science. From the very ancient time, man has been benefited from the various parts of animals and plants found around him. The animals and plants are found to be helping man in various ways in making his life much easier.
Understand human life -- We are curious to know about our own health. Why we eat? How we grow? How we see and hear? What is the importance of balanced diet? The knowledge of Biology can help us to get the right answer of all such questions and others like these.
Understand natural phenomena -- Natural phenomena like flowering of plants, breeding mechanisms and seasons of animals, social behavior of some insects , dispersal mechanism of seed etc can better understood by the study of Biology.
Understand mechanism of
Heredity - the transmission of characters from generations to generations.
Evolution - Development of higher organisms from simple ones
Adaptation – Adjustment of organisms.
Scientific theory- various experiment are carried out on crops, animals like mice, guinea pig and their application on man.
Fulfill the basic need – Skillful biological techniques can be used to fulfill the need of food, shelter, clothes and drugs by improving farming practices.
Control population -- The knowledge of reproductive physiology of man and other harmful animals and plants can be used in controlling their population.
Control epidemics -- The epidemics like Malaria, Encephalitis, Sleeping sickness due to insects as vectors can be controlled by knowledge of feeding mode, life cycle, breeding habit etc.
Conservation of wild life -- if we know the habitat, feeding habit, breeding season etc, we can easily conserve these rare type of wild life.
Careers in Biology
A. Pure Science - Zoology, Botany, Microbiology, Genetics Entomology etc.
B. Medical Science - Homeopathy, Allopathy including Dental, Nutrition. Etc
C. Applied Science – Apiculture, Forestry, Fisheries, Diary technology, sericulture, soil science, Food technology, Animal husbandry etc
Branches of Biology
Biology is vast subject. We can not study Biology as a whole in our life. Our life is very short. To make the study of Biology much easier, it has been divided into various branches or fields or disciplines. We can study the branches of our interests.
The branches of Biology on the basis of the structure and function:
Morphology -- the study of external features of organisms
Anatomy -- the study of internal structure of organisms as seen by naked eye.
Cytology – the study of structure and functions of cell and cell inclusions.
Histology -- the study of structure and functions of cells that make up the internal organs of organisms.
Physiology -- the study of the functioning of organs of organism.
The branches of Biology on the basis of the specific unit or field:
Toxicology – the study of the toxic substances and their effects
Embryology -- the study of the development of organism
Evolution -- the study of origin of life and development into modern plants and animals.
Microbiology -- the study of micro organisms or microbs.
Parasitology – the study of parasites and their effects.
Ecology – the study of relationship between living organism and environment.
Paleontology – the study of animal or plant fossil
The branches of Biology on the basis of the specific group of organisms:
Entomology – the study of insects.
Protozoology -- the study of unicellular organisms
Parazoology – the study of sponges.
Cnidology – the study of Coelenterates like Hydra etc
Bacteriology – the study of Bacteria.
Virology – the study of Virus
Ornithology – the study of Birds
The branches of Biology related to the medical science:
Cardiology – the study of structure and function of heart
Nephrology -- the study of structure and function of kidney
Oesteology – the study of bones
Endocrinology – the study of endocrine glands and hormones.
Neurology – the study of functioning of brain
Hematology – the study of blood.
Enzymology—the study of enzymes
Relation of Biology with other branches of Science
Biology has relationship with other branches of science. We can not study biology without the help of other sciences. We need the knowledge of other sciences to understand biology.
Relation of Biology with Chemistry
In side the cells as well as body of animals and plants there are inorganic substances and organic compounds.
Enzymes, hormones , vitamins and minerals are all chemicals. They take part in different vital activities.
The acid base balance maintains pH. It is required to carry out biological reactions in the body.
Chemical processes like diffusion, osmosis, plasmolysis, solubility play important role in biological system. These chemical processes help in absorption, excretion, filtration , ascent of sap, transpiration in animals and plants,
The electrolytes like Na + and K+ play role in conduction of nerve impulse in brain.
The subject Biochemistry shows the relation of Biology and Chemistry.
