Sexual Reproduction in Flowering Plants - Class 12 Biology - Chapter 1 - Notes, NCERT Solutions & Extra Questions
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Notes - Sexual Reproduction in Flowering Plants | Class 12 NCERT | Biology
Comprehensive Class 12 Notes on Sexual Reproduction in Flowering Plants
Introduction
Sexual reproduction in flowering plants is a fascinating and complex process that ensures genetic diversity and survival of species. This article delves deep into the topic, providing comprehensive notes ideal for Class 12 students.
The Importance of Sexual Reproduction in Flowering Plants
Sexual reproduction creates new variants, enhancing survival advantage. It is a crucial process for the perpetuation of species amidst environmental changes.
Overview of Class 12 Biology Curriculum on Plant Reproduction
Understanding the biology of reproductive processes in flowering plants forms a fundamental part of the Class 12 curriculum. These notes cover all essential aspects, providing a solid foundation for further studies.
Structure of a Flower
Main Parts of a Flower
Flowers are the reproductive organs of angiosperms (flowering plants). They comprise several parts, including petals, sepals, stamens, and pistils.
Morphology and Function of Floral Structures
Our intimate relationship with flowers is due to their aesthetic and emotional value. However, their primary role is to facilitate the process of sexual reproduction by producing gametes.
Male Reproductive Part: The Stamen
Structural Components of the Stamen
The stamen is the male reproductive part consisting of a filament and anther. The filament supports the anther, where pollen grains develop.
Microsporogenesis and Formation of Pollen Grains
Microsporogenesis occurs within the anthers, forming microspore tetrads through meiotic division. These microspores further develop into pollen grains, which are the male gametophytes.
Significance and Traits of Pollen Grains
Pollen grains are typically spherical and have a two-layered wall. The outer layer, called exine, is made of sporopollenin, highly resistant to environmental stress.
Female Reproductive Part: The Pistil
Structure of the Pistil
The pistil is the female reproductive organ comprising the stigma, style, and ovary. The stigma is the landing platform for pollen grains, while the ovary houses the ovules.
Details of the Ovule and Embryo Sac
Ovules are the site of female gametophyte development. Each ovule contains an embryo sac, formed through the process of megasporogenesis.
Process of Megasporogenesis
Megasporogenesis starts with the megaspore mother cell (MMC) undergoing meiotic division to produce megaspores. Only one functional megaspore develops into the embryo sac.
Pollination
Types of Pollination
Autogamy: Pollination within the same flower.
Geitonogamy: Transfer of pollen grains to another flower on the same plant.
Xenogamy: Transfer of pollen grains to a flower on a different plant.
Mechanisms of Pollination
Pollination can occur through biotic agents like insects and animals, or abiotic agents such as wind and water.
Role of Biotic and Abiotic Agents
Biotic agents include bees, butterflies, and birds, while abiotic agents encompass wind and water. Each type has specific adaptations to facilitate pollen transfer.
Pollen-Pistil Interaction
Recognition and Compatibility
The pistil recognises whether the pollen is compatible. If compatible, pollen germinates on the stigma and proceeds to fertilisation.
Process from Pollination to Fertilisation
After landing on the stigma, pollen grains germinate and form a pollen tube that travels down the style, eventually reaching the ovule for fertilisation.
Double Fertilisation
Process Description
Double fertilisation is a unique mechanism in flowering plants involving two fusion events. One male gamete fuses with the egg cell forming a zygote, and the other fuses with the polar nuclei forming the primary endosperm nucleus.
graph TD;
PollenGrain == Germination ==> PollenTube;
PollenTube == Reaches ==> Ovule;
Ovule == FirstGameteFuses ==> Zygote;
Ovule == SecondGameteFuses ==> Endosperm;
Zygote --> Embryo;
Endosperm --> Nutrient_for_Embryo;
Post-Fertilisation Events
Development of Endosperm
Endosperm development precedes embryo formation, providing essential nutrients. It can be either free-nuclear (non-cellular initially) or cellular.
Embryo Development Stages
Embryo development follows distinct stages—from proembryo to globular and heart-shaped forms before maturation.
Formation of Seed and Fruit
After fertilisation, ovules transform into seeds, and the ovary becomes the fruit. Seeds are protected by seed coats and can remain dormant or germinate under favourable conditions.
graph TD;
Ovule == Fertilization ==> Seed;
Ovary == Fertilization ==> Fruit;
Seed --> Dormancy;
Seed --> Germination;
Apomixis and Polyembryony
Mechanisms of Apomixis
Apomixis is a form of asexual reproduction mimicking sexual reproduction, enabling seed production without fertilisation.
Advantages and Agricultural Significance
Apomixis has significant implications in agriculture, ensuring uniform hybrid crop varieties without the need for repeated hybridisation.
Explanation of Polyembryony
Polyembryony refers to the occurrence of multiple embryos within a single seed, as seen in some Citrus and Mango varieties.
Conclusion
Understanding sexual reproduction in flowering plants encompasses knowing the intricate processes of flower structure, pollination, fertilisation, and subsequent seed and fruit development. This knowledge is critical not only for academic purposes but also for its practical applications in agriculture and horticulture.
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NCERT Solutions - Sexual Reproduction in Flowering Plants | NCERT | Biology | Class 12
Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
In an angiosperm flower, the development of male and female gametophytes takes place in the following parts:
Male gametophyte: The development occurs in the anther. Specifically, the microspores develop into pollen grains within the microsporangium located in the anther.
Female gametophyte: The development occurs in the ovule. Specifically, the megaspores develop into the embryo sac within the megasporangium located in the ovary.
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.
Attribute | Microsporogenesis | Megasporogenesis |
---|---|---|
Process | Formation of microspores from microspore mother cells (MMCs) | Formation of megaspores from megaspore mother cells (MMCs) |
Location | Occurs in the microsporangia (pollen sacs) of the anther | Occurs in the megasporangium (ovule) within the ovary |
Cell Division | Involves meiosis | Involves meiosis |
Type of Cell | Microspore Mother Cell (2n) | Megaspore Mother Cell (2n) |
End Product | Four haploid microspores (tetrads) | Four haploid megaspores (but typically only one is functional) |
Function | Leads to the formation of pollen grains (male gametophyte) | Leads to the formation of the embryo sac (female gametophyte) |
Type of Cell Division
Both microsporogenesis and megasporogenesis involve meiosis, a type of cell division that reduces the chromosome number by half, resulting in haploid cells.
Structures Formed
Microsporogenesis: The structure formed at the end of microsporogenesis is the microspore tetrad, eventually developing into pollen grains.
Megasporogenesis: The structure formed at the end of megasporogenesis is typically a functional megaspore, which will develop into the embryo sac (female gametophyte).
Important Phrases
Microspores are formed at the end of microsporogenesis and develop into male gametophytes (pollen grains).
Megaspores are formed at the end of megasporogenesis, with one functional megaspore giving rise to the female gametophyte (embryo sac).
Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
The correct developmental sequence of the given terms is:
Sporogenous tissue - This is the initial tissue from which the reproductive cells develop.
Pollen mother cell - Cells of the sporogenous tissue that undergo meiosis to form microspores.
Microspore tetrad - The result of the meiotic division of the pollen mother cells, forming a group of four microspores.
Pollen grain - Microspores that develop into pollen grains.
Male gametes - Formed within the pollen grain after mitotic division.
So, the sequence is: Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes.
With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
A typical angiosperm ovule along with the description of its parts.
Labeled Diagram
Parts of a Typical Angiosperm Ovule
Funicle: The stalk-like structure that attaches the ovule to the placenta in the ovary.
Hilum: The region where the body of the ovule fuses with the funicle. It acts as the junction between the funicle and the ovule.
Integuments: One or two protective layers encircling the nucellus, leaving a small opening called the micropyle at the tip.
Micropyle: A small opening at the tip of the ovule through which the pollen tube penetrates during fertilization.
Nucellus: The mass of cells enclosed within the integuments that contain abundant reserve food materials, providing nourishment to the developing embryo.
Embryo Sac: Also known as the female gametophyte, it is located within the nucellus and contains the egg apparatus, central cell, and antipodal cells.
Chalaza: The basal part of the ovule which lies opposite to the micropylar end.
Descriptions
Funicle: Connects the ovule to the ovary wall and supplies nutrients to the ovule.
Hilum: Acts as an attachment point where the ovule and funicle meet.
Integuments: Provide protection to the nucellus and embryo sac inside the ovule.
Micropyle: Facilitates the entry of the pollen tube for fertilization.
Nucellus: Acts as a nourishing tissue for the developing embryo sac.
Embryo Sac: The site of fertilization that develops into the seed after fertilization.
Chalaza: Marks the base of the ovule and helps in the differentiation of the end of the ovule.
This structure plays a critical role in the reproduction of angiosperms by facilitating the development of seeds from fertilized ovules.
What is meant by monosporic development of female gametophyte?
Monosporic development of the female gametophyte refers to the formation of the embryo sac from a single megaspore. In this process, the megaspore mother cell (MMC) undergoes meiotic division to produce four megaspores. However, only one of these four megaspores remains functional, while the other three degenerate.
Here are the key steps involved in monosporic development:
Megaspore Mother Cell (MMC) undergoes meiosis, resulting in four megaspores.
Three megaspores degenerate, leaving only one functional megaspore.
