Q & A ON REPRODUCTION IN ORGANISMS

Q1. What is life span?

Ans: Life span is the period from birth to natural death of an organism.

Q2. Define clone.

Ans: The individuals that are morphologically and genetically similar to the parent are called clone.

Q3. Mention the different means/ methods of asexual reproduction with example.

Ans: 

• Cell division – Protista, Monera
• Binary fission – Amoeba, Paramecium
• Budding – Yeast
• Zoospores (microscopic motile endogenous spores) – aquatic fungi, chlamydomonas
• Conidia (microscopic immotile exogenous spores)- pencillium
• External buds – hydra
• Internal buds like gemmules – sponges (spongilla)

Q4.Unicellular organisms are immortal. Justify.

Ans: Single celled organisms like amoeba & bacteria reproduce by cell division and there is no natural death for them. Hence they are considered as immortal.

Q5. How vegetative reproduction does take place in Bryophyllum?

Ans: The adventitious buds or epiphyllous buds arise from the notches present at the margin of leaves grow into independent plants.

Q6. Name the mode of reproduction that ensures creation of new variants.

Ans: Sexual reproduction.

Q7. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?

Ans: The progeny formed from asexual reproduction are genetically similar to the parents, but offsprings formed by sexual reproduction show genetic variations due to genetic recombination occurred during gamete formation and random

Q8. Name the species of plant that flowers once in lifetime.

Ans: Bamboo species flowers only once in lifetime generally after 50 – 100 years.

Q9. Between an annual and a perennial plant, which one has shorter juvenile phase? Give reason.

Ans: An annual has a shorter juvenile phase as its entire life cycle has to be completed in one growing season within a year.

Q10. Name the plant that flowers once in 12 years.

Ans: Strobilanthus kunthiana (Neelakuranji). It flowered during September – October 2006 which made the hilly areas of Karnataka, Kerala & Tamil Nadu appear as blue stretches.

Q11. In haploid organisms that undergo sexual reproduction, name the stage in the lifecycle when meiosis occurs?

Ans: Meiosis occurs during its post zygotic stage. As the organism is haploid meiosis cannot occur during gametogenesis.

Q12. A haploid organism produces gametes by mitosis. Does it mean that meiosis never occurs in such organisms

Ans: In haploid organisms, meiosis occurs during the germination of zygote because the zygote is the only diploid cell in the life cycle of such organisms.

Q13. All papaya plants bear flowers but fruits are seen only in Why?

Ans: Papaya is a dioecious plant. Only female plants produce fruits.

Q14. Why is fertilization in bryophytes and pteridophytes considered as internal fertilization?

Ans: The fertilization occurs inside the archegonium of these plants.

Q15. Why are meiosis & gametogenesis always interlinked?

Ans: The diploid organisms have to produce haploid gametes by meiosis to maintain diploidy through generations. So they are always interlinked.

Q16. Is there a relationship between the size of an organism and its life span? Justify your answer with two examples.

Ans: There is no relationship between the size and lifespan of an organism.

Eg: The size of crow and parrot is almost same but the life span is 15years and 150 years respectively. The Mango tree has a shorter life span compare to a Peepal tree though both are of the same size.

Q17. Define reproduction. What is its significance?

Ans: Reproduction is a biological process in which an organism gives rise to young ones (offsprings) of its own kind.

It enables the continuity of the species generation after generation. Thus ensures the continuity of every organism.

Q18. What is asexual reproduction? Mention its features.

Ans: It is a type of reproduction in which offspring are produced from a single parent without the involvement of the formation and fusion gametes. The features are

Q19. What is regeneration? Give example.

Ans: Regeneration is a process in which the animal regrows or repairs its lost or damaged body parts. Eg: Planaria, Starfish.

Q20. What is vegetative propagation? Why is it called asexual reproduction?

Ans: Vegetative propagation is a type of asexual reproduction in plants in which the somatic cells or vegetative parts give rise to new individuals. It is not biparental and does not involve the formation of gametes. So it is also called asexual reproduction.

