Gas exchange in plants Flashcards
When light, what processes do plants perform
Photosynthesis and respiration
What processes do plants do when dark
Just respiration
Do plants have any ventilation mechanisms?
No, plants rely entirely of diffusion
Characteristics of the leaf that enable gas exchange 4
Thin and flat
Air spaces in spongy mesophyll for gas circulation
Smaller airspace between cells of other tissues
Stomatal pores
Describe the diffusion journey 4
Diffuse through stomata
Diffuse through intracellular spaces between mesophyll cells
Gas dissolves in film of water covering cells and in cellulose cell wall
Gas diffuses into cell
In daylight which process is dominant
Photosynthesis
Direction off gas movements in daylight
CO2 in
O2 out
Gas movements in darkness
CO2 out
O2 in
Left adaptations for light harvesting? 4
Large SA
Can move, slowly,
Cuticle and epidermis are transparent
Leaves are thin
Benefit of leaves being able to move for light harvesting
They can be held in a position facing the light, phototropism
Benefit of cuticle and epidermis being transparent
Light can reach palisade mesophyll
Benefit of leaves being thin for light harvesting
Light can get to lower layers of the leaf
Adaptations of palisades mesophyll cells 4
Elongated
Densely packed
small air spaces between cells
Many chloroplasts
Chloroplasts can move in the cells
Benefit of chloroplasts being able to move in palisades cells
Can move to collect most sunlight or move away from strong light to avoid damage
How is the cuticle formed
It is secreted by the epidermis
What is the purpose of the waxy cuticle
Wax is a water proofing agent to reduce water loss throught the epidermis
How many waxy cuticle does a leaf have, and where
2: covers both upper and lower epidermis except from at stomata
Guard cells?
Cells in epidermis which can change shape to form a stomata for gas exchange
Do epidermal cells have chloroplasts
no they are transparent
Do guard cells have chloroplasts
yes
Explain how stomata open via guard cells
Water moves via osmosis into guard cells
Become turgid and curve away from each other
Bc inner wall is thicker and inelastic compared to outer wall
What characteristic of guard cells causes them to Ben’s open when turgid
Extra cellulose thickening on cell walls next to the stomata
How do guard cells obtain ATP for active transport
Chloroplasts build it
Regarding potassium ions and overall water potential, how do guard cells work 5
When dark: Potassium ions diffuse out of guard cells
Malate converted into insoluble starch
Water potential of cells increase
Water moves out of cells down potential grad
Turgor of cells reduces, they change shape and stomata close
Why does the conversion of malate to starch increase water potential
Starch is insoluble so has no osmotic effect
What word describes how inflated guard cells are
turgor
By what process do potassium ions enter guard cells in daylight
active transport
Xerophytes?
Plants adapted to survive in dry conditions
What are the 2 types of adaptation that allow the survival of xerophytes
physical and physiological
Example of a physiological adaptation of xerophytes
Close stomata during the day and open at night to reduce water loss
Disadvantage of xerophytes closing stomata in the day
Limits CO2 uptake, so limits rate of photosynthesis
Physical adaptation of xerophytes to reduce SA to minimise water loss
Leaves reduced to needles or spines
Physical adaptation of xerophytes to reduce water loss by careating a damp area to reduce the diffusion grad
Curled leaves: reduce air movements= shallow conc grad
Sunken stomata
Hairy leaves
Physical adaptation of xerophytes to access more water
Shallow roots covering large area
Characteristic of juvenile (shade) leaves
Darker green, more chloroplasts
Characteristic of mature (sun) leaves
Lighter green, fewer chloroplasts
Hydrophyte
Plants that live in water
How do hydrophytes maintain buoyancy
large air spaces in spongy mespohyll
Where are stomata of hydrophytes and why
On upper surface, allow gas to diffuse from air as lower surface is submerged
Describe waxy cuticle of hydrophytes and why
Thin/ non existent bc water loss isnt an issue
