Leaves And Leaf Structures Flashcards
Leaves are located where ?
Stem nodes, separated by internodes
Leaf arrangement is based on the number of what
Based on the number of leaves per node
Alternate
1 leaf per node
Opposite
2 leaves per node
Whorled
3 or more leaves per node
Blade
Expanded light collecting surface
Simple
Blade not divided into leaflets
Compound
Blade divided into leaflets
Pinnately compound
Leaflets connected to a rachis
Palmately compound
Leaflets connected to the end of a petiole
Blades will show a characteristics venation patterns like what?
Either netted (pinnately or palmately) or parallel
Petiole
Stem like part connecting blade to node
Petiole is flexible due to what
Collenchyma strands (also brings in CO2)
Stipule
Accessory leaf like structure at base of petiole, may be deciduous or missing entirely
Upper epidermis
Continues with stem surface compactly arranged cells covered by cuticle
Mesophyll
Specialized for photosynthesis, thin walled for rapid diffusion of co2
Lower epidermis
Stomata flanked by photosynthesis guard cells, trichromes for protection from herbivores or reflection of sunlight
Palisade
Elongated cells oriented perpendicular to leaf surface
Spongey
Loosely arranged oblong cells large air spaces for diffusion of gases
Veins
Xylem always above the Phloem, surrounded by layers of endodermis- like bundle sheath
Leaf Abscission
- Formation of abscission zone at petiole
- Cell walls of separation layer are allowed to weaken with no new fibers added
- Siberin is added to walls on the stem side, forming a water repellent protective layer continuous with the bark
- Enzymes then dissolve cell walls of separation layer and the leaf falls leaving a scar
Bud scales
To protect apical meristems and delicate young leaves
Cotyledons
“Seed leaves” to store nutrients for germination, monocots vs dicots
