Balbharti Maharashtra State Board Class 10 Science Solutions Part 2 Chapter 1 Heredity and Evolution Notes, Textbook Exercise Important Questions and Answers.
Maharashtra State Board Class 10 Science Solutions Part 2 Chapter 1 Heredity and Evolution
Question 1:
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ANSWER:
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Question 1: Read the following statements and justify same in your own words with the help of suituble examples.
a. Human evolution began approximately 7 crore years ago.
ANSWER:
The dinosaurs became extinct around 7 crore years ago and from that point human evolution began. Humans are thought to have evolved from monkey like animals which looked more or less like modern lemurs. These monkey like animals further evolved into ape like animals. Some of these ape like animals evolved into gibbon and orangutan while rest of them evolved into gorilla and chimpanzees.From their evolved, the first human like animal called Ramapethicus. The following table lists the evolutionary history of modern man:
Year | Evolution |
15 million years ago | Dryopithecus (ape-like) and Ramapithecus (man-like) |
3 − 4 million years ago | Man-like primates |
2 million years ago | Australopithecines, also called Homo habilis,lived in East Africa |
1.5 million years ago | Homo erectus |
1,000 − 40, 000 years ago | Neanderthal man |
75, 000 − 10, 000 years ago | Homo sapiens |
b. Geographical and reproductive isolation of organisms gradually leads to speciation.
ANSWER:
- Every species survives in specific geographical conditions. The requirements of food and habitat, is specific for each species. Their reproductive ability and period is also different.
- Therefore, the individuals from one species cannot reproduce with individuals from other species.
- When they are separated by a distance or geographical barriers they are said to be isolated geographically.
- When they cannot reproduce with each other, they are said to be isolated reproductively.
- The ancestor species of both these subspecies may be the same but due to isolation over a very long-time duration, there is genetic variation between the two. Therefore, the isolation leads to speciation.
c. Study of fossils is an important aspect of study of evolution.
ANSWER:
- Fossils offer palaeontological evidence for the evolutionary process.
- Due to some natural calamities the organisms get buried during ancient times.
- The impressions and remnants of such organisms remain preserved underground. The hot lava also traps some organisms or their impressions. All such formations form fossils.
- Study of fossils help the researcher to understand the characteristics of the organisms that existed in the past.
- Carbon dating method also helps in finding out exact age of the fossil. According to the structure of earth’s crust the fossils are obtained at specific depths.
- The oldest ones are obtained at the depth while the relatively recent ones occupy the upper surface. Thus fossils of invertebrates were seen in very old Palaeozoic era. Later were seen fossils of Pisces, Amphibia and Reptilia. The Mesozoic era was dominated by reptiles while Coenozoic era showed presence of mammals.
- In this way, study of fossils unfold the evolutionary secrets.
d. There is evidences of fatal Science among chordates.
ANSWER:
- Very young embryos of fish, amphibians, reptiles, birds and mammals show quite similar structure in the early stages.
- As the further growth takes place, they acquire different patterns.
- The initial similarity between the vertebrate embryos is an evidence that during evolution, there was a common ancestor for all the vertebrate classes.
- This is called embryological evidence for vertebrate evolution.
Question 3: complete the statements by choosing correct options from bracket.
(Genes, Mutation, Translocation, Transcription, Gradual development, Appendix)
a. The causality behind the sudden changes was understood due to ………… principle of Hugo de Vries.
ANSWER: Mutation
b. The proof for the fact that protein synthesis occurs through ……….. was given by George Beadle and Edward Tatum.
ANSWER: Genes
c. Transfer of information from molecule of DNA to mRNA is called as …………… process.
ANSWER: Transcription
d. Evolution means ………….
ANSWER: Gradual development
e. Vestigial organ ……….. present in human body is proof of evolution.
ANSWER: Appendix
Question 4: Write short notes based upon the information known to you.
