Class 8 Science : Practice Questions and Answers

The onset of menstruation (menarche) marks one of the key signs of female puberty. This process is regulated by hormonal changes and signals the body's preparation for reproduction.

Adolescence is the transitional stage of growth and development between childhood and adulthood. It involves physical, emotional, and psychological changes, including puberty, and lasts from about age 10 to 19.

A zygote is the fertilized egg formed when sperm and egg unite during fertilization. The zygote begins the process of cell division and development, eventually forming an embryo and later a fully developed organism.

In mammals, fertilization typically takes place in the fallopian tube. Here, the sperm meets the egg, and the fertilized egg (zygote) travels down to the uterus for implantation and development.

The primary function of the reproductive system in animals is to produce offspring. This ensures the continuation of the species. The reproductive organs in male and female animals facilitate the production of gametes (sperm and eggs), which combine to form a zygote that develops into a new organism.

Binary fission is the method by which bacteria reproduce asexually. In this process, a single bacterial cell divides into two identical daughter cells. It is a simple and efficient form of reproduction, allowing bacteria to multiply rapidly under favorable conditions.

Igneous rocks are formed from the cooling and solidification of molten magma or lava. Depending on where the cooling occurs (beneath the Earth's surface or during volcanic eruptions), these rocks can be classified as intrusive or extrusive.

Acids have the characteristic property of turning blue litmus paper red, which indicates their acidic nature. Acids generally have a sour taste, such as citrus fruits, and they can corrode metals.

Deforestation is the leading cause of biodiversity loss because it destroys the natural habitats of many species. As forests are cleared for agriculture, urban development, or logging, animals and plants lose their homes and are often unable to adapt or survive, leading to a decline in species diversity.

A flame is the result of rapid oxidation, also known as combustion, in which fuel reacts with oxygen. This exothermic reaction releases energy in the form of heat and light, creating the visible flame.

The combustion of petroleum products, such as gasoline and diesel, releases carbon dioxide (CO₂) and other greenhouse gases into the atmosphere. These gases trap heat, contributing to global warming, climate change, and environmental harm.

Coal is a fossil fuel formed from the remains of plants and animals that lived millions of years ago. It is considered a non-renewable resource and is primarily used for generating electricity and heating.

Fungi, particularly the genus Penicillium, are used to produce antibiotics such as penicillin. These antibiotics are effective in treating bacterial infections by inhibiting the growth of bacteria.

Influenza, commonly known as the flu, is caused by the influenza virus, which primarily affects the respiratory system. It is highly contagious and can lead to symptoms like fever, cough, and fatigue.

Mixed cropping refers to the practice of growing two or more crops on the same field at the same time. This practice helps in improving soil fertility, reducing pest infestation, and increasing the overall yield.

Maize (corn) is a kharif crop, which is typically sown at the beginning of the monsoon season and harvested at the end. These crops grow best in warm and wet conditions during the monsoon period.

Mitochondria are the energy-producing organelles of the cell, often referred to as the "powerhouses." They generate ATP (adenosine triphosphate), which provides the cell with the energy needed for various metabolic processes.

Copper is an excellent conductor of electricity because its atoms allow electrons to move freely, enabling electric current to flow easily through it. This is why copper is used in electrical wiring and circuits.

Sunlight is the main source of energy for plants, which they use to perform photosynthesis. During this process, plants convert sunlight into chemical energy, enabling them to produce food in the form of glucose.

Liquids have a definite volume but do not have a fixed shape. They flow and take the shape of the container they are placed in. The particles in a liquid are close together but can move past one another.