Explanation: Dissolved oxygen (DO) is the amount of oxygen available in water for aquatic organisms to breathe. For the healthy survival of most aquatic life, the DO level should be between 4 and 6 mg/L. Levels below 3 mg/L can lead to stress or suffocation, especially for fish and aerobic microorganisms. Higher DO levels are typical of clean, cold, and well-aerated waters, while polluted or stagnant waters often have lower oxygen levels due to organic decay.

Factors Affecting DO Levels:

• Temperature (higher temperature = lower DO)
• Organic pollution and bacterial activity
• Photosynthesis by aquatic plants and algae
• Water turbulence and aeration

Explanation: Antibodies (also called immunoglobulins) are specialized proteins produced by B-lymphocytes (a type of white blood cell) in response to the presence of foreign substances known as antigens (such as bacteria, viruses, or toxins). These antibodies recognize and bind specifically to the antigens to neutralize or destroy them, helping the body fight infections and build immunity. Antibodies are a vital part of the immune system and form the basis for vaccines and disease resistance.

Explanation: A carnivore is an animal that primarily eats the flesh of other animals. The tiger (Panthera tigris) is a true carnivore and an apex predator in its ecosystem. It has sharp canines and retractable claws adapted for hunting and tearing flesh. Tigers play a vital role in maintaining the ecological balance by controlling herbivore populations in forests.

Explanation: ASTROSAT is India’s first dedicated multi-wavelength space observatory launched by ISRO (Indian Space Research Organisation) on September 28, 2015. It is designed for astronomy research and studies celestial objects like stars, galaxies, black holes, and neutron stars in different wavelengths — including visible, ultraviolet, and X-ray bands. ASTROSAT helps scientists study high-energy astrophysical phenomena and provides data comparable to international missions such as NASA’s Hubble Space Telescope.

Explanation: The decibel (dB) is a unit used to measure the intensity or loudness of sound. It expresses sound level on a logarithmic scale relative to a standard reference intensity of 10^-12 watt/m², which is the faintest sound the average human ear can hear. Normal conversation is around 60 dB, city traffic about 80–90 dB, and sounds above 120 dB can cause pain or hearing damage. The decibel scale helps compare very large variations in sound intensity conveniently.

Explanation: Light from the Sun takes approximately 8 minutes and 20 seconds to reach the Earth. The average distance between the Earth and the Sun is about 149.6 million kilometers (1 Astronomical Unit). Since light travels at a speed of 3 × 10⁸ meters per second in a vacuum, it covers this distance in roughly eight minutes. This means that when we see sunlight, we are actually seeing it as it was about eight minutes earlier.

Explanation: The plasma membrane in eukaryotic cells is mainly made up of a phospholipid bilayer arranged in a fluid mosaic model. Each phospholipid molecule consists of a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails. This arrangement creates a semi-permeable barrier that regulates the movement of substances into and out of the cell. Embedded proteins, cholesterol, and carbohydrates contribute to transport, signaling, and membrane stability.

Explanation: Teflon, also known as polytetrafluoroethylene (PTFE), is the polymer used in making non-stick kitchenware. It has a very low coefficient of friction and is resistant to heat and chemicals, which prevents food from sticking to cookware surfaces.