Nutrition in Plants-III

Boron, manganese, and molybdenum are well-established essential micronutrients for plants. Nickel's status is debated in older curricula but is now considered essential for urease function in many plants. However, traditional exam resources often list only Fe, Mn, Zn, Cu, B, Mo, and Cl as essential, excluding nickel. This question reflects that traditional classification.

Carbon, hydrogen, oxygen, and nitrogen constitute approximately 99% of living matter by mass. Carbon forms the backbone of organic molecules, hydrogen and oxygen are abundant in water and organic compounds, and nitrogen is essential for proteins and nucleic acids. Sulfur and phosphorus, while important, are present in much smaller quantities than these four.

Elements used in large quantities by the plant are termed macronutrients, which can be further defined as primary and secondary. The primary nutrients include nitrogen (N), phosphorus (P) and potassium (K). These elements contribute to plant nutrient content, function of plant enzymes and biochemical processes, and integrity of plant cells. Deficiency of these nutrients contributes to reduced plant growth, health and yield. Thus, they are the three most important nutrients supplied by fertilizers. The secondary nutrients include calcium (Ca), magnesium (Mg) and sulphur (S).

Grana are absent in the chloroplast of algae.

The dark reaction of photosynthesis occurs in the stroma of chloroplast.

Photosynthesis is reductive because it reduces CO2 to carbohydrate (adding electrons/hydrogen). It is endergonic because it requires energy input (light energy to drive the process). It is anabolic because it builds complex glucose molecules from simple CO2, breaking down water in the process. Endergonic reactions always require energy input, unlike exergonic reactions that release energy.

The rate of photosynthesis (how fast it occurs at any moment) depends on light intensity (brighter light drives faster reactions), quality of light (specific wavelengths are absorbed), and temperature (affects enzyme activity). Duration (how long light is available) affects total photosynthetic output over time but not the instantaneous rate - a plant doesn't photosynthesize 'faster' just because the daylight period is longer.

The atmosphere (air) is the largest nitrogen reservoir, containing approximately 78% nitrogen gas (N2) by volume. This represents about 4×10^21 tons of nitrogen. While soil contains nitrogen in organic and inorganic forms, and the sea contains dissolved nitrogen, neither compares to the massive atmospheric reservoir. Rocks contain minimal nitrogen.

Minerals are absorbed by active transport.

Active uptake of minerals against their concentration gradient requires energy expenditure, typically in the form of ATP. This is fundamental to active transport mechanisms. While respiration produces this energy and root metabolism supports the process, the direct requirement for mineral uptake is the energy itself. Photophosphorylation occurs in chloroplasts for photosynthesis, not mineral absorption.

The process of conversion of ammonia to nitrite by microbes is called nitrification.

Rhizobium is a well-known nitrogen-fixing bacterium that forms symbiotic relationships with legume plants, converting atmospheric nitrogen into ammonia in root nodules. The question misspells it as 'Rhozobium', but this is clearly the intended answer. Acetobacter produces acetic acid, Mycoplasma lacks a cell wall, and Chlamydia is an intracellular pathogen - none fix nitrogen.

Spirogyra does not have the ability to fix nitrogen from the atmosphere.

Carbon is the most abundant element in plants by mass, constituting approximately 45% of plant dry weight. This is because plants are primarily composed of carbon-based compounds like cellulose, lignin, and other organic molecules built through photosynthesis. While nitrogen, iron, and manganese are essential nutrients, they are required in much smaller quantities than carbon.

Rhizobium forms a symbiotic relationship with legume roots, converting atmospheric nitrogen into ammonia through nitrogen fixation. This occurs in specialized root structures called nodules. Azotobacter is a free-living nitrogen fixer, while Nitrobacter and Nitrosomonas are involved in nitrification, not nitrogen fixation.

Calcium is essential for root growth as it promotes cell elongation and division in root meristems. It strengthens cell walls and membranes, enabling roots to elongate properly. Zinc is important for enzyme function but not specifically for root growth, while molybdenum and sulfur have other primary roles in plant metabolism.

Boron plays a critical role in seed germination by facilitating cell division and elongation in the emerging embryo. It's particularly important for pollen tube growth and sugar transport during germination. While iron, magnesium, and zinc are essential for various plant processes, boron has a more direct involvement in the early stages of seed development.

Boron is the element which is useful in the germination of seeds.

One of the major functions of magnesium (Mg) and iron (Fe) is the synthesis of chlorophyll.

K⁺ ions play a major role in controlling the opening and closing of stomata.