Bihar Board - Class 12 Biology - Chapter 1: Reproduction In Organisms Long Answer Question

Long answer type question

Question1 . Which is a better mode of reproduction, sexual or asexual? Why?
Ans: Sexual reproduction is a better mode of reproduction because of the following reasons:
Variation : Since fusion of gametes from different parents occurs during sexual reproduction, hence genetic recombination takes place causing variations.
Evolution : Variation being a major factor of natural selection, therefore, it plays an important role in evolution.
Adaptation : The offspring produced due to sexual reproduction adapt better to the changing environmental conditions.
Vigor and Vitality : Genetic recombination, interaction, etc. during sexual reproduction provide vigor and vitality to the offspring.

Question 3. Offsprings formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Ans: The offsprings obtained from sexual reproduction have better chances of survival because the genetic material of such organisms are formed from both the parents. Daughter organisms/offsprings show variation that leads to the evolution of species.
This statement is always true. The offspring produced due to sexual reproduction adapt better to the changing environmental conditions. Genetic recombination, interaction, etc. during sexual reproduction provide vigor and vitality to the offspring.


Question 4. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Ans: Production of offspring by a single parent without the formation and fission of gametes is called asexual reproduction. It involves only mitotic cell division that gives rise to the daughter cells which are genetically identical to the parent cell. Sexual reproduction is the production of offspring by two parents, male and female. It involves meiotic cell divisions producing haploid nuclei which on fusion produce offspring that are genetically different from their parents.


Question 5. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Ans: The difference between asexual and sexual reproduction are as follows :
In plants asexual reproduction is called vegetative reproduction because vegetative plant parts like rhizome, runner, sucker, tuber, bulb all are capable of producing offspring These parts give rise to daughter individuals without the involvement of two parents.


Question 6. What is vegetative propagation? Give two suitable examples.
Ans: Vegetative propagation is the formation of new plants from vegetative units. In plants, the units of vegetative propagation are runner, rhizome, sucker, tuber, offset, bulb, etc. These are capable of producing new offspring. These structures are called v vegetative propagules.
Modified tuberous roots of sweet potato, tapioca, yam, Dahlia and Tinospora can be propagated vegetatively when planted in soil. Small plants emerging from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger are other examples.

Question 7. Define:
(a)Juvenile phase
(b)Reproductive phase
(c)Senescent phase.
Ans: (a)Juvenile phase : All organisms have to reach a certain stage of growth and maturity in their life before they can reproduce sexually. That period of growth is called the juvenile phase. However, this phase is known as vegetative phase in plants. This phase is of different durations in different organisms.


(b)Reproductive phase: The end of juvenile/ vegetative phase marks the beginning of reproductive phase. During this phase, the organisms produce offspring. In higher plants, this phase can be easily seen when they come to flower but in animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behavior. The reproductive phase is also of variable period in different organisms like some plants, flower throughout the year while others show seasonal flowering. Animals like birds lay eggs seasonally “but when in captivity (as in poultry farms) can be made to lay eggs throughout the year. Placental female mammals undergo cyclical changes in reproductive organs during this phase.


(c) Senescent phase: It begins from the end of the reproductive phase. During this phase of life span, there is progressive deterioration in the body (like slowing of metabolism, etc.). Old age ultimately leads to death.


Question 8. Define external fertilization. Mention its disadvantages.
Ans: When fusion of the gametes takes place outside the body of the organisms, it is called external fertilization or external syngamy. An external medium like water is required for this form of fertilization. This form is found in many aquatic animals like fishes, amphibians, and the majority of algae.
In this, parents release eggs and sperm in the surrounding water, then fertilization and development of offspring occur externally. Disadvantages of external fertilization:
(i)if occurs only in aquatic mediums.
(ii)A chance factor is involved, requiring synchronous release of gametes nearby and absence of turbulence of water.
(iii)There is no protection for young ones. They are vulnerable to a number of predators.


Question 9. Differentiate between a zoospore and a zygote.
Ans: The zoospore is flagellated, motile, haploid or diploid spore formed inside a zoosporangium. It is the result of asexual reproduction.
The zygote is always diploid and formed by the fusion of gametes. It is usually non- flagellated and non-motile or motile. It is the net result of sexual reproduction.


