NCERT Solutions for Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants
Here are the NCERT Solutions for Class 12 Biology Chapter 1 titled Sexual Reproduction in Flowering Plants:
1. Name the parts of an angiosperm flower in which the development of male and female gametophytes take place.
Answer:
In an angiosperm flower, the male gametophytes develop inside the anthers, while the female gametophytes develop inside the ovules.
2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Answer:
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Microsporogenesis
: This process occurs in the anthers, where a diploid microspore mother cell undergoes meiosis to form haploid microspores. This results in the formation of pollen grains.
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Megasporogenesis
: This process occurs in the ovules, where a diploid megaspore mother cell undergoes meiosis to produce haploid megaspores. Only one of the four megaspores formed is functional, giving rise to the embryo sac.
Both processes involve meiosis, which is a type of cell division that reduces the chromosome number by half.
Structures formed
:
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Microsporogenesis: Pollen grain
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Megasporogenesis: Embryo sac
3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Answer:
The correct developmental sequence is:
Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes.
The process begins with the sporogenous tissue, which gives rise to pollen mother cells. These cells divide and form microspore tetrads. The tetrads separate to form individual pollen grains, which later mature to produce male gametes.
4. What is meant by monosporic development of female gametophyte?
Answer:
Monosporic development refers to the formation of a female gametophyte from a single functional megaspore. After meiosis, four megaspores are produced, but only one of them remains functional and develops into the female gametophyte, while the other three degenerate.
5. With a neat diagram, explain the 7-celled, 8-nucleate nature of the female gametophyte.
Answer:
The development of a 7-celled, 8-nucleate female gametophyte occurs as follows:
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After the first mitotic division of the megaspore, two nuclei form and migrate to opposite ends.
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These nuclei undergo further divisions to produce a total of eight nuclei, four at each end.
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At the micropylar end, three of these nuclei differentiate into the egg cell and two synergids.
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At the chalazal end, three nuclei differentiate into antipodal cells.
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The remaining two nuclei from each end form the polar nuclei at the center.
Thus, the female gametophyte consists of seven cells and eight nuclei.
6. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Answer:
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Chasmogamous flowers
are flowers that are open and expose their reproductive organs, allowing cross-pollination.
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Cleistogamous flowers
, on the other hand, are small and closed with unexposed reproductive organs, preventing cross-pollination. These flowers typically undergo self-pollination because the stigma and anther are in close proximity to each other.
7. Mention two strategies evolved to prevent self-pollination in flowers.
Answer:
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Dichogamy
: This occurs when the male and female reproductive organs mature at different times, preventing self-fertilization.
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Self-incompatibility
: A genetically controlled mechanism where the pollen from the same flower is unable to fertilize its own ovule.
8. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer:
Self-incompatibility is a genetic mechanism that prevents self-pollination, ensuring cross-pollination. In self-incompatible species, the pollen from the same flower cannot fertilize its own ovule, so no seed formation occurs.
9. What is the bagging technique? How is it helpful in a plant breeding programme?
Answer:
The bagging technique involves covering a flower with a protective bag to prevent unwanted pollen from reaching the stigma. This ensures that only the desired pollen fertilizes the flower. It is useful in plant breeding as it helps control pollination and ensures that only specific traits are passed on to the next generation.
10. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer:
Triple fusion is the fusion of one male gamete with two polar nuclei in the central cell of the embryo sac. This occurs after the pollen tube enters the ovule and releases two male gametes. One male gamete fertilizes the egg cell, forming the zygote, while the other fuses with the two polar nuclei to form the triploid endosperm. The nuclei involved in triple fusion are:
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One male gamete nucleus
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Two polar nuclei
11. Why do you think a zygote is dormant for some time in a fertilized ovule?
Answer:
The zygote remains dormant temporarily because the endosperm, which provides nutrients to the developing embryo, must first form through triple fusion. The endosperm nourishes the zygote until it is ready to develop into a mature embryo.
12. Differentiate between the following pairs:
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Epicotyl and hypocotyl
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Coleoptile and coleorrhiza
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Integument and testa
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Perisperm and pericarp
Answer:
Epicotyl vs. Hypocotyl
:
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Epicotyl
is the part of the embryo above the cotyledons and becomes the upper part of the stem.
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Hypocotyl
is below the cotyledons and develops into the part of the stem that forms the roots.
Coleoptile vs. Coleorrhiza
:
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Coleoptile
is a protective sheath that covers the plumule (young shoot) in grasses.
