Science [3 Mark Questions]

The variation are produced when the new generation reproduces, The second generation produced will have variations that they inherit from the first generation.
The organism can reproduce through two mode of reproduction:

1. Asexual reproduction.
2. Sexual reproduction.

1. Asexual reproduction: In Asexual reproduction is found by the division of parent organism into daughter nuclei. In case of bacteria, bacteria get divided into two individuals, each of them will divide again and give rise to two other organism. The four individual bacteria generated would be very similar with minor difference that occurred due to small inaccuracies in copying of DNA.
2. Sexual reproduction: In Sexual reproduction involves the fusion of gametes. The off springs show variations from their parents due to crossing over and exchange of gene segments. They are not exact copies of their parents, due to environmental factors certain favourable variations are also produced. Due to production of variations, sexually reproducing animals show very quick evolution.

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.

Acquired characters are acquired due to individual’s response to external stimuli. These traits develop because of constant exposure to a certain stimulus and the resultant response by the individual. Let us take the example of a certain cricketer who is an excellent batsman. He could become an excellent batsman because of several reasons. Some of them could be; his keen interest in the game, timely support from his family and friends, proper coaching at the right age and timely selection in the cricket team. All the cricketing ability could be acquired by him because of the way he responded to all the challenges and opportunity. But this does not mean that the son of this cricketer would become an excellent cricketer; because cricketing ability is not an inheritable character.
In fact, acquired characters just alter the phenotype of an individual. It has no effect on genotype. A character can only be inheritable when it changes the genotype of individual. Hence, acquired characters are not inherited.

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.

The accumulation is the variations of gradual changes which takes places in primitive organisms over millions of years and new organisms are formed.
There are four ways in which this can do. These are:

1. Natural selection: Those variations which give survival advantage to an organism are selected in nature and such traits increase in population.
2. Genetic drift: It occurs due to change in gene frequency due to accumulation of particular type of genes.
3. Geographical isolation: It leads to change in gene frequency leading to expression of one type of traits in a geographically isolated population.
4. DNA changes: Variations during DNA copying often leads to the formation of a new species.

Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.

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.

When a man having blood group A marries a woman having blood group B, two types of blood groups can be observed in their children. The possible blood group options are B and O in the ratio 1 : 1

All the human races appear to be different but they have a large number of common characters. The list of common characters can be very long but we can make a shorter list:

• Similar size of brain.
• Bipedal locomotion Hair of body.
• Ability to handle tools.
• Ability to communicate using language.
• Highly complex social behavior.
• Same body design.

All these characters show a common ancestry for all human races. Moreover, the fact that all human beings are able to interbreed keeps them under the same species.

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.

1. By studying their structural design: Homologous or anologous. It can give evidences of common ancestor. Forelimbs of humans and wings of birds look different externally. However, their skeletal structure is similar. Thus, their origin is similar, but functions are different. While wings help a bird in flight, the forearm helps human beings in various activities. These structures are called homologous organs.
2. By the study of fossils: A million years later, some dinosaurs died at the same place with their bodies getting buried on top of the sedimentary rock. As a result, the mud, containing the dinosaurs, also turned into rock. Now, if that area is excavated deeper, dinosaur and invertebrate fossils can also be found.
3. Comparing the DNA of different organisms: All species have the same genetic code. So we can trace some evolutionary relationship among the species.

It depends on our perspective through which we try to evaluate evolution. If complexity in body design is the parameter to define evolution, then human beings are more evolved than bacteria. Bacteria are unicellular while human beings are multicellular. Bacteria show cellular level of organization, while human beings show organ system level of organization. In terms of complexity human beings are definitely highly evolved compared to bacteria.But when we compare the ability of survival, then situation is quite opposite. Human beings are living in almost every part of the earth but they can live only on land. Moreover, in extreme environmental conditions, human beings make artificial facilities to counter the adverse conditions. This means their body is not adapted to withstand extreme climatic conditions. Bacteria, on the other hand, are known to be present almost everywhere on earth. They are known to live even in some of the harshest conditions; like Sulphur spring, crater of volcano, etc. Bacteria can survive in highly acidic environment and they can survive extreme temperatures. From this angle, bacteria can be considered as more evolved than human beings.

Animals which exhibit characters of two adjacent taxonomic group are called connecting links. They provide a very good example of evolution. For example Peripatus is a connecting link between annelids and arthropods.

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.

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. For example, in a family, a brother and sister are closely related and they have a common ancestor i.e. their parents. A brother and his cousin are also related but less than brother and sister because the brother and his cousin have a common ancestor i.e. grandparents. Grandparents were second generation whereas parents are first generation.

1. Two common signs of sexual maturation in boys and girls are as follows:

• Broadening of shoulder and chest in boys and development of mammary gland or breast in girls.
• The appearance of hairs on various body parts like the pubic area, armpits, and face.

2. The number of females will become very low in comparison to the males. Hence, there will be a huge imbalance between the male-female ratio in the population.
3. Chemical method of contraception e.g. Oral pills interferes with the hormonal balance of the body.
4. Birth rate and death rate are factors that determine the size of a population.

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.

Phylogenetics is the science of estimating and analyzing evolutionary relationships. Phylogenetic relationships among micro-organisms are especially difficult to discern. Molecular biology often helps in determining genetic relationships between different organisms. Nucleic acids (DNA and RNA) and proteins are 'information molecules' in that they retain a record of an organism's evolutionary history.
Molecular phylogeny uses such data to build a "relationship tree" that shows the probable evolution of various organisms.

1. The application of molecular phylogeny is in DNA barcoding, wherein the species of an individual organism is identified using small sections of mitochondrial DNA or chloroplast DNA.
2. One more application is used in determining a child's paternity, known as DNA fingerprinting.

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.

Yes, geographical isolation of individuals of a species leads to speciation. Splitting of existing species into two new species followed by their geographical isolation brings about reproductive isolation. Populations of a species get separated into two groups by accumulation of genetic variations in them. These newly formed groups are then isolated by any geographical barrier.
Reproductive isolation is absence of interbreeding between members of different species. Geographical barriers prevent interbreeding between two groups. This in turn causes isolation of gene pool of section of population from rest; inhibits gene flow (spread of genes between populations) and thereby leads to formation of new species.

1. X- Wild Cabbage (Brassica oleracea) is made to produce 5 different varieties of vegetables by artificial selection.
2. These 5 different looking vegetables are Cabbage, Kohlrabi, Kale, Broccoli, and Cauliflower.

3. The process of evolution involved in this example is known as Artificial Selection. Artificial Selection is the intentional reproduction of individuals having desired characteristics.