Biology 2 Marks Questions

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.