3.1 Gas exchange in flowering plants
● Respiration: uses oxygen, gives off carbon dioxide, occurs all the time in all
living cells in plant
● Photosynthesis: uses carbon dioxide, gives off oxygen, occurs only when light
only in plant cells containing chloroplasts
Adaptations of leaf for gas exchange (all about diffusion)
● Whole leaf
○ Large flat surface area exposed to air, large surface area to volume ratio
○ Many stomata pores, when open allowing movement of gases into and out
of air spaces inside leaf
○ Thin, short diffusion distance (internal)
● Internal structure
○ Many stomata open when sunlight (for ANY gas exchange)
○ Air spaces inside stoma surrounded by loosely packed mesophyll cells,
where gases diffuse into or out of living cells
○ Palisade mesophyll cells, site of most photosynthesis, in close contact
with air spaces, allowing gases used and produced by photosynthesis to
be exchanged with air in air spaces
○ Walls of both spongy and palisade mesophyll are thin, allowing gases to
pass through cell membrane into and out of cell
○ In air & surfaces of cells inside air spaces are moist, helps gases dissolve
and allows diffusion into and out of cells
○ Respiration is going on, all cells have close contact with air in air space,
important for gas exchange (oxygen → carbon dioxide)
○ Net diffusion through stomata - into leaf to air spaces then to cells/out of
leaf from cells to air space then out to air
Stomata and guard cells
● Each stoma made up of two guard cells with slight gap between them
● Guard cells contain chloroplasts (unlike other cells on epidermis)
● Guard cells can change in shape so that gap (stomatal pore) can increase in size
or close completely
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● Respiration: uses oxygen, gives off carbon dioxide, occurs all the time in all
living cells in plant
● Photosynthesis: uses carbon dioxide, gives off oxygen, occurs only when light
only in plant cells containing chloroplasts
Adaptations of leaf for gas exchange (all about diffusion)
● Whole leaf
○ Large flat surface area exposed to air, large surface area to volume ratio
○ Many stomata pores, when open allowing movement of gases into and out
of air spaces inside leaf
○ Thin, short diffusion distance (internal)
● Internal structure
○ Many stomata open when sunlight (for ANY gas exchange)
○ Air spaces inside stoma surrounded by loosely packed mesophyll cells,
where gases diffuse into or out of living cells
○ Palisade mesophyll cells, site of most photosynthesis, in close contact
with air spaces, allowing gases used and produced by photosynthesis to
be exchanged with air in air spaces
○ Walls of both spongy and palisade mesophyll are thin, allowing gases to
pass through cell membrane into and out of cell
○ In air & surfaces of cells inside air spaces are moist, helps gases dissolve
and allows diffusion into and out of cells
○ Respiration is going on, all cells have close contact with air in air space,
important for gas exchange (oxygen → carbon dioxide)
○ Net diffusion through stomata - into leaf to air spaces then to cells/out of
leaf from cells to air space then out to air
Stomata and guard cells
● Each stoma made up of two guard cells with slight gap between them
● Guard cells contain chloroplasts (unlike other cells on epidermis)
● Guard cells can change in shape so that gap (stomatal pore) can increase in size
or close completely
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