The functional megaspore undergoes mitotic divisions to form the embryo sac (female gametophyte).
With a neat diagram explain the 7 -celled, 8 -nucleate nature of the female gametophyte.
To explain the 7-celled, 8-nucleate nature of the female gametophyte, we need to delve into the structure of the mature embryo sac of angiosperms.
The process of megasporogenesis and embryo sac formation results in a mature female gametophyte (embryo sac) with the following structure:
8 nuclei that get organized into 7 cells.
Let's visualize this with a diagram and an explanation.
Diagram of a Mature Embryo Sac
Below is a schematic representation of the embryo sac at maturity:
Description and Layout:
Micropylar End (Top):
Egg Apparatus:
1 Egg Cell: Located centrally at the micropylar end.
2 Synergids: Flanking the egg cell on either side. The synergids have special cellular thickenings at their tips known as the filiform apparatus.
Central Cell:
2 Polar Nuclei: These two nuclei reside in a single large central cell. These nuclei are free in the cytoplasm before fertilization.
Chalazal End (Bottom):
3 Antipodal Cells: Located at the opposite end from the micropylar side. These cells often degenerate after performing their function.
Main Points:
Micropylar End has an egg apparatus consisting of 3 cells (1 egg cell + 2 synergids).
Central Cell contains 2 polar nuclei but counts as a single cell.
Chalazal End contains 3 antipodal cells.
Totaling the cells:
3 cells at the micropylar end (egg apparatus: 1 egg cell + 2 synergids).
1 central cell with 2 polar nuclei.
3 cells at the chalazal end (antipodals).
Therefore, the embryo sac is 7-celled but 8-nucleate:
7 cells because the central cell counts as one cell.
8 nuclei altogether: 3 (micropylar end) + 2 (central cell) + 3 (chalazal end).
This unique structure aids in double fertilization, characteristic of angiosperms, where one sperm nucleus fuses with the egg cell to form the zygote (zygote), and the other fuses with the two polar nuclei in the central cell to form the triploid endosperm.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Chasmogamous Flowers
Chasmogamous flowers are the typical flowers that open and expose their reproductive structures (anthers and stigma) to the external environment. This openness allows for pollination by external agents like wind, water, and animals. Examples include most garden flowers like roses, lilies, and sunflowers.
Cross-Pollination in Cleistogamous Flowers
Cleistogamous flowers, on the other hand, do not open at all. Their reproductive structures are enclosed within the buds. This means that cross-pollination cannot occur in cleistogamous flowers. The reasons are:
No Exposure: Since the flowers don't open, pollen from other flowers cannot reach the stigma.
Proximity of Anthers and Stigma: In cleistogamous flowers, anthers and stigma lie very close to each other within an enclosed space which ensures self-pollination.
Therefore, cleistogamous flowers invariably undergo self-pollination as there is no opportunity for pollen from another flower to reach them. This ensures a seed set even in the absence of pollinators but limits genetic variability.
Mention two strategies evolved to prevent self-pollination in flowers.
Two strategies evolved to prevent self-pollination in flowers are:
Temporal Separation: Pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive, or the stigma becomes receptive much before the release of pollen. This prevents self-pollination, as the timings do not align for self-pollen to fertilize the stigma.
Spatial Separation: Anther and stigma are positioned at different heights or locations within the flower. This spatial arrangement ensures that pollen from the same flower does not easily come in contact with the stigma, thereby encouraging cross-pollination.
Both these strategies, temporal and spatial separation, act to facilitate cross-pollination and thereby increase genetic diversity.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Self-incompatibility is a genetic mechanism in flowering plants that prevents self-pollination and thus encourages cross-pollination. It is a form of reproductive barrier that ensures that pollen from the same plant (or closely related plants) is unable to fertilize the ovules, leading to the generation of genetically diverse offspring.
In self-incompatible species, self-pollination does not lead to seed formation due to several reasons:
Pollen Germination Inhibition: The stigma can recognize whether the pollen is from the same plant or a different one. If the pollen is identified as self-pollen, the stigma prevents it from germinating on its surface.
Pollen Tube Growth Inhibition: Even if the self-pollen manages to germinate, the growth of the pollen tube is inhibited in the style. The pollen tube fails to reach the ovule, thereby preventing fertilization.
Abortive Fertilization: In some cases, even if the pollen tube reaches near the ovule, the gametes fail to fuse properly due to biochemical incompatibility, resulting in failed fertilization.
These mechanisms involve complex interactions between specific proteins and genetic markers expressed by the pollen and the pistil, leading to the recognition and rejection of self-pollen. This prevents inbreeding and encourages genetic diversity within the species.
What is bagging technique? How is it useful in a plant breeding programme?
Bagging Technique in Plant Breeding
Bagging is a significant technique used in plant breeding to ensure controlled pollination. When breeding new plant varieties, it's essential to prevent unwanted pollen from contaminating the stigma of the target plant. The bagging technique involves the following steps:
Emasculation: If the female parent has bisexual flowers, the anthers are removed from the flower buds before they dehisce (release their pollen). This is done using a pair of forceps.
Bagging: After emasculation, the flower buds are covered with a bag made of suitable material (usually butter paper) to prevent contamination from external pollen. In species with unisexual flowers, there is no need for emasculation, and the female buds are directly bagged.
Pollination: When the stigma becomes receptive, pollen grains from the desired male parent are dusted onto the stigma.
Rebagging: After the desired pollination, the flowers are rebagged to allow for fruit development without any external pollen interference.
Usefulness in Plant Breeding
The bagging technique is crucial in a plant breeding programme for several reasons:
Prevents Unwanted Pollination: By covering the flower buds, the technique ensures that only the desired pollen fertilizes the flower, preventing contamination by undesired pollen.
Ensures Controlled Crosses: It allows breeders to make specific crosses between selected parent plants, which is essential for developing new plant varieties with desirable traits.
Maintains Purity: The integrity of the breeding programme is maintained by ensuring that the cross is as intended without any external interference.
Accurate Results: The controlled environment provided by bagging results in more accurate and reliable outcomes in experimental cross-breeding.
By using the bagging technique, plant breeders can effectively manage the pollination process, leading to the development of improved and hybrid varieties with preferred characteristics.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Triple fusion is one of the key processes in the fertilization events of flowering plants (angiosperms). Here is a detailed explanation:
Location and Process
Triple fusion occurs within the embryo sac of the ovule, a structure found inside the ovary of a flower. The process is part of double fertilization, which is unique to angiosperms.
Entry: After the pollen grain lands on the stigma, it germinates to form a pollen tube which grows through the style and reaches the ovary.
Penetration: The pollen tube enters the ovule through an opening called the micropyle and then enters one of the synergids, cells surrounding the egg cell inside the embryo sac.
Release of Male Gametes: The pollen tube releases two male gametes (sperm cells) into the synergid.
Involvement of Nuclei
The nuclei involved in the triple fusion are:
One male gamete nucleus (haploid, n)
Two polar nuclei (each haploid, n) present in the central cell of the embryo sac
Fusion
One of the male gametes fuses with the two polar nuclei located in the central cell of the embryo sac. This fusion results in the formation of a triploid (3n) nucleus, known as the Primary Endosperm Nucleus (PEN).
Importance of Triple Fusion
The primary endosperm nucleus will develop into the endosperm, which provides nourishment to the developing embryo. This mechanism ensures that the developing embryo has a reliable source of nutrition.
Illustration
Here's a visual recap of the nuclei involved and the process of triple fusion:
$$ \text{Male gamete (n) + Two polar nuclei (n + n) \rightarrow Primary Endosperm Nucleus (3n)} $$
Thus, triple fusion plays a critical role in the development of seeds in flowering plants by forming the endosperm, which supports early growth and development.
Why do you think the zygote is dormant for sometime in a fertilised ovule?
In a fertilized ovule, the zygote remains dormant for some time to ensure that there is a sufficient supply of nutrients for the developing embryo. This dormancy allows the primary endosperm cell to divide and form the endosperm tissue, which serves as a nutritional source for the growing embryo. Hence, endosperm development precedes embryo development, providing the necessary support for the zygote when it eventually resumes activity and begins to develop into an embryo.
