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(a) Label the TWO components of phloem tissue indicated in the diagram - HSC - SSCE Biology - Question 17 - 2008 - Paper 1
Question 17
(a) Label the TWO components of phloem tissue indicated in the diagram. (b) Describe ONE theory about the processes responsible for the movement of materials throu... show full transcript
Worked Solution & Example Answer:(a) Label the TWO components of phloem tissue indicated in the diagram - HSC - SSCE Biology - Question 17 - 2008 - Paper 1
Step 1
Label the TWO components of phloem tissue indicated in the diagram.
Answer
The components of phloem tissue typically include:
- Sieve tube elements - These are responsible for the transport of sugars and other organic compounds.
- Companion cells - These cells assist sieve tube elements by providing them with metabolic support.
Step 2
Describe ONE theory about the processes responsible for the movement of materials through phloem tissue.
Answer
One prominent theory regarding the movement of materials in phloem tissue is the Pressure Flow Theory. According to this theory, the movement of sap through the phloem is driven by differences in turgor pressure between source and sink regions.
- Source: At the source (e.g., leaves), sugars are actively transported into the sieve tubes, leading to a high concentration of solutes.
- Osmosis: This causes water to enter the sieve tubes from the surrounding tissues, increasing turgor pressure.
- Flow: The increased pressure drives the sap toward areas of lower pressure, known as sinks (e.g., roots or growing tissues) where sugars are used or stored.
- Drainage: At the sink, sugars are removed from the sieve tubes, decreasing the solute concentration and, consequently, the turgor pressure, allowing for continuous flow.