Ch. 25, Part Two: Leaves

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