Download 08 - SCERT

BIOLOGY
Long, long ago...
even before the
dinosaurs... two
specks of life went
for a walk.
Did you notice Mini's doubt?
How might have those specks of life
formed?
Let us try to find out the answer for this
problem, shall we? What are the things you
have understood about life?
• Metabolism is the chief sign of life
• Metabolism takes place inside the cell
• Cell is the basic unit of life
If so, won't there be a relationship between
the formation of the cell and the origin of
life?
How might
have those
specks of life
been then?
The basic unit of life called cell is made
up of many substances like carbohydrate,
protein, fat etc. They have no life, do they?
The elements by which they are made up
of too have no life. Then how is it that life
originated when such non-living
components joined together? For the first
time in 1924, the Russian scientist Oparin
formulated a hypothesis on this.
Independently the English scientist, J.B.S.
Haldane, also reached a similar
conclusion.
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BIOLOGY
Oparin - Haldane Hypothesis
Gases like hydrogen, ammonia, water vapour and methane which were present in the
atmosphere of primitive earth reacted together to form simple organic molecules like
amino acids. This was the result of chemical reactions that took over thousands of
years. Lightning, ultraviolet rays from the sun, volcanic eruptions etc. favoured this by
providing the high energy required for these reactions. Following this the water vapour
present in the earth's atmosphere cooled causing rain for millions of years. This resulted
in the formation of oceans. Organic molecules formed in the atmosphere by the reactions
of inorganic compounds, dissolved in rain water and reached the oceans. They further
reacted with one another to form more complex molecules. In this way, due to changes
over millions of years, the first form of life originated on earth .
The Oparin - Haldane hypothesis was
later substantiated through many
experiments. Consider the chronology
given, collect more information
substantiating this hypothesis and
prepare notes in your Science diary.
could also synthesize the nitrogen
base, adenine, through these
experiments.
1963
Cyril Ponnamperuma :
Stanley Miller,Harold Urey :
1953
Cyril Ponnamperuma
Stanley Miller
Harold Urey
Recreated the conditions of
primitive earth in the laboratory and
synthesised amino acids from
substances like ammonia and
methane.
1961 Juan Oro :
Using the compounds which were
synthesised in Stanley Miller's
experiment as basic substances,
more amino acids and peptide
molecules were synthesised. He
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The SriLankan scientist Cyril
Ponnamperuma could prepare
adenosine molecules from inorganic
substances. This helped to explain
how nucleic acids were formed.
There are many other views related to the
origin of life.
The strongest one among them is that life
originated near volcanoes in the oceans.
The concept which states that life particles
originated elsewhere in the universe and
reached the earth, also exists nowadays.
This view is known as the Panspermia
concept.
BIOLOGY
You have learnt that the first biomolecule
was formed from inorganic molecules.
Since there was no free oxygen, the
organisms present at that time were
believed to be single-celled anaerobic
organisms with a very simple
organisation. But today, how many forms
of life including plants, animals and
microorganisms do we see!
How may they have evolved from the first
organism?
Cells
capable
of
photosynthesis were formed from early
anaerobes at some stage of evolution.
Consequently free oxygen was formed in
the atmosphere, and it is considered that
this led to the emergence of aerobic
organisms.
How long might have this process taken?
Record your guess.
....................................................................
Analyse the geological time scale given
below and record the validity of your
guess in the Science diary.
Origin of the earth
4600
4500
Origin of oceans
Chemical evolution
4000
First form of life
3500
Anaerobic micro organisms
capable of photosynthesis
3000
Aerobic microorganisms
capable of photosynthesis
Origin of multicellular
organisms
2500
Million years ago
The scientific world is unanimous in the
fact that the first cell was formed by the
combination of organic molecules.
2000
1500
1000
Illustration 8.1 - Geological Time Scale
How is it that so many diverse organisms were formed on the earth?
There are several theories regarding the formation of different species of organisms
through evolution. The scientist Jean Baptist Lamarck was the first to formulate his
thoughts on evolution in the form of a theory. Analyse the illustration and form inferences
based on the indicators given.
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BIOLOGY
A
B
C
Illustration 8.2
Indicators
¬ Compare the physical structure of the giraffes.
¬ What are the changes that occurred in the environment? What challenges did it
make on the giraffe?
¬ What are the changes that appeared in the physical structure of the giraffe to
overcome this challenge?
Lamarck argued that through continuous use of the neck (stretching), giraffes with
long necks evolved. He also argued that the ancestors of snakes had limbs, and their
disuse led to the evolution of the species of snakes without limbs. Lamarck's concept
is called the Theory of Inheritance of Acquired characters. Lamarck's theory could be
summarized as follows.
