Biology 3 Marks Question

Darwinian selection theory states that individuals with favourable variations are better adapted than individuals with less favourable variation. It means that nature selects the individuals with useful variation as these individuals are better evolved to survive in the existing environment. An example of such selection is antibiotic resistance in bacteria. When bacterial population was grown on an agar plate containing antibiotic penicillin, the colonies that were sensitive to penicillin died, where as one or few bacterial colonies that were resistant to penicillin survived. This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug. Hence, the resistant bacteria multiplied quickly as compared to non-resistant (sensitive) bacteria, thereby increasing their number. Hence, the advantage of an individual over other helps in the struggle for existence.

Drawin's finches

Thorns in Bougainvillea and tendrils in Cucurbita- examples of homology.

Organs with similar strucuture/same ancestry/anatomically same/same origin developed along different directions due to adapation/different needs, to perform different functions.For example the fore limbs of some animals (Vertebrates) like whales, bats, cheetah and human have similar anatomical strucuture (i.e. humerus, radius, ulna, carpals, metacarpals and phalanges) develop differently to meet different needs/to perform different functions.

1. Darwin finches/black birds (on Galapagos islands), evolved from original seed eating features, into insectivorous & vegetarian features in different habitat/islands.
2. Australian marsupials and placental mammals. Convergent evolution, more than one adaptive radiation occured in isolated geographical area.

• Disturbance in Hardy-Weinberg equilibrium is an indicator of change of frequency of alleles in a population, resulting in evolution.
• It is caused by genetic drift/gene flow or gene migration/mutation/genetic recombination/natural selection.

	Divergent	Convergent
1.	same structure developed along different direction.	Different structures evolving for the same function.
2.	due to adaptation to different needs.	due to adaptation to meet similar needs.
3.	Examples: Vertebrates heart & brain thorn of Bougainvillea and tendrils of cucurbita fore limbs of whales, bat, cheetah, humans.	Examples: Wing of bird & insects Potato & sweet potato Eye of Octopus & mammals Flippers of Penguins & dolphin

Ramapithecus	:	hairy/walked like gorillas and chimpanzees, more man like.
Dryopithecus	:	hairy/walked like gorillas and chimpanzees, more ape-like.
Neanderthal man	:	brain size is 1400cc, used hides to protect their body/buried their dead.

Homology	Analogy
Organisms having the same structure developed along different directions due to adaptations/different functions.	Different structures having the same function. (in different organisms)
Result of divergent evolution.	Result of convergent evolution.
Indicates common ancestry.	Does not indicate common ancestry.
Anatomically same structures.	Anatomically different structures.
Example: Forelimbs of whale - bats - cheetah – human// Thorns of Bougainvillea - tendrils of cucurbits.	Example: Wings of butterfly and birds// Sweet potato and potato.

1. The rates are faster/accelerated/current species extinction rate are estimated to be 100 - 1000 times faster than in the pre-human times.
2. Human activities.
3.  

1. Preventing habitat loss and fragmentation.
2. Checking overexploitation.
3. Preventing alien species invasion.
4. Preventing co-extinction.
5. Conservation/Preservation of species.

They will grow in areas that are polluted. Hence, moths that were able to comouflag themselves, i.e., hide in the background, Survived. This understanding is supported by the fact that in areas where industrialisation did not occur e.g., in rural areas, the count of melanic moths was low. This showed that in a mixed population, those that can better-adapt, survive and increase in population size. Remember that no variant is completely wiped out.

Before industrial revolution-the environment was unpolluted the lichens on the barks of trees-pale, white winged moths could easily camouflage, while the dark winged were spotted out by the birds for food-hence they could not survive, After industrial revolution the lichens became dark (due to soot deposit), This favoured the dark winged months while the white winged were picked by birds, The population of the former increased (naturally selected).

