Problem 103 - Objective Biology for NEET

Question

Assertion: Leguminous plants are nitrogen fixers. Reason: Leguminous plants have rhizobium in their root nodules.

Step-by-Step Solution

Answer

Yes, the assertion and reason are correct and the reason is the right explanation for the assertion. This is because Rhizobium bacteria in the root nodules of leguminous plants do help in fixing nitrogen, which is why these plants have a higher nitrogen content.

Step 1: Understanding the Assertion

Firstly, the assertion 'Leguminous plants are nitrogen fixers' needs to be analysed. Nitrogen fixing means converting the nitrogen from the air into forms that plants can use. Leguminous plants such as peas, beans and lentils are indeed known for this ability.

Step 2: Understanding the Reason

The reason 'Leguminous plants have rhizobium in their root nodules' should then be looked into. Rhizobium is a type of bacteria that live in the root nodules of leguminous plants. They do help in nitrogen fixation but it is necessary to know if they are the only reason that leguminous plants are nitrogen fixers.

Step 3: Connecting Assertion and Reason

The last step is to verify if the reason explains the assertion. Rhizobium bacteria in the root nodules of leguminous plants convert atmospheric nitrogen into a form that the plant can use. This helps the plant to increase its nitrogen content. Hence, the reason does explain the assertion that leguminous plants are nitrogen fixers.

Key Concepts

Leguminous Plants

Leguminous plants are uniquely capable of enriching the soil with nitrogen, a vital nutrient for plant growth. They include peas, beans, lentils, and other similar plants. One of the characteristics that make them special is their ability to engage in a symbiotic relationship with certain types of bacteria to fix nitrogen.

This ability allows leguminous plants to thrive in soil conditions where other plants might struggle. By fixing nitrogen from the atmosphere, they convert it into forms usable by plants, such as ammonia.

• Benefits: Increased soil fertility and reducing the need for chemical fertilizers.
• Environmental Impact: Promotes sustainable farming practices.

This process not only helps the legumes themselves grow better but also improves the soil quality for future crops.

Rhizobium Bacteria

Rhizobium bacteria play a crucial role in the nitrogen fixation process associated with leguminous plants. These bacteria live freely in the soil but form a symbiotic relationship specifically with legumes.

When they come into contact with the roots of these plants, they initiate a process known as infection that leads to the formation of structures called root nodules.

• Function: Convert atmospheric nitrogen into ammonia.
• Symbiosis: Receive carbohydrates and protection from the plant.

This partnership is mutually beneficial, as the bacteria help the plant obtain essential nutrients while the plant provides the bacteria with resources and a hospitable environment.

Root Nodules

Root nodules are small growths that appear on the roots of leguminous plants. Within these nodules, Rhizobium bacteria reside and work their magic.

The formation of nodules begins when Rhizobium bacteria infect the roots. As they penetrate the root cells, nodules begin to form as a structure where the bacteria can live.

• Structure: Protection for bacteria and a site for nitrogen fixation.
• Function: Facilitate the conversion of nitrogen into a plant-friendly form.

This setup ensures that nitrogen is continuously supplied to the plant, allowing it to grow healthily and contribute to the ecosystem's overall nutrient cycle.

Plant Nutrition

Nitrogen is a fundamental component of many cellular structures and processes in plants, including amino acids, proteins, and chlorophyll.

Plants obtain this essential nutrient mainly through the soil, but in the case of leguminous plants, the root nodule system provides an additional nitrogen source.

• Importance: Essential for growth, development, and reproduction.
• Sources: Atmospheric fixation by Rhizobium and soil absorption.

This additional nitrogen supply allows leguminous plants to grow in nutrient-poor soils and reduces dependency on synthetic nitrogen fertilizers, promoting eco-friendly agriculture.