BIOLOGY 3 Marks Question

• Population must be sufficiently large.
• Free flow of genetic materials is ensured through sexual reproduction.
• There should be negligible or nil migration in the population.

Hence, in these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry. Driving force behind the divergent evolution is adaptation in different environments.

1. Adaptive radiation: It is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).

2. Tiger cat/ banded ant eater/ Marsupial rat.

3. Wolf is a placental mammal, whereas Tasmanian wolf is a marsupial mammal.

1. Variations: There are differences among all individuals. These differences are called variations. According to Darwin, the variations are gradual (continuous) and those, which are helpful in the adaptations of an organism towards its surroundings would be passed on to next generation, while the other dissapears.

2. Formation of new species: Darwin considered that useful variatons are transmitted to the offspring and appear more prominently in succeeding generations. After some generations these continuous and gradual variations in the possessor would be so distinct that they form a new species.

1. Theory of chemical evolution or abiogenesis was proposed by Oparin and Haldane.
2. It states that the first form of life could have come from pre-existing non-living organic molecules (like RNA, proteins, etc.) and that formation of life was preceded by chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents.

Miller's experiment:

1. He created conditions similar to the primitive earth in the laboratory
2. Electric discharge was produced by using electrodes) in a closed flask, containing methane, hydrogen, ammonia and water vapour.
3. The temperature was kept at 800°C.
4. After a week, he observed formation of amino acids.
5. Such molecules must have reacted among themselves to form giant, self-replicating molecules, the first form of life.

1. Homology.
2. Analogy.
3. Analogy.
4. Analogy.
5. Analogy.
6. Analogy.

1. All living organisms (different species or types of plants and animals) that we see today were created as such.
2. The diversity of life forms was always the same, since the time of creation and will remain the same in future too.
3. Earth is about 4000 years old.

It is caused by one or more of the following:

1. Gene migration/ Gene flow:

• When a section of a population migrates to another population in another place, the gene frequencies change in both the populations.
• When gene migration occurs a number of times, there is gene flow.

2. Genetic drift: Due to some chance events, the allele frequency becomes so different that they become new species.
3. Natural selection: It is a process in which heritable variations enabling better survival are made to reproduce and leave more progeny; hence, there is a change in the allele frequency.
4. Genetic recombination: In sexually reproducing organisms, recombination of maternal and paternal alleles occurs during gametogenesis, it is a major cause of variation in the allele frequency

1. Anthropogenic actions, i.e. human activities have been found to enhance evolution.

Example:

1. Use of DDT has resulted in evolution of DDT-resistant mosquitoes.
2. Evolution of antibiotic or drug-resistant microbes.

2. When DDT was used for the first time, many mosquitoes died, but a few survived.
3. These few mosquitoes showed resistance to DDT and reproduced in the presence of DDT.
4. Most of the offspring were also resistant to DDT.
5. Hence, the mosquito populations of today consist mainly of DDT-resistant mosquitoes and hence, DDT is not effective.
6. In the absence of DDT, these DDT-resistant mosquitoes had no advantage over those mosquitoes, which were sensitive to DDT.
7. This is an example of evolution due to anthropogenic activities, i.e., anthropogenic evolution.

1. Early earth had innumerable free atoms of all those elements, which were essential for the formation of protoplasm.
2. Free atoms combined to form molecules and simple inorganic compounds.
3. The primitive atmosphere contained gases like CO₂, CO, N, H₂, etc. The nitrogen and carbon of the atmosphere combine with metallic atoms, forming nitrides and carbides water vapour and metallic carbides reacted to form the first organic compounds, methane (CH₄). Later on hydrogen cyanide was formed.

Torrential rain must have dissolved away and carried with it salts and minerals, and ultimately accumulated in the form of present occurance. Thus ancient oceanic waters contained large amounts of dissolved NH₃, CH₄, HCN, nitrides, carbides, various gases and elements.

The early compounds interacted and produced simple organic compounds such as simple sugars, nitorgenous bases, amino acids, glycerol, fatty acids, etc under the action of external forces such as solar radiations electrical discharges and like lightning and high energy radiations.

1. Fossils of dinosaurs provide palaeontological evidences for evolution.

• They represent extinct organisms.
• A study of fossils indicates the geological time period in which these organisms existed and that life forms varied over time.

2. Forelimbs of cheetah, bat, whale and humans provide evidences of evolution from comparative anatomy and morphology.

• The similarity in the anatomy of these organs indicates that the same structure has developed along different directions as adaptations to different needs; homology indicates common ancestry.

