Question

Which sequence of events gives rise to flaccid guard cells and stomatal closure at night?

• A. Low [Glucose] $\Rightarrow$ low osmotic pressure $\Rightarrow$ low pH $\Rightarrow$ high $pCO_2$
• B. Low $pH \Rightarrow$ high $pCO_2 \Rightarrow$ low [Glucose] $\Rightarrow$ low osmotic pressure
• C. Low osmotic pressure $\Rightarrow high \, pCO_2 \Rightarrow low pH \Rightarrow$ low [Glucose]
• D. High $pCO_2 \Rightarrow$ low pH $\Rightarrow$ low [Glucose] $\Rightarrow$ low osmotic pressure

Answer 1

Answer: (D)

Stomata are open during the day and close during night. There are certain factors affecting stomatal movement.

Stomatal opening during day	Stomatal closure during night
Rise in pH	Low pH
Low $pCO_2$	High $pCO_2$
High humidity	Dry environment
High osmotic pressure	Low osmotic pressure
High glucose	Low glucose