Smooth ER synthesizes lipids such as phospholipids and steroids. It also helps in detoxification. Protein synthesis occurs in rough ER, not smooth ER.

The International Day to Combat Desertification and Drought is observed annually on 17th June. This day was established by the United Nations to raise awareness about land degradation, desertification, and drought, which affect millions of people worldwide. Desertification refers to the degradation of land in arid and semi-arid regions, often caused by deforestation, overgrazing, poor irrigation practices, and climate change. It leads to reduced agricultural productivity, food insecurity, and displacement of populations. The observance encourages governments, organizations, and individuals to adopt sustainable land management practices. It also promotes international cooperation to address environmental challenges. The other dates mentioned are incorrect because the UN officially designated 17th June for this purpose. Recognizing such international days is important in exams as they reflect global awareness campaigns. Therefore, 17th June is the correct answer, highlighting efforts to combat environmental degradation and ensure sustainable land use.

Mars has two natural satellites, Phobos and Deimos. These moons were discovered in 1877 by astronomer Asaph Hall. They are small, irregularly shaped bodies, believed to be captured asteroids or formed from debris. Phobos is the larger moon and orbits very close to Mars, completing a revolution in about 7 hours. Deimos is smaller and orbits farther away, taking about 30 hours. Unlike Earth, which has one moon, and Mercury and Venus, which have none, Mars has two moons. This makes option B correct. These moons are of great scientific interest because they provide clues about the formation and evolution of the solar system. Future missions may explore them further. Thus, the correct answer is 2.

Stomata are tiny openings on the surface of leaves that regulate gas exchange and water loss. They are controlled by guard cells, which change shape based on water content. When guard cells gain water, they become turgid and open the stomata, allowing carbon dioxide to enter for photosynthesis. When they lose water, they become flaccid and close the stomata to prevent excessive water loss through transpiration. This mechanism is essential for plant survival, especially in dry conditions. It helps maintain water balance while still allowing necessary gas exchange. The other options are incorrect because gaining water opens stomata, and mutation is unrelated. Thus, stomata close when guard cells lose water, making option A correct. This concept is fundamental in plant physiology and ecology.

Villi are small, finger-like projections found in the inner lining of the small intestine. Their main function is to increase the surface area for absorption of nutrients. Each villus contains blood vessels and lymphatic vessels (lacteals) that help absorb digested nutrients such as glucose, amino acids, and fatty acids. This adaptation makes nutrient absorption highly efficient. The large intestine mainly absorbs water and salts and does not have villi. The stomach is involved in digestion but not absorption at this level. The liver processes nutrients but does not contain villi. Thus, the small intestine is the correct answer. This concept highlights the importance of structural adaptations in biological systems to enhance function. Understanding villi is crucial in topics like digestion, absorption, and diseases such as celiac disease, where villi are damaged.