Ncert science class 10 Questions & Answers

The book discusses several types of chemical reactions: combination reactions (where two or more reactants combine to form a single product), decomposition reactions (a single reactant breaks down into two or more products), displacement reactions (a more reactive element displaces a less reactive element from its compound), double displacement reactions (exchange of ions between two compounds), and oxidation-reduction (redox) reactions (involving gain or loss of oxygen/hydrogen or electrons).

The pH scale is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14. A pH of 7 is neutral, values below 7 are acidic, and values above 7 are basic. It's important because pH affects chemical reactions, biological processes (e.g., enzyme activity in the human body), and environmental conditions (e.g., soil pH for plant growth, acid rain). Maintaining appropriate pH levels is crucial in many contexts.

The human digestive system breaks down complex food substances into simpler, absorbable forms. It starts in the mouth with mechanical and chemical digestion, moves through the esophagus to the stomach where proteins are digested, then to the small intestine for further digestion and absorption of nutrients, and finally to the large intestine for water absorption and waste formation. Various enzymes and digestive juices aid this process.

Aerobic respiration occurs in the presence of oxygen, completely breaking down glucose into carbon dioxide, water, and a large amount of energy (ATP). It typically happens in mitochondria. Anaerobic respiration occurs in the absence of oxygen, partially breaking down glucose into products like lactic acid (in animals) or ethanol and carbon dioxide (in yeast), producing a much smaller amount of energy. It occurs in the cytoplasm.

The human heart is a four-chambered muscular organ that pumps blood throughout the body. It has two atria (upper chambers) and two ventricles (lower chambers). The right side pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the rest of the body. Valves ensure unidirectional blood flow, preventing backflow. Its rhythmic contractions maintain blood circulation, delivering oxygen and nutrients and removing waste.

Plants exhibit tropisms, which are growth responses to stimuli. Phototropism is the growth response to light; shoots grow towards light (positive phototropism), while roots grow away from it (negative phototropism). Geotropism (or gravitropism) is the growth response to gravity; roots grow downwards (positive geotropism), and shoots grow upwards (negative geotropism). These responses are mediated by plant hormones like auxins.

DNA (Deoxyribonucleic Acid) is the genetic material that carries hereditary information from parents to offspring. It contains the instructions for building and maintaining an organism. During reproduction, DNA is replicated and passed on, ensuring that offspring inherit traits from their parents. Variations in DNA sequences lead to genetic diversity, which is crucial for evolution and adaptation.

The laws of reflection state two principles: First, the angle of incidence is equal to the angle of reflection. This means the angle between the incident ray and the normal (a line perpendicular to the surface) is equal to the angle between the reflected ray and the normal. Second, the incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.

Electric current is measured using an ammeter. An ammeter must always be connected in series with the component through which the current is to be measured. This ensures that the entire current flows through the ammeter, allowing it to accurately measure the flow of charge. Ammeters have very low resistance to minimize their impact on the circuit's current.

Connecting appliances in parallel offers several advantages. Each appliance receives the full supply voltage, allowing them to operate at their rated power. If one appliance fails or is switched off, others continue to function independently. Also, each appliance can have its own switch, providing individual control. This contrasts with series connections where voltage divides, and a single failure breaks the entire circuit.

Electromagnetic induction is the process by which a changing magnetic field through a conductor (like a coil) induces an electric current in that conductor. This change can be caused by moving a magnet relative to a coil, or by changing the current in a nearby coil. This principle is fundamental to the operation of electric generators, transformers, and many other electrical devices, converting mechanical energy into electrical energy.

An ecosystem consists of two main components: biotic and abiotic. Biotic components include all living organisms, categorized as producers (e.g., plants), consumers (e.g., animals), and decomposers (e.g., bacteria, fungi). Abiotic components are the non-living physical and chemical factors of the environment, such as sunlight, temperature, water, soil, air, and minerals. These components interact to form a functional unit.

Conservation of natural resources is crucial for sustainable development and the well-being of future generations. Resources like water, forests, minerals, and fossil fuels are finite. Over-exploitation leads to depletion, environmental degradation (e.g., pollution, deforestation), and loss of biodiversity. Conservation ensures that these resources are used wisely, minimizing waste and promoting their availability for long-term human needs and ecological balance.

The ozone layer, found in the stratosphere, plays a vital role in protecting life on Earth by absorbing most of the Sun's harmful ultraviolet (UV) radiation. UV radiation can cause skin cancer, cataracts, and damage to crops and marine life. The ozone layer acts as a natural shield, preventing these dangerous rays from reaching the Earth's surface, thus maintaining a habitable environment.

Sexual reproduction involves the fusion of gametes (sperm and egg) from two different parents. Each parent contributes half of the genetic material, leading to a unique combination of genes in the offspring. Additionally, processes like crossing over during meiosis (gamete formation) further shuffle genetic material. This genetic recombination and the combination of traits from two parents result in significant variation among offspring, which is essential for evolution and adaptation.

Homologous organs are those that have a similar basic structural plan and origin but may perform different functions. For example, the forelimbs of a human, a bird, and a whale have similar bone structures but are used for grasping, flying, and swimming, respectively. Analogous organs, on the other hand, have different basic structural plans and origins but perform similar functions. An example is the wings of a bird and the wings of an insect, both used for flight but structurally very different.

Metals are generally lustrous, malleable, ductile, good conductors of heat and electricity, and solid at room temperature (except mercury). They tend to lose electrons to form positive ions. Non-metals are typically dull, brittle, poor conductors of heat and electricity (except graphite), and can be solids, liquids, or gases at room temperature. They tend to gain electrons to form negative ions.

The human eye accommodates by changing the focal length of its lens. This is achieved by the action of the ciliary muscles. When viewing distant objects, the ciliary muscles relax, making the suspensory ligaments taut and the lens thinner, increasing its focal length. For nearby objects, the ciliary muscles contract, relaxing the suspensory ligaments, allowing the lens to become thicker and more convex, thereby decreasing its focal length. This adjustment ensures the image is always focused on the retina.