Biology 5 Marks Questions

Chimps are more evolved than humans (The Times of India):
Chimpanzees are more evolved than humans, a study suggests. There is no doubt that humans are the more advanced species. But a comparison of 14,000 human and chimpanzee genes shows the forces of natural selection have and the greatest impact on our ape cousins. The researchers' discovery challenges the common assumption that our large brains and high intelligence were the gifts of natural selection. Humans and chimps followed different evolutionary paths from a common ape ancestor about 5 million years ago. Both underwent changes as the fittest survived to pass their genes on to future generations. But the US study shows that humans possess a 'substantially smaller' number of positively-selected genes than chimps.

Animals	Fossils
Man	Homo Sapiens
Dog	Leptocyon
Chimpanzee	Dryopithecus
Elephant	Moerither
Horse	Eohippus
Gorilla	Dryopithecus
Camel	Protylopus
Whale	Protocetus
Fish	Arandaspis
Octopus	Belemnite

1. Mosquitoes were not affected by the previous cream because they got adapted to the cream and became resistant.
2. Darwin's theory was based on the fact the organisms which adapt well will survive more in nature and gets selected by nature through the mode of natural selection.
3. Yes, the excess use of the cream leads to selection of mosquitoes in a short duration of time.
4. Vicky is knowledegble, scientific and observant.

1. There is no origin of life on earth today, because:

1. The atmosphere is oxidising and any molecule formed will be oxidized.
2. Any molecule formed will be devoured by other organisms.

2.  

1. Amino acids
2. Energy was provided

• by an electric discharge.
• by heating the water chamber.

3. Sunlight, (UV-rays) and lightning (electrical discharges).
4. His knowledge of the subject, desire to disseminate the knowledge and the concern for his neighbours.

Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.

• The novelty and brilliant insight of Darwin was this: He asserted that variations, which are heritable and which make resource utilisation better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny. Hence for a period of time, over many generations, survivors will leave more progeny and there would be a change in population characteristic and hence new forms appear to arise.
• The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Hence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution.

1. Such organs are called homologous organs, i.e. organs of different species which look different and perform different functions, but have the similar basic structure and embryonic origin.
2. Thorns of Bougainvillea and tendrils of Cucurbita are homologous organs in plants.
3. Divergent evolution.
4. Samya is inquisitive, intelligent and observant.

1. Philosophie Zoologique in 1809.
2.  

1. New needs in respect to changing environment.
2. Acquisition of characters.
3. Inheritance of acquired characters.

3. Other theories are:

1. Darwin's theory of natural selection.
2. de Vries mutation theory.
3. Modern synthetic theory of evolution.

4. The teacher was patient, knowledgeable and understanding.

Following are the three out of five factors which affect allele frequency in populations:

1. Genetic Drift: The change in the frequency of a gene variant in a population due to random sampling is called genetic drift. Genetic drift may cause a gene variant to disappear completely and result in reduced genetic variation.
2. Genetic Recombination: Production of offspring with traits which differ from parents is called genetic recombination.
3. Natural Selection: This theory is based on the premise that nature selects only those traits which help an organism to survive in the changed conditions. Natural selection leads to survival of the fittest. Those which are not fit to survive perish in the long run; paving the way for evolution of a new species.

Race: A race is an informal taxon and is kept below the species. This means that members from different races of the same species can interbreed.Breed: A breed is a specific group of domestic animals which are homogenous in appearance. This homogeneity has been achieved through selective breeding.
Cultivar: A selected group of plants which can be raised through vegetative propagation is called cultivar.
Variety: Variety is similar to a race but is used for the plants. Thus, a variety is an informal taxon which is kept below the species in the plant kingdom.

