Essential Plant Nutrients Practice Questions
20 free Essential Plant Nutrients practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following criteria is NOT required for an element to be considered 'essential' for a plant according to Arnon and Stout?
- A The plant cannot complete its life cycle without the element.
- B The requirement of the element must be specific and not replaceable by another.
- C The element must be directly involved in the metabolism of the plant.
- D The element must be present in the soil in high concentrations.
Correct answer: The element must be present in the soil in high concentrations.
An element is essential if the plant cannot complete its life cycle without it, its requirement is specific, and it is directly involved in metabolism. High concentration in soil is not a criterion; in fact, micronutrients are essential despite being needed in minute quantities.
Macronutrients are generally present in plant tissues in concentrations of more than:
- A 1 mmole per kg of dry matter
- B 10 mmole per kg of dry matter
- C 100 mmole per kg of dry matter
- D 1000 mmole per kg of dry matter
Correct answer: 10 mmole per kg of dry matter
Macronutrients are required in relatively large amounts, defined as more than 10 mmole per kg of dry matter. Micronutrients or trace elements are needed in concentrations less than 10 mmole per kg of dry matter.
Which group of elements is predominantly obtained by plants from $CO_2$ and $H_2O$ rather than from the soil?
- A N, P, K
- B C, H, and O
- C Ca, Mg, S
- D Fe, Mn, Cu
Correct answer: C, H, and O
Carbon, hydrogen, and oxygen are the framework elements of organic molecules in plants. They are primarily obtained from atmospheric CO₂ and water (H₂O), whereas all other essential mineral elements are absorbed from the soil.
Which of the following is a micronutrient required by plants?
- A Magnesium
- B Phosphorus
- C Zinc (Zn)
- D Calcium
Correct answer: Zinc (Zn)
Zinc (Zn) is a micronutrient needed in very small quantities. Magnesium, Phosphorus, and Calcium are macronutrients required in larger amounts for structural and physiological roles.
Which element is a critical component of energy-related chemical compounds like ATP?
- A Magnesium
- B Phosphorus
- C Nitrogen
- D Potassium
Correct answer: Phosphorus
Phosphorus is a constituent of nucleic acids, membrane phospholipids, and energy carriers such as ATP (Adenosine Triphosphate). It plays a central role in energy transfer and storage reactions in plants.
Magnesium is an essential element as it is the central atom in the structure of:
- A Hemoglobin
- B Chlorophyll
- C Cytochrome
- D Vitamin B12
Correct answer: Chlorophyll
Magnesium ($Mg^{2+}$) is the central metal ion of the chlorophyll molecule, which is vital for photosynthesis. It also activates enzymes involved in respiration and DNA/RNA synthesis.
Which micronutrient is required for the photolysis of water (splitting of water) during photosynthesis?
- A Copper (Cu)
- B Boron (B)
- C Manganese (Mn)
- D Zinc (Zn)
Correct answer: Manganese (Mn)
Manganese (Mn²⁺), along with Chlorine, is essential for the water-splitting (photolysis) reaction in Photosystem II. This reaction releases oxygen as a by-product of photosynthesis.
A plant element that helps in maintaining the anion-cation balance and the turgidity of cells is:
- A Nitrogen
- B Phosphorus
- C Potassium
- D Sulfur
Correct answer: Potassium
Potassium ($K^+$) is involved in opening and closing of stomata, protein synthesis, and maintaining turgidity. It is the major cation involved in maintaining osmotic balance within cells.
Which of the following elements is a component of the vitamins thiamine, biotin, and Coenzyme A?
- A Iron
- B Sulfur
- C Boron
- D Molybdenum
Correct answer: Sulfur
Sulfur is found in two amino acids (cysteine and methionine) and is a constituent of several coenzymes and vitamins like thiamine, biotin, and ferredoxin.
Iron is absorbed by plants in the form of:
- A Ferrous ions (Fe²⁺)
- B Ferric ions (Fe³⁺)
- C Elemental iron
- D Iron oxide
Correct answer: Ferrous ions (Fe²⁺)
Plants absorb iron primarily in the ferrous form (Fe²⁺). Although iron exists as Fe³⁺ in the soil, ferric reductase enzymes at the root surface reduce it to Fe²⁺ before uptake. Iron is essential for chlorophyll synthesis and electron transport.
