01. Heredity and Evolution | Science II | Class 10

Q1. Complete the following diagram.

Q2. Read the following statements and justify same in your own words with the help of a suitable examples.

(a.) Human evolution began approximately 7 crore years ago.

Ans. (a). The following justifications support the statement that human evolution began approximately 7 crore years ago:
i) The last dinosaurs disappeared approximately 7 crore years ago and since then the human evolution has began.
ii) The humans are thought to have evolved from monkey-like animals that looked more or less like modern lemurs.
iii) The tail of these monkey-like animals of Africa disappeared and also the development due to enlargement of brian the ape-like animals evolved.
iv) These ape-like animals lived in Africa evolved into gorilla, chimpanzee about 2.5 crore years ago.
v) From them the first human-like animal called Ramapethicus evolved.
The table below shows the evolutionary history of modern man:

(b.) Geographical and reproductive isolation of organisms gradually
leads to speciation.

Ans. (b). The following justifications prove that the geographical and reproductive isolation gradually leads to speciation :
i) Species is the group of organisms that can produce fertile individuals through natural reproduction.
ii) Normally the new species arises due to the variation, which passed from one generation to the next and get accumulated over the long period of time.
iii) This also happens when the population of same species splits up into two separate groups, which then get isolated from each other geographically by the barriers such as mountain ranges, river or the sea.
iv) The main factors which could cause speciation are the geographical isolation, genetic drift caused by drastic changes in the frequencies of particular genes and the variations caused in individuals due to natural selection.
Example: Formation of a new species:
Suppose there are two separate populations of beetles spread on a wide mountain range with widely distributed food. The population of beetles in that area will be very large. As beetles are small insects, which cannot travel to far off places. They gather food from nearby places. As a result, sub-populations of beetles are spread over that area. These sub-populations can lead to the formation of an entirely new species.

(c.) Study of fossils is an important aspect of study of evolution.

Ans. (c). The following justifications support the statement that the study of
fossils is an important aspect of study of evolution:
i) Large number of organisms get buried due to disasters like flood, earthquake, volcano, etc.
ii) Remnants and impressions of such organisms remain preserved underground, called as fossils. Study of fossils is an important aspect of study of evolution.
iii) It is used in palaeontology and anthropology for determining the age of human fossils and manuscripts.
iv) Once the age of fossil been determined by carbon dating technique, it becomes easy to deduce the information about other erstwhile organisms.
v) From such a study of fossils it is proven that vertebrates have been slowly originated from invertebrates.

(d.) Fetal science or embryology is used as an evidence of evolution.

Ans. (d). The following reasons support the statement that fetal science or embryology is used as an evidence of evolution:
i) Comparative study of embryonic developmental show extreme similarities during initial stages and those similarities decrease gradually.
ii) Similarities in initial stages indicate the common origin of all these animals.

Q3. Complete the statements by choosing correct options from bracket.

(Gene, Mutation, Translocation, Transcription, Gradual development, Appendix )

a. The causality behind the sudden changes was understood due to mutation principle of Hugo de Vries.

b. The proof for the fact that protein synthesis occurs through gene was given by George Beadle and Edward Tatum.

c. Transfer of information from molecule of DNA to mRNA is called as transcription process.

d. Evolution means gradual development.

e. Vestigial organ appendix present in human body is proof of evolution.

Q4: Write short notes based upon the information known to you.

(a.) Lamarckism:

i) Jean-Baptiste Lamarck gave the principle of use or disuse of organs.
ii) He 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.
iii) He explained his theory with examples, like the neck of giraffe has become too long due to browsing on leaves of tall plants by extending their neck for several generations; similarly, shoulders of the iron-smith have become very strong due to frequent hammering movements.
iv) Also the wings of birds like ostrich and emu have become weak due to no use. Legs of the birds like swan and duck have become useful for swimming due to living in water and snakes have lost their legs by modifications in their body for burrowing habit.
v) All these examples are types of acquired characters and are transferred from one to another generation. This is called as theory of inheritance of acquired characters or Lamarckism.