Q21. Although potato tuber is an underground part. It is considered as a stem. Give two reasons.

Ans: 

1. Potato tuber has nodes & internodes
2. Leafy shoots appear from the nodes

Q22. Which is a better mode of reproduction, sexual or asexual? Why?

Ans: Sexual reproduction is the better mode of reproduction because the better offspring are produced with genetic variations. Such variations enable the organisms to survive in unfavourable conditions or adapt to changing environmental conditions.

Q23. Define the following with examples

Ans: 

A) Oestrus cycle: The cyclical changes in the activities of ovaries & accessory ducts as well as hormones secretion during the reproductive phase of non-primate mammals like cows, sheep, rats, deers, dogs, tigers, is called Oestrus cycle.

Monoestrus animal: Single oestrus cycle in a year. Eg: Deer.

Dioestrus animal: Two oestrus cycle a year. Eg: Dog.

Polyoestrus animal: Many oestrus cycles in a year. Eg: Mouse.

B) Menstrual cycle: The cyclical changes in the activities of ovaries & accessory ducts as well as hormones secretion during the reproductive phase of primate mammals like monkeys, apes & humans is called Menstrual

C) Seasonal breeders: These are the organisms that reproduce only in some favourable Eg: Mammals living in natural & wild conditions.

D) Continuous breeders: These are the organisms that are reproductively active throughout their reproductive phase are called continuous

Eg: Human beings.

Q24. The cell division involved in gamete formation is not of the same type in different organisms. Justify.

Ans:  In haploid organisms showing haplontic life cycle, gamete formation involves only mitosis. In these diploid zygote undergoes meiosis to produce haploid organisms.

In diploid organisms showing diplontic or haplo-diplontic life cycle, gamete formation involves meiosis. In these, the zygote undergoes mitosis to produce diploid organisms.

Q25. Fertilization is not an obligatory event for fruit production in certain plants. Explain the statement.

Ans: Some fruits are developed from unfertilized ovary called parthenocarpic fruits. These are seedless fruits. Parthenocarpy can be induced by spraying growth hormones. So fertilization is not an obligatory event for fruit production. Example: grapes, pomegranate etc.

Q26. Define the following with examples

1. Bisexual animals or Hermaphrodites: The animals which possess both male and female reproductive organs in the same Eg: Tape worm, earth worm, leech, sponges etc.,
2. Unisexual animals or homophrodites: The animals which possess male or female reproductive Eg: Cockroach, round worm, human. These exhibit sexual dimorphism.
3. Homothallic plants or bisexual or monoecious: The plant body having both male and female reproductive Eg: Fungi, Hibiscus, cucurbita, coconut, chara, sweet potato.
4. Heterothallic plants or unisexual or dioecious: The plant body having either male or female reproductive Eg: Papaya, Date palm, Marchantia
   • The flowers with only stamens are called male flowers or staminate
   • The flowers with only pistil are called female flowers or pistillate

Q27. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than dioecious plant. Why?

Ans: In bisexual flowers, the anther and stigma lie close to each other and when the anther dehisce the pollen grains fall on stigma and pollination is effected even in the absence of pollinator. But in dioecious plants pollinator is necessary to bring about effective pollination.

Q28. Which of the following are monoecious and dioecious?

Ans: 

Earthworm – monoecious/hermaphrodite Chara – monoecious

Marchantia – dioecious

Cockroach – dioecious/homophrodites

Q29. Both coconut and date palm produce staminate flowers. One is monoecious & the other is dioecious. Write the difference.

Ans: Coconut palm is monoecious. It bears staminate and pistillate flowers in the same plant. Date palm is dioecious. It bears staminate flowers in one plant & pistillate flowers in another.

Q30. Identify each part in a flowering plant & write whether it is haploid or diploid or triploid.

Ans: 

1. Ovary – diploid
2. Anther – diploid
3. Egg cell – haploid
4. Pollen – haploid
5. Male gamete – haploid
6. Zygote – diploid g)Endosperm – triploid

7. Embryo sac (female gametophyte) – haploid