Tags & Description
leaf functions
-main photosynthetic organ of plants -transpiration
transpiration definition
movement of H2O (water) through plant and evaporation via the leaves
leaf morphology
-more variable in size, shape, arrangement, and other factors than the roots and stems -variations relfect evolutionary adaptations to different environments, herbivores, and photosynthetic needs
maxing leaf surface area pros
catches more light -> more photosynthesis / food production
maxing leaf surface area cons
loses water faster
blade
flat part of the leaf
blade alternate name
lamina
petiole
stalk of the leaf that attaches to the stem
stipule
at base of petiole, appendages
sessile
no petiole, has a sheath instead attached directly to the stem
sheath
"coat" from the blade that wraps around the stem
leaf arrangement definition
leaf arrangements on a stem in an ordered and predictable pattern
leaf arrangement function
maxes sun exposure
three basic patterns of leaf arrangement
alternate opposite whorled
alternate leaf arrangement
1 leaf per node
alternate leaf arrangement types
spiral distichous
spiral arrangement
leaves spiral/helixes around the plant, no columns
distichous arrangement
leaves arranged in two vertial columns on opposite sides of the stem (think 180 degrees)
opposite leaf arrangement
2 leaves per node
opposite leaf arrangement type
decussate
decussate arrangement
adjacent leaves pairs above and below are oriented 90 degrees differently
whorled leaf arrangement
3 or more leaves per node
leaf types
simple compound
simple leaves
have one leaf blade per petiole
compound leaves
have more than one leaf blade per petiole (leaflets)
compound leaf types
palmately compound pinnately compound bipinnately compound
palmate compound leaf
think of a hand, leaflets originate from one center
pinnate compound leaf
has a center rachis and leaflets come off of it
rachis
axis of a compound leaf or compound inflorescence
petiolule
the stalk of a leaflet
How can you tell if a leaf is a compound leaf and not multiple simple leaves?
look for axillary bud, that's the connection of petiole to the stem AND leaves are on the same plane, and not going out in different directions
bipinnate compound leaves
leaves compound twice (once on the rachis, and then another time on the petiolule)
advantages of compound leaves
advantage in windy environments (less continuous surface area to catch wind and break or become damaged) reduces transpiration
venation definition
the arrangement of veins in a leaf
venation types
pinnate parallel palmate
pinnate venation
main central vein, with veins coming off of that
pinnate venation found in...
eudicots
parallel venation
parallel veins that don't intersect
parallel venation found in...
grasses, monocots
palmate venation
palm-like vein spread from a center point
palmate venation found in...
eudicots
leaf margins
edges of the leaf
leaf margin types
smooth/entire serrate/toothed
smooth/entire margin
rounded leaf margin
serrate/toothed margin
leaf margin with "teeth"
Why are the shapes and sizes of leaves generally more variable than for stems and roots?
environmental adaptation, herbivore deterrent, photosynthesis
leaf origin
leaf primordia
leaf primordia
form near apical meristems forms leaves
leaf primordia composition
protoderm procambium ground meristem
Mature leaves usually lack ___________, which means, when they reach maturity, ___________.
primary meristems, that is their final size
leaf major tissues
leaf epidermis mesophyll vascular tissue
leaf epidermis functions
protects against bacteria/fungi water retention gas exchange
leaf epidermis origin
protoderm
leaf epidermis composition
single cell layer cuticle trichomes guard cells w/ stomata
trichome functions
sunlight protection (UV) keeping water off of plant herbivory protection excessive heat protection (insulation)
True or false: Cuticle does NOT affect gas exchange in a leaf.
True; the stomata are responsible for gas exchange
True or false: In most plants, water enters leaves via stomata
False; water can leave through stomata, however.
mesophyll
ground tissue of a leaf
mesophyll compostion
parenchyma cells with chloroplasts
mesophyll types
palisade parenchyma/mesophyll spongy parenchyma/mesophyll
palisade parenchyma
columnar, tightly packed cells main source of photosynthesis in leaves (lots of chloroplasts)
spongy parenchyma
spherical, aeration/holes between cells where gas exchange occurs, needs room for gases to move around
vascular tissue difference in leaves, comparing to stems / roots
in one leaf, vascular tissue can branch out or merge.
vascular tissue alternate name in leaves
leaf veins
vascular tissue general arrangement
layered on top of one another, rather than a bundle like in roots and stems
In different types of plants, vascular tissue arrangement...
can differ based on water availability
mesophytes
plants that require mesic environment
mesic
having or characterized by moderate or a well-balanced supply of moisture
mesophyte example
lilacs (Syringa)
mesophyte unique features
more stomata on bottom of leaf for water retention single layer of lower and upper epidermis cells
hydrophytes
plants needing a large supply of water
hydrophyte example
water lily (Nymphaeaceae)
hydrophyte unique features
sclereid for structural support stoma present on sides where air is accessable large number of intracellular spaces to float on the water (for water lilies) less vascular tissues
xerophytes
plants adapted to arid condition
xerophyte example
oleander (Nerium)
xerophyte unique features
stomatal crypt w/ sunken stoma hides stoma where it's less dry to further water retention sometimes has trichomes in the crypt
grass leaves found in...
C3 and C4 photosynthesis pathways
grass leaf unique features
bulliform cells
bulliform cells
huge cells part of upper epidermis that inflate with water, flattening/closing the leaf from environmental changes
difference in sun exposure leads to...
sun and shade leaves
sun leaves morphology changes
thicker, more palisade, but smaller overall leaf more vascular tissue extensiveness thicker epidermis
sun leaf function
photosynthesis focusing on more sun exposure main photosynthesis source
shade leaf morphology
less palisade parenchyma, but larger overall leaf flimsy larger surface area not as much energy put into them
shade leaf function
photosynthesis focusing on less sun exposure secondary photosynthesis source
leaf abscission definition
process of leaves separating from the stem
abscission layer
enzymes break down middle lamella builds up suberin on the stem side once the leaf breaks off
leaf abscission reason
from an environmental trigger (day length)
leaf abscission features
reusable ions and molecules are returned to stem occurs near base of petiole at abscission zone broken down chloroplasts show other pigments (carotenoids)
leaf modication types
tendrils (either stem or leaf mods) spines (either leaves or stipules) bracts bulb (underground leaves) insectivorous leaves
tendrils
either stem or leaf mods for grappling / supporting grape vines
spines
modded leaves / stipules protection against herbivory cacti
bracts
attracts pollinators poinsettas
bulb
underground leaves storage onions
insectivorous leaves
obtains nitrogen from insects and digest them pitcher plants, sundew, Venus fly trap