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.