1. Which tissue transports sucrose?
- Phloem
- Xylem only
- Epidermis only
Check the answer and reasoning
Phloem
Phloem moves assimilates between source and sink tissues.
Biology / IGCSE
Transport in plants
Xylem carries water and mineral ions from roots and also supports the plant.
Learning objectives
- Distinguish xylem from phloem.
- Explain transpiration.
- Evaluate evidence from a potometer.
The big idea
Xylem carries water and mineral ions from roots and also supports the plant. Phloem translocates sucrose and amino acids from sources to sinks, which can occur in different directions in different tubes.
Evaporation from leaf surfaces and diffusion through stomata drive transpiration. Root hair surfaces support water uptake. Wind, humidity, temperature and light affect water loss; a potometer measures uptake rather than directly measuring all water evaporated.
Worked example
A potometer bubble moves 12 mm in 3 minutes. Find its movement rate.
Follow the solution
Divide distance by time: 12/3=4 mm/min; converting this to water volume also needs tube area.
Investigate and explain
Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.
No exact PhET model is claimed for this topic. Use diagrams and supplied-data reasoning instead.
Check your understanding
2. A potometer bubble moves 12 mm in 3 minutes. Find its movement rate.
- 36 mm/min
- 4 mm/min
- 9 mm/min
Check the answer and reasoning
4 mm/min
Divide distance by time: 12/3=4 mm/min; converting this to water volume also needs tube area.
3. Does a potometer measure transpiration directly?
- Yes
- Only in bright light
- No
Check the answer and reasoning
No
It measures water uptake, and some absorbed water may be used or stored rather than transpired.