CBSE Class 12 Biology Reproduction In Organisms Assignment Set D

Very Short Answer Type Questions

Question. In which two of the following organisms is the fertilization external ?
Bony fishes, ferns, frog, birds.
Answer: Bony fishes and frogs. 

Question. Which of the following statements is true for date palm.
(i) It is monoecious producing both staminate and pistillate flowers in the same plant.
(ii) It is monoecious producing staminate flowers in one and pistillate flowers in another tree.
(iii) It is dioecious producing staminate flowers in one tree and pistillate flowers in another tree.
Answer: Statement (iii) is true. Date palm is a dioecious plant. 

Question. Name any two organisms and the phenomenon involved where the female gamete undergoes development to form new organisms without fertilisation.
Answer: (i) Rotifers/honeybees/some lizards/turkey.
(Any two)

Question. Why is a whiptail lizard referred to as parthenogenetic ? 
Answer: Whiptail lizard is referred to as parthenogenetic because the embryos of whiptail lizards are developed from egg without undergoing the process of fertilization. The unfertilized embryos gives rise to new organism. 

Question. Name the phase all organisms have to pass through before they can reproduce sexually.
Answer: Juvenile phase. In plants it is called as vegetative phase. Infact, it is the pre-reproductive period in the life cycle of an individual. 

Question. Name two animals that exhibit oestrous cycle.
Answer: Cow, sheep, rat, deer, dog, tiger, etc.

Question. The turkey usually produces females for several generations. How is this possible ?
Answer: This is possible due to parthenogenesis. In birds like turkey, only the female gamete undergoes development to form new organisms without fertilisation. This phenomenon is called parthenogenesis.

Question. Name the mode of reproduction that ensures the creation of new variants.
Answer: Sexual reproduction : It is a kind of reproduction where male and female gametes fuse together to form the diploid zygote. Zygote germinates and gives rise to new individual showing some variations. 

Question. Coconut plant is monoecious, while date palm is dioecious. Why are they called so ?
Answer: In coconut plant, both male and female flowers are present on the same plant whereas in date palm, both male and female flowers are present on the separate plants species.

Question. Mention the unique flowering phenomenon exhibited by Strobilanthes kunthianus (Neelakurinji) 
Answer: Strobilanthes kunthianus is a monocarpic plant. It flowers once in a life span of 12 years after which it dies. 

Short Answer Type Questions

Question. Why do moss plants produce very large number of male gametes ? Provide one reason. What are these gametes called ? 
Answer: In moss plants, water is the medium through which male gametes reach the female gamete. Hence, a large number of male gametes fail to reach the female gamete. This results in a great loss of male gametes. Therefore, to compensate for this loss the male gametes in moss plants are produced in very large number.
The male gametes in moss plant are called as the antherozoids. 

Question. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain.
Answer: Pea : Flowers of pea plants are bisexual, monoecious / self pollinated (to produce pods with viable seeds). 
Detailed Answer :
Pea plant bears bisexual flowers. Therefore, the single pea plant can produce viable seeds after selfpollination.
Papaya, on the other hand is a dioecious plant, bearing unisexual flowers that requires cross-pollination for viable seed production. Thus, they cannot produce viable seeds. 

Question. Angiosperms bearing unisexual flowers are said to be either monoecious or dioecious. Explain with the help of one example each.
Answer: Monoecious Angiosperms : Plants bear both male and female unisexual flowers on the same plant.
e.g., Cucurbits/coconut/maize.
Dioecious Angiosperms : Plants bear either male or female unisexual flowers on different plants.
e.g., Papaya/date palms.
Detailed Answer :
The plants are said to be monoecious if both male and female unisexual flowers are present on the same plant and if the unisexual male and female flowers are present on separate plants then they are called as dioecious.

Question. Meiosis is an essential event in the sexual life cycle of any organism. Give two reasons.
Answer: Meiosis is an essential event in the sexual cycle of any organism because :
(i) It maintains the number of chromosomes fixed (2n) from generation to generation. Haploid gametes are formed as a result of meiosis. Diploid (2n) condition is restored during fertilization.
(ii) It increases the genetic diversity and variation due to crossing over between homologous chromosomes and their random segregation.