Std 10: Heredity and Evolution notes

1. Complete the following diagram.

  Ans) a) Palaeontological b) Embryological

Q.2. Read the following statements and justify the same in your own words with the help of suitable examples.

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a. Human evolution began approximately 7 crore years ago.
Answer:

1. The Earth's ice age began approximately 7 crore years ago. During this period, dinosaurs became extinct. Mammals started evolving and diversifying rapidly. Due to climatic changes, forest cover reduced significantly.
2. The ancestors of monkey-like animals were Lemur-like animals that developed during this time.
3. Around 4 crore years ago, these monkey-like animals gradually lost their tails.
4. Their body size and brain capacity increased, leading to the evolution of ape-like mammals. These monkey-like ancestors shared evolutionary links with apes and human-like creatures.
5. Human evolution was marked by an increase in brain size, the ability to walk upright, and improved hand movements.
6. Human evolution actually began approximately 70 lakh (7 million) years ago, while the modern intelligent human evolved around 50,000 years ago.

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b. Geographical and reproductive isolation of organisms gradually leads to speciation.
Answer:

1. Every species survives under specific geographical conditions. Their food, habitat, reproductive ability, and breeding periods are different.
2. Therefore, individuals of one species cannot reproduce with individuals of another species.
3. When populations are separated by geographical barriers or long distances, they are said to be geographically isolated.
4. When organisms cannot reproduce with one another, they are reproductively isolated.
5. Though the ancestor species may be the same, long-term isolation causes genetic variations between populations. Over time, this leads to the formation of new species, known as speciation.

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c. Study of fossils is an important aspect of the study of evolution.
Answer:

1. Fossils provide palaeontological evidence for the process of evolution.
2. In ancient times, organisms were buried due to natural calamities.
3. Their impressions and remains got preserved underground. Sometimes hot lava trapped organisms or their impressions, forming fossils.
4. The study of fossils helps scientists understand the characteristics of organisms that lived in the past.
5. Carbon dating helps determine the exact age of fossils. Fossils are found at different depths in the Earth's crust.
6. Recent fossils are found near the surface, while older fossils are found deeper underground. Invertebrate fossils belong to the ancient Palaeozoic era, reptiles dominated the Mesozoic era, and mammals became common during the Coenozoic era.
7. Thus, the study of fossils helps reveal the secrets of evolution.

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d. There is evidence of embryological similarity among chordates.

Answer:

1. Early embryos of fish, amphibians, reptiles, birds, and mammals show many similar features.
2. As development continues, these embryos gradually develop different characteristics.
3. The similarity in early vertebrate embryos suggests that all vertebrates evolved from a common ancestor.
4. This is known as embryological evidence for evolution among vertebrates.

Q.3. Complete the statements by choosing correct options from brackets.

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

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

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

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

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

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c. Transfer of information from molecules of DNA to mRNA is called a -- -- -- process.
Answer:

Transfer of information from molecules of DNA to mRNA is called a transcription process.

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d. Evolution means -- -- -- --.
Answer:

Evolution means gradual development.

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e. The vestigial organ -- -- -- present in the human body is proof of evolution.
Answer:

The vestigial organ appendix present in the human body is proof of evolution.

Q.4. Write short notes based on the information known to you.

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a. Lamarckism
Answer:

1. Lamarck proposed the principle of “use and disuse of organs.” According to him, evolution occurs because of changes in the activities and usage of organs in organisms.
2. For example, giraffes developed long necks because they continuously stretched their necks to reach leaves on tall trees over many generations. Similarly, the strong shoulders of a blacksmith develop due to repeated hammering movements.
3. The wings of ostrich and emu became weak because they were not used for flying, while the webbed feet of ducks and swans developed because they live in water and use them for swimming.
4. Such characters developed during the lifetime of an organism are called acquired characters.
5. Lamarck believed that these acquired characters are transferred from one generation to another.

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b. Darwin’s theory of natural selection
Answer:

1. Charles Darwin became famous for his theory published in the book “Origin of Species.”
2. Darwin’s theory of natural selection is based on the idea of “survival of the fittest.”
3. Organisms reproduce in large numbers, producing more offspring than can survive.
4. Due to limited food and resources, organisms compete with one another for survival.
5. According to Darwin, organisms having favorable variations survive and reproduce successfully.
6. These selected organisms gradually form new species with specific characteristics.

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c. Embryology
Answer:

Embryology is the study of the formation and development of embryos and fetuses. It provides important evidence for evolution.

Comparative studies of vertebrate embryos show that embryos of different animals are very similar during the early stages of development. As development progresses, these similarities gradually decrease.

The similarity in the early stages of embryonic development indicates that different organisms have evolved from a common ancestor.

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d. Evolution
Answer:

Evolution refers to the gradual changes that occur in organisms over a very long period of time. It is a slow and continuous process that leads to the development of new forms of life.

Life is believed to have originated on Earth around 3.5 billion years ago. Initially, simple organic and inorganic molecules were formed from basic elements present on Earth.

These simple molecules gradually formed complex substances like proteins and DNA. Further evolutionary changes led to the formation of simple cells.

Continuous evolution resulted in the diversity of plants and animals found on Earth today, ranging from unicellular organisms like Amoeba and Chlorella to complex organisms like humans and banyan trees.

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e. Connecting link
Answer:

A connecting link is an organism that shows characteristics of two different groups of organisms.

