Uptake And Transport Of Mineral Nutrients

What is Mineral Nutrient Transport?

In plants, mineral nutrient transport is the means through which essential minerals and nutrients are taken up from the soil and mobilized in a plant to fuel physiological activities like photosynthesis, respiration, growth and other activities. In the majority of cases, it takes place in roots and is said to be active or passive.

These minerals are conducted in the xylem and phloem i.e., the plant's vascular system. This integrated transport system ensures that minerals are translocated in the plant to sustain growth and reproduction. Understanding these fundamental processes is critical for the advancement of plant nutrition and much more efficient agriculture in general.

Types of Mineral Nutrients

Based on the requirement of the nutrients, these are classified into two types:

Macronutrients

Macronutrients are required by the plants in large quantities. It includes:

• Nitrogen: Assists in making amino acids, proteins and chlorophyll.

• Phosphorus: Transport of energy throughout the cell, ATP, DNA, RNA

• Potassium: Enzyme Catalysis, Osmotic/ Ionic Regulation, Stomatal Regulation

• Calcium: Cell wall structure and integrity

• Magnesium: Chlorophyll, necessary enzyme activation

• Sulfur: Amino acids and vitamins

Micronutrients

Micronutrients are required by the plants in small quantities. It includes:

• Iron: Building block of Chlorophyll, electron carrier

• Manganese: Photosynthesis, nitrogen metabolism, a component of some enzymes.

• Zinc: For the functioning of enzymes, syntheses of proteins and proper regulation of growth and development.

• Copper: During photosynthesis and respiration and also as a structural component of lignin in cell walls.

• Molybdenum: In the fixation of nitrogen and reduction of nitrates.

• Boron: For the formation of cell walls and structural parts.

• Chlorine: Osmosis and ionic balance are required; it is also essential for photosynthesis.

• Nickel: Associated with urease activity and the metabolism of nitrogen.

Mechanisms Of Nutrient Uptake

The mechanism is described below-

Passive Transport

Passive transport moves the substances from higher concentration to a lower concentration i.e., down the gradient. It does not require any energy in the process.

Diffusion

• Diffusion is the process by which ions of nutrients move from a higher concentration to a lower concentration zone through the cell membrane.

• It is not an energy-dependent process.

Facilitated Diffusion

• Facilitated diffusion is a type of transport where molecules move across a cell membrane with the help of specific carriers or channel proteins.

• Unlike simple diffusion, it allows larger or polar molecules to pass through the lipid bilayer.

Active Transport

Active transport moves the substances from lower concentration to a higher concentration i.e., against the gradient. It requires ATP in the process.

Role of ATP

The expenditure of ATP is used to push nutrient ions against their concentration gradient. It allows the cells to develop higher levels of nutrients than are in the soil

Ion Pumps (H+ ATPase)

Proton pumps use ATP to develop an electrochemical gradient by forcing out of the cell H+ ions. That generates the gradient and hence drives the movement of other nutrient ions inside the cell down the gradient by co-transport.

Carrier Proteins and Channel Proteins

Carrier and channel proteins facilitate the passage by which nutrient ions cross the membrane. Carrier proteins bind to the nutrient ion and change conformation to take the nutrient ion across the membrane. Channel proteins are pores in the membrane that only allow specific ions to diffuse down the gradient

Transport of Nutrients Within The Plant

The transport is described below-

Xylem Transport (Inorganic Nutrients + Water)

Transpiration Pull

Transpiration pull is the process by which water and ions are transported from the roots to the leaves, the primary function of xylemic vessels. As the water evaporates from the leaf stomata, tension is developed which leads to the production of a negative pressure

Cohesion-Tension Theory

It describes that because of cohesion, the water molecules stick to the xylem vessel walls and make up a single column of water without any breaks. This way this continuous column is being dragged upwards by the force being generated because of the transpiration pull.

Role of Tracheary Elements

Specialised xylem cells like tracheids and vessel elements contribute to water and nutrient transport. Their structure allows easy transport as well as holding of the intact column of water without any failure.

Phloem Transport (Organic Nutrients)

Source-Sink Relationship

Movement of nutrients and organic products from 'source' regions, an example being leaf tissue, into 'sink' regions like root, tubers, and growth regions, into which regions of consumption or storage are spelt out.

Pressure Flow Hypothesis

Pressure flow hypothesis describes how the pressure flow of phloem sap rich in nutrients moves from the high-pressure source to the low-pressure sink across the phloem. Since there are osmotic pressure differentials due to the active loading and unloading of sugars from and into the phloem.

Role of Sieve Elements and Companion Cells

Sieve elements are the main tubes for the transport of nutrients in the phloem and are sap-filled with sieve between their cells. Thus the transport can be fast. There are companion cells that supplement the sieve elements by loading and unloading nutrients and maintaining metabolic functions necessary for transport.

Role of Xylem and Phloem in Mineral Transport

The vascular tissue system of the plant i.e., the xylem and phloem plays a crucial role in the transport of minerals, water and nutrients.

Importance of Mineral Nutrient Transport

The importance of mineral nutrient transport is:

• It maintains metabolic activities like photosynthesis and respiration.

• It enables the growth and tissue differentiation in plants.

• It ensures osmotic balance.

• It aids in fruit development as well as seed germination.

• It supports enzyme activity and chlorophyll formation.

Mineral Nutrient NEET MCQs (With Answers & Explanations)

The key concepts to be covered under this topic for different exams are:

• Mechanism of nutrient uptake

• Transport of nutrients

• Role of xylem and phloem

Practice Questions for NEET

Q1. Active absorption of mineral ions causes

1. High water potential in root

2. High water potential in soil

3. Low water potential in soil

4. None of these

Correct answer: 2) High water potential in soil

Explanation:

The water potential gradient in roots and, consequently, the uptake of water by osmosis are partially caused by the active uptake of ions. Maintaining cell turgor, aiding nutrient transfer, and sustaining physiological processes like transpiration and photosynthesis all depend on a steady supply of water, which is ensured by this process.

Hence, the correct answer is option 2) High water potential in soil.

Q2. Which of the following causes passive mineral absorption?

1. Pump proteins

2. Donnan equilibrium

3. Transfer proteins

4. All of these

Correct answer: 2) Donnan equilibrium

Explanation:

Mineral ions are absorbed passively without any use of energy. It is independent of metabolic inhibitors. This is explained by some theories, among which are the following:
Contact Exchange Theory: Direct exchange between soil and root surfaces by ions.
Carbonic Acid Exchange Theory: Involves carbonic acid in ion facilitation.
Donnan Equilibrium: A passive process that maintains charge equilibrium in the absence of active transporters but still enables the movement of mineral ions into plant roots across concentration gradients.

Hence, the correct answer is option 2) Donnan equilibrium.

Q3. What is the role played by the endodermal cells?

1. They facilitate passive absorption of mineral ions

2. They adjusts the quantity and types of solutes that reach the xylem

3. They actively transport ions in one direction only

4. Both b and c

Correct answer: 4) Both b and c

Explanation:

Active absorption of mineral ions occurs in root hair cells, where specific proteins are involved in pumping the ions from the soil into the cytoplasm of epidermal cells. The transport proteins within endodermal cells facilitate selective entry of only certain solutes through their plasma membranes, thus forming control points for the regulation of ions. The endodermis contains a suberin layer which must ensure active transport in only one direction; that is, minerals needed by the plant are being directed towards the xylem for transport upwards in the plant.

Hence the correct answer is option (4) Both b and c.

Also Read:

• MCQs on Uptake and Transport of Minerals

• Mass Flow Hypothesis

• Nitrogen Cycle

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