Science [3 Mark Questions]

The remains of dead animals or plants that lived in the remote past are known as fossils. The fossils provide evidence of evolution.
For example: a fossil bird called Archaeopteryx looks like a bird but it has many features which are found in reptiles. This is because Archaeopteryx has feathered wings like those of birds but teeth and tail like those of reptiles. Therefore, Archaeopteryx is a connecting link between the reptiles and birds and suggests that birds have evolved from reptiles. Thus, fossils provide evidence that the present plants and animals have originated from the previously existing ones through the process of continuous evolution.

Analogous organs: The organs having similar functions but different structures are called analogous organs. Homologous organs: The organs having similar structure and different functions are called homologous organs. They give the indication of common ancestor.Identification:
Homologous organs: Forelimbs of frog and forelimbs of a human. Analogous organs: Wings of an insect and wings of a bat.

The preserved remains or traces of dead plants and animals that lived in the geological past and were buried under the rocks millions of years ago are called fossils.
Fossils tell us about the process of evolution. Fossils give an idea about the structure of organisms and corresponding period of their existence in the past. Fossils found under different strata of earth across different geological locations, provide evidence of evolutionary relationship among existing and extinct species of organism. They give us clues about extinct species of organisms and reasons behind their disappearance from earth due to different conditions of climatic change in the past.

We have the following evidence from inanimate matter as conducted by MILEY and UREY in 1953 in the following ways:-

1. With the inspiration of JBS Haldane they created an experimental atmosphere similar as it was at the beginning of earth.
2. With the mixture of gases they stimulated lightning and passed off sparks in it.
3. At the end of the week they observed some organic compounds were formed like amino acids which make up protien and animate matters. Fact It was the proof of Earth's first kind of atmosphere, infact the whole environment.

Mendel conducted breeding experiments with garden peas-

1. He studied (pure) plants of a tall/short varieties.
2. He crossed them and obtained F1 progeny.
3. He found that F1 progeny was all tall plants.
4. He selfed the (hybrid) plants of F1 progeny.
5. He found that in F2 progeny there were tall as well as short plants.
6. The three quarter plants were tall and one quarter was short.

Dominance	Recessive
Dominance allele it is able to express itself even inthe presence of its recessive allele	Recessive allele of factor is unable to express its effect in the presence of dominant allele.
It does not require another similar allele to produce its effect on the phenotype. e.g., Tt is tal	It producse allele its phenotypic effect only in the presence of similar allele, e.g., tt is dwarf.
Dominant allele or factor can from complete polypeptide or enzyme for expressing its effects e.g., red colour of flower in pea.	The recessive allele an incomplete or defective polypeptide or enzyme so that the expression consists of absence of the effect of dominant allele, e.g., white flower colour in pea.

75% of the plants were with round seeds.

In evolutionary terms, we can say that bacteria has a ‘better’ body design than spiders, fish, and, chimpanzees. This is because though bacteria is one of the simplest and primitive life forms but it still inhabits and survives in some of the most inhospitable (most unfavourable) habitats such as hot springs, deep-sea thermal vents and ice in Antarctica. Most other organisms (including spider, fish and chimpanzees) cannot survive in such harsh environments.

X are trilobites, Y are ammonites and Z are dinosaurs.

The sex of a baby is determined by the type of male gamete that fuses with the female gamete. All human beings have 23 pairs of chromosomes in their nuclei. Out of these 23 pairs, the last pair is known as the sex chromosome. The human males have 23 pairs of chromosomes including XY sex chromosomes. Therefore, the male gamete has 22 chromosomes and either an X or Y sex chromosome.
Male gametes can be of two types: 22 + X or 22 + Y
Females have 23 pairs of chromosomes including XX sex chromosomes. Therefore, their gametes can only have 22 chromosomes and one X sex chromosome.
Type of female gametes: 22 + X

Thus, as the mother provides only X chromosome, the sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female. Thus, there are 50 percent chances of having either male or female child.