Relation with Physics
The bones and cartilages of body of animals provide the mechanical strength. They act as efficient levers with joints and muscle.
The lens of eye is for focusing light during image formation, ears are sensitive to change in sound waves.
Photobiology is related to the role of light in different biological processes like photosynthesis, photoperiodism, phototaxis and phototropism etc.
Use of energy and maintaining certain temperature of body.
The subject Biophysics shows the relation of Biology and Physics
Relation with Statistics and Mathematics
The researches in biology requires the knowledge of statistics and mathematics. Many interpretations in biology are based on the knowledge of statistics. The Mendelian ratio of monohybrid and dihybrid cross is the examples of relation of biology with statistics and mathematics.
Relation with Geography
Animals and plants are distributed at different regions of the earth. The north and south poles have similar climatic condition but only the south pole (Antarctica) has the Penguins. The polar bears are found only at the north poles. The Elephants are found only in Asia and Africa. This shows the relation of biology with the geography. It is called as Zoogeography or biogeography.
Biology as science of exception
Though there are different rules and regulations in the different branches of sciences, there are many exceptions in biology. So biology is called as the science of exceptions.
The red blood corpuscles(RBC) of mammals are without nucleus except Camels.
DNA is the hereditary materials in all except the Viruses.
The heart of reptiles are three chambered except the Crocodiles.
Fishes have gills for respiration but Protopterus (Nile lung fish) has lungs.
Larva develops into adult but American Salamander larva becomes sexually matured and gives birth to larva.
Birds are usually adapted for flying but certain birds like Kiwi, Ostrich can never fly.
Stems are usually aerial but ginger, potato have underground stem.
Mammals are viviparous but duck billed Platypus, Echidna is oviparous
General approach to understand life processes
The living beings have certain unified and basic characters by which they become different from non living things. Each and every living being is a complex entity which is made up of one or many cells. In the cells, there are different bio molecules. Micro molecules like water, salt, monosaccharide, amino acid etc and macro molecules like complex carbohydrate, protein and fats are present. The molecules interact, aggregate and participate in the vital activities of organisms. In this connection, Linus Pauling says that life results due to a relationship of molecules and not a property of any one molecule.
The life processes are given below
Nutrition -- it is the process of getting food. Green plants have chlorophyll. They can manufacture their food by the process known as photosynthesis. They are called autotrophs. Animals are not capable of synthesizing their food. They get their food either from plants or other animals. They are heterotrophs. The non green plants which take food from the dead bodies are called saprophytes.
Growth and metabolism-- plants and animals grow in their size. Plants grow in height indefinitely but animals grow in height for certain period. However there is growth all the time. It involves an increase in volume through the formation of new protoplasm with or without division of their structural units cells. Cells grow by addition of new protoplasm. This process of growth in living is called intussusceptions. It is irreversible. A crystal also grows but it is addition of new material at the surface. It is accretion. Metabolism is building up (anabolism) and breakdown ( catabolism) of body. It is a continuous process from birth to death.
Respiration – both animals and plants respire. They take O2 from atmosphere. They burn the food (glucose) to produce energy. It is aerobic respiration. The lower organism break down glucose with out O2 to produce energy. It is anaerobic respiration.
Excretion – the waste materials produced in side the body is discharged out. It is excretion. The lungs throw out CO2. The large intestine gives out undigested materials. The kidneys filter out the urea, uric acid etc. Animals discharges wastes as soon as possible. The plants can store in the part of body and throws after certain period. They also can use waste for mechanical strength.
Irritability and movement -- it is response to external or internal stimuli. Animals show quick response. The plants are slow to show the response. But there is rapid movement in insectivorous plants like Venus’s fly trap. In Mimosa (touch me not plant) the gentle pressure can make the folding of leaves.
Homeostasis - - it is the state of balance of salts, water, temp, pH etc. it is coordinating mechanism to keep the internal environment at steady or normal state.
Adaptability – all plants and animals are capable of undergoing certain changes in their structure, habit and habitat to become suitable to the environment. The fishes are adapted to live in water. Birds made them suitable to fly in air etc.