Question 10. Differentiate between gametogenesis from embryogenesis.
Ans: Differences between gametogenesis and embryogenesis are as follows :


Question 11. Describe the post-fertilization changes in a flower.
Ans: In sexual reproduction, events that occur after the formation of zygote are called post-fertilization events. In flowering plants, the zygote is formed inside the ovule. After fertilization the sepals, petals and stamens of the flower wither and fall off. But the pistil remains attached to the plant. The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into a die fruit that develops.a thick wall called pericarp which is protective in – function. After dispersal, seeds germinate under favorable conditions to produce new plants.


Question 12. What is bisexual flower?
Ans: Flowers in which male and female sex organs (stamens and carpels) are borne on the same flowers are called bisexual flowers. You can observe following bisexual flowers in your kitchen and colony gardens :
(i)Brassica (sarson) – Brassica campestris
(ii)Onion – Allium cepa
(iii)Garden Pea (Edible pea) – Pisum sativum
(iv)Petunia – Petunia hybrida
(v)China rose (shoe flower) – Hibiscus rosa- sinensis.


Question 13. Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Ans: The male or staminate flowers of cucurbits bear bright coloured petals and a prominent group of stamens. Male plants or staminate flowers do not bear fruits. The female or pistillate flowers bear fruits. In a fertilised young pistillate flower very small fruit is visible below petals and sepals. Some unisexual plants are : Papaya, Mulberry and Date-palm.


Question 14. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Ans: On the basis of the development of the zygote, animals are grouped into oviparous and viviparous. The oviparous animals such as reptiles and birds lay eggs. Their fertilized eggs are covered by hard calcareous shell and are laid in a safe place in the environment. After the incubation period, young ones hatch out. In viviparous animals such as the majority of mammals including human beings, the zygote develops into a young one inside the body of the female individual. After a certain growth period, the young ones are delivered by the female individual. Due to proper care and protection, the chances of survival of young ones are more in viviparous individuals. Oviparous offsprings are at a greater risk than viviparous ones


Question 15. How exogenous buds are developed by Hydra?
Answer: When buds are formed on the outer surface of the parent body, it is known as exogenous budding e.g. Hydra. In Hydra when food is plenty, the ectoderm cells increase and form a small elevation on the body surface. Ectoderm and endoderm are pushed out to form the bud. The bud contains an interior lumen in continuation with the parent's gastrovascular cavity. The bud enlarges, develops a mouth and a circle of tentacles at its free end. When fully grown, the bud constricts at the base and finally separates from the parent body and leads an independent life.


Question 16 Apolysis favors Taenia solium. How?
Answer: In the tapeworm, Taenia solium the gravid (ripe) proglottids are the oldest at the posterior end of the strobila. The gravid proglottids are regularly cut off either singly or in groups from the posterior end by a process called apolysis. This is very significant since it helps in transferring the developed embryos from the primary host (man) to find a secondary host (pig).


Question 17.Give the definition for
Arrhenotoky
Thelytoky
Amphitoky
Answer:
Arrhenotoky: In this type, only males are produced by parthenogenesis
eg: honey bees

Thelytoky: In this type of parthenogenesis only females are produced by parthenogenesis.
e.g: Solenobia

Amphitoky: In this type parthenogenetic egg may develop into individuals of any sex.
e.g: Aphis.

Question 18. Write a short note on the phases of the life cycle.
Answer:
Juvenile phase – Period of growth between the birth of an individual and reproductive maturity.
Reproductive phase – Period of growth when an organism attains reproductive maturity and produces new offsprings.
Senescent plane – Period of growth when the structure and functioning of the body start degenerating.


Question 19. What is Paedogenesis?
Answer: In paedogenetic parthenogenesis (paedogenesis) the larvae produce a new generation of larvae by parthenogenesis. It occurs in the sporocysts and Redia larva of liver fluke. It is also seen in the larvae of some insects,
e.g. Gall fly.