3. Thorns of Bougainvillea and tendril of Cucurbita also provide evidences from comparative anatomy and morphology.

• They represent homology (both are stem modifications) and homology represents common ancestry and divergent evolution.

1. The rate of appearance of new forms is linked to the lifespan of the species.
2. Microbes have the ability to divide and multiply to produce millions of individuals within hours.
3. A colony of bacteria (say A) growing on a given medium, has built-in variation in terms of ability to utilise a food component.
4. A change in the composition of the medium will allow only those individuals who can survive in the changed condition.
5. In due course of time, the variant population (say B) would outgrow the population A and appear as a new species; this would happen within a few days.
6. This is also true for microbes to develop antibioticresistant varieties.
7. Use of pesticides like DDT against mosquitoes has resulted in mosquito populations with DDT resistance within a few years.
8. For a change to occur in a fish or fowl would take million years, as their lifespans are in years.

1. When disruptive natural selection operates.
2. Mutation, gene flow genetic drift, recombination.
3. Charles Darwin.

1. He could not get desired results because:

• O₂ was used instead of H₂.
• Temperature maintained was 80°C instead of 800°C.

2. It was concluded that life could have come from pre-existing non-living organic molecules and their formation was preceded by chemical evolution.
3. Urey and Miller observed formation of amino acids when in a closed flask CH₄, H₂, NH₃ and water vapour were heated at 800°C in presence of electric discharge. Analysis of meteorite content also reveals similar compounds indicating that similar process are occurring elsewhere in space (Chemical evolution). Urey and Miller proved that life originated abiogenetically whereas theory of spontaneous generation emphasised that units of life called spores were transferred to different planets including Earth.

Artificial selection have been operated in the followings cases:

1. When the allele frequencies in a population remain stable and is constant from generation to generation, it is said to be in genetic equilibrium; it means the gene pool of the population remains constant.
2. Hardy-Weinberg principle
3. Two factors are:

• Genetic drift.
• Gene flow.

4. Gene flow/ Migration: When the individuals of a population migrate to another population, gene frequencies change in both the populations.

• New genes/ alleles are added to the second population while they are lost from the first population. If this migration happens a number of times, there will be gene flow.

1. Reducing atmosphere, i.e. the presence of hydrogen.
2. The absence of free oxygen.
3. High temperature and storms to provide energy.

1. When DDT was first used, most of the mosquitoes were sensitive to it and were therefore killed.
2. In the original population of mosquitoes, some individuals were resistant to DDT.
3. They did not have any advantage over the DDT-sensitive mosquitoes, in the absence of DDT.
4. They survived in the presence of DDT and reproduced; the offspring were also mostly DDT-resistant.
5. As a result, over a period of time almost the entire population came to consist of the resistant type.

1. S.L. Miller used this set up.
2. In the diagram, 'a' refers to electrode through which electric discharge was created
3. Miller observed a large number of simple organic compounds and some amino acids. He proved that organic compounds were basis of life.

1. Psilophyton.
2. Seed ferns.
3. Chlorophyte ancestors.
4. Ferns, Conifers, Seed ferns.
5. Tracheophyte ancestors.
6. Chlorophyte ancestors.

1. The given equation represents Hardy-Weinberg (genetic) equilibrium.
2. This principle stated that allele frequences in a population are stable and remain constant from generation to generation, i.e., the gene pool remains a constant; this is called genetic equilibrium.
3. The sum total of all the allele frequencies is one.
4. Individual frequencies are named as p and q, which represent the frequencies of alleles A and a respectively, in a population of diploid organisms.
5. The frequency of AA individuals is p², while that of aa is q² and Aa is 2pq; hence p² + 2pg + q² = 1, which is the binomial expansion of (p + q)².
6. Any deviation in the frequency of alleles represents an evolutionary change.

1. In England, before industrial revolution, there were more white-winged or dull-grey moths on the tree trunks, than the dark-winged or melanic moths.
2. In the collection of moths, carried out in the same area after industrial revolution, there were more dark-winged moths.
3. The explanation given for this observation was that predators will spot a moth against a contrasting background.
4. During the post-industrialisation period, the trunks became dark with the industrial smoke and soot.
5. Under this condition, white-winged moths did not survive as predators could easily spot these, while dark-winged or melanic moths survived better.
6. Before industrialisation, there used to be a thick growth of the almost white-coloured lichens on the tree trunks and in that background, the white-winged moths survived better, the dark-coloured moths were easily spotted and picked up by their predators.
7. In this case, the moths which were able to camouflage and hide in the background survived and increased their population size through reproduction.