Evolution -- organisms under go changes in their genetic material. These changes are passed on to offsprings in succeeding generation. Such changes are raw material for evolution. This property of evolution is a function of population of organism and not in individual organism.
Reproduction -- they can produce their own kind. Since the living things eventually die, reproduction ensures survival of the group. Living organism come from pre existing living organism.
Ageing and death -- ageing is the process of deterioration of body. The efficiency of working decreases slowly and gradually. At the end, there is the death. The heart beat and respiration are arrested. Death helps to maintain certain number in population. The decomposers act on dead body to convert into C, H O, N,S etc. These are returned to the nature for balance.
The word Biology comes from Greek words, Bios = life, logos= study, knowledge or discourse. It is the branch of Natural Science which deals with various aspects of living beings (animals and plants). Biology tries(seeks) to understand how animals and plants perform their life activities , how they interact with each other and with non living things. So, it is most appropriately called as the life science.
Though the definition of Biology is very simple, it is equally complex and extensive as it deals with various aspects of enormous number of living organisms spread in time and space.
This branch of science deals with structural organization of living organisms, functions of their body parts, habitat, relationship and interaction among themselves and surrounding. How they pass their specific characters to the next generation ? How do they evolve from simple or primitive to more advanced forms ?
Biology must have born very early in the remote past out of simple curiosity of man about himself and the living world around him. The study have begun in search of different articles of human use from living world so as to lead comfortable life. The science of living organism is as old as the history of man himself. However the first conceivable evidence of the study of living organisms comes from the work of great Greek philosopher Aristotle ( 384 – 322 BC) . He arranged all living organism in a hierarchy placing the simplest organism at the bottom and man at the top. Due to this creditable work, Aristotle is known as the Father of Biology. He is also known as the Father of Zoology and Founder of Embryology.
The term Biology was first used by French Naturalist Lamarck and Treviranus in 1801.
Scope of Biology
Biology is very much important branch of Natural Science. From the very ancient time, man has been benefited from the various parts of animals and plants found around him. The animals and plants are found to be helping man in various ways in making his life much easier.
Understand human life -- We are curious to know about our own health. Why we eat? How we grow? How we see and hear? What is the importance of balanced diet? The knowledge of Biology can help us to get the right answer of all such questions and others like these.
Understand natural phenomena -- Natural phenomena like flowering of plants, breeding mechanisms and seasons of animals, social behavior of some insects , dispersal mechanism of seed etc can better understood by the study of Biology.
Understand mechanism of
Heredity - the transmission of characters from generations to generations.
Evolution - Development of higher organisms from simple ones
Adaptation – Adjustment of organisms.
Scientific theory- various experiment are carried out on crops, animals like mice, guinea pig and their application on man.
Fulfill the basic need – Skillful biological techniques can be used to fulfill the need of food, shelter, clothes and drugs by improving farming practices.
Control population -- The knowledge of reproductive physiology of man and other harmful animals and plants can be used in controlling their population.
Control epidemics -- The epidemics like Malaria, Encephalitis, Sleeping sickness due to insects as vectors can be controlled by knowledge of feeding mode, life cycle, breeding habit etc.
Conservation of wild life -- if we know the habitat, feeding habit, breeding season etc, we can easily conserve these rare type of wild life.
Careers in Biology
A. Pure Science - Zoology, Botany, Microbiology, Genetics Entomology etc.
B. Medical Science - Homeopathy, Allopathy including Dental, Nutrition. Etc
C. Applied Science – Apiculture, Forestry, Fisheries, Diary technology, sericulture, soil science, Food technology, Animal husbandry etc
Branches of Biology
Biology is vast subject. We can not study Biology as a whole in our life. Our life is very short. To make the study of Biology much easier, it has been divided into various branches or fields or disciplines. We can study the branches of our interests.
The branches of Biology on the basis of the structure and function:
Morphology -- the study of external features of organisms
Anatomy -- the study of internal structure of organisms as seen by naked eye.
