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Answered on 21 Feb Learn Some Natural Phenomena
Sadika
The three destructive natural phenomena are:
Earthquakes: Earthquakes are the shaking of the Earth's surface caused by the sudden release of energy in the Earth's crust, resulting in the generation of seismic waves. They can cause widespread destruction of buildings, infrastructure, and landscapes, as well as tsunamis, landslides, and avalanches.
Volcanic Eruptions: Volcanic eruptions occur when magma, gas, and volcanic ash are expelled from a volcano's vent onto the Earth's surface. They can cause significant damage to surrounding areas, including the destruction of buildings, farmland, and infrastructure, as well as the formation of lahars (mudflows), pyroclastic flows, and volcanic ash clouds.
Tropical Cyclones (Hurricanes, Typhoons, Cyclones): Tropical cyclones are intense, rotating storm systems characterized by low atmospheric pressure, strong winds, heavy rainfall, and storm surges. They can cause extensive damage to coastal areas, including flooding, wind damage, and erosion, as well as widespread power outages and disruption of transportation networks.
Answered on 21 Feb Learn Some Natural Phenomena
Sadika
An electroscope is a simple device used to detect the presence and magnitude of electric charges. It operates based on the principle of electrostatic induction and the repulsion of like charges.
Here's how a basic electroscope works and its construction:
Construction:
Metal Leaf: The main component of an electroscope is a metal leaf, typically made of a lightweight metal such as aluminum or gold. The metal leaf is usually attached to a metal rod or wire, which is insulated from the surroundings by a non-conductive material, such as plastic or glass.
Support Structure: The metal rod holding the metal leaf is mounted vertically within a non-conductive container, such as a glass jar or case, to protect it from external influences.
Leaf Suspension: The metal leaf is suspended from the metal rod at its upper end, allowing it to move freely in response to electric charges.
Working:
Charging: To use the electroscope, it must first be charged. This can be done by bringing a charged object (such as a rubbed glass rod or a plastic comb) near the metal rod of the electroscope without touching it. The charged object induces a separation of charges in the metal leaf, causing like charges to be repelled and move away from the metal rod.
Leaf Movement: As the like charges in the metal leaf repel each other, the metal leaf diverges from the metal rod, moving outward to a certain extent. The degree of divergence depends on the magnitude of the charge induced on the metal leaf.
Observation: The divergence of the metal leaf is visually observed through a transparent window or opening in the container housing the electroscope. The greater the divergence of the metal leaf, the larger the magnitude of the electric charge present.
Discharging: Once the charged object is removed, the electroscope gradually discharges due to the movement of charges within the metal leaf. The metal leaf returns to its original position, indicating that the electric charge has dissipated.
Overall, an electroscope detects the presence of electric charges by observing the movement of a metal leaf in response to electrostatic forces. It is a simple yet effective tool for demonstrating the principles of electrostatics and for detecting the presence of electric charges in various objects and materials.
Answered on 21 Feb Learn Some Natural Phenomena
Sadika
The shock waves produced by an earthquake travel outward in all directions from the focus (hypocenter) of the earthquake. These waves propagate through the Earth's interior and along its surface, causing the ground to shake and vibrate as they pass through.
There are three main types of seismic waves produced by an earthquake: Primary (P) waves, Secondary (S) waves, and Surface waves. Each type of wave travels at different speeds and has different characteristics, but all propagate outward from the earthquake's focus.
Primary (P) Waves: P-waves are compressional waves that travel through the Earth's interior by alternately compressing and expanding the material they pass through. They are the fastest seismic waves and are capable of traveling through solids, liquids, and gases. P-waves are the first to arrive at seismograph stations following an earthquake and can propagate through the Earth's interior directly from the focus to the surface.
Secondary (S) Waves: S-waves are shear waves that travel through the Earth's interior by causing particles of the material to move perpendicular to the direction of wave propagation. Unlike P-waves, S-waves cannot travel through liquids or gases and are only able to propagate through solids. S-waves are slower than P-waves and arrive at seismograph stations after P-waves.
Surface Waves: Surface waves travel along the Earth's surface and are responsible for much of the shaking and damage observed during earthquakes. They are slower than both P-waves and S-waves and typically arrive at seismograph stations last. Surface waves have two main types: Love waves and Rayleigh waves. Love waves cause horizontal shearing motion in the ground, while Rayleigh waves cause both vertical and horizontal motion, similar to the motion of ocean waves.
Overall, the shock waves produced by an earthquake travel outward from the focus in all directions, causing the ground to shake and resulting in the seismic waves detected by seismographs stationed around the world.