Boron is primarily required by plants for:
- A Iron
- B Sulfur
- C Boron
- D Molybdenum
Correct answer: Sulfur
Sulfur is found in the amino acids cysteine and methionine, and is a constituent of vitamins and coenzymes including thiamine (B₁), biotin (B₇), and Coenzyme A. It also forms part of the iron-sulfur protein ferredoxin.
Which element is a component of the enzyme nitrogenase and nitrate reductase?
- A Zinc (Zn)
- B Copper (Cu)
- C Molybdenum (Mo)
- D Manganese (Mn)
Correct answer: Molybdenum (Mo)
Molybdenum is required in the smallest amount of all essential elements. It is a vital component of the enzymes nitrogenase (nitrogen fixation) and nitrate reductase (nitrogen assimilation).
Which of the following is considered a 'Beneficial Element' required by higher plants but not necessarily by all plants?
- A Sodium
- B Iron
- C Zinc
- D Copper
Correct answer: Sodium
Besides the 17 essential elements, there are beneficial elements like Sodium, Silicon, Cobalt, and Selenium. These are required by certain higher plants for specific physiological functions.
The concentration of an essential element below which plant growth is retarded is termed as:
- A Toxic concentration
- B Critical concentration
- C Optimal concentration
- D Saturation concentration
Correct answer: Critical concentration
The critical concentration is the threshold level of a nutrient. If the concentration falls below this point, the plant displays specific deficiency symptoms.
Chlorosis, the loss of chlorophyll leading to yellowing of leaves, is caused by the deficiency of:
- A Nitrogen
- B Magnesium
- C Calcium (Ca)
- D Potassium
Correct answer: Calcium (Ca)
Calcium is a structural component of the cell wall (calcium pectinate in the middle lamella) and is not easily remobilized from older tissues. Therefore, its deficiency symptoms appear first in young, developing parts of the plant.
Which of the following elements is relatively immobile in plants and thus deficiency symptoms appear first in young tissues?
- A Nitrogen
- B Magnesium
- C Calcium
- D Potassium
Correct answer: Calcium
Calcium is a structural component of the cell wall (calcium pectinate) and is not easily remobilized. Therefore, its deficiency symptoms appear first in the young, developing parts of the plant.
Necrosis, or the death of leaf tissue, is particularly associated with the deficiency of:
- A N, S, Mo
- B Ca, Mg, K, Cu
- C Fe, Mn, Zn
- D P, B, Si
Correct answer: Ca, Mg, K, Cu
Necrosis (tissue death) is characteristically caused by deficiency of Calcium, Magnesium, Potassium, and Copper. By contrast, deficiency of N, S, and Mo is more commonly associated with inhibition of cell division rather than necrosis.
Toxicity of Manganese in plants is often expressed by the appearance of brown spots surrounded by chlorotic veins and causes deficiency of:
- A Nitrogen and Phosphorus
- B Iron, Magnesium, and Calcium
- C Copper, Zinc, and Boron
- D Boron and Molybdenum
Correct answer: Iron, Magnesium, and Calcium
Manganese toxicity inhibits the uptake of Iron and Magnesium, and prevents Calcium translocation to the shoot apex. Thus, Mn toxicity symptoms are effectively a combination of Fe, Mg, and Ca deficiencies, appearing as brown spots surrounded by chlorotic veins.
Which element is an activator for both RuBisCO and PEP carboxylase?
- A Zinc (Zn)
- B Magnesium (Mg)
- C Iron (Fe)
- D Copper (Cu)
Correct answer: Magnesium (Mg)
Mg²⁺ is the essential activator for the primary CO₂-fixing enzymes in photosynthesis — RuBisCO in C3 plants and PEP carboxylase in C4 plants. It is also vital for ribosomal structural integrity and enzyme activation.
Alcohol dehydrogenase is activated by which of the following mineral ions?
- A $Mn^{2+}$
- B $Mo^{2+}$
- C $Zn^{2+}$
- D $Cu^{2+}$
Correct answer: $Zn^{2+}$
Zinc ions ($Zn^{2+}$) serve as an activator for the enzyme alcohol dehydrogenase. Zinc is also needed for the synthesis of the plant hormone auxin.