Cytology – the study of structure and functions of cell and cell inclusions.
Histology -- the study of structure and functions of cells that make up the internal organs of organisms.
Physiology -- the study of the functioning of organs of organism.
The branches of Biology on the basis of the specific unit or field:
Toxicology – the study of the toxic substances and their effects
Embryology -- the study of the development of organism
Evolution -- the study of origin of life and development into modern plants and animals.
Microbiology -- the study of micro organisms or microbs.
Parasitology – the study of parasites and their effects.
Ecology – the study of relationship between living organism and environment.
Paleontology – the study of animal or plant fossil
The branches of Biology on the basis of the specific group of organisms:
Entomology – the study of insects.
Protozoology -- the study of unicellular organisms
Parazoology – the study of sponges.
Cnidology – the study of Coelenterates like Hydra etc
Bacteriology – the study of Bacteria.
Virology – the study of Virus
Ornithology – the study of Birds
The branches of Biology related to the medical science:
Cardiology – the study of structure and function of heart
Nephrology -- the study of structure and function of kidney
Oesteology – the study of bones
Endocrinology – the study of endocrine glands and hormones.
Neurology – the study of functioning of brain
Hematology – the study of blood.
Enzymology—the study of enzymes
Relation of Biology with other branches of Science
Biology has relationship with other branches of science. We can not study biology without the help of other sciences. We need the knowledge of other sciences to understand biology.
Relation of Biology with Chemistry
In side the cells as well as body of animals and plants there are inorganic substances and organic compounds.
Enzymes, hormones , vitamins and minerals are all chemicals. They take part in different vital activities.
The acid base balance maintains pH. It is required to carry out biological reactions in the body.
Chemical processes like diffusion, osmosis, plasmolysis, solubility play important role in biological system. These chemical processes help in absorption, excretion, filtration , ascent of sap, transpiration in animals and plants,
The electrolytes like Na + and K+ play role in conduction of nerve impulse in brain.
The subject Biochemistry shows the relation of Biology and Chemistry.
Relation with Physics
The bones and cartilages of body of animals provide the mechanical strength. They act as efficient levers with joints and muscle.
The lens of eye is for focusing light during image formation, ears are sensitive to change in sound waves.
Photobiology is related to the role of light in different biological processes like photosynthesis, photoperiodism, phototaxis and phototropism etc.
Use of energy and maintaining certain temperature of body.
The subject Biophysics shows the relation of Biology and Physics
Relation with Statistics and Mathematics
The researches in biology requires the knowledge of statistics and mathematics. Many interpretations in biology are based on the knowledge of statistics. The Mendelian ratio of monohybrid and dihybrid cross is the examples of relation of biology with statistics and mathematics.
Relation with Geography
Animals and plants are distributed at different regions of the earth. The north and south poles have similar climatic condition but only the south pole (Antarctica) has the Penguins. The polar bears are found only at the north poles. The Elephants are found only in Asia and Africa. This shows the relation of biology with the geography. It is called as Zoogeography or biogeography.
Biology as science of exception
Though there are different rules and regulations in the different branches of sciences, there are many exceptions in biology. So biology is called as the science of exceptions.
The red blood corpuscles(RBC) of mammals are without nucleus except Camels.
DNA is the hereditary materials in all except the Viruses.
The heart of reptiles are three chambered except the Crocodiles.
Fishes have gills for respiration but Protopterus (Nile lung fish) has lungs.
Larva develops into adult but American Salamander larva becomes sexually matured and gives birth to larva.
Birds are usually adapted for flying but certain birds like Kiwi, Ostrich can never fly.
Stems are usually aerial but ginger, potato have underground stem.
Mammals are viviparous but duck billed Platypus, Echidna is oviparous
General approach to understand life processes
The living beings have certain unified and basic characters by which they become different from non living things. Each and every living being is a complex entity which is made up of one or many cells. In the cells, there are different bio molecules. Micro molecules like water, salt, monosaccharide, amino acid etc and macro molecules like complex carbohydrate, protein and fats are present. The molecules interact, aggregate and participate in the vital activities of organisms. In this connection, Linus Pauling says that life results due to a relationship of molecules and not a property of any one molecule.
