CIE iGCSE Co-Ordinated Science B8.4 Translocation Exam Style Questions Paper 4
Question
(a) Scientists investigate where translocation and transpiration occur in a plant stem.
The scientists test three plant stems:
- Stem A is left in its natural state
- Stem B has a ring of phloem removed
- Stem C has a ring of phloem and xylem removed
Fig. 4.1 shows the stems used.
(i) Table 4.1 is used to predict which processes occur in each stem.
Complete Table 4.1 by placing ticks (✓) in the correct boxes to predict which processes occur in each stem.
▶️Answer/Explanation
| stem A | stem B | stem C | |
|---|---|---|---|
| translocation occurs | ✓ | ||
| transpiration occurs | ✓ | ✓ |
Explanation:
– Stem A (Natural): Both processes occur normally as all vascular tissues are intact
– Stem B (Phloem removed): Only transpiration occurs because xylem is intact (phloem needed for translocation)
– Stem C (Both removed): Neither process occurs as both vascular tissues are disrupted
(ii) Compare the direction of movement of substances during translocation and transpiration.
▶️Answer/Explanation
1. Transpiration: Unidirectional (only upwards from roots to leaves)
2. Translocation: Bidirectional (can move both upwards and downwards in the plant)
Detailed comparison:
– Transpiration stream: Water and minerals move upwards through xylem from roots → leaves
– Translocation: Organic compounds (sugars, amino acids) move through phloem:
– Downwards: From leaves (source) to roots/storage organs (sink)
– Upwards: From storage organs to growing tips/new leaves
– Transpiration is passive (physical process), while translocation is active (requires energy)
(b) Xylem and phloem are specialised to transport substances including water around the plant.
(i) Name two other substances moved through the plant during translocation.
▶️Answer/Explanation
1. Sucrose
2. Amino acids
Additional substances:
– Other sugars (glucose, fructose)
– Hormones (auxins, cytokinins)
– Some mineral ions
– Note: These are transported in the phloem sap along with water
(ii) Describe one other function of xylem.
▶️Answer/Explanation
Mechanical support (provides structural strength to the plant)
Detailed explanation:
– Xylem vessels contain lignin (a tough, waterproof substance) in their cell walls
– This lignification makes xylem cells rigid and strong after they die
– Provides:
– Stem rigidity to keep plant upright
– Resistance to bending forces (wind, weight of branches)
– Structural framework for overall plant architecture
– Secondary function: Storage of water and nutrients