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2008 CBSE Questions bio class x-heredity and evolution Question paper



Course: SSLC   University/board: CBSE






QUESTIONS BIO CLASS X-HEREDITY AND EVOLUTION

1.Define heredity. Give example of inherited traits.

2.Why do asexually reproducing organisms show very little variation?

3.ow does creation of variation in a species promote survival?

4.Why did Mendel select pea plant in his experiment?

5.Why is the symbol used for a trait (tall) denoted by two letters such as TT,
Tt or tt?

6.Explain the result of Mendel's monohybrid cross.

7.What experiment would we do to confirm that F2 generation did in fact have a
ratio of 1:2:1?

8.What is dihybrid cross? What is the ratio of F2 hybrid?

9.How do traits get expressed?

10.Give example of animals in which sex is not genetically determined.

11.Define evolution, give examples.

12.Differentiate between inherited and acquired traits.

13.Narrate the contribution of Darwin.What is the limitation in his theory?

14.Define speciation. What factors could led to rise of a new species?

15.What is the relationship between classification and evolution?

16.What are homologous organs? Give examples?

17.What are analogous organs give examples?

18.How do study of fossils help in evolutionary process?

19.Give example to explain that evolution has taken place in stages not by a
single DNA change?

20.Why are human beings who look so different from each other in terms of size
colour and looks said to belong to same species?

21.What are characteristics?





ANSWERS




1.The transmission of characters from parents to offspring from one generation
to another is called heredity. Inherited traits are characters that are
transferred from one generation to another. E.g. Height, skin colour, ability
to roll tongue, hemophilia.

2.Asexually reproducing organisms have same genetic make up, so they show very
little variations which is due to (i) small inaccuracies in DNA copying
(mutation) , (ii) influence of environment which is not heritable.

3.The chance of survival depends on nature of variation. It has adaptive
advantage; the organism is selected by nature and survives. E.g. Heat
resistant bacteria.

4.(i) Small and easy to grow (ii) bisexual flower (iii) self fertilizing in
nature and also cross bread experimentally. (iii) Produce large number of
offspring (iv) life cycle completes in one season (v) available in many
contrasting characters.

5.Because each trait is influenced by both paternal and maternal DNA..

6.(i) Only one of the parental trait is observed in F1 progeny when two
contrasting character of a trait is considered. (ii) The trait which is seen
in F1 hybrid is dominant one. (iii)When F1 hybrid is self pollinated both the
characteristics appear in ratio of 3:1 which shows that F1 hybrid has the
traits of both characteristics.

7.By doing self pollination ,TT- 100% tall plants, Tt- 3:1 tall and dwarf
plants, tt- 100% dwarf plants

8.Two contrasting characters are taken at a time in this cross. F1 hybrid
shows only dominant characters. Ratio-9:3:3:1

9.(i)Chromosomes present in nucleus contain hereditary information. (ii)Chromosomes
are made up of DNA and protein. Its important component is
DNA.(iii)Chromosomes occur in pair, one comes from mother and others from
father.(iv)Part of DNA responsible for a trait is called gene.(v) A gene is
expressed in the form of proteins. E.g. for tallness of a plant if proteins
work efficiently a lot of hormone will be produced and the plant will be tall.

10.(I) snail-can change sex. (II) turtle-High incubation temperature leads to
develop female offspring. (III) Lizard-High incubation temperature leads to
develop male offspring.

11.It means 'unfolding or unrolling' change from one condition to another.
It means members of a species change generation after generation in accordance
with environmental requirements to turn into new species. It is the process of
cumulative change of living population and in the descendant populations of
organisms. Evolution is a change in the genetic composition of a population.
It is due to errors in DNA copying as a result of sexual reproduction.
Example---- (A) NATURAL SELECTION-It brings about adaptive relations between
organisms and environment by favoring the reproduction and survival of those
individuals which are found more suited in the given environment. (B) GENETIC
DRIFT—Random change in the frequency occurring by chance irrespective of its
being beneficial or harmful. In small population, for this reason some
unfavorable character may be fixed or beneficial character may be lost. (C)
Changes take place, but the change is not inherited in germ cells, so
reappear.

12.ACQUIRED TRAITS—(i) This character develops in an organism due to
influence of environmental condition, use and disuse of organs etc. (ii) The
characters are restricted to somatic cells only. (iii)The traits cannot be
inherited. E.g. decrease of weight due to starvation, strong muscle of a
wrestler. INHERITED TRAIT-(i) this character develops in an organism due to
change in the germ cells. The cause of the change is due to inaccuracies in
DNA copying. (ii) The trait is coded in genes of chromosomes.(iii) The trait
is inherited. E.g. colorblindness, hemophilia.

13.Charles Darwin explained how evolution might have occurred in nature from
simple to complex form and origin of species by natural selection.
Limitation—He could not explain how living organism originated on earth
surface.

14.SPECIATION is origin of new species. FACTORS-(i)natural selection (ii)
genetic drift (iii)reproductive isolation (iv)mutation

15.The more characteristics two species will have in common, the more closely
they are related. They will also have a common ancestor. Classification is
done basing on similarities and dissimilarities. So classification of species
is in fact a reflection of their evolutionary relationship.

16.The organs which have same fundamental structure but are different in
function are called homologues organs. E.g. fore limbs of frog, lizard, whale
and man.

17.The organs which have similar function but differ in structural details and
origin. E.g. Wings of bat, birds and insects.

18.Fossils are remains or impressions of the hard parts of the past
individuals in the strata of the earth. Since rocks are laid down
sequentially, with older rocks laid down before, and thus below, younger
rocks, the chronological sequence of an organism can be inferred from where
the fossils are found.

19.(a)Feathers were firstly developed in dinosaurs provide insulations in cold
weather, later on developed in birds used for flight, which indicated close
relationship between birds and reptiles. This also indicates character which
developed for one function is later used for entirely different function. (b)Eyes-
planaria-rudimentary eyes which are photosensitive spots. Insects-compound
eyes. Octopus and vertebrates-complex structure. The structure of eye in each
of these organism is different enough for them to have separate evolutionary
origin.(c)Very dissimilar structure may evolve from common ancestral design.
E.g.-from wild cabbage man has developed cabbage, cauliflower, kohlrabi, kale
and broccoli.

20.Because they can interbreed.

21.Characteristics are details of appearance or behaviour.








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