SAMACHEER CLASS 10 CHAPTER 19 NOTES

 

UNIT 19

  samacheer SCIENCE
CLASS 10

ORIGIN & EVOLUTION OF LIFE

INTRODUCTION

·     Living organisms – posses distinct characteristics, display organisational & fundamental unity, entail a mechanism of origin & evolution of diversities & maintain a balanced relationship with nature

·     Most aspects of evolution indicate – knowledge of the past – become essential for fully understanding the present

INTRODUCTION

·     Life on earth – changed through time

·     History of life – 2 aspects

·     Origin of life on earth

·     mechanism involved in gradual changes & adaptations of living organisms – through time – known as Evolution of life

ORIGIN OF EARTH

·     Origin of life – linked with origin of Earth

·     Big Bang Theory – explains origin of universe

·     BBT – proposes that – universe had an explosive beginning (Big Bang) – originated 15 billion years ago

·     Universe composed of – stars, clouds of gas & dust – form the galaxies

·     Solar system – probably created – when gaseous clouds – started to collapse – due to force of its own gravity – forming atoms & particles

·     Atoms, dust grains & gaseous disc – aggregated to form clumps – gave rise to planets

·     This forms solar system – of milky way galaxy

·     Earth – supposed to have been formed – about 4.5 billion years back

·     Life appeared – 500 million years – after formation of Earth

THEORIES ON ORIGIN OF LIFE

·     Many theories – postulated to explain – origin of life

·     Views on origin of life – put forth as

SPECIAL CREATION

·     This idea embodies that – life on Earth – divine creation

·     Also attributes to supernatural event – at a particular time in the past

·     Also emphasizes – life has not changed – ever since it’s origin

SPONTANEOUS GENERATION (ABIOGENEIS)

·     According to this theory – life originated spontaneously – from lifeless matter

·     It was believed – fishes originated from mud; frogs from moist soil; & insects from decaying matter

BIOGENESIS

·     Speculated by – Louis Pasteur (1862)

·     Life – originated from – pre-existing life

·     He showed that – pre-sterilised flask – kept closed airtight – with killed yeast – did not give rise to any life form

·     Another flask – kept open to air – living organisms arose – from killed yeast

EXTRA TERRESTRIAL OR COSMIC ORIGIN

·     Some scientists believe – life came from outer space

·     States that – units of life – called spores (panspermia) – transferred to different planets – including earth

·     This is still an idea of some astronomers  

CHEMICAL EVOLUTION OF LIFE

·     This idea developed by – Parin (1922) & Haldane (1929)

·     They proposed – with conditions prevailing on earth – life arose by – series of chemical reactions

·     First form of life – come from pre-existing non-living inorganic molecules – gave rise to diverse organic molecules – transformed into colloid system – to produce life

·     This modern concept – on origin of life – was accepted

EVIDENCES OF EVOLUTION

·     Evolution – better understood – only by observing – interrelationship between existing organisms – and relating the similarities with extinct organisms

·     Inter relationship of organisms – supported by evidences from different branches of biology

·     These evidences – support the concept – organisms evolved from common ancestors

EVIDENCES FROM MORPHOLOGY & ANATOMY

·     Comparative study of morphology & anatomy of animals – reveal – they posses common set of characteristics

HOMOLOGOUS ORGANS

·     Homologous organs – inherited from common ancestors – with similar developmental pattern in embryos

·     Forelimbs of mammals – homologous

·     Eg: human hand, front leg of cat, flipper of whale & bats wing

·     Look dissimilar & adapted for different functions

·     Mode of development & basic structure of bone – similar

ANALOGOUS ORGANS

·     Look similar & perform similar functions – but have different origin & developmental pattern

·     Function of wings of a bat, wings of bird & wings of insect – similar; but basic structures – different

VESTIGIAL ORGANS

·     Degenerated & non-functional organs – of animals – called vestigial organs

·     Same organs – well-developed & functional – in some related forms

·     Some vestigial organs in man – vermiform appendix, nictitating membrane, caudal vertebra, coccyx, etc.,

ATAVISM

·     Appearance of ancestral characters – in some individuals – called atavism

·     Eg: presence of rudimentary tail – in new born babies, presence of thick hair – on human body

 

EVIDENCES FROM EMBRYOLOGY

·     Study of comparative embryology of different animals – supports concept of evolution

