Question 1.
Complete the following diagram
Answer :
Question 2
Question 2.1 Read the following statements and justify same in your own words with the help of suituble examples.
Human evolution began approximately 7 crore (70 million) years ago.
Answer :
Human evolution began approximately 7 crore (70 million) years ago.
- Around 7 crore years ago, major climatic changes took place on Earth. Large reptiles like dinosaurs became extinct. After this, mammals started evolving and became more diverse. Due to climate change, forest cover also decreased.
- During this period, small tree-dwelling animals similar to lemurs evolved. These lemur-like animals are considered ancestors of monkey-like animals.
- Around 4 crore years ago, the tails of some monkey-like animals gradually reduced and disappeared.
- Their body size and brain size increased over time. This led to the formation of the first ape-like animals. From these monkey-like ancestors, two evolutionary lines developed — one leading to apes and the other to human-like animals.
- Later, important changes occurred such as increase in brain volume, ability to walk upright (bipedalism), and greater use of hands for handling objects and making tools.
- Although modern intelligent humans appeared only about 50,000 years ago, the process of human evolution actually started around 7 crore years ago.
Question 2.2 Read the following statements and justify same in your own words with the help of suituble examples.
Geographical and reproductive isolation gradually lead to speciation.
Answer :
Geographical and reproductive isolation gradually lead to speciation.
- Every species survives in particular geographical conditions. Each species has specific requirements for food, habitat, and climate. Their breeding season and reproductive ability are also different.
- Because of these differences, individuals of one species normally cannot reproduce with individuals of another species.
- When members of the same species get separated due to distance or physical barriers like mountains, rivers, or oceans, they are said to be geographically isolated.
- When two groups are unable to reproduce with each other, even if they live in nearby areas, they are said to be reproductively isolated.
- Originally, these separated groups may have had a common ancestor. However, due to isolation for a long period of time, genetic variations develop between them.
- Over time, these differences become so significant that they form new species. Thus, isolation ultimately leads to speciation.
Question 2.3 Read the following statements and justify same in your own words with the help of suituble examples.
Study of fossils is an important aspect of study of evolution.
Answer :
The study of fossils is an important aspect of the study of evolution.
- Fossils provide palaeontological evidence for the process of evolution.
- In ancient times, due to natural calamities like floods, volcanic eruptions, or earthquakes, many organisms got buried under soil, sand, or lava.
- The impressions or remains of these organisms remained preserved underground. Sometimes hot lava also trapped organisms or their imprints. These preserved remains are called fossils.
- By studying fossils, researchers can understand the structure and characteristics of organisms that lived in the past.
- The carbon dating method helps in determining the approximate age of fossils.
- According to the structure of the Earth’s crust, fossils are found at different depths. The oldest fossils are found in deeper layers, while relatively recent fossils are found in upper layers.
- For example, fossils of invertebrates are found in the very old Palaeozoic era. Later, fossils of fishes (Pisces), amphibians, and reptiles appeared. The Mesozoic era was dominated by reptiles, while the Coenozoic era showed the presence of mammals.
- Thus, the study of fossils helps in understanding the gradual changes in organisms and reveals the evolutionary history of life on Earth.
Question 2.4 Read the following statements and justify same in your own words with the help of suituble examples.
There is evidences of fatal Science among chordates.
Answer :
Among different chordates, there are embryological evidences of evolution.
- The very young embryos of fishes, amphibians, reptiles, birds, and mammals show very similar structures in their early stages of development.
- As development continues, these embryos gradually develop different features and acquire distinct body patterns.
- The initial similarity in the early stages of vertebrate embryos suggests that all these groups had a common ancestor during evolution.
- This similarity in embryonic development is known as embryological evidence for vertebrate evolution.
Question 3
3.1 The causality behind the sudden changes was understood due to ………… principle of Hugo de Vries.
Answer : Mutation
3.2 The proof for the fact that protein synthesis occurs through ……….. was given by George Beadle and Edward Tatum.
Answer : Genes
3.3 Transfer of information from molecule of DNA to mRNA is called as …………… process.
Answer : Transcription
3.4 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.
A . Lamarckism
Answer:
Lamarckism was proposed by Jean Baptiste Lamarck. It is based on two main ideas:
(a) Use and disuse of organs
(b) Inheritance of acquired characters
According to the theory of use and disuse, organs that are used regularly become well developed, while organs that are not used become weak and degenerate.
Examples:
- Giraffe developed a long neck by stretching to reach leaves.
- Blacksmith has strong arms due to continuous work.
- Ostrich and emu lost flying ability as they did not use their wings.
- Ducks developed webbed feet for swimming.
- Snake lost its limbs due to burrowing habit.
Lamarck believed that these acquired characters are passed to the next generation.
However, this theory is not fully accepted because acquired characters are not inherited genetically.
B. Darwin’s Theory of Natural Selection
Answer :
Charles Darwin proposed the theory of natural selection and explained the idea of “Survival of the Fittest.”
- Organisms reproduce in large numbers.
- There is constant competition for food, shelter, and mates.
- Only those organisms that are better adapted survive.
- The unfit organisms perish.
- The surviving organisms reproduce and pass their favorable traits to the next generation.
- Over a long period of time, this leads to formation of new species.
Darwin explained his theory in the book Origin of Species.
C . Embryology
Answer :
- Embryology is the study of developing embryos.
- In early stages, embryos of different vertebrates look very similar.
- As development continues, they become different.
- The similarity in early stages suggests that vertebrates have a common ancestor.