Differentiate between:
(a) hypocotyl and epicotyl; Make table
(b) coleoptile and coleorrhiza; Make table
(c) integument and testa;Make table
(d) perisperm and pericarp. Make table
(a) Hypocotyl vs Epicotyl
Feature | Hypocotyl | Epicotyl |
---|---|---|
Definition | The part of the embryonal axis below the cotyledons and above the radicle. | The portion of the embryonal axis above the cotyledons and terminating in the plumule. |
Position | Located below the cotyledons. | Located above the cotyledons. |
Function | Supports the seedling, connects the above-ground parts of the plant with the root. | Gives rise to the upper part of the stem and the first true leaves. |
Growth | Develops into the lower part of the stem. | Grows into the upper part of the stem. |
(b) Coleoptile vs Coleorrhiza
Feature | Coleoptile | Coleorrhiza |
---|---|---|
Definition | The sheath protecting the young shoot in monocotyledons, specifically in grasses. | The sheath covering the young root in monocotyledons, particularly grasses. |
Position | Surrounds the plumule or the young shoot. | Encloses the radicle or the young root. |
Function | Protects the emerging shoot as it penetrates the soil during germination. | Protects the emerging root and helps in its safe emergence into the soil. |
Appearance | Typically found in grass seedlings like maize and wheat. | Also observed in grass seedlings such as maize and wheat. |
(c) Integument vs Testa
Feature | Integument | Testa |
---|---|---|
Definition | Outer protective layers of cells surrounding the ovule of seed plants. | The outer protective coat of a seed, developed from the integuments of ovule. |
Origin | Develops directly from the ovule. | Formed from the integument as it matures and hardens during seed development. |
exposed to environmental factors like water absorption and gas exchange. | | | Role | Protects the ovule during its development as a part of the flower. | Protects the seed post-fertilization, and during dormancy and germination. |
(d) Perisperm vs Pericarp
Feature | Perisperm | Pericarp |
---|---|---|
Definition | Nutritive tissue inside seeds, derived from the nucellus. | The wall of the fruit that develops from the ovary wall after fertilization. |
Origin | Formed from the persistent nucellus around the embryo sac. | Formed from the ovary of the flower. |
Function | Provides nourishment to the developing seed, particularly in plants like beet and black pepper. | Protects the seeds and aids in their dispersal depending on the fruit type. |
Examples | Found in seeds like beet, pepper where it is more prominent. | Found in all fruiting plants and varies widely (e.g., fleshy fruits like mangoes or dry fruits like nuts). |
Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
An apple is called a false fruit because its formation involves not only the ovary but also other parts of the flower, primarily the thalamus (receptacle). In false fruits, non-ovarian tissue contributes significantly to the structure of the fruit.
Here’s a detailed view:
True Fruit: Develops only from the ovary and contains ovules that develop into seeds.
False Fruit (Pseudocarp): Involves other floral parts in addition to the ovary.
Parts of the Flower Forming the Fruit:
Ovary: Forms the inner core of the apple that contains the seeds.
Thalamus: Swells and becomes fleshy, surrounding the ovary, thereby forming the bulk of the apple we eat.
This is visually represented in the following figure from the chapter:
In summary, the apple's fleshy part primarily forms from the swollen thalamus, not the ovary alone, which classifies it as a false fruit.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Emasculation is the process of removing the anthers from a flower. This technique is typically performed when the flower is still in the bud stage to prevent the release of pollen.
When is emasculation employed?
Emasculation is used during the breeding process, specifically in cross-pollination or hybridization experiments.
Why does a plant breeder use this technique?
A plant breeder employs emasculation to ensure that:
Self-pollination is prevented: By removing the anthers, the flower cannot fertilize itself.
Controlled pollination: It allows the breeder to control the pollination process by introducing pollen from a desired male parent.
Prevent contamination: Bagging the emasculated flower ensures that no unwanted pollen contaminates the stigma.
In summary, emasculation is crucial for controlled breeding programs to develop desired hybrids or to introduce specific traits from one plant to another.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
To induce parthenocarpy through the application of growth substances, you should select fruits that are commercially valuable and commonly consumed but often have seeds that can be undesirable. Here are some examples and reasons:
Banana: While bananas naturally exhibit parthenocarpy, inducing parthenocarpy in other varieties could ensure seedless fruits, which are preferred by consumers.
Grapes: Seedless grapes are commercially very popular. Inducing parthenocarpy can help produce more seedless varieties that are easier to eat and preferred for making raisins.
Watermelon: Seedless watermelons are highly sought after since they offer a better eating experience without seeds, making them more convenient for consumption.
Apple: Though apples usually have few seeds, inducing parthenocarpy could produce completely seedless varieties, enhancing consumer appeal.
Tomato: Seedless tomatoes are desirable for culinary uses, especially in sauces and canned products, as they provide a smoother texture.
Inducing parthenocarpy in these fruits enhances their market value by improving consumer convenience and preference. Seedless varieties are easier to eat, process, and can lead to a higher commercial demand, thus benefiting both consumers and producers.
Explain the role of tapetum in the formation of pollen-grain wall.
The tapetum is the innermost layer of cells in the wall of the microsporangium (or anther) and plays a crucial role in the development of the pollen grain wall. Its main functions include:
Nourishment: The tapetal cells, which are rich in dense cytoplasm and often bi-nucleate, provide essential nutrients and enzymes that are vital for the development and maturation of microspores (pollen grains).
Secretion of Sporopollenin Precursors: The tapetum secretes precursor materials necessary for the formation of sporopollenin, which is the main component of the pollen grain's outer layer, the exine. Sporopollenin is one of the toughest organic polymers known and is highly resistant to degradation by physical or chemical agents.
Enzymatic Activity: The tapetum produces various enzymes which are involved in modifying the pollen wall structure, ensuring the proper formation of germ pores where sporopollenin is absent, facilitating pollen tube germination.
Transport of Materials: Tapetal cells may transport specific compounds to the developing pollen grains, such as lipids, proteins, and carbohydrates, which are essential for the viability and functionality of the pollen.
Callose Dissolution: After the pollen mother cells undergo meiosis to form microspore tetrads, the tapetum produces enzymes that break down the callose wall that surrounds each tetrad. This releases individual microspores, which can then develop into mature pollen grains.
In summary, the tapetum is essential for providing nutritional support, synthesizing vital components, and facilitating enzymatic processes that contribute to the formation of a robust and functional pollen grain wall.
What is apomixis and what is its importance?
Apomixis is a form of asexual reproduction that mimics sexual reproduction, whereby seeds are formed without fertilization. In apomictic plants, the diploid egg cell is formed without reduction division, and it can develop into an embryo without fertilization. There are several ways apomictic seeds can develop, including the formation of embryos from nucellar cells surrounding the embryo sac, as seen in many Citrus and Mango varieties, leading to seeds with multiple embryos, a phenomenon known as polyembryony.
Importance of Apomixis
True-to-type Progeny: Since apomictic reproduction bypasses meiosis and fertilization, the progeny are genetically identical to the parent plant. This ensures the retention of desirable traits in successive generations.
Stable Hybrid Traits: In agriculture, hybrids often have enhanced traits like higher yield or disease resistance. These traits can segregate in sexual reproduction, but apomixis preserves these hybrid traits across generations.
Cost-Effective Cultivation: Farmers do not need to purchase hybrid seeds every season as apomictic plants propagate true-to-type hybrid seeds, reducing costs significantly.
Conservation of Genetic Resources: Apomictic seeds can be used to maintain genetic lines without changes over long periods, which is crucial for conservation and breeding programs.
Production of Consistent Crops: It leads to uniformity in crops, which is beneficial for crop management and harvesting.
In conclusion, apomixis plays a crucial role in horticulture and agriculture due to its ability to maintain genetic stability and reduce costs associated with hybrid seed production. Research is ongoing to understand the genetics of apomixis and to potentially transfer apomictic traits to other hybrid crops.
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Ask Chatterbot AIExtra Questions - Sexual Reproduction in Flowering Plants | NCERT | Biology | Class 12
This graph is a typical cell cycle representing DNA content of various phases (1 to 4). Identify the phases based on changes in the DNA content and select the correct option.
A) $\mathrm{M}, \mathrm{G}_{1}, \mathrm{S}, \mathrm{G}_{2}$.
B) $\mathrm{G}_{2}, \mathrm{M}, \mathrm{G}_{1}, \mathrm{S}$.
C) $\mathrm{S}, \mathrm{G}_{2}, \mathrm{M}, \mathrm{G}_{1}$.
D) $\mathrm{G}_{1}, \mathrm{S}, \mathrm{G}_{2}, \mathrm{M}$.
The correct option is D) $\mathrm{G}_{1}, \mathrm{S}, \mathrm{G}_{2}, \mathrm{M}$.
In the $\mathrm{G}_{1}$ phase (Phase 1 in the graph), the DNA content remains constant at $2C$. This phase is characterized by normal cellular activities without DNA replication.
$\mathrm{S}$ phase (Phase 2 in the graph) is when DNA replication occurs, resulting in the DNA content progressively doubling from $2C$ to $4C$.
$\mathrm{G}_{2}$ phase (Phase 3 in the graph) follows the completion of DNA replication; hence the DNA content is stabilized at $4C$.
During the $\mathrm{M}$ phase (Phase 4 in the graph), mitosis takes place and DNA content is divided between two daughter cells, returning back to $2C$.
The sequence $\mathrm{G}{1}, \mathrm{S}, \mathrm{G}{2}, \mathrm{M}$ accurately accounts for these changes in DNA content through the cell cycle phases. Therefore, the correct option is D) $\mathrm{G}{1}, \mathrm{S}, \mathrm{G}{2}, \mathrm{M}$.
Mark the statements as True ($T$) or False ($F$) respectively.
I. Reproduction takes place in juvenile stage of life cycle.
II. Eyes of potato tuber are condensed internode.
III. During embryogenesis, zygote undergoes cell division and cell differentiation.
IV. Sexual reproduction is a complex and elaborate process.
A. $T, F, T, F$ B. $F, T, T, F$ C. $F, F, T, T$ D. $T, T, F, F$
The correct answer is Option C: $F, F, T, T$. Let's analyze each statement:
Statement I: Reproduction takes place in the reproductive or adult stage of an organism's life cycle, not in the juvenile stage. Hence, this statement is False.
