Translocation of Food in Plants | Pressure Flow Theory | Class 11 Biology Chapter 8 New Book 2025

Class 11 Biology Chapter 8 Plant Physiology | Translocation of Food | Pressure Flow Theory
Pressure Flow Theory explained in easy English for FSC 1st Year Biology (Punjab Board New Book 2025)
In this video, we explain Translocation of Food in Plants according to the Pressure Flow Theory (Mass Flow Hypothesis) from Class 11 Biology Chapter 8 – Plant Physiology, based on the new Punjab Board syllabus 2025.
Translocation of food is the movement of organic nutrients, mainly sucrose, from source regions like leaves to sink regions such as roots, fruits, seeds, and growing parts of the plant. This movement occurs through phloem tissue.
The Pressure Flow Theory, proposed by Ernst Münch, is the most widely accepted explanation for food transport in plants. According to this theory, food moves through phloem by mass flow due to a pressure gradient between source and sink.
At the source, sucrose is actively loaded into sieve tubes, which lowers water potential and causes water to enter from xylem by osmosis, creating high turgor pressure. At the sink, sucrose is removed, water potential increases, water moves out of phloem, and low pressure is developed. Due to this pressure difference, food flows from high pressure (source) to low pressure (sink).
This lecture includes:
• Definition of translocation of food
• Structure and role of phloem
• Source and sink concept
• Pressure Flow Theory step by step
• Role of pressure gradient
• Important exam-oriented points
This video is very useful for board exam preparation, concept clarity, and quick revision.
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Keywords:
Pressure Flow Theory, Translocation of Food, Class 11 Biology, FSC 1st Year Biology, Plant Physiology, Punjab Board Biology 2025, Phloem Transport, Mass Flow Hypothesis, Movement of Food in Plants, Source and Sink, Biology Lecture, Science Teaching Zone
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