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.