Fundamentals of Human Geography

Cnidarians, also called coelenterate, are mostly marine animals. They include the corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans. The relationship between cnidarians and dinoflagellate algae is termed as symbiotic, because both the animal host and the algae are benefiting from the association. It is a mutualistic interaction.

Fungi have several mutualistic relationships with other organisms. In mutualism, both organisms benefit from the relationship. Two common mutualistic relationships involving fungi are mycorrhiza and lichen.

Termites have a mutualistic relationship with protozoa that live in the insect's gut. The termite benefits from the ability of bacterial symbionts within the protozoa to digest cellulose. Hence option (d) is the correct answer.

Source Attribution: Chapter 2 Biological Classification, Chapter 4 Animal Kingdom, NCERT: Class XI Biology

The rotation of the earth about its axis affects the direction of the wind. This force is called the Coriolis force after the French physicist who described it in 1844. It deflects the wind to the right direction in the northern hemisphere and to the left in the southern hemisphere. The deflection is more when the wind velocity is high. Hence statement 1 is correct.

The Coriolis force is directly proportional to the angle of latitude. It is maximum at the poles and is absent at the equator. Hence statement 2 is correct.

The Coriolis force acts perpendicular to the pressure gradient force. The pressure gradient force is perpendicular to an isobar. The higher the pressure gradient force, the more is the velocity of the wind and the larger is the deflection in the direction of wind.

As a result of these two forces operating perpendicular to each other, in the low-pressure areas the wind blows around it. At the equator, the Coriolis force is zero and the wind blows perpendicular to the isobars. The low pressure gets filled instead of getting intensified. That is the reason why tropical cyclones are not formed near the equator.

Source: NCERT: Class XI Fundamentals of Physical Geography

Water vapour is a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four percent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one percent of the air. Hence, statement 1 is correct and statement 2 is not correct.

Water vapour also decreases from the equator towards the poles. It absorbs parts of the insolation from the sun and preserves the earth’s radiated heat, acting like a blanket that prevents the earth from becoming too cold or too hot.

Water vapour contributes to the stability and instability in the air.

Source: NCERT: Class XI Fundamentals of Physical Geography

Tropical cyclones originate and intensify over warm tropical oceans. The conditions favourable for the formation and intensification of tropical storms are:

• Large sea surface with temperature higher than 27° C;
• Presence of the Coriolis force;
• Small variations in the vertical wind speed;
• A pre-existing weak low-pressure area or low-level cyclonic circulation;
• Upper divergence above the sea level system.

The most proximate reasons for the lack of activity in the South Atlantic are sea surface temperatures that tend to run a shade cooler than ideal for tropical cyclone formation even in the southern summer, climatologically high values of vertical wind shear across that basin throughout the year, and a lack of pre-existing centers of rotation (vorticity) in that area.

Source: NCERT: Fundamental Geography

Much of the phosphorus on Earth is tied up in rock and sedimentary deposits, from which it is released by weathering, leaching, and mining. Phosphorus moves in a cycle through rocks, water, soil and sediments and organisms. Over time, rain and weathering cause rocks to release phosphate ions and other minerals. This inorganic phosphate is then distributed in soils and water. Hence, option (c) is the correct answer.

Source: NCERT: Class XII Biology Chapter 14 Ecosystem