Chapter 4 - Plant Cells and Tissues

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Introduction to Plant Cells – add stuff in here from ch 3

I.  Organization of the plant body – Vascular Plants

            A.  Vascular plants include plant organisms such as ferns, pine trees and flowering plants

            B.  Vascular plants are plants having specialized tissues that transport water and solutes through well developed

             roots, stems and leaves

            C.  Despite the vast morphological differences in vascular plants they all have a common mechanism for

            development and similar internal structure

            D.  the vascular plant body consists of an above ground shoot system and a below ground root  system

II.  Plant cells and tissues

A.      Meristems - where the cells activley divide in vascular plants;  these are localized regions of division activity

which continue for the duration of the plants life

1.    Meristems are sites where new cells are formed and the process of growth and differentiation starts

2.       Growth is the irreversible process of increase in size

                        3.  Differentiation refers to changes structurally and biochemically to a cell that result in

                                    specialized cell function

4.  Shoot apical meristem (SAM) and root apical meristems (RAM) form primary meristems

                        5.  Three Primary meristems function to form primary tissues and elongate shoot and roots

                        6.  primary meristems - protoderm, procambium and ground meristem

                         7.  Secondary meristem results in lateral growth thereby increasing the thickness and circumference of

                        roots and shoots, called secondary growth

                                    a.  not all plants have secondary meristems

                                    b.  some plants have two secondary meristems (vascular cambium and cork cambium)

            B.  Tissues are aggregates of cells and intercellular substances that function together in one or more specialized

            Tasks.  The main tissue systems of vascular plants are grouped into three categories

                        1.  Ground tissue system - in  leaves it forms the mesophyll and in young stems the pith and cortex

                        2.  Vascular tissue system - xylem which conducts water and solutes and phloem which conducts sugars

                        throughout the plant body

                        3.  Dermal tissue system - covers and protects the plants surface (epidermis and periderm)

            C.  Within each tissue system there are either simple or complex tissue

                        1.  Simple tissues are composed of aggregates of similar cells

a.       Parenchyma tissue – non meristematic tissues that have thin primary walls and are many

sided, may be involved in storage and/or secretion, so they have large vacuoles.  They assume various shapes and sizes related to their functions as they develop and mature.  Parenchyma tissues are composed of parenchyma cells, the most abundant of the cell types.  They are found in most higher plants.  Most parenchyma cells can divide, important in repairing damaged tissues.

                                                i.  parenchyma makes up the ground tissue system

ii.                   chlorenchyma are photosynthetic parenchyma with numerous chloroplasts found in leaves

                                                iii.  aerenchyma is parenchyma with large air spaces in aquatic plants like water lilies

                                                iv.  transfer cells are specialized with cell wall ingrowhts that increase the internal

                                                membrane surface area for transferring substances between cells

b.       Collenchyma tissue- cells have living protoplasm and may remain alive a long time.  They have thickened walls in the corners, are flexible, will stretch which makes them ideal as strengthening tissue.  Occur just beneath epidermis.  Walls are pliable as well as strong; provide strength and support for both growing organs and mature organs.  E.g. strings of celery

c.       sclerenchyma tissue - functions to support the weight of a plant organ normally impregnated with lignin.  2 forms:

                                          i.  fibers are long and narrow with thickened walls, proportionately tiny cavity; used in  ropes, strings, canvas, etc.

                                                ii.  sclerids (stone cells) are variously shaped and may occur singly or in clusters; e.g the gritty texture in pears

                        2.  Complex tissues make up the plants vascular tissue system, the dermal tissue system and the

                         secretory tissues.  Complex tissues are composed of different cell types

                                    a.  The vascular system consists of in interconnected network of bundles that is continuous

                                    throughout the body of the plant

                                    b.  the xylem is composed of tracheids and vessel members that conduct water and minerals

                                    absorbed by roots

                                                i.  When xylem is  found in leaves and young stems or in young roots it is referred to as

                                                primary xylem

                                                ii.  Xylem that is organized in a concentric cylinder pattern in stems in and roots is called

                                                secondary xylem

                                                iii.  tracheids are elongated cells with pointed ends

                                                iv.  Vessel members join their perforated end walls together to form a vessel

                                                v.  The secondary cell walls of tracheids and vessel members are highly lignified and

                                                wherever tracheids are in contact, pairs of pits are usually present.  water can be

                                                exchanged through either simple pits or bordered (bulging) pits.  In cone bearing trees,

                                                xylem is almost all tracheids.

vi.                  lateral conduction takes place in ray cells, which also function in food storage.  Rays radiate out from the center of stems and roots.

                                    c.  Phloem is a complex tissue that transports sugar through the plant

                                                i.  primary phloem is near primary xylem in young stems and leaves and in the vascular

                                                 cylinder of young roots

                                                ii.  secondary phloem occurs outside the secondary xylem in older stems and roots

                                                iii.  sieve tube members join end to end to form sieve tubes

                                                iv.  sieve tube members lose their nucleus and other organelles as they mature

                                                v.  companion cells are nucleated and one or more are connected to a sieve tube

                                                member, it is thought that they regulate metabolic activities of the sieve tube

                                                vi.  End walls of sieve tube members are called sieve plates - regions of small pores

                                                vii.  Phloem fibers are long tapered cells with lignified walls - used in making rope and

                                                fabric

                                    d.  The dermal tissue system consists of the epidermis and periderm

                                                i.  the epidermis is the outer covering of the plant and includes epidermal cells, guard

                                                cells and trichomes

ii.  The waxy cuticle helps keep moisture in and pathogens out – exceptionally resistant to

bacteria; has been recovered from fossil plants one million years old

                                                iii.  Guard cells regulate gas exchange through the stomates

                                                iv.  Trichomes are epidermal cell outgrowths that are single or multicelled

                                                v.  The periderm is a protective layer found in older roots and stems and is the result of

                                                secondary growth

                                                vi.  The periderm consists of phellem (cork) cells, phellogen or cork cambium and

                                                phelloderm.   The periderm is the bark, composed of cork cells.  While the protoplasm

                                                of cork is functioning, it secretes a fatty substance called suberin that makes cork cells

                                                waterproof and helps them protect tissue beneath bark. 

                                    e.  Secretory tissues such as laticifers secrete latex which discourages herbivores from eating

                                    the plant

Chapter 4 Lesson Objective/Homework

1.  What is the role of  meristematic cells and how do they differ from other cells?

2.  Describe the characteristics of parenchyma, collenchyma and sclerenchyma cells.

3.  How do simple and complex tissues differ?

4.  How does the dermal tissue protect the plant?  What is the basic structure of the dermal tissue system?

5.  What are the 2 complex tissues that form the vascular system, and how do they differ structurally?  What is the purpose of each one?

6.  What are the purposes of the ground tissue system?

7.  Compare and contrast vessel elements and tracheids.

8.  How do water conducting cells differ from those that transport food?

9.  Compare and contrast sieve tube members and sieve cells.  

10.  Describe the following meristems:  root and shoot apical meristems;  primary meristems (protoderm, ground meristem, procambium);  and  secondary meristems: (vascular cambium, cork cambium)

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