Question

Phloem sap is mainly composed of (a) Water + Glucose (b) Water + Fructose (c) Water + Cellulose (d) Water + Sucrose

Short answer

The correct answer is (d) Water + Sucrose.

Step-by-step solution

Identify the components of phloem sap

The first step is to have a clear understanding of what phloem sap is and what it is composed of. Phloem sap is a sugar-rich, liquid transport substance found in the plants. Other than water, it is primarily composed of sugars, the main one being sucrose.

Compare the composition with the options

The second step involves comparing this information with the given options. By understanding that the main sugar component in phloem sap is sucrose, it would become clear that the correct option is the one that includes water and sucrose.

Key concepts

The Plant Transport System

Understanding the plant transport system is crucial for students preparing for exams like the NEET, as well as for anyone interested in plant biology. The system consists of two main tissues: xylem and phloem. The xylem is responsible for the transportation of water and minerals from the roots to the other parts of the plant, functioning largely through transpiration pull and root pressure.

Meanwhile, the phloem transports the products of photosynthesis, such as sugars, from the leaves to the rest of the plant. This process is known as translocation and operates through a mechanism called the pressure-flow hypothesis. In essence, phloem moves nutrients to areas of the plant where they are needed for growth, storage, or energy. Thus, the phloem is integral in distributing the food produced by photosynthetic organs to various parts of the plant, including the growth sites and storage tissues.

Sucrose in Phloem

Sucrose plays a pivotal role in the phloem sap composition, effectively serving as the primary sugar transported throughout the plant. Produced in the mesophyll cells of leaves during photosynthesis, sucrose is a disaccharide consisting of one glucose and one fructose molecule. It is water-soluble, which makes it an efficient molecule for transportation within the aqueous medium of phloem.

After being synthesized in the leaves, sucrose is actively transported into the phloem's sieve-tube elements, where it increases the osmotic pressure, causing water to flow in from the xylem. This process creates a gradient, allowing the movement of sap from high-pressure areas near the leaves to lower pressure areas where the sucrose is utilized. The process is vital for growth and development, enabling parts of the plant that do not photosynthesize, like roots and developing shoots, to receive energy and carbon skeletons for metabolism.

Biology NEET Preparation

For students aiming to excel in competitive exams like NEET (National Eligibility cum Entrance Test), which is a prerequisite for pursuing medical courses in India, understanding topics like the composition of phloem sap is essential. Biology is a major section in these exams, and the plant transport system, including the understanding of phloem sap, is a frequent subject of questions.

To prepare effectively for the biology section of NEET, students should focus on gaining a comprehensive understanding of plant anatomy and physiology. This entails not just memorizing facts but grasping the underlying processes and mechanisms, such as the translocation of sucrose. Students can benefit from practicing with previous years' question papers, taking mock tests, and engaging with interactive educational resources that explain these concepts clearly and concisely. Understanding the real-world application of these concepts, such as the importance of sucrose transport for plant vitality, can also help in retaining the information and applying it in an exam setting.