Class 10 Science Chapter 8 Important Questions

No, depending upon the nature of variation different individual would have different kind of advantages. Environmental factor act on these variants and the variant more suited to the existing environment would survive.

In asexually reproducing organisms variation occurs due to inaccuracies in DNA copying at the time of nuclear division.
For example, one bacterium divides it will give rise to two bacteria. These daughter bacteria would be similar in body design but with subtle differences.
The resultant bacteria divide again and each bacterium will give rise to two bacteria in the next generation i.e., there would be four individuals. In the bottom row i.e., the four individuals will be different from each other. They may have differences of two type(i) some of the unique type of differences and differences inherited from their respective parents, who were different from each other.

The process by which traits and characteristic are reliable inherited or passed from the parents to the offspring is called heredity.

Experiences of an individual during its life time are in the somatic cells of the body. That is in non-reproductive tissues that cannot be passed to the next generation. Thus, they cannot contribute directly in evolution.

Law of dominance: When two homozygous individuals with one or more sets of contrasting characters are crossed the characters that appear in the hybrids are dominant characters.
Law of Segregation: Contrasting characters bought together in a hybrid remain together without being contaminated and when gametes are formed from the hybrid the two separate out from each other and only one enter each gamete.
Law of independent assortment: In heritance of more than one pair of contrasting characters simultaneously, the factors for each pair of characters assort independently of other pairs.

The branch of biology which deals with heredity and variations is known as genetic.

Deoxyribonucleic acid (DNA).

A trait is an organism results from the action of protein or proteins which is manufactured by a gene. Each protein is made by information from genes for that proteins. In the example of pea plant there are two genes for plant height T and t. T is dominant over t. In a heterozygous plant(Tt), only the gene T will be able to make protein as it is dominant over the t gene. This protein would be the growth hormone which will result in the plant being tall.

Different species use very different strategies for determination of sex of newborn individual. Some animals rely on environmental cue the temperature at which the fertilized eggs are kept determines the sex of newborn. In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined. In human being sex determined genetically.

Gene is function segment of DNA on a chromosomes occupying specific positions which carries out a specific biology function.

Garden pea.

Variation: There are differences in structure function, behavior and genetic makeup of different individuals of the same parent age, variety, race and species.
Acquired variation: They are somatic variations which develop in the lifetime of an individuals. Acquired variations are usually inheritable and die with the death of the individual.

F1 generation is the generation of hybrids derived from a cross between two genetically different homozygous individuals.
F2 generation is the generation produced as a result of interbreeding between individuals of F1 generation.

Offspring: It is an individual formed as a result of sexual reproduction involving the formation and fusion of two gametes. The genotype of an offspring is different from either of an offspring is different from either of the parents due to shuffling of chromosomes and their genes.

They are two types of crosses involving two groups of individuals where the male of one group is crossed with the female of the other and vice versa.

(i) Monohybrid cross: Monohybrid cross is that cross which is made to study the inheritance of a single pair of genes or factors of a character.
(ii) Dihybrid cross: It is a cross which is made to study the inheritance of two pairs of genes or two character.
(iii) Monohybrid ratio: It is the ratio which is obtained in the F2 generation when a monohybrids cross is made. It is usually 3:1 or 1:2:1.
(iv) Dihybrid ratio: It is the ratio which is obtained in generation when a dihybrid cross is studied. It is usually 9:3:3:1.

(a) Law of segregation: The two factor or alleles of an allomorphic pair separate out randomly during gamete formation and the paired condition is restored by random fusion of gametes during fertilization as per the principal of probability.
(b) Law of independent assortment: The two factors of each character separate out or assort independent of the factors of other characters at the time of gametogenesis and get randomly rearranged during fertilization.

Due to the following reason, Mandel selected garden pea for his experiment:
(i) Garden pea flowers are normally self-pollinated but can be easily cross-pollinated its self-pollinated is prevent.
(ii) Many varieties with distinguish contrasting character example smooth seed coat, wrinkled seed coat.
(iii) A large number of progeny can be can be produced in a short duration.
(iv) Its flower can be easily handled for experimentation.
Making of True Breeding: (i) He self-pollinated the pea plants for several successive generation of each variety to eliminate any offspring that was not true to the form of the trait.
(ii) He ensured that the seeds of a variety produced that only that type of plants and so on. For example, the seeds of white flower plants produced only white flowered plants in the successive generation.