Use or disuse of
organs depending
on living conditions
Changes in the
structure of
organs
Transmitted to
the next
generation
New species
of organism
evolves
Illustration 8.3
Lamarck's theory that the variations
acquired by an organism during its life
time are transmitted to the next
generation, was questioned.
Why do children born to mothers with
pierced ears have to pierce their ears
again? Record your inferences based on
the indicators given.
....................................................................
110
Indicators
—
Do the changes in the body that occur
in the life time of an organism affect
the structure of its genes?
—
Do the variations which do not affect
genetic constitution get transferred to
the next generation?
Is it clear why Lamarck's theory was
questioned?
BIOLOGY
It was Charles Darwin,
the famous naturalist,
who
presented
evolutionary thought
almost
logically
through scientific
research.
Galapagos Finches
The voyage which he
Charles Darwin
began
on
17 th
1809-1882
December 1831 became
a milestone in the history of evolution.
During his voyage the geographical area
which influenced and helped Darwin the
most was the Galapagos islands. The
different species of finches (Darwin's
finches) found in these islands led him to
think of evolution of species. There are 13
types of finches in 15 islands! Finches
which were similar in sound and nesting
habits showed differences in food and
food habits. Observe Illustration 8.4.
Record your inferences based on the
indicators.
Herbivorous
finch
Bud
Cactus finch
Seed eating large
ground finch
Buds
fruits
Large
seeds
Seed eating South American ground
finch
Small
seeds
Insects
small
insects
Seed eating medium
ground finch
Insectivorous
woodpecker finch
Illustration - 8.4.
Insectivorous small
tree finch
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BIOLOGY
Indicators
—
Can you find any relationship between
the structure of the beak and food
habits in finches?
—
How might have finches with different
types of beaks originated?
Darwin's Inference
The ancestors of insectivorous finches
migrated to Galapagos islands from South
America. These finches got isolated in
each of these islands and in the absence of
predators, got accustomed to the new
environment and evolved into different
types of finches.
The Galapagos islands with its rich
biodiversity is known as nature's rightful
cradle with regard to evolution.
Collect information about other organisms
of the Galapagos islands, their diversity
and its reasons, and record it in your
Science diary.
Galapagos Tortoises
These huge tortoises have a life span of more than 200 years.15 subspecies are found
here. They differ chiefly in the length of the neck and in the shape of the external shell.
Fig - 8.1.
Iguana
Terrestrial Iguana
Marine Iguana
Iguanas are a group of carnivorous
organisms belonging to the class Reptilia.
However herbivorous iguanas are seen only
in Galapagos. These include marine iguanas
which collect food from the sea and terrestrial
iguanas which eat cactus buds.
Fig - 8.2
Analysing the information collected during his voyage, Darwin formulated the theory
of evolution which he presented in his book 'The Origin of Species'.
Through the theory of natural selection Darwin presented how the evolutionary process
takes place. Observe Illustration 8.5. regarding natural selection. Analyse it on the basis
of indicators and record your inferences in the Science diary.
112
BIOLOGY
Over Production
Organisms tend to produce
more number of offsprings than
that can be sustained.
Struggle for Existence
Competition between
organisms for the limited
resources.
Limited Resources
Resources such as food, space etc. are limited.
Variations
Variations are found in
each species.
Organisms with
favourable variations.
Organisms with
unfavourable
variations.
Survive
Evolution
New species with
favourable variations.
Indicators
—
What are the circumstances that lead
to the struggle for existence?
—
Who survives in this competition?
—
Which are the stages that lead to the
formation of new species?
Hope you have understood what the
process of natural selection is. Write a
practical definition for it.
....................................................................
The British naturalist Alfred Russel
Wallace also arrived at Darwin's
inferences on evolution. Studies
conducted in the Indonesian islands etc.
led him to this. Even though the theory of
Get eliminated
Illustration - 8.5.
natural selection was
widely
accepted,
Darwin could not
explain how variations
occur and how they get
Alfred Russel
transferred to the next Wallace (1823-1913)
generation. This was the
major drawback he faced.
It was the progress of genetics that gave a
new impetus to evolutionary studies.
How far has the growth of genetics helped
to substantiate the concepts of evolution?
Based on the indicators, analyse the given
description and record your inferences in
the Science diary.
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BIOLOGY
The scientist, Hugo de
Vries, postulated a theory
which states that sudden
and heritable changes
lead to evolution. This is
known as mutation theory. Hugo de Vries
Neodarwinism is the
modern theory of evolution that explains
Darwin's evolutionary concepts in the light
of the latest information in genetics.