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Answered on 21 Feb Learn Cell – Structure and Functions
Sadika
Animal cells and plant cells share many similarities in structure and function, but there are several key differences between them. Here are some of the main differences:
Cell Wall:
Shape:
Vacuoles:
Chloroplasts:
Plastids:
Centrioles:
These are some of the main differences between animal cells and plant cells. Despite these differences, both types of cells share many common organelles and structures, such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and ribosomes, which are essential for their basic functions and processes.
Answered on 21 Feb Learn Crop Production and Management
Sadika
Crop production involves a series of practices aimed at cultivating crops efficiently and sustainably to ensure optimal yields. Here are some basic practices of crop production:
Site Selection and Preparation:
Seed Selection and Planting:
Soil Fertility Management:
Water Management:
Weed Control:
Pest and Disease Management:
Crop Monitoring and Maintenance:
Harvesting and Post-Harvest Handling:
By following these basic practices of crop production, farmers can maximize crop yields, minimize environmental impact, and ensure sustainable agricultural practices for future generations.
Answered on 21 Feb Learn Crop Production and Management
Sadika
Crops are plants cultivated by humans for food, fiber, fuel, medicinal purposes, or other uses. They are grown on agricultural land and are an essential component of agriculture, providing sustenance and resources for human consumption and various industries. Crops can be broadly classified into several categories based on their intended use, cultivation methods, and economic significance.
Here are two examples of crops explained in detail:
1. **Wheat (Triticum spp.):**
- Wheat is one of the most widely cultivated cereal crops worldwide and serves as a staple food for a large portion of the global population.
- Species of wheat commonly grown include common wheat (Triticum aestivum), durum wheat (Triticum durum), and spelt (Triticum spelta), among others.
- Wheat is a grass plant belonging to the Poaceae family and is cultivated in diverse climates ranging from temperate to tropical regions.
- It is an annual crop grown from seeds (grains) planted in the soil during the fall or spring seasons, depending on the growing region and variety.
- Wheat plants typically have slender, hollow stems (culms) topped with dense clusters of flowers (spikes) that develop into grain-bearing heads.
- The grains produced by wheat plants are harvested when mature and can be processed into various food products, including flour for bread, pasta, pastry, and breakfast cereals.
- Wheat is also used as fodder for livestock, as well as in the production of biofuels, alcoholic beverages (e.g., beer, whiskey), and industrial products (e.g., starch, gluten).
2. **Rice (Oryza sativa):**
- Rice is a primary staple food for a significant portion of the world's population, particularly in Asia, where it is a dietary staple and cultural symbol.
- Oryza sativa is the most widely cultivated species of rice, although other species, such as Oryza glaberrima (African rice), are also grown in certain regions.
- Rice belongs to the Poaceae family and is a grass plant that thrives in warm, humid climates with abundant water resources.
- It is an annual crop that is typically grown in flooded paddy fields or irrigated paddies to provide the necessary water and nutrients for optimal growth.
- Rice plants have long, slender leaves and produce flowers arranged in compact spikelets that develop into grains.
- The grains of rice are harvested when fully mature and can be processed into various forms, including white rice, brown rice, parboiled rice, and rice flour.
- Rice is a versatile food ingredient used in a wide range of culinary dishes, including main courses, side dishes, desserts, and beverages.
- In addition to its culinary uses, rice straw and husks are valuable byproducts used for animal feed, bedding, fuel, and construction material in many cultures.
Both wheat and rice are vital crops that provide essential nutrients and calories for human nutrition worldwide. They are cultivated on a large scale and contribute significantly to global food security and agricultural economies.
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Answered on 21 Feb Learn Pollution of Air and Water
Sadika
The gas primarily responsible for the greenhouse effect is carbon dioxide (CO2). However, other greenhouse gases, including methane (CH4), nitrous oxide (N2O), water vapor (H2O), and various fluorinated gases (e.g., hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride), also contribute to trapping heat in the Earth's atmosphere.
These greenhouse gases absorb and re-emit infrared radiation emitted by the Earth's surface, trapping heat energy within the atmosphere and leading to the warming of the planet. While water vapor is the most abundant greenhouse gas, its concentrations in the atmosphere are largely influenced by temperature changes and atmospheric dynamics. In contrast, carbon dioxide, methane, and nitrous oxide are long-lived greenhouse gases emitted through human activities such as burning fossil fuels, deforestation, agriculture, and industrial processes. They contribute significantly to enhanced greenhouse effect and global warming.
Answered on 21 Feb Learn Pollution of Air and Water
Sadika
Global warming refers to the long-term increase in the average temperature of the Earth's climate system, primarily attributed to human activities that release greenhouse gases into the atmosphere. The accumulation of greenhouse gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases, leads to the enhanced greenhouse effect, trapping heat within the Earth's atmosphere and causing the planet's temperature to rise.
