Chapter 2 Lecture Outline Tissues Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Outline  Organs and Tissues  Meristematic Tissues Apical Meristems Lateral Meristems Intercalary Meristems  Tissues Produced by Meristems Simple Tissues Complex Tissues

Organs and Tissues  Plants have three or four major groups of organs: Roots Stems Leaves Flowers  Each organ is composed of tissues. A tissue is a group of cells performing a similar function. There may be more than one tissue per organ.

Meristematic Tissues Apical Meristems  Meristems - Permanent regions of growth and active cell division  Apical Meristems - Found at the tips of roots and shoots Roots and shoots increase in length as the apical meristems produce new cells (= primary growth).

Meristematic Tissues Apical Meristems Primary meristems develop from apical meristems. – Protoderm – Ground Meristem – Procambium Primary meristems produce primary tissues.

Meristematic Tissues Lateral Meristems  Lateral Meristems - Produce secondary tissues that increase the girth of roots and stems (= secondary growth) Vascular Cambium - Produces tissues that function primarily in support and conduction. – Composed of a thin cylinder of brick-shaped cells that extends the length of stems and roots Cork Cambium - Lies outside vascular cambium just inside the outer bark – Produces bark

Meristematic Tissues Intercalary Meristems  Grasses and related plants do not have vascular cambium nor cork cambium. They have intercalary meristems. Intercalary Meristems – In vicinity of nodes (leaf attachment area) – Add to stem length

Tissues Produced By Meristems Simple Tissues  Parenchyma - Composed of parenchyma cells Parenchyma cells: – Thin, pliable walls – Usually 14-sided at maturity – Living cytoplasm, often containing large vacuoles and various secretions – May remain alive a long time – Have spaces between them Parenchyma cells  Simple Tissues - Consist of only one kind of cell

Tissues Produced By Meristems Simple Tissues Types of parenchyma tissue and cells: – Aerenchyma - Parenchyma tissue with extensive connected air spaces, usually in aquatic plants – Chlorenchyma - Parenchyma cells containing chloroplasts that function in photosynthesis – Transfer cells - Develop irregular extensions of inner wall that greatly increase surface area of plasma membrane o Nectaries of flowers

Tissues Produced By Meristems Simple Tissues  Collenchyma tissue - Contains collenchyma cells Collenchyma cells: – Living cytoplasm – May remain alive a long time – Cell walls thick, with uneven thickness – Pliable and strong, thus providing flexible support Collenchyma cells

Tissues Produced By Meristems Simple Tissues  Sclerenchyma tissue - Contains sclerenchyma cells Sclerenchyma cells: – Thick, tough, secondary walls, normally impregnated with lignin – Dead at maturity – Function in support – Two types: o sclereids o fibers

Tissues Produced By Meristems Simple Tissues o Sclereids – Stone Cells – Scattered in tissue – Cells as long as wide

Tissues Produced By Meristems Simple Tissues o Fibers o Much longer that wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section

Tissues Produced By Meristems Complex Tissues  Complex tissues - Composed of two or more kinds of cells Vascular tissues include xylem and phloem.  Xylem - Chief conducting tissue for water and minerals that are absorbed by the roots Composed of parenchyma cells, fibers, vessels, tracheids and ray cells

Tissues Produced By Meristems Complex Tissues Vessels – Long tubes made of vessel elements – Vessel elements: o Thick secondary cell walls o Open at both ends o Secondary walls develop irregularly o Perforation plate between end walls Vessels elements Spiral thickenings on vessel walls

Tissues Produced By Meristems Complex Tissues Tracheids – Tapered at the ends with pairs of pits that allow water to pass from cell to cell o Pits - Areas without secondary cell – Dead at maturity – Thick secondary cell walls – May have spiral thickenings on cell walls Rays - Function in lateral conduction and food storage – Composed of long-lived parenchyma cells Tracheids

Tissues Produced By Meristems Complex Tissues  Phloem - Conducts dissolved food materials produced by photosynthesis throughout plant Composed of sieve tube members, companion cells, fibers, parenchyma cells and ray cells

Tissues Produced By Meristems Complex Tissues Sieve Tube Members: – Lack secondary cell walls and nuclei – Lay end to end to form sieve tubes – Walls have sieve plates with small pores – Callose forms callus plug - Prevents leaking of sieve tube contents when cell injured Phloem Companion cells - Aid in conduction of food

Tissues Produced By Meristems Complex Tissues  Epidermis- Protective layer that is one cell- layer thick covering all plant organs Composed mostly of parenchyma cells, guard cells of stomata, secretory glands and hairs Leaf cross section

Tissues Produced By Meristems Complex Tissues Cutin - Fatty substance on the surface of outer walls of epidermis that forms cuticle – Wax secreted on cuticle – Cuticle and wax prevent water loss by evaporation o Resistant to bacteria and other disease organisms Root epidermal cells produce root hairs. – Increase absorptive area of root surface Leaves have stomata bordered by pairs of guard cells.

Tissues Produced By Meristems Complex Tissues Constitutes outer bark Primarily composed of cork cells – Dead at maturity – While still alive, cytoplasm secretes suberin (fatty substance) into walls. o Makes cork cells waterproof and helps protect phloem  Periderm - Replaces epidermis when cork cambium begins producing new tissue – Lenticels - Loosely arranged pockets of parenchyma cells formed by cork cambium that protrude through the surface of periderm. Allows for gaseous exchange.

Tissues Produced By Meristems Complex Tissues  Secretory Cells and Tissue Secretory cells may function individually or as part of a secretory tissue. – Flower nectar – Citrus oils – Glandular hair mucilage – Latex – Resins

Review  Organs and Tissues  Meristematic Tissues Apical Meristems Lateral Meristems Intercalary Meristems  Tissues Produced by Meristems Simple Tissues Complex Tissues