Problem 216 - Objective Biology for NEET

Question

Assertion: \(2,4 \mathrm{D}\) is selective weedicide Reason: \(2,4 \mathrm{D}\) is widely used to kill dicotyledonous weeds and doesn't affect mature monocotyledonous plant.

Step-by-Step Solution

Answer

The assertion and reason are both correct, and the reason effectively explains the assertion.

Step 1: Understand Key Terms

Selective weedicide refers to a type of herbicide that only affects particular types of plants, in this case, the dicotyledonous weeds. This allows the monocotyledonous plants to survive, as they are not affected by this weedicide.

Step 2: Identify Assertion and Reason

The assertion is that '2,4 D is a selective weedicide' and the reason is that '2,4 D is widely used to kill dicotyledonous weeds and doesn't affect mature monocotyledonous plants.'

Step 3: Evaluate Relation between Assertion and Reason

The reason can be evaluated to be true as it correctly states the working of 2,4 D and why it does not affect mature monocotyledonous plants. It is a known fact that 2,4 D works by affecting only the dicotyledonous weeds, thereby being a selective weedicide. Therefore, the assertion is correct and the reason is a correct explanation for the assertion.

Key Concepts

2,4 D

2,4 D, which stands for 2,4-dichlorophenoxyacetic acid, is a well-known selective weedicide. It is primarily used to control unwanted plant growth by targeting specific types of weeds. Uniquely, 2,4 D is designed to primarily affect dicotyledonous plants, making it highly advantageous for agriculture.

This chemical acts by mimicking the natural growth hormones found in plants, specifically the auxins. When applied to weeds, it stimulates excessive growth, leading to the death of the plant. However, the unique feature of 2,4 D is its selective nature, which primarily targets dicotyledonous plants and generally leaves monocotyledonous plants unharmed. This means farmers and gardeners can use it to effectively control weed populations without damaging crops sown in the same field.

2,4 D has been on the market since the 1940s and continues to be popular due to its effectiveness and relative safety when used correctly. It comes in several formulations, including liquid concentrates, ready-to-use liquids, and granular products, offering flexibility in application methods.

Dicotyledonous Weeds

Dicotyledonous weeds are a group of plants characterized by having two seed leaves, known as cotyledons, during germination. These types of weeds can be problematic in many agricultural settings because they often compete with crops for nutrients, water, and sunlight.

Some common examples of dicotyledonous weeds include:

• Ground ivy (Glechoma hederacea)
• Dandelion (Taraxacum officinale)
• Plantain (Plantago major)

These weeds can be quite aggressive, spreading quickly across fields and potentially reducing crop yields. This is where selective herbicides like 2,4 D become invaluable. By specifically targeting dicotyledonous plants, these herbicides can effectively reduce weed populations while preserving the health of crop plants, particularly those that are monocotyledonous.

Farmers must correctly identify dicotyledonous weeds to use the right chemical treatments effectively. As 2,4 D selectively targets these weeds, its application can greatly assist in managing unwanted plant species without affecting crop productivity.

Monocotyledonous Plants

Monocotyledonous plants, commonly known as monocots, have a single seed leaf, or cotyledon. This group includes many important crop species that form the foundation of agriculture worldwide. Some well-known examples of monocot plants are:

• Wheat (Triticum species)
• Corn (Zea mays)
• Rice (Oryza sativa)

Monocots are generally not affected by 2,4 D, which makes this weedicide particularly useful. In fields where monocot crops are grown, the application of 2,4 D can control unwanted dicotyledonous weeds without harming the crops. This selective action makes farming more efficient and sustainable, as it reduces the need for manual weed removal and minimizes crop damage.

Understanding the difference between monocotyledonous and dicotyledonous plants is crucial for effective weed management and the successful use of selective herbicides. Since monocots are not targeted by 2,4 D, it allows these plants to continue growing undisturbed, while the dicotyledonous weeds are eliminated. This balance supports increased agricultural productivity and sustainability.