Statement II: The 'eyes' of a potato tuber are actually the nodes on the modified stems of the plant, not condensed internodes. Therefore, this statement is False.
Statement III: During embryogenesis, the zygote undergoes both cell division and cell differentiation to develop into an embryo. This statement is True.
Statement IV: Sexual reproduction involves multiple stages including pre-fertilization, fertilization, and post-fertilization events, making it a complex and elaborate process. Thus, this statement is True.
In summary, Statements I and II are False, while Statements III and IV are True. Therefore, the answer is Option C: $F, F, T, T$.
Removal of the ring of tissue outside the vascular cambium from the tree trunk kills it because:
A. water cannot move up. B. roots become starved. C. shoot becomes starved. D. annual rings are not produced.
The correct option is B: roots become starved.
The vascular cambium is a vital plant tissue that is situated between the xylem and the phloem in the stems and roots of vascular plants. Since the phloem is located outside the xylem for most plants, removing the bark and the phloem in a complete ring around the stem can kill a tree. This is because, once the phloem is damaged, it can no longer transport nutrients down to the roots, depriving them of essential sustenance. Consequently, the roots become starved. On the other hand, the shoot can still sustain itself as it continues to photosynthesize and produce its own food.
Which statement(s) is/are true? (a) Open vascular bundles are found in dicot stem. (b) Porous wood is found in Pinus. (c) Cortex is made up of only parenchymatous cells. (d) Passage cells are found in endodermis of orchid roots.
A) a and b
B) b and c
C) c and d
D) a and d
The correct answer is Option D: a and d.
(a) Open vascular bundles are typically found in dicot stems, contrasting with monocot stems, which typically feature closed vascular bundles.
(b) Pinus, which is a type of gymnosperm, characteristically has non-porous wood. This differs from angiosperms, which usually have porous wood. Gymnosperms like Pinus lack vessels, which is why their wood is non-porous.
(c) While the cortex in plants’ stems or roots is indeed primarily composed of parenchyma, it is not composed exclusively of these cells. The outermost layer, known as the hypodermis, typically consists of a few layers of either collenchyma or sclerenchyma cells.
(d) Passage cells are specialized cells found in the endodermis of monocot roots. Orchids, being monocots, possess these passage cells in the endodermis of their roots.
Therefore, among the given options, only statements (a) and (d) are correct.
__________ flowers contain either pistil or stamen, while ____________ flowers contain both stamen and pistil.
A) Bisexual
B) Asexual
C) Unisexual
D) Regular
E) Irregular
The correct answers are:
A) Bisexual
C) Unisexual
Unisexual flowers are defined as those possessing either a pistil or a stamen but not both. Conversely, bisexual flowers feature both a pistil and a stamen, allowing them to self-pollinate.
How much percentage of pollen grains do angiosperms shed at 2-celled stage?
(A) >40%
(B) >50%
(C) >60%
(D) >70%
The correct answer is (C) >60%.
In angiosperms, more than 60% of the pollen grains are shed at the 2-celled stage. At this stage, each pollen grain consists of two cells: a generative cell and a vegetative cell. Subsequently, for the remaining less than 40% of pollen grains, the generative cell divides to form two male gametes, turning these grains into 3-celled pollen grains. Thus, the majority of pollen shedding occurs at the 2-celled stage.
Conjoint, collateral, open, and endarch vascular bundles are found in
A. monocot stem
B. monocot root
C. dicot root
D. dicot stem
The correct answer is Option A: monocot stem.
In the monocot stem, the vascular bundles are characterized as conjoint, collateral, open, and endarch. This unique combination of bundle characteristics helps to define and distinguish it structurally from other plant types.
Lignin and cellulose present in xylem vessels show affinity for water due to
A) Adhesive forces
B) Cohesive forces
C) Water potential
D) Wall pressure
The correct answer is Option A: Adhesive forces.
The walls of xylem vessels, which are made up of lignin and cellulose, exhibit an affinity for water primarily due to adhesive forces. Adhesion refers to the attraction between water molecules and the molecules of the vessel walls. This property is crucial for the ascent of sap in plants, assisting alongside the cohesive forces among the water molecules themselves.
Which of the following are the characteristics of self-pollinated plants?
A. Flowers are large and showy.
B. Flowers remain closed and do not open.
C. Stigma and anthers mature at the same time.
D. Pollen is produced in large quantity.
The characteristics of self-pollinated plants can be identified by certain distinctive features among the given options:
Option B: Flowers remain closed and do not open.
Option C: Stigma and anthers mature at the same time.
Explanation:
Self-pollinated plants often exhibit the following characteristics:
Flowers may be small and less conspicuous compared to those of cross-pollinated plants.
The proximity of stigma and anthers: These parts of the flower are positioned closely to ensure that pollen easily transfers to the stigma of the same flower.
Simultaneous maturity of sexual organs: Both stigma and anthers mature at the same time to facilitate the transfer of pollen at the optimal time.
Closed flower morphology: In rare cases, the flowers might not open at all, which ensures that the pollen does not disperse far and only pollinates the same flower.
Therefore, the correct answers are Option B and Option C.
If tall is dominant over short, then which of the following character will be expressed when both the dominant allele and recessive allele are present?
A) Tall
B) Short
C) Medium height
D) It is random
The correct option is A) Tall.
In genetics, dominance means that when both a dominant allele and a recessive allele are present in an individual, the trait associated with the dominant allele is always expressed. Therefore, if 'Tall' is the dominant trait and 'Short' is the recessive trait, the presence of both alleles (heterozygous condition) results in the expression of the tall trait. This principle holds true for a monohybrid cross where a single trait, such as height, is being studied.
State true or false: Flowers are attractive solely for the purpose of bringing the insect to it and enabling pollination.
A) True
B) False
The correct answer is B) False.
Flowers serve primarily as the reproductive structures of angiosperms. Their primary function revolves around the facilitation of reproduction through the process of pollination. The visually appealing petals of flowers play a crucial role in attracting insects, which is key for pollination. Insects, in search of nectar, interact with flowers such that the pollen grains—which are lightweight and sticky—adhere to the insects' body and wings. As these insects move to other flowers, they inadvertently transfer the pollen, thus facilitating the transfer from one flower to another—essential for successful pollination.
However, stating that attraction is solely for bringing insects and enabling pollination is an oversimplification. Flowers may also attract other pollinators such as birds and bats, and some flowers have evolved to rely on wind or water for pollination. Therefore, the statement that flowers have the sole purpose of attracting insects for pollination is false.
Which of the following is correct for Cycas reproduction?
A. Zooidogamy is followed by siphonogamy.
B. Siphonogamy is followed by zooidogamy.
C. Siphonogamy only.
D. Zooidogamy.
The correct answer is B. Siphonogamy is followed by zooidogamy.
In the reproduction of Cycas, the process begins with siphonogamy, which involves the formation of a pollen tube, followed by zooidogamy, where ciliated male gametes are involved. This sequence ensures the successful fertilization and subsequent development in Cycas reproduction.
Purebred tall pea plants are first crossed with purebred dwarf pea plants. The pea plants obtained in the F1 generation are then crossbred to produce the F2 generation of pea plants. (a) What do the plants of the F1 generation look like? (b) What is the ratio of tall plants to dwarf plants in the F2 generation? (c) Which type of plants were missing in the F1 generation but reappeared in the F2 generation?
(a) The plants in the F1 generation are all tall.
This is because tallness is the dominant trait over dwarfness. When purebred tall plants are crossed with purebred dwarf plants, all offspring will display the dominant trait, tallness.
(b) The ratio of tall to dwarf plants in the F2 generation is 3:1.
When the F1 generation plants, which are all tall but heterozygous, are interbred, the resulting F2 generation follows a typical Mendelian inheritance pattern: three-quarters of the plants are tall, and one-quarter are dwarf. This can be breakdown as:
TT (tall)
Tt (tall)
tT (tall)
tt (dwarf)
Thus, for every three tall plants, there is one dwarf plant.
(c) Dwarf plants were missing in the F1 generation but reappeared in the F2 generation.
In the F1 generation, all plants were tall, as tall is dominant. However, the recessive trait (dwarfness) which was 'hidden' in the F1 heterozygous plants (Tt), reappeared in the F2 generation among offspring who inherited two recessive alleles (tt).
The fusion of male and female gametes is termed as _______________.
The fusion of male and female gametes is termed as fertilization.
The correct sequence of reproductive stages seen in flowering plants is:
A. Gamete $\rightarrow$ zygote $\rightarrow$ embryo $\rightarrow$ seedling
B. Zygote $\rightarrow$ gamete $\rightarrow$ embryo $\rightarrow$ seedling
C. Seedling $\rightarrow$ embryo $\rightarrow$ zygote $\rightarrow$ gametes
D. Gamete $\rightarrow$ embryo $\rightarrow$ zygote $\rightarrow$ seedling
The correct option is A. Gamete $\rightarrow$ zygote $\rightarrow$ embryo $\rightarrow$ seedling
The male gamete is found within the pollen grain, produced in the anther of the stamen, and the female gamete is the egg, formed in the ovary of the pistil.
Fertilization occurs when the male and female gametes fuse together, forming the zygote.
This zygote then undergoes multiple divisions, developing into an embryo, which continues to mature inside the seed.
Finally, the seed germinates and develops into seedlings.