Branching descent: Different species descending from the common ancestor - get adapted in different habitats.
e.g. Darwins finches - varieties of finches arose from grain eaters/Australian marsupials- evolved from common marsupial.
Natural selection: A process in which heritable variations enable better survival of a species to reproduce in large number.
e.g. White moth surviving before the industrial revolution and black moth surviving after industrial revolution/Long necked giraffe survived/DDT resistant mosquito survive.

Migrate temporarily from the stressful habitat to a hospitable area/suspended activities/Form thick walled spores/Form dormant seeds/Hibernate during winter/Aestivate during summer/Planktons diapause.

Plants: Ephemeral mode (complete life cycle in short period)/Deep tap roots/Deciduous leaves/Waxy cuticle/sunken stomata/Succulence to storewater/C4 Pathway of Photosynthesis.
Animals: No sweating/uricotelic/deposition of fat insub epidermal layer/burrowing nature/thick skin/body covered with scales.

1. Gene frequencies in a population are stable, constant from generation to generation, until some change in frequency happens, due to some factor.
2. Gene migration/gene flow/gene drift/mutation/genetic recombination/natural selection.

1. From the original seed eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
2. The process of evolution of different species in a given geographical area starting from one point, and literally radiating to other areas of geography (habitats), is called adaptive radiation.

1. Fossils in different sedimentary layers indicate the geological period in which they existed.
2. They show that life forms varied over time.
3. New forms of life have arisen at different times in the history of earth.

Pasteur in his experiment took a flask containing sugar solution and added yeast to it , then boiled the contents of the flask so that yeast got killed.
In presterlized sealed flask, life did not come from killed yeast.
In open flask (open to air) life comes from pre existing life, new living organisms arose in presence of killed yeast.

Pre Industrialisation had more white winged moth against grey lichens on tree trunk, industrialisation led to deposition of soot & smoke on tree bark, making bark of trees dark, against the dark background white moth could easily be preyed upon, melanised moth could camouflage against dark bark, increased in number (through reproduction)/natural selection.

Darwin conjectured that all varieties are evolved on the Galapagos island itself, from original seed eating features, many other forms with altered beaks arose, became insectivorous, and vegetarian finches, adaptive radiation.

Adaptive Radiation - The process of evolution of different species in a given geographical area starting from a point and literally radiating to other geographical areas (habitats),
When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats) , then this can referred to as convergent evolution.
Example:

Placental mammals	Australian marsupials
Wolf	Tasmanian wolf
Mole	Marsupial mole
Anteater	Numbat (anteater)
Mouse	Marsupial mouse
Lemur	Spotted cuscus
Flying squirrel	Flying phalanger
Bobcat	Tasmanian tiger cat

Two pre-sterilised flasks with killed yeast, one sealed, other open to air, differential growth of life in two flasks/life was found only in open flask. // the following diagram can be considered in lieu of above explanation.
life comes from pre-existing life (it came from air entering the flask)/proved the theory of biogenesis.

Evolution of different species in a given geographical area starting from a point and literally radiating to other geographical areas habitat is called adaptive radiation.
A number of marsupials each different from other/Tasmanian Wolf/Tiger Cat/Banded Anteater/Marsupial Rat/Kangaroo/Wombat/Bandicoot/Koala/Marsupial mole/Sugar Glider, evolved from an ancestral stock, but all within Australian continent.
Darwin's finches, from original seed, eating features many other forms with altered beaks arose, enabling them to become insectivorous/vegetarian finches on the same (Galapagos) islands.

Anthropogenic activities have caused increased rate of evolution.

1. The excess use of herbicides and pesticides in the agricultural field by the humans to kill pests and insects has resulted in selections of resistant variety of pests and insects over a short time span the change favored resistance pests and insects which lead to their evolution.
2. The excess use of antibiotics has caused selection of drug-resistant microbes, the microbes sensitive to antibiotics died but few variants having resistance against it survived. This led to evolution of more fatal microbes.

Biogenesis -A living organism arises from another living organism.
Miller’s experiment -An electric discharge, was created in a closed flask containing CH4 - H2 -NH3, and water vapour at 800°C, which resulted in the formation of amino acids, supports chemical evolution.
//Miller’s experiment does not support Theory of Biogenesis it supports chemical evolution.