Some scientists have been studying this aspect of human evolution and have come with interesting observations which suggest the evolution is indeed taking place in modern humans. Some of the observations are as follows:

• Human evolution has accelerated since the discovery of farming about 10,000 years ago. There is substantial genetic difference between hunter gatherers and current humans.
• Human reproductive period has prolonged than it was 10,000 years ago. Earlier, the average life expectancy of human beings was about 30 years which is now more than double.
• Lactase persistence into adulthood is another sign of human evolution. All other mammals develop lactose intolerance because young ones are weaned away from mother’s milk after a certain age. Unlike humans; other mammals do not have the facility to consume other mammal’s milk. But human beings consume milk throughout their life because they get it from domesticated animals.
• Humans have also developed resistance to many infectious diseases. This is another sign of evolution.

However, evolution of modern humans cannot happen through geographical isolation because modern means of transport has blurred geographical boundaries. But evolution can happen because of genetic drift.

1. Any population has built in variation for every character.

Individuals with those characters which enable them to survive better in the given environment, would outbreed the others, who are less adapted. Fitness, according to Darwin, is reproductive fitness, i.e. individuals who are more fit in an environment leave more progeny than others.

These progenies survive better and more and more fit individuals are added to the population, i.e. natural selection.

The population thus comes to possess more fit individuals, i.e. nature selects the better fit invididuals and over a long period of time, through a number of generations, the population slowly becomes modified into a different form or a species, in the process called evolution, e.g. evolution of DDT-resistant mosquitoes.

2. The two key concepts of Darwinian theory are:

• Branching descent.
• Natural selection.

3.  

• Lemon thorn and Cucurbita tendrils are homologous-as both are stem modified
• Opuntia spines and pea tendrils are homologousas both are leaf modifications.
• Homologous organs are those organs in different groups of organisms, that are similar in basic structural and developmental patterns, but perform different functions and are superficially distinct.

1. Evidences that evolution of life forms took place on earth came from palaeontology, comparative anatomy and morphology, biochemical evidences and biogeographical evidences.
2. Palaeontological Evidences: Palaeontology is the study of fossils (i.e. remains of hard pans of life forms found in rocks). Rocks form sediments and a cross-section of the earth's crust depicts the arrangement of these sediments one over the other, during the long history of earth. Sediments of different aged rocks contain fossils of different life forms that lived and died during the formation of a particular segment. Some of them appear similar to modern organisms. They represent extinct organisms, like dinosaurs. The study of fossil in different sedimentary layers indicates the geological period in which they existed, the life forms varied over time and life forms that are restricted to certain geological time scale. Hence, new forms of life have evolved at different times in the history of earth. All this forms palaeontological evidence. The ages of these fossils are estimated by using methods like radiocarbon dating.

Main theories of evolution are:

1. Lamarckism or Theory of Inheritance of Acquired characters.
2. Darwinism or Theory of Natural Selection.
3. Mutation theory of De Vries.
4. Neo-Darwinism or Modern concept or Synthetic theory of evolution.

1. Fitness, according to Darwin, refers ultimately and only to reproductive fitness.
2. Those individuals who are better fit in an environment leave more progeny than the others; the population comes to possess more fit individuals, as nature selects for fitness.
3. The so-called fitness is based on characteristics which are inherited; hence there must be a genetic basis for getting selected and to evolve.
4. In other words, adaptive ability is inherited and has a genetic basis; fitness is the ability to adapt and get selected by nature.

Industrial Melanism: Industrial melanism in peppered moth (Biston betularia) is an example of natural selection. In England, 1850s before industrialisation there were more white-winged moths on trees than dark-winged or melanic forms. But after industrialisation, i.e. in 1920, dark-winged moths became more than white-winged moths. This is because during industrialisation, the tree trunks covered by white lichens became dark due to air pollution (dust and soot particles). Due to this, white-winged moths could be easily seen and eaten by the predators as they failed in camouflaging (hide or disguise the presence of a person, animal or object). This shows that in a mixed population, those that can adapt, survive better and increase their population size.
Chemical Resistance: It is another example of natural selection. The excess use of herbicides and pesticides leads to selection of resistant varieties of microbes in very less time. Likewise due to these anthropogenic actions antibiotic resistant bacteria are also appearing now-a-days. The above said industrial melanism and chemical resistance are also examples of evolution by anthoropogenic action. This tells us that evolution is a stochastic process, based on chance events in nature and chance mutation in the organism.

