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Chapter 12 – Reproduction in Plants -Long Questions and Answers (Solved Worksheet)
Explain the process of sexual reproduction in plants and its significance for genetic diversity.
Answer- Sexual reproduction in plants begins with the formation of flowers, which house the reproductive organs. Male gametes are found within pollen grains produced in the anther, while female gametes, or egg cells, reside in the ovules within the ovary. The process kicks off with pollination, where pollen grains are transferred to the stigma, often with the aid of wind, water, or pollinators like bees. Following pollination, a pollen grain germinates and forms a pollen tube that extends down the style to the ovary, reaching the ovule. The male gamete then travels down this tube to unite with the female gamete in the ovule, resulting in fertilisation.
The significance of this process lies in the resulting genetic diversity. Each zygote formed is genetically unique due to the combination of different sets of chromosomes from the parent plants. This genetic variation is fundamental for adaptation and evolution, as it gives rise to individuals with new characteristics that may be more suited to survival and reproduction in changing environmental conditions. It is this variation that enables plant species to develop resistance to diseases, adapt to new habitats, and ultimately, thrive.
Describe the different methods of asexual reproduction in plants and discuss the advantages of asexual reproduction.
Answer- Asexual reproduction in plants allows for the creation of new individuals without the fusion of gametes. There are several methods by which this can occur-
Regeneration– Certain plants can regenerate from fragments of the plant body. If a part is detached, it can grow into a new plant.
Budding- Buds may form on the parent plant that develops into new individuals. For example, potato tubers have buds or ‘eyes’ that can grow into new plants.
Vegetative propagation- Specific plant parts like stems, leaves, or roots can give rise to new plants. This can occur through runners (stolons) in strawberries, bulbils in garlic, or leaf cuttings in species like African violets.
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The advantages of asexual reproduction include the following-
Rapid propagation- It enables the production of many offspring in a short amount of time.
No need for pollinators- Plants can reproduce without the need for pollinators, which is beneficial if such animals are scarce.
Genetic Stability- Offspring are genetically identical to the parent, ensuring the preservation of successful genetic combinations.
Discuss the role of different plant parts in vegetative propagation and explain how this method benefits the plant species.
Answer- Vegetative propagation utilises the inherent ability of plants to reproduce from vegetative parts—such as stems, leaves, and roots—rather than from seeds. Each part serves a unique role in this process-
Stems- Stems like rhizomes and tubers are equipped to store nutrients, which support new growth. For instance, potatoes grow from buds called “eyes,” while plants like ginger use rhizomes.
Leaves- Some plants have evolved to reproduce using leaves. Bryophyllum, for example, has buds on the leaf margins that develop into new plants when they come into contact with soil.
Roots– Certain species such as sweet potatoes and dahlias can generate new shoots from their roots, taking advantage of their existing nutrient absorption systems.
The benefits of vegetative propagation are manifold. It ensures rapid multiplication, which is more efficient than seed reproduction, especially in a controlled environment. The genetic uniformity it provides is crucial for commercial cultivation of certain crop varieties, ensuring consistent quality and characteristics. Moreover, vegetative propagation can preserve the desirable traits of hybrids and bypass challenges associated with pollination, facilitating the cultivation of plants that might otherwise struggle to reproduce.
Explain the process of budding in yeast and its significance.
Answer- Budding in yeast is an exemplary mechanism of asexual reproduction that reflects the adaptability of this single-celled fungus. The process begins when a small bulge, or a bud, forms on the parent yeast cell. As the bud enlarges, the nucleus of the parent cell divides, and one nucleus migrates into the bud. The bud continues to grow until it is ready to separate, eventually detaching to become an independent organism.
The significance of budding in yeast lies in its efficiency and adaptability. It allows for rapid population growth under favourable conditions, like abundant food supply. This rapid multiplication is crucial for yeast’s survival, as it enables a swift response to environmental changes. Additionally, the budding process is highly adaptable; yeast cells can suspend budding during adverse conditions, ensuring their survival until conditions improve. This flexibility is a testament to the evolutionary success of yeast in various habitats.
Explain the process of fragmentation in algae and discuss its significance in the proliferation and adaptability of algal species.
Answer- Fragmentation is a straightforward yet highly effective form of asexual reproduction utilised by algae. It occurs when an alga, having reached a certain size or maturity, naturally breaks into pieces due to either environmental forces like water currents or through its own growth processes.
The broken fragments each possess the innate ability to develop into a new, independent alga, assuming the presence of favourable conditions such as adequate water and nutrient availability. These fragments adhere to surfaces or float to new locations, where they can establish new colonies.
The significance of fragmentation in algae lies in its simplicity and efficiency. This method allows algae to rapidly cover large areas, as seen in the green patches that form in ponds or along stagnant water bodies. The lack of complex reproductive mechanisms means that fragmentation can occur continuously and rapidly, which is advantageous for colonising and adapting to new environments. Algae can hence quickly take advantage of available resources and space, leading to large populations that can dominate an ecosystem.
Describe the process of spore formation in plants and its role in their lifecycle and survival.
Answer- Spore formation is a pivotal process in the life cycle of certain plants, particularly non-flowering plants like ferns and mosses, as well as fungi. Spores are produced by the parent organism in specialised cells called sporangia. These microscopic reproductive units are uniquely designed with a tough outer coat that shields them from harsh environmental factors, such as extreme temperature and dryness, allowing them to remain viable under conditions that would be unsuitable for the parent plant.
Once mature, spores are released and can be carried by wind or water to new locations, thanks to their lightweight nature. Upon encountering favourable conditions—a suitable substrate, moisture, and appropriate temperatures—they germinate and grow into new organisms.