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Coleorrhiza
is a protective sheath that surrounds the radical (young root) in grasses.
Integument vs. Testa
:
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Integument
is the outer covering of the ovule before fertilization.
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Testa
is the seed coat formed after fertilization, providing protection to the seed.
Perisperm vs. Pericarp
:
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Perisperm
is the part of the seed that provides nutrition, derived from the nucellus.
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Pericarp
is the part of the fruit that surrounds the seed and protects it.
13. Why is an apple called a false fruit? Which part of the flower forms the fruit?
Answer:
An apple is called a false fruit because it is derived from the thalamus (a part of the flower) rather than just the ovary. The fruit is formed from the thalamus and the ovary.
14. What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer:
Emasculation is the removal of stamens from bisexual flowers before the anther matures. Plant breeders use this technique to prevent self-pollination and ensure that only desired pollen fertilizes the flowers, thereby controlling the traits of the offspring.
15. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer:
Fruits like watermelon and muskmelon, which are usually seedless, would be ideal candidates for inducing parthenocarpy. This is because seedless fruits are in high demand, and parthenocarpy would allow for the production of such fruits without fertilization.
16. Explain the role of tapetum in the formation of pollen grain walls.
Answer:
The tapetum is the inner layer of the microsporangium that provides nutrition to developing pollen grains. It helps in the formation of the exine layer of the pollen grain, which is important for its protection and structural integrity. The tapetum also produces essential proteins, enzymes, and hormones needed for pollen maturation.
17. What is apomixis and what is its importance?
Answer:
Apomixis is the process where seeds form without fertilization. This process is useful in plant breeding because it allows for the production of hybrid seeds without the need for sexual reproduction. Apomixis ensures that hybrid characteristics are retained, making seed production more cost-effective.
Benefits of Solving NCERT Solutions for Class 12 Biology Chapter 1
Solving NCERT Solutions for Class 12 Biology Chapter 1 on Sexual Reproduction in Flowering Plants provide several key benefits that can significantly enhance students understanding and performance. Here are the benefits:
1.
Comprehensive Understanding of Sexual Reproduction
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The chapter focuses on the process of sexual reproduction in flowering plants, covering key aspects like the structure of flowers, formation of gametes, pollination, fertilization, and seed development. Solving NCERT solutions helps students thoroughly understand these processes step by step.
2.
Clear Explanation of Key Concepts
-
Concepts such as
anthers, stigma, style, ovary, ovules, pollination, fertilization, and double fertilization
are explained clearly in the NCERT solutions. This helps students grasp the underlying biological principles and their significance in plant reproduction.
3.
Boosting Problem-Solving Skills
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The NCERT solutions provide a wide range of problems, from basic to advanced, which encourage critical thinking and problem-solving. By solving these questions students improve their analytical skills and ability to answer both theoretical and application-based questions in exams.
5.
Clear Understanding of Pollination Mechanisms
-
The chapter discusses different types of pollination such as
self-pollination
and
cross-pollination
, along with the factors influencing them. The NCERT solutions help clarify these concepts, which are important for understanding how plants reproduce and the role of pollinators in nature.
6.
Preparation for Higher Studies
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A solid understanding of sexual reproduction in flowering plants is essential for more advanced topics in biology, such as genetics, plant breeding, and agricultural science. These solutions lay the groundwork for more complex subjects that students will encounter in higher education.
7.
Strengthens Understanding of Fertilization and Seed Formation
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The solutions guide students through the detailed process of fertilization, including
double fertilization
, which is unique to angiosperms. Understanding this process is crucial for understanding plant growth, seed development, and genetic inheritance.
8.
Improves Retention through Practice
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Solving various types of questions and referring to the NCERT solutions repeatedly helps students retain information. The solutions reinforce important concepts, ensuring that students are able to recall key processes when needed.
9.
Reduces Doubts and Confusion
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Students often have doubts regarding complex processes like fertilization and gametogenesis in plants. By practicing with NCERT solutions they can clarify these doubts, ensuring a clear understanding of the topic and better conceptual clarity.
10.
Time Management and Efficient Learning
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NCERT solutions help students focus on the most important aspects of the chapter, which aids in better time management. By practicing with these solutions, students can cover the entire chapter efficiently, allowing for ample time for revision and preparation.
11.
Increases Confidence in Answering Exam Questions
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Regular practice with NCERT solutions builds confidence in students. As they become more familiar with the question formats and the required answers, they will feel more prepared and confident during their exams.