Evolution of Man:

S. NO	Human Ancestors	Time of Origin	General FeaturesGeneral Features
(i)	Dryopithecus	25 mya	Ape-like, hairy, arms and legs of same length, large brain, ate soft fruits and leaves, walked like gorillas and chimpanzees.
(ii)	Ramapithecus	15 mya	More man-like, walked more erect, teeth like modern man.
(iii)	Australopithecus	2 mya	Fossils found in Tanzania and Ethiopia, man-like primates, 4 feet tall, walked upright, ate fruit, hunted with stone weapons, brain capacity was 400–600 cc.
(iv)	Homo habilis	2 mya	Fossils found in East Africa, first human-like being, brain capacity 650–800 cc, did not eat meat.
(v)	Homo erectus(Java man)	1.5 mya	Fossils found in Java, brain capacity 900 cc, ate meat.
(vi)	Homo sapiensneanderthalensis(Neanderthal man)	100,000 - 40,000year ago	Fossils found in east and central Asia, brain size 1400 cc, used hides to protect body, buried their dead.
(vii)	Homo sapiens(Modern man)	75,000 - 10,000years ago	Developed cave art, agriculture, started human civilisation.

Animal	Ancient Fossil
Horse	Pliohippus
Camel	procamelus
Elephant	Stegolophodon
Octopus	Belemnite
Nautilus	Gyrouros
Gibbon	Propliopithecus
Orangutan	Dryopithecus
Man	Homo sapiens neanderthalensis
Chimpanzee	Dryopithecus
Gorilla	Dryopithecus

Divergent evolution is the evolution of a number of different forms of animals or plants froms of a common ancestral form. The driving force behind, it is adaptations to newly involved habitat and the prevailing environmental conditions there. As the original population increases in size, it spreads out from its centre of origin to exploit new habitas and food resources. In this results in a number of populations each adapted to its particular habitat eventually these populations will differ from each other sufficiently to become new species. A good example of this process is the evolution of the Australian marsupials into species adapted as carnivores, herbivores, burrowers, fliers, etc. Another example is that of peritadactyl limb in mammals.

When two organisms in a particular geographical area show similar adaptive strategies, this is called convergent evolution. Many desert plants show convergent evolution in spite of the fact that they are not closely related. Cereus peruvianus is a species of cactus which is primarily found in the South America. Euphorbia virosa is found in most parts of the world.
Both the plants are unrelated but show similar adaptations in order to conserve water. Following are some similarities in them:

• Stem is modified into fleshy succulent greenish parts which store water and carry out photosynthesis.
• Leaves are modified into spines in order to prevent water loss through transpiration.
• Roots penetrate much deeper in the ground to access water.

These examples show analogous organs which are manifestations of convergent evolution.

Before industrialisation population of white-winged moths was more than the black-winged moth. This is because white wings of moth helped them in camouflaging. Thus, they were not picked by the predators and survived. But dark-winged moths were picked up by the predators due to their contrasting colour.
When lichens did not survive and tree trunks become dark because of industrial smoke or soot. This resulted in better chances of survival of dark wings in moths. This showed that evolution is apparently reversible. The same theory would apply when industries will be removed. Removal of industries would help in bringing down population level. This will help in lichens to once again flourish on tree trunks and the tree trunks will gain a whitish layer of lichens. This will result in survival of more white wings in the moths.

