Andhra Pradesh BIEAP AP Inter 2nd Year Zoology Study Material 7th Lesson Organic Evolution Textbook Questions and Answers.
AP Inter 2nd Year Zoology Study Material 7th Lesson Organic Evolution
Very Short Answer Questions
Question 1.
What is panspermia?
Answer:
According to Cosomozoic theory, life might have existed all over the universe in the form of resistant spores called panspermia. They might have reached the earth accidentally.
Question 2.
Define prebiotic soap. Who coined the term?
Answer:
Prebiotic soup word is coined by J.B.S.Haldane. Haldane called the ocean prebiotic soup. All the reactions which lead to the formation of organic molecules like sugars, amino acids, fatty acids purines and pyramids etc., occurred in the ocean so it was described as the prebiotic soup.
Question 3.
How did-eukaryotes evolve?
Answer:
Eukaryotes evolved probably by two processes.
- Prokaryotes lived in the ancestral eukaryotes symbiotically and evolved into organelles such as mitrochondria and plastids.
- The endo membrane system of eukaryotes might have evolved by the infolding of plasma membrane of the ancestral prokaryotes.
Question 4.
What are the components of the mixture used by Urey and Miller in their experiments to simulate the primitive atmosphere?
Answer:
Urey and Miller -used a mixture of water vapour, methane, ammonia and hydrogen in their experiments to simulate the primitive atmosphere.
Question 5.
Mention the names of any four connecting links that you have studied.
Answer:
Connecting links clearly explain the path of evolution.
- Peripatas between annelida and arthropoda.
- Prototherians between reptilia and mammalia.
Question 6.
Define Biogenetic law, giving an example.
Answer:
It was proposed by Ernst Haeckel. It states that ontogeny repeats phylogeny which means the development history of an organism repeats the evolutionary history of its ancestor Eg : Tadpole larva of frog, it resembles fish both externally and internally. It possesses a, tail, gills and two chambered heart like that of fish. Later it metamorphoses into adult frog.
Question 7.
Define atavism with an example.
Answer:
Sudden appearance of some vestigial organs in a better developed condition is called atavism.
Eg : Tailed human baby
Question 8.
Cite two examples to disprove Lamarck’s inheritance of acquired characters.
Answer:
- Well developed muscles of athletes are not inherited to their children.
- Making perforations to pinna for wearing ornaments has been in practice in India for past several centuries. However no girl child is bom with readymade perforations . in their pinna.
Question 9.
Who influenced Darwin much in formulating the idea of Natural Selection.
Answer:
Three scientists influenced Darwin, they are :
- T.R.Malthus – On the principles of population
- Sir Charles lyell – Principle$ of Geology
- Alfred Russel Wallace – On the tendency of varieties do depart from original types.
Question 10.
What is common between Darwinism and Lamarckism?
Answer:
Presence of variations is common to Darwinism and Lamarckism.
Question 11.
What is meant by genetic load. Give an example.
Answer:
The existence of deletorious genes within the populations is called genetic load.
Eg: Genes for Sickle cell anaemia – The individuals homozygous for Sickle cell gene usually die early due to anaemia. .
Question 12.
Distinguish between allopatric and sympatric speciations.
Answer:
Allopatric speciation :
Speciation occurring in which first geographical isolation occurs, then secondly reproductive isolation occurs.
Sympatric speciation :
Reproduction isolation occurs without geographical isolation.
Question 13.
Mention the scientific names of ape like and man like earlier primates. Which man like primate first used hides to cover the bodies?
Answer:
- Scientific name of ape like primate – Dryopithecus
- Scientific name of man like primate – Ramapithecus
- Homo neanderthalensis – They used hides to protect their body.
Short Answer Questions
Question 1.
Distinguish between homologous and analogous organs.
Answer:
1. Homologous organs :
The organs which have similar structure and origin but not necessarily the same function are called homologous organs. Eg : The appendages of vertebrates such as the flippers of whale, wings of bat, forelimbs of horse, paw of cat and hands of man have a common pattern in the arrangement of bones even though their external form and functions may vary to suit their mode of life.
2. Analogous organs :
The organs which have dissimilar structure and origin but perform the same function are called the analogous organs. Eg : Wings of butterfly and wings of a bird.
Question 2.
Write a short note on the theory of mutations.
Answer:
Theory of mutation was proposed by Hugo de Varies, who coined the term mutation.
Mutations are sudden, random inheritable changes that occur in organisms. Hugo de Varies observed this phenomenon in the evening primrose plant Oenothera lamarckiana, which shows different forms like
- O. brevistylis – with small style.
- O. levifolia – with smooth leaves.
- O. gigas – with the giant form.
- O. nanella – with dwarf form.
These characters are inherited to the progeny.
- Darwin called mutations as sports of nature or saltations.
- Bateson called them as discontinuous variations
Salient features of mutation theory :
- Mutations occur from time to time in naturally breeding population.
- Mutants differ from their parents.
- Mutations are inheritable.
- Mutations occur in any direction i.e., they are random.
- They are discontinuous and not accumulated over generations.
