Parts of the Plant: Leaves

THE FOOD FACTORY OF THE PLANT

Functions of Leaves

• Leaves primarily produce all food used by the plant or stored for later use by plants and animals.

Types of Leaves• There are 2 types of leaves:• Simple: made up of 1 main part

• Compound: made up of 2 or more parts

Leaves as an Identification Characteristic:

• Leaves vary greatly from plant to plant. Look at and compare different plant leaves by their:

• shapes, margins, size, arrangement on the stem, and leaf scars.

External Leaf Structure(Parts of a leaf)

● Blade – main body of the leaf; large, usually flat part of the leaf

● Tip – top of the leaf blade● Margin –leaf edge; differ greatly● Midrib – Large, central vein; is vascular

tissue, moves moisture and minerals● Veins – smaller than midrib, extend out

into the leaf● Base – the bottom of the leaf blade● Petiole – leaf stem, attaches to the stem

of a plant

External Leaf Structure

Internal Leaf Structure

Internal Leaf Structure● Inside, leaves have specialized cells that

perform very important tasks:

● The skin of the leaf called the epidermis is a single layer of cells. Its function is to protect the leaf from loss of too much moisture.

● There are special cells in the leaf skin called guard cells.

Internal Leaf Structure● Guard cells open and close a small space

or pore on the underside of the leaf called stoma to allow the leaf to breathe and transpire, (give off moisture and exchange gases such as carbon dioxide and oxygen.

● In the center of the leaf are 2 kinds of food-making cells:

● Palisades cells● Spongy cells

Internal Leaf Structure

Floating inside both of these cells are many tiny green bodies known as choroplasts.

Each chloroplast contains many molecules of the green pigment chlorophyll.

Internal Leaf Structure• Vascular Tissue – specialized tissue that

transport of materials in and out of the leaf.

• Phloem [flow-em]- moves manufactured out of the leaf.

• Xylem [zi-lim] – moves moisture and minerals into the leaf.

Internal Leaf Structure

• Covering both the upper and lower epidermis is a waxy layer that protects the leaf from moisture loss.

Processes Occuring in the Leaf

● Several processes occur in the leaf:● Photosynthesis● Transpiration● Respiration

Photosynthesis

Autotrophs: Producers- make sugars themselves.(Green plants, algae, some bacteria)

Autotrophs trap energy from sunlight and use this trapped energy to build carbohydrates in the process called

● Photosynthesis – translated from greek:

● Photos = light● Syntithenai = to put together

● Basically: putting things together with light.

● Photosynthesis puts together sugar molecules (glucose) using energy from light

Light: the most important ingredient of photosynthesis.

White light consists of a mixture of all the colors from red to violet.

We see certain colors because they are being reflected by the object viewed.

● All other colors are being absorbed into the object.

● Most plants are green because they contain chlorophyll.

● Chlorophyll reflects green and some yellow while absorbing energy of the other colors of sunlight.

● This is the energy stored in the carbohydrates produced by photosynthesis.

● Most plants use the colors blue and red most effeciently.

● They are found at opposite ends of the color spectrum.

● Blue is most beneficial to plants.

Photosynthesis● Photosynthesis begins as water enters

the food-making cells containing chloroplast from tiny veins in the blade.

● Air space between the cells are filled with carbon-dioxide and other gases.

● Light strikes the chloroplasts.

Photosynthesis● Photosynthesis is the process by which

carbon dioxide and water in the presence of light are converted to sugar and oxygen.

● Light Energy● 6 CO2 + 6 H2O = C6H12O6 + 6 O2● Chlorophyll

Photosynthesis● The energy absorbed from the light

split's the water molecules into molecules of hydrogen and oxygen.

● The hydrogen then combines with carbon dioxide, which results in a simple sugar.

● Oxygen left over from this process is released into the air through the stoma in the leaf.

Transpiration ● occurs as the sun warms the water

inside the blade.● The warming changes much of the water

into vapor.● This gas can then escape through the

stomata.

Transpiration ● Transpiration helps cool the inside of the

leaf because the escaping vapor has absorbed heat.

● Simply, transpiration is the plant giving off moisture and an exchange of gas.

Transpiration ● Transpiration also helps keep water

flowing up the stem from the roots.● Water forms a continuous column as it

flows up the roots, through the stem, and into the leaves.

● Increases turgid pressure in the plant.● As water molecules are lost through

transpiration, the entire column of water is pulled upward.

Transpiration

Respiration ● In respiration plants consume oxygen

and give off carbon dioxide the same as animals.

● Roots, stems and leaves all use (breathe in) oxygen as they grow and give off (exhale) carbon dioxide.

● This happens all the time, but more so at night than during the day.

Respiration ● At night photosynthesis cannot occur.● The guard cells lose water. This causes

the guard cells to become limp, closing the stomata.

● With the stoma closed, CO2 does not enter the leaf, and H2O does leave.

● Since photosynthesis does not occur at night, there is no need for CO2.