Chapter 1 – Heredity and Evolution
1. Complete the following diagram.
Ans:
2. Read the following statements and justify the same in your own words with the help of suitable examples.
a. Human evolution began approximately 7 crore years ago.
Ans:
(i) Last dinosaurs disappeared approximately seven crore years ago.
(ii) At that time, monkey-like animals were said to have evolved from some ancestors who were more or less similar to the modern lemurs.
(iii) Thus, human evolution began approximately seven crore years ago.
b. Geographical and reproductive isolation of organisms gradually leads to speciation.
Ans:
(i) Species is the group of organisms that can produce fertile individuals through natural reproduction.
(ii) Each species grows in a specific geographical condition. Their food, habitat, reproductive ability and period is different.
(iii) Along with genetic variation, geographical and reproductive changes are responsible for formation of new species.
(iv) Hence, geographical and reproductive isolation leads to speciation.
c. Study of fossils is an important aspect of study of evolution.
Ans:
(i) Large number of organisms got buried due to disasters like floods, earthquakes, volcanoes, etc.
(ii) Remnants and impressions of such organisms remain preserved underground. These are called fossils.
(iii) With the help of carbon-dating techniques, it is easy to determine the age of fossils.
(iv) Once the age of fossils has been determined, it becomes easy to deduce information about other erstwhile organisms.
(v) Hence, the study of fossils is an important aspect of the study of evolution.
d. There is evidence of fatal science among chordates.
Ans:
(i) It is believed that chordates have originated from invertebrates.
(ii) It is difficult to find out from which invertebrate group the chordates were developed.
(iii) Chordate ancestors were soft bodied animals, hence they were not preserved as fossils.
(iv) Thus, there is evidence of fatal science among chordates.
3. Complete the statements by choosing correct options from brackets.
(Gene, Mutation, Translocation, Transcription, Gradual development, Appendix)
1. The causality behind the sudden changes was understood due to _____ principle of Hugo de Vries.
Ans: Mutation
2. The proof for the fact that protein synthesis occurs through _____ was given by George Beadle and Edward Tatum.
Ans: Gene
3. Transfer of information from molecule of DNA to mRNA is called as _____ process.
Ans: Transcription
4. Evolution means _____.
Ans: Gradual development
5. Vestigial organ _____ present in human body is proof of evolution.
Ans: Appendix
4. Write short notes based upon the information known to you.
a. Lamarckism
Ans:
(i) Jean-Baptiste Lamarck proposed that morphological changes occurring in living organisms are responsible for evolution and the reason behind those morphological changes is activities or laziness of that organism.
(ii) The neck of giraffes has become too long due to browsing on leaves of tall plants by extending their neck for several generations.
(iii) Shoulders of ironsmiths have become very strong due to frequent hammering movements.
(iv) Wings of birds like emu and ostrich have become weak due to no use.
(v) Legs of birds like swans and ducks have become useful for swimming due to living in water.
(vi) Snakes have lost their legs by modification in their body for burrowing habit.
(vii) All these examples are types of acquired characters and are transferred from one generation to another. This is called the theory of inheritance of acquired characters or Lamarckism.
(viii) Development of organs due to specific activities or their degeneration due to no use at all was widely accepted but transfer of those characters from generation to generation was rejected.
(ix) Because it had been verified many times that modifications brought in us are not transferred to the next generation and thereby Lamarck’s theory was disproved.
b. Darwin’s theory of natural selection.
Ans:
(i) Charles Darwin, an English biologist published the theory of natural selection, which preaches the survival of the fittest.
(ii) According to him, all organisms reproduce prolifically.
(iii) These organisms compete with each other and only those organisms who show modification, sustain long.
(iv) Natural selection also plays important role because nature selects only those organisms which are fit to live and the rest perish.
(v) These sustained and selected organisms reproduce and give rise to new species with their own specific characteristics.
(vi) This theory was widely accepted for a long time, however it had some objections to it.
(vii) Irrespective of all these objections, Darwin’s work on evolution has been a milestone.
c. Embryology.
Ans:
(i) Embryology is the science which deals with the study of development of an organism from an embryo.
(ii) Comparative study of embryonic developmental stages of various vertebrates shows that all embryos have extreme similarities during initial stages.
(iii) Those similarities decrease gradually.
