Problem 37 - Objective Biology for NEET

Question

The function of soil is to (a) Supply mineral to plants (b) Harbour the nitrogen fixing bacteria (c) Hold water and supply air to root (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) - All of these.

Step 1: Analyze Option (a)

Option (a) declares that soil provides minerals to plants. This is indeed one of the main roles of soil. Roots absorb minerals from the soil, which are essential for plant growth.

Step 2: Analyse Option (b)

Option (b) suggests that soil hosts nitrogen-fixing bacteria. This is accurate, as specific bacteria in the soil convert atmospheric nitrogen into a form that plants can use for their physiological processes.

Step 3: Analyze Option (c)

Option (c) states that soil retains water and supplies air to the roots. This function is also true, as soil's water-holding capacity affects the water availability for plant uptake, and air in the soil includes oxygen necessary for root respiration.

Step 4: Evaluate the Answer

The student should comprehend that all options (a), (b), and (c) represent the functions of soil. Thus, the correct answer to the given problem would be (d) - All of these.

Key Concepts

Mineral Absorption

Plants rely on their roots to absorb essential minerals from the soil. These minerals include nutrients like nitrogen, potassium, phosphorus, calcium, magnesium, and sulfur, all vital for healthy plant growth and development. The soil acts as a reservoir for these nutrients.
This absorption process happens through tiny structures called root hairs. These increase the root surface area, allowing for more efficient uptake of minerals.
Minerals are dissolved in soil water, and the roots absorb them through active and passive transport. Active transport requires energy to move minerals from a lower to a higher concentration, while passive transport doesn’t require energy.

• Plants need essential minerals for photosynthesis, enzyme function, and protein synthesis.
• Without these nutrients, plants cannot grow properly or produce fruits and flowers.

Thus, mineral absorption is a fundamental soil function, as it supports plant nutrition and growth.

Nitrogen Fixation

Nitrogen fixation is a crucial soil function that involves converting atmospheric nitrogen ( N_2 ) into a usable form for plants. This process is mainly carried out by specific bacteria in the soil. These bacteria, such as Rhizobium, form symbiotic relationships with legume plants, including peas, beans, and lentils.
Legume roots develop nodules where these bacteria reside, transforming nitrogen gas into ammonia ( NH_3 ). This ammonia is then converted into nitrates and nitrites, which plants can easily absorb.
Even non-leguminous plants benefit from this process indirectly, as fixed nitrogen gets incorporated into the soil, enriching it:

• Nitrogen is essential for making amino acids, proteins, and DNA.
• Healthy nitrogen levels in soil improve plant growth and increase agricultural yields.

Nitrogen fixation is therefore vital for sustaining plant life and promoting soil fertility.

Water Retention and Root Aeration

Water retention and root aeration are key functions of soil that support plant health and growth. Water retention refers to the soil's ability to hold water, providing plants with a consistent supply of moisture.
If soil lacks good water retention capacity, plants may suffer from drought stress, while over-retaining water can lead to waterlogging and root rot.
A good balance ensures that plants have enough water to sustain their growth without experiencing excess or deficiency.
On the other hand, root aeration is crucial because roots need oxygen to breathe. Soil needs to be porous enough to allow air circulation; this ensures that roots have access to the oxygen required for cellular respiration:

• Proper soil structure promotes both water retention and aeration.
• Maintaining soil's physical properties is important for optimal plant health.

Altogether, these soil properties collectively create a suitable environment for plant growth.