·     Embryos – from fish to mammals – similar in early stages of development

·     Differentiation of their special characters – appear in latter stages of development

 

BIOGENETIC LAW OR RECAPITULATION THEORY

·     Given by Ernst Haeckel

·     According to the theory – ontogeny recapitulates phylogeny

·     Stages of development of the individual animal – repeats evolutionary history – of the entire race of animal

EVIDENCES FROM PALAEONTOLOGY

·     Palaeontology – study of fossils

·     Leonardo da Vinci – Father of Palaeontology

·     Study of fossils – helps to understand – evolution of many invertebrates & vertebrates

·     Fossil records show – evolution has taken a gradual process – from simple to complex organisms

·     Origin of modern birds – supported by evidences from palaeontology

ARCHAEOPTERYX

·     Oldest known fossil bird

·     Early bird-like form – found in Jurassic period

·     Considered as – connecting link between – reptiles & birds

·     Had wings with feathers – like a bird

·     Had long tail, clawed digits & conical teeth – like reptile

THEORIES OF EVOLUTION

·     Life – evolved along with evolution of earth

·     Evolution – gradual change – occurring in living organisms – over a period of time

·     Formation of new species – due to changes in specific characters – over several generations – in response to natural selection – called evolution

·     Natural changes occurring – explained through – theories of evolution – proposed by – Lamarck & Darwin

LAMARCKISM

·     Jean Baptiste Lamarck (1744-1829) – French naturalist – theory of evolution

·     His theory of evolution – published in ‘Philosophic Zoologique’ (1809)

·     Popularly known as – ‘Theory of inheritance of Acquired characters or ‘Use and Disuse Theory’ or ‘Lamarckism’

PRINCIPLES OF LAMARCKISM

INTERNAL VITAL FORCE

·     Living organisms or their parts – tend to increase in size continuously

·     Increase in size – due to inherent ability of the organism

ENVIRONMENT & NEW NEEDS

·     Change in environment – brings changes in the organisms – according to their needs

·     Organisms develop – certain adaptive characters – in response to environmental changes

·     Adaptations – may be in the form of – development of new body parts

USE AND DISUSE THEORY

·     Lamarck’s use and disuse theory states – if an organ – used constantly – it develops & strengthens well

·     When an organ – not used for a long time – gradually degenerates

·     Ancestors of giraffe – had short neck & short forelimbs

·     Due to shortage of grass – forced to feed on leaves from trees

·     Continuous stretching of – their neck & forelimbs – resulted in – development of long neck & long forelimbs

·     Example of constant use of an organ

·     Degenerated wing of Kiwi – example for organ of disuse

THEORYOF INHERITANCE OF ACQUIRED CHARACTERS

·     When there is change in environment – animals respond to the change

·     They develop – adaptive structures

·     Characters developed by animals – during their life time – in response to environmental changes – called acquired characters

·     According to Lamarck – acquired characters – transmitted to offsprings – by the process of inheritance

DARWINISM OR THEORY OF NATURAL SELECTION

·     Charles Darwin (1809 – 1882) – great naturalist & philosopher – 18^th century

·     Born in England – in 1809

·     While in college – through his friendship with – Professor J.S. Henslow – fascinated towards nature

·     At that time – British Admiralty – planned a voyage of exploration – 5 years – on a ship named – H.M.S.Beagle – around South America

·     Dr. Henslow – asked to nominate a young naturalist for the voyage

·     Darwin – got the opportunity

·     During the 5 years (1831-1835) – he visited many parts of the world – a number of islands – Galapagos island & Pacific island

·     He observed – nature of land, plants & animals – of the region he visited

·     Further worked for 20 yrs – to develop – theory of natural selection

·     Darwin – published his observations & conclusions – under the name – ‘Origin of Species’ (1859)

·     The book of Darwin – demonstrates the fact of evolution

·     Elaborates – theory of natural selection for evolution

PRINCIPLES OF DARWINISM

OVER PRODUCTION

·     Living beings – have the ability – to reproduce more individuals – form their own progeny

·     Have capacity to multiply – in geometrical manner

·     This will increase reproductive potential leads to overproduction

STRUGGLE FOR EXISTENCE

·     Due to over production – population increases drastically

·     But space to live & food availability – same

·     Creates intense competition – among organisms – for food & space – leading to struggle

