BIOLOGY 2 Marks Questions

1. Forelimbs of cheetah and mammals: This is divergent evolution and these structures are homologous.
2. Flippers of dolphins and penguins: The example of convergent evolution they are not similar in structure but they perform a similar function.
3. Wings of butterflies and birds: The are look same in structure, they are not atomically similar is structure though they perform similar function they called analogues.
4. Forelimbs of whales and mammals: This is divergent evolution and these structures are homologous.

1. Analogous organs or structures are those that are similar in function but different in origin.

From the given options, following are the analogous structures:

• Eyes of octopus and mammals perform the same basic visual function but they differ in the origin of their retina.
• Tubers of sweet potato and potato perform the same function of food storage but they are modifications of root and stem, respectively.

2. The kind of evolution represented by analogous organs or structures is convergent evolution as they have different origins but evolve similar traits with evolution to perform the same function.

1.  

1. Forelimbs of whales and bats.

4. Thoms of Bougainvillea and tendrils of Cucurbita.

2. Divergent Evolution.

Original stock of seed-eating finches migrated to different habitats (of Galapagos Islands), adapted to different feeding methods, by altered beak structure, evolved into different types of finches.

Homologous organs divergent evolution.
Thorns of Bougainvillea and tendrils of Cucurbita.

1. Pre-historic cave art.
2. Agriculture/Human Settlement.

(i) & (ii) Analogous.
(iii) & (iv) Homologous.

1. First mammals.
2. First amphibians (lived both on land and in water)/fish with stout and strong fins which could move on land and go back to water.
3. First human-like being/hominid/brain capacity from 650-800 cc/did not eat meat.
4. Brain around 900 cc/ate meat.

The same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous.Eg. Thron of Bougainvillea and Tendrils of Cucurbita represent homology.

Gene Flow occurs due to emigration or immigration resulting in the change in the frequency of alleles of a gene within the gene pool of a population. A population with active gene flow will not obey the Hardy-Weinberg principle.
Genetic Drift is a sudden change in the frequency of genes and their alleles within a gene pool of a population over a very short duration of time. A population experiencing such a phenomenon will also not obey Hardy-Weinberg principle. Genetic drift can occur due to natural or artificial selection a like.

Wings of birds and wings of butterflies are example of analogous organs and they exhibit convergent evolution. Organisms developing different structures but have the same function is called convergent evolution.

• Differential reproduction: The phenomenon in which all organisms who reach reproductive stage reproduce with varying degree of success, some reproduce more offsprings and some reproduce only few and other reproduce none depending upon their degree of fitness.
• Reproductive isolation: The biological phenomenon in which the individual belonging to same species reproduce among themselves, to maintain the species integrity. Both these terms are used in reference to natural selection.

The study of distribution of various organisms in different parts of the earth is called biogeography. All the varieties of Darwin’s finches have evolved on the same island itself from a common seed-eating ancestor due to adaptive radiation.

In such a population natural selection and random mating does not occur. This is because both these process promotes evolution which disrupts the Hardy Weinberg equilibrium.

S. No	Placental mammal	Marsupial mammal
(i)	Anteater	Numbat
(ii)	Lemur	Spotted cuscus
(iii)	Bob cat	Tasmanian tiger cat
(iv)	Wolf	Tasmanian wolf

Lobefins fish have stout and strong fins, so they can move on land and swim in water to maintain a dual lives like amphibians.

Methane, ammonia, hydrogen and water vapour.

Eyes of Octopus and those of mammals or the wings of butterfly and those of birds are analogous structures, which have resulted from convergent evolution.

• They have not evolved from common ancestors.
• It is the similar habitat that has resulted in similar adaptive features in different groups of organisms towards the same function.

Artificial selection refers to the selection of superior traits of plants and animals by man which it wants to perpetuate. It involves selective breeding of organisms and takes a shorter span of time. The different plant and animal breeding programmes are best known examples of artificial selection.

• Evolution is not a direct process in terms of determinism.
• As the environment changes, due to meteorological, biological and other physical activities, the organisms which are better adapted to the changed environment are selected by nature in a much lesser time scale.
• It is also true for natural selection and evolution of antibiotic-resistant strains of bacteria in a time scale of months.
• So, evolution is a stochastic process based on chance events in nature and chance mutation in the organism.

The process involving formation of new species from the existing species is called speciation.
Two events leading to speciation are:

1. Interbreeding among different populations or species.
2. Migration.

Ontogeny: Ontogeny is embryonic development, i.e. the origin and development of an organism from an embryo to an adult.
Phylogeny: Phylogeny is ancestral history, i.e. the evolutionary development and history of a species or higher taxonomic grouping of organisms.