(iv) Similarities in initial stages indicate the common origin for all these animals.
d. Evolution.
Ans:
(i) Evolution is a gradual change occurring in living organisms over a long duration.
(ii) This is a very slow-going process through which development of organisms is achieved.
(iii) All the stages of changes occurring in various components ranging from stars and planets in space to the biosphere present on the earth should be included in the study of evolution.
(iv) Formation of new species due to changes in specific characters of several generations of living organisms as a response to natural selection is called evolution.
(v) Different theories about origin and evolution of life have been proposed till today of which theory of gradual development of living organisms is accepted.
(vi) According to this theory, the first living material (Protoplasm) has been formed in the ocean. In due course of time, a unicellular organism was formed.
(vii) Gradual changes took place in unicellular organisms from which larger and more complex organisms were formed. Duration of all these changes is about 300 crore years.
(viii) Changes and development in living organisms has been all round and multi-dimensional and this led to evolution of different types of organisms. Hence, this overall process is called evolution which is organizational.
(ix) Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.
e. Connecting link.
Ans:
(i) Some plants and animals show some morphological characters by which they can be related to two different groups; hence, they are called connecting links.
(ii) For example: In Peripatus, characters like a segmented body, thin cuticles and parapodia are present like annelida and worms. Similarly, these animals show tracheal respiration and an open circulatory system similar to arthropods. This indicates that Peripatus is the connecting link between annelida and arthropoda.
(iii) Similarly, Duck Billed Platypus lays eggs like reptiles but shows relationship with mammals too due to the presence of mammary glands and hair.
(iv) Lungfish perform respiration with lungs irrespective of being a fish.
(v) These examples indicate that mammals have evolved from reptiles and amphibians from fishes.
5. Define heredity. Explain the mechanism of hereditary changes.
Ans:
(i) Heredity is the transfer of biological characters from one generation to another via genes.
(ii) Living organisms can produce new individuals like themselves due to genes only and some of those genes are transmitted to the next generation without any changes.
(iii) Due to this, some of the characteristics of parents are transmitted to their offsprings.
(iv) However, sometimes sudden changes occur in those genes.
(v) Sometimes any nucleotide of the gene changes its position and that causes a minor change which is called a mutation.
(vi) Some mutations may be minor but some may be considerable.
For example: Mutation may cause genetic disorders like sickle cell anaemia.
6. Define vestigial organs. Write names of some vestigial organs in human body and write the names of those animals in whom same organs are functional.
Ans:
(i) Degenerated or underdeveloped useless organs of organisms are called vestigial organs.
(ii) Appendix is a vestigial organ in humans, but is fully functional in ruminants.
(iii) Muscles of ear pinna are vestigial in humans but are useful in monkeys for movement of ear pinna.
7. Answer the following questions.
a. How are the hereditary changes responsible for evolution?
Ans:
(i) Formation of new species due to changes in specific characters of several generations of living organisms as a response to natural selection is called evolution.
(ii) At present, crores of species of plants, ranging from Chlorella to Banyan tree and animals ranging Amoeba to giant whale are existing on earth.
(iii) First primitive cell may have been formed from the mixture of different types of organic and inorganic compounds.
(iv) There may have been some differences among these cells and according to the principle of natural selection, some may have shown good growth and some may have perished which could not adjust with surroundings.
(v) Sustaining and selected organisms can perform reproduction and thereby, give rise to the new species with their own specific characters.
b. Explain the process of formation of complex proteins.
Ans:
(i) Information about protein synthesis is stored in the DNA. Synthesis of appropriate proteins as per requirement is necessary for the body.
(ii) These proteins are synthesized by DNA through RNA. This is called ‘the central dogma of life’.
(iii) mRNA is produced as per the sequence of nucleotides on DNA. Only one of the two strands of DNA are used in this process.
(iv) The sequence of nucleotides in mRNA being produced is always complementary to the DNA strand used for synthesis. This process of RNA synthesis is called transcription.
(v) The mRNA formed in the nucleus comes in cytoplasm. It brings in the coded message from DNA.
(vi) The message contains the codes for amino acids. The code for each amino acid consists of three nucleotides. It is called triplet codons.
(vii) mRNA is made up of thousands of triplet codons.
(viii) As per the message on mRNA, amino acids are supplied by the tRNA.
