Biology / AS level
Water evaporating from mesophyll surfaces lowers leaf water potential.
Water evaporating from mesophyll surfaces lowers leaf water potential. Cohesion among water molecules supports transmission of tension through continuous xylem columns, while roots absorb water along water-potential gradients.
Phloem transports assimilates through sieve tubes associated with companion cells. Loading at a source and unloading at a sink can establish pressure-driven bulk flow. A storage organ may act as a sink at one time and a source later, so direction is contextual rather than always downward.
Water uptake is 0.8 cm³ in 4 minutes. Find uptake rate.
Divide volume by time: 0.8/4=0.20 cm³ per minute; uptake is a proxy for transpiration.
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.
Cohesion between water molecules
Hydrogen bonding contributes to cohesion within the transpiration stream.
0.20 cm³/min
Divide volume by time: 0.8/4=0.20 cm³ per minute; uptake is a proxy for transpiration.
No, it is commonly a sink
A developing fruit consumes or stores imported assimilates and is therefore a sink in that context.