Thursday 30 April 2020
Describe the process of gaseous exchange in terrestrial plants
Gaseous exchange occurs in
the spongy mesophyll; During the day, air diffuses into large air spaces of the
spongy mesophyll; through the stomata; the carbon (IV) oxide in the air
diffuses into photosynthetic cells; in solution form; during photosynthesis, carbon
(IV) oxide is used up; while oxygen is produced; some of the oxygen is used in
respiration; while the rest diffuses out of the leaf; through the stomata;
During the night, air diffuses into the air spaces; through the stomata; the
air dissolves into the film of moisture; oxygen in the air diffuses into the
cells; and is used for respiration; carbon (IV) oxide produced; diffuses out
through stomata; due to a concentration gradient/diffusion gradient; At night,
carbon (IV) oxide accumulates in the leaf since photosynthesis does not occur;
some gaseous exchange also takes place through the cuticle; and through the
epidermis of young leaves, roots and stems; some plants exchange gases through
breathing roots/pneumatophores; older stems exchange gases through lenticels
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