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Q 1. (a)What is the
homology between fore limb of frog, lizard and wing of a bird? What does
it indicate?
(b)State one function each of forelimbs of
(i) Human being,
(ii)
birds
Solution
(a)All of these are
similar in fundamental structure but perform different functions. It indicates
that more similarity in the fundamental structure, more close is the
relationship among the species.
(b)Function of forelimbs are:
(i) Fore limbs of
human beings - Eating and writing
(ii) Forelimbs of birds - flying
Q 2. (a) Why traits such as
intelligence and knowledge cannot be passed on to the next generation? (b) How
can we say that birds are closely related to reptiles and have evolved from
them?
Solution
(a) Traits such as
intelligence and knowledge are not inheritable traits and they do not change
the DNA of the germ cells and therefore cannot be passed on to the progeny. (b)
Birds are closely related to reptiles and have evolved from them.This can be said
because traits such as feathers were first seen in reptiles like dinosaurs,
which performed the function of providing insulation to them in cold weather
although they could not fly using the feathers but birds adapted the feathers
for flight. This means that birds are very closely related to reptiles, as
dinosaurs were reptiles.
Q 3. Mention some of the
tools for tracing evolutionary relationships among species.
Solution
The tools that can
be used to trace evolutionary relationships among species are: i. Excavation
ii. Time-dating iii. Determining DNA sequences iv. Studying
fossils
Q 4. List two ways by which
we can estimate the age of fossils.
Solution
Two ways by which we can
estimate the age of fossils: i. Relative method in which the fossils found in
upper layers of earth are of recent origin than the ones found in deeper
layers. ii. Carbon dating is the method in which the age of fossils is found by
comparing the carbon-14 radioactivity left in fossils with the carbon-14
radioactivity present in the living objects today.
Q 5. The genotype of green
stemmed tomato plants is denoted as GG and that of purple stemmed tomato plants
as gg. Whenthese twoare crossed
(i) What colour of stem would you expect in
their F1 progeny?
(ii) What is the percentage of purple stemmed
plants in F2 progeny if F1 plants are self
pollinated?
(iii) In what ratio would you find the genotype of GG and Gg
in the F2 progeny?
Solution
(a) F1 -Progeny
- green (b) Purplestemmedplant -25% (c) Ratio of GG and Gg is 1:2:1
Q 6. (a) If a purple flowered
pea plant (PP) is crossed with a white flowered pea plant (pp), will we have
white flowered pea plant in F1 generation? Why or why not?
(b)What do you mean by dominant and recessive trait?
Solution
a) No. This is because
all the F1 progeny plants show the genetic make up 'Pp', which
results in purple flowers, as 'P' purple coloured flower trait is dominant over
the white trait. b) Dominant trait is a genetic trait that is expressed even if
there exists only one copy of that gene in the individual. Recessive trait is a
genetic trait that is expressed only when two copies of the gene are present.
Q 7. What is a monohybrid
cross?
Solution
Monohybrid cross is a
kind of breeding experiment that considers only one character or trait at a
time.
Q 8. Who was the first
person to devise the principles of inheritance?
Solution
Principles of inheritance
was proposed by Gregor Johann Mendel.
Q 9. In Mendel's
experiments what is the meaning of term dominance?
Solution
In monohybrid cross where
only a single trait is studied at a time, only one of the contrasting
characters appears in F1 progeny. The character that expresses itself is known
as dominant character and phenomenon is called ‘dominance".
Q 10. What are fossils?
What do they tell about the process of evolution?
Solution
Fossils are the
impressions or remains of ancient life found preserved in sedimentary rocks,
snow or oil. Information given by fossils:
(i) Fossils reveal that the life
form which existed earlier do not exist today.This suggests that the living
forms are ever changing.
(ii) Fossils indicate the time when these organisms
existed on earth.
(iii) Fossils indicate about the extent of evolution that has
taken place when they are compared with their present forms.
Q 11. What do you mean by
the term variation?
Solution
Variation refers to the
number of changes that appear among the same members of species and their
offspring as a result of genetic recombination.
Q 12. How has the method of
artificial selection by humans helped in the evolution of
different vegetables?
Explain in brief with the help of an example.
Solution
Humans have cultivated
wild cabbage and generated different vegetables. Example: i. Some farmers
wanted to have very short distances between leaves of wild
cabbage and produced the common variety of 'cabbage'. ii. When farmers opted
for the arrested flower development of wild cabbage plant, it led to the
production of broccoli. iii. Some farmers went in for sterile flower of
wild cabbage and developed another variety of cabbage called cauliflower.
iv. When farmers opted for the swollen part of wild cabbage, it led to the
production of Kohlrabi v. Finally, the farmers wanted to grow large leaves
of wild cabbage and ended up producing a leafy vegetable called Kale.