For example, Peripatus is considered a connecting link between annelids and arthropods. It has segmented body structure and parapodia-like organs similar to annelids, while it also shows tracheal respiration and an open circulatory system like arthropods.

Another example is the duck-billed platypus, which acts as a connecting link between reptiles and mammals. It lays eggs like reptiles but also possesses mammary glands like mammals.

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Q.5. Define heredity. Explain the mechanism of hereditary changes.
Answer:

Heredity is the transmission of characteristics from parents to their offspring.

Mechanism of hereditary changes:

1. Hereditary changes or diversity occur because of genetic variation.
2. In sexually reproducing organisms, male and female gametes fuse during reproduction. As a result, the offspring receives a combination of genes from both parents and shows mixed characteristics.
3. Sometimes sudden changes called mutations occur in genes. Even a small change in a nucleotide sequence can produce noticeable changes in the characteristics of an organism.
4. If mutations occur in the DNA of germ cells, these changes are passed on to the next generation through heredity.

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Q.6. Define vestigial organs. Write names of some vestigial organs in the human body and write the names of those animals in whom same organs are functional.
Answer:

Vestigial organs are underdeveloped and non-functional organs that were functional in ancestors or are functional in some other animals.

The human body has several vestigial organs such as the coccyx (tailbone), wisdom teeth, body hair, and appendix.

• The coccyx is functional as a tail in monkeys and many other animals.
• Ear muscles are functional in animals like rabbits, cows, and horses for movement of the ear pinna.
• The appendix is functional in ruminant animals where it helps in the digestion of cellulose.

Q.7. Answer the following questions.

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a. How are hereditary changes responsible for evolution?
Answer:

1. Offspring inherit genetic information from their parents through the process of heredity.
2. Inherited traits may undergo modifications due to genetic variations or chromosomal changes.
3. These hereditary variations accumulate over generations.
4. Beneficial variations help organisms survive better in nature.
5. Through natural selection, these changes gradually lead to the evolution of new species.

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b. Explain the process of formation of complex proteins.
Answer:

1. Genes present on DNA contain the information required for protein synthesis.
2. The information from DNA is copied into messenger RNA (mRNA) through the process called transcription.
3. The mRNA moves from the nucleus to the cytoplasm and attaches to ribosomes.
4. Transfer RNA (tRNA) brings specific amino acids to the ribosome according to the sequence of codons on mRNA.
5. Amino acids join together by peptide bonds to form a polypeptide chain.
6. The polypeptide chain folds into a specific three-dimensional structure to form a complex protein.

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c. Explain the theory of evolution and mention the proof supporting it.
Answer:

The theory of evolution states that living organisms have gradually changed over a long period of time and evolved from simpler forms to more complex forms.

According to Darwin’s theory of natural selection, organisms produce more offspring than can survive. Due to limited resources, there is competition among organisms. Those organisms with favorable variations survive and reproduce successfully, while others perish. Over many generations, these favorable changes accumulate and give rise to new species.

Proofs supporting evolution:

1. Fossil evidence: Fossils provide information about extinct organisms and show gradual evolutionary changes.
2. Anatomical evidence: Similar internal body structures in different organisms suggest common ancestry.
3. Embryological evidence: Early embryos of vertebrates show similarities, indicating common origin.
4. Vestigial organs: Presence of non-functional organs like appendix and coccyx in humans supports evolution.

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d. Explain with suitable examples the importance of anatomical evidence in evolution.
Answer:

1. Different groups of animals show similarities in their internal body structure and anatomy.
2. For example, the forelimbs of humans, bulls, bats, and whales have similar arrangements of bones and joints.
3. Though these organs perform different functions and appear different externally, their internal structure is similar.
4. Such similarities indicate that these organisms may have evolved from a common ancestor.
5. Thus, anatomical evidence helps in understanding the process of evolution.

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e. Define fossils. Explain the importance of fossils as proof of evolution.
Answer:

Fossils are the preserved remains, impressions, or traces of ancient organisms buried in the Earth’s crust.

Importance of fossils:

1. Fossils are formed when organisms get buried due to natural disasters such as floods, earthquakes, or volcanic eruptions.
2. After death, the intake of carbon stops and only the decay of radioactive carbon-14 continues.
3. By measuring the ratio of carbon-14 to carbon-12, scientists can determine the age of fossils using the carbon dating method.
4. Older fossils are found in deeper layers of the Earth’s crust, while newer fossils are found near the surface.
5. Fossils of invertebrates belong to the ancient Palaeozoic era, reptiles dominated the Mesozoic era, while mammals and birds became common during the Cenozoic era.
6. Thus, fossils provide important evidence about the origin, history, and evolution of organisms.

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f. Write the evolutionary history of modern man.
Answer:

1. Human ancestors evolved from lemur-like animals.
2. Around 7 crore years ago, monkey-like animals evolved from these ancestors.
3. About 4 crore years ago, the tails of these monkey-like creatures gradually disappeared.
4. Their body size and brain volume increased, and opposable thumbs developed, leading to the evolution of ape-like animals.
5. One evolutionary line gave rise to apes such as gibbons, orangutans, gorillas, and chimpanzees.
6. Another evolutionary line gave rise to human-like ancestors around 2 crore years ago.
7. Due to climatic changes, forests decreased and some apes started living on land instead of trees.
8. Gradually, changes occurred in the vertebral column and pelvic girdle, enabling upright walking.
9. Hands became free from locomotion and developed better grasping and manipulative abilities.
10. Over a long period of evolution, modern human beings developed with advanced intelligence and skills.