GSEB Class 12 Biology Solutions Chapter 1 Reproduction in Organisms

Question 1. Why is reproduction essential for organisms?
Answer: Reproduction is crucial for a species to maintain its lineage across generations, ensuring continued existence. However, it is not individually required for a single organism's survival.

🎯 Exam Tip: Focus on distinguishing between species survival and individual survival when explaining the essence of reproduction.

Question 2. Which is a better mode of reproduction: sexual or asexual? Why?
Answer: Sexual reproduction is considered superior because it introduces genetic variation and inherited traits during the reproductive process. This variability aids in the development of new species and adaptation to changing environments.

🎯 Exam Tip: When comparing reproductive modes, always emphasize genetic variation as the primary advantage of sexual reproduction.

Question 3. Why is the offspring formed by asexual reproduction referred to as clone?
Answer: Offspring produced through asexual reproduction are described as clones because they are genetically identical and exact replicas of their parent. These individuals, sharing identical genetic and morphological characteristics, are termed clones.

🎯 Exam Tip: Define "clone" clearly by highlighting both genetic and morphological similarity to the parent in asexual reproduction.

Question 4. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Answer: Progeny from asexual reproduction are genetically identical to the parent, exhibiting no variation. In contrast, sexual reproduction introduces genetic structural changes, leading to variation in the offspring. This variation is crucial for organisms to adjust and adapt to environmental shifts.

🎯 Exam Tip: Focus on genetic similarity (asexual) versus genetic variation (sexual) and the adaptive benefits of variation for a comprehensive answer.

Question 5. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Answer:In asexual reproduction, a single parent is capable of producing offspring. Consequently, the resulting progeny are not only identical to each other but also precise copies of the parent.
Sexual reproduction involves the formation and fusion of male and female gametes, which can be from the same individual or different individuals of opposite sexes. The fusion creates a zygote that develops into a new organism. Progeny from sexual reproduction are not identical to their parents.
Vegetative reproduction is regarded as a type of asexual reproduction because it also involves a single individual producing offspring that are genetically identical to one another and to the parent plant.

🎯 Exam Tip: Clearly list the key differences (number of parents, genetic similarity) for asexual and sexual reproduction, then relate vegetative reproduction back to asexual reproduction's core characteristics.

Question 6. What is vegetative propagation? Give two suitable examples.
Answer: Vegetative propagation refers to the process where new plants are regenerated from parts of vegetative organs. This can occur naturally or artificially. Natural vegetative reproduction happens through structures like stems, roots, leaves, and other reproductive organs.
Examples include: Rhizomes (e.g., ginger, banana) and Stem tubers (e.g., potato), Root (e.g., Albizia lebbeck).

🎯 Exam Tip: When defining vegetative propagation, ensure you mention it can be natural or artificial and provide clear, distinct examples for different plant parts.

Question 7. Define a. Juvenile phase b. Reproductive phase c. Senescent phase
Answer:(a) Juvenile phase: This is the period of growth in an organism's life, known as the vegetative phase in plants.
(b) Reproductive phase: This phase is when organisms gain the capacity to produce offspring.
(c) Senescent phase: This is the period during which organisms progressively lose their ability to reproduce offspring.

🎯 Exam Tip: Clearly define each phase by its primary biological characteristic (growth, reproduction, decline in reproduction) to distinguish them effectively.

Question 8. Explain why meiosis and gametogenesis are always interlinked?
Answer: Gametogenesis is the process of producing gametes. Gametes are haploid by nature and are formed from diploid gametic cells. For these diploid cells to produce haploid gametes, they must undergo meiotic division, which reduces the chromosome number by half. This ensures that when two gametes fuse during fertilization, the resulting zygote restores the diploid chromosome number of the species.

🎯 Exam Tip: Emphasize the reduction in chromosome number during meiosis and how this is critical for maintaining species' chromosome count after fertilization.

Question 9. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
Answer:a. Ovary - diploid (2n)
b. Anther - diploid (2n)
c. Egg - haploid (n)
d. Pollen - haploid (n)
e. Male gamete - haploid (n)
f. Zygote - diploid (2n)

🎯 Exam Tip: Remember that gametes and structures directly involved in carrying them (like pollen grains) are haploid (n), while somatic tissues and the zygote are diploid (2n).

Question 10. Define external fertilization. Mention its disadvantages
Answer: External fertilization occurs when the union of an egg and sperm takes place outside the female's body, typically in an aquatic environment. A major disadvantage is the high chance of male gametes being lost during transport in water, which can lead to fertilization failure. Consequently, organisms employing external fertilization often produce thousands more male gametes than female gametes to compensate for these losses.

