Mineral Nutrition

(a) The major portion of the dry weight of plants comprises of carbon, hydrogen and oxygen.

Dry weight $=$ Weight recorded after drying the plant or part of a plant at temperatures higher than the ambient air temperature (e.g., around 65 - 100 degrees $C$ ), to drive off the water.

(b) Minor elements are those which are required by plants in very small amounts.

These elements have a significant role in enzyme activities (zinc activates carboxylases, carbonic anhydrase and various dehydrogenases).

(a) Manganese and iron are micronutrients required in trace amounts.

Concentration of nitrogen in dry matter is $15000 mg$./gm.

Concentration of carbon in dry matter is $45,000 mg / gm$.

(c) Essential micro elements are $Fe, Mn, Zn$, $B, Cu, Mo$ and essential macronutrionts are $C, H, N, P, S, Ca, K, Mg$.

(b) A plant requires magnesium for chlorophyll synthesis.

All four rings bind with metal atom magnesium $(Mg++)$, which remain present at the center of chlorophyll molecule.

(b) Manganese is essential for many plant functions.

Some of them are: The assimilation of carbon dioxide in photosynthesis.

It is involved in the Hill Reaction where water is split during photosynthesis.

It aids in the synthesis of chlorophyll and in nitrate assimilation.

Manganese activates fat forming enzymes.

It functions in the formation of riboflavin, ascorbic acid, and carotene.

It functions in electron transport during photosynthesis.

(b) Magnesium is a macronutrient.

Micronutrients are essential elements that are required by plants in small amounts.

They include $Fe, Cu, B, Mo, Mn, Cl$, and $Ni$.

Macronutrients, on the other hand, are those essential elements that are required by plants in larger amounts.

The examples include $C, H$, $O, N, S, P, K, Ca$ and $Mg$.

(a) Photolysis is catalysed by the proteinbound inorganic complex containing manganese ions (oxygen evolving complex) of photosystem II.

Photolysis is the process by which water is split into oxygen, which is released into the atmosphere, and hydrogen.

The hydrogen then becomes bonded to the coenzyme NADP to form NADPH and is transferred to the Calvin Cycle along with ATP.

(c) Cadmium is not an essential element for plants.

Phosphorus is a macronutrient and iron and manganese are micronutrients for plants.

Among all the heavy metals, cadmium is considered to be the one that is most toxic for plants.

Hence, cadmium concentrations in the plants can be measured by the effects it has on plant growth.

It inhibits the photosynthetic rate and production of chlorophyll and its activity.

(b) Calcium is not remobilized from the leaves to the fruits, like potassium, phosphorus and sulphur.

It occurs abundantly in a non-exchangeable form such as anorthite $(CaAl_2 Si_2 O_8)$.