(ix) For this purpose, tRNA has an ‘anticodon’ having a complementary sequence to the codon on mRNA. This is called ‘translation’.
(x) The amino acids brought in by tRNA are bonded together by peptide bonds with the help of rRNA.
(xi) During this process, the ribosome keeps on moving from one end of the mRNA to the other end by the distance of one triplet codon. This is called ‘translocation’.
(xii) Many such chains come together to form complex proteins.
c. Explain the theory of evolution and mention the proof supporting it.
Ans:
(i) According to the theory of evolution, the first living material (protoplasm) has been formed in the ocean.
(ii) In due course of time, a unicellular organism was formed.
(iii) Gradually, changes occurred in the unicellular organism from which larger and more complex organisms were formed.
(iv) All those changes were slow and gradual. Duration of all these changes is about 300 crore years.
(v) Changes and development in living organisms has been all round and multi-dimensional and this led to evolution of different types of organisms.
(vi) Hence, this overall process is called evolution which is organizational.
(vii) Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.
(viii) To support the theory of evolution, various types of evidence are available.
(ix) Inspite of many adaptive differences in protoplasm and cell, the manifestation of life processes like growth, reproduction, metabolism are essentially same in all organisms.
(x) Morphological evidence supports the theory. It is seen that all plants have stem, root, leaf and are green in colour and those having green colour carry out photosynthesis. Similarly, it is seen that animals have appendages, eyes, nose, ears, etc.
(xi) Anatomical evidence like the bone structure of a human arm, a bulls leg, a bat’s wing and a whale fin have similar structures attributing that they have developed from common ancestors.
(xii) Vestigial organs like tailbone or coccyx present in humans indicate the link between humans who have lost a tail and monkeys who have a tail.
(xiii) At embryological level, similarities are observed during the initial stage which indicates common origin.
(xiv) Thus, there is a little evidence which supports the fact that evolution is sequential.
d. Explain with suitable examples importance of anatomical evidences in evolution.
Ans:
(i) There doesn’t seem any superficial similarity between a human hand, a cat’s foreleg, the flipper of a whale and the patagium of a bat.
(ii) Use of each of these structures is different in respective animals.
(iii) However, there is a similarity in structure of bones and bony joints in organs of each of these animals.
(iv) This similarity indicates that these animals show anatomical evolution.
e. Define fossil. Explain importance of fossils as proof of evolution.
Ans:
(i) Remnants and impressions of organisms which get buried remain preserved underground. These are called fossils. Study of fossils is an important aspect of the study of evolution.
(ii) Carbon consumption of animals and plants stops after death and since then, only the decaying process of C-14 occurs continuously.
(iii) In case of dead bodies of plants and animals, instead of remaining constant, the ratio between C-14 and C-12 changes continuously as C-12 is non-radioactive.
(iv) The time passed since the death of a plant or animal can be calculated by measuring the radioactivity of C-14 and the ratio of C-14 to C-12 present in their body.
(v) This is a carbon dating method. It is used in determining the age of human fossils and manuscripts.
(vi) Once the age of fossils has been determined, it becomes easy to deduce information about other erstwhile organisms. It seems that vertebrates have slowly originated from invertebrates.
f. Write evolutionary history of modern man.
Ans:
(i) Approximately seven crore years ago, monkey-like animals are said to have evolved from some ancestors who were more or less similar to the modern lemurs.
(ii) The tails of these monkey-like animals of Africa are said to have disappeared about 4 crore years ago.
(iii) Evolution of some of the 2 crore years old species of apes seems to have occurred in different ways. They had to use their hands more for eating food and other work.
(iv) First human-like animal recorded was ‘Ramapithecus’ ape from East Africa.
(v) This ape grew up in size and became more intelligent and evolved about 40 lakh years ago.
(vi) Skilled humans appeared to be members of the genus Homo.
(vii) About 15 lakh years ago, humans walking with erect posture evolved and existed in China and Indonesia of the Asian continent.
(viii) Evolution of an upright man continued in the direction of developing its brain for the period of about 1 lakh years.
(ix) Brain of a 50 thousand year old man had been sufficiently evolved to the extent that it could be considered as a member of the class-wise-man (Homo sapiens).
(x) Neanderthal man can be considered as the example of wise-man.
(xi) The Cro-Magnon man evolved about 50 thousand years ago and afterwards, this evolution had been faster than the earlier.