GSEB Class 12 Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 1. Name the parts of an angiosperm flower in which development of male and female gametophyte takes place.
Answer: The development of the male gametophyte initiates from the pollen grain. Following pollination, these pollen grains germinate, giving rise to male gametes or sperms. The female gametophyte, also known as the embryo sac, develops within the ovule, specifically inside the nucellus.
In simple words: Male gametophytes develop from pollen grains, which produce sperm after germination. Female gametophytes (embryo sacs) form inside the ovules within the flower's nucellus.

🎯 Exam Tip: Understanding the precise locations for gametophyte development (pollen grain for male, ovule/nucellus for female) is crucial for describing angiosperm reproduction accurately in exams.

Question 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:

Microsporogenesis	Megasporogenesis
1. This process involves the formation of microspores from the pollen mother cell through meiotic division.	1. This process involves the formation of megaspores from the megaspore mother cell through meiotic division.
2. Pollen grains are the structures produced at the completion of this event. It occurs within the anther's pollen sac.	2. An egg cell is formed inside the embryo sac at the completion of this event.

Both microsporogenesis and megasporogenesis involve **meiosis** (reductional division).
At the end of microsporogenesis, **pollen grains** are formed.
At the end of megasporogenesis, the **egg cell** (within the embryo sac) is formed.
In simple words: Microsporogenesis creates pollen grains from pollen mother cells in the anther, while megasporogenesis creates an egg cell from a megaspore mother cell in the ovule. Both processes use meiosis.

🎯 Exam Tip: Clearly distinguishing between these two processes, especially the cell division type (meiosis) and the final products (pollen grains vs. egg), is vital for high scores.

Question 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, and male gametes.
In simple words: The process starts with sporogenous tissue, which forms pollen mother cells, then microspore tetrads, leading to pollen grains, and finally male gametes.

🎯 Exam Tip: Remember this sequence as it outlines the key stages of male gametophyte development in angiosperms, a common conceptual question.

Question 4. What is meant by monosporic development of female gametophyte?
Answer: Monosporic development of the female gametophyte refers to the process where only one functional megaspore, out of the four formed in a megaspore tetrad, contributes to the development of the entire female gametophyte or embryo sac.
In simple words: Monosporic development means the female gametophyte (embryo sac) forms from just one single megaspore, even though a tetrad of four megaspores is initially produced.

🎯 Exam Tip: Focus on the "mono" aspect – a single functional megaspore is the defining characteristic of this development type.

Question 5. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Answer: Chasmogamous flowers are those with exposed anthers and stigmas, similar to the typical flowers of many plant species, allowing for easy access for pollinating agents. Examples include Oxalis and Viola.
Cross-pollination cannot occur in cleistogamous flowers. This is because cleistogamous flowers never open, keeping their anthers and stigmas enclosed and in close proximity to each other. Consequently, only self-pollination is possible in these flowers.
In simple words: Chasmogamous flowers are open and exposed, while cleistogamous flowers remain closed. Cross-pollination cannot happen in cleistogamous flowers because they never open, ensuring only self-pollination.

🎯 Exam Tip: Differentiate chasmogamous (open) from cleistogamous (closed) flowers. For cleistogamous flowers, remember that their closed nature prevents cross-pollination and guarantees self-pollination.

Question 6. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule. Arts, Antipodals
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक विशिष्ट एंजियोस्पर्म ओव्यूल (बीजांड) की अनुदैर्ध्य काट को दर्शाता है। इसमें विभिन्न भागों को दर्शाया गया है जैसे चलाजा, न्यूसेलस, भ्रूणकोष (एंब्रियो सैक), बीजांडकाय (इंटेगुमेंट), हाइलम, फ्यूनिकुलस, माइक्रोपाइल, सहायक कोशिकाएँ (सिनर्जिड), अंडकोशिका (एग), और द्विगुणित द्वितीयक केंद्रक। यह एंजियोस्पर्म में मादा युग्मकोद्भिद के विकास को समझने के लिए आवश्यक है। The Pistil, Megasporangium (ovule), and Embryo sac:
The gynoecium represents the female reproductive whorl of the flower, comprised of carpels. Each carpel is typically composed of three parts: the ovary, style, and stigma.
The pistil constitutes the female reproductive component of the flower. If the ovary is formed by a single carpel, it is termed monocarpellary. If it comprises two carpels, it is bicarpellary, and if it has more than two carpels, it is multicarpellary. When carpels are fused, the pistil is syncarpous; if they remain free, it is apocarpous.
The Megasporangium or ovule:
The ovule is a small, oval-shaped structure that attaches to the placenta via a short stalk called the funicle or funiculus. The point where the funiculus connects to the ovule body is termed the hilum. Inside the ovule, the parenchymatous tissue is known as the nucellus, which is enveloped by one or two protective layers called integuments. These integuments leave a small opening at the apex, known as the micropyle.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मादा युग्मकोद्भिद के विकास की विभिन्न अवस्थाओं को दर्शाता है। इसमें मेगास्पोर मदर सेल से लेकर कार्यात्मक मेगास्पोर और फिर पतित मेगास्पोर बनने की प्रक्रिया दिखाई गई है, साथ ही अंत में एक पूर्ण विकसित भ्रूणकोष को भी दर्शाया गया है जिसमें अंडकोशिका, सहायक कोशिकाएँ, द्वितीयक केंद्रक और प्रतिध्रुवी कोशिकाएँ (एंटीपोडल्स) शामिल हैं। यह मादा युग्मकोद्भिद के गठन के चरणों को स्पष्ट करता है। The basal region of the ovule, from which the integuments originate, is termed the chalaza. Within the nucellus, the embryo sac (female gametophyte) is observed. The embryo sac typically contains eight nuclei: three at the micropylar end forming the egg apparatus (consisting of a central egg cell and two synergids), and three cells at the chalazal end forming antipodals. A diploid secondary nucleus is situated in the center of the embryo sac. P. Maheswari, known as the father of angiosperm embryology in India, categorized the female gametophyte of flowering plants into three primary types based on the number of megaspore nuclei involved in development: monosporic, bisporic, and tetrasporic embryo sacs.
Typically, a single hypodermal nucellar cell, designated as the primary archesporial cell, differentiates at the apex, beneath the epidermis. This primary archesporial cell undergoes periclinal division, forming an outer parietal (wall) cell and an inner primary sporogenous cell. The primary sporogenous cell then directly functions as a single megaspore mother cell.
The diploid spore mother cell typically undergoes reduction division (meiosis), leading to the formation of four megaspores arranged in a linear tetrad. The process of megaspore formation from the megaspore mother cell is termed megasporogenesis. Of these four megaspores, the three upper megaspores at the micropylar end degenerate and disappear. The remaining megaspore, located at the chalazal end, becomes functional. It significantly enlarges and absorbs nutrients from the nucellus, forming the female gametophyte or embryo sac.
The haploid nucleus undergoes three successive mitotic divisions, resulting in an eight-nucleate female gametophyte or embryo sac. The female gametophyte is commonly of the 8-nucleate type, comprising one egg cell, two synergids, and three antipodals. If the embryo sac develops from a single uninucleate megaspore, it is known as monosporic embryo sac development (polygonal type).
After the first division, the two daughter nuclei migrate towards the opposing poles of the cell. These nuclei then undergo two more successive divisions, resulting in eight nuclei – four at the micropylar end and four at the chalazal end. One nucleus from each pole moves to the center (polar nuclei) and fuses to form a single diploid secondary nucleus.
The three cells at the micropylar end of the embryo sac subsequently form the egg apparatus, which consists of a central large egg cell and two synergids. The three cells at the chalazal end form the antipodals. A fully developed embryo sac, along with the nucellus, integuments, and funiculus, collectively constitutes a mature ovule.
In simple words: An angiosperm ovule is a small structure with a stalk (funiculus), a protective covering (integuments), and internal nutritive tissue (nucellus) containing the embryo sac. The pistil is the female part, comprising ovary, style, and stigma, and can be monocarpellary (one carpel) or multicarpellary (multiple carpels, fused or free). The female gametophyte develops from one megaspore inside the ovule, eventually forming an 8-nucleate, 7-celled embryo sac with an egg, synergids, antipodals, and a central diploid nucleus.

