Unpacking the Pressure-Flow Hypothesis: My Phloem Translocation Map - kssm form 5 biology

 Phloem translocation felt abstract until I diagrammed the pressure-flow hypothesis:

• At source (leaf), companion cells actively load sucrose into sieve tubes, lowering water potential.
• Water enters by osmosis, creating high turgor pressure.
• At sink (root or fruit), sugars unload, raising water potential—and pressure—so fluid flows from source to sink.

Seeing pressure gradients on paper made it click: sap moves from high-pressure source to low-pressure sink.

Sample SPM Question

“Outline the pressure-flow mechanism of translocation and give one piece of supporting evidence.”

I answered:

• Describe loading/unloading and pressure gradients.
• Cite ringing experiments (girdling blocks downward flow) as evidence.

Blog 5: “Factors That Shape Plant Transport: My Experiments on Transpiration & Translocation”

Once I had processes down, I tested how environmental factors affect them. I varied:

• Light intensity: raised lamp wattage, saw bubble speed double
• Humidity: enclosed shoot in a damp chamber, transpiration halved
• Wind: directed a fan at the leaf, transpiration rate climbed

I also tracked sugar movement under low temperature, noting phloem flow slowed—validating that translocation depends on metabolic activity in companion cells.

Sample SPM Question

“Describe how light intensity and humidity influence transpiration rate in plants.”

I structured my answer:

• Light opens stomata, increasing transpiration.
• High humidity reduces water potential gradient, decreasing transpiration.

By writing these posts in my own voice—sketching diagrams, running simple experiments, and tackling sample SPM questions—I’ve turned the KSSM Form 5 DLP topic Transport in Plants from abstract theory into memorable, exam-ready knowledge.