Leaves: Morphology, Anatomy, Types & Modification

Definition Of Leaves

Leaves can be defined as the primary organs for photosynthesis in most plants and are mostly structured and flat thin and green designed to capture light and the exchange of gases

Leaves are used the carry out the process of photosynthesis, in which plants execute the conversion of energy, which is in light form into chemical energy, which provides the much-needed nutrient that encourages growth and development.

Morphology Of Leaves

Leaf morphology can be discussed as the study of their outer structure, and is quite a variable and dependent variable and is dependent on their species within the various plant species.

External Structure

Externally, the leaves comprise a host of structures that exert influence on the aesthetic and physiological features of the leaf.

Blade (Lamina)

• This is the flat and usually the most broad part of the leaf.

• This would be the major location for photosynthesis.

• Contains the veins which are for transporting nutrients and water.

Petiole

• This is the stem that connects the leaf blade to the stem.

• It supports the leaf blade.

• Transports nutrients and water between the blade and the stem.

Stipules

• These are small leaf-like appendages found at the base of the petiole.

• May protect young leaves or the bud.

• Will abscise as the leaf matures.

Base

The part of the leaf where it connects to the stem.

• sheathing

• clasping

• Many shapes (eg) Rounded, heart-shape

Venation Of Leaves

Describes the pattern of veins in leaves.

Parallel

• Veins parallel with each other.

• Common in monocots (eg) grasses.

Reticulate

• Veins form a net-like structure.

• Common in dicots.

• Connected veins enhance efficient nutrient and water passage.

Leaf Margins

The margins describe the leaf blade's edges.

Entire

• Smooth and unbroken edges.

• Occurs in many simple leaves.

Serrate

• A pointed appearance.

• They point towards the leaf tip.

• Occurs in leaves such as rose and elm.

Lobed

• Indented appearance, forming lobes.

• Occurs in leaves such as maple and oak.

Leaf Shapes

Leaf shape can vary widely, and the shape is essential to its identification.

Ovate

• Egg-shaped and broad at the base.

• Occurs in many fruit trees.

Lanceolate

• Lance-shaped–longer than wide and tapering to a smooth, elliptical curve.

• E.g. Camellia, guava.

Anatomy Of leaves

• The anatomy of the leaf is essential in the roles of the leaves.

• The tissues of the leaves were placed into layers each serving different roles.

Epidermis

• A single layer of cells that comprises the epidermis layer of the leaf.

• It is covered with a waxy cuticle to minimise water loss.

• It has stomata that permit the exchange of gases.

Mesophyll

• Palisade mesophyll: closely packed cells that are abundant in chloroplasts and photosynthesising cells.

• Spongy mesophyll cells: loosely packed cells that are airy to enable easy gaseous exchange.

Vascular Bundles

• Xylem: conducts water and minerals to the leaves from the roots.

• Phloem: transports sugars and other nutrients to the rest of the plants from the leaves.

Stomata And Gaseous Exchange

Stomata are small minute openings on leaf surfaces that facilitate the easy passage of gases during the process of gaseous exchange.

Anatomy Of Stomata

• They are around two guard cells surrounding a.

• Occurs mainly in the lower epidermis.

Function Of Stomata

• It allows gas exchange, i.e., CO2 in and O2 out.

• It reduces the loss of water called transpiration.

Leaf Adaptations For Photosynthesis

Leaves have several adaptations for promoting the photosynthesis rate.

Chloroplasts And Chlorophyll

• Chlorophyll is found in the chloroplast, which captures light.

• Chlorophyll captures light energy to carry out photosynthesis.

Types Of Cells

• Chlorenchyma is differentiated into palisade and spongy mesophyll.

• Cells and tissues are arranged in such a way to capture maximum light energy.

Types Of Leaves

Leaves are classified as:

Simple Leaves

Simple leaves have without division of the lamina more than one blade.

Compound Leaves

Compound leaves have a division comprising one leaflet.

Pinnate Compound Leaves

• Leaflets are arranged along both sides of a central axis (rachis).

• Examples: neem, rose.

Palmate Compound Leaves

• Leaflets radiating from a single point at the end of the petiole.

• Examples: maple, horse chestnut.

Special Types Of Leaves

Some special types of leaves are:

Needles

• Present in conifers.

• Long, thin and pointed.

• Modified to water conversance and cold vagaries.

Scale Leaves

• Small, and overlapping; common in woody plants.

• Protect buds and prevent water loss.

Spines And Thorns

• Modified as a hard, sharp leaf to defend against herbivores.

• Examples are cacti and hawthorn.

Leaf Modifications

Leaves can be modified towards adaptations to suit the environment.

Leaf Modifications For Storage

• Some leaves store water and nutrients

Succulent Leaves

• Thick and fleshy to store the water.

• Common in arid environments.

• Examples are aloe and agave.

Leaf Modifications For Defense

Certain leaves are modified to protect the plant.

Spines And Thorns

• Sharp and pointed to deter herbivores

• Examples: cacti, acacia

Leaf Modifications For Climbing

Some leaves help the plants in climbing and provide support, too

Tendrils

• Example: peas, grapes

• Thin, coiling structures that help the plant in climbing.

Leaf Modifications For Reproduction

• Some leaves help the plant in reproduction.

• Reproductive leaves (e.g. Bryophyllum).

• Leaves produce plantlets that can grow in a new plant.

Other Modifications

• Leaves can also be modified for the capture and digestive of insects

• Insectivorous Plants (e.g. Pitcher Plants, Venus Flytrap)

• Obtain nutrients from prey in nutrient-poor environments.

Functions Of Leaves

Leaves serve some of the essential functions of the plant.

Photosynthesis

• Trapping light energy to make food (glucose).

• Involves chloroplasts and chlorophyll.

Transpiration

• Loss of water vapour from stomata.

• Assist in the transport of nutrients and cooling the plant.

Storage

• Some leaves store water and nutrients (e.g. succulent leaves).

Defence

• Modified leaves (spines, thorns) protect the plant against herbivores.

Economic Importance Of Leaves

Leaves are of economic importance.

Food and Spices

• Many leaves are consumed as veggies (e.g. chard,.

Flavourings

• Examples like bay leaves and mint

Medicines

• They are also used as leaves for traditional to modern medicines such as neem and eucalyptus.

Industrial Use

• In making tea, essential oils, and dyes.

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