🎯 Exam Tip: For ovule structure, practice drawing and labeling the main parts (funiculus, hilum, integuments, micropyle, chalaza, nucellus, embryo sac). For the pistil, remember the terms monocarpellary, bicarpellary, multicarpellary, syncarpous, and apocarpous, and their definitions.

Question 7. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक परिपक्व मादा युग्मकोद्भिद (भ्रूणकोष) की संरचना को दर्शाता है, जिसमें 7 कोशिकाएं और 8 केंद्रक होते हैं। इसमें माइक्रोपाइल छोर पर एक अंडकोशिका और दो सहायक कोशिकाएँ (जिनमें फ़िलिफॉर्म उपकरण होते हैं) दिखाई गई हैं। चलाजा छोर पर तीन प्रतिध्रुवी कोशिकाएँ (एंटीपोडल्स) हैं, और केंद्र में एक बड़ी केंद्रीय कोशिका है जिसमें दो ध्रुवीय केंद्रक (पोलर न्यूक्लियाई) होते हैं। यह मादा युग्मकोद्भिद की विशिष्ट संरचना को समझाता है जो निषेचन में महत्वपूर्ण भूमिका निभाती है। The haploid nucleus undergoes three successive mitotic divisions, leading to the formation of an eight-nucleate female gametophyte or embryo sac. Typically, the female gametophyte is an 8-nucleate type, consisting of one egg cell, two synergids, and three antipodals. If the embryo sac develops from a single uninucleate megaspore, it is known as monosporic embryo sac development (polygonal type).
After the first division, the two daughter nuclei migrate towards the opposite poles of the cell. These nuclei then undergo two more successive divisions, resulting in eight nuclei – four at the micropylar end and four at the chalazal end. One nucleus from each pole moves to the center (polar nuclei) and fuses to form a single diploid secondary nucleus.
The three cells at the micropylar end of the embryo sac then form the egg apparatus, which comprises a central large egg cell and two synergids. The three cells at the chalazal end form the antipodals. A fully developed embryo sac, including the nucellus, integuments, and funiculus, collectively constitutes a mature ovule.
The synergids have specialized cellular thickenings called the filiform apparatus at the micropylar tip.
In simple words: A mature female gametophyte (embryo sac) has 7 cells and 8 nuclei: an egg cell and two synergids at one end, three antipodal cells at the other, and a large central cell with two polar nuclei.

🎯 Exam Tip: Focus on accurately drawing and labeling the 7-celled, 8-nucleate embryo sac. Remember the location and function of each cell type: egg, synergids (with filiform apparatus), polar nuclei (central cell), and antipodals.

Question 8. Mention two strategies evolved to prevent self-pollination in flowers.
Answer: Two strategies that have evolved to prevent self-pollination in flowers are:
1. Dichogamy: This refers to the asynchronous maturation of anther and stigma within the same flower. This ensures that pollen is released either before or after the stigma becomes receptive, thus making self-pollination unlikely in bisexual flowers.
2. Dicliny (Unisexuality): In this condition, stamens and carpels are located in different flowers. If a plant has only male or only female flowers (dioecious), self-pollination is impossible. If both male and female flowers are on the same plant but separate (monoecious), geitonogamy (pollination between flowers on the same plant) may occur, but autogamy (self-pollination within the same flower) is prevented.
3. Self-sterility (Self-incompatibility): The pollen grains from a bisexual flower are unable to germinate or grow on the stigma of the same flower, due to genetic barriers.
In simple words: Flowers prevent self-pollination by having anthers and stigmas mature at different times (dichogamy), by having separate male and female flowers (dicliny), or through genetic self-incompatibility which prevents pollen from its own flower from fertilizing it.

🎯 Exam Tip: When explaining strategies, clearly define each term (dichogamy, dicliny, self-sterility) and briefly describe how it prevents self-pollination.

Question 9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer: Self-incompatibility is a genetic mechanism found in angiosperms that actively prevents self-pollination. It involves the development of genetic barriers that inhibit successful fertilization between individuals of the same species or between different individuals of genetically similar types.
In plants exhibiting this phenomenon, the physiological response prevents the germination of pollen grains and subsequently inhibits the growth of the pollen tube on the stigma of the same flower. This blockade prevents the fusion of gametes and, consequently, the development of an embryo. As a direct result, no seed formation takes place, even if pollen lands on the stigma.
In simple words: Self-incompatibility is a genetic block that prevents a flower's own pollen from fertilizing its ovules. It stops pollen germination or pollen tube growth on the stigma, so no gamete fusion or seed formation occurs.

🎯 Exam Tip: Emphasize the genetic basis of self-incompatibility and explain the physiological mechanisms (no pollen germination/pollen tube growth) that prevent seed formation.

Question 10. What is bagging technique? How is it useful in a plant breeding programme?
Answer: Bagging is a technique used in plant breeding where emasculated bisexual flowers are covered with a bag (usually made of butter paper) to prevent unwanted pollination.
This method is crucial in plant breeding for two main reasons:
1. It prevents accidental self-pollination in emasculated flowers.
2. It prevents contamination of the stigma by undesirable foreign pollen grains, ensuring that only pollen from selected varieties is used for cross-pollination.
In simple words: Bagging involves covering emasculated flowers with a bag. This prevents unwanted pollen from landing on the stigma, ensuring controlled cross-pollination with desired pollen in breeding programs.

🎯 Exam Tip: Define bagging clearly and explain its dual benefit: preventing self-pollination and contamination by foreign pollen, which are key for controlled breeding.

Question 11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer: Triple fusion is the process of fusion between one male gamete and two polar nuclei, occurring within the embryo sac of an angiosperm. When pollen grains land on the stigma, they germinate and produce a pollen tube, which grows through the style and enters the ovule.
Subsequently, the pollen tube enters one of the synergids and releases two male gametes. Of these two male gametes, one fuses with the egg cell nucleus to form a zygote (syngamy). The other male gamete then fuses with the two polar nuclei located in the central cell, leading to the formation of a triploid primary endosperm nucleus (PEN). Since this process involves the fusion of three haploid nuclei (one male gamete and two polar nuclei), it is termed triple fusion. This event results in the formation of the endosperm, which provides nutrition to the developing embryo.
In simple words: Triple fusion is when one male gamete fuses with the two polar nuclei inside the embryo sac, forming a triploid primary endosperm nucleus. This happens in the central cell and leads to the formation of endosperm, which nourishes the embryo.