Q 13. (a) Give the pair of
contrasting traits of the following characters in pea plant and mention which
is the dominant and recessive trait. i) Yellow seed ii) round seed (b)What is
inheritance?
Solution
(a) i) Yellow:
dominant Green: recessive ii) Round: dominant
Wrinkled: recessive (b)Inheritance is the transmission of
genetically controlled characteristics (or traits) from one generation to the
next generation.
Q 14. What will happen when
a pea plant with violet flowers is cross bred with pea plant having white
flowers?
Solution
Consider a pea plant
with violet flower (VV) and a pea plant with white flower (vv) Gametes formed:
Plant having violet flowers: V V
Plant having white flowers:
v v The F1 generation
thus produced: v v V Vv Vv V Vv Vv All plants of F1 generation
will have violet flowers as factor for the violet colour is the dominant trait
and white colour is the recessive trait.
Q 15. Describe the
mechanism that determines the sex of a child.
Solution
In humans, the females
have XX sex chromosome while the males have XY chromosome. When the X
chromosome of female unites with X chromosome of male, a girl will be born and
when X chromosome of females unites with Y chromosome of male, a boy will be
born. Thus, the Y chromosome of male (father) determines the sex of child.
Q 16. Distinguish between
analogous organs and homologous organs. Identify the analogous and homologous
organs amongst the following: Wings of an insect, wings of a bat, forelimbs of
frog, forelimbs of human
Solution
Analogous Organs Homologous
Organs Organs having dissimilar origin and structural plan but perform similar
functions are called analogous organs. Organs having similar origin and
structural plan but perform different functions are called homologous organs.
Analogous organs - Wings of an insect and wings of a bat. Homologous organs -
Forelimbs of frog and forelimbs of human.
Q 17. Mrs. Kumar is
pregnant for the last three months and she goes for regular check-up to her
doctor. During her last visit, the doctor asked Mrs. Kumar to get an ultrasound
done. Both Mr. and Mrs. Kumar went to a radiologist and got the ultrasound
done. Once the ultrasound is over, Mr. Kumar asked the doctor whether the baby
in the womb is a boy or a girl.
(a) What should the doctor reply to the couple?
(b) Is it ethical to determine the sex of a child?
(c) What should government
do to discourage sex determination?
Solution
(a) The doctor should not
tell the sex of the foetus. (b) No, it is not ethical to determine the sex of a
child. (c) The government should ban the process of sex determination and
should punish or fine whosoever does so.
Q 18. Birds are very
closely related to reptiles. Justify your answer with a suitable example.
Solution
Feather provided
insulation to dinosaurs in cold weather. Later in the evolutionary
process, feathers were used for flight in birds. Because dinosaurs were
reptiles, it means that birds are closely related to reptiles.
Q 19. (a) How Archaeopteryx
serves as a connecting link between birds and reptiles? (b) What do you mean by
the term evolution?
Solution
(a) Archaeopteryx looks
like a bird but it has many other features which are found in reptiles. It has
feathered wings like those of birds but teeth and tail like those of reptiles.
Archaeopteryx is, therefore, a connecting link between the reptiles and birds
and hence suggests that the birds have evolved from the reptiles.
(b) Evolution
may be defined as the formation of wide varieties of organisms which have been
evolved from pre-existing organisms through their gradual changes (variations)
since the beginning of life.
Q 20. (a) State Mendel's
first law of inheritance. (b) How the age of fossils is obtained by carbon
dating?
Solution
(a) According to Mendel's
first law of inheritance the characteristics (or traits) of an organism are
determined by internal 'factors' which occur in pairs. Only factor of each pair
of such factors can be present in a single gamete.
(b) All the living
objects contain some carbon-14 atoms which are radioactive. When a living
object dies and forms fossil, its carbon-14 radioactivity goes on decreasing
gradually. In the carbon dating method, the age of fossils is found by
comparing the carbon-14 radioactivity left in fossils with the carbon-14
radioactivity present in living objects today.
Q 21. Explain the theory of
natural selection given by Darwin.
Solution
Darwin proposed the
theory of natural selection to understand the process of evolution. According
to this theory, nature itself selects various traits or characteristics that
will suit the members of a species. And thus the individuals who have those
traits will be able to survive and reproduce to maintain the continuity of
their species while others who are not able to survive perish over time.
Q 22. Why it is more
appropriate to compare the process of evolution with branches of a tree rather
than with a ladder?