The life processes are given below
Nutrition -- it is the process of getting food. Green plants have chlorophyll. They can manufacture their food by the process known as photosynthesis. They are called autotrophs. Animals are not capable of synthesizing their food. They get their food either from plants or other animals. They are heterotrophs. The non green plants which take food from the dead bodies are called saprophytes.
Growth and metabolism-- plants and animals grow in their size. Plants grow in height indefinitely but animals grow in height for certain period. However there is growth all the time. It involves an increase in volume through the formation of new protoplasm with or without division of their structural units cells. Cells grow by addition of new protoplasm. This process of growth in living is called intussusceptions. It is irreversible. A crystal also grows but it is addition of new material at the surface. It is accretion. Metabolism is building up (anabolism) and breakdown ( catabolism) of body. It is a continuous process from birth to death.
Respiration – both animals and plants respire. They take O2 from atmosphere. They burn the food (glucose) to produce energy. It is aerobic respiration. The lower organism break down glucose with out O2 to produce energy. It is anaerobic respiration.
Excretion – the waste materials produced in side the body is discharged out. It is excretion. The lungs throw out CO2. The large intestine gives out undigested materials. The kidneys filter out the urea, uric acid etc. Animals discharges wastes as soon as possible. The plants can store in the part of body and throws after certain period. They also can use waste for mechanical strength.
Irritability and movement -- it is response to external or internal stimuli. Animals show quick response. The plants are slow to show the response. But there is rapid movement in insectivorous plants like Venus’s fly trap. In Mimosa (touch me not plant) the gentle pressure can make the folding of leaves.
Homeostasis - - it is the state of balance of salts, water, temp, pH etc. it is coordinating mechanism to keep the internal environment at steady or normal state.
Adaptability – all plants and animals are capable of undergoing certain changes in their structure, habit and habitat to become suitable to the environment. The fishes are adapted to live in water. Birds made them suitable to fly in air etc.
Evolution -- organisms under go changes in their genetic material. These changes are passed on to offsprings in succeeding generation. Such changes are raw material for evolution. This property of evolution is a function of population of organism and not in individual organism.
Reproduction -- they can produce their own kind. Since the living things eventually die, reproduction ensures survival of the group. Living organism come from pre existing living organism.
Ageing and death -- ageing is the process of deterioration of body. The efficiency of working decreases slowly and gradually. At the end, there is the death. The heart beat and respiration are arrested. Death helps to maintain certain number in population. The decomposers act on dead body to convert into C, H O, N,S etc. These are returned to the nature for balance.
Monday, June 8, 2009
Monday, April 13, 2009
theories of evolution
Lamarckism
Organic evolution
The doctrine of organic evolution states that the present day organisms are modified but lineal descendants of species that lived in former geological times and that more complex and highly differentiated forms have evolved from simpler ones by gradual modifications. It is still in operation.
One of the first attempts to explain the organic evolution was made by French Biologist Jean Baptiste Lamarck n 1809. he outlined his ideas in his book Philosophie Zoologique published in 1809.
This theory is based on observation that the changes in the environment lead to the changed pattern in the species.
This theory consists of four postulates or facts
Tendency to grow - the internal forces of life tends to increase in size of parts of an organism on the whole up to a certain limit. The limit is determined by life itself.
Formation of new organs - new organ or a part in the body is formed due to long felt need or want. For example webbed toes in duck.
Effects of use and disuse - the more frequently and continuously and animal used an organ; the more it was strengthened, developed and enlarged. If an organ wan not used, it gradually weakened and finally disappeared. For example legs of snake.
Inheritances of acquired character -- all changes which organism acquire during life time are acquired characters. These characters are inherited in the generations. The acquire characters go on accumulating through generations and finally in long course of time produce organism entirely different from the pre existing ones. So, this theory is also known as Theory of acquired characters. For example, Giraffe developed long neck and long legs by continuous effort and stretching to reach the higher level of trees. The longer neck and legs produced, passed on to the next generations. Over long period of time after successive generations, the present day Giraffe with long neck and leg were evolved.