Question 20. Differentiate between asexual and sexual reproduction.
Answer: Asexual Reproduction:
 Involves only one parent
Only mitotic cell division takes place.
Offsprings are genetically identical to parents.
Gametes are not produced
Sexual Reproduction:
Involves two parents (male & female)
Both mitosis & meiosis takes place.
Offsprings genetically differ from the parents.
Gametes are produced.


Question 21. Describe the regeneration process noticed in living organisms.
Answer:Regeneration is regrowth in the injured region. Regeneration was first studied in Hydra by Abraham Trembley in 1740. Regeneration is of two types, morphallaxis and epimorphosis. In morphallaxis, the whole body grows from a small fragment e.g. Hydra and Planaria. When Hydra is accidentally cut into several pieces, each piece can regenerate the lost parts and develop into a whole new individual. The parts usually retain their original polarity, with oral ends, by developing tentacles and aboral ends, by producing basal discs.
Epimorphosis is the replacement of lost body parts. It is of two types, namely reparative and restorative regeneration. In reparative regeneration, only certain damaged tissue can be regenerated, whereas in restorative regeneration severed body parts can develop
e.g. starfish, tail of wall lizard.


Question 22. Given an account on the following terms.
Hologamy
Isogamy
Anisogamy
Merogamy
Paedogamy
Answer:
Hologamy: In Hologamy, the adult individuals do not produce gametes, but they themselves act as gametes and fuse to form new individuals.
E.g: Trichonympha
Isogamy: Fusion of morphologically & physiologically similar gametes.
E.g: Monocystis.
Anisogamy: Fusion of morphologically & physiologically dissimilar gametes.
Eg: Vertebrates.
Merogamy: Fusion of small-sized morphologically different gametes (microgametes)
Paedogamy: Fusion of young individuals produced immediately after the mitotic division of the adult parent cell.


Question 23. Give reasons for the following:
Some organisms like honey bees are called parthenogenetic animals
A male honey bee has 16 chromosomes whereas its female has 32 chromosomes
Answer: (1) Among honey bees, the queen bee and worker bees develop from fertilized eggs whereas the drones develop from unfertilized eggs. Hence the honey bees are parthenogenetic animals showing incomplete parthenogenesis.
(2) Female honey bees (Queen or worker bees) are diploid having 32 chromosomes since they develop from the fertilized egg. On the other hand, the male honey bees (drones) develop from unfertilized egg possessing only 16 chromosomes (i.e., Haploid)


Question 24. Differentiate between the following:
(a) Binary fission in amoeba and multiple fission in Plasmodium
(b) Budding in yeast and budding in Hydra
(c) Regeneration in lizard and Planaria
Answer: (a) Binary fission in amoeba and multiple fission in Plasmodium
Binary fission in amoeba: In binary fission of amoeba, the plane of division is hard to observe. The nucleoli disintegrate. The nucleus divides mitotically, forming two nuclei. The cell constricts in the middle, so the cytoplasm divides forming two daughter cells.
Multiple fission: In Multiple fission of plasmodium, the oocyte or schizont divides into many similar daughter cells simultaneously. Nucleus undergoes repeated mitosis producing many nuclei without the division of cytoplasm. Later the cytoplasm divides & encircles each nucleus forming many daughter cells oocyte undergoes sporogony forming sporozoites. Schizont undergoes schizogony forming merozoites.
(b) Budding in yeast and budding in Hydra:
Budding in Yeast: Yeast is a cellular organism in which the bud develops as a small protuberance following the nuclear division and finally detached to a new individual.
Budding in Hydra: Hydra is a multicellular organism where the bud from the parents body grows gradually and finally gets detached.
(c) Regeneration in lizard and Planaria:
Regeneration of Lizard: If the tail of the lizard is cut and removed, a new tail will regenerate in the damaged part. In lizard only the new tail is regenerated.
Regeneration of Planaria: If a planarian worm get cut then each half regenerates the lost part resulting in two worms.
In planaria, the cut removed part developed into an entire worm.


Question 25. How is the juvenile phase different from the reproductive phase?
Answer: Juvenile phase: Juvenile phase is the period of growth between the birth of an organism and before its reproductive maturity.
Reproduction phase: Reproductive phase is the period of growth after the juvenile phase when an individual attains reproductive maturity and reproduces.

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