10th Science Unit 19 Origin and Evolution of Life Book Back Answers
10th Science Unit 19 Origin and Evolution of Life book back answers for all 26 questions in the 2026-27 Samacheer Kalvi (Tamil Nadu) textbook.
Unit 19 traces how the universe, the Earth and life itself began. You will study the Big Bang idea, older beliefs like special creation and spontaneous generation, Pasteur's work on biogenesis, and the chemical evolution view of Oparin and Haldane. The unit then looks at proof of evolution from body structure, embryos and fossils, plus the ideas of Lamarck and Darwin, variation, fossilisation and ethnobotany. Book-back questions include multiple choice, fill in the blanks, matching, short answers on homologous, analogous and vestigial organs, Archaeopteryx and long answers comparing the two theories.
Answers at a glance
I Choose the correct answer
I Choose the correct answer
Biogenetic law (Recapitulation theory) was given by Ernst Haeckel.
It states that the stages of development of an individual animal (ontogeny) repeat the evolutionary history of its race (phylogeny).
b) Ontogeny recapitulates phylogeny
Jean Baptiste Lamarck published his theory in 'Philosophic Zoologique' (1809).
It is known as the Theory of Inheritance of Acquired Characters or the Use and Disuse theory.
c) Jean Baptiste Lamarck
Palaeontology is the branch that deals with the study of fossils.
So palaeontologists work with fossil evidences, such as Archaeopteryx, the oldest known fossil bird.
b) Fossil evidences
The radioactive carbon (C14) dating method was discovered by W.F. Libby (1956).
After death, C14 in the body only decays; measuring the remaining C14 gives the time since death, so it suits recently formed fossils.
a) Radio-carbon method
Ethnobotany is the study of a region's plants and their uses through the traditional knowledge of local people.
The term was coined by J.W. Harshberger in 1895.
b) J.W. Harsbberger
II Fill in the blanks
The characters developed by the animals during their life time, in response to the environmental changes are called ______________.
Lamarck said organisms respond to environmental change by developing new adaptive structures during their lifetime.
Such newly developed traits are named acquired characters, and Lamarck believed they are passed on to offspring.
acquired characters
Some organs lose their function and become reduced in size, though they are well developed and functional in related forms.
These are called vestigial organs, e.g. vermiform appendix, nictitating membrane, coccyx in man.
vestigial organs
A bat's wing and a human hand look different and do different jobs, but their bone structure and mode of development are similar.
Organs inherited from a common ancestor with a similar developmental pattern are homologous organs.
homologous
Charles Darwin, after his five-year voyage on H.M.S. Beagle, worked for 20 years and published 'Origin of Species' in 1859.
In it he explained evolution by the theory of natural selection (survival of the fittest).
Charles Darwin
III State true or false. Correct the false statements
The 'use and disuse theory' is one of the principles of Lamarckism, published by Jean Baptiste Lamarck in 'Philosophic Zoologique' (1809).
Charles Darwin proposed the theory of Natural Selection (Darwinism) in his book 'Origin of Species' (1859).
False — The 'use and disuse theory of organs' was postulated by Jean Baptiste Lamarck.
The homologous organs look similar and perform similar functions but they have different origin and developmental pattern.
Organs that look similar and perform similar functions but have different origin and developmental pattern are analogous organs, e.g. wings of a bat, a bird and an insect.
Homologous organs are inherited from common ancestors with a similar developmental pattern and basic structure, though they may perform different functions, e.g. forelimbs of human, cat, whale and bat.
False — The analogous organs look similar and perform similar functions but they have different origin and developmental pattern.
Archaeopteryx, the oldest known fossil bird of the Jurassic period, is considered a connecting link between reptiles and birds.
It had feathered wings like a bird and a long tail, clawed digits and conical teeth like a reptile, showing that birds evolved from reptiles.
