Science [2 Mark Questions]

A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring’s.
Plant species: Wheat, Paddy, Sunflower etc.
Animal species: Cat, Dog, Tiger, etc.

Forelimb of humans and forelimb of lizard are the homologous organs and the wing of insect and the wing of bird are analogous organs.

The presence of homologous organs in different animals provides evidence for evolution by telling us that they are derived from the same ancestor who had the ‘basic design’ of the organ on which all the homologous organs are based.

Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring, and those characteristics which do not help are not passed on.

For a trait of an organism to be inherited, it should bring about a change in the genes present in the reproductive cells or gametes of that organism. The traits acquired during the life time of a person do not bring about a change in the genes present in its reproductive cells or gametes and hence they are not inherited by the offsprings.

1.  

1. E is recessive.
2. E is dominant.

2. The colour of their eyes is brown.
3. Combination ee will produce children with blue eyes.
4. Combination EE or Ee will produce children with brown eyes.

Human evolution has been studied by using the various tools of tracing evolutionary relationships like excavating (digging earth), carbon-dating, studying fossils and determining DNA sequences.

The changes in DNA during reproduction are mainly responsible for evolution. The changes which take place in the DNA of species go on accumulating from one generation to the next. So, if the changes in the DNA of any two species are less, then the two species are quite close to one another in evolutionary terms. But if the changes in the DNA of two species are much more, then the two species will be far apart from one another in evolutionary terms. Thus, it is the characteristic of the extent of change in the DNA which is being used to determine how close two species are in evolutionary terms.

1. The gene for red petals is dominant, while the gene for white petals is recessive.
2. The gene for red petals can be represented by R and the gene for white petals can be represented by r.

Brown hair color genes are dominant and the red hair color genes are recessive ; The genotype of brown hair is BB (dominant always represented by capital letter) and that of red hair bb (Recessive represented by small letter)

The chromosomes which determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes? X and Y chromosomes.

The wings of a butterfly and the wings of a bat cannot be considered homologous because though the function of wings in both the cases is same but they have different basic design. The butterfly has a fold of membranes as wings which are associated with few muscles but has no bones whereas the wings of bat are supported by bones.

According to Mendel’s first law of inheritance: The characteristics (or traits) of an organism are determined by internal ‘factors’ which occur in pairs. Only one of a pair of such factors can be present in a single gamete.

Sometimes a species may completely die out. It may become extinct. Once a species is extinct, its genes are lost forever, it cannot reemerge at all. The small numbers of surviving tigers are a cause of worry because if they all die out and become extinct, their genes will be lost forever. Our coming generations will not be able to see Tigers at all.

1. Combination Bb will give brown eyes.
2. Combination bb will give blue eyes.
3. Combination BB will give brown eyes.

Mendel first crossed pure bred tall pea plants with pure bred dwarf pea plants and found that only tall pea plants were produced in the first generation. No dwarf pea plants were obtained in F1 generation. Mendel concluded that the first generation showed the traits of only one of the parent plants; tallness. The trait of other parent plant, dwarfness, did not show up in the progeny of first generation. Mendel then crossed the tall pea plants of the first generation (F Generation) and found that tall plants and dwarf plants were obtained in the second generation (or F generation) in the ratio of 3 : 1. Mendel noted that the dwarf trait of the parent pea plant which had seemingly disappeared in the first generation progeny reappeared in the second generation. In this way, Mendel’s experiments with tall and dwarf pea plants showed that the traits may be dominant and recessive.

Geographical isolation is the major factor in the speciation of sexually reproducing animals because it interrupts the flow of genes between their isolated populations through the gametes.

1. Tall: Tt will have tall plants because of the presence of T which is dominant gene and t is recessive gene.
2. Dwarf plants: It is dwarf due to the presence of both the recessive genes.
3. Tall plants: These plants are tall due to the presence of both the dominant genes.

Genes are the units of heredity which transfer characteristic from parents to their offspring’s during reproduction. Genes are located on the chromosomes.

Bacteria have simpler body plan when compared with human beings. Both of them have evolved differently. Bacteria can inhabit most of the unfavourable habitats such as hot springs, deep- sea thermal vents and the ice in Antarctica.

Mendel choose pea plants for studying inheritance because pea plants had a number of clear cut differences which were easy to tell apart. Another reason for choosing pea plants are they were self pollinating and many generations can be produced in a short time span.

No, because mother has a pair of X chromosomes. All new born babies will inherit an Xchromosome from mother whether they are baby boys or baby girls.

Geographical isolation will not be a major factor in the speciation of a self pollinating plant because it does not depend on other plants for its process of reproduction to be carried out.

1. Green seed: Yellow is dominant: Green is recessive.
2. Wrinkled seed: round is dominant: wrinkled is recessive.

Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out reproduction.

1. Give the modern name for this ‘factor’.
2. State where these factors are found in gametes.

Analogous Organs: Organs which performs similar function but are different in structure and origin.
Example: wings of a bird and wings of an insect.
Homologous Organ: Organs which have different functions but similar structure and origin.
Example: fore arm of frog, lizard, bird and human.

1. Tall plant.
2. Dwarf plant.
3. Female.
4. Male.

The presence of analogous organs indicates that even the organisms having organs with different structures can adapt to perform similar functions for their survival under hostile environmental conditions. Thus, the presence of analogous organs in different animals provide evidence for evolution by telling us that though they are not derived from common ancestors, they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment.