PLS 144 Leafs

Cuticle

Waxy coating reducing water loss.

Epidermis

Protective upper/lower cell layers, often with cuticle.

Trichomes (leaf hairs)

Hair-like outgrowths from the epidermis; reduce water loss, reflect radiation, deter herbivores.

Pubescence

General term for hairiness of leaves; adaptation to heat and water stress.

Stomata

Pores in epidermis allowing gas exchange.

Guard cells

Cells controlling stomatal opening and closing.

Mesophyll

Internal leaf tissue specialized for photosynthesis, includes palisade and spongy layers.

Palisade mesophyll

Columnar cells below upper epidermis, rich in chloroplasts; main site of photosynthesis.

Spongy mesophyll

Loosely arranged cells with air spaces aiding gas exchange.

Veins

Vascular bundles containing xylem and phloem.

Veins (vascular bundles)

Contain xylem and phloem for water, nutrient, and sugar transport.

Bundle sheath cells

Cells surrounding vascular bundles, important in C4 photosynthesis.

Chloroplast

Organelle where photosynthesis occurs.

Grana

Stacks of thylakoids.

Thylakoids

Membrane sacs where light reactions occur.

Stroma

Fluid inside the chloroplast where Calvin cycle occurs.

Bulliform cells

Large epidermal cells that facilitate leaf rolling under drought stress.

Leaf blade (lamina)

Flat photosynthetic surface of the leaf.

Petiole

Stalk connecting leaf blade to stem.

Leaf margin

Edge of the leaf blade; may be entire, serrated, or lobed.

Entire margin

Smooth-edged leaf.

Lobed margin

Deeply indented edge (e.g., oak, maple).

Serrated margin

Saw-toothed edge.

Sunken stomata

Stomata recessed below epidermis, reducing transpiration.

Glaucous surface

Leaf surface covered with a whitish waxy bloom, reducing radiation load.

Waxy coating

Hydrophobic surface preventing water loss and pathogen entry.

Scale leaves

Small, scale-like leaves (e.g., cedars, junipers).

Simple leaf

Single blade (e.g., oak, maple).

Compound leaf

Blade divided into leaflets (e.g., ash, walnut).

Pinnately compound

Leaflets arranged along a central axis (rachis).

Pinnately compound leaf

Leaflets arranged along both sides of a common axis.

Palmately compound

Leaflets radiating from one point (e.g., horse chestnut).

Palmately compound leaf

Leaflets radiating from a single point (like fingers from a hand).

Oblong leaf

Longer than wide with nearly parallel sides.

Cordate leaf

Heart-shaped leaf.

Ovate leaf

Egg-shaped, broader at base.

Linear leaf

Very narrow and elongated.

Lanceolate leaf

Long, narrow, tapering to tip.

Lobed leaf

Leaf with deep indentations but not divided into leaflets.

Needle leaf

Narrow, needle-like leaves typical of conifers.

Needle leaves

Thin, needle-like leaves (e.g., pines).

Drip tip

Extended pointed tip aiding water runoff in tropical rainforests.

Succulent leaves

Thickened leaves for water storage.

Deciduous leaves

Leaves shed seasonally.

Evergreen leaves

Leaves persisting multiple years.

Photosynthesis equation

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂.

Overall photosynthesis

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂.

Calvin cycle

In stroma: uses ATP & NADPH to fix CO₂ into sugars.

Light reactions

In thylakoids: convert light → ATP & NADPH, release O₂.

Photorespiration

Rubisco reaction with O₂ reducing photosynthetic efficiency.

Respiration

Breakdown of sugars to release ATP and CO₂.

Diffusion

Passive movement of CO₂ and O₂ through stomata/air spaces.

Osmosis

Water movement across membranes due to solute gradients.

Transpiration

Loss of water vapor through stomata.

Stomatal conductance

Measure of gas exchange capacity through stomata.

Leaf cooling

Temperature regulation via transpiration and convection.

Water Use Efficiency (WUE)

Ratio of photosynthesis (carbon gain) to transpiration (water loss).

Opening (stomata)

K⁺ enters guard cells → water uptake → swelling opens pore.

Closing (stomata)

K⁺ exits guard cells → water leaves → cells shrink, pore closes.

Chlorophyll

Green pigment absorbing red/blue light for photosynthesis.

Carotenoids

Accessory pigments that absorb excess light and provide photoprotection.

Anthocyanins

Pigments that provide red/blue coloration and photoprotection.

Accessory pigments

Carotenoids, xanthophylls that expand light absorption and protect chlorophyll.

PAR

400–700 nm light usable in photosynthesis.

PAR (Photosynthetically Active Radiation)

Light in the 400–700 nm range used for photosynthesis.

Action spectrum

Wavelengths most effective in photosynthesis.

Absorption spectrum

Wavelengths absorbed by pigments.

Photoinhibition

Reduction of photosynthetic capacity due to excess light.

Reflection

Portion of light (especially green) reflected by leaves.

Transmission

Light passing through leaves.

Photons

Packets of light energy; shorter wavelengths = higher energy.

Energy balance equation

Rn = H + LE + G (net radiation = sensible heat + latent heat + ground heat).

Rn (Net radiation)

Absorbed – emitted energy balance.

H (Sensible heat flux)

Heat transfer by conduction/convection.

LE (Latent heat flux)

Energy loss through evaporation/transpiration.

G (Ground heat flux)

Heat stored in or released from leaf/ground.

Light compensation point

Light intensity at which photosynthetic CO₂ uptake equals respiration CO₂ release.

Light saturation point

Light intensity at which photosynthesis no longer increases with additional light.

Parallel venation

Veins run parallel (typical of monocots).

Reticulate venation

Branching vein network (typical of dicots).