The world we see, inanimate and animate, is only the success stories of evolution. When we describe the story of this world we describe evolution as a process. On the other hand when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection. We are still not very clear whether to regard evolution and natural selection as processes or end result of unknown processes.

Yes, I agree. Gene flow occurs through generations. By studying specific allele frequencies, we can predict the human migratory patterns in prehistory and history. Studies have used specific genes/ chromosomes/ mitochondrial DNA to trace the evolutionary history and migratory patterns of humans. (The project is known as the Human Genographics Project).

Mammals like Horse, Hippopotamus, Rabbit and Bear.

Age of a living tree can be determined by comparing the diameter of the trunk with average growth factor of that species. Average growth factor of a species can be found from records. Diameter can be calculated by measuring the girth of the trunk.

The organs with different structural designs and developmental origin but performing similar functions are called analogous organs. Trunk of an elephant is analogous to human hand.

1. Presence of free oxygen in present day atmosphere.
2. Existence of living organisms.

Natural disaster like earth quake can be the cause for extinction of species. During the long period since the origin and diversification of life on earth there were five episodes of mass extinction of species.

The organs which have different developmental origin and structural design but perform similar functions are called analogous organs. The wings of birds and insects are analogous organs indicating that they have different ancestors but show a convergent evolution.

Similar evolution in species of different lineage is called convergent evolution. Convergent evolution happens in an isolated geographical area. Flippers of dolphin and penguin are examples of convergent evolution. In both animals; flippers have different origins but serve similar purpose.

• Homology: Tendrils of Cucurbita and thorns of Bougainvillea.
• Analogy: Sweet potato (root modification) and potato (stem modification) to store food.

The increasing order of evolution in plants is as on Zosterophyllum-Ferns-Ginkgo-Gnetales.

1. There are limited natural resources.
2. Populations are stable in size except for seasonal fluctuations.
3. Varying characteristics in members of a population, i.e. no two members of a population are identical even though they look superficially similar.
4. Variations are generally inherited.
5. Population size has two facts, i.e. theoretically it grows exponentially if everybody reproduced maximally but in reality, population size is limited, due to the competition among the individual for resources. Those, which are better adapted could survive and will reproduce at the cost of others, i.e. who are less adapted in the environment.

• The forelimbs of whales, bats and cheetah (or bat, horse and humans) are the result of divergent evolution.
• Divergent evolution is the evolutionary process, where the same structure develops along different directions in different groups of organisms as adaptations to different needs.
• The structures evolved are homologous organs; homology indicates common ancestry.
• Thorns of Bougainvillea and tendrils of Cucurbits are also homologous structures.

1. The characteristics which enable some population or individuals to survive better in natural conditions (foods, climate, physical factors) would outbreed others (survival of the finest).
2. Thus, those organisms, which are better fit or adapt well will survive and get selected by nature, which furthers their evolution. This is called natural selection.

Australopithecus lived in the East African grassland:

1. They were probably not taller than four feet.
2. They walked upright.
3. They hunted with stone weapons, but essentially ate fruits.

• Brachiosaurus and Stegosaurus lived early in the history.
• Tyrannosaurus and Triceratops lived later.

Fitness, according to Darwin, refers ultimately and only to reproductive fitness. Those who are better fit in an environment would outbreed others, who are less fit in that environment; they leave more progeny (with more fit individuals) than others. They will survive better and are selected by nature (natural selection) to reproduce and increase their population size.

• The biodiversity we see today is the story of evolution, i.e. evolution is considered as a process, that has resulted in various life forms.
• If we talk about the life on earth, evolution is considered as a consequence of the process, called natural selection.
• It is difficult to decide, whether evolution and natural selection are processes or end results of some unknown processes.

Paleontology is the study of fossils. It indicates:

1. The geological time period in which the organisms existed.
2. That life forms varied over time and certain life forms are restricted to certain geological time spans.
3. That new forms of life have appeared at different times in the history of earth.

No, human evolution cannot be called adaptive radiation because adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage, which is not the case with human evolution.

It indicates that predators will spot a moth against a contrasting background.

1. After industrialisation, the tree trunks became dark due to deposition of soot and smoke; under such a condition, the white winged moths stood out conspicuously and easily detected by the predators and hence they reduced in number
2. The dark-winged moths could merge with the black colour and they escaped the predators and hence increased in number.

Three evolutionary features of mammals:

• Mammals are endothermic vertebrates.
• Have hair and fur on the body.
• Have mammary glands.