At the time of entering into ovule, the pollen tube has:
A) Three male nuclei
B) Two male nuclei
C) One gamete nucleus
D) Four male gametes
The correct answer is B) Two male nuclei.
At the moment it enters the ovule, the pollen tube contains two male nuclei. These are crucial for the process of fertilization in plants.
Alleles for a trait occur singly in gametes and are restored in the F1 generation by
A. fertilization
B. gametogenesis
C. sporulation
D. pollination
The correct answer is A. fertilization.
Fertilization is the process where male and female gametes (sperm and egg cells, respectively) fuse together. This fusion brings together alleles from both parents, restoring the diploid state of chromosomes in the zygote. Thus, the alleles that occur singly in each gamete are combined and restored in the F1 generation through fertilization.
Choose the correct statement:
A. The meiocyte of maize and the cells in the aleurone layer of maize have the same number of chromosomes.
B. A female gamete is never motile.
C. Bryophytes produce gametes by mitosis.
D. Neelakuranji is a monocarpic biennial.
The correct answer is C. Bryophytes produce gametes by mitosis.
Here is why the other statements are incorrect:
A. The meiocyte of maize and the cells in the aleurone layer of maize have the same number of chromosomes: False. The meiocyte of maize is diploid, whereas the cells in the aleurone layer are triploid.
B. A female gamete is never motile: False. In certain species, particularly among fungi and algae, the female gamete can be motile.
D. Neelakuranji is a monocarpic biennial: False. Neelakuranji is actually a perennial plant.
In summary, for option C, it is known that the plant body of bryophytes is haploid, and thus gametes are produced through mitosis in order to maintain the haploid state during reproduction.
Pollination in this kind of plant occurs primarily with the help of:
A. wind
B. insects
C. water
D. humans
The correct answer is B. insects
Pollination in plants that have bright and colorful petals, such as a rose, typically occurs via insects. These attributes attract insects, which facilitate the transfer of pollen.
"What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer."
Chasmogamous flowers are characterized by having exposed anthers and stigmas because they open upon reaching maturity.
Cleistogamous flowers, in contrast, never open. This structural form leads to inevitable self-pollination since the anthers and stigma remain enclosed, making them inaccessible to other pollinators. Therefore, cross-pollination cannot occur in cleistogamous flowers due to their permanent closure. Nonetheless, these flowers still manage to produce seeds through self-pollination.
Which of the following can't be detected in amniocentesis?
A) Sex of fetus
B) Down's syndrome
C) Jaundice
D) Turner's syndrome
The correct answer is C) Jaundice.
Amniocentesis is a diagnostic procedure primarily used to analyze the chromosomal patterns in the cells found in the amniotic fluid surrounding the fetus. It is effectively employed to determine the sex of the fetus and to detect genetic or chromosomal abnormalities such as Down's syndrome and Turner's syndrome. However, jaundice is not a genetic condition; it is a condition related to liver function and bilirubin metabolism, which is not detectable through genetic testing like amniocentesis. Thus, amniocentesis cannot detect jaundice.
Which of these is applicable to insect-pollinated flowers?
A) Flowers are very small and are produced in large quantities.
B) Flowers are not prominent and without nectar.
C) Flowers are conspicuous and scented, having nectar.
D) None of these.
The correct answer is C) Flowers are conspicuous and scented, having nectar.
Insect-pollinated flowers exhibit certain characteristics to attract insects for the purpose of pollination. These flowers are typically large, brightly colored, and often grouped in noticeable clusters known as inflorescences. They also produce scent and nectar to attract and reward the pollinating insects, making them distinct from flowers that rely on wind or other non-animal agents for pollination.
Why is a fruit not produced in hibiscus after fertilization?
The main reason a hibiscus does not produce fruit after fertilization is because the seeds that develop will not resemble the parent plant.
How many different types of gametes will be produced by a plant having genotype $A A B b C c$?
A) 1
B) 2
C) 3
D) 4
The correct option is D) 4
When considering the genotype $AA, Bb, Cc$:
The gene combination for $AA$ can only form one type of gamete concerning the A allele because both alleles are identical.
For $Bb$, where the alleles are heterozygous, two types of gametes can be formed either carrying the B allele or b allele.
Similarly, $Cc$ can also provide two types of gametes, either carrying the C allele or c allele.
Therefore, by considering all possible combinations of the different alleles from each gene, we get: $$ 1 \text{ (from } AA\text{)} \times 2 \text{ (from } Bb\text{)} \times 2 \text{ (from } Cc\text{)} = 4 \text{ different types of gametes}. $$
Hence, the plant with genotype $AA, Bb, Cc$ can produce four different types of gametes.
Pineapple arises from the fusion of embryos from multiple flowers.
A) True
B) False
The correct answer is A) True.
Pineapple is a multiple fruit that forms from the fusion of the ovaries of multiple flowers. Each segment of a pineapple is derived from a flower's ovary, making the entire pineapple a cluster of fused fruits developed from a group of flowers.
A homozygous plant having round (R) and yellow (Y) seeds is crossed with a homozygous plant having wrinkled (r) and green (y) seeds:
(a) Give the scientific name of the plant on which Mendel conducted his hybridization experiments. (b) Give the genotype of the F1 generation.
(c) Give the dihybrid phenotypic ratio and the phenotype of the offspring of the F2 generation when two plants of the F1 generation are crossed.
(d) Name and state the law that explains the dihybrid ratio.
(e) Give the possible combinations of gametes that can be obtained from the F1 hybrid.
(a) Scientific Name: Pisum sativum (commonly known as garden pea).
(b) Genotype of the F1 Generation: When a homozygous plant (RRYY) for round and yellow seeds is crossed with a homozygous plant (rryy) for wrinkled and green seeds, all offspring (F1) will have the genotype RrYy. This genotype exhibits round and yellow seeds due to the dominance of the alleles R (round over wrinkled) and Y (yellow over green).
(c) Dihybrid Phenotypic Ratio and Phenotype of F2 Offspring: - The phenotypic ratio of the F2 generation from two F1 hybrids (RrYy x RrYy) is 9:3:3:1: - 9 Round Yellow (RRYY, RRYy, RrYY, RrYy) - 3 Round Green (RRyy, Rryy) - 3 Wrinkled Yellow (rrYY, rrYy) - 1 Wrinkled Green (rryy)
(d) Law Explaining the Dihybrid Ratio: - Law of Independent Assortment: This genetic principle states that the alleles of different genes segregate independently of one another during the formation of gametes. This law explains why the dihybrid phenotypic ratio 9:3:3:1 arises in the F2 generation.
(e) Possible Combinations of Gametes from the F1 Hybrid: - The F1 hybrids (RrYy) produce four types of gametes due to the process known as independent assortment. The gamete combinations are: - RY (Round Yellow) - Ry (Round Green) - rY (Wrinkled Yellow) - ry (Wrinkled Green) These combinations occur because each gamete randomly receives either allele (R or r) and either allele (Y or y).
Suppose in a flower of mustard each microsporangium possesses 20 pollen mother cells. Then, what is the total number of male gametes formed by this flower? A. 3840 B. 480 C. 240 D. 120
To solve for the total number of male gametes formed by a mustard flower, follow these calculations:
Number of stamens in the flower: Mustard flowers typically have six dithecous (having two thecae) stamens.
Total microsporangia per stamen: Each stamen contains two thecae, each having two microsporangia. Therefore, each stamen has (2 \times 2 = 4) microsporangia.
Microspore mother cells per microsporangium: Each microsporangium contains 20 pollen mother cells.
Total microspore mother cells in one stamen: $$ 20 \text{ cells} \times 4 \text{ microsporangia} = 80 \text{ cells} $$
Total microspore mother cells in all stamens: $$ 80 \text{ cells/stamen} \times 6 \text{ stamens} = 480 \text{ cells} $$
Number of pollen grains per microspore mother cell: Each microspore mother cell undergoes meiosis to produce 4 pollen grains.
Total pollen grains produced: $$ 480 \text{ cells} \times 4 \text{ grains/cell} = 1920 \text{ pollen grains} $$
Since each pollen grain produces 2 male gametes, the total number of male gametes formed is: $$ 1920 \text{ pollen grains} \times 2 \text{ gametes/grain} = 3840 \text{ gametes} $$
Therefore, the correct answer is 3840 male gametes, option A.
Flowers which have a single ovule in the ovary and are packed into an inflorescence are usually pollinated by:
A. Water B. Bee C. Wind D. Bat
The correct answer is C. Wind.
Wind-pollinated flowers, also known as anemophilous flowers, typically have a single ovule in each ovary and are grouped closely together in an inflorescence. These flowers are designed to facilitate wind pollination, featuring:
Well-exposed stamens, allowing pollen to be easily carried away by the wind.
Pollen grains that are light and non-sticky, enhancing their dispersal through wind currents.
Large, feathery stigmas which are effective at trapping airborne pollen grains.
An example of a plant with wind-pollinated flowers is the corn cob.
If the chromosome number in a gamete of an apple plant cell is 17, then what would be the number of chromosomes in the meiocyte of that plant?
A) 17
B) 34
C) 68
D) 51
The correct answer is B) 34.
Explanation:A meiocyte is a diploid cell, which means it contains two sets of chromosomes. It undergoes meiosis to generate haploid gametes, each containing half the number of chromosomes present in the meiocyte.