The role of spore formation is twofold- it facilitates wide dispersal, allowing the plant species to spread across diverse environments, and it ensures survival. The durable nature of spores means they can outlast periods of adversity, lying dormant until the environment is suitable for growth. This resilience and adaptability make spore-producing plants particularly successful in colonising new and challenging environments.
Describe the process of pollination in plants, the different agents involved, and explain how it contributes to genetic diversity.
Answer- Pollination in plants is a crucial reproductive process where pollen grains, containing the male gametes, are transferred from the anther (male reproductive part) to the stigma (female reproductive part) of a flower. This can occur within the same flower, between flowers of the same plant (self-pollination), or between flowers of different plants of the same species (cross-pollination).
Various agents facilitate pollination, including wind, water, and animals, primarily insects. Wind-pollinated plants produce large quantities of light, dry pollen that can be easily blown to other flowers, while water-pollinated plants release pollen into the water to drift to other flowers. Insects, such as bees and butterflies, are attracted by nectar and the vivid colours of flowers; as they move from flower to flower, they inadvertently deposit pollen on the stigmas.
The importance of pollination lies in its contribution to genetic diversity, particularly through cross-pollination. When pollen from one plant fertilises another, it combines different genetic materials, leading to offspring with varied genetic expressions. This diversity is fundamental for adaptability and survival, as it allows plant populations to withstand environmental changes and disease pressures, ultimately supporting the dynamic balance of ecosystems.
Explain the structure of a flower and the roles of its male and female reproductive parts in sexual reproduction.
Answer- A flower is the reproductive unit of angiosperms (flowering plants) and is composed of both male and female parts, unless it is unisexual.
The male part, the stamen, consists of-
Anther- The site of pollen grain production, which contains male gametes.
Filament- A supportive stalk that positions the anther to facilitate the dispersal of pollen.
The female part, the pistil, includes-
Stigma- The sticky top surface that captures and holds pollen.
Style- The elongated structure through which pollen tubes grow to reach the ovary.
Ovary- The base that contains ovules where the female gametes are formed.
During sexual reproduction, pollen grains must reach the stigma, germinate, and grow a pollen tube down the style to reach an ovule in the ovary. Once an ovule is fertilised by male gametes from pollen, it develops into a seed, and the ovary typically grows into a fruit.
Discuss the differences between self-pollination and cross-pollination, and outline the advantages and disadvantages of each.
Answer- Self-pollination occurs when pollen from the anther of a flower pollinates the same flower or another flower on the same plant. This method ensures that pollen is not wasted and that fertilisation will occur without reliance on external agents. However, it reduces genetic diversity, which can lead to an accumulation of deleterious traits and reduce the population’s ability to adapt to changing environments.
Cross-pollination, on the other hand, involves the transfer of pollen from the anther of one plant to the stigma of another plant of the same species. It promotes genetic diversity, which enhances the adaptability of a species and can lead to the development of traits that improve survival and reproduction. The disadvantages include reliance on pollination agents, which can be unpredictable, and the energy cost associated with attracting these agents, such as producing nectar or fragrances.
Explain the process of fertilisation in flowering plants and describe its significance.
Answer- Fertilisation in flowering plants is a complex process that ensures sexual reproduction. It begins with pollination, where pollen grains from the male reproductive organ, the stamen, are transferred to the female reproductive part, the pistil. Once the pollen grain lands on the stigma, it germinates and forms a pollen tube that extends through the style to reach the ovule housed within the ovary.
Within the ovule, the male gamete travels down the pollen tube and fuses with the female gamete, or egg, to form a zygote. This union of gametes results in fertilisation, and the zygote is the first cell of the new plant, containing genetic information from both parents.
The significance of fertilisation is multifaceted-
Genetic Diversity- Fertilisation shuffles genetic material, allowing for genetic variation. This variation is essential for the adaptability of plants to changing environments and the evolution of species.
Species Continuity- It ensures the continuation of species by producing offspring with a mix of genetic traits from both parents.
Initiation of Development- The zygote represents the beginning of a new organism, initiating the process of embryonic development, which eventually leads to a mature plant.
Describe the various methods of seed dispersal and explain why seed dispersal is necessary for plants.
Answer- Seed dispersal is the mechanism by which seeds are spread from their parent plant to new locations, and it can occur through several methods-
Wind Dispersal- Plants like drumsticks and maples produce winged seeds that the wind can carry away.
Water Dispersal- Seeds that float, like coconuts, have adaptations like a fibrous coat that allow them to be dispersed by water.
Animal Dispersal- Seeds with hooks or spines, such as those of Xanthium, attach to animal fur and are carried to new places.
Explosive Mechanisms- Some plants, like balsam, have fruits that burst open to eject the seeds away from the parent plant.
The necessity of seed dispersal stems from the need to-
Reduce Competition- If seeds were to fall and grow directly beneath the parent plant, they would compete for light, space, and nutrients.
Expand Territory- Dispersal allows plants to colonise new habitats, which can be crucial for their survival in changing environmental conditions.
Promote Genetic Diversity- By spreading offspring over a wider area, seed dispersal promotes outcrossing and reduces the likelihood of inbreeding.
What is the role of fruits in the reproduction of flowering plants?
Answer- Fruits play a pivotal role in the reproduction of flowering plants by acting as vessels for protecting and dispersing seeds. Once fertilisation occurs, the ovary of the flower develops into a fruit, and the ovules mature into seeds. The fruit serves several functions-
Protection- It encases the seeds, safeguarding them from predators and environmental stresses.
Nourishment- The fruit often provides nutrients to the developing seeds and can attract animals, which can aid in dispersal.
Dispersal- Different characteristics of fruits, such as being tasty and nutritious to animals or adapted for transport by wind or water, are essential for seed dispersal. This dispersal is crucial for the propagation of the plant species and colonisation of new areas.
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