(ii) to introduce variation among the individuals of a species;
(iii) to maintain and to inherit the genetic constitution or genetic make up.
Q. 2. Which is a better mode of reproduction: sexual or asexual? Why?
Ans. Sexual mode of reproduction is better because it is biparental reproduction and introduces variation among offsprings and their parents (in a population) due to crossing over and recombination during gamete formation by meiosis.
Q. 3. Why is the offspring formed by asexual reproduction referred to as clone?
Ans. In asexual reproduction, the offspring is morphologically and genetically identical to the parent and to each other. Hence it is called clone.
Q.4. Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Ans. Offspring formed due to sexual reproduction have better chances of survival because:
(i) In sexual reproduction, the offspring may be hybrid vigour which may adapt better with the environment.
(ii) In sexual reproduction, genetic variation is introduced among the offsprings. So, the range of tolerance or biological tolerance increases.
(iii) Sexual reproduction occurs in adverse conditions in lower plant kingdom, so sexual spores survive in adverse conditions.
Sexual reproduction may noc always show better chances of survival because the offspring may be inferior to the parents.
Q.5.How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Ans. Progeny from asexual reproduction:
(i) The progenies have similar genetic make up.
(ii) The progenies are not only identical to one another but are exact copies of their parents, i.e., clone of the parent.
(iii) Variation is absent.
(iv) Variation may occur due to mutation.
(v) Progeny is less adaptable to changes in environment.
Progeny from sexual reproduction:
(i) The progenies have different genetic make up.
(ii) The progenies are different from each other and dissimilar to the parent.
(iii) Variation is a common phenomenon.
(iv) Variation occurs due to mutation, crossing over and recombination.
(v) Progeny is more adaptable to changes in environment.
Q.6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Ans. For difference, Refer to Basic Concepts Point 2.
Vegetative reproduction is considered as a type of asexual reproduction because:
(i) It is uniparental reproduction.
(ii) There is no involvement of gamete or sex cell.
(iii) Cell division is mitotic and no reductional division takes place.
(iv) Vegetative propagules are somatic cells.
Q.7. What is vegetative propagation? Give two suitable examples.
Ans. In plants, the vegetative propagules (runner, rhizome, sucker, etc.) are capable of producing new offsprings by the process called vegetative propagation. As the formation of these vegetative propagules does not involve both the parents, the process involved is asexual.
Examples: (i) Adventitious buds in the notches along the leaf margins of Bryophyllum grow to form new plants. (ii) Potato tuber having buds when grown, develops into a new plant.
Q.8. Define (i) Juvenile phase, (ii) Reproductive phase, (iii) Senescent phase.
Ans. (i) It is the pre-reproductive phase in which all organisms require a certain growth and maturity in the life before reproducing sexually.
(ii) Reproductive phase is the phase in the life cycle, where organisms possess all the capacity and potential to reproduce sexually. It is the end of juvenile phase or vegetative phase.
(iii) It is the post-reproductive phase in the life cycle where an organism slowly loses the rate of metabolism, reproductive potential and show deterioration of the physiological activity of the body.
Q. 9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Ans. Higher organisms have resorted to sexual reproduction to (:i) get over the unfavourable condition.
(ii) introduce variation to enable better adaptive capacity, biological tolerance and competitive edge.
(iii) restore high gene pool in a population.
(iv) restore vigour and vitality of the race.
(v) get proper parental care during vulnerable stage.
Q. 10. Explain why meiosis and gametogenesis are always interlinked?
Ans. Gametogenesis (formation of male and females gametes) is associated with reduction in chromosome number thus, the gamete formed contains half chromosome set of the parental cell. So, gametogenesis is interlinked with meiosis because in meiosis, reduction of chromosome number from diploid set (2n) to haploid set (n) takes place.
Q. 11. Identify each part in a flowering plant and write whether it is haploid(n) or diploid (2n).
(a) Ovary (ft) Anther
(c) Egg (d) Pollen
(e) Male gamete (/) Zygote.
Ans. (a) Diploid (2n) (b) Diploid (2n)
(c) Haploid (n) (d) Haploid (n)
(e) Haploid (n) (f) Diploid (2n)
Q. 12. Define external fertilisation. Mention its disadvantages.
Ans. The fusion of compatible gametes outside the body of an organism is called external fertilisation, e.g., in frog. Disadvantages of external fertilisation:
(i) It requires a medium for fusion of gametes.
(ii) The young ones are often exposed to the predators and no parental care is taken. Q.
Q.13. Differentiate between a zoospore and a zygote.
(i) These are endogenously asexually produced unicellular, naked and motile spores having one or two flagella.
(ii) It may be haploid or diploid.
(iii) Zoospore takes part in dispersal.
(i) Zygote is diploid cell formed by fusion of male and female gametes.
(ii) It is always diploid.
(iii) Zygote do not have significant role in dispersal.
Q. 14. Differentiate between gametogenesis from embryogenesis.
(i) The formation of gametes from meiocytes (gamete mother cell).
(ii) This is a pre-fertilisation event.
(iii) The cell division during gametogenesis is meiotic.
(iv) It occurs inside reproductive organs.
(v) It produces haploid gamete.
(i) The formation of embryo from zygote cell.
(ii) This is a post-fertilisation event.
(iii) The cell division during embryogenesis is mitotic.
(iv) It occurs outside or inside the female body.
(v) It gives rise to diploid embryo.
Q. 15. Describe the post-fertilisation changes in a flower.
Ans. The post-fertilisation changes that take place in a flower are as follows:
(i) The formation of zygote (inside ovule) which later develops into an embryo and primary endosperm cell which develops into endosperm (provide nourishment to the growing embryo) takes place.
(ii) While the sepals, petals and stamens are shed, the pistils remain intact.
(iii) The fertilised ovule develops into seeds.
(iv) The ovary matures into a fruit that later develops a thick, protective wall called pericarp.
(v) Seeds after dispersal germinate under favourable conditions which later develop into a new plant.
Q. 16. What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Ans. A flower which possess both the male and female reproductive structures, i.e., both stamen and carpel is called a bisexual flower.
S. No. Common name
(i) China rose
Q. 17. 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. A staminate or male flower has only stamens and no carpel. A pistillate flower has only carpel and no stamens. Plants that bear unisexual flowers are papaya and date palm.
Q. 18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Ans. In viviparous animals, the young one develops inside the body of the female organism. As a result of this, the young one gets better protection and nourishment for proper development.
In case of oviparous animals, they lay egg and the young one develops inside the calcareous shell outside the body of the female.
So, the young ones are not effectively protected and nourished and are vulnerable to predators. So, they are at greater risk as compared to the offsprings of the viviparous animals.