SPECIATION: The process of formation of one or more new species from the existing one by evolutionary means is known as speciation.
NATURAL SELECTION: The process in nature by which, according to Darwin's theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.

To know about the extinct or previously existing animals we can look at the fossils. Fossils and not just the buried teeth, skull and bones but can also be the footprints of any animal are the outlines of the Fallen leaves or plants which under the pressure of the layers of soil becomes preserved as fossils. The study of fossils is known as paleontology.

• Different life forms have evolved during the course of evolution. Classification deals with the grouping of these life forms into groups and sub groups based on similarities and differences.
• The more characteristics any two species have in common, more closely they are related.
• Thus classification helps in tracing the evolutionary relationship between the two organisms. Hence, evolution and classification are interlinked.

Chromosomes are made of proteins and DNA. They are present in the nuclei of the cells. In sexually reproducing organisms, the gametes undergo meiosis and hence, each gamete contains only half set of chromosomes. When two gametes fuse, the zygote formed contains the full set of chromosomes. Hence, the formation of gametes by meiosis helps to maintain the number of chromosomes in progenies.

In human beings, sex is determined by the sex chromosomes. Males have XY constitution of sex chromosomes. Females have XX constitution of sex chromosomes Sex of child depends on what happens during fertilization.

1. If a sperm carrying X chromosome fertilizes an ovum which carries X chromosome, then the child born will be a girl.
2. If a sperm carrying Y chromosome fertilizes an ovum which carries X chromosome, then the child born will be a boy.

The process by which new species develope from the exiting species is known as speciation.
Important factors which could lead to the formation of a new species are as follows:

• Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
• Geographical isolation of a population caused by various types of barriers like mountain ranges, river, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
• Variation caused in individuals due to natural selection.
• Sometimes the sub-population becomes reproductively isolated by ecological barriers. Therefore it occurs within the same geographical area and within the original population.

Acquired Traits	Inherited Traits
Traits developed during lifetime.	Traits presents since the birth.
Cannot be inherited that is do not pass to the off springs.	Are inherited by the off springs.
Not in the genes. for example behavior, art of playing an instrument.	In the genes. For example hair colour, height.

Evolution is a slow change in the body design and other characteristics of an organism over a long period of period that ultimately causes the formation of new speciation from pre-existing species. Different forms of organisms/ life have evolved during the course of evolution.
Classification deals with grouping of these organisms into groups and subgroups based on their similarities and differences. The more characteristics any two species have in common more closely they are related/ will have a more recent ancestor and vice versa. Thus, classification helps tracing the evolutionary relationships between the two organisms hence classification and evolution are interlinked.

Differences between Acquired Traits and Inherited Traits:

Acquired Traits	Inherited Traits
These are somatic variations.	These are genetic variations.
Acquired traits develop due to the effects of environmental factors, use and disguise of organs and special (conscious) efforts.	Inherited traits develop due to a reshuffling of genetic material and mutations.
These traits develop throughout the lifetime of an individual.	These traits are transferred (inherited) by the parents to their offspring.
Example- Learning of dance, music, etc. and muscular body of a wrestler.	Example- Attached or free earlobe and curly hair.

Natural selection is the phenomenon by which the nature selects those species which possess survival advantage over the other species. According to theory of natural selection, there is "struggle for existence" within the species of a population for the environmental resources and this struggle leads to survival of certain organisms and elimination of the less competent species. Thus, in this competition, some organisms might undergo genetic changes which help them in their survival. The better adapted organisms would, thus, survive and pass on their traits to next generation, gradually leading to evolution.
Speciation is a process of formation of new species from the existing one due to reproductive isolation of a part of its population. This reproductive isolation can occur due to geographical isolation of a part of population.
With time, the genetic drift will accumulate different variations in each of the geographically separated sub-populations. Ultimately, all the individuals of these two groups will isolate reproductively, thus, leading to formation and evolution of new species. Thus, we can say that both natural selection and speciation lead to the evolution of species on earth.