• Ernst Haeckel proposed embryological support for organic evolution.
• It was disapproved by Ernst Von Baer.
• He noted that embryos never pass through the adult stage of other animals.

The fossil Archaeopteryx is a connecting link between reptiles and birds and provide evidence that birds have evolved from reptiles. Its features are:

1. It has beak and wings like that of a birds.
2. It has teeth and scales like that of a reptiles.

The sudden change in appearance or variations in an individual or a population are called mutations. They lead to the new phenotypes. Though mutations are random and occur at very slow rates, they are sufficient to create considerable genetic variations for speciation to occur.

Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms. Trypsin (ancient enzyme) is present from protozoa to mammals.

Nascent oxygen is a highly reactive substance. It can react with many molecules; including the DNA. This can result in unwanted mutations which may threaten the life forms. Hence, nascent oxygen is supposed to be toxic to aerobic life forms.

Oparin-Haldane’s theory states that the first life form originated from non-living organic molecules like RNA, protein, etc. Yes, life can be originated abiotically inside the laboratory under controlled conditions.

1. Rhyniaceae.
2. Psilophytaceae (in a restricted and revised sense).
3. Trimerophytaceae.

• S.L. Miller used this set-up.
• The electrodes (a) are used to create an electric discharge, similar to the lightning in the primitive earth; it was to provide energy.
• The formation of amino acids proved the chemical evolution, which preceded the origin of life.

1. Darwin’s finches.
2. Australian marsupials.

Gene frequency represent percentage of an allele in relation to total number of alleles of a gene in interbreeding population, while sum total of genes and alleles is called gene pool.

Pollen has an outer layer called exine which is made of sporopollenin. It is the most resistant organic material known. It can withstand high temperature, strong acids and alkali as well. No enzyme that degrades sporopollenin is so far known.

When DDT was used for the first time, maximum mosquitoes died but few survived due to variation in the population. These mosquitoes showed resistance to DDT and survived to reproduce successfully in the presence of DDT and gradually such mosquito population became DDT resistant due to natural selection.

Both of them are stem modifications and thus are structurally similar but both have different functions. Thus, they are homologous structures as tendrils and thorns both arise in axillary position and hence are modified branches but tendrils help in climbing and thorns protect the plant.

Alfred Wallace made the following conclusions:

1. New life forms arise and evolve in due course of time.
2. All the existing forms of life share certain similarities and common ancestors.
3. These ancestors lived at different periods in the history of earth.
4. The geological history closely correlates with the biological history.

Frequency of B allele = all of BB + ½ of Bb = 22 + 31 = 53%
Frequency of b allele = all of bb + ½ of Bb = 16 + 31 = 47%.

Oparin and Haldane proposed the theory of origin of life. Initially, on the primitive earth there was no atmosphere. The volcanic eruption and molten mass released water vapour, methane, carbon dioxide, and ammonia which formed earth’s atmosphere. The earth’s atmosphere was reducing one, i.e., no free oxygen was present. Huge amount of energy was liberated from lightning, and UV rays as there was no ozone layer.

Evolution is not a direct process. As environment changes the organisms are better adapted to changed environment are selected by nature. Therefore, it is termed as stochastic process.

Since RNA was unstable and prone to mutations, DNA evolved from RNA with chemical modifications that makes it more stable.
DNA has double stranded nature and has complementary strands. These further resist changes by evolving a process of repair.

Creation and variation occur in a sexually reproducing population as a result of crossing over during meiosis and random fusion of gametes. It is however the organisms that are selected over a period of time which are determined by the environmental conditions. In other words, the environment provides the direction with respect to adaptations so that the organisms are more and more fit in terms of survival.

Lamarck's Theory:

• Lamarck's theory is known as theory of Inheritance of acquired characters.
• According to this theory, organisms undergo certain changes to adapt themselves to the environment.
• These characters acquired by an organism during its life time, are passed on to the progeny, e.g. the long neck of giraffe was explained by Lamarck, as an outcome of these animals having to stretch their necks constantly to eat the leaves on the upper branches of the trees.

Hardy-Weinberg equilibrium is not applicable for large population because as migration of a part of population takes place gene frequency also changes and may lead to founder effect.

1. Australopithecus.
2. Homo habilis.

The atmosphere will be reducing, i.e., no free oxygen will be present. There must be continuous supply of energy like that from lightning, thunder, volcanic eruption and stellar radiation. The presence of autocatalyst or self-replicating molecules is essential.