·     Struggle for existence – 3 types

o  INTRA SPECIFIC STRUGGLE

§  Competition – among individuals of same species

o  INTER SPECIFIC STRUGGLE

§  Competition – between organisms of different species – living together

o  ENVIRONMENTAL STRUGGLE

§  Natural conditions – extreme heat or cold, drought & floods – affect existence of organism

VARIATIONS

·     Occurrence of variation – characteristic feature – of all plants & animals

·     Small variations – important for evolution

·     According to Darwin – favourable variations – useful to organism; unfavourable variations – harmful or useless

SURVIVAL OF THE FITTEST OR NATURAL SELECTION

·     During struggle for existence – organisms overcome the challenges – survive & adapt to surrounding environment

·     Organisms – unable to face the challenge are unfit to survive & disappear

·     Process of selection of organism – with favourable variation – called Natural selection

ORIGIN OF SPECIES

·     According To Darwin – new species originates – by gradual accumulation – of favourable variations – for a number of generations

 

VARIATION

·     Sexual reproduction – involves meiosis – helps in recombination of genes – during gametic fusion

·     Leads to – differences in the phenotype of offsprings – from its parents

·     Differences – called variation

·     Variation – differences among individuals of same species – and offsprings of same parent

·     Variation – raw material – play important role in evolution

·     Evolution – not possible without variation

TYPES OF VARIATION

SOMATIC VARIATION

·     Variations – that affect the body (somatic) cells – of organisms – called Somatic variation

·     Not inheritable

·     Occur due to – environmental factors

GERMINAL VARIATION

·     Variations – produced in germ cells – of organisms – called Germinal Variation

·     They are inherited

·     They may be present in ancestors – or may occur suddenly

·     Classified into 2 types

o  Continuous variation

o  Discontinuous variation

CONTINUOUS VARIATION

·     Small variations – occur among individuals of a population

·     Also called – fluctuating variations

·     Occur by – gradual accumulation in population

·     Eg: Skin colour, height & weight of an individual, colour of eye, etc.,

 

DISCONTINUOUS VARIATION

·     Sudden changes – occur in an organism – due to mutations

·     Donot have – intermediate forms

·     These variations – not useful for evolution

·     Eg: short legged Ancon sheep, six or more digits (fingers) in human, etc

·     Discontinuous variation – basis for mutation theory – proposed by De Vries

RELATIONSHIP BETWEEN MUTATION & VARIATION

·     Mutation & variation – 2 events – involved in evolution

·     Mutation – arises due to – errors that occurs – during DNA replication – or exposure to UV rays or chemicals

·     Mutation – leads to variation – brings about changes – in a single individual 

PALEOBOTANY

·     Paleobotany – derived from Green words

·     Paleon – old; botany – study of plants

·     A branch of paleontology – deals with recovery & identification of plant remains – of geological past

·     Plant fossil – any preserved part of a plant – died long back

·     Fossils – prehistoric impressions – may be hundred to millions of years old

·     Most of the plant fossils – disarticulated parts of plants

·     Rare to find – plants to be preserved as whole

IMPORTANCE OF FOSSILS

·     Throw light – on phylogeny & evolution of plants

·     Fossils plants – gives historical approach – to plant kingdom

·     Useful – in classification of plants

·     Fossil plants – used in – description & comparative anatomy

KASPAR MARIA VON STERNBERG

·     Father of Paleobotany

·     (1761-1838) – born in Europe

·     Established – Bohemian National Museum – in Prague

·     Deemed to be – founder of Modern Paleobotany 

BIRBAL SAHANI

·     Father of Indian Paleobotany

·     (1891-1949)

·     Presented his research – on 2 different areas of Paleobotanist

·     Anatomy & morphology of Paleozoic ferns

·     Fossil plants of Indian Gondwana formations

 

FOSSILIZATION

·     Process of formation of fossil in rocks – fossilization

·     Common methods of fossilization

·     Petrification, molds & cast, carbonization, preservation, compression & infiltration

PETRIFICATION

·     Minerals – silica slowly penetrate in – and replace original tissue – forms rock like fossil

·     This method – can preserve hard & soft parts

·     Most bones & wood fossils – petrified

MOLD & CAST

·     Replica of a plant or animal – preserved in sedimentary rocks

·     When the organism – buried in sediment – dissolved by underground water – leaving hollow depression – called mold