Solution
The process of evolution
shows similarity when it is compared to the branches of a tree in place of a
ladder. It is because of the fact that due to the requirements of changing
environment, organisms show some changes or modifications in their existing
structures which later on gets inherited in the new generation also. As these
changes occur in already existing structures the process of evolution said to
progress from simple to complex level rather than from a previous step to the
new one as in case of a ladder.
Q 23. Guinea pig having
black colour when crossed with guinea pig having same colour produced 100
offsprings out of which 75 were black and 25 were white. Now find out. (a) What
is the possible genotype of the guinea pig? (b) Which trait is dominant and
which trait is recessive? (c) What is this cross called as, and what is the
ratio of F2 progeny obtained from these cross?
Solution
(i) Possible genotype of
the guinea pig : Bb X Bb
(ii) Black is dominant and white is recessive.
(iii)
Monohybrid cross. Phenotypic ratio=3:1
Q 24. Describe any three
ways in which individuals with a particular trait may increase in a population.
Solution
Different ways in
which individuals with a particular trait
may increase in population are:variation,natural selection
and genetic drift. i. Variation:Variations are defined
as the occurrence of differences among the individuals.
No two individuals are exactly alike. Variations
arising during the process of reproduction can be inherited
and leads to increased survival of individuals.
ii.Natural selection: It results in adaptations in population to fit their
environment better. Thus, natural selection directs evolution in the population
of a particular species. iii.
Genetic drift: The change in the frequency of certain genes in
a population over generations is called genetic
drift.
Q 25. Mention the
contribution of Lamarck in understanding the concept of evolution.
Solution
Lamarck proposed a theory
that defined the process of evolution and how it occurs. Major postulates of
his theory are: i. ‘Use and disuse of organs’ on long term basis leads to
changes in the body structure of individuals. These changes are inheritable and
later on bring about evolution. ii. The number of changes that appear as a
result of evolution are all acquired by individuals during their life time as
per the reQ uirement of changing
environment.
Q 26. (i)What does the
forelimb of bird and forelimb of human being indicates?
(ii)Explain the term
analogous organs with examples.
Solution
(a) The forelimb of bird
and forelimb of human being are homologous organs. (b) Analogous organs-
Those organs which have different basic structure but have similar appearance
and perform similar functions are called analogous organs. Example- Wings of an
insect and a bird have different structures but perform similar functions.
Q 27. What will happen if
due to some accident, changes occur in the gene frequency of members of sub
population of a species? Also, identify the name of this phenomenon.
Solution
This phenomenon is known
as ‘Genetic drift’. It is said to occur when the genetic make up of organisms
change a bit accidentally. As these changes occur without any kind of
adaptation they have no survival advantage.
Q 28. What is speciation?
Describe in brief the factors that control the process of speciation.
Solution
Speciation: The formation
of a new and distinct species in the course of evolution is called speciation.
Factors controlling process of speciation:
(i) Genetic Drift: It is a mechanism
of evolution and refers to random fluctuations in the frequencies of alleles
from generation to generation due to chance events.
(ii) Mutation: It
occurs when a gene is damaged or changed in such a way as to alter the genetic
message carried by that gene.
(iii) Natural selection: It is the process
whereby organisms better adapted to their environment tend to survive and
produce more offsprings.
(iv) Migration: It is the periodic seasonal movement
of organisms from one geographic region to another, typically coinciding with
available food supplies or breeding seasons.
Q 29. What are the
evidences that can be used to study organic evolution?
Solution
The evidences that
are used to study organic evolution in nature are basically grouped in three
categories: i. Morphological and anatomical evidences: These evidences include
the study of homologous, analogous and vestigial organs to trace evolutionary
relationships. ii. Embryological evidences: These evidences include the study
of development of embryo from an egg to an adult in different organisms (animal
groups). iii. Palaeontological evidences: These evidences deal with the study
of fossil records to know about how far this evolutionary relationship goes.
Q 30. Study the given data
and answer the Q uestions that follow: 1 2 3 Parental plant cross
fertilized and seeds collected F1 Generation offspring F2 Generation
offspring after self pollination of F1 hybrid Male parent-
Round Yellow seeds Female Parent- Wrinkled Green seeds All seeds- round Yellow
314- round yellow 110-Round Green 102-Wrinkled yellow 32-wrinkled Green (a)
What is the term given to this type of cross? (b) What does the data in column
2 indicate? State how did you arrive at this conclusion.
Solution
(a) Dihybrid Cross. (b)
Round shape and yellow colour in the pea plants are the dominant traits. In F1 generation,
the offsprings are hybrid ones i.e. RrYy. When both dominant and recessive
traits are present together then only dominant traits are expressed.
