Made up of 4 different parts:
- Phloem fibres
- Phloem parenchyma
- Sieve tubes
- Companion cells
The sieve tubes and companion cells are both involved with the mass flow hypothesis.
Sieve Tubes
- Cell membrane broken down
- Fluid cytoplasm
- No vacuole
- No nucleus
With the end of the sieve wall broken down, it allows inter-cellular movement.
- Have plasmodesmata.
- Very metabolically active.
- High number of mitochondria.
- May provide energy for translocation (mass movement).
Osmotic Pressure
The movement of solutes from a high hydrostatic pressure to a low hydrostatic pressure.
Evidence to Support Mass Flow Hypothesis
- Solution under pressure.
- Evidence for concentration gradient.
- Observation of sieve tubes.
- Movement of the virus through the plant.
- No movement of the virus when no photosynthesis.
Evidence against Mass Flow Hypothesis
- Get the impression of steady flow, this is wrong.
- Certain things move in different ways.
Frequently Asked Questions
What is phloem tissue?
Phloem tissue is a plant’s vascular tissue responsible for transporting organic materials in plants’ bodies.
What are the components of phloem tissue?
Phloem tissue comprises phloem fibres, phloem parenchyma sieve tubes and companion cells.
What are sieve tubes in phloem tissues?
Phloem tissues have specialized sieve tube cells that join end to end and form long sieve tubes to transport organic materials in plants.
What is mass flow in phloem tissue?
Sucrose is loaded in phloem tissue at the source (leaves), which pulls water in sieve tubes generating high hydrostatic pressure at the source. This pressure derives fluid towards the sink where sucrose is unloaded from sieve tubes, decreasing the pressure there.