Key aspects of global warming include:
Temperature Rise: Global warming results in an overall increase in temperatures across the Earth's surface and atmosphere. While temperature changes may vary regionally and seasonally, long-term trends show a consistent pattern of warming.
Climate Change: Global warming is a driver of climate change, influencing various climate phenomena such as changes in precipitation patterns, shifts in weather systems, alterations in storm intensity and frequency, and disruptions to ecosystems and biodiversity.
Glacial Melting and Sea-Level Rise: Rising temperatures contribute to the melting of glaciers, ice caps, and polar ice sheets, leading to the loss of land ice and contributing to sea-level rise. This poses risks to coastal communities, ecosystems, and infrastructure.
Ocean Warming and Acidification: Global warming also affects the Earth's oceans, leading to increases in ocean temperatures and changes in ocean chemistry. Warmer oceans can disrupt marine ecosystems, coral reefs, and fisheries, while ocean acidification, resulting from the absorption of CO2, can harm marine organisms with calcium carbonate shells or skeletons.
Extreme Events: Global warming is associated with an increased frequency and intensity of extreme weather events, including heatwaves, droughts, heavy rainfall, floods, hurricanes, and wildfires. These events can have significant socio-economic impacts, affecting agriculture, water resources, human health, and infrastructure.
Human activities driving global warming include the burning of fossil fuels (coal, oil, and natural gas) for energy production, transportation, industry, and agriculture, as well as deforestation, land-use changes, and industrial processes. Efforts to mitigate global warming involve reducing greenhouse gas emissions, transitioning to renewable energy sources, increasing energy efficiency, enhancing carbon sequestration, and adapting to the impacts of climate change.
Answered on 21 Feb Learn Reproduction in Animals
Sadika
Metamorphosis is a biological process undergone by certain organisms during their life cycle, involving distinct changes in form, structure, and physiology as they transition from one developmental stage to another. Metamorphosis is particularly common among insects, amphibians, and some other groups of animals. The process typically involves distinct stages, often including larval, pupal, and adult phases, each with its own specialized morphology and behavior. There are two primary types of metamorphosis:
Complete Metamorphosis (Holometabolism):
Incomplete Metamorphosis (Hemimetabolism):
Metamorphosis allows organisms to exploit different ecological niches and adapt to diverse environments throughout their life cycles. It enables specialization of body structures and behaviors for specific functions, such as feeding, growth, reproduction, and dispersal. By undergoing metamorphosis, organisms can optimize their survival and reproductive success in changing environmental conditions, enhancing their evolutionary fitness and ecological resilience.
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Answered on 21 Feb Learn Reproduction in Animals
Sadika
Fertilization is the process in reproduction where male and female gametes (reproductive cells) fuse to form a zygote, which eventually develops into a new individual. In most organisms, fertilization involves the fusion of a sperm cell (male gamete) with an egg cell (female gamete), resulting in the formation of a diploid zygote with a complete set of chromosomes. Fertilization typically occurs following the fusion of gametes during intercourse or reproductive interactions.
Examples of fertilization in different organisms include:
Humans: In humans, fertilization occurs when a sperm cell from the male reproductive system (produced in the testes) fuses with an egg cell (ovum) from the female reproductive system (released from the ovary during ovulation) in the fallopian tube. The fusion of sperm and egg forms a zygote, which undergoes further development and implantation in the uterus, leading to pregnancy.
Plants: In flowering plants, fertilization involves the fusion of a pollen grain (carrying male gametes) with an ovule (containing female gametes) within the ovary of a flower. Pollination, the transfer of pollen from the male reproductive organ (stamen) to the female reproductive organ (pistil) of a flower, precedes fertilization. Once a pollen grain reaches the stigma of a compatible flower, it germinates and forms a pollen tube, through which sperm cells travel to the ovule for fertilization.
Fish: In many fish species, external fertilization occurs where female fish release eggs (ova) into the water, and male fish release sperm (milt) to fertilize the eggs externally. The sperm and eggs meet in the water column, and fertilization occurs externally. This is common in fish species such as salmon and trout.
Frogs: Amphibians like frogs typically undergo external fertilization. During mating, a male frog releases sperm (in the form of sperm packets called spermatophores) onto the eggs released by the female frog. Fertilization occurs externally, often in water bodies like ponds or streams where the eggs are laid.
Invertebrates: Many invertebrates, including sea urchins, insects, and some marine invertebrates, undergo internal fertilization. In these organisms, sperm is deposited directly into the female's reproductive tract, where it fertilizes the eggs.
These examples demonstrate the diversity of fertilization processes across different organisms, each adapted to suit the reproductive strategies and environmental conditions of the species involved.
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