🎯 Exam Tip: Clearly state the nuclei involved (one male gamete + two polar nuclei), the ploidy (triploid), and the product (primary endosperm nucleus, leading to endosperm) of triple fusion. Emphasize its location in the embryo sac's central cell.

Question 12. Differentiate between: a. hypocotyl and epicotyl b. coleoptile and coleorhiza c. integument and testa d. perisperm and pericarp
Answer:
a. Hypocotyl and Epicotyl:
(i) Hypocotyl: This is the embryonic axis portion situated below the level of the cotyledons.
(ii) Epicotyl: This is the embryonic axis portion found above the level of the cotyledons.
b. Coleoptile and Coleorhiza:
(i) Coleoptile: In the embryonic axis of monocots, just above the scutellum's attachment point, the epicotyl contains a shoot apex and a few leaf primordia, all encased within a hollow, foliar structure known as the coleoptile.
(ii) Coleorhiza: In the monocot embryonic axis, the lower end comprises the radicle and root cap, both enclosed within an undifferentiated sheath called the coleorhiza.
c. Integument and Testa:
(i) Integument: This refers to the protective covering of the ovule.
(ii) Testa: After fertilization, the integument transforms into the hard seed coat, or testa.
d. Perisperm and Pericarp:
(i) Perisperm: These are the persistent remnants of the nucellus found inside some seeds, which serve as a nutritive tissue.
(ii) Pericarp: This is the fruit wall, which develops from the ovary wall after fertilization.
In simple words: Hypocotyl is below cotyledons, epicotyl is above. Coleoptile covers the shoot in monocots, coleorhiza covers the root. Integument is the ovule covering, testa is the seed coat. Perisperm is nucellus remnant in seed, pericarp is the fruit wall.

🎯 Exam Tip: For differentiation questions, provide clear, concise definitions for each term. Focus on their location, origin, and specific function to highlight their differences effectively.

Question 13. Why is apple called false fruit? Which part of the flower forms the fruits?
Answer: The apple is referred to as a false fruit because it does not primarily develop from the ovary. Instead, it originates from the thalamus of the flower. Following fertilization, the thalamus swells and becomes the fleshy, edible part of the apple.
Typically, the ovary of the flower develops into the fruit after fertilization.
In simple words: An apple is a false fruit because its main edible part comes from the thalamus, not solely from the ovary. Usually, the ovary forms the fruit.

🎯 Exam Tip: Remember the distinction between true fruits (developed solely from ovary) and false fruits (developed from other floral parts like the thalamus) and provide apple as a prime example of the latter.

Question 14. What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer: Emasculation is the manual process of removing the anthers from a bisexual flower before they mature and dehisce (release pollen), without causing any damage to the female reproductive part (pistil).
Plant breeders employ this technique in bisexual flowers to:
1. Obtain a desired variety of a plant by cross-pollinating it with specific, chosen pollen grains.
2. After emasculation, the flowers are typically covered with a bag (bagging) before they open, which ensures that the stigma is pollinated only by pollen grains from desirable varieties and prevents contamination by unwanted pollen.
Later, mature, viable, and stored pollen grains from the desired parent are dusted onto the bagged stigma, facilitating artificial pollination to achieve the desired plant variety.
In simple words: Emasculation is removing anthers from a bisexual flower to prevent self-pollination. Plant breeders use it to control cross-pollination with specific pollen, ensuring the development of desired plant varieties.

🎯 Exam Tip: Focus on the 'why' – emasculation ensures controlled cross-pollination by preventing self-pollination and contamination, which is key for genetic improvement in breeding programs.

Question 15. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer: If parthenocarpy can be induced using growth substances, fruits like grapes, oranges, and pomegranates would be ideal choices.
The reason for selecting these fruits is their high economic importance. Inducing parthenocarpy in these fruits would lead to the production of seedless varieties, which are generally preferred by consumers due to enhanced eating quality and convenience, thereby increasing their market value and appeal.
In simple words: Fruits like grapes, oranges, and pomegranates would be chosen for induced parthenocarpy because creating seedless varieties makes them more economically valuable and appealing to consumers.

🎯 Exam Tip: Connect the concept of parthenocarpy (seedless fruit) to practical applications, specifically the economic benefit of producing seedless varieties of commercially important fruits.

Question 16. Explain the role of the tapetum in the formation of pollen-grain walls.
Answer: The tapetum constitutes the innermost wall layer of the anther, surrounding the sporogenous tissue. Its primary function is to provide nutrition to the developing pollen grains.
Beyond nutrition, the tapetum plays several critical roles in pollen wall formation:
- Secretion of hormones and various enzymes necessary for pollen development.
- Transportation of nutrients to the developing pollen grains from the surrounding anther tissues.
- Production of Ubisch bodies, which are coated with sporopollenin. These Ubisch bodies contribute to the thickening and robust structure of the exine (outer layer of the pollen grain wall).
- Secretion of pollenkit, an oily and sticky substance that covers the mature pollen, aiding in insect pollination.
- Secretion of proteins that enable pollen to be compatible with the stigma during fertilization.
In simple words: The tapetum is the innermost layer of the anther wall, crucial for nourishing developing pollen grains. It secretes substances like Ubisch bodies (for exine thickening) and pollenkit, and transports nutrients, all vital for pollen wall formation and maturation.

🎯 Exam Tip: Remember that tapetum's main role is nourishment, but also highlight its contributions to exine formation (sporopollenin via Ubisch bodies) and pollen viability/compatibility for comprehensive understanding.

Question 17. What is apomixis and what is its importance?
Answer: Apomixis refers to the formation of seeds without the process of fertilization, essentially a form of asexual reproduction that mimics sexual reproduction. It encompasses a range of developmental processes that alter the reproductive functions within the ovule of flowering plants, converting what would normally be a sexual process into an asexual one.
The potential impacts of apomixis are significant:
- Hybrid seed propagation: Farmers can directly propagate hybrid seeds without the hybrid losing its genetic makeup through sexual crossing, ensuring the "breeding true" of desirable traits. This eliminates the need to purchase new hybrid seeds every year, reducing cultivation costs.
- Disease reduction and germplasm flow: For vegetatively propagated tuber crops like cassava, potato, and yams, apomixis can help eliminate or reduce propagule-borne diseases. It can also substantially increase germplasm flow and expand potential growing regions for these crops.
In simple words: Apomixis is asexual seed formation without fertilization, mimicking sexual reproduction. Its importance lies in allowing farmers to grow hybrid seeds that consistently reproduce desired traits without needing new seeds each year, and in reducing disease spread in some crops.

🎯 Exam Tip: Define apomixis as asexual reproduction leading to seed formation without fertilization. Highlight its primary importance in agriculture: maintaining hybrid vigor over generations and reducing cultivation costs for farmers.

GSEB Class 12 Biology Sexual Reproduction In Flowering Plants Additional Important Questions And Answers

Question 1. Name the protective substance present on the pollen envelope to tide over the adverse conditions.
Answer: Sporopollenin.
In simple words: Sporopollenin is the extremely resistant substance found in the outer layer of the pollen grain, protecting it from harsh environmental conditions.

🎯 Exam Tip: Sporopollenin is a highly durable substance; remember its name and its key role in protecting pollen grains.

