Leaf Anatomy PDF

# Leaf Anatomy By: Dr. Abeer Sayed Moawad ## Plant Cells - **Cytology** is the scientific study of cells; the unit of the living organisms. - A plant cell is characterized by the presence of a cell wall surrounding a plasma membrane which encloses the cytoplasm where cellular organelles are found...

# Leaf Anatomy By: Dr. Abeer Sayed Moawad ## Plant Cells - **Cytology** is the scientific study of cells; the unit of the living organisms. - A plant cell is characterized by the presence of a cell wall surrounding a plasma membrane which encloses the cytoplasm where cellular organelles are found. - The cytoplasm together with the nucleus is called the protoplasm. - The nucleus carries the hereditary material. ### Main Features of Plant Cells The main features that characterize plant cells from other eukaryotic organisms are: 1. Presence of a cell wall composed of cellulose, hemicellulose, pectin, and lignin. - Cell wall of fungi is made of chitin. - Cell wall of bacteria is made of peptidoligan. 2. Presence of plastids 3. Presence of a large vacuole 4. Plant cells have **plasmodesmata** that connect the protoplasm of neighboring cells. ## Plant Anatomy Plant anatomy is also known as micromorphology of plants and plant histology. - It is concerned with the microscopic structure of the cells, tissues, and organs of plants. ## Plant Tissues - A group of cells with identical form and function is known as **tissue**. ### Types of Plant Tissues #### Meristematic Tissue - Cells are capable of cell division. #### Permanent Tissue - Mature cells are incapable of cell division. ##### Simple Tissue - Tissue composed of a single type of cell ##### Complex Tissue - Tissue composed of more than one type of cell ### Classification of Plant Tissues - Plant tissues are divided into three main groups: - **Dermal Tissues** - **Ground Tissues** - **Vascular Tissues** ## Dermal Tissues - Dermal tissues occur on the surface of plants. - Dermal tissue is a complex tissue consisting of: - **epidermal cells** - **stomata** - **trichomes (hairs)** ### Epidermal Cells 1. **Single Layer** 2. **No intercellular spaces** 3. They show different shapes, sizes, and arrangements depending on the plant. - The cell wall might be straight or wavy. 4. Covered with a **cuticle** (water impermeable substance, cutin) - The cuticle may be smooth, warty, or striated. 5. Upper epidermis differs from the lower epidermis. ### Stomata - These are openings in the epidermis. - A stoma is made of a pair of similar cells, called **guard cells**. - There is a pore in the center called an **osteole** for gaseous exchange. - Stomata occur in both surfaces of the leaf or only on the lower surface. - The epidermal cells surrounding the stoma are called **subsidiary cells**. - Stomata are divided into four different types based on the arrangement of the subsidiary cells. #### Types of Stomata 1. **Ranunculaceous** or **Anomocytic** - The subsidiary cells are of similar size. - e.g. Digitalis 2. **Cruciferous** or **Anisocytic** (unequal celled) - The stoma is surrounded by usually three unequal-sized subsidiary cells. - e.g. Belladonna. 3. **Paracytic** or **Rubiaceous** (parallel celled) - The stoma is surrounded by two subsidiary cells. - The long axes of the subsidiary cells are parallel to the osteole - e.g. Senna. 4. **Diacytic** or **Caryophyllaceous** (cross celled) - The stoma is surrounded by subsidiary cells having their long axes perpendicular to the osteole. - e.g. Mentha. ### Trichomes (Hairs) - Hairs are outgrowths (projections) of epidermal cells of variable shape and size. #### Types of Trichomes - If a trichome is short and conical, it is called a **papillae**. - This type of trichome is described as **papillosed** - e.g. Coca - If a trichome is long, it is called a **trichome** or **hair**. #### Classification of Trichomes - Trichomes are classified into **glandular** and **non-glandular** types. #### Non-glandular Hairs ##### Unicellular 1. **Unbranched** - Cottony - Cystolith - Papillae 2. **Branched** ##### Multicellular 1. **Unbranched** - Uniseriate - Biseriate - Pluriseriate 2. **Branched** - Simple - Peltate - Candelabra - Stellate #### Glandular Hairs ##### Unicellular Stalk - Unicellular head - e.g. Mentha - Bicellular Head - e.g. Digitalis - Multicellular head - e.g. Labiaceous hair in Mentha and clavate hair in Belladonna. ##### Multicellular Stalk - Uniseriate stalk - Biseriate stalk and biseriate head or compositae type. - Pluriseriate stalk and a head with multicellular head. - Branched stalk; the branch ending in a head.