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

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 TissuesApical 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 TissuesApical Meristems

• Primary meristems develop from apical meristems.– Protoderm

– Ground Meristem

– Procambium

• Primary meristems produce primary tissues.

Meristematic TissuesLateral 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 TissuesIntercalary 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 MeristemsSimple 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


• 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 membraneo Nectaries of flowers


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


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


o Sclereids – Stone Cells

– Scattered in tissue

– Cells as long as wide


o Fiberso Much longer that wide and contain lumen (tiny cavity)

Fibers in cross section and longitudinal section

Tissues Produced By MeristemsComplex 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


• Vessels – Long tubes made of vessel elements– Vessel elements:

o Thick secondary cell walls

o Open at both endso Secondary walls

develop irregularlyo Perforation plate

between end walls

Vesselselements

Spiral thickenings on vessel

walls


• Tracheids – Tapered at the ends with pairs

of pits that allow water to pass from cell to cello 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


Phloem - Conducts dissolved food materials produced by photosynthesis throughout plant • Composed of sieve tube members, companion cells,

fibers, parenchyma cells and ray cells


• 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


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


• 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 evaporationo 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.


• 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.


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

Documents

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