Given that the chromosome number in a gamete of an apple plant is 17, the meiocyte, having twice the number of chromosomes as a gamete, would therefore have: $$ 2 \times 17 = 34 $$ Thus, the number of chromosomes in the meiocyte of the apple plant is 34.
Which one among the following is known as an encapsuled embryo?
A) Seed
B) Pollen grain
C) Fruit
D) Embryo sac
The correct answer is A) Seed.
A seed contains the encapsulated embryo, which is a crucial stage of the plant life cycle where the new plant begins to develop from the fertilized ovule. The seed provides protection and nutrients to the embryo.
Pollengrains (option B), are the male microgametophytes of seed plants and do not encapsulate an embryo, but rather serve to fertilize the female part. Fruits (option C) are the structures that form from the ovary of flowering plants and usually contain seeds, but are not themselves embryos. Finally, the Embryo Sac (option D) houses the female gametophytes — it includes the egg nucleus but is not an embryo itself, and it develops into a seed only upon successful fertilization.
Growth of plants is not promoted by:
A. Cytokinins B. Auxins C. Gibberellins D. Abscisic acid
The question asks which hormone does not promote the growth of plants. To answer this, let’s review the roles of each hormone listed in the options:
Cytokinins: They are involved in cell division and are known to promote the growth of plants by stimulating cell division in roots and shoots.
Auxins: These hormones play a critical role in apical dominance, which is the phenomenon where the main, central stem of the plant grows dominantly over the side shoots. Auxins promote the lengthening of stems, thus enhancing the plant's growth.
Gibberellins: Similar to auxins, gibberellins help in increasing the length and height of the stem. They are vital in boosting the overall growth of plants.
Abscisic acid: Unlike the other hormones listed, abscisic acid acts primarily as a growth inhibitor. It is involved in processes like the wilting of leaves and seed dormancy, which are essentially functions that do not promote growth but rather slow it down.
Given this information, the correct answer is:
D. Abscisic acid
Abscisic acid does not promote growth; instead, it serves functions that generally inhibit growth and development in plants.
Two similar pea plants are growing on two different islands separated by a vast ocean. The phenomenon of geographical isolation will:
A. not be seen as the plants get self-pollinated. B. not be seen as the plants get pollinated by regions. C. be seen as the plants do not get pollinated and ocean water currents. D. reproduces asexually.
Answer: A. not be seen as the plants get self-pollinated.
Explanation
Two similar pea plants are growing on two different islands, separated by a vast ocean. This setup presents a potential case for geographical isolation. However, geographical isolation typically leads to species developing different traits due to lack of interactions and gene flow between isolated populations, often resulting in the evolution of new species.
In this scenario, however:
Self-pollination is a key characteristic of pea plants. This means each plant can fertilize itself without the need for pollination from other plants. Since pea plants have both male and female reproductive parts within the same flower, they are inherently capable of self-pollination.
Given that these pea plants can self-pollinate, they do not rely on external factors for reproduction. Therefore, even though they are geographically isolated by the ocean, the separation does not impact their reproductive process.
The physical barrier (ocean) does not affect their genetic makeup or reproductive success because there is no need for cross-pollination between the islands.
Consequently, geographical isolation in terms of gene flow and the development of new traits due to isolation is not applicable here. The plants on each island will continue to grow and reproduce identically due to self-pollination, maintaining the same traits despite their separation.
Thus, Option A is correct. The phenomenon of geographical isolation will not be seen in these pea plants due to their ability to self-pollinate.
Reticulate venation is not found in leaves of: A. Onion B. Rose C. Radish D. Tulsi
The question asks us to identify among the given options (Onion, Rose, Radish, and Tulsi) which plant does not exhibit reticulate venation in its leaves.
Venation is the pattern of veins in the leaves of a plant, which are crucial for the transportation of water and nutrients. Reticulate venation, where veins form a net-like pattern, is generally found in dicot plants. Another type, parallel venation, where veins run parallel to one another, is typical of monocot plants.
Analyzing the options:
Onion: This plant, part of the monocots, generally has leaves with parallel venation.
Rose: Known as a dicot, the rose exhibits the net-like or reticulate venation.
Radish: Similarly, being a dicot, radish leaves also show reticulate venation.
Tulsi (Basil): Another dicot, Tulsi leaves too demonstrate reticulate venation.
Given this information, the correct answer is: A. Onion, which does not have reticulate venation, but rather shows parallel venation.
Plants normally growing on sand are known as -
A) Lithophytes
B) Xerophytes
C) Chasmophytes
D) Psammophytes
Plants that normally grow on sand are specifically referred to as Psammophytes. This type of vegetation has adapted to thrive in sandy environments, which typically have low nutrient content and water retention capacity. Understanding the different types of specialized plants, we observe:
Lithophytes: These are plants that grow on rocks.
Xerophytes: Adapted to environments with scarce water, such as deserts.
Chasmophytes: Grow in crevices of rocks where organic matter can accumulate.
Given these distinctions, the correct answer to the question is: D) Psammophytes.
Budding type of Reproduction is found in:
A. Peepal
B. Bryophyllum
C. Rose
D. Sugar Cane
Budding type of reproduction is a form of vegetative reproduction where new individuals develop from buds produced on the parent organism. The correct option for a plant that reproduces by budding among those listed is Bryophyllum.
In Bryophyllum, certain leaves have marginal buds; these buds can form along the edges or margins of the leaves. Over time, when these leaves mature and eventually fall onto the soil, the marginal buds can give rise to new plants. Each of these new plants grows and develops as a new individual, independent of the parent plant.
This type of reproduction uniquely illustrates vegetative reproduction by leaves, specifically through budding, a process where parts of the plant body become detached and grow into new, identical plants. This method is particularly significant as it doesn't involve seeds or spores but occurs through simple vegetative growth and natural propagation.
Thus, the correct answer from the given options is: B. Bryophyllum. Options A (Peepal), C (Rose), and D (Sugar Cane) do not primarily use budding for reproduction.
Which of the following is a plant hormone?
A) Insulin
B) Thyroxin
C) Cytokinin
D) Oestrogen
The question asks which of the provided options is a plant hormone. Let's review each option:
Insulin - This hormone is involved in the utilization of glucose and is found in humans and other animals but not in plants.
Thyroxin - This is a thyroid hormone involved in metabolism, specifically found in animals.
Cytokinin - This hormone promotes cell division and is involved in the growth and various functions of plants, including in their development and aging processes.
Oestrogen - Known as a female reproductive hormone, it is predominant in animals.
From the information reviewed, the correct answer is: Cytokinin (Option C), as it is the only hormone among the options that is found in plants and plays a crucial role in their growth and development.
The Anther contains:
A. Sepals
B. Ovules
C. Pistil
D. Pollen grains
In flowering plants, the anther is a key part of the male reproductive structure known as the stamen, which also includes a filament supporting the anther. The anther is crucial because it houses and produces pollen grains, which contain the male gametes necessary for reproduction.
The options provided in the question are:
Sepals, which are the green, leaf-like structures that protect the developing bud.
Ovules, which develop into seeds after fertilization.
Pistil, the female reproductive part of a flower.
Pollen grains, which are produced in the anther and carry the male gametes.
From these options, it's evident that the anther specifically contains pollen grains. This is important for the plant's reproduction process, as these grains carry the male gametes that, upon reaching a female ovule, lead to fertilization and the production of the next generation through the formation of a zygote.
Therefore, the correct answer is:
D. Pollen grains
Pollination in Maize is carried out by:
A Insect
B Water
C Air
D Animal
Pollination in maize is a critical biological process which determines the plant's ability to reproduce and produce kernels. The process of pollination refers to the transfer of pollen grains. These pollen grains contain the male gametes from the flowers of one plant to the stigma of another plant, facilitating fertilization.
In the case of maize, the pollination is primarily carried out by wind. This means that the pollen grains are released from the male parts of the plant (known as tassels) into the air. The wind then carries these grains to nearby plants where they land on the receptive female part called the silk, leading to fertilization.
Therefore, the correct answer from the provided options is:
C Air
The other options including insects, water, and animals do not generally play a role in the pollination of maize. These agents, while significant for many other plant species, are not the primary pollinating agents for maize, which relies mostly on wind for this essential process.
Which of the following have naked seed?
A. Algae
B. Bryophyta
C. Gymnosperm
D. Angiosperm
The term "naked seeds" refers to seeds that are not enclosed within a fruit; this is typical of gymnosperms.
Here's a breakdown of the options given:
Algae (A) - These are primitive plants, mostly aquatic and do not produce seeds at all, hence they cannot have naked seeds.
Bryophyta (B) - Includes mosses and liverworts, which also do not produce seeds. They reproduce via spores.
Gymnosperms (C) - This group of plants includes conifers like pines and firs, which produce seeds that are not enclosed in an ovary; the seeds are exposed on scales or leaves, which categorizes them as having naked seeds.
Angiosperms (D) - These are flowering plants where the seeds are enclosed within a fruit, thus they do not have naked seeds.
Therefore, among the options listed, gymnosperms are the correct answer as they are known for having naked seeds. This corresponds with option C. Thus, the correct answer to the question is:
C. Gymnosperm
Seed is a modification of:
A. ovary
B. ovule
C. thalamus
D. all of these
Seeds in flowering plants, also known as angiosperms, develop as a result of the process of fertilization. This process involves the fusion of male and female gametes. Specifically, after fertilization, several transformations occur within the flower, with one of the most crucial being that the ovule transforms into a seed.