🎯 Exam Tip: Key points for external fertilization are "outside the body," "water medium," and the significant "risk of gamete loss," necessitating high gamete production.

Question 11. Differentiate between a zoospore and a zygote.
Answer:A zoospore is an asexual, motile spore that uses a flagellum for movement. Also known as a swarm spore, these are produced by certain algae and fungi for multiplication.
A zygote, in contrast, is a diploid cell resulting from fertilization, specifically the fusion of two haploid cells-typically an ovum from a female and a sperm cell from a male-to form a single diploid cell.

🎯 Exam Tip: Clearly state that zoospores are for asexual reproduction and are motile, while zygotes are the product of sexual reproduction (fertilization) and are diploid.

Question 12. Differentiate between gametogenesis from embryogenesis.
Answer:Gametogenesis is the biological process where diploid or haploid precursor cells undergo division and differentiation to produce mature haploid gametes. Depending on the organism's life cycle, gametogenesis involves meiotic division of diploid gametocytes or mitotic division of haploid gametogenous cells. In flowering plants, male gametes form within the pollen grain through the division of a generative cell, and female gametes are produced in the ovule's embryo sac.
Embryogenesis is the process of embryo formation and development. It begins with the fertilization of the ovum, which becomes a zygote. The zygote then undergoes rapid mitotic divisions and cellular differentiation, with little growth, to form a genetically replicated embryo. Plant embryogenesis involves asymmetric cell division and differentiation of undifferentiated cells from a fertilized ovule, leading to a mature embryo during seed development.

🎯 Exam Tip: Highlight that gametogenesis produces reproductive cells (gametes), while embryogenesis involves the development of a multicellular organism (embryo) from a fertilized egg.

Question 13. Describe the post-fertilization changes in a flower.
Answer: Post-fertilization, several changes occur in a flower: the sepals, petals, and stamens wither and detach, while the pistil remains attached. The ovary develops into the fruit, and the ovule matures into the seed. The zygote within the ovule develops into an embryo. After dispersal, these seeds will germinate under favorable conditions to produce new plants.

🎯 Exam Tip: Focus on the transformation of the key floral parts: ovary to fruit, ovule to seed, and zygote to embryo, and the fate of accessory organs.

Question 14. What is a bisexual flower?
Answer: A bisexual flower is one that contains both male and female reproductive organs, specifically both the stamen (male) and the pistil (female).

🎯 Exam Tip: The definition of a bisexual flower should clearly mention the presence of *both* male and female reproductive structures.

GSEB Class 12 Biology Reproduction in Organisms Additional Important Questions and Answers

Question 1. Study the relation of the given pair and fill up the blanks
a. : Hydra : : : Penicillium
b. Algae : Zoospores : : Sponges :
c. Monoecious palm : Coconut : : Dioecious palm :
d. Primates : Menstrual cycle : : Non primates :
e. Unisexual male : Staminate : : Unisexual female :
Answer:a. Conidia
b. Gemmule
c. Date palm
d. Oestrus cycle
e. Pistillate

🎯 Exam Tip: This type of question requires recalling specific examples of reproductive methods (conidia, gemmule) or floral/cycle types (dioecious, oestrus cycle, pistillate) for various organisms.

Question 2. Differentiate between staminate and pistillate flower. Give the term for this condition of flower.
Answer:* The unisexual male flower is called staminate; it bears only the stamen. * The unisexual female flower is called pistillate; it bears only the pistil. * The terms used to describe this condition, where male and female flowers are on separate plants or distinct on the same plant, are heterothallic or dioecious.

🎯 Exam Tip: Clearly define each term based on the presence of either male or female reproductive organs and then provide the botanical term for the overall condition of having separate sexes.

Question 3. In sexually reproducing organisms during reproduction, male gametes are produced in huge numbers. Why?
Answer: In nearly all organisms, female gametes are stationary, while male gametes are mobile. Male gametes must navigate a medium to reach the female gametes. A significant proportion of them fail to reach their destination. To offset this considerable loss during transport, male gametes are produced in numbers several thousand times greater than female gametes.

🎯 Exam Tip: Highlight the motility of male gametes, the stationary nature of female gametes, and the high attrition rate of male gametes as reasons for their mass production.

Question 4. The cyclical changes in the ovaries of female placental mammals during the reproductive phase differ in primates and nonprimates.
a. What is this cycle called in primates and nonprimates respectively?
b. Distinguish between seasonal and continuous breeders.
Answer:a. In primates, this cycle is known as the menstrual cycle, whereas in nonprimates, it is called the oestrus cycle.
b. Many mammals in natural environments exhibit reproductive cycles only during specific favorable seasons; these are termed seasonal breeders. In contrast, continuous breeders are reproductively active throughout their entire reproductive phase.