Following are the reason for Mandel success:
1. He had the knowledge of science and math.
2. Mandel conducted his experiment by considering the inheritance only or a few pair of character at a time
3. His work was methodical.
4. He selected pea plant having many contrasting characters. Luckily, they did not show incomplete dominance or linkage.
5. He gathered dates statistically and then analysed. He used Law of Probability in analyzing experimental data.

(a) The trait which is expressed in F1 generation is called dominant traits and The traits which remains hidden in presence of dominant trait is called recessive. Recessive trait is never expressed in presence of dominant traits.
(b) Genes control traits: Genes produce particular proteins which produce particular enzymes. For example, tallness trait in a pea plant. The tallness of the plant depends upon the amount of a particular hormones produced. For this related enzymes is necessary which depends upon the genes. Thus genes control traits.

Genetics is the science of heredity and variations which includes studied of the transmission of traits from parents to the offsprings and the occurrence of differences among the individuals.
Contribution of Mandel: Mandel did this experiments on garden pea and discovered the scientific principals which govern patterns of inheritance etc., the principal of inheritance. He explained that contrasting characters are controlled by units which he called factors. Today this factors are known as genes.

Genes are located at a specific position on a chromosome.
Chemical name of genes: Chemically genes is a segment of deoxyribonucleic acid(DNA) consisting of specific sequence of the nucleotides. The sequence of the constituent nucleotides determines the functional property of a genes.

Both parents contribute equally to the DNA of progeny during actual reproduction. In order to determine the traits in the progeny, both parent must contribute a copy of the same gene. It means that each parents have two seeds of all the genes, one inherited from each parent. This mechanism indicates that each germ cell must have any one gene set.

Chromosomes which are related to determination of sex of a new born baby are called sex chromosomes. Male human being have a pair of sex chromosomes in which one in normal size called X chromosome and other is a short on called Y. thus in male human being XY chromosomes are present. Female human beings have a perfect pair sex chromosome, both called XX. A child who inherit a Y chromosome from father will be a boy.

Eyes colour or height traits cannot be changed or acquired in the lifetime because they are controlled by genes which an individual inherit from his/her parents. So such traits are genetically inherited and are transmitted one generation to the next generation.
Power to left weight and reading French can be acquired during lifetime by practicing. Such acquired character does not change or germs plasm. These changes are in non-reproductive tissues and cannot be passed to the progeny. They are not genetically inherited.

The following traits cannot pass on the progeny.
(ii) Absence of tail in a mouse.
(iii) Low weight of a starving beetle.
Reason: Because these traits are in non-reproductive tissue and do not cause change in genes of the germ cells.
Rudimentary eyes of planaria is due to genes of germ cell which is transmitted from generation to generation.

Mandal conclude after carrying out experiments with two differentiate traits pea plants that traits are independently inherited that’s why the inheritance of a pair of factor is independent of the other pair of factors.

(i) Green (as G denotes dominant gene and is expressed in all plants of F₁ generation).
(ii) 25% in F₂ generation raised by self-pollinated F₁ plants.
(iii) GG-25%
Gg plants 50%
Thus ratio is 1:2 in F₂ progeny.

(a) F₁ progeny were all tall plants because gene dwarfness is recessive. Its genome would be Tt (all tall due to presence of T dominance gen).
(b) Phenotype ratio of the F₂ progeny would 3:1 (3tall:1dwarf).
(c) F₁ progeny have both the traits (Tt). As tallness dominant (T) over (t) dwarf trait. So F₁ progeny exhibit dominant trait(Tall) and dwarf trait(t) remains hidden. In F₂ generation shows 3:1 phenotypic ratio. The F₂ generation did in fact have
1(Pure tall) TT:2 (Hybrid tall) (Tt):1 (Pure dwarf) (tt)

Evolution can be defined as the changes in the genetic composition of a population with the passage of each generation. Evolution can be defined as the gradual unfolding of the organism from preexisting organism through change since the beginning of life. The origin of life is very much associated with evolution. Evolution or the organic evolution is the study of how complex organism of today evolved from the simpler form of the past.

The traits acquired by an organism during a lifetime are variation in the somatic cells. These variations are not passed on to the progeny as the progeny is formed from gametes which arise from the reproductive tissue of the organism.

Organisms multiply in large numbers but the number of survivals is roughly constant. There is struggle for existence and due to acting upon by natural selection on variation there is survival of th fittest, which leads to the formation of the new species.

