Class 10 Science Chapter 8 Board Questions

DNA copying cannot be perfectly accurate always. This leads to accumulation of variation, which results in evolution.

Gene migration or gene flow from a population to a new area is known as genetic drift.

Natural selection and variation are the basic events in evolution.

Age of the fossil can be estimated by:
(a) Digging the layer of the earth- deeper the fossil, older it is and nearer the surface would be more recent ones.
(b) Studying the amount of C14 (radioactive isotope of C) in the fossils. Since it has half life, therefore by quantitative analysis we can give approximate time period when that organisms would have existed.

Such a baby will have XY, therefore will be a male.

In snail and garden lizard, sex is determined by outside temperature.

9:3:3:1.

Theory of evolution was given by Charles Darwin.

Group of individuals that have similar features and are capable of interbreeding, are said to belong to a species.

(i) Geographical isolation.
(ii) Genetic drift.
(iii) Natural selection.

Homologous organs- Forelimbs of lizard and forelimbs of bird. Both have same structure but different functions.
Analogous organs- Wings of an insect and wings of a bat. Both have different structure but same function.

Birds developed features, as they evolved to become warm blooded animals to protect them from cold. But slowly, these features also helped them to evolve for aerial mode of life in search of food, shelter etc.

(i) Dinosaur is vertebrate.
(ii) Ammonite is an invertebrate.

Variations are these changes and process is evolution.

(i) Evolution.
(ii) Speciation.

Our teeth and elephant’s tusks are homologous organs as both have same basic structure but different functions. We use ours for chewing while elephants use theirs to hold things.
Analogous organs indicate that even the organisms having different structures can adapt to perform similar functions for their survival under given similar environmental conditions.

It can be done in many ways:
(a) The fossils found in upper layer are recent and the ones that are deeper are older.
(b) By radio-active carbon dating.

On crossing pure tall and pure short pea plants, the F1 generation was tall (but not pure). It was heterozygous for tall.

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

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

Gregor Johann Mandel, through consistence studies on garden pea arrived that laws of inheritance.
He used plants that were pure breeding for a trait and considered contrasting character like- tall and short size, round and wrinkled seeds, white and violet flower etc.
In his experiment he crossed plants with contrasting character, studied the progeny of first generation(F₁) and second generation(F₂) and calculated ratios of plants with contrasting that were original paternal type or different.
For example, he crossed a tall pea plant with a dwarf pea plant. He found that in first generation(F₁) all the plants produced were tall. Since F₁ plants are all tall and genotypically are “Tt” they have inherited “t” from one parent which is not expressed, as it results in dwarf plant.

Organisms used by Mandel for his experiment was pea plant. Mandel took a pure tall plant (TT) and crossed with a pure dwarf (tt) plant. The progeny thus obtained was called F₁ progeny.
Then he self-pollinated the F₁ progeny to obtained F₂ generation. In F₂ generation He found that 75% were tall and 25 were dwarf. 1TT: 2Tt:1tt.

DNA id Deoxyribonucleic acid. It is generally located within the nucleus. It is the basic structure that make up the chromosome. It carries complete information for that organism. DNA is capable of replicating thus making its own copies for reproduction it is mandatory that the cell must pass on the information to the next generation since DNA is capable of dividing so it plays most important role in reproduction.

(a) A gene is specific portion of DNA occupy a specific location.
(b) It provide information for protein synthesis.
(c) It also provides stability to the species.
Thus any change in genes will bring about change in DNA.

(a) Round yellow:9
Round green:3
Wrinkle yellow:3
Wrinkle green:1
(b) All wrinkled and green.
(c) All round and yellow.

DNA that contains all the information is the main factor responsible for inherited trait.
Outcomes of Mendel’s experiments.
(a) Both parent contribute equally toward progeny.
(b) Trait may be either dominant or recessive.
(c) A dominant trait will be expressed in both heterozygous and homozygous conditions while recessive traits will be expressed only in homozygous condition.
(d) The traits are inherited independent of each other.

(i) Since females have XX, so the male fly inherits X chromosome from his mother only.
(ii) A female fly produces only one type of gamete all with X chromosome.
(iii) Male fly produces two types of gametes 50% with X and 50% with Y.

Let us study the example of beetles. Let the original beetle population be red. If due to variation a green beetle was produced it would have survival advantage over red beetle. Thus, green beetles would be naturally selected, and will grow in number.
If few of these green beetles move to some other area, adapt to changed environment and after few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.
Thus, due to Natural selection and Genetic Drift, a new species of beetles is formed.

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

Let us study the example of beetles. Let the original beetle population be red. If due to variation a green beetle was produced it would have survival advantage over red beetle. Thus, green beetles would be naturally selected, and will grow in number.
If few of these green beetles move to some other area, adapt to changed environment and after few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.
Thus, due to Natural selection and Genetic Drift, a new species of beetles is formed.