(b.) Darwin’s theory of natural selection

Ans. (i) Charles Darwin had collected innumerable specimens of plants and animals and depending upon the observations of those specimens.
ii) Darvin published in his book titled Origin of Species, the theory of natural selection which preaches the survival of fittest.
iii) Darwin explains that all the organisms reproduce prolifically i.e. all the organisms compete with each other in a life- threatening manner.
iv) In this competition, only those organisms sustain which show the modifications essential for winning the competition. However, besides this, natural selection also plays important role because nature selects only those organisms which are fit to live and the rest perish.
v) Sustaining and selected organisms can perform reproduction and thereby give rise to the new species with their own specific characters.
vi) Darwin’s theory of natural selection was widely accepted for long duration. However, some objections were raised against the theory.
Some of the main objections are :
1. Natural selection is not the only factor responsible for evolution.
2. Darwin did not mention any explanation about useful and useless modifications.
3. There is no explanation about slow changes and abrupt changes.
Irrespective of all these objections, Darwin’s work on evolution has been a milestone.

(c.) Embryology:

Ans. (i) Embryology is the study of formation and development of embryo and foetus.
ii) Comparative study of embryonic developmental stages of various vertebrates have proved that all embryos show extreme similarities during initial stages and those similarities decrease gradually.
iii) Similarities in initial stages indicate the common origin of all these animals.

(d.) Evolution

Ans. (i) Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.
ii) According to the theory of evolution the first living material (protoplasm) has been formed in ocean.
iii) In due course of time, unicellular organism was formed.
iv) Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed.
v) All those changes were slow and gradual and the duration of all these changes is at most 300 crore years.
vi) Changes and development in living organisms had been all round and multi-dimensional and this led to evolution of different types of organisms. Hence, this overall process is called as evolution which is organizational.

(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 as connecting links.
ii) Examples are : In Peripatus, characters like segmented body, thin cuticle, and parapodia-like organs are present.
iii) These animals show tracheal respiration and open circulatory system similar to arthropods. This indicates that Peripatus is connecting link between annelida and arthropoda.
iv) Similarly, duck billed platypus lays eggs like reptiles but shows relationship with mammals too due to presence of mammary glands and hairs.
v) Lung fish performs respiration with lungs irrespective of being fish.
vi) These examples indicate that mammals are evolved from reptiles and amphibians from fishes.

Q5: Define heredity. Explain the mechanism of hereditary changes.

Ans. (i) Heredity is defined as, the transfer of biological characters from one generation to another via genes.
ii) Johann Gregor Mendel a pioneer in modern genetics around 1886, proposed that heredity is controlled by factors, which are now believed to be segments of chromosomes or genes.
iii) The characters or traits are passed on from parents to off-springs in the form of genetic information and this genetic information is stored in molecules called DNA (Deoxyribonucleic acid).
iv) During reproduction, a child receives genetic information from both the parents in the form of DNA i.e. 50% genetic information is passed on from the father’s DNA whereas rest 50% information is passed on by the mother’s DNA. Hence a child closely resembles its parents and has traits similar to both of them.
v) The commonly observed heritable features or triats are eye color, curly hair, a particular type of ear lobe, hair on ears etc.

Q6: 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 as vestigial organs.
ii) Sudden development of new tissues or organs for living in changing environment is not possible, instead, existing organs undergo gradual changes.
iii) Mostly, a specific structure in the body is useful under certain situation. However, same structure under different situation may become useless or even harmful.
iv) Such structure begins to degenerate under such situation as per the principle of natural selection. It takes thousands of years for a structure to disappear.
v) Such organ, though non-functional in certain organism, it may be functional in other organisms i.e. it is not vestigial in other organisms.
vi) Appendix, which is useless to human, is useful and fully functional organ in ruminants.
vii) Similarly, muscles of ear pinna, which are useless to human, are useful in monkeys for movement of ear pinna.
viii) Various vestigial organs like tail-bone (coccyx), wisdom teeth, and body hairs are present in body of human being.

Q7: Answer the following questions.

(a.) How are the hereditary changes responsible for evolution?

Ans: The hereditary changes are responsible for evolution in the following ways:
i) Heredity is the transfer of biological characters or triats from one generation to another via genes.
ii) The triats that are passed from one generation to the next generation are called as inherited triats, as they are inherited by the offspring from the parents.
iii) Evolution refers to the gradual change occurring in living organisms over a long duration.
iv) These favorable changes help organism in survival with the changing environment and have an advantage over other organisms, that fail to survive.
v) Thus changes in the inherited characters provide better chances of survival and reproduction resulting in evolution of species.

(b.) Explain the process of formation of complex proteins.

