Reproduction In Organisms Class 12th Biology CBSE Solution

Class 12th Biology CBSE Solution

Exercises
Question 1.

Why is reproduction essential for organism?


Answer:

Reproduction is essential for the organism because-

1) It enables the continuity of species on the earth.

2) It helps in the transfer of gene characteristics from one generation to another.


Question 2.

Which is a better mode of reproduction: sexual or asexual? Why?


Answer:

In Sexual reproduction new individuals produced after cell division exhibit variation. Variations increase the adaptability of an organism to its changing environmental conditions whereas asexual reproduction does not bring about variations in offspring, therefore sexual reproduction is better mode of reproduction.



Question 3.

Why is the offspring formed by asexual reproduction referred to as clone?


Answer:

Offspring formed by asexual reproduction are always morphologically and genetically identical because they have the same gene as their parent, therefore referred to as clone.



Question 4.

Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?


Answer:

Yes, this statement is always true.

Explanation: Offspring formed due to sexual reproduction have better chances of survival because sexual reproduction exhibit variations and these variations are important for survival of species. Offspring which do not exhibit variations and are exact copies of their parent (as in asexual reproduction) occupy the same niche or place in the ecosystem. The populations tends to get wiped out if this area gets altered due to natural or manmade causes. However under such conditions individuals with variations can colonise other habitats and survive.



Question 5.

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


Answer:

The progeny formed from asexual reproduction is always morphologically and genetically identical or clone to their parents since they possess exact copies of DNA of their parent whereas in sexual reproduction DNA copying is accompanied by creation of new cellular apparatus. The cell divides and produces new cells, which exhibits variations. So, differences are found in morphological and physiological features of progeny as DNA copies generated during sexual reproduction are similar but not identical.



Question 6.

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


Answer:



Vegetative reproduction is also considered as asexual reproduction because in this type of reproduction also new plants are formed from vegetative cells and it does not involve fusion of gametes. The new plants can be formed from root, stem or leaves.



Question 7.

What is vegetative propagation? Give two suitable examples.


Answer:

Vegetative propagation is formation of new plant from vegetative parts or propagules of the parent .e.g.

1. Stem tubers develop new plants in the region of eyes. e.g. potato


2. Tap root branches develop adventitious buds and form new plants. E.g. Guava



Question 8.

Define

Juvenile phase,


Answer:

Juvenile phase- also called vegetative phase. It is the period of growth in an organism after its birth and before it reaches reproductive maturity. This phase is of different duration in different organisms.



Question 9.

Define

Reproductive phase,


Answer:

Reproductive phase- also known as maturity phaseor puberty, as reproductive structures mature during this phase. It is a period when an organism reproduces sexually.



Question 10.

Define

Senescent phase.


Answer:

Senescent phase-This is the last phase of life span and ultimately leads to death. It is the period when an organism loses the ability to reproduce and grows old.



Question 11.

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


Answer:

Higher organisms have resorted to sexual reproduction in spite of its complexity because sexual reproduction exhibits variations and these variations lead to evolution of better organisms and thus provides better chances of survival.



Question 12.

Explain why meiosis and gametogenesis are always interlinked?


Answer:

Meiosis is also known as reduction division as the amount of genetic material is reduced to half in this division. Formation of gametes involves meiosis as gametes produced by organisms are haploid i.e. having only one set of chromosomes, and formation of gametes is called gametogenesis. Therefore, meiosis and gametogenesis are always interlinked.



Question 13.

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

(a) Ovary ———————————

(b) Anther ———————————

(c) Egg ———————————

(d) Pollen ———————————

(e) Male gamete ———————————

(f) Zygote ———————————


Answer:

(a) Ovary —diploid (2 n)


(b) Anther —diploid (2n)


(c) Egg —haploid ( n)


(d) Pollen —haploid ( n)


(e) Male gamete —haploid (n)


(f) Zygote —diploid (2n)


Explanation: Since ovary & anther undergoes only mitotic divisions during their development in which chromosome number remains the same, so these structures are diploid. The zygote is formed by the fusion of both male and female gametes (haploid structures) .So, when two haploid structures fuse the resultant is a diploid structure i.e.zygote.


Egg, pollen, male gamete undergoes meiosis during their development, which reduces the chromosome number to half , hence these are haploid structures.



Question 14.

Define external fertilisation. Mention its disadvantages.


Answer:

External fertilization is the process in which fusion of male and female gametes takes place in external medium i.e. outside the female body. It mainly occurs in water animals for e.g. Frog, fish etc.

Disadvantages of external fertilization- External fertilization leads to wastage of large number of eggs , so eggs has less chance of fertilization.



Question 15.

Differentiate between a zoospore and a zygote.


Answer:




Question 16.

Differentiate between gametogenesis from embryogenesis.


Answer:




Question 17.

Describe the post-fertilisation changes in a flower.


Answer:

In post- fertilization changes the zygote divides many times and forms an embryo within the embryo. The ovule gets converted into seed and develops a tough coat. Ovary ripens as fruit and embryo develops into a seedling during germination.



Question 18.

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.


Answer:

Plants having both male and female reproductive organs in the same flower are called bisexual flowers.

E.g. Hibiscus –Rosa sinensis


Mustard- Brassica campestris


Sunflower-Helianthus annus


Lily- Lilium candidum


Pea- Pisum sativum



Question 19.

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?


Answer:

A staminate flower is a male flower as it bears only stamens whereas a pistillate flower is a female flower as it bears only pistils.


Staminate flower Pistillate flower

E.g. Of plants bearing unisexual flowers- Papaya, cucumber, watermelon, maize etc.


Question 20.

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


Answer:

Oviparous animals lay eggs outside the body so they are under continuous threat of various environmental conditions and predators whereas in viviparous animals development of young ones takes place inside the body where they're protected and have constant nutrition avaliable to them. Therefore, offspring of oviparous animals are at a greater risk as compared to viviparous animals.


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