- Therefore, comparative embryology provides evidence for evolution .
D. Evolution
Answer :
- Evolution is the gradual change in living organisms over a long period of time.
- It leads to formation of new species.
- Evolution occurs due to natural selection and genetic variations.
- The process takes millions of years.
- Due to evolution, biodiversity increases and organisms become better adapted to their environment.
- Darwin’s theory of natural selection is widely accepted to explain evolution.
E. Connecting Link
Answer :
- Connecting links are organisms that show characteristics of two different groups.
- They help in understanding evolutionary relationships.
Examples:
- Peripatus – Connecting link between Annelida and Arthropoda.
- Annelid features: segmented body, parapodia
- Arthropod features: open circulatory system, tracheal respiration
- Duck-billed platypus – Connecting link between reptiles and mammals.
- Reptile feature: lays eggs
- Mammal features: mammary glands, hairy skin
- Lungfish – Connecting link between fishes and amphibians.
- Fish characteristics
- Has lungs like amphibians
- Connecting links help in understanding the direction and stages of evolution.
Question 5
Define Heredity. Explain the mechanism of hereditary changes.
Answer :
Heredity:
Heredity is the process by which biological characters are transmitted from parents to offspring through genes.
Mechanism of hereditary changes:
- Mutation:
Sudden changes in DNA are called mutations. These changes may alter hereditary characters and introduce variations. - Crossing over during meiosis:
During meiosis, exchange of genetic material occurs between homologous chromosomes. This creates new combinations of genes.
As a result, gametes carry different hereditary characters, leading to variation in offspring.
Question 6
Define vestigial organs. Give examples in humans and mention animals where they are functional.
Answer :
Definition:
Vestigial organs are underdeveloped or degenerated organs that no longer perform their original function.
According to natural selection, such organs are gradually disappearing, but this process takes millions of years.
Examples in humans:
- Appendix – Vestigial in humans; functional in ruminants for digestion.
- Ear muscles – Non-functional in humans; functional in monkeys and cattle.
- Coccyx (tail bone) – Remnant of tail in humans; functional tail in many animals.
- Wisdom teeth – Useful in ancestors but mostly useless now.
- Body hair – Reduced compared to other mammals.
Question 7
a. How are hereditary changes responsible for evolution?
Answer :
Hereditary characters are passed from parents to offspring through genes.
- Some genes help organisms adapt better to the environment.
- Such beneficial genes are selected by nature.
- Individuals with favorable genes survive and reproduce more.
- Unfavorable genes are eliminated through natural selection.
Over a long period, accumulation of beneficial hereditary changes leads to evolution.
Thus, hereditary variation is the raw material or fuel for evolution.
b. Explain the process of formation of complex proteins.
Answer :
Protein synthesis follows the central dogma:
DNA → RNA → Protein
1. Transcription:
- mRNA is formed using DNA as a template.
- DNA strands separate.
- Complementary RNA nucleotides are added.
- Uracil replaces thymine.
- mRNA carries the genetic code from nucleus to cytoplasm.
- Genetic code is in triplet form called codon.
2. Translation:
- Each codon codes for one amino acid.
- tRNA brings specific amino acids.
- Anticodon on tRNA matches with codon on mRNA.
3. Translocation:
- Ribosome moves along mRNA codon by codon.
- rRNA helps join amino acids by peptide bonds.
- Polypeptide chains form and fold into complex proteins.
c. Explain the theory of evolution and mention proofs supporting it.
Answer :
Theory of Evolution:
- First life originated in oceans as protoplasm.
- It evolved into unicellular organisms.
- Gradually, more complex organisms developed.
- Evolution is slow and takes millions of years.
- New species arise through gradual changes.
Proofs (Evidences) of Evolution:
- Morphological evidence
- Anatomical evidence
- Vestigial organs
- Palaeontological evidence (Fossils)
- Connecting links
- Embryological evidence
d. Importance of anatomical evidence in evolution
Answer :
Internal structures of different animals show similarities.
Example:
- Human hand
- Forelimb of bull
- Wing of bat
- Flipper of whale
All have similar bone structure but different functions.
This similarity indicates a common ancestor.
Thus, anatomical evidence supports evolution.
E. Define fossil. Explain importance of fossils as proof of evolution.
Answer :
Definition:
Fossils are preserved remains or impressions of ancient organisms.
Importance:
- Formed when organisms are buried due to natural calamities.
- Lava and sediments preserve remains.
- Carbon dating helps determine age.
- Older fossils are found deeper in the Earth’s crust.
- Invertebrates found in older layers (Palaeozoic era).
- Reptiles dominated Mesozoic era.
- Mammals appeared in Coenozoic era.
Fossils help trace evolutionary history.
f. Evolutionary history of modern man
Answer :
- Humans evolved from lemur-like ancestors.
- Around 7 crore years ago, monkey-like animals evolved.
- Around 4 crore years ago, tails gradually disappeared.
- Brain and body size increased; opposable thumb developed.
- Ape-like animals evolved.
- One line led to apes (gibbon, orangutan, gorilla, chimpanzee).
- Another line led to human-like animals around 2 crore years ago.
- Climate became dry; forest cover reduced.
- Apes came down to land and became terrestrial.
- Changes occurred in pelvic girdle and vertebral column; hands became free for manipulation.
- Important stages:
Ramapithecus → Australopithecus → Neanderthal man → Cro-Magnon - Brain development increased intelligence.
- Later cultural evolution began: agriculture, animal rearing, civilization, science, industry.
Thus, modern man evolved gradually over millions of years.