Convergent - Different structures evolving in the same direction in different organisms eg. wings of butterfly and of birds/eye of octopus and of mammals/the flippers of penguins and dolphins/sweet potato and potato.
Divergent - Same structure evolving in different directions in different organisms eg. forelimbs of whales, bats, cheetah and humans/vertebrate hearts or brains/thorns of Bougainvillea and tendrils of cucurbita.

1. Australia.
2. Adaptive Radiation The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitat) is called adaptive radiation.
3. (Convergent evolution/Adaptive Convergence) Organisms coming from different stock, evolved similar features and adapted to same habitat.

1.  

	Analogous Organs	Homologous Organs
i.	Those organs which are structurally dissimilar but functionally similar are called analogous organs.	Those organs, which are structurally similar but functional dissimilar are called homologous organs.
ii.	They lead to convergent evolution.	They lead to divergent evolution.
iii.	Eg. Wings of birds and insects.	Eg. Forelimbs of terrestrial vertebrates such as frog, lizard, bird, bat, horse, man.

2. Following are the analogous structure from the given list:

1. Wings of butterfly and birds.
2. Tubers of sweet potato and potato.

1.  

	Homo habilis	Homo erectus
1	This creature probably lived in East African grassland around two mya	This creature lived about 15 mya and its fossils were discovered in Java in 1891.
2	Brain capacity of this creature was 650–800cc.	Brain capacity was around 900cc.
3	They did not eat meat.	They probably ate meat.

2. Silurian, Carboniferous, Jurassic.

Study of fossils is called Paleontology:

1. The rocks of early era contain less number of fossils than the rocks of later era and fossils of only simple marine invertebrates are in these rocks, which indicate that life originated in sea as simple form.
2. The distribution of fossils indicates that fossils became more and more complex as we proceeded from earliest to recent rocks.
3. On the basis of fossil study, it has been shown that the early organisms were very different from their modern forms.

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.

The organs, which have the same fundamental structure but are different in functions are called homologous organs. The homologous structures are a result of divergent evolution. The forelimbs of pigeon is an organ homologous to hand of man.

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.

Whales, bats, Cheetah and human (all mammals) share similarities in the pattern of bones of forelimbs. Though these forelimbs perform different functions in these animals, they have similar anatomical structure. All of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.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.

He used particular type of flasks in his experiment.
His flasks were pre-sterilised and heat-killed yeast culture was kept in them.

1. One flask was kept closed and the other was left open.
2. He showed that in the closed pre-sterilised flask, life did not come from the killed yeast; in the other flask that was kept open, life appeared from killed yeast. This dismissed the theory of spontaneous generation.
3. He concluded that life can come from pre-existing life.

The three most important criteria for designating a Mendelian population are as follows:

• 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.

Pasteur invented the swan-necked flask to create an environment known not to grow microorganisms. After sterilizing a nutrient broth in these flasks, he removed the swan necks of the controls. Microorganisms grew only in the controls, refuting spontaneous generation.

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.

It is an example of analogous organ as the basic structure of the wings of butterfly is different from that of the wings of the bat. Their function is similar and is used for flying.

1. Fossils of dinosaurs provide palaeontological evidences for evolution. Different aged rock sediments contain fossils of different life forms who probably died during the formation of the particular sediment. Some of them appear similar to modern organisms. They represent extinict organisms (e.g. dinosaurs).
2. Forelimbs of cheetah, bat, whale and human provide evidences from comparative anatomy and morphology. These organisms share similarities in the pattern of bones of forelimbs. Though these forelimbs perform different functions in these animals, they have similar anatomical structure.
3. Thorns of Bougainvillea and tendril of Cucurbita provide evidences from comparative anatomy and morphology. The thorns of these plants represent homology. They are not anatomically similar structures, though they perform similar functions. Hence, analogous structures are a result of convergent evolution. These evidences indicate that the evolution of life forms has indeed taken place on earth.

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.