True
IV Match the following
| Column A | Column B |
|---|---|
| a) Atavism | caudal vertebrae and vermiform appendix |
| b) Vestigial organs | a forelimb of a cat and a bat's wing |
| c) Analogous organs | rudimentary tail and thick hair on the body |
| d) Homologous organs | a wing of a bat and a wing of an insect |
| e) Wood park | radiocarbon dating |
| f) W.F. Libby | Thiruvakkarai |
Show steps (6)
a) Atavism – reappearance of ancestral characters, e.g. rudimentary tail and thick hair on the body.
b) Vestigial organs – degenerated, non-functional organs in man, e.g. caudal vertebrae and vermiform appendix.
c) Analogous organs – similar function but different origin, e.g. a wing of a bat and a wing of an insect.
d) Homologous organs – same basic structure and origin but different functions, e.g. a forelimb of a cat and a bat's wing.
e) Wood park – the fossil wood park is at Thiruvakkarai, Villupuram district.
f) W.F. Libby – discovered the radioactive carbon (C14) dating method, i.e. radiocarbon dating.
a - rudimentary tail and thick hair on the body, b - caudal vertebrae and vermiform appendix, c - a wing of a bat and a wing of an insect, d - a forelimb of a cat and a bat's wing, e - Thiruvakkarai, f - radiocarbon dating
V Answer in a word or sentence
A human hand, a front leg of a cat, a front flipper of a whale and a bat's wing look dissimilar and adapted for different functions. What is the name given to these organs?
These organs are inherited from common ancestors and have a similar mode of development and basic bone structure.
They look dissimilar and are adapted for different functions, yet are built on the same plan.
Such organs are called homologous organs.
Homologous organs
Archaeopteryx is the oldest known fossil bird, found in the Jurassic period.
It had wings with feathers like a bird, and a long tail, clawed digits and conical teeth like a reptile.
So it is treated as a connecting link between reptiles and birds.
Archaeopteryx
The branch of biology that deals with the study of fossils is palaeontology.
Leonardo da Vinci is called the Father of Palaeontology.
The study of plant fossils in particular is called palaeobotany.
Palaeontology
VI Short answers questions
The degenerated wing of a kiwi is an acquired character. Why is it an acquired character?
Kiwi is a bird whose ancestors had well-developed wings for flight.
The kiwi lived in an environment where flight was not needed, so the wings were not used for a long time.
According to Lamarck's 'use and disuse theory', an organ which is constantly used develops well, while an organ that is not used gradually degenerates.
So the degenerated wing developed during the lifetime of the bird in response to the change in environment; such characters developed during life time are called acquired characters and, according to Lamarck, are inherited by the offspring.
The kiwi's wing degenerated due to continuous disuse in response to environmental change during its life time, so it is an acquired character (Lamarck's use and disuse theory).
Archaeopteryx is the oldest known fossil bird, found in the Jurassic period.
It had bird-like characters: wings with feathers.
It also had reptilian characters: a long tail, clawed digits and conical teeth.
Since it possesses characters of both reptiles and birds, it is considered a connecting link between reptiles and birds, supporting evolution.
Archaeopteryx shows both reptilian characters (long tail, clawed digits, conical teeth) and bird characters (feathered wings), so it is a connecting link between reptiles and birds.
Definition: Ethnobotany is the study of a region's plants and their practical uses through the traditional knowledge of the local culture of people. The term was coined by J.W. Harshberger in 1895.
Importance: It provides the traditional uses of plants and gives information about certain known and unknown useful plants.
The ethnomedicinal data serves as a useful source of information for chemists, pharmacologists and practitioners of herbal medicine.
Tribal communities use plant parts like bark, stem, roots, leaves, flower buds, flowers, fruits, seeds, oils, resins, dyes and gum to treat diseases such as diarrhoea, fever, headache, diabetes, jaundice, snakebite and leprosy.
It is also relevant to nutrition, health care, cottage industries, economic upliftment, conservation of biodiversity and sustainable use of plant resources.