ANSWER: Lamarck gave the principle of 'use or disuse of organs’. He proposed that the reason behind evolution was the changes in the morphological activities of the organism. For example: giraffe has a long neck because it used to browse on leaves of tall plants by extending their neck for several generations, shoulders of iron smith are strong due to repetitive hammering movements, wings of ostrich and emu are weak because they are not used for flying, legs of birds and swan are used for swimming because they live in water. These characters are termed as acquired characters which are transferred from one generation to another.
b. Darwin’s theory of natural selection
ANSWER:
Darwin’s theory of natural selection: Darwin is famous for the theory which he published in the book titled ‘Origin of Species’. In this book he explained the theory of natural selection which talks about the survival of the fittest. He stated that there is a continuous competition between organisms for survival and the strongest of all survives. The chances of survival are higher for organisms which show modifications which will help them to survive. He also said that, nature also plays an important role in the selection of the fittest. Nature selects only those organisms which are capable of adapting to the changing situations while the rest which are incapable to do so perish away. The organisms which are selected by the nature then reproduce and give rise to new species which have their own characteristics
c. Embryology
ANSWER:
Embryology is the study of the formation and development of embryo and foetus. Embryology is used as one of the evidences of evolution. Comparative study of embryos in vertebrates shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually. This similarity in the development of embryos represents common origin of organisms.
d. Evolution
ANSWER:
Evolution refers to the gradual change which occurs in an organism over a long duration of time. It is a slow going process which results in the development of the organism. Life originated on earth about 3.5 billion years ago. It is believed that there might have been presence of simple elements on earth which may have given rise to simple organic and inorganic molecules. From these simple molecules, complex molecules like proteins, DNA etc. may have been formed. Other evolutionary changes may have resulted in the formation of simple cells and the result of the continuous evolution on earth is the several species of plants and animals which exist on earth. Today, the diversity on earth varies from unicellular Amoeba to a human being and from a unicellular algae like Chlorella to huge Banyan tree.
e. Connecting link
ANSWER:
Connecting link refers to plant and organisms which show characteristics related to two different groups. For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle and parapodia-like organs which are similar to annelids. It also shows tracheal respiration and open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals as it lays eggs like reptiles and has mammary glands like mammals.
Question 5: Define heredity. Explain the mechanism of hereditary changes.
ANSWER:
Heredity refers to the passing of traits from parents to offsprings either through asexual or sexual reproduction. Gregor Johann Mendel (1822 – 1884) was the first to carryout the study on the transmission of characteristics from the parents to the offsprings. He proposed that heredity is controlled by factors, which are now believed to be segments of chromosomes or genes.
These traits are passed on in the form of genetic information from parents to offsprings. This genetic information is stored in molecules called DNA. During the process of reproduction, the child receives genetic information from both the parents in the form of DNA. 50% genetic information is passed on from the paternal DNA whereas rest 50% information is passed on by the maternal DNA. This is why a child closely resembles its parents and has traits similar to both of them. Commonly observed heritable features are curly hair, a particular type of ear lobe, hair on ears etc.
Question 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
ANSWER:
Vestigial organs is a term used for organs which are degenerated, underdeveloped or useless for an organism. Usually, with the changes in the outer environment, the organs undergo a gradual change in order to cope up with those changes. Presence of vestigial organs is an indication that they were useful for our ancestors but as we evolved with the changing surroundings, these structures lost their functionality but our still found in our bodies. It is not compulsory that if an organ is vestigial for humans, so will it be for other organisms too.
Question 7: Answer the following questions.
a. How are the hereditary changes responsible for evolution?
ANSWER:
b. Explain the process of formation of complex proteins.
ANSWER: The synthesis of proteins occurs according to the central dogma. The central dogma explains how genetic information flows from DNA to RNA to make a functional protein.
It suggests that DNA contains all the information required to synthesise a protein and the RNA acts as a messenger which carries this information to ribosomes (a type of cell organelle). The central dogma is represented as:
Transcription: Transcription results in the formation of an mRNA using DNA as a template. This process takes place in the nucleus. You must be aware that DNA is made up of two strands. But in this process only one strand of DNA is required and this one strand is used as the template for the synthesis of the mRNA.
An enzyme, RNA polymerase, helps in this process. It helps in copying the information from DNA strand to mRNA. Once this process is complete, the RNA polymerase dissociates from the strand and the newly synthesised mRNA is released from the nucleus.
Like DNA, RNA is also made up of nucleotides but there is a difference. RNA contains the nucleotide Uracil (U) instead of thymine which is present in DNA. This uracil pairs with adenine just like thymine.
Once the process of transcription is complete, the newly synthesised mRNA is released from the nucleus into the cytoplasm.
Translation: The newly synthesised mRNA contains information in the form of codons. A codon is a sequence of 3 DNA or RNA nucleotides that correspond with a specific amino acid. Since, these codons contain 3 nucleotides, they are called triplet codon.