Question 2. Given below is the picture of pollen germination. Observe it and answer the following questions. a. When does the pollen germination begin? b. What is the role of the two male gametes in angiosperm fertilization? c. What is the result of fertilization?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक परागकण के अंकुरण की प्रक्रिया को दर्शाता है। इसमें परागकण से निकलने वाली पराग नलिका (पॉलन ट्यूब) और उसके अंदर मौजूद दो नर युग्मकों (मेल गेमेट्स) के साथ-साथ ट्यूब न्यूक्लियस को दिखाया गया है। यह परागकण के अंकुरण और पराग नलिका के विकास को समझाता है, जो निषेचन के लिए महत्वपूर्ण है। a. Pollen germination commences when the pollen grains land on a receptive stigma.
b. In angiosperm fertilization, the two male gametes play distinct roles: one male gamete fuses with the egg cell, while the other male gamete fuses with the central cell's secondary nucleus.
c. The result of fertilization is the formation of a zygote (from the fusion with the egg cell) and a primary endosperm nucleus (from the fusion with the secondary nucleus).
In simple words: Pollen germination starts on the stigma. One male gamete fertilizes the egg, forming a zygote, and the other fertilizes the secondary nucleus, forming the primary endosperm nucleus, both crucial for seed development.

🎯 Exam Tip: For pollen germination, remember it starts on the stigma. For male gametes, differentiate their roles in double fertilization: one for the egg (zygote) and the other for the secondary nucleus (endosperm).

Question 3. What technical term is applied to fruits formed without fertilization?
Answer: Parthenocarpy.
In simple words: Fruits that develop without fertilization are called parthenocarpic fruits.

🎯 Exam Tip: The term "parthenocarpy" is fundamental for describing seedless fruit formation without fertilization.

Question 4. Endothecium, Tapetum, Epidermis, Middle layers. These are the parts of another wall. a. Arrange them in an order according to the occurrence in the anther wall. b. What is the function of tapetum?
Answer:
a. The correct order of layers in the anther wall, from outermost to innermost, is: Epidermis, Endothecium, Middle layers, Tapetum.
b. The tapetum's primary function is to provide nutritive tissue for the developing pollen grains, ensuring their proper growth and maturation.
In simple words: The anther wall layers are Epidermis, Endothecium, Middle layers, and Tapetum (from outside to inside). The tapetum nourishes the growing pollen.

🎯 Exam Tip: Memorize the correct sequence of anther wall layers and explicitly state the tapetum's role in pollen nourishment and wall development.

Question 5. List the general characteristics of the pollen grains of wind-pollinated plants.
Answer: The pollen grains of wind-pollinated plants generally exhibit the following characteristics: they are smooth, dry, light, non-sticky, and some may even be winged to facilitate easy dispersal by wind.
In simple words: Wind-pollinated pollen grains are typically smooth, dry, light, and non-sticky, sometimes with wings, to be easily carried by the wind.

🎯 Exam Tip: Focus on attributes that aid airborne dispersal: light, dry, non-sticky, and sometimes winged. Contrast these with insect-pollinated pollen (sticky, often heavy).

Question 6. Observe the diagram
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक परागकण के विकास के चरणों को दर्शाता है। पहले हिस्से (a) में एक परागकण चतुष्क (पॉलन ग्रेन टेट्राड) का एक विस्तृत दृश्य है। दूसरे हिस्से (b) में एक माइक्रोस्पोर से परागकण में परिपक्व होने की अवस्थाएँ दिखाई गई हैं, जिसमें एक रिक्तिका (वैक्यूओल), केंद्रक (न्यूक्लियस), असममित धुरी (एसिमेट्रिक स्पिंडल), और फिर वनस्पति कोशिका (वेजिटेटिव सेल) और जनन कोशिका (जेनरेटिव सेल) का निर्माण शामिल है। यह परागकण के बनने की प्रक्रिया को स्पष्ट करता है। a. To copy this diagram and label: (i) Intine, (ii) Exine, (iii) Vegetative cell, (iv) Generative nucleus.
b. This structure represents a mature pollen grain.
c. The ploidy of the given structure (pollen grain) is haploid.
In simple words: The diagram shows a mature pollen grain, which is a haploid structure containing vegetative and generative cells, enclosed by intine and exine.

🎯 Exam Tip: Be able to identify and label the key parts of a mature pollen grain (exine, intine, vegetative cell, generative cell/nucleus) and state its haploid nature.

Question 7. Observe the given diagram. a. What is the structure shown here? b. How many nuclei were there in its young stage? c. What are the upper three cells together called?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक परिपक्व भ्रूणकोष (एम्ब्रियो सैक) की संरचना को दर्शाता है, जिसमें अंड उपकरण (एग अपैरेटस) और प्रतिध्रुवी कोशिकाएँ (एंटीपोडल्स) स्पष्ट रूप से दिख रही हैं। अंड उपकरण में एक अंडकोशिका और दो सहायक कोशिकाएँ शामिल हैं, जबकि केंद्रीय कोशिका में दो ध्रुवीय केंद्रक होते हैं। यह मादा युग्मकोद्भिद की 7-कोशिकीय, 8-केंद्रकीय व्यवस्था को दर्शाता है। a. The structure shown here is an Embryo sac (or Female gametophyte).
b. In its young stage (before mitotic divisions), the megaspore had a single nucleus. After subsequent mitotic divisions, it typically becomes an 8-nucleate structure before cellularization.
c. The upper three cells together (at the micropylar end) are called the Egg apparatus, which consists of one egg cell and two synergids.
In simple words: The diagram shows an embryo sac. In its early stage, it had one nucleus, which multiplied to eight. The three cells at the top collectively form the egg apparatus.

🎯 Exam Tip: Identify the embryo sac (female gametophyte) correctly. Remember its development from a single nucleus and the composition of the egg apparatus (egg cell + synergids).

Question 8. Fertilization in Angiosperms is called double fertilization because here two male gametes take part in fertilization. a. Which cells do this male gamete fertilize? b. What are the products of fertilization? c. Explain the ploidy of the two products.
Answer:
a. The two male gametes fertilize different cells: one male gamete fertilizes the egg cell, and the other male gamete fertilizes the central cell's secondary nucleus.
b. The products of this double fertilization are the zygote and the primary endosperm nucleus (PEN).
c. The ploidy of the two products is as follows:
(i) Zygote: It is diploid (2n), formed by the fusion of a haploid male gamete (n) and a haploid egg cell (n).
(ii) Primary Endosperm Nucleus (PEN): It is triploid (3n), formed by the fusion of a haploid male gamete (n) and the two haploid polar nuclei (n + n) from the central cell.
In simple words: In double fertilization, one male gamete fertilizes the egg cell to form a diploid zygote, and the other male gamete fertilizes the secondary nucleus to form a triploid primary endosperm nucleus.

🎯 Exam Tip: Clearly state the components of double fertilization: syngamy (male gamete + egg = zygote, 2n) and triple fusion (male gamete + two polar nuclei = primary endosperm nucleus, 3n). Knowing the ploidy levels is essential.

Question 9. State the function of a suspensor.
Answer: The primary function of a suspensor is to push the developing embryo deeper into the endosperm. This strategic positioning ensures that the embryo is optimally located for absorbing nutrients from the endosperm, which is vital for its growth and development.
In simple words: The suspensor pushes the growing embryo into the endosperm, allowing it to absorb necessary nutrients for development.

🎯 Exam Tip: Remember the suspensor's role in positioning the embryo and facilitating nutrient uptake from the endosperm.