Mendel took pea plants with contrasting characteristics- tall plant and dwarf (short) plant. On cross pollination, he got all tall plants in F1 generation. Then by self pollination of F1 tall plants, he produced second generation (F2) consisting of tall and short plants in the ratio of 3:1. Then he concluded that, ‘T’ (tall) trait is dominant while ‘t’ trait for shortness is recessive.

Three factors/evidences and their roles.

1. Analogous organs– organisms with similar looking organs may have different origin.
2. Homologous organs— organisms with apparently different looking organs may have similar origin.
3. Fossils— allow us to make estimates of how far back evolutionary relationships go. Fossils when chronologically arranged help in tracing the evolutionary history of an organism.

There is a pair of genes for each characteristic of an organism, one is dominant gene and the other is recessive gene. Each parent passes only one of the two genes of the pair for each characteristic to its progeny through gametes. Thus, the male gamete and the female gamete carry one gene for each characteristic from the gene pairs of the parents. When a male gamete fuses with a female gamete during fertilisation they make a new cell called zygote which grows and develops to form a new organism having characteristics from both the parents which it has inherited through genes.

The total number of chromosomes present in both human male and female is 46. Out of these, two chromosomes are the sex chromosomes. In human males, the two sex chromosomes present are X and Y, while in human female, both sex chromosomes are X.
During sexual reproduction, the new individual is formed by the fusion of gametes from both the parents. These gametes are haploid in nature, i.e. they contain only one set of the chromosomes. They are formed by the meiosis, a type of cell division which reduces chromosome number to half. When these haploid gametes fuse during fertilization, the two nuclei of these two gametes fuse and the chromosome number is then restored to normal. Hence, the progeny formed has the same number of chromosomes as that of the parents.

1. A fossil bird called Archaeopteryx looks like a bird but it has many Features which are found in reptiles. Archaeopteryx has feathered wings like birds but teeth and tail like those of reptiles. Therefore Archaeopteryx is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles.
2. Insects, octopus, planaria and vertebrates posses eyes but these animals can not be put together on the bases of eyes because structure of eyes in each of there organisms is different which suggests their separate evolutionary origins. Thus all these animals are put in different groups.

Acquired	Inherited
The acquired traits are the traits which are experienced by an individual during his life time.	Inherited traits are distinguishing qualities or characteristics which one acquires from the ancestors.
The acquired traits of an organism cannot be passed on to its future generations.	The inherited traits of an organism are passed on to its future generations
For e.g., 'low weight' of beetle. 'cut tail' of a mouse.	For e.g., red colour of beetles, fur coat of guinea pigs.

Factors responsible for rise of a new species are:

1. Genetic drift: Over a generation, genetic drift may accumulate which lead to the formation of a new species.
2. Natural selection: Due to natural selection, variation may occur which lead to the formation of a new species.
3. DNA change: Variation during DNA copying often lead to the formation of a new species.

Such traits are called acquired traits. Acquired traits are experienced by an individual during his lifetime. These traits involve changes in non-reproductive cells (somatic cells) which are not transferred to germ cells. So, these traits cannot be passed on to the next generation.
For example- Learning skills like swimming, dancing, cooking, body building, etc are acquired traits and can not be passed on to the next generation.

Fossils are formed in the following way:Usually, when the organisms die, their bodies decompose and be lost. But sometimes the body or at least some parts may be trapped in an environment that does not let it decompose completely and eventually harden and retain the impression of the body parts. All such preserved traces of living organisms form fossils.
Two methods to determine the age of fossils:

1. When dug into the Earth, the fossils closer to the surface are more recent as compared to the fossils found in deeper layers.
2. The fossils can also be dated by detecting the ratios of different isotopes of the same element in the fossil material. This process is known as radiocarbon dating.