·     Mold – shows original shape – but does not reveal internal structure

·     Minerals or sediment – fill hollow depression – forms a cast

PRESERVATION

·     Original remains – preserved in ice or amber (tree sap)

·     They protect organisms – without decaying

·     Entire plant or animal – preserved

COMPRESSION

·     When an organism dies – hard parts of their bodies – settle – at bottom of the sea bed – covered by sediment

·     Sedimentary process – continuously goes on – fossils formed

INFILTRATION OR REPLACEMENT

·     Precipitation of minerals – takes place – later on infiltrate the cell wall

·     Brought about by minerals – silica, calcium carbonate & magnesium carbonate

·     Hard parts – dissolved & replaced by minerals

DO YOU KNOW?

LIVING FOSSILS

·     Living organisms – similar in appearance – to fossilized distant ancestors

·     Usually do not have – extinct close features

·     Eg: Ginko biloba

DETERMINATION OF AGE OF FOSSILS

·     Age of fossils – determined by radio active elements – present in it

·     May be carbon, uranium, lead or potassium

·     Used in paleobotany & anthropology – for determining age of human fossils & manuscripts

RADIOACTIVE CARBON (C¹⁴) DATING METHOD

·     Discovered by W.F. Libby (1956)

·     Carbon consumption of animals & plants – stops after death

·     After death – decaying of C¹⁴ occurs continuously

·     Time passed since death – of plant or animal – calculated by measuring – amount of C¹⁴ present in their body

MORE TO KNOW

GEOLOGICAL TIME SCALE

·     A system of chronological dating – relates geological rock strata to time

·     Used by geologists, paleontologists & other Earth scientists – to describe the timing & relationships of events – occurred during Earth’s history

DO YOU KNOW?

·     THIRUVAKKARAI FOSSIL WOOD PARK (VILLUPURAM DISTRICT, TAMIL NADU)

·     2 million years ago – tree trunks buried along the river

·     In course of time – organic matter – replaced by silica & fossilized

·     They retained – colour, shape & texture – converted into solid rocks

·     Annular rings, texture, colour of layers, nodes & every properties of plant – still visible

ETHNOBOTANY

·     Study of a region’s plants & their practical uses – through traditional knowledge – of local culture of people

·     Term ‘Ethnobotany’ – coined by J.W.Harshberger (1985) – to include study of plants – used by primitive & aboriginal people

·     Though this discipline – existed for ages – ethnobotany emerged as a new academic branch of natural science – in 20^th century

ASPECTS OF ETHNOBOTANY

·     Ethnobotany – has relevance with – problems of nutrition, health care & life support system, faith in plants, cottage industries, economic upliftment, conservation of biodiversity & sustainable use of plant resources

IMPORTANCE OF ETHNOBOTANY

·     Provides traditional uses of plant

·     Gives information about – certain unknown & known useful plants

·     Ethnomedicinal data – useful source of information – for chemists, pharmacologists & practitioners of herbal medicine

·     Tribal communities – use ethnomedicinal plant parts – barks, stem, root, leaves, flower bud, flowers, fruits, seeds, oils, resins, dyes, gum – for treatment of diseases – diarrhoea, fever, headache, diabetes, jaundice, snakebites, leprosy, etc.,

ASTROBIOLOGY / EXOBIOLOGY

·     Astrobiology / Exobiology – science which looks for – presence of extra terrestrial life in universe

·     Deals with – origin, evolution & distribution of life – in the universe

·     Also investigate – possibility of life in other world

·     Major concept – habitable zone

·     Theory explains – any planet can support – existence of life – if it fulfills – 2 important criteria

·     Must have – right mass – to retain atmosphere

·     Must have an orbit at right distance from sun (star) – that it allows liquid water to exist

·     It should be neither too hot nor too cold

·     Often referred as – Goldilock zone for life

·     In our solar system – Earth – only planet in Goldilocks zone

·     This zone varies – as star evolves

·     Mars – also been habitable

·     Life on Mars – Likely to be the creatures – we find in extreme environments on Earth

·     Organisms – live in extreme environment on earth – called extremophiles

·     Our own solar system – have many areas – different from Earth – find presence of life – similar to extremophile bacteria

DO YOU KNOW?

·     NASA – developing Mars 2020 astrobiology

·     To investigate – astrobiologically relevant ancient environment on Mars, its surface geological processes & possibility of past life on Mars & preservation of biosignatures within accessible geological materials