Draw backs
Lamarck’s theory is rejected because acquired characters are never inherited. Acquired characters can bring changes in body or somatic cells, but not in the germ cells.
August Weismann proved that acquired characters affect the body and are somatic; they can not be inherited since they do not affect germ cells. Any variation must be present in the germ cells if they are to be inherited. In one experiment, he cut tail of mice for 20 generations, mouse produced after that have same length of tail. No decrease in length at all.
This theory could not produce any example from plants.
Darwinism
Charles Darwin and Alfred Russell Wallace jointly contributed a paper in 1858 putting forward the view that species had evolved by process of natural selection of those races most fitted to survive in particular surroundings. According to this theory, living organisms have common origin and through a series of small changes in the organism generation after generation new species are formed. This theory is known as theory of Natural Selection or Darwinism.
The theory of Natural Selection can be explained under following observations and consequences.
over production of offspring
Every lining organism tends to increase in a geometrical manner. Such reproductive
Potential of different species may be easily observed in nature. A single pair of English sparrow would be the ancestor of over 275 billion individuals in 10 years if they and their descendants could reproduce at their natural rate without any check. In case of slowest breeding animals like elephants, one pair of elephants in 800 years could have 29 million descendants in the absence of any check.
Total number of survivors remain nearly constant
In spite of their capacity to increase, population remains nearly constant. In case of fishes, they can lay large no of eggs, all the eggs do not hatch. Large number of fingerlings dies or killed before they reach reproductive age. Even in case of human beings, the mortality of infants is much higher. Besides, these are different checks by which population can not increase so high.
struggle for existence
the available food and other resources can support only a limited number of organisms . So animals and plants have to struggle for their existence.
Intraspecific struggle
Intraspecific struggle or competition occurs among the individuals of same species. This type of completion is fierce due to similar requirements. This may be for food, shelter and mate.
Interspecific struggle
This type of competition is found between two individuals of different species. The very common object for this type of competition is food.
Predation
There are different carnivore animals which kill and feed on the herbivores. These animals are said to be predators. Due to predation also no o animals are kept within limit.
Environmental struggle
Living organisms struggle with adverse environmental conditions like drought, heat cold, lightening, earthquake, volcanic eruption heavy rainfall flood etc. Besides out break of diseases, war etc can kill large no. of animals and plants.
variations and heredity
Individuals always try to become better adopted to utilize the resources and to survive successfully. For this they may have certain modifications or changes in their bodies. These changes are called variations. Variations are of two types. Some variations are harmful which make the animal unfit but some variations are useful or favorable. Useful variations are quite significant and make organisms fit in their environment. The same variation may be harmful at one environment but useful at other environment. Variations are inherited in the progeny and therefore progeny have better chances of survival.
Survival of fittest or Natural Selection
Those individuals having favorable variations would survive and propagate their kind. They can increase their population. Herbert Spencer called it survival of the fittest. Those which are fit can survive. According to Darwin, it is Natural Selection. Only those animals having favorable variations are selected. The animals with harmful variations will decline and one day they will become extinct.
Origin of species
Useful variations are accumulated generation after generation for thousands of years. After long time, the generations produced will be quite different from parents. This is the emergence of new subspecies. These new subspecies later on form different species. In this way new species in originated. Some process of variations with heredity accompanied by natural selection was sufficient over the vast geological time to produce all the living animals of today.
Natural Selection is admitted today as the most probable explanation of evolution. With the scanty of knowledge of the nature of variations and heredity before 1900, little could be added to what Darwin knew of the phenomena.
Criticism
A. Mutation is the process in which sudden large variations occur in the animal’s body. It is now proved that mutation has powerful role in evolution. Darwin ignored mutation.
B. Darwin could not identify the heritable variation and non heritable variation. Because only the heritable variations are counted.
