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18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?

Oviparous organisms are those organisms which lay fertilised or unfertilised eggs whereas viviparous organisms are the ones that give birth to young ones. The offsprings of oviparous animals are considered to be at a greater risk as compared to offsprings of viviparous animals because of the following reasons: 1. In oviparous animals, the development of offsprings occurs outside the body of the...

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?

 

Cucurbits bear unisexual flowers. These type of flowers bear either male or female reproductive organs. It means that a staminate flower bears only stamen i.e. male reproductive organ while pistillate flower contains only pistil i.e. female reproductive organ. So you can identify staminate and pistillate flowers on the basis of the presence of male and female parts respectively. Another example...

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.

Bisexual flowers are those flowers which possess both male and female reproductive parts i.e. stamen and pistil respectively. Some of the common bisexual flowers that you will be able to collect in your neighbourhood are given below: Common name  Scientific name  Rose Rosa indica Sadabahar                Catharanthus roseus China rose  Hibiscus rosa-sinensis Tulsi Ocimum sanctum  

15. Describe the post-fertilisation changes in a flower.

The post fertilisation changes that occur in a flower are as follows:  1. Formation of zygote occurs in the ovule. zygote further develops into an embryo. 2. The ovary develops into the fruit while the ovary wall develops into pericarp. 3. Ovules develop into seeds 4. Sepals, petals and stamens wither and fall off while pistils remain attached to the plant.  

14. Differentiate between gametogenesis from embryogenesis.

Differentiation between gametogenesis and embryogenesis is as follows: Gametogenesis        Embryogenesis The process of formation of gametes is called gametogenesis The process of formation of the embryo is called embryogenesis This process involves meiotic divisions that lead to the formation of gametes This process involves mitotic division that leads to the development of a zygote...

13. Differentiate between a zoospore and a zygote.

  The differences between zoospore and zygote are as follows:      Zoospore            Zygote  It is an asexual reproductive body  It is the result of sexual reproduction Zoospores contain flagella, so they are motile The zygote does not contain flagella, so it is non-motile  Zoospores can be haploid in some organisms and diploid in some others A zygote is formed as a result...

12. Define external fertilisation. Mention its disadvantages.

External fertilisation refers to the fusion of male and female gametes outside the body of the organism. The disadvantages of external fertilisation are as follows: 1. External fertilisation requires an aquatic medium 2. Offsprings produced are highly vulnerable to predators 3. Parental care is not provided to offsprings

11. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).

    (f ) Zygote

Diploid (2n) A zygote is formed after fertilisation of male and female gametes which are haploid (n). Thus, zygote is diploid (2n).

11. Identify each part in a flowering plant and write whether it is haploid
(n) or diploid (2n).

    (e) Male gamete    _______________

Haploid (n) Male gametes in plants are formed by mitosis in pollen grain which is a haploid structure. Thus, male gametes are haploid (n). 

11. Identify each part in a flowering plant and write whether it is haploid
(n) or diploid (2n).

    (d) Pollen     _____________________

Haploid (n) Pollen grains are haploid i.e. they contain one set of chromosomes

11. Identify each part in a flowering plant and write whether it is haploid
(n) or diploid (2n).

    (c) Egg    __________________

 

 

11. Identify each part in a flowering plant and write whether it is haploid
(n) or diploid (2n).

    (b) Anther ______________

Diploid (2n) The anther is the male reproductive part of a flower. It is diploid (2n) i.e. it consists of 2 sets of chromosomes.   

11. Identify each part in a flowering plant and write whether it is haploid
(n) or diploid (2n).
    (a) Ovary ________________

Diploid (2n) The ovary is the part of the flower and its ploidy is 2n.  

10. Explain why meiosis and gametogenesis are always interlinked?

 

Meiosis refers to the cell division which causes a reduction in the number of chromosomes by half and gametogenesis is the formation of male and female gametes. These two terms are often interlinked because gamete formation in diploid organisms occurs through meiosis only. The number of chromosomes in diploid organisms must be reduced to half because if this doesn't happen then the zygote after...

9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?

Higher organisms have resorted to sexual reproduction because sexual reproduction enables these organisms to survive during unfavourable conditions. It tends to induce genetic variability in these organisms which further becomes a cause of the evolution of better-adapted species.     

8. Define

    (c) Senescent phase.

Senescent phase refers to the post-reproductive phase in which an organism not just loses its reproductive potential but also the rate of metabolism slows down and there is deterioration of vital activities of the body. 

8. Define

    (b) Reproductive phase

Reproductive phase refers to that phase of an organisms' life cycle in which it attains reproductive maturity and become able to produce gametes and mate. This phase is marked by certain hormonal changes. 

8. Define
    (a) Juvenile phase,

All organisms have to reach a particular growth stage before they attain reproductive maturity. This pre-reproductive period of growth is called juvenile phase in animals. In plants, this phase is known as the vegetative phase. The duration of the juvenile phase varies in different organisms.   

7. What is vegetative propagation? Give two suitable examples.

Vegetative propagation is a method of asexual reproduction in plants. In this method, a vegetative part of a plant gives rise to new plants. This vegetative part which has the ability to produce new plants is called vegetative propagule. Some common vegetative propagules are runner, rhizome, sucker, tuber, offset, bulb etc. Vegetative propagation is of two types i.e. natural vegetative...

6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?

 Differences between sexual and asexual reproduction are as follows:         Asexual reproduction         Sexual reproduction  It involves a single parent  It involves two parents There is no requirement of sex organs and gametes Gamete formation occurs in sex organs It involves somatic cells of the body it involves germ cells of the body Offsprings produced in asexual reproduction...
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