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

Speciation- It is the process of formation of new species from an existing one. Factors that can lead to speciation are
(i) Natural selection.
(ii) Geographical isolation.
(iii) Migration- Genetic drift.

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

Human beings have artificially selected certain variants that arose in nature by chance. This led to evolution of different species.
For example, wild cabbage was cultivated and its variants were selected due to different advantages, by artificial selection.
(a) Short distances between leaves- led to formation of modern day cabbage.
(b) Arrested flowers development- Broccoli.
(c) Sterile flowers- Cauliflowers.
(d) swollen pats- Kohlrabi.
(e) Large leaves- Kale.

The earliest evidence for human race were found in Africa.
Some of our ancestors left Africa in search of food and shelter, in other areas and stayed on. Slowly, we migrated to most parts of the world.
They settled in different parts and adapted. There was mixing in these populations so they evolved as different races.

(a) Even after cutting tail of a mouse its progeny continues to have tail. This is because ‘no tail’ is an acquired trait. The mouse continuous to have information for presence of tail in its DNA and hence the progeny will have tail.
(b) Archaeopteryx has reptilian features as presence of tail, vertebrate, teeth etc.

(a) When a small group of individuals move away and there is a large barrier between them this smaller group will accumulate variation. This may ultimately lead to formation of new species. Thus, this leads to speciation due to geographical isolation.
(b) DNA is self-replicating i.e., it can make its copies. This is the property used as a tool in genetic engineering.

(i) Homologous structure in vertebrates are wings in birds and forelimbs in lizard.
(ii) They are so named as they have same structural design but different function.
(iii) Such structure gives us idea about common ancestry.

Two uses of fossils are:
(a) To help study evolution of plant and animals.
(b) To know past climatic conditions.
(c) To help calculate geological time etc.
Evidence of favour of organic evolution:
(i) Fossils help to identify an evolutionary relationship between apparently
different species.
(ii) The older fossil present deeper, are simpler in body design as compared to those present in upper layers which are more recent.
This clearly provides evidence in favour of organic evolution.

The traits that a person acquires during one’s life time and not by virtue of his/her genes are known as acquired traits.
These traits are not present on our genes in reproductive cells. Hence they cannot be inherited. Since these changes are in the non-reproductive cells and thus cannot be passed on to the germ cells hence are not inheritable by the future generation. An organism requires them for himself in his life time due to his environment.

Speciation is the formation of new species from the pre-existing ones due to accumulation of changes in such a way that group of individuals of one species can no longer inherited. This result in formation of two new independent species.
Factors responsible for speciation are:
(i) Natural selection- Nature select due to survival advantages.
(ii) Genetic drift- Due to accumulation of changes over generation in sub-population.
(iii) Geographical isolation- In different geographical locations the natural selection acts differently on different sub-population because of varying abiotic/biotic factors.
(iv) Mutation- DNA changes can be severe and hence the germ cells of two cannot fuse giving rise to new species.

Variation are relatively small changed that occur due to error during DNA copying in asexual reproduction or fusion of gametes in sexual reproduction. These changes are subtle, maintaining the basic body design. Sometime these variations may be such that they give an advantage during adverse condition and hence help I survival. This is how variation helps in continuation of species.

DNA is the basic source of making proteins in the cells. The basic event in reproduction or fusion of gametes in asexual reproduction is the creation of a DNA copy. Cells use chemical reaction to build copies of their DNA. This creates two copies of the DNA in a reproducing cell and they will need to be separate from each other. DNA copying occurs accompanied by the creation of an additional cellular apparatus. The DAN copies then separate each having its own cellular apparatus for maintaining life process.

Inherited character are blood group, eye colour etc., whereas acquired character are being sportsman, dancer or scientist etc. Inherited character is transmitted from parent to the progeny as they are present on our genes. While acquired traits are those which a person acquires during his life time. Thus they are not inheritable.

Change in colour is an inherited trait so it is transmitted to the next generation and can provide survival advantages to the species. For example, in population of green and red beetles, green beetles protect themselves from crows that feed on them by hiding un green leaves. But red beetles can be easily spotted. Thus over a period of time only green beetles grow in number as their rate of survival will be higher and red beetles with decreasing population will be under threat.

Colour change needs not always give survival advantages. For example, if there is a population of red and blue beetles in an area. An elephant who happens to pass by may step on this population. Thus survival is only chance and not due to selection. Hence survival here is due to chance and no advantages due to change in body colour.