Question 10. Names of some parts of the female reproductive structure before fertilization, are given. Match them with the modified part after fertilization.
Answer:

A (Before Fertilization)	B (After Fertilization)
Ovule	Seed
Integument of ovule	Seed coat
Ovary	Fruit
Ovum	Zygote
Secondary nucleus	Endosperm

In simple words: After fertilization, the ovule becomes the seed, its integument becomes the seed coat, the ovary develops into the fruit, the ovum becomes the zygote, and the secondary nucleus develops into the endosperm.

🎯 Exam Tip: This matching exercise is crucial for understanding post-fertilization changes in angiosperms. Clearly connect each pre-fertilization structure with its corresponding post-fertilization derivative.

Question 11. Cleistogamous flowers are invariably autogamous. Explain.
Answer: Cleistogamous flowers are flowers that never open their floral parts. Because these flowers remain permanently closed, the anthers and stigma are positioned very close to each other. This physical proximity, combined with the enclosed environment, ensures that pollen grains released from the anthers of the same flower will inevitably fall onto and pollinate its own stigma. Consequently, there is no opportunity for cross-pollination from other flowers, making cleistogamous flowers invariably autogamous (self-pollinating).
In simple words: Cleistogamous flowers stay closed, so their anthers and stigma are always close together. This guarantees that pollen from the same flower will pollinate its own stigma, making them always self-pollinating.

🎯 Exam Tip: The key point is that cleistogamous flowers *never open*. This physical characteristic directly leads to mandatory self-pollination (autogamy).

Question 12. Compare the given pair and fill up the blanks. a. Grasses : Wind pollination :: Zostera : .......... b. Fragrant flower : Insect :: Light and nonsticky pollen : ..........
Answer:
a. Grasses : Wind pollination :: Zostera : Water pollination
b. Fragrant flower : Insect :: Light and non-sticky pollen : Wind pollination
In simple words: Zostera uses water for pollination, similar to how grasses use wind. Fragrant flowers attract insects for pollination, just as light, non-sticky pollen is adapted for wind pollination.

🎯 Exam Tip: This question tests knowledge of different pollination agents and the corresponding adaptations of flowers/pollen. Associate Zostera with water and light/non-sticky pollen with wind.

Question 13. Water is considered as the pollinating agent in some plants. Name any two water-pollinated plants.
Answer: Two examples of water-pollinated plants are Vallisneria and Zostera.
In simple words: Vallisneria and Zostera are examples of plants that rely on water for pollen transfer.

🎯 Exam Tip: Remember specific examples of hydrophilous (water-pollinated) plants like Vallisneria and Zostera.

Question 14. Autogamy, geitonogamy, and xenogamy are the three types of pollination based on the source of pollen. You have a monoecious and dioecious plant in your garden. Which among the above said pollination do not occur in each plant?
Answer:
- Monoecious plant: In a monoecious plant (both male and female flowers on the same plant), autogamy (self-pollination within the same flower) may or may not occur depending on other mechanisms like dichogamy or self-incompatibility, but **xenogamy** (cross-pollination between different plants) can occur. Geitonogamy (pollination between different flowers on the same plant) is also possible. If the question implies which *cannot* occur under typical circumstances, it's more about preventing autogamy or favoring xenogamy. However, if looking for what is *naturally precluded*, the phrasing leads to different interpretations. Let's re-evaluate based on the common understanding in textbook questions.
Revisiting the original answer format which is specific about what *does not occur*:
Monoecious - Autogamy (if mechanisms exist to prevent it, otherwise it can occur)
Dioecious - Autogamy and Geitonogamy
Let's refine the answer to match the expected educational context precisely:
In a monoecious plant, where male and female flowers are on the same individual, **autogamy** may not occur if the plant has specific devices to prevent it (e.g., dichogamy or self-incompatibility). However, geitonogamy and xenogamy are possible. For the purpose of "do not occur", typically it refers to the intrinsic mechanisms that prevent it.
In a dioecious plant, where male and female flowers are on separate individuals, both **autogamy** (self-pollination within a flower) and **geitonogamy** (pollination between flowers on the same plant) cannot occur because the entire plant is either male or female. Only xenogamy is possible.
So, based on the provided answer structure:
Monoecious - Autogamy (This implies that if a monoecious plant has mechanisms to prevent autogamy, then it doesn't occur. It's a slightly simplified textbook answer.)
Dioecious - Autogamy and Geitonogamy
In simple words: In monoecious plants (male and female flowers on the same plant), autogamy (self-pollination within one flower) might not happen if protective measures are present. In dioecious plants (separate male and female plants), neither autogamy nor geitonogamy (pollination between flowers on the same plant) can occur.

🎯 Exam Tip: Clearly distinguish between monoecious and dioecious plants. Understand that autogamy is generally prevented by specific mechanisms in many monoecious plants, while in dioecious plants, both autogamy and geitonogamy are inherently impossible due to the separation of sexes.

Question 15. Continuous self-pollination results in inbreeding depression. Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination. Explain any four such mechanisms.
Answer: Continuous self-pollination often leads to inbreeding depression, which is a reduction in fitness and vigor due to increased homozygosity. To counteract this, flowering plants have evolved various mechanisms to discourage self-pollination and promote cross-pollination:
1. Dichogamy: The anthers and stigma within the same flower mature at different times. This temporal separation prevents self-pollination by ensuring that pollen is released either before or after the stigma becomes receptive.
2. Herkogamy: The anthers and stigma are positioned at different locations within the flower. This spatial separation physically obstructs pollen transfer from the anther to the stigma of the same flower.
3. Self-incompatibility: This is a genetic mechanism where a flower's own pollen is unable to germinate on its stigma or the pollen tube fails to penetrate the pistil. It's a biochemical barrier preventing fertilization.
4. Unisexuality (Dicliny): The stamens and carpels develop in separate flowers. If male and female flowers are on different plants (dioecious), both autogamy and geitonogamy are prevented. If they are on the same plant but in separate flowers (monoecious), autogamy is prevented.
In simple words: Plants prevent self-pollination through mechanisms like dichogamy (anther and stigma mature at different times), herkogamy (anther and stigma are in different positions), self-incompatibility (genetic block against self-pollen), and unisexuality (separate male and female flowers).

🎯 Exam Tip: Focus on understanding how each mechanism (dichogamy, herkogamy, self-incompatibility, unisexuality) physically or genetically prevents self-pollination and promotes outcrossing, thereby avoiding inbreeding depression.

Question 16. Removal of anthers from the flower bud of female parents is an important step in hybridisation. a. Name the step and explain the purpose. b. What is the importance of "bagging"?
Answer:
a. The step of removing anthers from the flower bud of female parents is called **Emasculation**. Its primary purpose is to **avoid self-pollination**. By removing the anthers before they release pollen, the breeder ensures that the ovules of the chosen female parent are fertilized only by desired pollen from another selected parent.
b. The importance of 'bagging' is to **protect the emasculated stigma from contamination by unwanted pollen grains**. After emasculation, the pistil is covered with a bag (usually made of butter paper). This prevents any foreign or undesirable pollen from landing on the stigma, thereby ensuring that only the pollen from the chosen male parent (dusted later by the breeder) achieves fertilization for hybrid seed production.
In simple words: The removal of anthers is called emasculation, done to prevent self-pollination. Bagging then protects the emasculated flower's stigma from unwanted pollen, ensuring only desired cross-pollination for hybrid production.

