Mineral Nutrition

(b) Azotobacter is free-living, aerobic, non-photosynthetic nitrogen fixer.

(c) Etiolation is the response of a plant to stimuli.

When plant seeds are grown in insufficient light, (either in partial or complete absence of light) the seedlings will have long, weak stems, smaller and fewer leaves because of longer internodes, and a pale yellow colour (chlorosis).

This is due to a lack of chlorophyll.

The increase in height helps the plant reach a possible source of light faster.

(c) Potassium is not a constituent of any enzyme but is an activator of enzymes.

Potassium is an essential mineral and is found in more amounts in actively dividing cells such as buds, young leaves, root tips, etc.

It has some other roles like regulating stomatal movement and protein synthesis.

(d) Phosphorus and nitrogen are essential elements normally required in large quantities by plants.

(c) Iodine is the only such element which is an essential mineral for animals but is not required by plants.

The natural iodine content in soil is low.

While iodine is not an essential nutrient for plant growth, fertilizing with iodine derivatives has been shown to aid in biomass production and increase the antioxidant levels in plants which provide drought and stress resistance.

(c) Nutrients which are required in large amounts in functioning of plant are known as macronutrients eg.

$Ca, Mg, N$.

Nutrients required in trace amounts are known as micronutrients.

Manganese is a micronutrient for plants essential for synthesis of chlorophyll.

It is also required for activation of enzymes of respiration and nitrogen metabolism.

(a) Roots do not expend energy on this type of mineral absorption.

So application of a metallic inhibitor will retard the process.

(a) Manganese is an activator of enzymes.

Copper is essential for photosynthesis.

Molybdenum is a cofactor of enzymes.

Boron assists in sugar transport.

(a) Iron is absorbed by plants in the form of ferrous ions.

Plants uptake iron in its reduced forms, $Fe^{2+}$ (ferrous form) or $Fe^{3+}$ (ferric form).

Another mechanism involves the release of protons $(H^{+})$ and reductants by the plant roots, to lower $pH$ levels in root zone.

Iron is considered a micro-nutrient because only small amounts are required to aid in normal plant growth.

Plants can suffer iron deficiency with symptoms of chlorosis and stunted growth, but plants can also take in too much iron, especially under certain growing conditions.

(a) Molybdenum is part of nitrogenase (a Mo-Fe protein) essential for nitrogen fixation.