Leaves and Epidermis Flashcards
most dicot mature leaves have: (4)
petiole
flattened blade (lamina)
network of vascular bundles
stipules at base of petiole
vascular tissue arranged in veins, two general patterns
- parallel veins (monocots and gymnosperms)
- reticulate veins (dicots and ferns)
leaf attachment to stems
internode - space between leaf attachment to points
leaves typically attached to stems at nodes with petioles
stipules - paired, leaf-like appendages at base of leaf
phyllotaxy
arrangement of leaves on stem
- alternate: one leaf per node
- opposite: two leaves per node
- whorled: three or more leaves per node
abscission meaning and process
- deciduous plants drop (abscise) leaves seasonally
- abscission is the process by which leaves are shed, occurs from changes in abscission zone near base of petiole
- protective layers of cells coated and impregnated with suberin, to seal off leaf scar
- separation layer of pectins in middle lamella are broken down by enzymes, at petiole and stem border
internal structure of leaves (3)
epidermal tissue - protection and gas exchange
mesophyll tissue (ground tissue) - photosynthesis
vascular tissue - form veins to transport organic molecules, water, minerals between leaves and rest of plant
leaf epidermis
single layer of cells covering entire leaf surface
- devoid of chloroplasts
- coated with cuticle and surface waxes provide protection from water loss, light irradiation, and pathogen attack
- surface waxes also serve as semi-permeable barrier and regular gas exchange and water evaporation
- trichome hairs control moisture loss and predation
- waste materials may accumulate in epidermal cells
leaf epidermis: trichomes
trichome “hairs” - uni/multicellular outgrowths of epidermis
primary function: defence, esp insects
- can be simple physical barriers and deterrents to insect movement OR can be glands secreting essential oils
purpose of essential oils
prevent predation (taste) and act as insect repellent and antimicrobials
stomata
- regulates gas exchange between leaf interior and atmosphere
- lower epidermis has thinner layer of cutin and is perforated by numerous stomata
- more sophisticated than lenticels, can open and close stoma openings with turgor pressure of guard cells
2 types of mesophyll (internal structure) in dicot leaves
palisade mesophyll - elongated cells usually located immediately below upper epidermis (tightly packed)
spongy mesophyll - cell located below this layer and loosely packed and have air spaces to allow CO2 diffusion
both photosynthesize, have chloroplasts
monocot leaf internal structure
- don’t have differentiated palisade and spongy layers, all mesophyll is same
- often have bulliform cells flanking the central vein
bulliform cells
partly collapse under dry conditions, causing leaf to fold and reduce transpiration
specialized leaves: storage
succulent leaves are modified for water storage
- have parenchyma cells with larger vacuoles for water storage
- often found in desert (arid) plants
- leaves appear swollen and have shiny appearance due to thick, waxy cuticle
specialized leaves: spines
modified leave that reduce leaf surface and water loss, while also protecting from herbivory
