| Experiments that prove mass flow theory | - Ringing experiments
- Tracer experiments |
| Ringing experiments | - If a ring of bark (which includes xylem + phloem) is removed from a woody stem
- Bulge forms above ring
- The fluid from bulge has a HC of sugars than the fluid from below the ring
- Evidence that there's a downward flow of sugars |
| Radioactive tracers | - Such as radioactive carbon
- Can be used to track movement of organic substances in a plant |
| Radioactive tracers experiment | - Supplying part of plant with a radioactive substance
- It will be present in organic substances e.g sugars, moved by translocation
- Can be tracked using autoradiography
- Results show translocation of substance from source to sink |
| Autoradiography | - Tracks movement of substances
- Shows where radioactive tracer has spread
- Plant is killed
- Plant placed on photographic film
- Radioactive substance present where film is black |
| More evidence that translocation of organic molecules occurs in the phloem | - Phloem cut sap oozes out, pressure gradient exists
- Aphids |
| Aphids | - Type of insect that feeds on plants
- Pierce phloem, then bodies are removed leaving mouthparts, allows sap to flow out
- Sap flows out quicker towards the leaves than down stem, pressure gradient exists |