The process of production of a new DNA molecule from an already existing DNA molecule through chemical reactions is known as DNA copying. It is accompanied by the creation of new cellular apparatus so that the daughter DNA and parent DNA can be separated.Importance of DNA copying:

1. It helps in the transmission of characteristics from parents to offspring.
2. It helps in the maintenance of the chromosomal number in the new cell.

Speciation is the the formation of new and distinct species in the course of evolution.Reasons for speciation’s are:

1. Reproductive isolation.
2. Genetic drift.
3. Geographical isolation.
4. Natural selection.

He experiences and qualifications that a person earns during his/her lifetime are examples of acquired traits. These traits cannot be inherited, as they do not affect genetic makeup of an organism. In fact, these traits develop due to use and disuse of organs, or due to direct affect of environment. Thus, they are not passed on to the next generation. For example, a wrestler develops large muscles because of his training programme; it does not mean that his offspring will necessarily have large muscles. Similarly, if a lady pierces her nose, the children produced to her will not have pierced nose by birth.
Traits can be passed on to the next generation only when they have some direct effect on the genes. For example, if a mutation is caused in the germ cells of a person due to exposure to some harmful radiations, it is highly likely that the mutation caused will be passed on to the subsequent generations.

The two distinguishing features between the acquired traits and the inherited traits is stated below in tabulate form:

Acquired Traits	Inherited Traits
Acquired traits are not inherited but develop during the lifetime of an individual.	Inherited traits are those which are obtained from parents or caused by a change in its genes (or DNA).
These cannot be passed on to the future generations.	These can be passed to the future generations.
These cannot direct evolve. For example: muscular body of wrestler.	These can directly evolve. For example: fused ear lobes.

Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors. This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

1. The eyes seen in planaria, insects, octopus and vertebrates vary greatly in their structure. These organisms can be used for studying evolution of eyes as the eyes of planaria are simple without lens, insects have compound eyes and vertebrates have highly specialized eyes. However, all of them perform the same function of vision. Hence, a common evolutionary origin can be established.
2. Birds like reptiles have developed wings. Although the way the wings are used is different because it was used for providing insulation from cold in case of reptiles whereas it is used for flight in case of the birds. But this shows that wings are analogous organs and the reptiles and birds adapted in a similar manner in hostile conditions.

The evidence was given by Stanley L. Miller and Harold C. Urey in 1953. They assembled an atmosphere similar to that thought to exist on early earth over water. This was maintained by them at a temperature just below 100 degree celsius and sparks were passed through the mixture of gases to stimulus lightening. At the end of week, they found that 15% of the carbon had been converted to simple compounds of carbon including amino acids which make up protein molecules.

Comparing of DNA is known as molecular phylogeny species deduced from fossils record to be closely related are more similar in their DNA than as species thought to be more distinctly related.
Tracing evolutionary relationships between organisms is called as phylogeny while studying structures of various DNAs to establish evolutionary relationships between them is called as, while studying structures of various DNAs to establish evolutionary relationships between them is called as molecular phylogeny.

Although variations of genes (also known as alleles) can be selected for because they help or hinder an organism, other mutations can have no effect. When the allele itself is not responsible for the change in its frequency in a population, genetic drift is acting on the allele. the frequency of these genes can change drastically over time, especially with the smallest populations.
In the largest populations, the allele frequency of each gene stays relatively stable. This happens because the genes are not affecting fitness, and thus do not have a natural selection pressure against or for the allele. In the smallest populations, the frequency of these genes can fluctuate greatly. Some become fixed within the population, while others disappear. These chance events which lead to changes in frequency are called genetic drift.

	Acquired Traits	Inherited Traits
1.	Development: The traits develop during life time of an individual.	The traits are obtained from the parents.
2.	Nature: They are somatic variations.	They are genetic variations.
3.	Cause: Acquired traits develop due to direct effect of environment, use and conscious efforts.	The traits develop due to mutations and reshuffling of genetic material.
4.	Fate: They die with the death of the individual. Ex. Muscular body of a wrestler.	They are passed on to the next generation. Ex. Fused and free ear lobes.