Water Uptake and Roots
Which structures on root hair cells increase the surface area for water absorption?
Root hairs
Which plant tissue transports water and mineral ions from roots to leaves?
Xylem
What is the loss of water vapour from the leaves and other aerial parts of a plant called?
Transpiration
Which plant tissue transports sucrose and amino acids?
Phloem
Which instrument is commonly used to estimate water uptake by a leafy shoot during an investigation?
Potometer
By which process does water enter root hair cells from the soil?
Osmosis
In which direction does water usually move through the xylem?
Upwards, from roots towards stems and leaves
Through which openings in the leaf does most water vapour diffuse out?
Stomata
What is the movement of assimilates through the phloem called?
Translocation
What should be done to the cut end of a shoot when setting up a potometer to reduce air entering the xylem?
Cut the shoot under water
What is the function of root hair cells?
To absorb water and mineral ions from the soil
Are mature xylem vessel elements living or dead?
Dead
Which cells control the opening and closing of stomata?
Guard cells
Give one example of a source and one example of a sink in a plant.
Source: a photosynthesising leaf; sink: a growing root or developing fruit
What is the independent variable in an experiment investigating how wind speed affects transpiration?
Wind speed
Why do root hair cells have a large surface area?
To increase the rate of absorption of water and mineral ions
Which substance strengthens xylem vessel walls and helps prevent them from collapsing?
Lignin
How does increased wind speed usually affect the rate of transpiration?
It increases the rate by removing moist air around the leaf
Name the two main types of cells associated with transporting assimilates in phloem tissue.
Sieve tube elements and companion cells
Why should other conditions, such as temperature and light intensity, be kept constant when investigating the effect of wind speed?
To ensure that changes in water uptake are due to wind speed rather than other variables
The soil water potential is higher than that of a root hair cell. In which direction will water move, and by what process?
Water moves from the soil into the root hair cell by osmosis
Explain how the structure of a xylem vessel makes it suitable for transporting water.
It forms a continuous hollow tube with no end walls, allowing water to flow; lignified walls provide strength and prevent collapse
Explain why a plant usually transpires faster in hot, dry and windy conditions than in cool, humid and still conditions.
Higher temperature increases evaporation and diffusion; low humidity increases the water vapour gradient; wind removes moist air around the leaf
Why can translocation occur both upwards and downwards in a plant?
Assimilates move from sources to sinks, which may be above or below the source
A potometer bubble moves 30 mm in 5 minutes. Calculate the mean rate of bubble movement in mm per minute.
30/5 = 6 mm/min