(a) Fossils are important evolutionary evidence to show what kind of organisms existed earlier. Archeopteryx is a fossil dinosaur with wings. This proves that it has features of both reptiles as well as birds. Hence we can say that birds evolved from reptiles.
(b) These organisms cannot be grouped together as the structure of eye in each is very different. This means that they have separate evolutionary origin.

Any division from original trait in a species is variation. Sometimes these variations may give added advantage of being of the nature so as to give better adaptability in changed conditions. Hence it increases the chances of survival. Smaller population of species would enforce inbreeding with the population which would result in fewer variations. This would also result in inbreeding depression and expression of recessive traits, thereby making it prone to diseases or extinction. Hence environmentalists are worried about smaller population.

The process by which we know how various life forms have come into being from the previously existing ones is known as evolution.
Evolution cannot be equating with progress this is because
(i) Evolution is caused due to variation in original form.
(ii) This may lead to formation of new species. But it does not mean that original type may not exist.
(iii) It only leads to more complex body designs.
(iv) The simplest life form i.e., bacteria exist till day and are found in all types of habitats from hot water springs to cold temperature regions etc. Bacteria are also one of the oldest life form known. So we can safely say that evolution cannot be equate with progress.

While studying evolution of various life forms it is observed that from a single point or ancestor there may be originated different lines, each leading to formation of a new species.
For example, both the humans and chimpanzee have many common feature which suggests that both would have had a common ancestor. Also it is not as if one species is eliminated to give rise to new one. Homologous organs explain this well. Forelimbs of a frog, lizard, bird and horse have common design but different function. This clearly suggest that all these organisms belonging to different group originated from a common ancestor. They evolved in their own way to perform and adapt to their mode of life to give rise to current forms. Hence it is more appropriate to compare the process of evolution with branches of a tree than with a ladder.

(a) Since it is given that green is recessive and red seeds are dominant hence green colour of seeds will reappear only in F2 generation. This is because both parent are not hybrid for this trait and hence the two recessive gene will come together only in F2.
(b) Fossil are formed only when the dead part are hard and get buried immediately without getting decomposed. In case of A may be left its imprints as fossil while B may be decomposed and hence has not formed fossil.
(c) Since more characteristic are shared between C and D therefore they are more closely related.
(d) The insect buried in hot mud is more likely to be preserved better because it will not decompose quickly. Also the mud will harden on cooling retaining the impression of body parts of the insect.

Chromosomes are long DNA stands present in nucleus carrying gene for a trait. Hence they are hereditary material. In an organism each cell has two copies of a chromosomes one each from a male and female parent. In sexually reproducing organisms where fusion of gamete take place one chromosomes from each pair is taken up in formation of a germ cell by a special cell division called meiosis. When two germ cell fuse they restore the original number of chromosomes in the progeny.

The inbuilt tendency of variation either due to error in DNA copying due to sexual reproduction both result in some changes in the existing population of an organism. This continuous change ultimately leads to evolution. It occurs due to change in DNA which keep accumulating generation ultimately giving rise to new species.
Fossil provide evidence for evolution as they are preserved traces of living organisms. The fossils are formed when on death of an organism the body does not decompose instead it get trapped in an environment where it gets preserved. For example, an organism getting trapped in volcanic lava will not decompose. On cooling the lava will harden and retain the impression of the body parts of that organisms as fossil.

(a) Homozygous plants whether for dominant or recessive trait have both is genes for that trait. Thus they always produce similar gametes resulting in pure breeding plants.
(b) When the two chromosomes in the homologous pair are different that’s why one is dominant and other recessive such that pair is said to be heterozygous.
(c) Speciation can be defined as the formation of new species in term of evolution take place. Reproductive isolated is a collection of behavior, mechanism and physiological process they prevent the member of two different species which cross or mate from producing offspring or which ensure that may be produce is not fertile. Speciation is isolated as a genetic change in the new speciation between two previously interbreeding population of the same species.

(a) This a dihybrid cross.
(b) All plant is inflated with yellow pod plants.
(c) In F2 generation new combatants are produced as a traits are assorting independently. The law given by Mandel is Law of Independent Assortment which states that in a dihybrid cross where two different character are being studied which may be present together in an individual are inherited independently of each other in next generation.

(a) Gene is a particular segment of DNA on a chromosome that is capable of a codding for a polypeptide.
(b) Speciation may take place by
(i) Migration
(ii) Mutation
(iii) Genetic drift
(iv) Natural selection

(a) Natural selection: It is selection of certain trait in nature in an individual in a population of a particular species. This leads to survival advantage and hence variation leading ultimately to speciation.
(b) Thorn of Bougainvillea and tendril of Passiflora both are modified stem i.e., both have similar structure but doddering function. Thorn of Bougainvillea protests plants from being grazed while tendril of passiflora helps the plant to climb up a support. Hence they are homologous organs.