Stomatal aperture is formed between guard cells because :
(a) Thickness of its inner wall is more than its outer wall
(b) Thickness of its outer wall is more than its inner wall
(c) Thickness of wall of epidermal cell is more than its outer wall
(d) Thickness of wall of epidermal cell is less than its outer walls

Dear Student,

Each stoma is surrounded by pair of kidney-shaped guard cells. Guard cells carry out photosynthesis. These guard cells have thinner elastic outer walls and thicker less elastic inner walls.



Due to these, the guard cells are able to curve outwards during the day, thereby opening the stomatal pores.  Thus they are able to carry out photosynthesis.

Option A is thus correct answer. 

 
Regards,