Ethnobotany is the study of a region's plants and their uses based on traditional knowledge; it reveals useful plants, supplies ethnomedicinal data for drug research and helps in health care and conservation of biodiversity.
The age of fossils is determined by the radioactive elements present in them, such as carbon, uranium, lead or potassium.
The common method is the radioactive carbon () dating method, discovered by W.F. Libby (1956).
Carbon consumption by plants and animals stops after death, and from then on only the decay of continues.
By measuring the amount of remaining in the body, the time passed since the death of the plant or animal can be calculated.
This method is used in paleobotany and anthropology to find the age of human fossils and manuscripts.
The age of a fossil is found from the radioactive elements in it, mainly by the radioactive carbon () dating method of W.F. Libby, which measures the left after death.
VII Long answer questions
Show steps (7)
Overproduction: Living beings reproduce and multiply in a geometrical manner, so many more offspring are produced than can actually survive.
Struggle for existence: Since food and space remain the same while population increases, intense competition arises. It is of three types — intraspecific (among individuals of the same species), interspecific (between different species living together) and environmental (extreme heat, cold, drought, floods).
Variations: Variation is a characteristic feature of all plants and animals. Darwin said favourable variations are useful to the organism while unfavourable variations are harmful or useless.
Survival of the fittest: Organisms with favourable variations overcome the challenging situation, survive and adapt to the surroundings. Those unable to face the challenges are unfit and are eliminated from the environment.
Natural selection: The process of selection of organisms with favourable variation by nature is called natural selection. Nature thus acts as the selecting agent.
Inheritance of favourable characters: The selected favourable variations are passed on to the offspring and get gradually accumulated generation after generation.
Origin of species: By the gradual accumulation of favourable variations over a number of generations, new species originate. Hence natural selection continuously changes the characters of populations and drives evolution.
Overproduction leads to struggle for existence; organisms with favourable variations survive (natural selection), pass on these variations, and their gradual accumulation over generations forms new species — so natural selection drives evolution.
Show steps (8)
Origin — Homologous organs: They are inherited from common ancestors and have a similar developmental pattern in embryos.
Origin — Analogous organs: They have different origin and different developmental patterns; they are not inherited from a common ancestor.
Structure — Homologous organs: Their basic structure (arrangement of bones) is similar, though outwardly they may look dissimilar.
Structure — Analogous organs: They look similar externally but their basic structures are entirely different.
Function — Homologous organs: They are adapted for different functions in different animals.
Function — Analogous organs: They perform similar functions.
Example — Homologous: Forelimbs of mammals — human hand, front leg of a cat, flipper of a whale and a bat's wing; all have humerus, radius, ulna, carpals, metacarpals and phalanges.
Example — Analogous: Wings of a bat, wings of a bird and wings of an insect — all used for flight but structurally different.
Homologous organs have common ancestry and same basic structure but different functions, while analogous organs have different origin and structure but perform similar functions.
Show steps (8)
Fossilization: The process of formation of fossil in the rocks is called fossilization. A plant fossil is any preserved part of a plant that has died long back; most plant fossils are disarticulated parts, as whole plants are rarely preserved.
Petrifaction: Minerals like silica slowly penetrate into and replace the original organic tissue, forming a rock-like fossil. It can preserve both hard and soft parts; most wood and bone fossils are petrified.
Mold and Cast: When the plant gets buried in sediment it is dissolved by underground water leaving a hollow depression called a mold, which shows the original shape but not the internal structure. When minerals or sediment fill this hollow, a cast is formed.
Carbonization: The plant remains are preserved as a thin carbon film in the rock.
Preservation: Original remains are preserved in ice or amber (tree sap), which protect the organism from decay; the entire plant or animal is preserved.
Compression: When an organism dies, the hard parts settle at the bottom of the sea bed and are covered by sediment. Sedimentation continues and fossils are formed.
Infiltration or Replacement: Precipitation of minerals such as silica, calcium carbonate and magnesium carbonate takes place and they infiltrate the cell wall. The hard parts are dissolved and replaced by these minerals.