The options given were:
A. ovary
B. ovule
C. thalamus
D. all of these
While the ovary of the flower develops into the fruit post-fertilization, it is specifically the ovule that undergoes the transformation to become the seed.
Thus, the correct answer to the question "Seed is a modification of:" is:
B. ovule.
Genotypic ratio of $F_{2}$ generation in monohybrid cross is:
A $3:1$
B $9:3:3:1$
C $1:2:1$
D $1:3$
In a monohybrid cross, two individuals are crossed who are heterozygous for one particular gene. Typically, this involves a trait governed by one gene, where each parent contributes one of two alleles: a dominant (e.g., A) and a recessive (e.g., a). The parents in the original cross are usually pure-breeding (homozygous), e.g., AA and aa. Their offspring ($F_1$ generation) are all heterozygous (Aa). When these $F_1$ individuals self-pollinate or are crossed with each other, the resultant $F_2$ generation exhibits a genetic variability.
Predicting the outcome can be represented using a Punnett square. The Punnett square for a monohybrid cross of $F_1$ generation (Aa x Aa) segregates the alleles as follows:
AA: one offspring
Aa: two offspring
aa: one offspring
Thus, the genotypic ratio of the $F_2$ generation for this monohybrid cross is 1:2:1, where:
1
homozygous dominant (AA)2
heterozygous (Aa)1
homozygous recessive (aa)
Correct Answer:
Option C: 1:2:1
This genotypic ratio corresponds specifically to monohybrid crosses involving one gene with two alleles showing complete dominance.
A leguminous plant grown in an autoclaved, sterilized soil fails to produce root nodules because:
A. Autoclaved soil is not good for root growth. B. Autoclaved soil is devoid of bacteria. C. Autoclaving reduces $N_{2}$ content of soil. D. Plants cannot form root hairs in such soil.
Leguminous plants rely on a symbiotic relationship with a particular type of bacteria known as Rhizobium to produce root nodules. These nodules are crucial for the process of nitrogen fixation, where Rhizobium converts atmospheric nitrogen into ammonia. This conversion is essential because plants can only absorb nitrogen in the form of ammonia or nitrates.
The reason a leguminous plant grown in autoclaved, sterilized soil fails to produce root nodules is that the autoclaving process eliminates all microorganisms, including the Rhizobium bacteria. Without these bacteria, the plant cannot perform nitrogen fixation nor develop the root nodules necessary for this symbiotic process.
Therefore, the correct answer is: B. Autoclaved soil is devoid of bacteria.
This answer highlights the importance of Rhizobium bacteria in the formation of root nodules and the nitrogen fixation process, demonstrating why sterilized soil, though free of pathogens, is not conducive for the growth of leguminous plants in this aspect.
The girth of stem increases due to the activity of: A. lateral meristem. B. apical meristem. C. intercalary meristem. D. apical and intercalary meristem.
The increase in the girth of the stem is facilitated by the activity of the lateral meristem, as indicated by option A.
Explanation:
Meristems are specialized regions in a plant where cells continuously divide and differentiate. The type of meristem involved in increasing the diameter or girth of the stem is the lateral meristem, also known as the vascular cambium. Here are the detailed functions of each type of meristem mentioned:
Lateral Meristem (Vascular Cambium and Cork Cambium):The lateral meristem is primarily responsible for the secondary growth of the plant. This growth increases the thickness of the stem. The vascular cambium, part of the lateral meristematic tissue, contributes to the formation of additional xylem and phloem. Meanwhile, the cork cambium helps in the development of bark, replacing the epidermis in woody plants. This meristem is located between the cortex and the phloem.
Apical Meristem:Located at the tips of roots and shoots, the apical meristem contributes to a plant's vertical growth (height and length). It does not play a role in increasing the stem's girth.
Intercalary Meristem:Found mainly at the nodes (areas where leaves attach), the intercalary meristem helps in the regeneration or elongation of plant segments, such as stems and leaves, especially after injury.
Considering the role of each meristem, it is clear that the lateral meristem (Option A) is directly involved in enhancing the girth of a stem, which includes increasing the thickness and strengthening the woody part of the stem. This makes A the correct answer.
In the experiment conducted by Mendel, RRyy (round, green) and rrYY (wrinkled, yellow) seeds of pea plant were used. In the F2 generation, 240 progeny were produced, out of which 15 progeny had specific characteristics. What were the characteristics?
A. Round and green B. Round and yellow C. Wrinkled and yellow D. Wrinkled and green
From the given question and transcript, we are analyzing Mendel’s dihybrid cross experiment involving pea plants with two differing traits: seed shape and seed color. Initially, he crossed RRyy (round, green) with rrYY (wrinkled, yellow), and in the F2 generation, 240 progenies were obtained with various genetic combinations.
Based on Mendel's laws and the dihybrid cross ratio, the phenotype ratio is typically expected to be 9:3:3:1 for the traits, where the traits would appear as:
9 round and yellow
3 round and green
3 wrinkled and yellow
1 wrinkled and green
Given that 15 progenies have a specific characteristic and the characteristic being sought after aligns with a probability of 1/16 (as per the mentioned ratio), the logical deduction is that this misalignment occurs in the least frequent category. 1/16 of 240 is approximately 15, confirming the category with the fewest individuals.
From the transcript clean-up and the general understanding of the dihybrid cross, those 15 progenies in the F2 generation characterized by the 1/16 phenotype ratio represent the trait combination that is wrinkled and green.
Thus, the correct answer from the options provided is: D. Wrinkled and green.
Small cut pieces of soft stems are placed in a growth medium with the following plant hormones. Which combination of plant hormones will show the slowest growth?
A. Auxin + Cytokinin
B. Gibberellins + Auxin
C. Gibberellins + Cytokinin
D. Abscisic Acid + Auxin
To determine which combination of plant hormones will show the slowest growth in small cut pieces of soft stems, it is essential to understand the function of each hormone mentioned in the options:
Auxin is known for promoting root formation and is generally associated with cell elongation and differentiation. Cytokinins are involved in promoting cell division, Gibberellins mainly aid in stem elongation and germination, while Abscisic Acid (ABA) typically acts as a growth inhibitor and plays a crucial role in stress responses by limiting growth.
Comparing the options:
Auxin + Cytokinin: Both promote various types of growth and cell division.
Gibberellins + Auxin: Again, both these hormones promote growth—gibberellins in stem elongation and auxin in root formation.
Gibberellins + Cytokinin: This combination supports growth through stem elongation and cell division.
Abscisic Acid + Auxin: This stands out because Abscisic Acid is known as a growth-limiting hormone and generally works to inhibit processes that other growth-promoting hormones like auxin would stimulate.
Given the roles these hormones play, the combination that would most likely show the slowest growth is Abscisic Acid + Auxin. This is because abscisic acid's inhibitory effect on growth can counteract the growth-promoting effect of auxin more significantly than other combinations where both hormones promote growth.
Conclusion: Option D (Abscisic Acid + Auxin) is the correct answer, as it combines a strong growth inhibitor with a growth promoter, likely resulting in minimal overall growth due to the inhibitory action of abscisic acid.
You find a herbaceous flowering plant growing in your school garden, having leaves with parallel venation. Choose the correct additional features the given plant would be possessing:
I. It has no secondary vascular tissues II. Its flower possesses three sepals III. It possesses a taproot IV. Its embryo has 2 cotyledons
A. I and III
B. I and III
C. II and IV
D. III and IV
The features of a herbaceous flowering plant with parallel venation found in a school garden, here's the solution broken down:
Parallel venation is typically found in monocot plants.
No secondary vascular tissues: Monocots generally do not have secondary vascular tissue, such as secondary xylem and phloem. These are compounds typically found in dicots.
Flower possesses three sepals: Monocot flowers usually come in multiples of three, including the sepals.
Fibrous root system: Monocots usually have a fibrous root system instead of a taproot.
One cotyledon: Monocots bear seeds with only one cotyledon, unlike dicots, which have two.
Correct Answer: Options I and II
Statement I, "It has no secondary vascular tissues," aligns with the characteristics of monocots.
Statement II, "Its flower possesses three sepals," is also characteristic of monocot plants, where the floral organs typically appear in multiples of three.
Thus, the two correct features that describe additional characteristics of the given plant (monocot) are: It has no secondary vascular tissues, and Its flower possesses three sepals.
Options Analysis
Option C (II and IV) is incorrect because monocots have only one cotyledon.
Option D (III and IV) is incorrect as monocots do not have a taproot system and have only one cotyledon.
Option A (I and III) does not align because monocots have a fibrous root system, not a taproot.
Conclusion
The correct characteristics that can be associated with the given plant given its parallel venation and nature of being a monocot are that the plant has no secondary vascular tissues and its flower possesses three sepals. This corresponds to Option C, which should list (I and II), although it might be a typo in the user's options list since the correct pair is actually addressed in the video transcript.
A tall plant $(\mathrm{TT})$ is crossed with a dwarf plant (tt). All $F_{1}$ plants showed tall phenotype. Which of the following correctly defines a test cross?