Mutations in genes and chromosomes
will lead to variations within species.
When they undergo natural selection, only
those which conform to the changed
environment exist and the others get
eliminated.
Another reason for the origin of new
species is isolation. Continental drift and
natural calamities are reasons for
isolation. Natural obstructions caused as
a result of the formation of deserts,
mountains, rivers, etc. also lead to
isolation. In groups of animals so isolated,
variations may increase over the years
due to continuous mutations and new
species are formed.
Pouched mammals which enjoyed a wide
distribution in other continents too are
now found only in Australia. Australia lost
the terrestrial connection with Asia due to
continental drift and these groups of
animals were isolated there. But in other
continents mammals evolved to form new
species. Unable to withstand the
competition from these newly evolved
mammalian species, the pouched
animals that inhabited there became
extinct. Similarly, it is also believed that
the ancestors of camels migrated from
America to Africa and Asia . The Arabian
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camel and the Bactrian camel evolved as
a result of isolation in new regions.
Arabian Camel
The camel which is
adapted to the life
in the desert
Bactrian Camel
The camel which is
adapted to live in
extreme cold conditions
Fig - 8.3.
Indicators
—
What are the causes of variations in
living organisms?
—
Why are primitive mammals like the
pouched mammals and egg-laying
ones confined to Australia only?
—
What explanation can you give for the
origin of two species of camels
according to different climatic
topographic groups?
Find more evidences for ascertaining the
distribution and evolution of organisms
in relation to continental drift and write
them down in the Science diary.
Now you have a fair understanding of the
great men who have contributed to the
branch of evolutionary science. Collect
more information about them, their
studies, their contributions etc. and
prepare a document on evolutionary
history.
BIOLOGY
You have understood that evolutionary theories have been formulated by observing
organisms and studying their relationships with the surroundings. Can't the
morphological characteristics of diverse organisms and the environment in which they
live, give answers for evolutionary secrets?
Observe Figure 8.4 and compare the structure
humerus
ulna
metacarpals
carpals
radius
Forelimb of Man
Forelimb of crocodile
Flipper of whale
Wing of bird
Fig.8.4 Structure of the forelimbs of organisms
¬ Are the differences seen in the
morphology of organisms seen in the
anatomy also? What is the reason?
....................................................................
Haven't you understood the basic unit of
life, the cell? You know that there are many
similarities in cell structure and life
processes of all organisms. Find them on
the basis of indicators and note them in
the Science diary.
Indicators
—
Protoplasm
— Cell organelles
—
Cell respiration
— Excretion
Classification has great relevance in the
study of biology. You have learnt that in
classification, organisms are grouped into
large groups based on their similarities
and small groups based on their
differences.
How far do the morphological features, life
processes and classification substantiate
the concept of a common ancestor in
evolution? Discuss and note down the
inferences.
....................................................................
Isn't it possible to gather evidences of
evolution from organisms that lived
earlier as from organisms that live today?
Fossil studies provide a lot of information
about ancient organisms and the direction
of evolution. Fossils are remnants or traces
of organisms that lived in the past,
preserved in the earth crust. The branch
of science which deals with fossils is
called Paleontology.
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BIOLOGY
Analyse Figure 8.5 based on indicators and hold a discussion on how fossils become
evidences of evolution. Draw inferences therein.
Fossil of spider trapped inside amber
Foot print of the human ancestor
Australopithecus in lava
Fossilised pine trees
Fossil of woolly mammoth seen embedded
in ice at Yamal Peninsula in Russia in 2007
Fig - 8.5 Different types of fossils
Fossil of Archaeopteryx which has
both the characteristics of reptiles
and birds
Archaeopteryx
(Reconstruction)
Fig - 8.6
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BIOLOGY
Indicators
¬ In what forms are fossils seen?
....................................................................
¬ What are the reptilian characters in
Archaeopteryx?
$ Vertebral column extends upto the
tail
$ .............................................................
$ .............................................................
$ What are the inferences regarding
evolution that can be drawn from the
fossil of Archaeopteryx?
....................................................................
The evolutionary stages of vertebrates
such as amphibians, reptiles, birds and
mammals could be satisfactorily
explained through fossil studies.
The evolutionary history of mammals like
horses and elephants could almost be fully
understood through fossil studies.
Observe Illustration 8.6.
Asian Elephant
Moretherium
Pheomea
Stegodon
Evolutionary History of Elephant
African Elephant
Illustration 8.6.
Draw inferences on the evolution of the elephant from Illustration 8.6. and note them
down in your Science diary.
