Biology 9700 · AS & A Level · The gas exchange system
The gas exchange system — practice question
The pressure of water vapour inside leaves and the pressure outside them can be measured. The difference between these two pressures is called the leaf vapour pressure deficit (LVPD). LVPD is one factor that affects the rate of transpiration. Scientists investigated how changing the LVPD altered the transpiration rate in several flowering plant species that live in a range of habitats. Two of these species were Nerium oleander, which is adapted to grow in hot, dry conditions, and Helianthus annuus, which is not adapted to survive in hot, dry conditions. Fig. 5.1 shows how increasing the LVPD affected the transpiration rates of the two species. All other factors were kept constant.
(a)[3]
Compare the findings for the two species shown in Fig. 5.1.
(b)[4]
State and explain two adaptations visible in the leaves of N. oleander in Fig. 5.3 and Fig. 5.4. One adaptation must be visible in Fig. 5.3 and one adaptation must be visible in Fig. 5.4.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “No transpiration when $\text{LVPD}=0\,\text{kPa}$” …