Morphological and comparative anatomical evidences:

• The phylogenetic history can be revealed by comparative study of external and internal structures.
• The organs with same structural design and origin but different functions are called homologous organs. For example, the forelimbs of some animals like whales, bats and cheetah have similar anatomical structure, i.e., humerus, radius, ulna, carpals, metacarpals and phalanges.
• Due to different needs, some structures developed differently. This is called divergent evolution.
• Other examples include vertebrate hearts or brains in animals; thorn and tendrils of Bougainvillea and cucurbita in plants.
• The organs which are anatomically different but functionally similar are called analogous organs. For example, wings of butterfly and birds.
• Due to same function, different structures evolve similarly. This is called convergent evolution.
• Other examples include eye of octopus and mammals; flippers of penguins and dolphins; sweet potato (root modification) and potato (stem modification).

1. The forelimbs of cheetah, bats and human have a similar anatomical structure. These have bones, humerus, radius, ulna, carpals, metacarpals and phalanges. It indicates divergent evolution, where the same structure has developed along different directions as adaption to different needs. Such structures are called homologous organs and homology indicates common ancestry.
2. The members of a population vary in characteristics even though they look similar. The population will increase exponentially but the natural resources are limited leading to more competition. The individuals which are fit and adapt themselves are able to survive. They grow reproduce and survive. This is called natural selection by Darwin.

1. The resources of the nature are limited, so the size of population of a species is limited.
2. The size of the population is fixed, except for some seasonal fluctuations.
3. Each and every member of a population shows variation for every character.
4. It is found in microbial or bacterial population growing in a culture that if everybody in a population reproduces to its maximum capacity, the population will grow exponentially.
5. The population size in an ecosystem is limited–due to competition among individuals for limited resources and only those fit individuals utilise the resources at the cost of other to reproduce. Darwin suggested that nature creates some pressure on the population which eliminates some individuals and some better adapted ones survive. This natural pressure at each and every generation creates some small variation in a population, accumulation of which for many generations leads to origin of new species.

1. Fossils help in tracing the organic evolution in following ways:

1. Fossils represent modes of preservation of ancient species.
2. Fossils help in establishing evolutionary traits among organisms and their ancestors.
3. Fossils help in establishing the time period in which organisms lived.
4. Fossils provide good evidence of the structure and lifestyle of animals (and even plants) from the past.
5. They provide a record of the remains of long-extinct species.

2. Miller Urey Experiment:

Miller and Urey were two scientists who believed Oparin and Haldane and wanted to prove their theory. So, they performed the famous ‘Miller- Urey experiment’ in the lab.

• They replicated the environmental and atmospheric conditions that may have existed in the primitive earth in their lab by taking gases like methane, ammonia, hydrogen and water vapour in a closed vessel.
• When they came back to check the results of their experiment after a week, they detected the presence of amino acids, nitrogen bases, fats, and sugar.
• With these results, the theory of gradual chemical evolution was accepted.
• This experiment gave the other scientists to piece the remaining pieces together.

The forelimb of vertebrates are pentadactyl, i.e. consist of same bones humerus, radius, ulna, carpals, metacarpals and phalanges, but differ in their function in different organisms The forelimbs of the following animals got modified as shown below.

1. Whale are modified for swimming.
2. Bat and bird are modified for flying.
3. Horse are modified for running.
4. Frog are modified for leaping.
5. Man are modified for grasping. This indicates common ancestry and homology based on divergent evolution.

Mendel conducted a series of experiments on pea plants to come out with his theories on variations. For this, Mendel observed reproduction of pea plants for many generations and tabulated and analysed those findings. He could attribute the origin of variations to some ‘factors’ which may have been present in the organism. At that time, scientists did not know about genes.
Darwin was about 10 years older than Mendel and hence it can be said that he was born in the same era. He would have had access to same technology and information as Mendel had. Moreover, he was on an exploration in which conducting a Mendelian experiment could not have been possible. While Mendel’s study was focused on a single species; Darwin’s study was encompassing much wider scope, i.e. of almost the whole species present at that time. Their respective goals of study were also entirely different.
There is least likelihood that Darwin would have been able to explain the origin of variations.