Question 1

Which of the following statements best explains why plants cannot use atmospheric nitrogen ($N_2$) directly for their nutritional needs?

Accepted Answer

Plants lack the enzymes necessary to break the strong triple bond in $N_2$ molecules.

Question 2

A farmer notices that the older leaves of his crop are turning yellow, while the younger leaves remain green. Which nutrient deficiency is most likely responsible, and why?

Accepted Answer

Magnesium deficiency, because magnesium is mobile and deficiency symptoms appear in older leaves.

Question 3

Which of the following best describes the main source of the dry mass of a typical herbaceous plant?

Accepted Answer

Carbon dioxide ($CO_2$) assimilated from the atmosphere.

Question 4

A plant is growing in soil that is rich in all nutrients except for molybdenum. What is the most likely consequence for the plant?

Accepted Answer

The plant may become weak or die, as even a deficiency in a micronutrient like molybdenum can be fatal.

Question 5

Which of the following is a function of potassium ($K^+$) in plants?

Accepted Answer

It is required for the opening and closing of stomata.

Question 6

Why are loamy soils considered the most fertile for plant growth?

Accepted Answer

They have a balanced mixture of sand, silt, and clay, providing both good drainage and nutrient retention.

Question 7

Which of the following best describes the mutualistic relationship between legumes and nitrogen-fixing bacteria?

Accepted Answer

The bacteria provide fixed nitrogen to the plant, and the plant supplies carbohydrates to the bacteria.

Question 8

A plant growing in a pot is watered with distilled water only, and no minerals are added. After several weeks, the plant shows stunted growth and yellowing leaves. Which of the following best explains this observation?

Accepted Answer

Distilled water lacks the essential mineral nutrients required for plant growth.

Question 9

Which of the following is NOT a macronutrient required by plants?

Accepted Answer

Iron ($Fe^{2+}$)

Question 10

A scientist is studying a plant that grows on the branches of trees but does not harm the host plant. It absorbs water and minerals from rain. What type of plant is this?

Accepted Answer

Epiphyte

Question 11

Which of the following best explains why over 90% of the water taken up by a plant is lost by transpiration?

Accepted Answer

Transpiration is necessary for nutrient uptake and cooling the plant.

Question 12

Which of the following is a likely consequence of excessive application of a micronutrient fertilizer to a crop?

Accepted Answer

The crop may suffer toxicity symptoms and reduced growth.

Question 13

Which of the following best describes the role of mycorrhizae in plant nutrition?

Accepted Answer

They increase the surface area for water and mineral absorption.

Question 14

A plant growing in an acid bog supplements its nutrition by trapping and digesting insects. What is the main reason for this adaptation?

Accepted Answer

To obtain nitrogen and minerals that are scarce in the soil.

Question 15

Which of the following equations best represents the process of photosynthesis in plants?

Accepted Answer

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

Question 16

Which of the following is a real-world example of how crop rotation benefits soil fertility?

Accepted Answer

Alternating legumes with nonlegumes increases soil nitrogen through symbiotic nitrogen fixation.

Question 17

Which of the following best explains why symptoms of a nutrient deficiency may appear first in young leaves for some nutrients and in older leaves for others?

Accepted Answer

It depends on whether the nutrient is mobile or immobile within the plant.

Question 18

Which of the following is a micronutrient that functions as a cofactor in the electron transport chains of chloroplasts and mitochondria?

Accepted Answer

Iron ($Fe$)

Question 19

A plant is showing signs of chlorosis (yellowing of leaves). Which of the following could be a possible cause?

Accepted Answer

Deficiency of magnesium, which is a component of chlorophyll.

Plant Nutrition: Essential Elements, Uptake, and Soil Quality

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