- They are full-fledged and so there are no intermediate forms.
- They are subjected to natural selection.
Question 3.
Explain Darwin’s theory of natural selection with industrial melanism as an experimental proof.
Answer:
Darwin’s theory of natural selection does not explain what exactly evolution is, but explains how evolution might have occurred in nature. A classical example for natural selection is industrial melanism, exhibited by peppered moth-Biston betularia. These moths were available in two colours grey and black. Grey moths were abundant before industrial revolution in all over England. The reason for the existence of large number of grey moths during that period was camouflage on the trunks of trees.
But after the establishment of industries in England, black coloured moths were more and grey forms were less. This is due to pollution from industries in the form of soot turned barks of trees into black. So grey moths were easily identified and were more predated by birds. Thus grey moths decreased in number, black moths increased in the population.
Thus natural selection favoured the melanic moths (black) to reproduce more successfully. Natural selection of darker forms in response to industrial pollution is known as industrial melanism.
Question 4.
Discuss the role of different patterns of selections in evolution.
Answer:
Natural selection is a process by which the organisms are physically, physiologically and behaviorally better adopted to environment, survive and reproduce.
It is mainly of three types :
- Stabilizing selection,
- Directional selection,
- Disruptive Selection.
1. Stabilizing selection (Centrifetal selection) :
This selection operates in a stable environment. In this process, the organisms with average phenotype are preserved where as the extreme individuals from both the ends are eliminated. Hence it does not promote any evolutionary change that leads to specification, but maintains the phenotypic stability within the population over generations.
Eg : In England weight of newborn babies were studied in a large sample. Greater mortality was found in the babies whose weight was greater or lesser than the average weight of 81bs.
2. Directional selection :
This selection operates in an environment which gradually undergoes changes. It works by constantly removing the individuals from one end and constantly shifting the average value of fitness towards the other end of phenotypic distribution.
Eg : In case of giraffes the average value of the length of neck shifted towards the long-neck. Stabilizing selection takes over the directional selection. Once the average value of the phenotype coincides with the new optimum environmental conditions.
3. Disruptive selection (Centrifugal selection) :
This selection operates when homogenous environment changes into a heterogenous type. In this process, the organism of both the extreme phenotypes are selected while the individuals with average phenotype are eliminated. This can split the population into two or more sub-populations or species populations.
Eg : In California the sunflower population was divided into two sub-populations. One was adapted to dry area and the other was adapted to wet area.
Question 5.
Write a short note on Neo-Darwinism.
Answer:
It was proposed by Fischer, Sewall Wright, Mayr. According to this theory, five basic factors are involved in the process of Organic evolution. They are :
- Gene mutations
- Chromosomal mutations
- Genetic recombinations
- Reproductive isolation
1. Gene mutations :
Heritable changes in the structure of a gene are called gene mutations or point mutations. They alter the phenotypic character of the individuals. Thus, gene mutations tend to produce Variations in the offspring.
2. Chromosomal mutations:
Heritable changes in the structure of chromosomes called chromosomal mutations. They also bring about variations in the phenotype of organism which lead to the occurrence of variations in the offspring.
3. Genetic recombinations :
Recombinations of genes due to crossing over during meiosis are responsible for bringing genetic variability among the individuals of the same species.
4. Natural selection :
Natural selection does not produce any genetic changes, but it favours some genetic change while rejecting others.
5. Reproductive isolation:
The absence of gene exchange between population is called the reproductive isolation. It plays a great role in giving rise to new species and preserving the species integrity.
Question 6.
In a population of 100 rabbits which is in Hardy-Weinberg equilibrium, 24 are homozygous long eared. Short ears are recessive to long ears. There are only two alleles for this gene. Find out the frequency of recessive allele in the population.
Answer:
Number of rabbits in the population with Hardy-Weinberg equilibrium = 100
Number of dominant homozygous long eared rabbit = 24
Frequency of homozygous dominant long eared rabbits (P²) = \(\frac{1}{100}\) × 24 = 0.24
Frequency of dominent allele (P) = 0.49
Frequency of recessive allele = q = 1 – 0.49 = 0.51
Question 7.
What is meant by genetic drift ? Explain genetic drift citing the example of Founder Effect.
Answer:
The change in the frequency of a gene that occurs merely by chance and not by selection, in small proportion is called genetic drift.
Suppose, for a gene with two alleles, the frequency of a particular allele is 1% (e = 0.01) the probability of losing that allele by chance from small population is more. The end result is either fixation or loss of that allele.
Genetic drift tend to reduce the amount of genetic variation within the population mainly by removing the alleles with low frequencies. It can examplified by Founder and Bottleneck effect.
Founder effect:
If a small group of individuals fro,m a population starts a new colony in an isolated region, those individuals are called the founders of the new population. The allelic frequency of their descendants are similar those of the founders rather than to their ancestral parent population.
Eg : O+ve blood group is present in nearly 100% of the red Indians. It means the forefathers of the Red Indians tribe were predominantly O+ve and they isolated themselves reproductively from other population.