$ What are the important changes in the body that happened in the evolution of
elephants?
$ Many air cavities were formed inside the cranium.
$ Number of teeth decreased. Molars modified in a specific way.
$ ......................................................................................................................................
What are the evidences provided by palaeontology in support of the theory of
evolution? After discussion note down the inference in your Science diary.
Towards Man
Hope you have understood that complex organisms are formed from simpler
organisms. Many structural variations have occured in human beings too as in other
organisms. Of these, the favourable variations led to the origin of modern man.
.................................................................................................................................
What are the characteristics which make man different from other organisms?
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BIOLOGY
How is it that man evolved into an organism with many special characteristics ? Analyse
Illustration 8.7. based on indicators.
Loris
Man
Chimpanzee
Gorilla
Orangutan
Lemur
Tarsier
Gibbon
Monkey
Prosimians
• Nocturnal
• Solitary
• Feeds on small insects
Cercopithecoidea
• Diurnal
• Colonial life
• Food-fruits and leaves
Hominoidea
The large family including
Man and chimpanzee
Primates
• 5 fingers in arms and legs
• Flat nails
• Opposable thumb
• Eyes that can be focussed simultaneously on one object
• A pair of nipples
Illustration-8.7.
Indicators
• Which is the common group that
includes man and monkeys?
• Do you agree with the saying that man
has evolved from monkey? Why?
• Which group of organisms has the
118
most proximity to man?
Not only fossil studies but comparison
with the organisms which are considered
as closely related to man in evolution have
helped to draw inferences about the
direction of human evolution.
BIOLOGY
Analyse the given description and Illustration 8.8 that shows the difference between
the amino acids in the β chain of haemoglobin in organisms and Table 8.1 on the basis
of indicators. Prepare short notes on the evolution of man.
Molecular Biology and Evolution
The branch of science which analyses the
phenomenon of life at the level of
molecules is known as Molecular Biology.
The living body is made up of many biochemical molecules. The difference in the
arrangement of these molecules in
proteins and genes of organisms would
help us understand the distance between
them in the phylogenetic tree.
Globin is the protein part of haemoglobin
that gives blood its red colour.
Haemoglobin consists of two α chains
having 141 amino acids and two β chains
having 146 amino acids. Amino acids in
the α , β chains are different in each
species.
The reason for the possible changes in
the amino acids of the protein is the
mutations occurring in the sequence of
nucleotides of the genes that control
protein synthesis. The rate of mutation in
nucleotides can be found out by the
molecular study of DNA. Through this the
period of separation of different groups
of organisms from their common ancestor
can be ascertained. It has been inferred
from molecular studies that man and
chimpanzee separated from an ancestor
who lived 70 lakhs years ago.
Man
Dog
Rhesus
monkeyv
Gorilla
Chimpanzee
Illustration - 8.8.
Comparison of man with other animals based on the variations in the
number of amino acids in β chain of haemoglobin
Man
Chimpanzee
Gorilla
0
1
Rhesus monkey Dog
8
16
Table - 8.1.
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BIOLOGY
Indicators
—
Which is the organism that is the most closely related to man from the evolutionary
view point?
—
What are the inferences that may be arrived at from the illustration?
In Search of the Origin of Man
Palaeoanthropology is a rapidly progressing branch of science which investigates human
evolution. Many groups are working in the field of human fossil research. Try to know
some of them.
Eugene Dubois
1891
An evolutionist of Dutch origin.
Discovered Homo erectus, the most
important link of human evolution. Since
it was discovered from the Java Islands of
Indonesia, the fossil is known as Java Man.
Donald Johanson
1971
1976
Palaeoanthropologist. Discovered the
oldest fossil, Australopithecus. This fossil
became popular as Lucy
Fig - 8.7.
The skull of
Java Man
Leakey Family
The family which is involved in research
to find out links in human evolution.
Mary Leakey discovered footprints of the
ancestors of man embedded in lava in
Tanzania.
Research works to find out evolutionary links have brought to light a large number of
fossils. The history of human evolution would become more clear with the discovery
of more and more fossils. Given below is some information about human evolution,
based on available evidences. Analyse them and illustrate the human evolutionary
tree.
Dryopithecus
Animal which is considered as the common
ancestor of Man and Chimpanzee. Their fossils
were discovered from Africa, Europe and the
Sivalik hills of India. Supposed to have lived
from 20 million to 14 million years.
Fig - 8.8. Dryopithecus(Reconstruction)
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BIOLOGY
Ardipithecus
Homo habilis
First ancestor of man, who is considered
to have lived 4.4 million years ago. Their
fossils were discovered from the Afar
regions of Ethiopia. It is inferred that this
ancestor of man began walking on two
legs.
