On hot, dry days, guard cells often close microscopic openings in plant leaves, conserving water. this is an example of
a. environmental factors causing gene mutation
in plants
b. finite resources acting as selecting agents for
evolution
c. a feedback mechanism for maintaining homeostasis
d. differentiation in plants as a result of stimuli

A feedback mechanism for maintaining homeostasis.

Explanation:

In science term, Homeostasis is defined as a mechanism by virtue of which animal or plant cells will try to maintain the equilibrium state in the internal environment using feedback mechanism within the system.

It is also very important to maintain a good communication between the internal organs to maintain the internal environment. A proper functioning body whose needs are met is generally observed in the process of homeostasis.

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.