Ans. The formation of proteins takes place through the following steps :
i) The proteins are synthesized by DNA through the RNA and this process is called as Central Dogma.
ii) Central Dogma explains that all the information for protein synthesis is stored in DNA, and RNA acts as messenger which carries this information to ribosomes, the cell organelle.
This process is represented by : 

iii) Transcription :
mRNA is produced as per the sequence of nucleotides on DNA. Only one of the two strands of DNA is used in this process. The sequence of nucleotides in mRNA being produced is always complementary to the DNA strand used for synthesis. Besides, there is uracil in RNA instead of thymine of DNA. This process of RNA synthesis is called as transcription.
iv) The mRNA formed in nucleus comes in cytoplasm. It brings in the coded message from DNA. The message contains the codes for amino acids. The code for each amino acid consists of three nucleotides, called as triplet codon.
v) Translation : Each mRNA is made up of thousands of triplet codons. As per the message on mRNA, amino acids are supplied by the tRNA. For this purpose, tRNA has anticodon having complementary sequence to the codon on mRNA. This is called as translation.
vi) Translocation : The amino acids brought in by tRNA are bonded together by peptide bonds with the help of rRNA. During this process, the ribosome keeps on moving from one end of mRNA to other end by the distance of one triplet codon. This is called as translocation.
vii) At the end of this process a protein is formed that undergoes further modifications to form a fully functional protein.

(c.) Explain the theory of evolution and mention the proof supporting it.

Ans. i) Evolution is the gradual change occurring in living organisms over a long duration. This is a very slow-going process through which development of organisms is achieved.
ii) Formation of new species due to changes in specific characters of several generations of living organisms as a response to natural selection, is called as evolution.
iii) Different theories about origin and evolution of life have been proposed till today of which theory of Gradual development of living organisms is accepted.
iv) According to this theory, first living material (protoplasm) has been formed in ocean. In due course of time, unicellular organism was formed.
v) Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed.
vi) All those changes were slow and gradual and duration of all these changes is at most 300 crore years.
vii) Changes and development in living organisms had been all round and multi-dimensional and this led to evolution of different types of organisms. Hence, this overall process is called as evolution which is organizational.
viii) Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.
Evidences of Evolution:
1. Morphological Evidences: Various similarities like structure of mouth, position of eyes, structure of nostrils and ear pinna and thickly distributed hairs on body are seen in animals whereas similarities in characters like leaf shape, leaf venation, leaf petiole, etc. occur in case of plants.
2. Anatomical Evidences: There is similarity in structure of bones and bony joints in organs of human hand, foreleg of ox, flipper of whale and patagium of bat and each of those animals.
3. Vestigial Organs: Appendix, which is useless to human, is useful and fully functional organ in ruminants. Similarly, muscles of ear pinna, which are useless to human, are  useful in monkeys for movement of ear pinna. Various vestigial organs like tail-bone (coccyx), wisdom teeth, and body hairs are present in body of human being.
4. Palaeontological Evidences: The age of fossil determined by carbon dating technique, helps to deduce the information about other erstwhile organisms. It seems that vertebrates have been slowly originated from invertebrates.
5. Connecting Links: Duck billed platypus lays eggs like reptiles but shows relationship with mammals too due to presence of mammary glands and hairs. Lung fish performs respiration with lungs irrespective of being fish. These examples indicate that mammals are evolved from reptiles and amphibians from fishes.
6. Embryological Evidences: Embryos of various vertebrates show extreme similarities during initial stages and those similarities decrease gradually. Similarities in initial stages indicate the common origin of all these animals.

(d.) Explain with suitable examples importance of anatomical evidences in evolution.

Ans. The anatomical evidences help us to study how species have evolved over a period of time.
i) If we carefully observe, there doesn’t seem any superficial similarity between human hand, foreleg of ox, flipper of whale and patagium of bat.
ii) Similarly, use of each of those structures is different in respective animals.
iii) However, there is similarity in structure of bones and bony joints in organs of each of those animals.
iv) This similarity indicates that those animals may have common ancestor.

(e.) Define fossil. Explain importance of fossils as proof of evolution.

Ans. Study of fossils is an important aspect of study of evolution.
i) Large number of organisms get buried due to disasters like flood, earthquake, volcano, etc. The remnants and impressions of such organisms remain preserved underground and are called as fossils.
ii) The 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 ratio of C-14 to C-12 present in their body, called as carbon dating method.
v) It is used in palaeontology and anthropology for determining the age of human fossils and manuscripts.
vi) Once the age of fossil been determined by such technique, it becomes easy to deduce the information about other erstwhile organisms.
vii) One important conclusion supported by the palaeontological evidence is that vertebrates have been slowly originated from invertebrates.

(f.) Write evolutionary history of modern man.

Ans. Answer same as Q2. (a).

*********************

2 Comments

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.