1. The graph depicts disruptive natural selection. This type of selection tends to eliminate intermediate types.
2. The other two types of natural selection are,

1. Directional selection Large number of individuals acquire value other than mean character value.
2. Stabilising selection Large number of individuals acquire mean character value.

Archaeopteryx is a connecting link between reptiles and birds. It shows features of both birds and reptiles giving an evidence that birds have evolved from reptiles.

Study of fossils is called paleontology: The fossils throw light on past life in following ways,

1. Distribution of fossil gives information about habitat of an organism.
2. Establishes phylogenetic links.
3. Some fossils provide evidence of connecting link.
4. Age of the organisms can be determined by fossils.
5. Fossils also throw light on morphology and anatomy of past life.

Yes, I agree. Gene flow occurs through generations. By studying specific allele frequencies, we can predict the human migratory patterns in pre-history and history. Studies have used specific genes/ chromosomes/ mitochondrial DNA to trace the evolutionary history and migratory patterns of humans. (The project is known as the Human Genographics Project).

Darwinian Concept	de Vries Concept
According to Darwin, speciation occurs with the accumulation of minor heritable variations.	According to de Vries, mutations arising suddenly in a population, are responsible for speciation.
Evolution was gradual and occurs through a number of generations.	Evolution occurs in a large single-step mutation (saltation).
Variations are small and directional.	Mutations are random and directionless.

Convergent evolution is the evolutionary process, where anatomically different structures in different groups of organisms evolve towards the same function, in similar habitats.

• Such structures in different groups of organisms which perform similar function, but are anatomically different, are called analogous organs.
• The tuber of potato (stem modification) and the tuber of sweet potato (root modification) are analogous as they perform the function of storage of food.

The theory of spontaneous generation held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. For instance, it was hypothesized that certain forms such as fleas could arise from inanimate matter such as dust, or that maggots could arise from dead flesh.

Recent studies on self consciousness says gibbons are the nearest to human in this respect. Apes and orangutans came next. Among domestic animals, dog and other members of canidae family show subtle self consciousness.

The universe is about 15-20 billion years old. It comprises of huge clusters of galaxies, which contains stars, clouds of gas and dust. According to the Big Bang theory given by Abbe Lemaitre (1931), our universe arose as cataclysmic eruption. The temperature lowered and the gases like hydrogen and helium were formed sometimes later. By the force of gravitation, the gases condensed and galaxies were formed.

The primitive earth or primordial earth contained large amounts of hydrogen, nitrogen, water vapour, ammonia and gases evolved from molten lava but no free oxygen was found. The primitive atmosphere was reducing which favoured abiotic origin of life.

Yes, aquatic life forms get fossilised in the sediments of the water bodies. Later, sediments forms the part of sedimentary rocks in which fossils, are deposited.

Darwinian theory of evolution:

• Charles Darwin, based on his observations during a sea voyage around the world in the ship H.M.S. Beagle, concluded the following:
• Varying degrees of similarities can be observed between existing life forms and those that existed millions of years ago.
• There has been gradual evolution of life forms with new forms arising at different periods of history.
• Any population has built-in variations in characteristics which adapt it better to environment.
• The characteristics which enable some populations or individuals to survive better in natural conditions (climate, food, physical factors) would out-breed others (Survival of the fittest).
• Those populations which are better fit (reproductively fit) in an environment will be selected by nature and will survive more (Natural selection).
• Adaptability is inherited and fitness is the end result of ability to adapt and get selected by nature.

Mutations are not as commonly occurring, most of them are negative. Mutations mostly are recessive however traits responsible for evolution are dominant.

Survival of fittest means that those that survive are called fit. Organisms with useful adaptations survive in the long run and are considered to be fit.

The organs with same structural design and developmental origin but differing in their functions are called homologous organs. Forelimbs of human being are homologous to forelimbs of whales and bats.

1. Dryopithecus.
2. Ramapithecus.
3. Australopithecus.
4. Homo habilis.
5. Homo erectus.
6. Cro-Magnon man.
7. Homo sapiens.

Migration may cause enrichment of the gene pool of such alleles that are being selected for, or annul the effects of selection through replenishment of alleles that were selected against by nature.

The rate of reproduction among the different individuals in a population varies. Some produce more offsprings and some produce only few offsprings. This biological phenomenon is called differential reproduction. So, the reproductively fit individual produces more offsprings than other. They are thus selected by nature to survive and evolve into new species.