🎯 Exam Tip: Differentiate emasculation (removing anthers) from bagging (covering the stigma). Both are critical sequential steps in artificial hybridization to control pollination and ensure desired crosses.

Question 17. The endosperm is the nutritive tissue of the growing embryo. Inside a tender coconut two types of endosperms are seen. Name the type of endosperms and the structure that represents each type.
Answer: The endosperm serves as the nutritive tissue for the developing embryo. In a tender coconut, two distinct types of endosperms are observed:
a. **Free nuclear endosperm**: This type is represented by the **coconut water**. It consists of numerous free nuclei suspended in a liquid medium, resulting from repeated nuclear divisions without immediate cell wall formation.
b. **Cellular endosperm**: This type is represented by the **white kernel (flesh)** of the coconut. It forms as cell walls begin to develop around the free nuclei, leading to a solid tissue.
In simple words: A tender coconut has two kinds of endosperm: the liquid coconut water is free nuclear endosperm, and the solid white flesh is cellular endosperm, both nourishing the embryo.

🎯 Exam Tip: Remember the coconut as a classic example showing both free nuclear (water) and cellular (kernel) endosperm, highlighting their structural differences and nutritive roles.

 

Question 18.The embryo is the structure developed from a zygote, after many divisions. The embryo undergoes many changes until it becomes embryo proper.
a. Give the structure of a mature embryo.
Answer:a. A mature embryo in dicots features an axis with two cotyledons, while in monocots, it has one cotyledon. The upper extremity of this embryonic axis is known as the plumule, and its lower end is termed the radicle.
In simple words: A mature embryo consists of an axis with cotyledons; the plumule is the shoot-forming part, and the radicle develops into the root.

🎯 Exam Tip: Understanding the structural components of a mature embryo is crucial for explaining seed germination and plant development in assessments.

 

Question 19.All fruits are produced from the ovary of a fertilized flower. Write an exception to this statement and explain.
Answer:In certain plants, some flower parts, in addition to the ovary, contribute to fruit development. These are termed 'false fruits.' For instance, in an apple, the thalamus develops into the edible, fleshy structure, rather than the ovary forming the entire fruit.
In simple words: False fruits, like apples, grow from flower parts other than just the ovary, such as the thalamus.

🎯 Exam Tip: Distinguishing between true and false fruits, along with specific examples, is a common question, so remember the role of accessory floral parts.

 

Question 20.Fruits are formed for the protection of seeds. But certain fruits are produced without seed.
a. What are these fruits called?
b. What chemicals are used to induce the production of seedless fruits?
c. Give two examples of naturally occurring seedless fruits.
Answer:a. Such fruits are known as parthenocarpic fruits.
b. Chemicals like Indole Acetic Acid and Gibberellic acid are commonly utilized to induce parthenocarpy.
c. Naturally occurring seedless fruits include banana and grapes.
In simple words: Seedless fruits are called parthenocarpic fruits and can be induced by certain chemicals; bananas and grapes are natural examples.

🎯 Exam Tip: Know the definition of parthenocarpy, the hormones involved, and be ready to provide examples of both induced and naturally seedless fruits.

 

Question 21.Find the relation of the plant ‘Lupinus arcticus' with 'seed dormancy'.
Answer:The plant *Lupinus arcticus* holds the record for the longest documented seed dormancy period, extending up to 10,000 years.
In simple words: *Lupinus arcticus* has an exceptionally long seed dormancy, capable of surviving for 10,000 years.

🎯 Exam Tip: This question tests knowledge of specific biological records related to dormancy, highlighting the plant's unique adaptation for survival across vast timelines.

 

Question 22.Apomixis is a form of asexual reproduction that mimics sexual reproduction. Is the statement correct? Explain.
Answer:Yes, this statement is correct. Apomixis represents a unique mechanism where seeds are produced without the involvement of fertilization. Therefore, it is essentially asexual reproduction. However, because a diploid cell within the ovule develops into an embryo without fertilization, the process superficially resembles sexual reproduction in its outcome (seed formation).
In simple words: Yes, apomixis is asexual reproduction that creates seeds without fertilization, but it appears like sexual reproduction because seeds are formed.

🎯 Exam Tip: Define apomixis clearly and explain why it's considered both asexual and a mimic of sexual reproduction, focusing on the lack of fertilization but the presence of seeds.

 

Question 23.Apomixis will reduce the cultivation cost of hybrid plants. Explain.
Answer:Hybrid seeds are typically expensive and necessitate annual replenishment because the progeny produced from these seeds do not consistently exhibit the desired parental traits due to segregation. If hybrid plants are converted into apomicts, they will consistently produce offspring genetically identical to the parent, eliminating character segregation. This allows farmers to reuse the seeds from their hybrid crops year after year without purchasing new ones, thereby significantly lowering cultivation costs.
In simple words: Apomixis in hybrid plants would mean seeds always produce identical offspring, saving farmers the cost of buying new hybrid seeds every year.

🎯 Exam Tip: Focus on the economic advantage of apomixis for hybrid crop cultivation, specifically how it eliminates the need for repeated purchase of costly hybrid seeds by preventing genetic segregation.

 

Question 24.Give the technical terms of the following explanation
a. Formation of seedless fruits without fertilization.
b. Organisms are formed from unfertilized female gamete.
Answer:a. Parthenocarpy
b. Parthenogenesis
In simple words: Seedless fruit formation without fertilization is parthenocarpy, while organisms developing from unfertilized female gametes is parthenogenesis.

🎯 Exam Tip: Accurately distinguish between parthenocarpy and parthenogenesis, focusing on their respective outcomes-seedless fruits versus new organisms from unfertilized gametes.

 

Question 25.With the help of labelled diagrams, depicting the stages of a microspore maturing into a pollen grain.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक परागकण के विकास के चरणों को दर्शाता है। इसमें एक परागकण टेट्राड, एक बड़ा परागकण जिसमें केंद्रक और रिक्तिकाएं हैं, एक असममित धुरी के साथ केंद्रक विभाजन, और अंत में एक वनस्पति कोशिका और एक जनन कोशिका वाला परिपक्व परागकण शामिल है। यह परागकण के आंतरिक (इंटाइन) और बाहरी (एक्साइन) परतों के साथ-साथ वनस्पति और जनन केंद्रकों को भी दर्शाता है।
In simple words: A microspore develops into a mature pollen grain through cellular division, forming a vegetative cell and a generative cell.

🎯 Exam Tip: When asked to draw and label, ensure all specified parts like intine, exine, vegetative cell, and generative nucleus are clearly marked, and the diagram accurately reflects the stages of maturation.

 

Question 26.In the adjacent figure of a typical dicot embryo, label the parts (i), (ii), and (iii). State the function of each of the labelled parts.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक विशिष्ट द्विबीजपत्री भ्रूण को दर्शाता है। इसमें तीन मुख्य भागों को लेबल किया गया है: (i) प्रंकुर, जो पौधे के तने और पत्तियों का निर्माण करता है; (ii) बीजपत्र, जो भ्रूण को पोषण प्रदान करते हैं; और (iii) मूलांकुर, जो जड़ प्रणाली में विकसित होता है। यह आरेख भ्रूण के प्रारंभिक विकासवादी संरचना को समझने में मदद करता है। i. Plumule ii. Cotyledons iii. Radicle
i. The plumule develops into the plant's shoot system.
ii. Cotyledons serve as the first leaves and provide food supply to the developing embryo.
iii. The radicle develops into the root system.
In simple words: In a dicot embryo, the plumule grows into the shoot, cotyledons store food, and the radicle forms the root.