Life originated on earth from in organic elements and compounds under extreme atmospheric condition (such as very high temperature, electric discharges, reducing atmosphere, etc) By formation of complex organic compound such as amino acid.

Darwin’s theory natural selection can be explained on the basis of following main points:
1. Over production: All the living organisms produce offspring much more in number and beyond the availability of food and space. If the all the offspring remain alive and reproduce soon there will be overcrowding.
2. Variation: Members of population vary in physical, physiological and adaptive capacities. Individuals which adaptive variations survive only and those which do not have are perished. Therefore, variations with in a species enable the nature to exercise her selection.
3. Struggle for existence: Over producing and variations ensure compQ39.etition to obtain its iota of food, space and mate. This competition is called struggle for existence. Which has interspecific, intraspecific and environmental dimensions.
4. Survival of the fittest/ natural selection: The ensuing competition is very tough. The natural conditions operating on the individual acting as a selective force. Only those individuals with favourable variations and are able to survive and are adapted to the available conditions.
5. Inheritance of useful variation: The individual who have been selected by nature, pass on their useful variation to the offspring of next generation.
6. Speciation: The useful variation is preserved and accumulated in the individuals of the species which ultimately lead to origin of new species.

Analogous organ: The organ which are developmentally and structurally very different but perform the same function are called analogous organ.
Example: The wings of a bird and an insect perform the same function of flying. The wings of a bird have a support of skeleton, flesh and feather but insects have a fold of membrane as wing associated with a few muscles. Thus, wings of a bird and an insect are developmentally and structurally very different. So they are analogous organs.

(i) Fish scales and mollusc shell are analogous structure because both are protective in nature but different in origin.
(ii) Trunk of elephant and hand of chimpanzee are analogous structure because both are prehensile in functioning but different in origin. (Elephant trunk is extension of proboscis) and structure.
(iii) Wing of a bird and wing of a bat are analogous structure both are similar in functioning but different in origin.
(iv) Nails of human being and claw of cat are homologous structure because these are similar in origin and different in functioning.
(v) Ginger and sweet potato analogous structure all those these are storage structure. Because ginger is a stem modification while sweet potato is a root modification.

Fossils are the remains of part of living organisms or their impression or castes that lived in distant past and are present as direct evidence in the rocks.

The fossil study considered significant because
(i) Broad historical sequence of biological evolution can be built up.
(ii) Phylogeny of man, horse and elephant has been worked out.
(iii) Habits and behavior of extent species can be inferred.
(iv) Reliable information of ancient environment and climate can obtain.
(v) Fossils provide direct evidence of past life.
(vi) These provide convincing proof of organic evolution.

Fossils: A fossil is the record of an organism that lived in the geologic past. Remains, impressions, cast, mold and traces of organism of past have been preserved in the earth crust as fossils. Fossils help us to build up broad historical sequence of biological evolution. For e.g. the study of fossils of equidae family provides reliable record of evolution. Dawn horse five toed Echippus give rise to mesohipuss which in turn develop into several lines of evolution.

Fossils: Remains, impressions, cast of past geologic ages have been preserved in the earth crust are called fossils.
Determining the age of fossils: There are two methods:
(i) This is relative the fossils we find closer to the surface are more recent then the fossils we find in deeper layer of earth crust.
(ii) The second way of dating fossils is by detecting the ratios of different isotopes of same element in the fossil material.

In fact in ancient time some dinosaurs head feather although they could not fly using the feathers. Birds seem to have alter adapted the feathers. This means that birds have evolved from reptile since dinosaurs were reptile.

Homologous organ: The organ which have same origin, which have same origin, which have same structural plan and site of origin but differ in functions in different organisms are called homologous organs.
Homologous organs support evolution:
(i) The similarities of structure and origin of organs indicate that all vertebrate had common ancestors. For example, the forelimbs of humans, whale and bat show structural similarities but functional dissimilarities. Forelimbs in humans used for grasping or holding the things and in in whale for swimming.
(ii) All the organs and systems of the vertebrates show fundamental similarities that’s why homology which indicate towards common ancestry. Thus, homologous organs point that the organic evolution has taken place.

