PL_LESSON 3: LEAVES

LEAVES

Elicits image of foliage leaves

Large, flat, green structure that photosynthesizes

LEAVES

Protection

Support

Storage

Nitrogen procurement

LEAVES

carry out photosynthesis, which in turn produces glucose and oxygen.

primordia in terminal or lateral buds

Leaves develop from the

Concentrate solar energy for photosynthesis.

Collect carbon-dioxide.

Gas exchange in stomata.

FUNCTION OF LEAVES

BLADE OR LAMINA

Flat, light-harvesting portion of the leaf

Ventral / Adaxial (upper): captures sunlight

Dorsal / Abaxial (under): studded with stomata

BLADE OR LAMINA Two sides

MIDRIB

MIDVEIN

TRICHOMES

Provides shade on the upper surface of the leaf.

TRICHOMES

Prevents rapid air movement, and thus slows down water loss from stomata.

TRICHOMES

Makes walking or chewing difficult for insects.

Glandular trichomes

secrete powerful stinging compounds that deter herbivores.

PETIOLE OR STALK

Attaches the blade to the stem

spicules

In many species, this bears two small flaps of tissue at its base called

ABCISSION ZONE

Leaf base

ABCISSION ZONE

Cells are involved in cutting off the leaf as it becomes useless

abscission

After___ , adjacent undamaged cells become corky, forming a protective leaf scar 

abscission

Zone where petiole was attached to the stem

abscission

Without this, leaves might tear off irregularly, leaving it vulnerable to pathogen

Petiolate

Plants with petioles

Petiolate

Prevents shading of other leaves

Petiolate

Having stalks attached to lamina

Petiolate

Allows cooling of leaves

Sessile

Plant without petioles

Sessile

Blade directly attached to stem

Sessile

Helps conserve water

Leaf sheathes

Found on monocots

Leaf sheathes

Leaf base wraps around the stem

veins

The __ of leaves are bundles of vascular tissue

Parallel Venation

Reticulate Venation

LEAF VENATION

Entire (smooth)

Toothed

Lobed

Otherwise modified

The leaf margin may be:

COMPOUND LEAVES

Divided into several parts

rachis

The acting stem __; it is an extension of the petiole.

Palmately compound

leaflets arise from a common point

Pinnately compound

leaflets arise at several locations along an elongate axis (the rachis)

Pinnately compound

attached individually in the rachis

Transpiration

water loss through epidermis

Stomatal crypts

on the lower epidermis are a type of leaf adaptation that enables the plant to survive very dry climates.

Cuticle

waxy covering of the leaf

Epidermis

covers the upper and lower part of leaf

Mesophyll Layer

middle layer of the leaf

Mesophyll Layer

comprised of the palisade and spongy layer

Veins

contains the vascular bundles (xylem and phloem)

Epidermis

protects the inner structures of the leaf

Epidermis

where transpiration, loss of water through evaporation to the atmosphere, occurs

Epidermis

contains the stomata and trichomes

: transparent layer

Palisade Mesophyll

main photosynthetic tissue of plants

: usually one layer thick, somewhat organized

Spongy Mesophyll:

has lots of airspaces, unorganized

: sometimes lacking

Leaflets never bear buds in the axils of their petiolules.

The tip of the rachis never has a terminal bud.

Leaflets are always arranged in two rows, never in a spiral, whorled, or decussate phyllotaxy

three guidelines to distinguish a simple leaf from a pinnately compound leaf.

meristematic

actively dividing

stipules

In dicots, buds are protected by

older

In monocots, __ leaf primordia protect younger primordia

SUCCULENT

Leaves that are thick and fleshy

SUCCULENT

Survive in desert habitats.

SUCCULENT

Reduced surface-tovolume ratios, favoring water conservation.

SUCCULENT

The mesophyll contains very few air spaces.

SUCCULENT

Mesophyll more transparent so photosynthesis may occur deeper in the leaf

SCLEROPHYLLOUS FOLIAGE LEAVES

Have sclerenchyma as a layer below the epidermis and in the bundle sheets.

SCLEROPHYLLS OF CONIFERS

Leaves of conifers are sclerophylls with thick cuticles.

SCLEROPHYLLS OF CONIFERS

They usually contain unpalatable chemicals.

The shapes may be needle-like or flat and scale-like

BUD SCALES

Small modified leaves that form a tight layer around the stem tip.

BUD SCALES

Protect dormant buds in the winter.

SPINES

Modified leaves of axillary buds.

SPINES

Needle sharp projections.

SPINES

They are protective and made primarily of fibers.

SPINES

Lignified walls make them hard and resistant to decay

TENDRILS

Modified leaves whose cells can

Sense contact with objects.

Coil around objects and use them for support.

TENDRILS

Grow indefinitely.

TENDRILS

Do not photosynthesize

REPRODUCTIVE LEAVES

Seedlings can develop on mature leaves (e.g. kataka-taka)

BRACTS

Modified leaves that is usually mistaken for petals by insects, attracts pollinators (e.g. poinsettia and bougainvillea)

PITCHERS AND FLYTRAPS

Carnivorous, usually found in nutrient poor soils (e.g. pitcher plants and venus fly-trap

SUCCULENT LEAVES

Store large amounts of water and other nutrients (e.g. Aloe vera)