Plant Structure continued

A leaf is made up of many specialized cells and tissues as illustrated in the image below:

1. Cuticle - The cuticle is a waxy, water resistant covering that protects the leaf from excessive absorption of light and evaporation of water. 2. Upper Epidermis - These cells appear on the top of the leaf and are transparent and colourless. They allow light to pass through to mesophyll cell where most of photosynthesis takes place. The epidermis lack chloroplasts therefore no photosynthesis takes place. 3. Palisade Mesophyll - These cells are arranged close together and contain chloroplasts. These photosynthetic cells form the bulk of plant leaf. 4. Spongy Mesophyll - These cells also contain chloroplast, but not as many as the palisade cells. The spongy mesophyll cells are not as densely packed together. This allows more surface area for gas exchange.

5. Lower Epidermis - These cells appear on the bottom of the leaf and are transparent and colourless. They allow light to pass through to mesophyll cell where most of photosynthesis takes place. The epidermis lack chloroplasts therefore no photosynthesis takes place. 6. Stoma - Stomata (pl.) are small openings located on the underside of the leaf of most plants. These small openings allow for oxygen, carbon dioxide, and water vapour to move into and out of the leaf. 7. Guard Cells - Guard cells are specialized epidermal cells that contain chloroplasts. Guard cells regulate the opening and closing of the stoma. When weather conditions are hot and dry, the guard cells collapse and the stoma closes.

The process that regulates the opening and closing of the stoma involves the movement of ions and water. This animation shows how the shape of the guard cells affects the condition of the stoma.animation Well it would if it worked! Grrrrrr.

8. Xylem - Xylem are specialized structures that transport water and minerals from the roots to the rest of the plant. 9. Phloem - Phloem cells are specialized structures that transport carbohydrates produced in the leaves to all parts of the plant. 10. Vascular Bundle - The veins of the leaf contain both xylem and phloem cells.

Classifying Plants You briefly explored the different types of plants in the diversity unit. In this unit, you will take a closer look at the differences that exist between the species of plants.

Vascular Tissue The transportation of materials within multicellular organisms is vital for survival. Plants require water, minerals, sugars, etc., to circulate throughout its tissues and cells. Some plants lack specialized structures to carry out this transportation and simply rely on the process of diffusion. Other plants contain specialized structures that move materials throughout the plant.

Non vascular plants lack these specialized structures. They have poorly developed roots, stems and leaves. They must exist in moist environments for reproduction and transportation to occur. These plants cannot grow very tall and do not provide much nourishment for humans. Non vascular plants include mosses, liverworts and hornworts.

Vascular plants contain specialized structures called xylem and phloem. These tissues move materials throughout the plant. The xylem is composed of dead cells and it transports water and mineral from the ground upwards. The phloem is composed of living tissue and it transports sugars from the leaves to the other areas of the plant.

Vascular plants can be divided into two categories: gymnosperms and angiosperms.

Gymnosperms are plants that produce cones instead of flowers. They include pine, furs, spruce, ginkgoes and cycads. These types of plants thrive in environments that have long cold winters and low nutrients in the soil. Gymnosperms are important for the Canadian economy as the wood from these trees is used to for construction, fuel and pulp and paper.

Angiosperms are more diverse than gymnosperms and include flowering plants. All angiosperms produce food, although not all the food is edible. Included in this group are grasses, wheat, rice, corn, fruits, vegetables and wildflowers. Angiosperms provide nourishment, fibre for clothing and medicinal ingredients. In addition, the wood from these plants can also be used as building materials.

Angiosperms are divided into monocots and dicots.

Monocots and Dicots Angiosperms are divided into two subclasses monocotyledon (monocots) and dicotyledon (dicots). Most angiosperms are monocots and include grasses, wheat, rice and bananas. Dicots include the tomato plant, cacti, maple and oak trees. The name of each subclass is determined by the structure of its seeds. A seed is made up of three parts: seed coat, embryo and endosperm.

Monocots have only one seed leaf (cotyledon) whereas dicots have two seed leaves. Seed leaves provide nourishment. Monocots get their nourishment from the endosperm. It is believed that monocots came from an early dicot plant.

Homework You have learned that angiosperms are divided into monocots and dicots. The division was made based upon the structure of their seeds. Monocots contain one cotyledon and dicots contain two cotyledons. However, there are many more differences between monocots and dicots. Using the following criteria listed below, compare monocot and dicot plants. Your comparison should be completed using an organized data table. Criteria: Vascular Bundles; Leaf Venation; Roots; Flowers; Pollen; Secondary Growth.