Problem 149 - Objective Biology for NEET

Question

Which of the following experiment showed that food in plant is transported through phloem? (a) Avena curvature experiment (b) Girdling experiment (c) Bell-jar experiment (d) None

Step-by-Step Solution

Answer

The correct answer is (b) Girdling experiment. This experiment demonstrated that food in plants is transported through phloem.

Step 1: Understand the options

Review each of the experiments provided in the options. The Avena curvature experiment is related to auxin and phototropism, the bell-jar experiment is related to photosynthesis, and the girdling experiment deals with the transport of food in plants.

Step 2: Identify relevant experiment

Based on the evaluations from Step 1, it becomes clear that the girdling experiment is the relevant experiment. The girdling experiment involves the removal of a ring of bark, which includes the phloem layer, from a stem of a plant. This disrupts the downward movement of food in the plant, thus demonstrating the role of phloem in food transportation.

Step 3: Make the conclusion

The experiment that showed that food in plants is transported through phloem is the girdling experiment. None of the other listed experiments has direct relevance to the process of food transportation within plants through phloem tissues. Therefore, the correct option is (b) Girdling experiment.

Key Concepts

Girdling Experiment

The girdling experiment is a classic botanical technique that helps demonstrate the vital role of the phloem in transporting food within plants. In this experiment, a ring of bark, containing the phloem layer, is carefully removed from the stem of a plant. Without the phloem, the downward flow of nutrients, which typically carries sugars produced through photosynthesis from leaves to other parts of the plant, is halted. This interruption results in the accumulation of sugars above the girdled section because they cannot move past the severed phloem. Consequently, the portion of the plant situated below the girdle often becomes deprived of these essential nutrients. This experiment effectively shows how vital phloem is for plant nutrition. Phloem's primary function is to act as a conduit for transporting organic nutrients, mostly sucrose, from the leaves (where photosynthesis occurs) to growing and storage regions of the plant. The accumulation of nutrients above the girdled area provides a visual and measurable way to affirm this transport process, making the girdling experiment a key method in plant physiology studies.

Plant Physiology

Plant physiology is the study of the functions and vital processes of plants. It encompasses a wide range of topics about how plants grow, develop, and adapt to their environments. Understanding plant physiology is crucial as it provides insights into essential processes like photosynthesis, respiration, transpiration, and nutrient transport. Key areas:

• Photosynthesis: This is the process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. It's the primary source of energy for nearly all ecosystems.


• Respiration: Unlike what might be assumed, plants also respire, consuming oxygen and releasing carbon dioxide. This process helps them extract energy from glucose.


• Transpiration: The loss of water vapor through stomata in leaves. It's a process that facilitates water movement in the plant and plays a role in nutrient transport.


• Nutrient Transport: Plants have complex vascular systems consisting of xylem and phloem. The xylem primarily carries water and minerals from roots to the rest of the plant, whereas phloem distributes the products of photosynthesis.

Studying plant physiology allows scientists and farmers to optimize plant health and production, improve crop yields, and develop sustainable agricultural practices.

Food Transport in Plants

The transportation of food in plants is primarily managed by the phloem tissues. This process is crucial for the survival, growth, and reproduction of plants, as it ensures that all parts of the plant receive the necessary nutrients. The transportation mechanism involves several steps:

• Photosynthesis in Leaves: Plants synthesize food mainly in their leaves, converting sunlight into chemical energy in the form of glucose, which is later transformed into sucrose.


• Loading of Sucrose into Phloem: The sucrose is actively loaded into the phloem sieve tubes at the source points (primarily the leaves), facilitated by specific transport proteins. This creates a concentration gradient that draws in water, generating pressure.


• Pressure-Flow Mechanism: This process, also called mass flow hypothesis, describes how the generated pressure pushes the sucrose solution through the phloem towards sink areas (roots, fruits, growing shoots) where the sucrose is unloaded and utilized or stored.

Understanding food transport in plants is essential for appreciating how plants maintain their energy balance and facilitate growth. This knowledge is also critical in agricultural practices, horticulture, and any field involving plant cultivation and resource management.