Heredity & Evolution

NCERT Exemplar Problems

Part 2

Question 13: Select the correct statement

1. Tendril of a pea plant and phylloclade of Opuntia are homologous
2. Tendril of a pea plant and phylloclade of Opuntia are analogous
3. Wings of birds and limbs of lizards are analogous
4. Wings of birds and wings of bat are homologous
   
   Answer: (a) Tendril of a pea plant and phylloclade of Opuntia are homologous

Explanation: They are modified stems but serve different functions in different plants. We know that organs with similar origin/design are called homologous structures.

Question 14: If the fossil of an organism is found in the deeper layers of earth, then we can predict that

1. the extinction of organism has occurred recently
2. the extinction of organism has occurred thousands of years ago
3. the fossil position in the layers of earth is not related to its time of extinction
4. time of extinction cannot be determined
   
   Answer: (b) the extinction of organism has occurred thousands of years ago

Explanation: Newer fossils are deposited in layers above older fossils.

Question 15: Which of the following statements is not true with respect to variation?

1. All variations in a species have equal chance of survival
2. Change in genetic composition results in variation
3. Selection of variants by environmental factors forms the basis of evolutionary processes.
4. Variation is minimum in asexual reproduction
   
   Answer: (a) All variations in a species have equal chance of survival

Explanation: Useful variations stand a chance of survival because nature selects only the useful variations.

Question 16: A trait in an organism is influenced by

1. paternal DNA only
2. maternal DNA only
3. both maternal and paternal DNA
4. neither by paternal nor by maternal DNA
   
   Answer: (c) both maternal and paternal DNA

Explanation: Both parents equally contribute to the DNA of an individual.

Question 17: Select the group which shares maximum number of common characters

1. two individuals of a species
2. two species of a genus
3. two genera of a family
4. two genera of two families
   
   Answer: (a) two individuals of a species

Explanation: The lowest taxon shows the maximum number of common characters. Species is the lowest taxon.

Question 18: According to the evolutionary theory, formation of a new species is generally due to

1. sudden creation by nature
2. accumulation of variations over several generations
3. clones formed during asexual reproduction
4. movement of individuals from one habitat to another
   
   Answer: (b) accumulation of variations over several generations

Explanation: Theory of sudden creation has long been disproved by scientists. It is the accumulation of variations over successive generations which results in origin of a new species.

Question 19: From the list given below, select the character which can be acquired but not inherited

1. colour of eye
2. colour of skin
3. size of body
4. nature of hair
   
   Answer: (c) size of body

Explanation: Traits in other options are always inheritable traits.

Question 20: The two versions of a trait (character) which are brought in by the male and female gametes are situated on

1. copies of the same chromosome
2. two different chromosomes
3. sex chromosomes
4. any chromosome
   
   Answer: (b) Two different chromosomes

Explanation: This obeys Mendel’s First Law of Inheritance.

Question 21: Select the statements that describe characteristics of genes

1. genes are specific sequence of bases in a DNA molecule
2. a gene does not code for proteins
3. in individuals of a given species, a specific gene is located on a particular chromosome
4. each chromosome has only one gene

1. (i) and (ii)
2. (i) and (iii)
3. (i) and (iv)
4. (ii) and (iv)
   
   Answer: (b) (i) and (iii)

Explanation: A gene codes for a protein, and a chromosome can have many genes. So, statements (ii) and (iv) are incorrect.

Question 22: In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is

1. 1 : 3
2. 3 : 1
3. 1 : 1
4. 2 : 1
   
   Answer: (c) 1 : 1

Explanation: Following combinations of genotype emerge in F2 generation: TT (1), tt(1) and Tt (2). This shows that ratio of pure tall (TT) to pure short (tt) is 1:1.

Question 23: The number of pair (s) of sex chromosomes in the zygote of humans is

1. One
2. Two
3. Three
4. Four
   
   Answer: (a) One

Explanation: The sex chromosomes are in the 23rd pair.

Question 24: The theory of evolution of species by natural selection was given by

1. Mendel
2. Darwin
3. Morgan
4. Lamarck
   
   Answer: (b) Darwin

Question 25: Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that

1. reptiles have evolved from birds
2. there is no evolutionary connection between reptiles and birds
3. feathers are homologous structures in both the organisms
4. birds have evolved from reptiles
   
   Answer: (d) Birds have evolved from reptiles