🎯 Exam Tip: Knowing the names and specific functions of the plumule, cotyledons, and radicle is essential for understanding seed germination and seedling development.

 

Question 27.How does the development of male gametophyte or pollen take place?
Answer:The haploid microspore, which is essentially the pollen, is the foundational structure of the male gametophyte. Its development begins even before it is shed from the anther. During germination, the microspore nucleus shifts to a position adjacent to the spore wall and undergoes division to form two distinct cells: a larger vegetative cell and a smaller, denser generative cell. The exine layer then ruptures near the germ pore, leading to the emergence of a delicate tubular structure called the pollen tube, into which the tube nucleus migrates. Concurrently, the generative cell divides further to produce two male gametes.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक माइक्रोस्पोर से नर युग्मकोद्भिद् (परागकण) के विकास को दर्शाता है। इसमें बीजाणु रंध्र, केंद्रक, जनन कोशिका, वनस्पति कोशिका, और बाद में पराग नलिका का बनना और उसमें नर युग्मक की उपस्थिति दिखाई गई है। यह परागकण के अंकुरण और युग्मक निर्माण की प्रक्रिया को स्पष्ट करता है।
In simple words: A microspore develops into a pollen grain by forming a vegetative cell and a generative cell, which then produces two male gametes, and a pollen tube emerges.

🎯 Exam Tip: Describe the stages of male gametophyte development, including the roles of the vegetative cell, generative cell, and pollen tube, emphasizing the cell division process.

 

Question 28.Give the structure of self-pollinated flower, cross-pollinated, and cleistogamous flower. Differentiate between self-pollination and cross pollination.
Answer:a. Self-pollinated flowers, b. Cross-pollinated flowers, c. Cleistogamous flowers
**Self-pollination:**
1. This process involves the transfer of pollen grains from the anther to the stigma of the same flower (or the same plant).
2. Pollination typically occurs via direct contact.
3. The anthers and stigma mature simultaneously and are positioned in close proximity.
4. This results in minimal chances of new genetic varieties.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख तीन प्रकार के फूलों को दर्शाता है। पहला चित्र (a) एक स्व-परागित फूल को दिखाता है जहाँ परागकण एक ही फूल के अंदर स्थानांतरित होते हैं। दूसरा चित्र (b) एक पर-परागित फूल को दर्शाता है जहाँ परागकण एक फूल से दूसरे फूल में स्थानांतरित होते हैं। तीसरा चित्र (c) एक क्लिस्टोगैमस फूल को प्रदर्शित करता है जो कभी नहीं खुलता, जिससे केवल स्व-परागण ही संभव होता है।
**Cross-pollination:**
1. This involves the transfer of pollen grains from the anther of one flower to the stigma of another flower on a different plant, but belonging to the same species.
2. Pollination can occur through various agents like wind, water, or animals.
3. Anthers and stigma may mature at different times and are not necessarily in close proximity.
4. This process leads to variations in each new generation, contributing to evolution.
In simple words: Self-pollination happens within the same flower or plant, leading to less genetic variation, while cross-pollination involves pollen transfer between different plants of the same species, increasing variation.

🎯 Exam Tip: Clearly define self-pollination and cross-pollination, then detail their mechanisms, maturity patterns of reproductive parts, and the genetic outcomes (variation vs. homogeneity).

 

Question 29.Explain the role of the tapetum in the formation of pollen-grain walls.
Answer:The tapetum constitutes the innermost wall layer of the microsporangium. Its cells can be uni-, bi-, or multinucleate and are characterized by dense cytoplasm. The tapetum plays several crucial roles:
- Secretion of hormones and various enzymes vital for pollen development.
- Transportation of nutrients to the developing pollen grains.
- Production of Ubisch bodies, which become coated with sporopollenin, a substance that contributes to the thickening and resilience of the exine (outer pollen wall).
- Secretion of pollenkit, an oily substance found on the surface of mature pollen grains.
- Secretion of proteins that are essential for pollen compatibility during fertilization.
In simple words: The tapetum provides nutrition, secretes enzymes and hormones, forms Ubisch bodies for exine thickening, and produces pollenkit, all crucial for pollen grain wall formation and development.

🎯 Exam Tip: Focus on the tapetum's multifaceted role, especially its nutritional support and contribution to the structural integrity (exine formation via sporopollenin) and surface properties (pollenkit) of pollen grains.

 

Question 30.Draw a labelled diagram of L.S of pistil
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक फूल के अनुदैर्ध्य काट को दर्शाता है जिसमें पराग नलिका का विकास होता है, और एक स्त्रीकेसर (पिस्टिल) के अनुदैर्ध्य काट को दिखाता है जो पराग नलिका के मार्ग को प्रदर्शित करता है। इसमें पराग नलिका, अंडाणु, केंद्रक, बीजांडद्वार, सहायक कोशिकाएं और एक अंड कोशिका जैसे महत्वपूर्ण भागों को स्पष्ट रूप से लेबल किया गया है, जो निषेचन प्रक्रिया के मार्ग को समझने में मदद करता है।
In simple words: The diagram illustrates the longitudinal section of a pistil and the path of a pollen tube during fertilization.

🎯 Exam Tip: For diagrams, ensure clear and accurate labeling of all essential parts of the pistil and the pollen tube's path, as this demonstrates a complete understanding of the reproductive anatomy.

 

Question 31.Differentiate between non-albuminous and albuminous seeds with examples.
Answer:- **Non-albuminous seeds** are characterized by the absence of residual endosperm, as it is completely utilized during the embryo's development. Examples include peas and groundnuts.
- **Albuminous seeds**, conversely, retain a portion of the endosperm because it is not fully consumed during embryo development. Examples include wheat, maize, barley, and castor.
In simple words: Non-albuminous seeds have no endosperm left (like peas), while albuminous seeds keep some endosperm (like wheat) for nourishment.

🎯 Exam Tip: The key difference lies in whether the endosperm is fully consumed by the embryo or persists in the mature seed; be ready with specific examples for each type.

 

Question 32.Define pollination.
Answer:Pollination is defined as the transfer of pollen grains from the anther to the stigma of a flower.
In simple words: Pollination is when pollen moves from a flower's anther to its stigma.

🎯 Exam Tip: A precise and concise definition of pollination is crucial; remember it involves the transfer from anther to stigma.

 

Question 33.Mention the scientific term used, for modified form of reproduction in which seeds are formed without fusion of gametes.
Answer:The scientific term for a modified form of reproduction where seeds are produced without the fusion of gametes (fertilization) is apomixis.
In simple words: The scientific term for seed formation without gamete fusion is apomixis.

🎯 Exam Tip: This question tests your recall of specific biological terminology; ensure you correctly identify apomixis as reproduction without fertilization but resulting in seeds.

 

Question 34.Describe the structure of a typical embryo sac found in flowering plants. Why is it generally referred to as monosporic?
Answer:The development of a gametophyte or embryo sac from a megaspore is known as megagametogenesis. During this process, the megaspore nucleus undergoes three successive mitotic divisions, leading to the formation of eight haploid nuclei. The megaspore enlarges into an oval-shaped structure called the embryo sac. Within this structure, the polar nuclei may fuse to form a secondary nucleus. The embryo sac is typically termed monosporic because it develops from a single functional megaspore.
In simple words: A typical embryo sac has eight nuclei and forms from one megaspore, which is why it's called monosporic.