Example: At Thiruvakkarai fossil wood park (Villupuram district), tree trunks buried about 2 million years ago had their organic matter replaced by silica; they retained colour, shape, texture, annular rings and nodes and turned into solid rocks.
Plant parts buried in sediments become fossils through petrifaction, mold and cast, carbonization, preservation in ice/amber, compression and infiltration (replacement) by minerals.
IX Higher Order Thinking Skills (HOTS)
Arun was playing in the garden. Suddenly he saw a dragon fly sitting on a plant. He observed the wings of it. He thought it looked similar to a wing of a crow. Is he correct? Give reason for your answer.
Arun is only partly correct — the two wings look alike and do the same work (flight), but they are not the same kind of organ.
The wing of a dragonfly (insect wing) and the wing of a crow (bird wing) have different origin and different developmental pattern; the bird wing has bones while the insect wing does not.
Organs that look similar and perform similar functions but differ in origin and development are called analogous organs.
So the resemblance is only functional; it shows adaptation to flight, not descent from a common ancestor.
He is wrong in thinking they are the same structure — the wings of a dragonfly and a crow are analogous organs (similar function, different origin and development).
Fossils are the preserved remains or imprints of ancient life forms and ancient habitats, preserved by natural processes in rocks.
Palaeontology, the study of fossils, helps us trace the line of evolution of many invertebrates and vertebrates.
Fossil records show that evolution has been a gradual process from simple to complex organisms.
The age of a fossil can be found using radioactive elements like , so the sequence of appearance of organisms in time can be arranged.
Connecting-link fossils like Archaeopteryx (wings and feathers like a bird; long tail, clawed digits and conical teeth like a reptile) show how one group arose from another.
Fossil imprints preserve ancient life forms, and their structure and age reveal the gradual evolution of simple organisms into complex ones.
Octopus, cockroach and frog all have eyes. Can we group these animals together to establish a common evolutionary origin. Justify your answer.
No, they cannot be grouped together on the basis of eyes alone.
Octopus (a mollusc), cockroach (an insect) and frog (a vertebrate) belong to very different groups; their eyes differ in basic structure and in their pattern of development.
Such organs, which perform the same function (seeing) but have different origin and developmental pattern, are analogous organs.
Analogous organs show similar adaptation to a need, not inheritance from a common ancestor; only homologous organs (like the forelimbs of man, cat, whale and bat) prove common ancestry.
No — their eyes are analogous organs, similar in function but different in origin and development, so they do not indicate a common evolutionary origin.
Quick check
Biogenetic law states that ______________
Question 1 of 5Show answer
Answer: (2) Ontogeny recapitulates phylogeny
Biogenetic law (Recapitulation theory) was given by Ernst Haeckel.
It states that the stages of development of an individual animal (ontogeny) repeat the evolutionary history of its race (phylogeny).
Paleontologists deal with
Question 2 of 5Show answer
Answer: (2) Fossil evidences
Palaeontology is the branch that deals with the study of fossils.
So palaeontologists work with fossil evidences, such as Archaeopteryx, the oldest known fossil bird.
The term Ethnobotany was coined by
Question 3 of 5Show answer
Answer: (2) J.W. Harsbberger
Ethnobotany is the study of a region's plants and their uses through the traditional knowledge of local people.
The term was coined by J.W. Harshberger in 1895.
The 'use and disuse theory' was proposed by ______________.
Question 4 of 5Show answer
Answer: (3) Jean Baptiste Lamarck
Jean Baptiste Lamarck published his theory in 'Philosophic Zoologique' (1809).
It is known as the Theory of Inheritance of Acquired Characters or the Use and Disuse theory.
The best way of direct dating fossils of recent origin is by
Question 5 of 5Show answer
Answer: (1) Radio-carbon method
The radioactive carbon (C14) dating method was discovered by W.F. Libby (1956).
After death, C14 in the body only decays; measuring the remaining C14 gives the time since death, so it suits recently formed fossils.