Transport in Plants
- As the leaves produce starch as a result of photosynthesis, it is converted to sucrose to get transported to various parts of the plant.
- Sucrose production is noted as source (or) phloem loading and the target point is referred to as sink (or) phloem unloading.
- The sucrose enters the sieve tube by piercing companion cells [Active transport with symplastic pathway) and mixes with water that enters from the adjacent Xylem into sieve tube due to osmosis to form sap.
- The sap at one end creates high hydrostatic pressure and hence moves along the sieve tube until the bottom point where hydrostatic pressure is low through passive transport.
- Again the sap through symplastic pathway crosses the companion cells to reach the sink.
- During unfavourable seasons, food molecules are moved from the roots (source) to leaf (sink).
- Phloem transport of food is also considered to be a mass/ bulk/pressure flow by a scientist named Munch with help of a flowmeter.
View this video for the topic from 48:02 to 53:38
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