Leaf Structure and Functions

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Questions and Answers

What is the defining characteristic of a sessile leaf?

It has a thick cuticle.
It has a long petiole.
The blade attaches directly to the stem. (correct)
It is highly variable in shape.

The epidermis of a leaf does not have any stomata.

False (B)

What tissue covers the upper and lower surfaces of a leaf?

Epidermis

A leaf typically consists of epidermis, __________, and other tissues.

mesophyll

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Match the following leaf components with their functions:

Epidermis = Covers the upper and lower surfaces Mesophyll = Site of photosynthesis Stomata = Regulates gas exchange Hairs = Reduces water loss

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Which type of trichome is characterized as having a body that ends in two branches?

Simple-branched (D)

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All covering trichomes are unicellular in nature.

False (B)

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What is a peltate trichome?

A very short stalk surrounded by a plate-like structure formed of closely joined cells.

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The ____________ trichome consists of radiating unicellular hairs.

Stellate

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Match the types of covering trichomes with their descriptions:

Unicellular = Consisting of a single cell Multicellular = Formed of more than one cell Branched = Includes both simple-branched and stellate Unbranched = Includes uniseriate and biseriate types

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Flashcards

Branched Unicellular Hairs

Hairs on plants that are single-celled and branched. Found commonly in plants belonging to the Cruciferae family.

Unbranched Unicellular Hairs

Hairs on plants that are single-celled but not branched. Found commonly in plants belonging to the Senna genus.

Multicellular Hairs

Hairs that are formed of multiple cells and can either be branched or unbranched. These are more complex than unicellular hairs.

Uniseriate Multicellular Hairs

Multicellular hairs that consist of a single row of cells.

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Biseriate Multicellular Hairs

Multicellular hairs that consist of two rows of cells, each row containing one or more cells.

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Sessile Leaf

A leaf blade that directly attaches to the stem, without a stalk (petiole).

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Epidermis (Leaf)

The outermost layer of a leaf, covering the upper and lower surfaces. It protects the leaf and controls gas exchange.

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Stomata

Tiny openings on the lower epidermis of a leaf, allowing for gas exchange (CO2 in, O2 out).

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Mesophyll

The inner layer of a leaf, containing cells responsible for photosynthesis. This is where the 'food' is made.

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Lamina (Leaf)

The flat, expanded part of a leaf, where photosynthesis mainly occurs.

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Study Notes

Leaf Structure

Leaves begin as meristematic cells. After formation, these cells stop dividing and mature.
Leaf growth occurs through cell enlargement, not cell division.
A complete leaf has three main parts: leaf base, petiole (leaf stalk), and lamina (leaf blade).

Petiole (Leaf Stalk)

Connects the leaf blade to the stem.
Carries materials to and from the blade.
Helps position the leaf for optimal light absorption.

Lamina (Leaf Blade)

The broad, flat part of the leaf.
Typically has a midrib and lateral veins.
Contains tissues for photosynthesis and transport.
Different leaf types display various forms, sizes, and structures.

Leaf Blade Structure

Epidermis: The outer protective layer.
Mesophyll: The photosynthetic tissue (contains layers, e.g., palisade and spongy).
Vascular tissue: Veins for transporting water and nutrients.

Hairs (Trichomes)

Extensions of epidermal cells, coming in diverse forms (e.g., branched or unbranched).
Protect leaves from microbial organisms and insects.
Some secrete oils or substances (glandular).
Some are simply structural coverings (non-glandular).

Leaf Types

Petiolate: A petiole connects the leaf blade to the stem.
Sessile: The leaf blade attaches directly to the stem, without a petiole.
Simple: A single undivided blade.
Compound: Divided into leaflets, with each leaflet having its own stalk.

Stomata

Small pores on the leaf epidermis, typically found on the underside.
Regulate gas exchange (CO2 in, O2 out).
Are guarded by guard cells.
Various types of stomata exist with different subsidiary cell arrangements.

Mesophyll

Contains palisade layer and spongy layer.
Palisade layer responsible for photosynthesis.
Spongy layer containing air spaces for gas exchange.
Arrangement of mesophyll differs in various leaf types (isobilateral and dorsiventral).

Leaf Analysis and Structure (by image provided)

Many different types of leaves and plant species are shown in the images
Constituents, origins, chemical tests, and surfaces preparations are also listed.