Science Answer the following questions: [5 M]

1. The animal A could be a bird or a bat, animal B could be lizard, animal C could be human, animal D could be frog, animal E could be an insect.
2. Forelimbs of A, B, C, and D are called homologous organs because they have the same basic structure but different functions.
3. It suggests that these organisms have evolved from a common ancestor.
4. It is because forelimbs of animal A and wings of animal E have different basic structures but perform a similar function.
5. Animals A and E do not have a common ancestor.

1. X is birds, Y is reptiles and Z is Archaeopteryx.
2. Forelimbs like those of X and Y are called homologous organs.
3. X and Z had feathers.
4. Z had teeth and tail like Y.
5. The correct evolutionary sequence is Y → Z → X.

The sex of a child depends on what happens at fertilisation:

1. If a sperm carrying X chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a girl. This is because the child will have XX combination of sex chromosomes.
2. If a sperm carrying Y chromosome fertilises an ovum (or egg) which carries X chromosome, then the child born will be a boy. This is because the child will have XY combination of sex chromosomes.

Yes, only those variations that confer advantage to an individual organism will survive in a population. This will become clear from the following example. Suppose there is a population of red beetles in the green bushes and a colour variation arises during reproduction so that one beetle is now green in colour (instead of red). This variation offers advantage of survival because the green beetle can mix up with green bushes, it cannot be spotted and eaten up by a crow and hence its population will increase. If, however, the variation had produced a blue coloured beetle, then this colour could not offer any survival advantage because blue beetle in green bushes could be easily spotted by a crow and eaten by it.

1. Organs P and Q are known as analogous organs.
2. Wings of an insect and a bird are like P and Q.
3. Organs R and S are called homologous organs.
4. Forelimbs of humans and wings of birds are like R and S.

1. It is a process of evolution.
2. The green colour of the beetle is an inherited trait, which can be passed on to the next generation.
3. It helps in survival of green beetle as it can mixing with green bushes, and hide from predators.
4. The production of green colour has been brought about by a change in the DNA of the reproductive cells.

The genetic makeup of the tall parent can be depicted as:

3. TtWW: As the question says, Tall Pea plants bearing violet flowers; Tallness is a dominant trait and is always represented by capital letters so ‘T’ and short/dwarfness is represented by small letters so ‘t’ – hence Tt. Violet Flowers is a dominant trait and is represented by capital letters so ‘W’. The progeny had short plants but no white flowers which means that Violet flowers are being passed on. Therefore, the genotype of the tall parent can be depicted as TtWW. There is a dominant gene for tallness which suppresses the recessive gene for height and for all violet flowers were present in tall pea plant.

The process by which new species develop from the existing species is known as speciation. New species are formed when the population of same species splits into two separate groups which then get isolated from each other geographically by the barriers such as mountain ranges, rivers or the sea. The geographical isolation of the two groups of population leads to their reproductive isolation due to which no genes are exchanged between them. However, breeding continues within the isolated populations producing more and more generations. Over the generations, the processes of genetic drift (random change in gene frequency), and natural selection operate in different ways in the two isolated groups of population and make them more and more different from each other. After thousands of years, the individuals of these isolated groups of population become so different that they will be incapable of reproducing with each other even if they happen to meet again. We then say that two new species have been formed.

The characteristics or traits in animals and plants are controlled by genes. For example the transmission of color of hair from the parents to the child. If a mother has black hair and the father has blonde hair and the child has black hair then the transmission of genes for hair colour from the mother and father to the child is as follows: Mother’s cell contains two genes HH for black hair. Both the genes HH are dominant genes, so the mother has black hair. Father’s cell contains two genes (hh) for blonde hair. The two genes hh are recessive genes, so the father has blonde hair. Now, during the process of reproduction, the mother transmits one of the dominant genes H for black hair to the child and the father transmits one of his recessive genes h for blonde hair to the child. Due to this, the child has the genes Hh for her hair. Now the gene H for black hair is the dominant gene but the gene h for blonde hair is the recessive gene. The dominant gene H for black hair shows its effect due to which the child has black hair.

The theory of origin of life on earth was given by J.B.S Haldane. He suggested in 1929 that life must have developed from the simple inorganic molecules (such as methane, ammonia,hydrogen sulphide, etc.) which were present on the earth soon after it was formed. He said that the conditions on earth at that time (including frequent lightning) could have converted simple inorganic molecules into complex organic molecules which were necessary for life. These complex organic molecules must have joined together to form first primitive living organisms. Haldane also suggested from theoretical considerations that life (or living
organisms) originated in the sea water.

When Mendel crossed pure-bred tall pea plants with pure-bred dwarf pea plants, he found that only tall pea plants were produced in the F generation. When Mendel further crossed the tall pea plants of the F generation, he found that the tall plants and dwarf plants were obtained in the ratio 3 : 1 in the F generation. Mendel noted that all the pea plants produced in the F generation were either tall or dwarf. There were no plants with intermediate height (or medium height) in-between the tall and dwarf plants. In this way, Mendel’s experiment showed that the traits (like tallness and dwarfness) are inherited independently. This is because if the traits of tallnes and dwarfness had blended (or mixed up), then medium sized pea plants would have been produced.

Evolution is the sequence of gradual changes that takes place in the primitive organisms over vmillions of year in which new species are produced. Darwin’s theory of evolution is known as:"The Theory of Natural Selection". It can be described as follows:

1. Within any population there is natural variation. Some individuals have more favourable variations than others.
2. Even though all species produce a large number of offspring’s, populations remain fairly constant naturally.
3. This is due to the struggle between members of the same species and different species for food, space and mate.
4. The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favourable variations survive and reproduce. This is called natural selection.
5. The individuals having favourable variations pass on these variations to their progeny from generation to generation.
6. These variations when accumulated over a long period of time, lead to the origin of a new species.

Column I		Column II
i.	Fossil	c.	Petried remains of the perhistoric life
ii.	A theory of evolution	b.	Survial of the fitted
iii.	Probale ancestor of birds	e.	Archaeopteryx
iv.	Charles Dawin	a.	A famous evolutionist
v.	Gregor Mendal	d.	Father of genetics