Question

Root pressure develops due to (a) Passive absorption of ions (b) Active absorption of ions (c) Active absorption of glucose (d) None of these

Short answer

The correct answer is (b) Active absorption of ions.

Step-by-step solution

Understand the concept of root pressure

Root pressure is a phenomenon in plants caused by active transport of mineral nutrient ions into the root xylem. Because of osmosis, water follows the ions into the xylem, creating a slight pressure.

Match the understanding with the given options

From the provided options, the option that describes active transport of ions is (b) Active absorption of ions, which aligns with the cause of root pressure.

Choose the correct answer

Therefore, based on the understanding of root pressure, option (b) Active absorption of ions is the correct answer.

Key concepts

Active Transport

Active transport is a crucial biological process through which cells move molecules and ions across their membranes against their concentration gradient. This movement requires the cell to expend energy, often in the form of adenosine triphosphate (ATP), which differentiates it from passive transport that occurs without the input of cellular energy.

In the context of plant physiology, root cells use active transport to absorb essential mineral nutrient ions from the soil, such as potassium (K⁺), magnesium (Mg²⁺), and nitrate (NO₃^-). These ions are often at a lower concentration inside the roots than in the soil, necessitating the use of energy for absorption. The energy supplied by the cell enables the transport proteins in the cell membrane to carry these nutrients into the plant against the concentration gradient, thereby playing a pivotal role in the nutrition and health of the plant.

Mineral Nutrient Ions

Plants require a range of mineral nutrient ions for their growth and development, each serving specific roles in plant tissues. They are essential components of vital biological molecules and contribute to various physiological functions. For instance:

• Nitrogen (often absorbed as nitrate, NO₃^- or ammonium, NH₄⁺) is integral to amino acids, proteins, and chlorophyll.
• Phosphorus (as phosphate, PO₄^3-) is involved in energy transfer processes and the formation of DNA and RNA.
• Potassium (as K⁺) regulates stomatal opening and closing which affects transpiration and photosynthesis.
• Calcium (as Ca²⁺) is a structural component of cell walls and is necessary for cell division and growth.

The uptake of these ions through active transport establishes a concentration gradient which is essential for various plant processes, including the movement of water which is closely tied to the generation of root pressure.

Plant Physiology

Plant physiology encompasses the study of how plants function, including the processes of nutrient uptake, transport, metabolism, and growth. A fundamental aspect of plant physiology is the transport system, involving the xylem and phloem, which circulate water, mineral nutrients, and sugars throughout the plant.

Root pressure is a vital concept within plant physiology that illustrates how roots actively take up nutrients and water from the soil. It often occurs at night when transpiration is low, and it aids in pushing water upwards through the xylem to reach various parts of the plant. However, root pressure alone is not typically strong enough to lift water to the tops of tall trees; that process is primarily driven by transpiration pull, a topic that also falls under the broad umbrella of plant physiological studies.

Osmosis

Osmosis is the passive movement of water molecules through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration to achieve equilibrium. In plants, this means that water moves from the soil, where there is relatively more water and less solute, into the root cells, which contain a higher concentration of solute due to actively transported mineral ions.

With the influx of mineral nutrient ions through active transport, there is an accumulation of solute within the root xylem. Consequently, water follows osmotically, resulting in an increase in hydrostatic pressure within the xylem – this pressure is what we refer to as root pressure. It is part of what enables plants to transport water from their roots to their leaves against the force of gravity, albeit root pressure does so over modest distances and in certain conditions.