A. $T T\left(F_{1}\right) \times T t(P)$
B. $T t\left(F_{1}\right) \times T t(P)$
C. $F_{1} \times T t(P)$
D. $T t\left(F_{1}\right) \times P$
A test cross is performed to determine the genetic makeup (genotype) of an organism exhibiting a dominant phenotype but unknown genotype. This is done by crossing the organism with another that is homozygous recessive for the trait in question.
In the question provided, all $F_1$ plants arising from a cross between a homozygous tall plant ($\mathrm{TT}$) and a homozygous dwarf plant ($\mathrm{tt}$) exhibit the tall phenotype. This means that the $F_1$ plants have a heterozygous genotype ($\mathrm{Tt}$) since they show the dominant trait (tallness), but carry a recessive allele (t).
To perform a test cross, you would cross the $F_1$ plants with a plant that is homozygous recessive for the trait. The purpose is to reveal the recessive phenotype in the offspring (if the recessive allele is present in the tested organism), thus confirming whether the $F_1$ generation plants are indeed heterozygous.
Referring to the provided options:
A: $\mathrm{T T (F_1) \times T t (P)}$ - This is incorrect as it involves a cross between a homozygous dominant and a heterozygous plant, which is not a test cross setup.
B: $\mathrm{T t (F_1) \times T t (P)}$ - This is also incorrect as crossing two heterozygous plants does not conform to test cross protocol.
C: $\mathrm{F_1 \times T t (P)}$ - Incorrect, as the 'P' should be homozygous recessive for a proper test cross.
D: $\mathrm{T t (F_1) \times tt}$ - This is a typical setup for a test cross, where the $F_1$ heterozygous plants are crossed with a homozygous recessive plant.
Therefore, the correct answer defining a test cross is: D: $\mathrm{T t (F_1) \times tt}$ – This involves crossing the $F_1$ heterozygous tall plants ($\mathrm{Tt}$) with the homozygous recessive dwarf plants ($\mathrm{tt}$) to determine the genetic makeup of the $F_1$ individuals.
You discover a new species of a plant. You also discover that it produces motile sperm and dominant generation has diploid cells. It belongs to:
A. Bryophyte
B. Angiosperm
C. Gymnosperm
D. Pteridophyte
To determine the classification of such a plant, it's important to consider key aspects of plant reproduction and lifecycle structures.
Bryophytes, primarily nonvascular plants like mosses, typically have a dominant gametophyte stage, which is haploid, and have motile sperm. However, the diploid generation (sporophyte) is generally not dominant in these plants.
Gymnosperms and Angiosperms (flowering plants) also possess motile sperm in some cases and do show a dominant diploid generation in their lifecycles. However, in angiosperms, motility in sperm is not commonly observed due to the presence of pollen tubes that aid in sperm transport.
Pteridophytes, which include ferns and their allies, prominently feature both motile sperm and a dominant sporophytic stage that is diploid. This group fits well with both the motility of sperm and the diploid dominance that was observed in your new plant species.
Given these details:
The dominant diploid generation aligns with the sporophytic phase seen in Pteridophytes, unlike the mostly gametophyte dominant lifecycle of Bryophytes.
The presence of motile sperm is characteristic of Pteridophytes and some groups of both Gymnosperms and Bryophytes, but only Pteridophytes fit both the traits well, given the dominance of the sporophyte phase.
Thus, the correct answer that aligns with these characteristics is:
D. Pteridophyte
Which of the following group of plants are also called as naked seeded plants?
A. Algae
B. Ferns
C. Gymnosperms
D. Moss
The correct answer to which group of plants is also called "naked-seeded" plants is C. Gymnosperms.
In the plant kingdom, we classify species into several categories based on their characteristics. One such classification is based on whether their seeds are exposed or not. "Naked-seeded" refers to seeds that are not enclosed within an ovary; instead, they are directly exposed to the environment.
Algae are simple organisms often found in aquatic environments and do not produce seeds at all, eliminating this option.
Both Ferns and Mosses belong to groups (fern to Pteridophytes and moss to Bryophytes) that reproduce via spores rather than seeds. Therefore, these are also incorrect choices.
The term "Gymnosperms" literally means "naked seeds". These are vascular plants where the seeds are not protected by an ovary or fruit. Key traits of gymnosperms include the absence of flowers and ovaries, making it evident that the seeds remain exposed. This exposure is why we describe them with the specific term naked-seeded. Therefore, the correct answer is C. Gymnosperms.
In herbaceous plants, "guttation" takes place by:
A) Stomata
B) Hydathodes
C) Root hair
D) Flowers
In herbaceous plants, guttation refers to the process where water is lost in the form of droplets from the leaves. This phenomenon occurs not through common structures such as stomata (which primarily facilitate gas exchange and transpiration), nor through root hairs or flowers but through specialized structures known as hydathodes. These are pores located on the leaf edges where guttation occurs, allowing the release of water droplets.
Hence, the correct answer is: B) Hydathodes
Which of the following phytohormones helps in fruit ripening?
A. Auxin
B. Gibberellin
C. Cytokinin
D. Ethylene
Ethylene is the phytohormone responsible for fruit ripening. Let's analyze how:
Auxin, option A, predominantly aids in growth and development of plants but does not directly contribute to fruit ripening.
Gibberellin, option B, is mostly associated with increasing plant height and aiding in other growth functions, but not specifically with ripening of fruits.
Cytokinin, option C, plays a crucial role in cell division, which is also unrelated to the direct process of fruit ripening.
The correct answer is D. Ethylene, as it is the only phytohormone among the given options that specifically facilitates the ripening of fruits. Ethylene is a gaseous plant hormone that triggers the ripening process, making fruits soften and change in color.
Thus, the correct choice is option D.
Which of the following plants do unisexual flowers occur in?
A. Mustard B. Tomato C. Pea D. Watermelon
Unisexual flowers are those where a single flower has either male or female reproductive organs, not both. This contrasts with bisexual flowers, where both male and female reproductive parts are present in the same flower.
Mustard, Tomato, and Pea plants all have bisexual flowers, where each flower contains both male (stamens) and female (pistils) reproductive organs.
Watermelon, however, produces unisexual flowers. This means each flower is either male or female, but not both.
Therefore, the correct answer is: D. Watermelon
This plant exhibits unisexual flowers, where the individual flowers are specialized exclusively for either male or female reproduction.
Which growth hormone is responsible for apical dominance? A. Auxin B. Gibberellin C. Cytokinin D. Ethylene
The growth hormone responsible for apical dominance is Auxin.
Apical dominance is a phenomenon where the central stem of the plant is dominant over other side stems. This means the main stem grows stronger and faster compared to the lateral stems, suppressing their growth. Apical dominance ensures that the plant grows more vertically, enhancing its ability to capture sunlight and reproduce.
The hormone responsible for this process is Auxin. Auxin promotes vertical growth via concentration in the main stem, restraining the growth of lateral stems effectively leading to apical dominance.
Therefore, the correct answer to the question is: A. Auxin.
Which of the following parts of the potato plant help it to reproduce?
Option 1) Bud
Option 2) Flower
Option 3) Leaf
Option 4) Root
Correct Option: A) Bud
Potatoes are unique in that they are a special kind of stem known as a tuber, which grows underground. These tubers have buds called 'eyes' on their surface. Any part of the potato that contains an eye or bud is capable of growing into a new plant, thus aiding in the reproduction of the potato plant.
The life span of common water hyacinth seed is about _______ .
A. 2 years
B. 10 years
C. 52 years
D. 24 years
The correct option is D: 24 years.
The common water hyacinth releases about 3000 seeds, and although not all of these seeds can develop into individual plants, the seeds have a lifespan of nearly 24 years. This extended lifespan is a crucial factor contributing to the massive proliferation of this invasive aquatic plant across almost all continents.
The sweet, fleshy edible middle layer of the fruit is called ______________.
A. epicarp
B. pericarp
C. endocarp
D. mesocarp
The correct option is D: mesocarp.
The mesocarp is the mid-layer of the pericarp, situated between the epicarp and the endocarp. The mesocarp is the nutritious, fleshy part of the fruit that is consumed, located between the skin (epicarp) and the seed (endocarp).
Ovary matures to form the seed while ovule forms fruit.
Option 1) (i) seed, (ii) fruit
Option 2) (i) carpel, (ii) fruit
Option 3) (i) fruit, (ii) seed
Option 4) (i) seed, (ii) cotyledons
The correct option is Option 3: (i) fruit, (ii) seed.
Explanation:
The ovary matures to form the fruit while the ovules form seeds after fertilization.
Mendel conducted his breeding experiments on:
Pisum sativum
Triticum aestivum
Felis catus
Musca domestica
The correct option is A: Pisum sativum.
Gregor Mendel, the father of genetics, conducted his breeding experiments on pea plants, scientifically known as *Pisum sativum*. This choice was pivotal due to the plant's distinct characteristics and ease of cultivation.
To clarify why the other options are incorrect:
Triticum aestivum refers to wheat, which is not the subject of Mendel's experiments.
Felis catus is the scientific name for cats, a species completely unrelated to Mendel's genetic studies.
Musca domestica is the housefly, which Mendel did not use in his breeding experiments.
Mendel's work with *Pisum sativum* led to the foundation of modern genetics as he was able to determine the fundamental laws of inheritance.
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