Chapter 7 Leaves

leaves

originate as primordia in buds

petiole

stalk; leaves sessile if they don't have this (e.g. monocots)

vascular bundles

network of veins

stipules

at base of petiole

leaves of flowering plants

associated with leaf gaps, have axillary buds at base

simple leaf

single blase

compound leaf

devided into leaflets

pinnately compound leaf

leaflets in pairs along rachis (petiole)

bipinnately compound leaf

leaflets subdivided

palmately compound leaves

all leafletss attached at some point at end of petiole

photosynthesis

green leaves capture light energy; trap and store energy in sugar molecules that are constructed from water and carbon dioxide

stomata

tiny pores on lower surfaces of leaves; allow carbon dioxide to enter and oxygen to diffuse out; water vapor also escapes here

guard cells

control water loss via stomata by opening or closing pores of stomatal apparatus

functions of leaves

waste accumulation and disposal; movement of water absorbed by roots (transpiration, guttation)

transpiration

water evaporates from leaf's surface

guttation

root pressure forces water out hydathodes at tips of leaf veins in some plants

nodes

where leaves attach to stems

internodes

stem regions between nodes

alternate

one leaf per node

opposite

two leaves per node

whorled

three or more leaves at node

venation

arrangement of veins in a leaf or leaflet blade

pinnately veined leaves

main midvein included within enlarged midrib; secondary veins branch out from midvein

palmately veined leaves

several primary veins fan out from base of blade

monocots

primary veins parallel

dicots

primary veins diverge in various ways (netted, reticulate)

three regions of leaves

epidermis, mesophyll, veins

epidermis

single layer of cells coating surface; devoid of chloroplasts, coated with cuticle; protection, accumulatio of wastes, glands; stomata here

mesophyll

most photosynthesis occurs here

palisade mesophyll

compactly stacked, barrel-shaped parenchyma cells, commonly in two rows; contains most of leaf's chloroplasts

spongy mesophyll

loosely arranged parenchyma cells with abundant air spaces

veins

scattered throughout mesophyll; consist of xylem and phloem surrounded by bundle sheath

shade leaves

larger, thinner, fewer well defined mesophyll layers, fewer chloroplasts, fewer hairs

leaves of arid regoins

reduce loss of water by having thick, leathery leaves, fewer stomata or sunken stomata, water retaining leaves or no leaves, dense hairy coverings

leaves of aquatic areas

less xylem and phloem; no differentiated mesophyll; large air spaces

tendrils

modified leaves that curl around rigid objects (climbing plants, support weak stems)

spines

modified leaves that reduce leaf surface and water loss and protect from herbivores (e.g. cacti)

thorns

modified stems arise in axils of leaves of woody plants

succulent leaves

water storage, parenchyma with large vacuoles, e.g. desert plants

fleshy leaves

store carbohydrates (onions, lillies)

flower-pot leaves

develop into urn-like pouches; home to ant colonies

window leaves

succulent desert plants of Africa; buried in ground except for exposed end that has transparent, thick epidermis and transparent water storage cells underneath; allows light into leaf while buried leaves keep plant from drying out

reproductive leaves

walking fern - new plants at leaf tips

air plant- tiny plantlets along leaf margins

floral leaves

aka bracts, at bases of flowers or flower stalks (poinsetta, Clary's Sage)

insect-trapping leaves

grow in swampy areas/bogs with N-deficient soil

bladderworts

submerged or floating in shallow water; tiny bladders on leaves have trap doors that trap insects inside

autumnal changes in leaf color

chloroplasts contian chlorophyll (green) and carotenoids (yellows) and anthocyanins (red, blue); chlorophyll breaks down in fall and other colors revealed

abscission

leaves are shed; result of changes in abscission zone near base of petiole; protective layer and separation layer

human relevance

landscaping, food, dyes, perfumes, ropes, twine, drugs, beverage, insecticides, waxes, aesthetics

trichomes

Tiny hairs that give leaf a fuzzy appearance, help reduce the evaporation of water from the plant.