C. Natural selection is not a creating or initiating force but only directing or controlling factor. Natural selection operated only after variations have appeared. It accounts for preservation rather that origin of favorable variation.
D. Darwin’s theory does not show how natural selection is brought about nor does it explain the origin of non useful variations.
E. This theory explained the survival of the fittest but not arrival of the fittest.
Neo Darwinism
On these and several other grounds it is now held by many scientists that the theory of natural selection is not only the factor in evolution. Darwin and his contemporaries were not aware of cytological and genetic information which became available later on. Since Darwin’s time interest has not lessened in the matter of how evolution has taken place. At present, the most widely accepted theory of evolution incorporates many of Darwin’s ideas into a frame work of genetics. Neo Darwinism is modification of Darwin’s theory taking into account the results of more recent work.
Scientist like Dobzhansky, RA Fischer, Julian Huxley, JBS Haldane Sewell Wright, Hugo de vries etc contributed to the Neo Darwinism.
It is based on following facts.
Mutation -- it is the sudden heritable change which occur in the chromosome.
Genetic recombination -- crossing over in the meiotic division brings changes in the genetic composition. It is responsible for the variations in the population.
Natural Selection -- useful variations are preserved by natural selection.
Genetic drift or Sewell Wright Effect -- variation in gene frequencies within populations can occur by chance than by natural selection. It is important in small or isolated population.
Reproductive isolation -- it can help to bring more changes in new environment. When not mixed, they become more and more different from one another.
Organic evolution
The doctrine of organic evolution states that the present day organisms are modified but lineal descendants of species that lived in former geological times and that more complex and highly differentiated forms have evolved from simpler ones by gradual modifications. It is still in operation.
One of the first attempts to explain the organic evolution was made by French Biologist Jean Baptiste Lamarck n 1809. he outlined his ideas in his book Philosophie Zoologique published in 1809.
This theory is based on observation that the changes in the environment lead to the changed pattern in the species.
This theory consists of four postulates or facts
Tendency to grow - the internal forces of life tends to increase in size of parts of an organism on the whole up to a certain limit. The limit is determined by life itself.
Formation of new organs - new organ or a part in the body is formed due to long felt need or want. For example webbed toes in duck.
Effects of use and disuse - the more frequently and continuously and animal used an organ; the more it was strengthened, developed and enlarged. If an organ wan not used, it gradually weakened and finally disappeared. For example legs of snake.
Inheritances of acquired character -- all changes which organism acquire during life time are acquired characters. These characters are inherited in the generations. The acquire characters go on accumulating through generations and finally in long course of time produce organism entirely different from the pre existing ones. So, this theory is also known as Theory of acquired characters. For example, Giraffe developed long neck and long legs by continuous effort and stretching to reach the higher level of trees. The longer neck and legs produced, passed on to the next generations. Over long period of time after successive generations, the present day Giraffe with long neck and leg were evolved.
Draw backs
Lamarck’s theory is rejected because acquired characters are never inherited. Acquired characters can bring changes in body or somatic cells, but not in the germ cells.
August Weismann proved that acquired characters affect the body and are somatic; they can not be inherited since they do not affect germ cells. Any variation must be present in the germ cells if they are to be inherited. In one experiment, he cut tail of mice for 20 generations, mouse produced after that have same length of tail. No decrease in length at all.
This theory could not produce any example from plants.
Darwinism
Charles Darwin and Alfred Russell Wallace jointly contributed a paper in 1858 putting forward the view that species had evolved by process of natural selection of those races most fitted to survive in particular surroundings. According to this theory, living organisms have common origin and through a series of small changes in the organism generation after generation new species are formed. This theory is known as theory of Natural Selection or Darwinism.
The theory of Natural Selection can be explained under following observations and consequences.
over production of offspring
Every lining organism tends to increase in a geometrical manner. Such reproductive
Potential of different species may be easily observed in nature. A single pair of English sparrow would be the ancestor of over 275 billion individuals in 10 years if they and their descendants could reproduce at their natural rate without any check. In case of slowest breeding animals like elephants, one pair of elephants in 800 years could have 29 million descendants in the absence of any check.
