Learn: Mass Transport in Plants (Xylem, Transpiration, Phloem Translocation)

Welcome!You've already learned about gas exchange and mass transport in mammals, including the heart, blood vessels, and haemoglobin. Now, let's build on that knowledge to explore how plants transport water, minerals, and sugars through their xylem and phloem.

What is Mass Transport in Plants?Mass transport is the movement of substances over long distances within plants. It involves two key systems: xylem for water and minerals, and phloem for sugars and other organic molecules. This process ensures plants have the resources needed for growth and survival.

Xylem and Water MovementThe xylem transports water and dissolved minerals from the roots to the leaves. It consists of hollow, dead cells arranged end-to-end, forming tubes. Water moves upwards due to the cohesion-tension theory, which relies on water's cohesive properties and the evaporation of water from leaves (transpiration).

TranspirationTranspiration is the evaporation of water from a plant’s leaves, mainly through the stomata. This creates a tension that helps pull water up through the xylem. Factors like temperature, humidity, wind speed, and light intensity can affect the rate of transpiration.

Phloem and TranslocationThe phloem transports sugars (such as sucrose) and other organic substances made during photosynthesis from leaves to other parts of the plant. This process is called translocation. The sugars are moved as part of a solution called phloem sap.

Mass Flow HypothesisThe mass flow hypothesis explains how sucrose moves in the phloem. Sucrose is actively transported into the phloem, lowering the water potential. Water enters by osmosis, increasing pressure. This pressure drives sucrose to areas of lower pressure, such as roots or storage organs.

Evidence for Mass FlowScientists have conducted experiments to support the mass flow hypothesis. These include tracer experiments, where radioactive isotopes trace sugar movement, and ringing experiments, where removing phloem disrupts sugar transport but not water movement.

Review Time!You've learned about xylem, transpiration, phloem, and the mass flow hypothesis. Let’s test your understanding with a few questions!