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Leaves are the powerhouse of plants. In most plants, leaves are the major site of food production for the plant. Structures within a leaf convert the energy in sunlight into chemical energy that the plant can use as food. Chlorophyll is the molecule in leaves that uses the energy in sunlight to turn water (H2O) and carbon dioxide gas (CO2) into sugar and oxygen gas (O2). This process is called photosynthesis.
A leaf is made of many layers that are sandwiched between two layers of tough skin cells (called the epidermis). The epidermis also secretes a waxy substance called the cuticle. These layers protect the leaf from insects, bacteria, and other pests. Among the epidermal cells are pairs of sausage-shaped guard cells. Each pair of guard cells forms a pore (called stoma; the plural is stomata). Gases enter and exit the leaf through the stomata.
Most food production takes place in elongated cells called palisade mesophyll. Gas exchange occurs in the air spaces between the oddly-shaped cells of the spongy mesophyll.
Veins support the leaf and are filled with vessels that transport food, water, and minerals to the plant.
Leaves come in many sizes and shapes; they are often used to help identify plants. Some leaves are flat and wide; others are spiky and thin. Plant spines (like cactus spines) are actually modified leaves.
air space - intercellular gaps within the spongy mesophyll. These gaps are filled with gas that the plant uses (carbon dioxide - CO2 ) and gases that the plant is expelling (oxygen - O2, and water vapor).
axil - the angle between the upper side of the stem and a leaf or petiole.
chlorophyll - a molecule in leaves that can use light energy from sunlight to turn water and carbon dioxide gas into sugar and oxygen (this process is called photosynthesis). Chlorophyll is magnesium-based and is green.
compound leaf - a leaf that is divided into many separate parts (leaflets) along a midrib (the rachis). All the leaflets of a compound leaf are oriented in the same plane.
crenate - having rounded teeth.
cuticle - the waxy, water-repelling layer on the outer surface of a leaf that helps keep it from dying out (and protect it from invading bacteria, insects, and fungi). The cuticle is secreted by the epidermis (including the guard cells) and is often thinner on the underside of leaves. The cuticle is generally thicker on plants that live in dry environments.
entire - having a smooth edge with neither teeth nor lobes.
epidermis - the protective, outler layer of cells on the surface of a leaf. The guard cells (and stoma) are part of the epidermis. The surface of many leaves is coated with a waxy cuticle which is secreted by the epidermis.
guard cell - one of a pair of sausage-shaped cells that surround a stoma (a pore in a leaf). Guard cells change shape (as light and humidity change), causing the stoma to open and close.
lamina - the blade of a leaf.
leaf apex - the outer end of a leaf; the end that is opposite the petiole.
lobed - divided into rounded or pointed sections and the incisions (cuts) go less than halfway to the midrib.
mesophyll - the chlorophyll-containing leaf tissue located between the upper and lower epidermis. These cells convert sunlight into usable chemical energy for the plant.
midrib - the central rib of a leaf - it is usually continuous with the petiole.
palisade mesophyll - a layer of elongated cells located under the upper epidermis. These cells contain most of the leaf's chlorophyll, converting sunlight into usable chemical energy for the plant.
parted (or cleft) - the margins between the irregular teeth go more than halfway to the midrib.
petiole - a leaf stalk; it attaches the leaf to the plant.
photosynthesis - the process in which plants convert sunlight, water, and carbon dioxide into food energy (sugars and starches), oxygen and water. Chlorophyll or closely-related pigments (substances that color the plant) are essential to the photosynthetic process.
pinnate - a compound leaf that is made up of many small leaflets arranged in pairs on either side of a long central midrib (the rachis). There is often a single terminal leaflet at the end of the midrib.
serrate (or toothed) - having small, pointy teeth that point toward the tip of the leaf.
spongy mesophyll - the layer below the palisade mesophyll; it has irregularly-shaped cells with many air spaces between the cells. These cells contain some chlorophyll. The spongy mesophyll cells communicate with the guard cells (stomata), causing them to open or close, depending on the concentration of gases.
stem - (also called the axis) the main support of the plant.
stipule - the small, paired appendages (sometimes leaf-life) that are found at the base of the petiole of leaves of many flowering plants.
stoma - (plural stomata) a pore (or opening) in a plant's leaves where water vapor and other gases leave and enter the plant. Stomata are formed by two guard cells that regulate the opening and closing of the pore. Generally, many more stomata are on the bottom of a leaf than on the top.
vein (vascular bundle) - Veins provide support for the leaf and transport both water and minerals (via xylem) and food energy (via phloem) through the leaf and on to the rest of the plant.
Leaf Shape Book
A short book about leaves to print, with pages on leaf anatomy, a maple maze, match the leaves, leaf facts, and leaf questions.
Leaf Color Book
A short book about colors to print for early readers, with pages for the student to color and write a short phrase.
How Many Leaves?
Printable Activity Book
A short, printable book about the numbers from 1 to 10 for early readers, with pages for the student to cut out, count, color and copy a short phrase.
Printable Read and Answer Worksheet
A printable worksheet on leaves, with a short text, a picture to label, diagrams to look at, and questions to answer. Or go to the answers.
Leaf External Anatomy
Label Me! Printout
Read the definitions then label the leaf.
Label Me! Printout
Read the definitions then label the leaf margins (including entire, serrate, crenate, lobed, and parted).
Leaf Cross Section Diagram
Label Me! Printout
Read the definitions then label the cross section of the leaf.
Leaf Structure and Function:
Printable Read-and-Answer Worksheet
A printable worksheet on leaves, with a short text, a cross section of a leaf to label, and questions to answer. Or go to the answers.
Label Me! Printout
Label the flowering plant anatomy diagram using the glossary of plant terms.
Click on an underlined word for more information on that subject.
If the plant term you are looking for is not in the dictionary, please e-mail us.
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