🎯 Exam Tip: Remember the specific names for the cycles in primates (menstrual) and nonprimates (oestrus). For breeders, focus on whether reproduction occurs only during specific seasons or continuously.

Question 5. Harish observed two different types of papaya plants in his garden. One produced male flowers only and the other type produced female flowers as well as fruits.
a. What are these types of plants called in which male and female flowers seen separately?
b. Name another plant with the same feature.
c. If both male and female flowers are seen separately in the same plant, what do you call them? Give examples.
Answer:a. Dioecious
b. Date palm
c. Monoecious, e.g. Coconut, cucurbits

🎯 Exam Tip: Distinguish clearly between dioecious (male and female flowers on different plants) and monoecious (male and female flowers on the same plant, but separate) and provide relevant examples for each.

Question 6. In the animal world, some organisms have both male and female reproductive organs.
a. What do you call such organisms?
b. Give two examples.
Answer:a. Hermaphrodites
b. Earthworm, sponges etc.

🎯 Exam Tip: The key term is "hermaphrodites" for organisms possessing both reproductive systems; provide distinct animal examples.

Question 7. In Fishes as well as amphibians where does syngamy occur. What type of fertilization occurs.
Answer: In lower animals such as fishes and amphibians, syngamy takes place outside the body, specifically in water media. Therefore, this type of fertilization is classified as external fertilization.

🎯 Exam Tip: Remember that syngamy outside the body, particularly in aquatic environments, defines external fertilization.

Question 8. Syngamy is the fusion of gametes to produce zygotes. But in some organisms like rotifers, honey bees and even some lizards, syngamy doesn't occur. Then how do these organisms produce young ones? Name the phenomenon.
Answer: In these organisms, the female gamete develops into a new organism without undergoing fertilization. This phenomenon is known as parthenogenesis.

🎯 Exam Tip: The absence of syngamy coupled with offspring development from an unfertilized egg is the hallmark of parthenogenesis.

Question 9. a. Differentiate oviparous and viviparous with examples. b. In which of these two types, is the chances of survival of young ones, greater? Why?
Answer:a. Oviparous animals lay eggs, typically covered by a hard calcareous shell, in a safe location. After a period of incubation, these eggs hatch into young ones. Examples include reptiles and birds.
Viviparous animals retain the fertilization product-the zygote-within the female's body. After reaching a specific stage of growth, the young ones are delivered from the body. An example is human beings.
b. The chances of survival for young ones are greater in viviparous organisms. This is due to the extensive embryonic care and protection provided inside the mother's body.

🎯 Exam Tip: Clearly state where development occurs (outside vs. inside the body) for each type, and link internal development directly to increased embryonic care and protection for better survival rates.

Question 10. Match the following asexual reproductive methods or structures with the respective organisms.

🎯 Exam Tip: Memorize the common examples of organisms and their corresponding asexual reproductive strategies for accurate matching.

Question 11. Why do internodal segments of sugarcane fail to propagate vegetatively even when they are in contact with damp soil?
Answer: Internodal segments of sugarcane fail to propagate vegetatively because they lack the initial cells or buds necessary for producing roots and shoots.

🎯 Exam Tip: The key reason for propagation failure in internodal segments is the absence of meristematic tissue or buds, which are crucial for initiating new growth.

Question 2. Draw a labelled diagram for asexual reproduction in the following.
i. Budding in yeast
ii. Binary fission in amoeba.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र यीस्ट में मुकुलन (Budding) और अमीबा में द्विखंडन (Binary fission) द्वारा अलैंगिक जनन की प्रक्रिया को दर्शाता है। यीस्ट में, एक छोटा उभार (मुकुल) मूल कोशिका से विकसित होता है और अंततः एक नई बेटी कोशिका बनाता है। अमीबा में, कोशिका का केंद्रक और फिर साइटोप्लाज्म दो भागों में विभाजित हो जाता है, जिससे दो नई बेटी अमीबा कोशिकाएँ बनती हैं।

🎯 Exam Tip: For diagrams, ensure clear labeling of key structures like nucleus, parent cell, daughter cell, bud for yeast, and the division process for amoeba.

Question 3. What is a bulbil?
Answer: A bulbil is a modified branch or offshoot that detaches from the parent plant. When it falls onto suitable soil, it can grow into a new, independent plant. Agave is an example of a plant that produces bulbils.

🎯 Exam Tip: Define bulbil as a vegetative propagule, highlighting its ability to detach and grow into a new plant, and provide Agave as a classic example.