The oldest fossil of the genus, Homo,
which expresses the biological and
behavioural characteristics of modern
man. Their fossils were discovered from
the Olduvai mountain folds of Tanzania.
An ancestor of man, who has practical
knowledge of using weapons.
Considered to have lived from 2.25 million
years to 1.44 million years.
Fig - 8.9Ardipithecus (Reconstruction)
Fig - 8.11. Homo habilis (Reconstruction)
Australopithecus
Australopithecus fossils were discovered
from south east Africa. These ancestors
of man were considered to have lived 3
to 3.2 million years ago.
Homo erectus
Considered to have lived 1.8 million
years ago. In 1976 the full skull of Homo
erectus was discovered from Eastern
Africa. Found to have used advanced
stone weapons. Supposed to have good
intelligence and physical strength.
Fig - 8.10. Australopithecus afarensis - Lucy
(Reconstruction)
Fig - 8.12. Homo erectus (Reconstruction)
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BIOLOGY
Homo neanderthalensis
The first fossil of Homo neanderthalensis
was discovered in the
Neander Valley in
Germany in 1856.
Considered to have
lived from 50000 to
30000 years. It is
found that he invented
weapons for tearing
hunted prey and had
used fire. DNA
studies show that
Neanderthal man and
modern
man
separated 50000
years ago.
Fig - 8.13. Homo neanderthalensis
(Reconstruction)
•
Changes in the body structure to suit
bipedal walking.
•
Developed brain
•
It can be understood that evolution
towards modern man is not merely a
biological evolution. Progress in
urbanisation and cultural evolution were
accompanying changes. Hasn't man many
physical limitations when compared to
other organisms even when he has many
unparalleled characteristics? Find out
what are the physical limitations of human
beings?
...................................................................
He survives his limitations because of his
developed intelligence, does'nt he?
Where are We Moving to?
An important step which led to man's
progress is the discovery of agriculture.
Cromagnon (Homo sapiens)
What are the major discoveries of man
which led to agricultural progress?
$ Production of high yielding varieties
of organisms.
Fossil of this
modern man was
discovered first in
France. It is
considered that
the stage of
cultural growth
started from this
ancestor of man.
$
Man has mastered the skill to create
variations in character artificially, which
happened naturally earlier. Is it right to
say that now man interferes with the
evolutionary process keeping nature
aside? Discuss.
You have understood that all organisms
that we see in the biosphere are the result
of a long term evolutionary process.
Fig - 8.14 Cromagnon
(Reconstruction)
What are the major trends in the evolution
of modern man?
122
We can understand that the origin and
extinction of different species is a common
phenomenon
occurring
in
the
uninterrupted flow of time. Often mass
extinction of organisms have occurred on
BIOLOGY
earth due to natural phenomena. Find out
the reasons for the disappearance of the
following organisms from the earth and
record them in the Science diary.
There are many organisms which are
extinct or which are under the threat of
extinction due to human interference.
Collect information about them and
prepare a red list.
Will man be responsible for one more
mass extinction? Don't his actions point to
that?
Fig 8.15
Fig 8.16
Golden Frog
Dodo
When compared to other organisms, man
is a creature having unique physical and
intellectual qualities. Hence it is our duty
to preserve nature blissfully.
Man who has the ability to think, should
act witfully in using nature while
conserving it too!
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BIOLOGY
Follow up Activity
1. 'Life and living organisms are the main
evidences of evolution'. Which
indicators from those given below
would you consider to describe how
in this statement life becomes
evidence of evolution? How will it
substantiate evolution?
— Structure of body
— Organ systems
— Genetic constitution
— Metabolism
What are the indications given by the nose
and the bones of the fore limb and the hind
limb of this organism? What are the
inferences that can be reached about
evolution from this fossil?
3.
Observe the cartoon
The pests are
not dying even
after persistent
spraying?
Hi…..Hi…..
2. Observe the picture
Tiktaalik (reconstruction)
Tiktaalik fossil
The picture represents the fossil of
Tiktaalik, an organism resembling fish,
discovered in 2004 and its reconstruction.
Take note of their characteristics found out
through fossil analysis.
•
Scales and gills like fish
•
Fins
•
Flat head
•
Eyes and nose in the upper part of
the head
•
Fins that are half-fin and half fore/
hind limb bones.
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Have pesticides become ineffective or
have pests become strong?
Analyse the cartoon on the basis of the
theory of natural selection and note down
your inferences.