Total number of survivors remain nearly constant
In spite of their capacity to increase, population remains nearly constant. In case of fishes, they can lay large no of eggs, all the eggs do not hatch. Large number of fingerlings dies or killed before they reach reproductive age. Even in case of human beings, the mortality of infants is much higher. Besides, these are different checks by which population can not increase so high.
struggle for existence
the available food and other resources can support only a limited number of organisms . So animals and plants have to struggle for their existence.
Intraspecific struggle
Intraspecific struggle or competition occurs among the individuals of same species. This type of completion is fierce due to similar requirements. This may be for food, shelter and mate.
Interspecific struggle
This type of competition is found between two individuals of different species. The very common object for this type of competition is food.
Predation
There are different carnivore animals which kill and feed on the herbivores. These animals are said to be predators. Due to predation also no o animals are kept within limit.
Environmental struggle
Living organisms struggle with adverse environmental conditions like drought, heat cold, lightening, earthquake, volcanic eruption heavy rainfall flood etc. Besides out break of diseases, war etc can kill large no. of animals and plants.
variations and heredity
Individuals always try to become better adopted to utilize the resources and to survive successfully. For this they may have certain modifications or changes in their bodies. These changes are called variations. Variations are of two types. Some variations are harmful which make the animal unfit but some variations are useful or favorable. Useful variations are quite significant and make organisms fit in their environment. The same variation may be harmful at one environment but useful at other environment. Variations are inherited in the progeny and therefore progeny have better chances of survival.
Survival of fittest or Natural Selection
Those individuals having favorable variations would survive and propagate their kind. They can increase their population. Herbert Spencer called it survival of the fittest. Those which are fit can survive. According to Darwin, it is Natural Selection. Only those animals having favorable variations are selected. The animals with harmful variations will decline and one day they will become extinct.
Origin of species
Useful variations are accumulated generation after generation for thousands of years. After long time, the generations produced will be quite different from parents. This is the emergence of new subspecies. These new subspecies later on form different species. In this way new species in originated. Some process of variations with heredity accompanied by natural selection was sufficient over the vast geological time to produce all the living animals of today.
Natural Selection is admitted today as the most probable explanation of evolution. With the scanty of knowledge of the nature of variations and heredity before 1900, little could be added to what Darwin knew of the phenomena.
Criticism
A. Mutation is the process in which sudden large variations occur in the animal’s body. It is now proved that mutation has powerful role in evolution. Darwin ignored mutation.
B. Darwin could not identify the heritable variation and non heritable variation. Because only the heritable variations are counted.
C. Natural selection is not a creating or initiating force but only directing or controlling factor. Natural selection operated only after variations have appeared. It accounts for preservation rather that origin of favorable variation.
D. Darwin’s theory does not show how natural selection is brought about nor does it explain the origin of non useful variations.
E. This theory explained the survival of the fittest but not arrival of the fittest.
Neo Darwinism
On these and several other grounds it is now held by many scientists that the theory of natural selection is not only the factor in evolution. Darwin and his contemporaries were not aware of cytological and genetic information which became available later on. Since Darwin’s time interest has not lessened in the matter of how evolution has taken place. At present, the most widely accepted theory of evolution incorporates many of Darwin’s ideas into a frame work of genetics. Neo Darwinism is modification of Darwin’s theory taking into account the results of more recent work.
Scientist like Dobzhansky, RA Fischer, Julian Huxley, JBS Haldane Sewell Wright, Hugo de vries etc contributed to the Neo Darwinism.
It is based on following facts.
Mutation -- it is the sudden heritable change which occur in the chromosome.
Genetic recombination -- crossing over in the meiotic division brings changes in the genetic composition. It is responsible for the variations in the population.
Natural Selection -- useful variations are preserved by natural selection.
Genetic drift or Sewell Wright Effect -- variation in gene frequencies within populations can occur by chance than by natural selection. It is important in small or isolated population.
Reproductive isolation -- it can help to bring more changes in new environment. When not mixed, they become more and more different from one another.
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