Process of translation:
- After the mRNA is released into the cytoplasm, it reaches the ribosomes where the process of translation occurs. Each mRNA can be made up of thousands of triplet codons.
- Two other types of RNAs, i.e. tRNA and rRNA, also participate in this process.
- Each tRNA has an anticodon which has the sequence complementory to the codon on mRNA. These tRNAs supply the amino acids as per the codons on the mRNA.
- The amino acids which are brought by the tRNA are joined together by peptide bonds. This process is carried out with the help of rRNA.
- During this process, the ribosome moves from one end of the mRNA to the other by a process known as translocation.
c. Explain the theory of evolution and mention the proof supporting it.
ANSWER:
structure of mouth, position of eyes, structure of nostrils and in plants, similarities in characters like leaf shape, leaf venation, leaf petiole represent common ancestry.
Connecting links- Connecting links refers to plant and organisms which show characteristics related to two different groups. For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle, and parapodia-like organs which are similar to annelids. It also show tracheal respiration and open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals because it lays eggs like reptiles and has mammary glands like mammals.
Embryological evidence- Embryology is used as one of the evidences of evolution. Comparative study of embryos shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually. This similarity in the development of embryos represents common origin of organisms.
d. Explain with suitable examples importance of anatomical evidences in evolution.
ANSWER:
Anatomical evidences help us to study how species have evolved over a period of time. Analogous structures support the theory of evolution and explain the fact that how species build up adaptations in order to fit in an environment whereas homologous structures help us to understand common ancestry. For example, if we compare the hands of humans with cat’s foreleg, flipper of whale and patagium of bat, we see that each of these organism use these structures are differently. But still there is a similarity between the structure of bones and joints which indicates that somewhere or the other these animals may have originated from common ancestors. This is an example of homology. Another example which explains analogous features is the arctic fox and the ptarmigan bird, Both of them change colours from dark brown to white during seasonal changes. They do not show common ancestry in way but since, they are found in the same habitat they are adapted to colour change.
e. Define fossil. Explain importance of fossils as proof of evolution.
ANSWER: The evolutionary history of modern man is as follows:
Year | Evolution |
15 million years ago | Dryopithecus (ape-like) and Ramapithecus (man-like) |
3 − 4 million years ago | Man-like primates |
2 million years ago | Australopithecines, also called Homo habilis,lived in East Africa |
1.5 million years ago | Homo erectus |
1,000 − 40, 000 years ago | Neanderthal man |
75, 000 − 10, 000 years ago | Homo sapiens |
f. Write evolutionary history of modern man.
ANSWER:
(2) Around seven crore years ago, monkey-like animals evolved from some of these lemur like animals.
(3) Then after about 4 crore years ago, in Africa the tails of these monkey like creatures very gradually disappeared.
(4) Simultaneously, there was enlargement in their body and brain volume too. The hands also improved and were provided with opposable thumb. In this way, ape-like animals were evolved.
(5) These ape-like animals independently gave rise to two lines of evolution, one giving rise to apes like gibbon and orangutan in the South and North-East Asia and gorilla and chimpanzee which stayed in Africa around 2.5 crores of years ago.
(6) The other line of evolution gave rise to human like animals around 2 crore years ago.
(7) The climate became dry and this resulted into reduction of forest cover. This made arboreal apes to descend on the land and start terrestrial mode.
(8) Due to this, there were changes in the pefvic
girdle and vertebral column. The hands were also freed from locomotion and thus they became more manipulative.
(9) Later, journey of hominoid species started from around 2 crores years ago. The first record of human like animal is ‘Ramapithecus’ ape from East Africa.
(10) Ramapithecus → Australopithecus → Neanderthal man → Cro-Magnon are the important steps in human evolution.
(11) Neanderthal man was said to be the first wise man. The increasing growth of brain made man more and more intelligent and thinking animal.
(12) Later, more than biological evolution, it was cultural evolution, when man started agriculture, animal , rearing. There was development of civilizations, arts and science etc. About 200 years ago there were industrial inventions and thus man now rules the earth.
Project:
Project 1.
Make a presentation on human evolution using various computer softwares and arrange a group disscussion over it in the class room.
Project 2.
Read the book – ‘Pruthvivur Manus Uparcich’ written by Late Dr. Sureshchandra Nadkarni and note your opinion on evolution.
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