Everything Life Sciences Grade 10

Figure 6.24: Spiny leaves have a small surface area to decrease transpiration.

• Leaf arrangement: vertical leaf arrangement (like proteas) decrease the surface area
  exposed to the sun in the heat of the day, In rosette arrangements the upper leaves
  shield the lower leaves from the Sun.


• Rolling of leaves:When leaves roll up, water vapour gets trapped in the tunnel made
  by the leaf, therefore reducing the water potential gradient, and therefore reducing the
  rate of transpiration.

Wilting and guttation DUMMY

We just discussed transpiration, and how leaves are constantly losing water vapour to the

environment. However, what happens when there is not enough water in the soil to replace

the water that was lost? Similarly, what happens when there is too much water? In the next

section we discuss wilting, and why plants wilt and get ‘floppy’ in hot weather or after a long

drought. We will also look at ways that plants can rid themselves of extra water when there

is too much water in the environment and the plant has to cope with high root pressure and

a low transpiration rate.

Wilting

Plants need water to maintain turgor pressure. Turgor pressure is what provides the plant

with much of its structural support. Have a look at Figure 6.25 which shows the effect of

osmosis on the turgidity of cells.

Figure 6.25: Cells in solutions with different concentrations

178 6.3. Transpiration