The following methods help us in tracing evolutionary relationships:
(i) Study of Homologous organs: Organs which have similar structure and components are called homologous organs. For example, limbs of bird, frog, human may look different have similar structure and components. Such a homologous characteristic helps to identify an evolutionary relationship between apparently different species.
(ii) Study of analogous organs: Analogous organs are similar in function but different in structure and components. For example, forelimbs of birds and bat are used for flying but their origin and components are not common. Thus study of analogous organs revels difference in their ancestry and their evolutionary relationship.
(iii) Study of Fossils: All impression casting of body or hard remains of ancient life in the sedimentary rocks are called fossils. Study of fossils help in:
(a) Approximate existence of organisms.
(b) Interrelationship of ancient life.
(c) Co-relation of form of life existing today and their line of evolution from ancient life.

(a) The wing of bat and bird are analogous organs because their designs, structure and components are very different. As wing of bats are skin folds stretched mainly between elongated finger whereas wings of birds are a feathery covering all along the arm.
(b) (i) Natural selection.
(ii) Genetic drift or genetically changes such as changes in chromosomes number.

Yes, geographical isolation of sub-populations of a population of a specie leads to genetic drift. This may impose limitations to sexual reproduction of the separated population. Slowly the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

(i) Genetic drift: Due to genetic drift there will be accumulation of different changes in each sub-population. The leaves of gene flow between them will decrease if they are further isolated, it will be more on a small sub-population.
(ii) Over generations, genetic drift will accumulate, causing different changes in the populations.
(iii) Natural selection may also operate differently in the different geographical location.
(iv) Together, genetic and natural selection will make the population more and more different from each other. As a result, members will be incapable of reproducing with each other. Changes may be due to change in DNA or number of chromosomes.

Let us take the example of red beetle live in some bushes with green leaves. Red beetles are identified easily by predator crow.
(i) One beetle that is green in colour instead of red coloured formed due to variation caused by sexual reproduction.
(ii) Population of green beetles increase as crows are not able to identify them amongst green leaves of bush.
(iii) A variant, blue beetles arise due to sexual reproduction. Blue beetles are also identified by crows.
Suppose at this point, an elephant stamps the bushes where little live. By chance a few beetles of blue colour survived so population of blue beetle increased.
Now, it is obvious that the frequency of an inherited trait changed over generations. Since genes control traits. We can say that the frequency of certain gene in a population changed over generations.
This essence the idea of evolution.
In first case i.e. emergence of green beetle from red beetle gave survival advantage. Here, natural selection is exerted by the crows. Thus, natural selection is directing evolution of the beetle population.
In the second situation, the colour change gave no survival advantage. But accident in small populations can change the frequency of some gene. This the notion of genetic drift, which provides diversity without provides diversity without any adaptation.

Natural selection and genetic drift both help in the generation of a new species. Examples: (i) Suppose there is population of red beetles in some bushes with green leaves. A colour variation arises during reproduction, so that there is one beetle that is green in colour instead of red. This green beetle and produces progeny beetles with green colour.
(ii) Crows (which eat beetles) cannot identify green beetles on green leaves but easily identify red beetles and eat them away. As a result, population of green beetles will increase and population of red beetles will decrease tremendously. Thus, natural selection is directing evolution in the beetle population through crows.
(iii) Suppose an advantage beetle might go from one site A to another site B or a beetle picked up by a crow from one site A and dropped in the other site B without being eaten. This will result in the genes of the migrant beetle entering a new population, that is genetic drift. This migrated beetle from site A will reproduce with the local population of site B.
Over generations, genetic drift and natural selection will result in these two isolated sub-population of beetle becoming more and more different from each other. Finally, members of these two groups will be incapable of reproducing with each other even if they happen to meet. Thus, new species of bodies are being generated.

An artificial classification is based on similarities and difference between organisms whereas a natural classification also takes into account the evolutionary relationship among the organisms.

(i) By detecting the ratios of different isotopes of the same element in the fossil material based on the half-life of the element. The element mainly considered is carbon.
(ii) Relative method: The fossil found nearer to the surface of earth are consider more recent than the fossils found in the deeper layer of the earth.

Over more than 2000 years cultivated wild cabbage as a food plant and generated different vegetable from it by selection.
For example, broccoli for arrest flower growth
For sterile flower cauliflower, some have selected for swollen part like Kohlrabi.
For larger leave- Kale.

(i) Kohlrabi
(ii) Cauliflower
(iii) Broccoli
(iv) Red cabbage
(v) Kale

Human evolution is a part of biological evolution concerning the emergence of humans as a distinct species. It is the subject that seeks to understand and describe how this change and development occurred. The study of human evolution encompasses many scientific discipline most notably physical anthropology, linguistic and genetics. The term human in the context of human evolution refer to the human species.