🎯 Exam Tip: Explain the 8-nucleate, 7-celled structure of the embryo sac and clearly state that it is monosporic because it originates from a single functional megaspore.

 

Question 35.What is funiculus?
Answer:The funiculus is the stalk of the ovule.
In simple words: The funiculus is the small stalk that attaches the ovule to the placenta.

🎯 Exam Tip: Know basic anatomical terms; the funiculus is simply the stalk connecting the ovule to the placenta.

 

Question 36.Describe the structure of a typical embryo sac found in a flowering plant. Why is it generally referred to as monosporic?
Answer:A typical embryo sac is characterized by an 8-nucleate and 7-celled structure. Six of these eight nuclei become enveloped by cell walls and organize into distinct cells. The remaining two nuclei, known as polar nuclei, reside in the center of the large central cell. Three cells are clustered together at the micropylar end, forming the egg apparatus, which includes one female gamete (egg cell) and two synergids. These synergids feature special cellular thickenings called the filiform apparatus at their micropylar tip. The three cells situated at the chalazal end are called antipodals. The embryo sac is termed monosporic because it develops from a single functional megaspore.
In simple words: A mature embryo sac typically has seven cells and eight nuclei, including an egg, synergids, antipodals, and polar nuclei; it's called monosporic because it develops from one megaspore.

🎯 Exam Tip: Provide a detailed description of the 7-celled, 8-nucleate structure, including the specific cells and nuclei, and clearly explain why "monosporic" is used.

 

Question 37.a. Draw a schematic labelled diagram of a fertilised embryo sac of an angiosperm.
b. Describe the stages in embryo development in a dicot plant.
Answer:a.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक एंजियोस्पर्म के निषेचित भ्रूण थैली के विकास को दर्शाता है। इसमें माइक्रोस्पोर मदर सेल, मेगास्पोर डायड, और मेगास्पोर टेट्राड सहित मेगास्पोरजनन के विभिन्न चरण दिखाए गए हैं। साथ ही, यह 2, 4 और 8-केंद्रक वाले भ्रूण थैली के चरणों और अंततः एक परिपक्व भ्रूण थैली को भी प्रस्तुत करता है, जिसमें अंडा कोशिका, सहायक कोशिकाएं, प्रतिध्रुवी कोशिकाएं, और द्वितीयक केंद्रक जैसे महत्वपूर्ण भागों को लेबल किया गया है।
b. Embryo development initiates at the micropylar end of the embryo sac, where the zygote is located. Zygote division typically occurs only after a certain amount of endosperm has formed, which ensures a guaranteed nutritional supply for the developing embryo. The later stages of embryogeny are consistent across monocotyledons and dicotyledons. In a dicotyledonous embryo, the zygote first forms a pre-embryo, which then progresses through globular and heart-shaped stages before becoming a mature embryo. A dicot seed's embryo consists of an embryonal axis, two cotyledons, a plumule, and a radicle or root tip, with the root tip being covered by a root cap.
In simple words: Dicot embryo development starts from a zygote, forming a pre-embryo, then globular and heart-shaped stages, eventually becoming a mature embryo with a plumule, radicle, and two cotyledons, all nourished by endosperm.

🎯 Exam Tip: For part (a), ensure all stages of megaspore and embryo sac development are accurately drawn and labeled. For part (b), describe the sequential stages of dicot embryo development, highlighting the significance of endosperm formation.

 

Question 38.a. Draw a longitudinal sectional view of a typical anatropous ovule to show the site where double fertilization takes place. Label any four major parts of the ovule.
b. How do the male gametes that are present in the pollen groans reach the site mentioned by you import (a) to cause double fertilization?
Answer:a.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक विशिष्ट अनाट्रोपस बीजांड का अनुदैर्ध्य काट दर्शाता है, जहाँ दोहरा निषेचन होता है। इसमें बीजांड के मुख्य भाग जैसे नाभिक (हिलम), बीजांडवृंत (फ्यूनिकल), बीजांडद्वार (माइक्रोपाइल), बाहरी और आंतरिक अध्यावरण, बीजांडकाय (न्यूसेलस), भ्रूण थैली और चलाज़ल ध्रुव स्पष्ट रूप से लेबल किए गए हैं। यह चित्र पराग नलिका के प्रवेश और दोहरे निषेचन के स्थल को समझने में मदद करता है।
b. In the embryo sac, double fertilization occurs. The pollen tube, after reaching the ovule, releases the two male gametes into the cytoplasm of one of the synergids. One male gamete then fuses with the egg cell, a process known as syngamy, forming the zygote. The other male gamete fuses with the two polar nuclei located in the central cell, which is termed triple fusion, leading to the formation of the primary endosperm nucleus. Both syngamy and triple fusion happen concurrently in the embryo sac, collectively known as double fertilization.
In simple words: Male gametes travel through the pollen tube to the embryo sac; one fuses with the egg (syngamy) and the other with polar nuclei (triple fusion), both part of double fertilization.

🎯 Exam Tip: For part (a), draw a clear L.S. of the anatropous ovule and label four key parts accurately. For part (b), meticulously explain the path of male gametes, the entry into the embryo sac, and the two distinct fusion events of double fertilization.

 

Question 39.a. Draw the embryo sac of a flowering plant and label (i) central cell, (ii) chalazal end of the embryo sac, and (iii) synergids.
b. Name the cell that develops into the embryo sac and explain how this cell leads to the formation of the embryo sac. Also, mention the role played by the various cells of the embryo sac.
Answer:a.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक विशिष्ट अनाट्रोपस बीजांड और एक परिपक्व भ्रूण थैली को दर्शाता है। इसमें बीजांड के विभिन्न भाग जैसे नाभिक, बीजांडवृंत, बीजांडद्वार, अध्यावरण और चलाज़ल ध्रुव लेबल किए गए हैं। परिपक्व भ्रूण थैली में सहायक कोशिकाएं, अंड कोशिका, केंद्रीय कोशिका, और प्रतिध्रुवी कोशिकाएं दिखाई गई हैं, जो निषेचन के लिए आवश्यक संरचनाएं हैं।
b. The cell that develops into the embryo sac is the functional megaspore. The process of megaspore formation from the megaspore mother cell is called megasporogenesis. The nucleus of the functional megaspore undergoes three rounds of mitotic division to produce two nuclei, which move to opposite poles, forming the 2-nucleate embryo sac. Further mitotic divisions lead to 4-nucleate and then 8-nucleate stages of the embryo sac. The two nuclei in the central cell are known as polar nuclei. The three cells grouped at the micropylar end constitute the egg apparatus, which includes the egg cell and two synergids. The three cells at the chalazal end are called antipodals. A typical mature angiosperm embryo sac is 8-nucleate and 7-celled.
In simple words: The embryo sac develops from a functional megaspore through mitotic divisions to form a 7-celled, 8-nucleate structure, including the egg apparatus, central cell with polar nuclei, and antipodals.

🎯 Exam Tip: For part (a), ensure accurate and clear labeling of the central cell, chalazal end, and synergids. For part (b), detail the megasporogenesis process, the mitotic divisions, and the specific arrangement and roles of the different cells within the mature embryo sac.