RBSE Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms

Rajasthan Board RBSE Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms Textbook Exercise Questions and Answers.

RBSE Class 12 Biology Solutions Chapter 1 Reproduction in Organisms

RBSE Class 12 Biology Reproduction in Organisms Textbook Questions and Answers

Question 1. 
Why is reproduction essential for organisms?
Answer:
Reproduction ensures the continuity of various species on the earth. It is also essential to introduce variations among the individuals of a species and to maintain and to inherit the genetic constitution or genetic make - up.

Question 2. 
Which is a better mode of reproduction : sexual or asexual? Why?
Answer:
Sexual reproduction is a better mode of reproduction. It allows the formation of new varients by the combination of the genetic material from two different individuals, typically one of each sex. Sexual reproduction involves the fusion of male and female gamete to produce varients, which are not identical to their parents and to themselves. These variations allow the individual to adapt to constantly changing environments. Sexual reproduction also leads to the evolution of better suited organisms which ensure greater survival of a species.

Question 3. 
Why is the offspring formed by asexual reproduction referred to as clone?
Answser:
In the process of asexual reproduction, only one parent is involved and there is no fusion of the male and female gamete. As a result, the offsprings so produced are morphologically and genetically similar to their parents. Therefore, these are called clones.

Question 4. 
Offspring formed due to sexual reproduction have better chance of survival. Why? Is this statement always true?
Answer:
Offspring formed due to sexual reproduction have better chances of survival because they accumulate genetic variations, many of which may be helpful for better adaptation to the environment. Sexual reproduction occurs in adverse conditions in lower organisms, so sexual spores survive in adverse condition. It is not always necessary that the offspring produced by sexual reproduction has better chances of survival. Under some circumstances, asexual reproduction is more advantageous for certain organisms. For instance, some organisms who do not move from one place to another and are well settled in their environment. Also, asexual reproduction is a fast and quick mode of reproduction which does not consume much time and energy as compared to sexual reproduction.

Question 5. 
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Answer:
Since asexual reproduction involves only one parent and offsprings are produced by mitotic cell division. They are genetically identical to the parent, and hence, do not show any variation. While sexual reproduction involves fusion of male and female gametes which are formed meiotically in two different parents, hence, offsprings are genetically different from their parents and among themselves.    

Question 6. 
Distinguish between asexual and sexiial reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Answer:
Difference between Asexual and Sexual Reproduction:

Since vegetative reproduction does not involve meiosis and fusion of ganietes, it is considered as a type of asexual reproduction.

Question 7. 
What is vegetative propagation? Give two suitable examples.
Answer:
Vegetative Propagation: It is a mode of asexual reproduction in which new plants are obtained from the vegetative part (e.g., root, stem, leaves etc.) of plants. Vegetative parts of plants such as rhizome, tubers, runners, corn etc., can be used as propagules for raising new plants.
Examples:

• Vegetative propagation by potato tuber.
• Vegetative propagation by leaves in Bryophyllum.

Question 8. 
Define:
(a) Juvenile Phase.
(b) Reproductive Phase.
(c) Senescent Phase.
Answer:
(a) Juvenile Phase: All organisms reach a certain stage of growth and maturity in their life before they reproduce sexually. This period of growth is known as juvenile phase or vegetative phase.
(b) Reproductive Phase: it is the period when an organism reproduces sexually.
(c) Senescent Phase: It is the period when an organism grows old and loses the ability to reproduce.

Question 9. 
Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Answer:
Most organisms reproduce sexually. Although sexual reproduction involves more time and energy, higher organisms have resorted to sexual reproduction in spite of its complexity. This is because this mode of reproduction helps in introducing new variations in offsprings through the combination of the DNA from two different individuals. These variations allow the individual to cope with various environmental conditions and thus, make the organism better suited for the environment. Variations also lead to the evolution of better organisms and therefore, provide better chances of survival. On the other hand, asexual reproduction does not provide genetic differences in the offsprings produced.

Question 10. 
Explain why meiosis and gametogenesis are always interlinked?
Answer:
Gametogenesis is the formation of both types of gametes i.e., male and female. These are always haploid. A haploid parent produces gametes by mitosis. But in majority of organisms, parent body is diploid. Thus, diploid organisms produce haploid gametes by meiosis. At the end of meiosis, only one set of chromosomes is present in each gamete.

Question 11. 
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
(b) Anther - Diploid
(c) Egg - Haploid
(d) Pollen - Haploid
(e) Malegamete - Haploid
(f) Zygote - Diploid.

Question 12. 
Define external fertilization, mention its disadvantages.
Answer:
External Fertilization: When the fusion of male and female gametes take place outside the body of an organism, it is called external fertilization. 
Disadvantages of External Fertilization:

• It requires a medium for fusion of gametes.
• It is not ensured and there are chance of wastage and distruction of gametes. 
• The young ones are often exposed to predators and no parental care is provided.

Question 13. 
Differentiate between a Zoospore and a Zygote.    
Answer:
Difference between Zoospores and Zygote:

Question 14. 
Differentiate between gametogenesis from embryogenesis.
Answer:
Difference between Gametogenesis and Embryogenesis:

Question 15. 
Describe the post fertilization changes in a  flower.
Answer:
The post fertilization changes that occur in a flower are as follows:

1. The formation of zygote (inside the ovule) which later develop into an embryo and primary endosperm cell which develops into endosperm (provide naurishment to growing embryo) takes place.
2. The sepals, petals and stamens are shed, the pistil remains intact.
3. The ovary matures into a fruit that later develops a thick, protective wall called pericarp.
4. Seeds after dispersal germinate under favourable conditions which later develop into a new plant.

Question 16. 
What is bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names?
Answer:
Bisexual Flower: A flower which has both the essential or reproductive whorls i.e., androecium and gynoecium, is called bisexual flower.
Name of five bisexual flowers:

1. Sarson: Brassica campestris
2. Pea: Pisum sativum
3. Gurhal: Hibiscus rosa - sinensis
4. Kaner: Nerium indicum
5. Neem: Azadirachta indica.

Question 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?
Answer:
Cucurbit plant bears unisexual flowers as these flowers have either the stamen or the pistil. The staminate flowers bear bright, yellow coloured petals along with stamens that represent the male reproductive structure. On the other hand, the pistillate flowers bear only the pistil that represents the female reproductive structure. Other examples of plants that bear unisexual flowers are corn, papaya, cucumber etc.

Question 18. 
Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Answer:
Oviparous animals lay their eggs outside body. As a result, the eggs of these animals are under continuous threat from various environmental conditions. On the other hand, in viviparous animals, the development of the egg takes place inside the body of female. Hence, the offspring of an egg laying or oviparous animal is at greater risk as compared to the offspring of a viviparous animal. Which gives birth to its young ones.