Question

Read the following statements and select the incorrect ones. (i) The co-ordinated activities of the legume and Rhizobium bacteria depend on chemical interactions between the symbiotic partners. (ii) Leguminous roots secrete chemical attractants that attract Rhizobium bacteria living nearby. (iii) \(N, P\) and \(K\) usually do not get deficient in soil due to their low plant requirement. (iv) Nitrogen cycle is regular circulation of nitrogen amongst living organisms with its reservoir pool in lithosphere and cycling pool in atmosphere. (a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (ii), (iii) and (iv)

Short answer

(c) (iii) and (iv) are the incorrect statements.

Step-by-step solution

Analyze Statement (i)

This statement is correct. The symbiosis between legumes and Rhizobium bacteria is indeed based on chemical interactions that allow them to communicate and establish a mutual relationship. No action is needed regarding this statement.

Analyze Statement (ii)

This statement is accurate. Leguminous plants do secrete chemicals that attract Rhizobium bacteria, which is crucial for the symbiotic relationship, as the bacteria fix nitrogen that benefits the plant. No action is needed for this statement.

Analyze Statement (iii)

This statement is incorrect. Nitrogen (N), Phosphorus (P), and Potassium (K) are macronutrients that are often limiting in soils because they are required in large amounts by plants. This statement should be selected as incorrect.

Analyze Statement (iv)

This statement mixes up information. While the nitrogen cycle does involve the regular circulation of nitrogen among living organisms, its reservoir pool is in the atmosphere in the form of nitrogen gas (N2), not in the lithosphere. The cycling pool involves various forms, including atmospheric nitrogen. This statement is also incorrect and should be selected.

Select Incorrect Statements

From the analysis in previous steps, the incorrect statements are (iii) and (iv). The correct answer is (c) (iii) and (iv).

Key concepts

Symbiotic Relationship Between Legumes and Rhizobium

In the wondrous world of biology, a fascinating partnership exists between legumes and Rhizobium bacteria—a classic example of a symbiotic relationship. This relationship is crucial for the nitrogen cycle, allowing atmospheric nitrogen to be converted into a form that plants can absorb and use.

Legumes, such as peas and beans, have unique structures in their roots called nodules. Inside these nodules, Rhizobium bacteria reside and carry out a process known as nitrogen fixation. The bacteria convert nitrogen gas from the atmosphere into ammonia, a form of nitrogen that plants can utilize for growth.

In return, the legumes provide the bacteria with carbohydrates and a protected environment. This reciprocal exchange is the cornerstone of the symbiosis. The legume benefits by receiving an essential nutrient for proteins and DNA synthesis, while the bacteria gain sustenance and a niche to flourish in.

Macronutrients in Soil

Plants, like all living organisms, require nutrients to thrive, and three of the most important are nitrogen (N), phosphorus (P), and potassium (K). These elements are known as macronutrients because plants need them in large quantities.

Nitrogen is indispensable for the formation of amino acids, the building blocks of proteins. Phosphorus plays a key role in energy transfer within plants, being a part of ATP, the energy currency of the cell, as well as nucleic acids. Potassium is vital for osmoregulation and enzyme activation.

The Importance of Macronutrients

Deficiencies in any of these macronutrients can severely hinder plant growth and lead to diminished health. For example, nitrogen deficiency is often marked by yellowing leaves, while a lack of phosphorus can stunt growth and cause dark green or purple coloring. Insufficient potassium might result in weak roots and poor resistance to disease.

These nutrients are often added to soil in the form of fertilizers to enrich and maintain soil fertility, ensuring the robust growth and health of crops.

Plant Nutrient Deficiency

When plants don't receive the macronutrients they require, they exhibit specific symptoms attributed to nutrient deficiency. These deficiencies can significantly impact plant development, crop yield, and overall health.

Recognizing the Signs

Visual clues on plants can indicate what specific nutrient they lack. For instance, nitrogen deficiency usually results in older leaves turning a pale green or yellow because nitrogen is mobile within the plant and moves to support new growth. Phosphorus deficiency can lead to smaller leaves that might have a bluish-green tint or reddish-purple edges. A lack of potassium often causes leaf edges to appear burned and can also lead to poor fruit quality.

Correct diagnosis of plant nutrient deficiencies is crucial for addressing these issues effectively. Gardeners and farmers often rely on soil tests and plant tissue analyses to determine which nutrients are missing and then can supplement accordingly. Fertilizers—synthetic or organic—are commonly applied to replenish these vital nutrients and restore plant health.