Plant gas exchange Flashcards
(36 cards)
How do the shape of leaves help with gas exchange?
Thin (short diff pathway), large SA, permeated by air spaces
Draw and label a general leaf
Waxy cuticle, upper epidermis, palisade mesophyll and spongy mesophyll (both with chloroplasts), vascular bundle (xylem, phloem and bundle sheath), air spaces, lower epidermis, stomata, guard cells
Roles of stomata?
Gas exchange of o2 and co2 in photosynthesis and respiration
Reduction of water loss
Function of waxy cuticle?
Reduce h2o less but also reduces gas exchange
When do plants mostly respire and only photosynthesis?
Mostly respire at night/ warm temperatures
Photosynthesis during the day
Structure of palisade cells in palisade mesophyll
Elongated and compacted into a layer of cells
Contains most chloroplasts
How do chloroplasts in the palisade mesophyll arrange themselves?
According to light intensity to get maximum absorbance of sunlight
Structure and function of spongy mesophyll
-Loosely packed cells with air spaces between them for counter current flow of gas exchange of co2 into cells from air spaces and o2 out into air spaces
-Moist cells for gas exchange
What makes the stomata open and close?
The guard cells around it
How do the stomata open/ close?
In light/ sufficient am. of h2o:
-Chloroplasts in guard cells make ATP via photosynthesis
-ATP used in active transport of K+ into guard cells
-Causes starch to convert into malate ions, which decreases water pot.
-H2O enters via osmosis
-Guard cell expands
-Ends of guard cells are thicker then the centre, causing a curve and stomatal pore opening
In dark/ insufficient am. of h2o:
-K+ ions are released from guard cells
Def of hydrophyte and example
Plant that lives in an environment where h2o isn’t limited e.g. water lily, where leaves on water and root in water
Structure and features of a general hydrophyte?
-Only stomata on upper epidermis as no possible gas exchange underwater
-No/little waxy cuticle as not worried about h2o loss
-Air spaces for buoyancy
-No hairs, rolled leaves or sclerenchyma fibres
Def of xerophyte and example?
Plants that has evolved where h2o is scarce e.g. cactus and marram grass
Structure and adaptations of a xerophyte
-Waxy cuticle to reduce h2o loss
-Many stomata on upper epidermis
In marram grass:
-Stiff interlocking hair to trap h2o vapour
-Large thin-walled epidermal cells that are in rolled leaves
-Stiff with sclerenchyma fibres for structure
-Sunken stomata
These are to create a damp environment to maintain water pot. grad
Def and example of a mesophyte?
Plant that has evolved in conditions of adequate h2o supple
How do mesophytes survive winter?
Shedding of leaves, surviving underground or as dormant seeds
Draw and label the structure of a dicotyledon root
Epidermis, cortex, endodermis ( with Casparian strip) , pericycle, cambium, phloem, xylem
Structure of cortex
Made up of waxy suberin
Position and structure of endodermis in root
Layer of cells around pericycle where there is vascular tissue
Has Casparian strip
Difference in arrangement of vascular tissue in stem vs root
Stem- Around the edge of the stem
Root- Middle
How do root hairs help with absorption of h2o?
Provide large SA and are freely permeable
Describe the apoplast pathway in plants
-Soil solution (with h2o) soaks into cellulous fibres in epidermal cells an travels across the root through the cell walls (most h2o taken up like this)
Location, function of Casparian strip
Around cells of endodermis made up of suberin
Prevent h2o + mineral ions from seeping into cells (waterproofing)
How does the Casparian strip block the apoplast pathway
Causes the h2o and minerals ions to seep into the cytoplasm (into the symplast route) through the plasma membrane from the cell walls. Mineral ions use protein carriers and A.T to enter