Earth's atmosphere:

• Water vapour, methane, carbon dioxide and ammonia that were released from the molten mass covered the surface.
• The UV rays from the sun broke up water into hydrogen and oxygen.
• The lighter hydrogen escaped into the atmosphere.
• Oxygen combined with ammonia and methane to form carbon dioxide and other gases.
• Later ozone was formed from the oxygen.

Abiotic synthesis means origin of life from non-living constituents, i.e., chemical evolution of life states that diverse organic molecules were synthesised from inorganic constituents. These complex organic molecules adapt to autocatalyst property, i.e., self-duplication or self-replication. This idea was proposed by Oparin and Haldane. It was experimentally proved by Urey and Miller.

S. No.	Homo habilis	Homo sapiens
(i)	The brain capacities were between 650-800cc.	During ice age between 75,000-10,000 years ago modern Homo sapiens arose.
(ii)	They probably did not eat meat.	Pre-historic cave art developed about 18,000 years ago.
(iii)	They were the makers of stone tools.	Agriculture came around 10,000 years back and human settlements started.

These are the terms to classify organisms according to their evolutionary history. Simple organisms have simple structural and functional organisation and are considered primitive, whereas complex organisms have complex structural and functional organisation and are said to have arise from simple organisms.

1. Lobefins are the fish with stout and strong fins, that could move on land and go back to water, they must have lived about 350 mya and were thought to be extinct.
2. In 1938, a Coelacanth (lobefin) was caught in South Africa.
3. Though no specimens of these are left with us, they evolved into the first amphibians.
4. These were the ancestors of modern day frogs and salamanders.

Frequency of B allele = all of BB + of Bb
= 22 + 31 = 53%
Frequency of b allele = all of bb + of Bb
= 16 + 31 = 47%.

Energy for life to originate must have been provided by heat, cosmic rays and lightning. Cyanobacteria was the first organism to release oxygen into the atmosphere.

Silurian, Devonian, Carboniferous, Permian.

1. Psilophyton.
2. Seeds and ferns.
3. Chlorophyte ancestor.
4. Ferns, conifers and seed ferns.
5. Tracheophyte ancestor.
6. Chlorophyte ancestor.

In the story of moths in England; white winged moths survived because whitish lichens proliferated on tree trunks during pre-industrialisation days. White-winged moths had better chances of survival against a whitish background. But when the tree trunks become dark due to pollution, the white-winged moths perished; and dark-winged moths reappeared and survived. Thus, evolution of white wings was reversed because of pollution. This shows that evolution is apparently reversible.

The organs which have same basic structural design and development origin but differ in their uses and functions are called homologous organs. The forelimbs of some animals have similar anatomical structure. They possess humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs, e.g., forelimbs of man, whales, bats, cheetah, indicates that they have common ancestors, thus supporting organic evolution.

Embryology, anatomy, palaeontology and biogeography provided evidences for organic evolution.

Lamarck’s theory of evolution states that use and disuse of an organ can bring about a change in that organ which is then acquired and passed on to the next generation, e.g., the long neck of giraffe was explained by Lamarck, as an outcome of these animal to stretch their neck constantly to eat the leaves from the upper branches of the trees.

The sum total of all the allelic frequencies of a stable population is one.
The factors which affect Hardy-Weinberg's equilibrium are as follows:

1. Gene migration/ gene flow.
2. Genetic drift.
3. Mutation.
4. Genetic recombination.
5. Natural selection.

The disturbance in genetic equilibrium in a population, would result in evolution.

1. Convergent evolution.
2. Convergent evolution.
3. Convergent evolution.
4. Divergent evolution.

1. There are inheritable variation among the members of a population.
2. Many more individuals are produced each generation that can survive and reproduce.
3. Individuals with adaptive characteristics are more likely to be selected to reproduce by the environment.
4. Gradually, over long periods of time, a population can become well adapted to a particular environment.
5. The end result of organic evolution is many different species, each adapted to specific environments.

Methane, carbon dioxide, ammonia and water vapour.

1. Homo erectus.
2. Neanderthal man.
3. Homo habilis.
4. Dryopithecus and Ramapithecus.

Earth was supposed to have been formed about 4.5 billion years back in the solar system of our milky way galaxy. Its surface was covered with water vapour, methane, carbon dioxide and ammonia released from molten mass.
Subsequently, the ozone layer was formed. fu it cooled, the water vapour fell as rain and filled all depressions to form oceans and other water bodies.

Pelycosaurs and Therapsids.

1. All vertebrate embryos develop a row of gill slits, which are functional only in fish and tadpole larva and not in other vertebrates.
2. Notochord is present in all vertebrate embryos.

Such similarities indicate that they have descended/ evolved from a common ancestor.