Q 31. (a) What is
speciation?
(b) Explain whether the traits like eye colour or height is
genetically inherited or not.
(c)Do power to lift weight and reading French
also belong to same category? Justify your answer.
Solution
(a) The process in which
new species are formed from the preexisting species is known as speciation.
(b)
Yes, traits like eye colour or height is genetically inherited because they can
be passed on from one generation to the next. (Inherited characters)
(c)No,
power to lift and reading French does not belong to same category as it cannot
be passed on from one generation to the next (as they are acquired characters)
Q 32. A black mouse mates
with a brown mouse, and all the offsprings are black.
(a) Why are no brown
offsprings produced?
(b) If two of the black offsprings mate with each other
what kind of offspring would you expect and in what proportions? Give reason
for your answer.
Solution
(a) Because black colour
genes are dominant over brown colour genes.
(b) Three black mice and one brown
mouse will be obtained in F2 generation. It is a monohybrid
cross.
Q 33. Briefly explain
Darwin's theory of evolution.
Solution
(i) Within any
population, there is natural variation. Some individuals have more favourable
variations than others.
(ii) Even though all the species produce a large number
of offsprings, populations remain fairly constant naturally.
(iii) This is due
to the struggle between members of the same species and different species for
food, space and mate.
(iv) The struggle for survival within populations
eliminates the unfit individuals. The fit individuals possessing favourable
variations which survive and reproduce. This is called natural selection.
(v)
The individuals having favourable variations pass on these variations to their
progeny from generation to generation.
(vi) These variations when accumulated
over a long period of time, leads to the origin of a new species.
Q 34. Explain the term
analogous organs with the help of an example.
Solution
Analogous organs have different
origin and different basic structure but are present in organisms to perform
the same functions. For example: wings of a bird and wings of a bat have the
same function i.e. help them to fly but structurally they are different. Wings
of a bird are present in the form of feathery covering while in case of bat
wings are the skin folds between elongated fibers.
Q 35. What do you mean by
the term evolution?
Solution
Evolution is a
gradual and continuing process of change that occur over a period of time, due
to slight variations in genetic compositions as well as changes in environment,
leading to formation of new species.
Q 36. What is the
importance of DNA copying in reproduction? Why is variation beneficial to the
species but not necessary for the individual? Explain.
Solution
DNA copying is essential
part of reproduction because it ensures that same blue print of the body design
is maintained. Variation for the species is beneficial for adaptation and
better survival. It may result in the formation of new species; however in an
individual variation may not always be beneficial and may lead to disease or
disorders, hence variation is beneficial for the species but not for an
individual.
Q 37. "A brother and
sister are more related to each other as compared to the case when any one of
them is related with his/her cousin". Through this statement what will we
get to know about their ancestors?
Solution
A brother and sister are
more closely related to each other which mean that they have common ancestors
more recently as compared to the case when any one of them (brother or sister)
is related to the cousin. A brother and sister have their “parents” in common
while a brother or sister and cousin have “grandparents” in common.
Q 38. (a) Mendel selected
garden Pea plant for his experiments. List two reasons. (b) State the meaning
of recessive and dominant genes.
Solution
(a) Mendel selected
garden Pea plant for his experiment because
(i) It is normally self -
pollinated but can be easily cross - pollinated.
(ii) It has traits with
distinctly contrasting forms and also it has a short life span.
(b) (i)
Recessive genes - Those genes which are notable to express themselves in the
presence of their allele are called recessive genes.
(ii) Dominant genes -
Those genes which are able to express themselves in the presence of their
allele are called dominant genes.
Q 39. Describe briefly the
origin of earliest members of human species and how they were spread in
different parts.
Solution
It was found that the
earliest members of human species i.e. Homo sapiens were found in
Africa. From there some members stayed in Africa while others migrated and
spread out in various parts like Central Asia, Eurasia, South Asia, Australia
etc. These species travelled both backwards and forwards from a common place
where they initially originated and then evolved and settled as either a new
separate group or sometimes re-mixed with the original group.
Q 40. Describe the law of
independent assortment with the help of an example.
Solution
The law of independent
assortment states that during dihybrid cross when two characters are studied
simultaneously then factors for a particular trait (character) are inherited in
the new progeny irrespective of each other. For example: When a pea plant with
round and yellow seed (RRYY) is cross bred with plant having wrinkled and green
seeds (rryy). ry ry RY RrYy RrYy RY RrYy RrYy The
new progeny (F1 generation) has all plants with round and yellow seeds. When
these are self pollinated ratio of 9:3:3:1 is obtained which depicts their
independent inheritance. RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy
RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy
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