Moving Food Through A Plant Flashcards
How do we believe food is transported through a plant?
Via mass-flow hypothesis
What method of transport is utilised during mass-flow hypothesis?
Active transport.
What is a source?
The area where sugars are made or collected.
What is a sink?
The area where sugars are needed.
Explain the process of the mass-flow hypothesis.
Sugars enter the phloem from the source, causing water to enter. They both move down a pressure gradient to the sink, where they are pumped out by active transport.
Why does water move into the source?
The movement of sugars into the phloem creates a gradient, decreasing water potential, so water move in.
How does pressure change at the source and sink?
At the source, pressure is higher. At the sink, pressure is lower.
What do substances use to move from source to sink?
The pressure gradient.
What is translocation?
The movement of sugars from source to sink.
What evidence suggests mass-flow hypothesis is correct?
- When phloems are punctured, the rate of sap flow points to a pressure gradient.
- Sampled sap from the source has a higher sucrose concentration from that in the sink.
- Viruses can be detected moving via active transport to the roots.
What evidence mass-flow-hypothesis is incorrect>
- The hypothesis says that bulk flow should occur at the same rate, in the same location, but many scientists have claimed to detect different substances moving in different directions in one tube.
Describe the structure of phloem tube cells.
The phloem cell is comprised of sieve tubes - elongated cells joined in a chain- and sieve plates - perforations in the ends of each cell, as well as companion cells, as sieve tubes do not have any organelles, and cannot repair themselves.
